https://orcid.org/0000-0002-8586-9930
Gregg Semenza, MD, PhD is professor of Genetic Medicine at the Johns Hopkins School of Medicine, in the United States. He is known for his discovery of hypoxia-inducible factor 1 (HIF-1), which allows cells to adapt to oxygen-poor environments. He shared the 2019 Nobel Prize in Physiology or Medicine for ‘discoveries of how cells sense and adapt to oxygen availability’ with William Kaelin Jr and Peter J. Ratcliffe.
Your studies have paved the way in understanding some of the pathophysiological mechanisms underlying cardiovascular disease and to potential therapeutic interventions. Could you tell us what led to your ground-breaking discovery of HIF-1?
When I arrived at Johns Hopkins as a postdoctoral fellow, I decided to investigate the mechanisms regulating expression of the human erythropoietin (EPO) gene using transgenic mice. After several years spent identifying sequences near and far that were required for EPO gene expression in liver and kidney, I focused on investigating the mechanism regulating increased expression of the EPO gene in response to anaemia in vivo or when the human Hep3B hepatoblastoma cell line was subjected to hypoxia in tissue culture. We identified a short DNA sequence downstream of the EPO gene that is now known as the hypoxia-response element or HRE, which endowed a reporter gene with hypoxia-induced expression. We found that exposing Hep3B cells to 1% O2 for 4 h induced the presence of a nuclear factor capable of binding to the HRE, and we named this DNA-binding activity, HIF-1 (Figure 1).1 We used the binding of HIF-1 to the HRE as the means to purify the protein from 120 L of HeLa cells grown in suspension culture. Starting with the discovery of HIF-1 as an activator of EPO gene transcription, we now know of over 8000 RNAs with expression that is induced by HIF-1 or HIF-2 in response to hypoxia in one cell type or another.
Autoradiograph of the gel shift assay through which Prof. Gregg Semenza with his research group identified hypoxia-inducible factor 1. The original autoradiograph is now in the Nobel Prize Museum in Stockholm. Lanes 1 and 2 contain a DNA fragment from the hypoxia-response element. Lanes 3 and 4 contain the same DNA fragment with a three base-pair change which eliminates the ability of the HRE to direct hypoxia-induced gene expression. The big arrow points to a band that is present in Lane 1 but not in any other lane. This is hypoxia-inducible factor 1. Reprinted from Semenza1 with permission from Elsevier Inc.
Credit of the Prof. Gregg Semenza photograph to Jay van Rensselaer, Johns Hopkins Medicine.
Can you explain how HIFs might have both a protective effect, such as in ischaemic cardiovascular disease, and may also conversely contribute to disease pathogenesis?2
The fundamental role of HIFs is to maintain oxygen homeostasis by balancing supply and demand. Hypoxia-inducible factor 1 turns on the expression of genes that increase O2 delivery and genes that decrease O2 consumption. The protective effect of HIFs in ischaemic cardiovascular disease was demonstrated by studying the effect of aging on the response to acute ischaemia. We performed unilateral femoral artery ligation using mice of different ages. Young mice—2 months old—recovered blood flow in the limb without any permanent tissue damