Drs. William Kaelin Jr., Peter Ratcliffe, Gregg Semenza Win Nobel Prize In Medicine For Research On How Oxygen Shapes Physiology and Pathology
The Nobel Prize in Physiology or Medicine 2019 has been awarded to William G. Kaelin Jr., Sir Peter J. Ratcliffe, and Gregg L. Semenza for their discoveries of how cells sense and adapt to oxygen availability.

Animals use to convert food into useful energy. Mitochondria in our cells take fat, sugar, and protein and 'burn' it into ATP, a common currency our muscles and organs use.
But how cells adapt to changes in levels of oxygen has long been unknown.

Kaelin, Ratcliffe, and Semenza discovered how cells can sense and adapt to changing oxygen availability. They identified molecular machinery that regulates the activity of genes in response to varying levels of oxygen. They established the basis for our understanding of how oxygen levels affect cellular metabolism and physiological function. Their discoveries have also paved the way for promising new strategies to fight anemia, cancer and many other diseases.


When oxygen levels are low (hypoxia), HIF-1α is protected from degradation and accumulates in the nucleus, where it associates with ARNT and binds to specific DNA sequences (HRE) in hypoxia-regulated genes (1). At normal oxygen levels, HIF-1α is rapidly degraded by the proteasome (2). Oxygen regulates the degradation process by the addition of hydroxyl groups (OH) to HIF-1α (3). The VHL protein can then recognize and form a complex with HIF-1α leading to its degradation in an oxygen-dependent manner (4). 

Oxygen sensing is central to a large number of diseases. For example, patients with chronic renal failure often suffer from severe anemia due to decreased hormone erythropoietin (EPO) expression. EPO is produced by cells in the kidney and is essential for controlling the formation of red blood cells, as explained above. Moreover, the oxygen-regulated machinery has an important role in cancer. In tumors, the oxygen-regulated machinery is utilized to stimulate blood vessel formation and reshape metabolism for effective proliferation of cancer cells.

Intense ongoing efforts in academic laboratories and pharmaceutical companies are now focused on developing drugs that can interfere with different disease states by either activating, or blocking, the oxygen-sensing machinery.

Oxygen sensing allows cells to adapt their metabolism to low oxygen levels: for example, in our muscles during intense exercise. Other examples of adaptive processes controlled by oxygen sensing include the generation of new blood vessels and the production of red blood cells. Our immune system and many other physiological functions are also fine-tuned by the O2-sensing machinery. Oxygen sensing has even been shown to be essential during fetal development for controlling normal blood vessel formation and placenta development.

2016 LASKER AWARDS:

2016 Albert Lasker Basic Medical Research Award

Oxygen sensing – an essential process for survival

William G. Kaelin, Jr.

Dana-Farber Cancer Institute, Harvard Medical School

Peter J. Ratcliffe

University of Oxford, Francis Crick Institute

Gregg L. Semenza

Johns Hopkins University School of Medicine

For the discovery of the pathway by which cells from humans and most animals sense and adapt to changes in oxygen availability – a process essential for survival.

The 2016 Albert Lasker Basic Medical Research Award honors three physician-scientists for their discovery of the pathway by which cells from human and most animals sense and adapt to changes in oxygen availability, a process that is essential for survival. Scientists had long appreciated that the success of today’s dominant life forms hinges on oxygen, yet little was known about their responses to it. William G. Kaelin, Jr. (Dana-Farber Cancer Institute/Harvard Medical School), Peter J. Ratcliffe (University of Oxford/Francis Crick Institute), and Gregg L. Semenza(Johns Hopkins University School of Medicine) illuminated the core molecular events that explain how almost all multicellular animals tune their physiology to cope with varying quantities of the life-sustaining element, thus exposing a unique signaling scheme. 

The researchers’ findings touch a tremendous array of biological processes, and the details they have unearthed present possible strategies for revving up or reining in these activities. Such ventures might lead toward new therapeutics for a wide range of disorders, including some types of anemia, cardiovascular disease, and cancer.

Energizing hypoxic genes

Animals require oxygen to extract energy from food, but too much of the chemical creates peril, as certain oxygen-containing compounds wreak molecular havoc. To handle this challenge, organisms have evolved honed systems to furnish optimal supplies. For example, many creatures use red blood cells to transport oxygen to tissues deep within their bodies. When its concentration sags, the body generates the hormone erythropoietin, which boosts red blood-cell production. 

In the early 1990s, Semenza and Ratcliffe were trying to understand how oxygen deprivation—hypoxia—triggers the erythropoietin gene. They and others identified a DNA sequence that is necessary for hypoxia-dependent activation. Placement of this DNA stretch next to other genes renders those genes inducible by low-oxygen conditions too. Semenza showed that protein from the nucleus sticks to this DNA-control region, but only when oxygen is scarce. Furthermore, sequence alterations that eliminate protein binding to DNA also obliterate hypoxia-spurred gene stimulation. Perhaps, he proposed, the nuclear protein, which he called Hypoxia-Inducible Factor 1 (HIF-1), sits down on DNA when cells lack oxygen and rouses adjacent genes. 

Semenza and postdoctoral fellow Guang Wang achieved a major breakthrough in 1995, when they purified HIF-1 and found that it contains two protein partners, HIF-1α and HIF-1β.  The HIF-1α component was novel, and they isolated its gene from human cells. HIF-1α vanished quickly when Semenza shifted cells from low- to high-oxygen conditions. 

A profusion of HIF-1-driven genes 

Erythropoietin in adults is produced predominantly by specialized kidney cells, and scientists had long thought that mechanisms governing its manufacture were peculiar to those cells. With HIF-1 and its binding sequences in hand, Ratcliffe and Semenza upended this idea.

In complementary work, the scientists showed that hypoxia provokes HIF-1 to bind and activate target genes in many mammalian cells that do not make erythropoietin. Their observations suggested that multiple kinds of cells use HIF-1 to goad numerous genes in response to low-oxygen conditions.

Semenza and Ratcliffe subsequently confirmed this idea, and the list of hypoxia-induced genes expanded rapidly. In 1996, for instance, Semenza demonstrated that HIF-1 activates the gene for a key participant in blood-vessel formation, vascular endothelial growth factor (VEGF). This result extended HIF-1 into another key system by which the body can augment oxygen delivery. These and other findings established that HIF-1 lies at the core of an elaborate physiological network that ensures advantageous responses to oxygen.

Smothering HIF-1

The observation that the amount of HIF-1 plummets when cells are shifted to high-oxygen conditions squared with the factor’s hallmark ability to activate target genes only when oxygen is limited. It also raised a crucial question: What drives HIF-1 destruction? The answer came from an unexpected direction. 

A familial cancer syndrome called von Hippel-Lindau (VHL) disease owes its pathology to faulty versions of a particular protein. William Kaelin was trying to figure out how defects in this VHL protein cause the illness. The classic VHL tumor is composed of inappropriate, newly formed blood vessels, and surplus VEGF characterizes these growths; excessive erythropoietin production also can occur. Kaelin wondered whether VHL influences activity of the genes for these and other hypoxic-induced substances. 

In 1996, he and his colleagues grew human cells with and without operational VHL. Then they measured the abundance of several messenger RNAs, including VEGF’s, that normally disappear in response to oxygen. Even when oxygen was plentiful, VHL-defective cells contained large amounts of these mRNAs. Addition of intact VHL restored normal hypoxia-dependent quantities. 

Kaelin then showed that VHL’s capacity to quash the accumulation of particular mRNAs in rich oxygen conditions relies on its ability to physically assemble with several other proteins, including one that was later shown to mark certain proteins for destruction by attaching the chemical tag ubiquitin. Ubiquitin is the signal that sends certain proteins to the cell’s incinerator, the proteasome (Albert Lasker Basic Medical Research Award, 2000). Research soon established that HIF-1α is degraded through the ubiquitin pathway when oxygen is profuse. 

In 1999, Ratcliffe and colleagues demonstrated that the oxygen-dependent elimination of HIF-1α depends on VHL. Furthermore, under conditions that jam the proteasome, VHL and HIF-1α are present in the same protein assembly. Ratcliffe proposed that VHL interacts with HIF-1α under high-oxygen conditions and targets it for destruction. 

Kaelin subsequently found that VHL binds directly to HIF-1α—and that optimal binding requires a region in HIF-1α that was known to be needed for its oxygen-triggered destruction. He, Ratcliffe, and others showed that the same region is ubiquitinated and that defects in VHL prevent addition of the chemical tag. Together, these observations established that the VHL assembly directs ubiquitination of HIF-1α when oxygen is present. 

A crucial oxygen-based modification

Ratcliffe and Kaelin wondered what allows VHL to bind HIF-1α under high- but not low-oxygen conditions. Independently, they used various tricks to block the ubiquitin pathway, thereby allowing HIF-1α to accumulate even when oxygen abounds. Their observations suggested the existence of an enzyme that modifies HIF-1α such that it can snag VHL. 

To identify the presumptive HIF-1α modification, both teams homed in on the region of HIF-1α that grabs VHL. Elimination of a single amino acid—a proline—in this region abrogates VHL’s ability to attach ubiquitins and thus safeguards HIF-1. Further analysis revealed that this proline had picked up an oxygen atom next to one of its hydrogens. HIF-1α had thus acquired a chemical modification called a hydroxyl group. 

Together, these and other findings indicated that a prolyl hydroxylase, named for its deeds, adds a hydroxyl to a critical proline in HIF-1α, thereby rendering HIF-1α recognizable by VHL and fostering its consequent ruin. Because prolyl hydroxylases require molecular oxygen to do their jobs, the observations, published in 2001, explained why HIF-1α is not degraded under hypoxic conditions and thus, how the enzyme translates oxygen levels into HIF-1α stability (see figure).

The experiments had not, however, uncovered the specific prolyl hydroxylase that acts on HIF-1α, and the amino acid sequence around the hydroxylated HIF-1α proline did not match target sites for known prolyl hydroxylases. In collaboration with Christopher Schofield (University of Oxford), Ratcliffe proposed that the enzyme belongs to a larger molecular family. Ratcliffe and, independently, Steven McKnight (University of Texas Southwestern Medical Center) identified three related prolyl hydroxylases that govern the cellular response to oxygen in mammals.

Ratcliffe subsequently demonstrated that hydroxylation of another proline in HIF-1α also promotes its oxygen-dependent, VHL-mediated demolition. Soon afterward, others found that hydroxylation of a different amino acid incapacitates HIF-1α as well, but in a different way. 

Breathing new life into therapies

We now know that HIF-1 and its molecular relatives regulate a plethora of genes whose products influence a vast number of biological processes. Harnessing the HIF pathway for therapeutic purposes hence offers fertile potential. 

For example, prolyl hydroxylase inhibitors that preserve HIF and thus incite erythropoietin gene activity hold hope of reversing anemia. Results in animals as well as humans show promise, and several companies are pursuing this possibility. Interfering with HIF prolyl hydroxylases might also promote blood-vessel growth and other adaptations to hypoxia that would combat conditions resulting from inadequate circulation.

On the flip side, thwarting HIF might quell malignancies, in part because many tumors draw nourishment from extra blood vessels they construct. A compound that foils HIF-2α, a close relative of HIF-1α, is currently in early clinical trials for kidney cancer.  

Kaelin, Ratcliffe, and Semenza have unveiled the fundamental workings of HIF, which presides over a complex and exquisitely controlled response to oxygen fluctuations. Their discoveries have revealed secrets about a cornerstone of life on Earth.

by Evelyn Strauss

Key Publications of William G. Kaelin, Jr.

Iliopoulos, O., Levy, A.P., Jiang, C., Kaelin, W.G., Jr., and Goldberg, M.A. (1996). Negative regulation of hypoxia-inducible genes by the von Hippel-Lindau protein. Proc. Natl. Acad. Sci. USA. 93, 10595-10599.  

Ohh, M., Park, C.W., Ivan, M., Hoffman, M.A., Kim, T.-Y., Huang, L.E., Chau, V., Pavletich, N., and Kaelin, W.G., Jr. (2000). Ubiquitination of hypoxia-inducible factor requires direct binding to the β-domain of the von Hippel-Lindau protein. Nat. Cell Biol. 2, 423-427. 

Ivan, M., Kondo, K., Yang, H., Kim, W., Valiando, J., Ohh, M., Salic, A., Asara, J.M., Lane, W.S., and Kaelin, W.G., Jr. (2001). HIF targeted for VHL-mediated destruction by proline hydroxylation: implications for O2 sensing. Science. 292, 464-468. 

Ivan, M., Haberberger, T., Gervasi, D., Michelson, K.S., Gunzler, V., Kondo, K., Yang, H., Sorokina, I., Conaway, R.C., Conaway, J.W., and Kaelin, W.G., Jr. (2002). Biochemical purification and pharmacological inhibition of a mammalian prolyl hydroxylase acting on hypoxia-inducible factor. Proc. Natl. Acad. Sci. USA. 99, 13459-13464. 

Kaelin, W.G., Jr. and Ratcliffe, P.J. (2008). Oxygen sensing by metazoans: the central role of the HIF hydroxylase pathway. Mol. Cell. 4, 393-402.

Key Publications of Peter J. Ratcliffe

Maxwell, P.H., Pugh, C.W., and Ratcliffe, P.J. (1993). Inducible operation of the erythropoietin 3' enhancer in multiple cell lines: evidence for a widespread oxygen-sensing mechanism. Proc. Natl. Acad. Sci. USA. 90, 2423-2427.

Maxwell, P.H., Wiesener, M.S., Chang, G.-W., Clifford, S.C., Vaux, E.C., Cockman, M.E., Wykoff, C.C., Pugh, C.W., Maher, E.R., and Ratcliffe, P.J.  (1999). The tumour suppressor protein VHL targets hypoxia-inducible factors for oxygen-dependent proteolysis. Nature. 399, 271-275.

Jaakkola, P., Mole, D.R., Tian, Y.-M., Wilson, M.I., Gielbert, J., Gaskell, S.J., von Kriegsheim, A., Hebestreit, H.F., Mukherji, M., Schofield, C.J., Maxwell, P.H., Pugh, C.W., and Ratcliffe, P.J. (2001). Targeting of HIF-α to the von Hippel-Lindau ubiquitylation complex by O2-regulated prolyl hydroxylation. Science. 292, 468-472.

Epstein, A.C.R., Gleadle, J.M., McNeill, L.A., Hewitson, K.S., O’Rourke, J.F., Mole, D.R., Mukherji, M., Metzen, E., Wilson, M.I., Dhanda, A., Tian, Y.-M., Masson, N., Hamilton, D.L., Jaakkola, P., Barstead, R., Hodgkin, J., Maxwell, P.H., Pugh, C.W., Schofield, C.J., and Ratcliffe, P.J. (2001). C. elegans EGL-9 and mammalian homologs define a family of dioxygenases that regulate HIF by prolyl hydroxylation. Cell. 107, 43-54.

Cockman, M.E., Lancaster, D.E., Stolze, I.P., Hewitson, K.S., McDonough, M.A., Coleman, M.L., Coles, C.H., Yu, X., Hay, R.T., Ley, S.C., Pugh, C.W., Oldham, N.J., Masson, N., Schofield, C.J., and Ratcliffe, P.J. (2006). Post-translational hydroxylation of ankyrin repeats in IkB proteins by the HIF asparaginyl hydroxylases, FIH. Proc. Natl. Acad. Sci. USA 103, 14767-14722.

Key Publications of Gregg L. Semenza

Semenza, G.L., Nejfelt, M.K., Chi, S.M., and Antonarakis, S.E. (1991). Hypoxia-inducible nuclear factors bind to an enhancer located 3' to the human erythropoietin gene. Proc. Natl. Acad. Sci. USA. 88, 5680-5684.

Semenza, G.L. and Wang, G.L. (1992). A nuclear factor induced by hypoxia via de novo protein synthesis binds to the human erythropoietin gene enhancer at a site required for transcriptional activation. Mol. Cell. Biol. 12, 5447-5454.

Wang, G.L. and Semenza, G.L. (1995). Purification and characterization of hypoxia-inducible factor 1. J. Biol. Chem. 270, 1230-1237.

Wang, G.L., Jiang, B.-H., Rue, E.A., and Semenza, G. L. (1995). Hypoxia-inducible factor 1 is a basic-helix-loop-helix-PAS heterodimer regulated by cellular O2 tension. Proc. Natl. Acad. Sci. USA. 92, 5510-5514.

Forsythe, J.A., Jiang, B.-H., Iyer, N.V., Agani, F., Leung, S.W., Koos, R.D., and Semenza, G.L. (1996). Activation of vascular endothelial growth factor gene transcription by hypoxia-inducible factor 1. Mol. Cell. Biol. 16, 4604-4613.
 

William G. Kaelin, Jr
Making Sense of the UnexpectedThe 2016 Albert Lasker Basic Medical Research Award is being awarded to Greg Semenza, WilliamKaelin, and Peter Ratcliffe for discovery of the pathway by which human and animal cells sense andadapt to changes in oxygen availability—an essential requirement for survival. Bill and Peter joinedCell editor Joa? o Monteiro in an informal conversation about science, medicine, designing experiments,and training the next generation.Joao Monteiro: Do you remember how you two first met?William Kaelin: I saw a poster in a meeting in Paris,presented by Patrick Maxwell, one of Peter’s studentsat the time. He was kind enough to tell me that Peter hadwork in press related to deregulation of HIF and the effectof the VHL gene in kidney cancer cells and that I shouldget to know his mentor. I think we first startedcommunicating within about a year of that. Does that soundabout right, Peter?Peter Ratcliffe: That’s about right, Bill. Patrick was in factone of a series of trainee nephrologists, including Chris Pughand others, who joined the laboratory and made a tremendousimpact. The work was in progress, but it was not in press. Thattook quite a while, actually.WK: Patrick and I understood that the next questions wouldbe related to how the interaction between VHL and HIF wasregulated by oxygen, and he said I should really be speakingwith Peter. I think I reached out to Peter probably sometime inlate 2000—I’m guessing when we started to have some of thedata that led to our Science paper in 2001.PR: That’s right. We both knew we had somethinginteresting, but we didn’t know that we had pretty well exactlythe same thing until those submissions to Science. Therewere other sites of interaction, which were slightly puzzlingbut came clear later. It’s always reassuring when awell-respected colleague has the same results as one’s ownlab.JM: Let me ask you, Peter, how did you get involved withthese questions?PR: It’s a long and torturous journey. I got in from the oxygensensingangle, which was a quest for me in slightly differentways from the outset. I trained as a nephrologist and wasinterested in why the kidney was susceptible to shock.Clinically one often sees kidney injury in people with low bloodpressure. It was believed that this had something to do with theunusual countercurrent circulation of the kidney, which createsa very low oxygen tension in the interior of the organ, thoughthis has never been fully understood. From there, I becameinterested in understanding why the kidney can make thehormone erythropoietin in response to reduced oxygenavailability, but not as a response to reduced blood flow. Ithought it might have something to do with the circulation that Ijust spoke about, but we didn’t resolve that one either. To myknowledge it isn’t understood to this day. The next transitionwas to consider the oxygen-sensing process itself, which webelieved was very special and exclusive to the kidney. That’show I got into the field, rather roundabout. All that was in the1980s.JM: When did you realize that oxygen sensing and the HIFpathway would become such a central signaling pathway,important in so many systems and on so many different celltypes?PR: Well, I can remember pretty well to the moment theradiograph was coming out of the developer. As I was saying, itwas believed that oxygen sensing was a special property ofparticular tissues and cells. We were working on hepatomacells, which were sensitive to oxygen tension, and I wanted toestablish a system to study how this process was regulated.William G KaelinDana-Farber Cancer Institute,Harvard Medical SchoolPeter RatcliffeNuffield Department of Medicine,University of OxfordCell 167, September 22, 2016 a 2016 Published by Elsevier Inc. 1CELL 9167Please cite this article in press as: Making Sense of the Unexpected, Cell (2016), http://dx./10.1016/j.cell.2016.08.048Because we had this strong prejudice that oxygen sensing wasnot widespread, we chose COS cells that don’t makeerythropoietin and (so we thought) shouldn’t be able to senseoxygen. They make a very good system for expression cloning,and that’s what we wanted them for: to provide a recipient cell.When we transfected the cells with the reporter gene, to mysurprise, the results suggested that oxygen sensing washappening in COS cells too. I was initially irritated when I sawthe results because I had a planned set of experiments, whichwas obviously disabled by these findings. However, the morewe thought about it, the more we realized that theconsequences of that result might be rather profound.WK: I think that this beautifully illustrates two points that I’msure Peter would agree with me on. The first is the point I try todrum home with students all the time, which is how oftenimportant discoveries start with unexpected behavior with oneof the controls. The second, as I once heard a Nobel Prizewinner say, is that a surprisingly high number of what wouldhave been great discoveries probably wind up in the wastepaper basket because they didn’t fulfill people’s biases. Whenthings don’t fulfill your biases, sometimes they tend to beignored or discarded. But retrospectively, you realize howimportant the observation was. I thought that was a greatvignette Peter just described.PR: That’s my experience, and I agree with you. I think manyof the most important results in my lab initially irritated me.WK: I have a saying, which is probably an over-simplification,that engineers live for the expected results, and scientists livefor the unexpected results.JM: You both also are physician-scientists. Do you think thatthis background influenced the way that you do science? Did itmake a difference regarding the type of questions that youasked or the way that you approached them?PR: I thought it made me more forceful. I was 35 years oldwhen I started this project. I think that, as a physician, you getmore confident about dealing with unknowns. I always found ithelpful not to be too shy to ring up for advice and push untilyou’ve got the advice you needed. A bit of that was drawn fromhigh-pressure clinical medicine. You have to get things donethere, you have to make decisions. But there is one essentialdifference between the two. In the clinic, if you don’t know whatto do, do nothing. In the lab, if you don’t know what to do, dosomething. In the clinic, the experiment is ongoing before youreyes, so you just need to wait and more information will come.Whereas in the lab, of course, that can’t possibly happen.JM: What about you, Bill?WK: Part of my answer relates to your first question, abouthow I got into the field of oxygen sensing. When I was a youngphysician, I was pretty sure I was going to be a practicingclinician. I had actually done a so-called chief residency atJohns Hopkins. Chief residents love rare eponymoussyndromes like von Hippel-Lindau [VHL] syndrome becausethey can use them to assert their authority on rounds. If atrainee steps out of line, they can embarrass them by askingthem questions about such rare entities. Clinicians also tend tomemorize differential diagnoses—all the possible causes forany symptom or sign you might encounter on the wards. Whenthe Hippel-Lindau gene was cloned, I knew what cancers it waslinked to, such as kidney cancer. I knew that those tumors werevery rich in blood vessels, so I hoped that studying VHL wouldteach us something about kidney cancer. If not, it would at leastteach us something about how the angiogenesis is controlled. Q1Another obscure fact about VHL-associated tumors is thatthey occasionally cause the body to produce too many redblood cells. What angiogenesis and erythropoiesis have incommon is that they’re normally induced by hypoxia. It seemedto me that the tumors in VHL disease were behaving as if theyconstantly thought they were hypoxic and were sending out thedistress signals that would normally be induced by hypoxia.This experiment of nature, if you will, could help us begin tounderstand the molecular circuitry of oxygen sensing.JM: Looking toward the future, where do you think that theoxygen-sensing field is going? What questions are exciting youright now?WK: We continue to be interested in whether there aresettings where pharmacologically modulating the HIF pathwaywould be beneficial and could be exploited for therapeuticpurposes. As you may know, there are drugs that target the HIFpathway that have advanced to phase III trials for treatinganemia. I think the pre-clinical data are suggestive that, incertain diseases such as in heart attack and stroke,manipulating the HIF pathway pharmacologically might also behelpful. Those would be situations where you would want toramp up the HIF response. Conversely, in a variety of cancers,we wonder whether dampening the HIF response might be auseful thing to do. I think that’s going to be particularly true forcancers linked to loss of VHL, for instance. There are a lot ofpharmacological opportunities to be explored.‘‘It’s always reassuring when awell-respected colleague hasthe same results as one’s ownlab.’’‘‘The point I try to drum homewith students all the time . ishow often importantdiscoveries start withunexpected behavior with oneof the controls.’’2 Cell 167, September 22, 2016CELL 9167Please cite this article in press as: Making Sense of the Unexpected, Cell (2016), http://dx./10.1016/j.cell.2016.08.048From a more basic or fundamental level, it remains to be seenhow many other enzymes in the cell are regulated by oxygen,whether there are other proteins that, like HIF, are prolylhydroxylated or undergo oxygen-dependent modification.There is also good reason to think that VHL has functions otherthan modulating or regulating HIF. There have been hints ofHIF-independent functions of VHL, but there are a lot ofunknowns there.JM: What about you, Peter? What are you interested in thesedays?PR: Pretty much the same thing but with a somewhatdifferent bias. We now work quite closely with Chris Schofield,who is a chemist and is designing novel inhibitors. We’reinterested in whether different inhibitors can meet differentmedical challenges and believe that with sufficient investmentthis will be possible. I admire the people going forward withphase III trials for anemia. It looks really promising, and we hopeit works. But we think that more inhibitors, more pharmacology,and lots more experimental medicine are required to tease outwhat is possible. A drug for ischemia—for low or inadequateblood flow, for instance—would be a terrific addition to thepharmacopeia.Just as Bill said, we’re also interested in other forms ofhydroxylation, their regulation. And also in cancer. I feel it mightbe worth debating whether we think that deregulation of the HIFpathway causes cancer. I suspect that both pro- andanti-tumorigenic effects of the HIF switch require re-balancingor fine tuning as cancer develops.WK: I think there are quite a few review articles that wouldsuggest, largely based on guilt by association, that HIFuniversally promotes tumor growth and we should bedeveloping HIF inhibitors. That’s based largely on the fact thatupregulation of HIF is often associated with a bad prognosis,but that could be because aggressive tumors outgrow theirblood supplies and could become hypoxic and upregulate HIF.It’s certainly true that HIF activates genes involved in tumorgrowth, but as Peter just indicated, there’s really far morenuance than that.The bottom line is here, I think context is going to matterand we’re going to have to figure out, probably on acancer-by-cancer basis, when HIF is largely pro-tumorigenic,anti-tumorigenic, or neither. Which HIF paralog is involved, inwhat stage, and so on. I think there’s mounting evidence that, insome settings, HIF might actually be anti-tumorigenic or mightsimply be window dressing and have nothing to do with thetransformed phenotype whatsoever. I think that we will have totease this apart before we rationally design or use HIF inhibitorsin the clinic.JM: Switching gears a bit, what’s your approach to trainingyoung scientists? Has it changed in the past 20 years?WK: By now, you’ve probably figured out that Peter and I arealmost twin sons of different mothers. I think we’re not going todisagree on too many things here. Getting back to the point wejust discussed, I try to emphasize to people that the power ofthe experiment usually lies in the thoughtfulness of the negativeand the positive controls. We try to make sure that, when weput together papers, you can see the positive and the negativecontrols. We also try, whenever possible, to providecorroborating lines of evidence for our conclusions.Another saying I have is that there are two kinds of scientists.There is the scientist whose great fear in life is being second,and there is the scientist whose greatest fear in life is beingwrong. I try to tell people that, over the course of time, I’d ratherwe were in the second camp. So we may get second place nowand then, but let’s try to make sure that what we publish is goingto be correct now, correct in 10 years, and correct in 100 years.That doesn’t mean that, on further review, with the benefit oftime, additional interpretations won’t arise. But at least theexperiments themselves will have been well conductedand well controlled. The final thing I try to impress uponmy trainees is, again, another old saying: ‘‘It’s as hard towork on an uninteresting and unimportant problem as itis to work on an interesting and important problem.’’ SoI push my trainees to try to identify questions that we agreeare interesting and important and that will move the fieldforward.JM: Great. Peter, I imagine that you agree with most of that.Any differences on the way you run your lab?PR: Sure. There is an issue that is quite interesting in Bill’scomments that speaks to your perceptions of how you controlexperiments, where you set the bar to accept that a result istrue. There’s an order to these things as well as a question ofsecurity. You first hunt an interesting result, and then youcontrol it to make sure that it is correct. But first you hunt it.Otherwise, people waste a lot of time setting up controls forexperiments that are never going to work anyway. There’s moreto it than simple care. There’s sort of an art to balancing howaggressively you make the first observations and then howbrutally you control it. We’re both clinicians, and I’ve been anactive clinician a long time. I tend to take the same approachto running my lab and the decision-making process. What isthe prior probability of this all being true, and what is thepost-experimental probability of it being true?That means that I’m integrating the ‘‘security’’ of all sorts ofdifferent types of data. Not every scientist uses that. I haveworked with people who take experimental results in isolationat face value. Of course, these people are much lessconstrained by prejudice. They’re perhaps, you could argue,more likely to discover things, but they’re also more likely tomake mistakes, as they sometimes disregard a lot of data whenthey come to a final conclusion. Actually making accuratediagnoses in the clinic and accurate interpretation of laboratoryresults are not dissimilar processes. They both requireconsidering all manner of possibilities and then great care incoming to a conclusion. I try to teach this type of decisionmaking, as it impinges on many different things.‘‘You first hunt an interestingresult, and then you control it tomake sure that it is correct.’’Cell 167, September 22, 2016 3

Acceptance Remarks, 2016 Lasker Awards Ceremony

I grew up during the space race, so science and engineering were celebrated and supported throughout my childhood and our household had toys that fostered curiosity and creativity, including a microscope and chemistry sets.

In high school, I attended an NSF-sponsored summer program for 32 mathematically gifted students that changed my life.   I was delighted to learn that I wasn’t the least gifted of the 32 but I certainly had, due to my abysmal study habits, the lowest grades.  I learned that school was more fun when I was challenged, that it is really helpful to be surrounded by people who are smarter than you are, and that I, too, could get good grades if I actually did my homework.

As a premed, I floundered in a research laboratory working on an independent study project that was uninteresting, unimportant, and, as I would later correctly show, undoable.  My mentor rewarded me with a “C+,” noting on my transcript that “Mr. Kaelin appears to be a bright young man whose future lies outside of the laboratory.” This painful experience convinced me I was going to be a clinician rather than a scientist, and I approached my clinical training accordingly.  I even served as Chief Resident at Johns Hopkins, honing my knowledge of obscure diseases such as von Hippel-Lindau Disease.

Years later, I discovered, thanks to outstanding mentorship from David Livingston, that I actually could do science.   And my clinical practice convinced me that we desperately needed better cancer treatments based on a deeper understanding of cancer pathogenesis.

I like mathematics, medicine, and science because I like solving puzzles, and I like answers that are objectively verifiable.  Science gathers knowledge, and engineering applies that knowledge to useful purposes.   For most of my career, I benefited from the wise decision in our country to have the public sector support basic scientific research, where the timelines and deliverables are too unpredictable for investors, and to let the private sector decide when a line of investigation is ripe for application and commercialization.   Although this bargain served American biomedical research well, one hears repeated calls to treat science as though it were engineering, tying funding to anticipated outcomes and impact.  This is troubling because many practices that are useful for managing engineering projects are antithetical to good science.  For example, building teams and harmonizing goals is often essential for large engineering projects.  Early stage science, however, is often driven by creative individuals who follow their curiosity and are willing to go where their science takes them.    Forcing scientists into teams and holding them to predetermined deliverables can create herd mentality and stifle the heretical thinking that is often needed for transformative discoveries.

JFK knew it would take a decade to put a man on the moon because it was fundamentally an engineering challenge rather than a scientific challenge. It does scientists and, more importantly, patients and their families, a disservice when fundraisers and policy makers overpromise and oversimplify with respect to our greatest biomedical challenges, including cancer.

I am very proud to receive this award on behalf of the talented young scientists who have worked in my laboratory over the years, to share it with such esteemed colleagues, and to dedicate it to my beloved wife Carolyn, who died last summer. 

Key Publications of William G. Kaelin, Jr.

Iliopoulos, O., Levy, A.P., Jiang, C., Kaelin, W.G., Jr., and Goldberg, M.A. (1996). Negative regulation of hypoxia-inducible genes by the von Hippel-Lindau protein. Proc. Natl. Acad. Sci. USA. 93, 10595-10599.  

Ohh, M., Park, C.W., Ivan, M., Hoffman, M.A., Kim, T.-Y., Huang, L.E., Chau, V., Pavletich, N., and Kaelin, W.G., Jr. (2000). Ubiquitination of hypoxia-inducible factor requires direct binding to the β-domain of the von Hippel-Lindau protein. Nat. Cell Biol. 2, 423-427. 

Ivan, M., Kondo, K., Yang, H., Kim, W., Valiando, J., Ohh, M., Salic, A., Asara, J.M., Lane, W.S., and Kaelin, W.G., Jr. (2001). HIF targeted for VHL-mediated destruction by proline hydroxylation: implications for O2 sensing. Science. 292, 464-468. 

Ivan, M., Haberberger, T., Gervasi, D., Michelson, K.S., Gunzler, V., Kondo, K., Yang, H., Sorokina, I., Conaway, R.C., Conaway, J.W., and Kaelin, W.G., Jr. (2002). Biochemical purification and pharmacological inhibition of a mammalian prolyl hydroxylase acting on hypoxia-inducible factor. Proc. Natl. Acad. Sci. USA. 99, 13459-13464. 

Kaelin, W.G., Jr. and Ratcliffe, P.J. (2008). Oxygen sensing by metazoans: the central role of the HIF hydroxylase pathway. Mol. Cell. 4, 393-402.

Peter J. Ratcliffe

Acceptance Remarks, 2016 Lasker Awards Ceremony
 I am deeply honoured to receive the Lasker Foundation Award for Basic Medical Research today.

I’d like to reflect for a moment on the many twists and turns that brought me to this fortunate position. One still clear in my mind dates to the Lancaster Royal Grammar School, circa 1970. I was a tolerable schoolboy chemist and intent on a career in industrial chemistry. The ethereal (but formidable) Headmaster appeared one morning in the chemistry classroom. ‘Peter’ he said with unnerving serenity ‘I think you should study medicine’. And without further thought, my university application forms were changed. To this day, I am unsure whether he felt I would be a good doctor or a bad chemist. But the experience is (I think) a reminder of the role of serendipity in a scientific career, at least in mine.

I did train in medicine, as a nephrologist, and came to research rather late, fascinated by the extraordinary sensitivity with which the kidneys regulate the hormone erythropoietin in accordance with blood oxygen content. I felt that the process was interesting and might be tractable. At the time, the erythropoietin gene had recently been identified, so there was a new opportunity for study.  But some felt, with the emerging success of recombinant erythropoietin treatment, that understanding how the hormone was regulated was niche area, unlikely to be of general importance.

Key Publications of Peter J. Ratcliffe

Maxwell, P.H., Pugh, C.W., and Ratcliffe, P.J. (1993). Inducible operation of the erythropoietin 3' enhancer in multiple cell lines: evidence for a widespread oxygen-sensing mechanism. Proc. Natl. Acad. Sci. USA. 90, 2423-2427.

Maxwell, P.H., Wiesener, M.S., Chang, G.-W., Clifford, S.C., Vaux, E.C., Cockman, M.E., Wykoff, C.C., Pugh, C.W., Maher, E.R., and Ratcliffe, P.J.  (1999). The tumour suppressor protein VHL targets hypoxia-inducible factors for oxygen-dependent proteolysis. Nature. 399, 271-275.

Jaakkola, P., Mole, D.R., Tian, Y.-M., Wilson, M.I., Gielbert, J., Gaskell, S.J., von Kriegsheim, A., Hebestreit, H.F., Mukherji, M., Schofield, C.J., Maxwell, P.H., Pugh, C.W., and Ratcliffe, P.J. (2001). Targeting of HIF-α to the von Hippel-Lindau ubiquitylation complex by O2-regulated prolyl hydroxylation. Science. 292, 468-472.

Epstein, A.C.R., Gleadle, J.M., McNeill, L.A., Hewitson, K.S., O’Rourke, J.F., Mole, D.R., Mukherji, M., Metzen, E., Wilson, M.I., Dhanda, A., Tian, Y.-M., Masson, N., Hamilton, D.L., Jaakkola, P., Barstead, R., Hodgkin, J., Maxwell, P.H., Pugh, C.W., Schofield, C.J., and Ratcliffe, P.J. (2001). C. elegans EGL-9 and mammalian homologs define a family of dioxygenases that regulate HIF by prolyl hydroxylation. Cell. 107, 43-54.

Cockman, M.E., Lancaster, D.E., Stolze, I.P., Hewitson, K.S., McDonough, M.A., Coleman, M.L., Coles, C.H., Yu, X., Hay, R.T., Ley, S.C., Pugh, C.W., Oldham, N.J., Masson, N., Schofield, C.J., and Ratcliffe, P.J. (2006). Post-translational hydroxylation of ankyrin repeats in IkB proteins by the HIF asparaginyl hydroxylases, FIH. Proc. Natl. Acad. Sci. USA 103, 14767-14722.
 

 Gregg L. Semenza

CELL ESSAY

Acceptance Remarks, 2016 Lasker Awards Ceremony

Many of us who conduct biomedical research do so with what could be described as a religious fervor. This would not have come as a surprise to Mary Lasker. She once told a reporter, “I am opposed to heart attacks and cancer the way one is opposed to sin.”

Amen.

Seven months ago, Antonin Scalia died. He had a heart attack, which occurs when the flow of blood through one of the coronary arteries is blocked, cutting off the heart muscle’s supply of oxygen. 

Eight months ago, David Bowie died of liver cancer. Cancer cells invade surrounding tissue, make their way into blood vessels, and spread throughout the body. What are they searching for? My guess is oxygen.

Over the last 25 years, we’ve worked to understand how a family of proteins, which we called hypoxia-inducible factors, controls the ability of cells, tissues, and organ systems to respond to changes in oxygen availability.  Our work began with an attempt to figure out how expression of the erythropoietin gene was turned on when the body was deprived of oxygen. Now we know that more than 2,000 other genes are regulated in a similar manner.

Looking forward, I’d like to think that within the next decade drugs that stimulate hypoxia-inducible factors will be used to treat anemia and cardiovascular disease, while drugs that inhibit these factors will prolong the lives of cancer patients.

So this is my religion:  I am filled with Wonder at the outcome of 4 billion years of evolution here on our speck in the universe and Hope regarding our opportunity to improve the lives of those around us through basic science discoveries and their translation to clinical practice.

Well, I began with Mary Lasker, so I’ll end with Albert. As you know, Mr. Lasker was a successful advertising executive. He was in charge of accounts for products like Sunkist oranges and Pepsodent toothpaste before he and Mary began their crusade to promote biomedical research. Coincidentally, my grandfather also worked for an advertising agency here in Manhattan. His account was for a product called Wonder Bread.

Thank you.

Key Publications of Gregg L. Semenza

Semenza, G.L., Nejfelt, M.K., Chi, S.M., and Antonarakis, S.E. (1991). Hypoxia-inducible nuclear factors bind to an enhancer located 3' to the human erythropoietin gene. Proc. Natl. Acad. Sci. USA. 88, 5680-5684.

Semenza, G.L. and Wang, G.L. (1992). A nuclear factor induced by hypoxia via de novo protein synthesis binds to the human erythropoietin gene enhancer at a site required for transcriptional activation. Mol. Cell. Biol. 12, 5447-5454.

Wang, G.L. and Semenza, G.L. (1995). Purification and characterization of hypoxia-inducible factor 1. J. Biol. Chem. 270, 1230-1237.

Wang, G.L., Jiang, B.-H., Rue, E.A., and Semenza, G. L. (1995). Hypoxia-inducible factor 1 is a basic-helix-loop-helix-PAS heterodimer regulated by cellular O2 tension. Proc. Natl. Acad. Sci. USA. 92, 5510-5514.

Forsythe, J.A., Jiang, B.-H., Iyer, N.V., Agani, F., Leung, S.W., Koos, R.D., and Semenza, G.L. (1996). Activation of vascular endothelial growth factor gene transcription by hypoxia-inducible factor 1. Mol. Cell. Biol. 16, 4604-4613.
 

BenchMarksInto Thin Air: How We Sense and Respond to Hypoxia Craig B. Thompson1,* 1Department of Cancer Biology and Genetics, Memorial Sloan Kettering Cancer Center, New York, NY 10065, USA*Correspondence: thompsonc@mskcc.orghttp://dx./10.1016/j.cell.2016.08.036This year’s Lasker Basic Medical Research Award is shared by William Kaelin, Peter Ratcliffe, andGregg Semenza for discovery of the pathway by which cells sense and adapt to changes in oxygenavailability, which plays an essential role in human adaptation to a wide variety of physiologic andpathologic conditions.One thing we all learned in grade school isthat oxygen is really important. Each timewe breathe, oxygen is taken up throughour lungs into the bloodstream andcarbon dioxide is expelled. The oxygenconsumed is essential for producing arobust energy supply with which to maintainthe viability and function of the 40trillion cells within our bodies. This isbecause our cells have two major mechanismsfor producing ATP from glucose:glycolysis, which can take place anaerobicallybut is highly inefficient at generatingATP, and oxidative phosphorylation,which maximizes ATP yield but requiresoxygen. Cells can also use oxidativephosphorylation to produce ATP fromfatty acid and amino acid degradation,further increasing the amount of energythat can be extracted from nutrients.Since the metabolic demands of a complexnervous system or muscle-basedmotility are impossible without efficientATP production, the harnessing of environmentaloxygen for energy productionwas essential for the development ofmulticellular animal life as we know it.As a result, how cells catabolize nutrientsand oxygen to produce the ATPrequired to maintain cellular bioenergeticshas been the subject of numerous scientificprizes. Moreover, when it becameclear that organs such as the brain, heart,and muscle are uniquely dependent onefficient production of ATP through oxidativephosphorylation, another generationof prizes was awarded for the discoveryand characterization of proteins, such ashemoglobin and myoglobin, that caneither carry oxygen to or buffer oxygenreserves in these vital tissues. Despitethese extraordinary accomplishments,until recently, one aspect of oxygen metabolismremained unresolved—namely,how animals sense and adapt to changinglevels of oxygen availability, a functionthat is essential for adaptation to highaltitudes and is dysregulated in diseasestates such as cardiopulmonary failureor anemia. This year’s Lasker BasicResearch Award is being awarded tothree scientists for their discovery ofthe central oxygen-sensing system thatallows animals to sense and adapt tophysiological variations in oxygen.Finding the FactorAlthough William Kaelin, Peter Ratcliffe,and Gregg Semenza worked independently,their work collectively uncoveredthe molecular mechanism by which organismssense and adapt to low oxygenlevels, or hypoxia. The solution to theproblem began with erythropoietin, ahematopoietic growth factor producedby the liver and kidney. Erythropoietinpromotes generation of red blood cellsin the bone marrow, thereby raising theblood’s oxygen carrying capacity.In an elegant series of experiments thatstarted with his interest in learning moreabout gene regulation mechanisms, Semenzamade the key initial discoveriesthat broke open the field. Using transgenicmice, he uncovered sequencespecificbinding of a transcription factorto the hypoxia-response element (HRE)in the 30 enhancer region of erythropoietinwhen liver cells were subjected to hypoxia(Semenza and Wang, 1992), and then biochemicallypurified the factor (Wang et al.,1995), a heterodimer that he dubbedHIF-1 (hypoxia inducible factor 1). Bothcomponents of this heterodimer weremembers of the bHLH-Pas family of transcriptionfactors, and while the HIF-1bcomponent (also known as ARNT) wasconstitutively expressed, expression ofHIF-1a varied in an oxygen-dependentfashion.Betting that HIF-1 did more than regulateerythropoietin expression, Semenzastarted digging deeper. A critical advancecame when he discovered that HIF-1aalso induced vascular endothelial growthfactor (VEGF), which plays a key role inangiogenesis (Forsythe et al., 1996). Thissuggested that HIF-1a was at the centerof an oxygen-sensing mechanism importantfor controlling both the generation ofthe vascular system and the productionof red cells to carry O2 within the bloodstream.To confirm the essential roleof HIF-1 in these organismal processes,Semenza then made HIF-1a mutantmice. In the absence of HIF-1a, he indeedfound that vascular development and oxygen-dependentgene expression wereseverely impaired, leading to embryoniclethality (Iyer et al., 1998).Over this time period, Semenza’swork was complemented and extendedby the work of Peter Ratcliffe. Oxygensensing was long thought to be a propertyrestricted to a specialized set of celltypes, but Ratcliffe showed that HREDNA binding activity was regulated in anoxygen-dependent fashion in all cell typeshe tested (Maxwell et al., 1993). This suggestedthat HIF-1 was a part of a universalcellular response mechanism to changesin oxygen availability. Ratcliffe confirmedthis by demonstrating that the genesencoding glycolytic enzymes were alsoregulated by hypoxia response elementsin their enhancers (Firth et al., 1994).Thus, HIF-1 was not only responsible forlong-term adaptation to hypoxia at theorganismal level, but also could dynamicallyregulate the rate of glycolysis, theoxygen-independent mechanism of ATPgeneration, at the cellular level.Cell 167, September 22, 2016 a 2016 Elsevier Inc. 1CELL 9155Please cite this article in press as: Thompson, Into Thin Air: How We Sense and Respond to Hypoxia, Cell (2016), http://dx./10.1016/j.cell.2016.08.036Clues from the ClinicUnlike Semenza and Ratcliffe, Kaelincame upon the oxygen adaptation pathwaythrough his efforts to make sense ofobservations in the cancer biology field.From his clinical training, he knew thatcertain kidney tumors had increasedvasculature and lost the tumor suppressorV(H)L, first identified in the von Hippel-Lindausyndrome. However, the cloning ofV(H)L had not provided any insights intoits potential molecular function. In 1995,Kaelin’s group was one of several toshow that V(H)L formed a complex withElongin B, Elongin C, and CUL2 (Kibelet al., 1995). Since Elongin C and CUL2showed homology to the yeast proteinsSKP1 and Cdc53, the V(H)L/Elongin/CUL2 complex might function as a ubiquitinligase and therefore control proteinstability. But how did this lead to increasedvasculature of kidney tumors? Kaelinhypothesized that the absence of V(H)Lmight lead cells to produce the angiogenicfactor VEGF. Indeed, he found that V(H)Ldeficiency led to constitutive upregulationof HIF-dependent targets defined byRatcliffe and Semenza, including VEGF,even in the presence of oxygen (Iliopouloset al., 1996).Making the Oxygen LinkBased on these discoveries, both Ratcliffeand Kaelin went on to uncover asimple and elegant post-translationaloxygen-sensing mechanism. They firstshowed that V(H)L acted as an E3 ubiquitinligase for HIF-1a and that ubiquitinationof HIF-1a led to its degradation. Inback-to-back papers in 2001, Ratcliffeand Kaelin reported that HIF-1a underwentproline hydroxylation in the presenceof oxygen and that V(H)L specificallybound hydroxylated HIF-1a to target it fordegradation in an oxygen-dependentfashion (Ivan et al., 2001; Jaakkola et al.,2001). This of course raised a question:what was controlling the oxygen-dependenthydroxylation of HIF-1a? Ratcliffe,Kaelin, and Steve McKnight independentlyreported the discovery of a familyof prolyl-4-hydroxylases with this function(Bruick and McKnight, 2001; Ivan et al.,2002; Epstein et al., 2001). A second oxygen-dependentmechanism of HIF-1a hydroxylation,this time on asparagine residues,was subsequently found to blockthe ability of HIF-1a to recruit transcriptionalcoactivators (Lando et al., 2002).This provided cells with a back-up systemto block any residual HIF-1 that hadescaped degradation from activatingtranscription of target genes.Sensing More Than Just OxygenThe discovery of HIF-1a-modifying hydroxylasesled to a broader interest inthe role of these enzymes as metabolitesensors. In addition to their originallydescribed function as oxygen sensors,subsequent studies have shown thatthey can also be regulated by other reactants,as well as the products of the reactionsthey carry out. Each of the enzymescontains a catalytic Fe2+ in the active siteto hydroxylate targets using oxygen andalpha-ketoglutarate (aKG) as reactants,producing succinate and carbon dioxideas byproducts (Figure 1). Sustained inhibitionof HIF hydroxylation in hypoxia isalso accomplished in part through lactatedehydrogenase (LDH-A)-dependent conversionof aKG to L-2-hydroxyglutarate(L-2HG). The resulting L-2HG acts as acompetitive inhibitor of aKG binding tothe HIF hydroxylases (Harris, 2015).The broader relevance of this metabolicsensor pathway in cancer becameevident in studies involving two other tumorsuppressor syndromes with a hypervascularmicroenvironment similar to thatobserved in V(H)L mutant renal cell carcinomas.In these tumor syndromes, lossof-functionmutations in either succinatedehydrogenase or fumarase led to highlevels of HIF-1 in the presence of oxygen.Without these enzymes, the TCA cycleintermediates succinate and fumarateaccumulate, leading to end productinhibition of the HIF hydroxylases. Thus,accumulation of succinate and/or fumaratecan prevent hydroxylation of HIFeven in an oxygen-rich environment.The HIF-1 prolyl hydroxylases have alsobeen shown to be redox sensors. Boththe catalytic Fe2+ and cysteines requiredfor HIF-1’s three-dimensional structureare highly susceptible to inactivation byFigure 1. Oxygen-Dependent Regulation of the HIF-1 Transcription Factor by ProlylHydroxylasesUnder normoxic conditions, the HIF-1a component of the heterodimeric transcription factor, HIF-1,undergoes hydroxylation through the enzymatic activity of prolyl hydroxylases. The resulting prolylhydroxylation of HIF-1a is recognized by the tumor suppressor V(H)L, leading to V(H)L-dependentrecruitment of a ubiquitin ligase complex and HIF-1a ubiquitination and proteosomal degradation. In thereaction carried out by prolyl hydroxylases, the concentration of oxygen is rate limiting. This allows thehydroxylation reaction to regulate the accumulation of HIF-1a in direct relation to oxygen availability.Under hypoxic conditions, the accumulating HIF-1a dimerizes with HIF-1b, leading to nuclear translocationand binding to hypoxia-response elements (HRE) in genes required for hypoxic adaptation.Sequence-specific DNA binding of HIF-1 leads to the recruitment of transcriptional co-activators such asp300 and the transcription of target genes that stimulate increased vascularization (VEGF), enhance theoxygen carrying capacity of blood (erythropoietin), stimulate oxygen-independent production of ATPthrough glycolysis (LDH-A), and suppress TCA cycle activity and oxidative phosphorylation (PDHK).2 Cell 167, September 22, 2016CELL 9155Please cite this article in press as: Thompson, Into Thin Air: How We Sense and Respond to Hypoxia, Cell (2016), http://dx./10.1016/j.cell.2016.08.036oxidation under conditions where themitochondrial electron transport chainactivity exceeds cellular ATP consumption.The redox sensitivity component ofthe proline hydroxylases thus allows cellsto adapt not only to hypoxia but alsoconditions when glucose metabolism exceedscellular ATP demand. Under theseconditions, HIF-1-induced expression ofpyruvate dehydrogenase kinase (PDHK)suppresses TCA cycle activity, andHIF-1 induction of LDH-A redirects glycolyticpyruvate into lactate for excretionfrom the cell. Thus, HIF-1 can protect cellsnot only from hypoxia, but also fromexcess nutrient catabolism, by directingcell metabolism from the highly efficientoxidative phosphorylation to the less effi-cient glycolysis, thus preventing redoxstress.Beyond ATP ProductionThe discovery that the activity of HIFprolyl hydroxylases are dynamicallyregulated within the physiological rangeof oxygen concentration has led to arenewed interest in the role of oxygenin controlling other cellular activities. Asa result, a number of additional oxygen-dependentenzymes have emergedas potential regulators of cellular adaptationto hypoxia. For example, boththe TET family of DNA methyl cytosinehydroxylases and the Jumonji family ofhistone demethylases carry out similarmolecular reactions to the proline hydroxylases.These enzymes hydroxylatemethyl groups on DNA and proteins,respectively. Like the HIF-1-prolyl andasparaginyl hydroxylases, they also useaKG and oxygen as reactants to hydroxylatesubstrates and decarboxylateaKG. Since these enzymes have beenimplicated in the regulation of chromatinaccessibility during cellular differentiation,their oxygen dependence hasbeen proposed to provide a potentialmolecular explanation for why in mostadult mammalian tissues, stem cellmaintenance is carried out in relativelyhypoxic niches.Impairment of the aKG-dependentdioxygenases involved in histone andDNA demethylation has been shown toresult from cancer-causing mutations ineither isocitrate dehydrogenase (IDH) 1or 2. These IDH mutations result in a neomorphicenzymatic activity that producesD-2-hydroxyglutarate, which competeswith aKG for binding to this family ofdioxygenases, thereby impairing DNAand histone demethylation (Harris, 2015).These results suggest that the chemistryinvolved in aKG-dependent dioxygenasefunction may be used reiteratively inmetazoan biology to drive not only adaptivemetabolic responses to hypoxia, butto also regulate embryonic development/differentiation under suboptimal nutrientconditions, such as oxygen depletionand TCA cycle dysfunction.New Appreciation for OxygenIt took just under a decade for Kaelin,Ratcliffe, and Semenza to unravel thiselegant oxygen-sensing system. However,it is only in the last 15 years that scientistshave begun to fully appreciate thebroad implications of their discovery. Forexample, HIF-1 plays an essential role inorganismal adaptation to high altitudes,congestive heart failure, chronic obstructivepulmonary disease, and other formsof pulmonary distress and contributes tostroke, coronary artery disease, and cancer.It also plays a critical role in cellularbioenergetic adaptation to prevent redoxstress and to preserve macromolecularsynthesis under both normoxic and hypoxicconditions.The role of aKG-dependent dioxygenasesin cell processes beyond HIF-1adestabilization has led to a broaderappreciation of the role of oxygen inmammalian cell biology well beyond itsuse in oxidative phosphorylation. It isnow appreciated that a wide variety ofother cellular processes are controlledby oxygen-dependent enzymes whosedynamic range of activity occurs withinthe physiologic variation in oxygen levelsof viable tissues. Oxygen is required notjust for the maintenance of ATP production,it is increasingly recognized as acritical component of the regulation of awide variety of host events includingcellular differentiation, immune defense,and tissue repair.REFERENCESBruick, R.K., and McKnight, S.L. (2001). Science294, 1337–1340.Epstein, A.C., Gleadle, J.M., McNeill, L.A., Hewitson,K.S., O’Rourke, J., Mole, D.R., Mukherji, M.,Metzen, E., Wilson, M.I., Dhanda, A., et al. (2001).Cell 107, 43–54.Firth, J.D., Ebert, B.L., Pugh, C.W., and Ratcliffe,P.J. (1994). Proc. Natl. Acad. Sci. USA 91, 6496–6500.Forsythe, J.A., Jiang, B.H., Iyer, N.V., Agani, F.,Leung, S.W., Koos, R.D., and Semenza, G.L.(1996). Mol. Cell. Biol. 16, 4604–4613.Harris, A.L. (2015). Cell Metab. 22, 198–200.Iliopoulos, O., Levy, A.P., Jiang, C., Kaelin, W.G.,Jr., and Goldberg, M.A. (1996). Proc. Natl. Acad.Sci. USA 93, 10595–10599.Ivan, M., Kondo, K., Yang, H., Kim, W., Valiando,J., Ohh, M., Salic, A., Asara, J.M., Lane, W.S., andKaelin, W.G., Jr. (2001). Science 292, 464–468.Ivan, M., Haberberger, T., Gervasi, D.C., Michelson,K.S., Gu¨ nzler, V., Kondo, K., Yang, H., Sorokina,I., Conaway, R.C., Conaway, J.W., andKaelin, W.G., Jr. (2002). Proc. Natl. Acad. Sci.USA 99, 13459–13464.Iyer, N.V., Kotch, L.E., Agani, F., Leung, S.W.,Laughner, E., Wenger, R.H., Gassmann, M., Gearhart,J.D., Lawler, A.M., Yu, A.Y., and Semenza,G.L. (1998). Genes Dev. 12, 149–162.Jaakkola, P., Mole, D.R., Tian, Y.M., Wilson, M.I.,Gielbert, J., Gaskell, S.J., von Kriegsheim, A.,Hebestreit, H.F., Mukherji, M., Schofield, C.J.,et al. (2001). Science 292, 468–472.Kibel, A., Iliopoulos, O., DeCaprio, J.A., and Kaelin,W.G., Jr. (1995). Science 269, 1444–1446.Lando, D., Peet, D.J., Gorman, J.J., Whelan, D.A.,Whitelaw, M.L., and Bruick, R.K. (2002). GenesDev. 16, 1466–1471.Maxwell, P.H., Pugh, C.W., and Ratcliffe, P.J.(1993). Proc. Natl. Acad. Sci. USA 90, 2423–2427.Semenza, G.L., and Wang, G.L. (1992). Mol. Cell.Biol. 12, 5447–5454.Wang, G.L., Jiang, B.H., Rue, E.A., and Semenza,G.L. (1995). Proc. Natl. Acad. Sci. USA 92, 5510–5514.Cell 167, September 22, 2016 3    CELL 9155

A false dichotomy plagues American medical schools. The dichotomy states that basic scientists make discoveries and physicians apply discoveries to patients.  This year’s Lasker Awards expose the fallacy of this dichotomy.  The Basic Award goes to three physicians and the Clinical Award goes to three basic scientists. The physicians discovered a fundamental property of nature, and the basic scientists translated discoveries into a cure for a fatal liver disease.

The Basic Award recognizes three physicians who discovered the universal mechanism by which animals respond to a deficiency of oxygen.  The three doctors are Gregg Semenza of Johns Hopkins, Peter Ratcliffe of Oxford and William Kaelin of Harvard. 

Our cells use oxygen much like a fireplace does—oxygen combines with carbon to release energy. Cells cannot store oxygen.  They require a constant supply.  When deprived of oxygen, brain and heart cells die within minutes.  The result is a stroke or a heart attack.  The body needs to sense oxygen deficiency and to correct it.

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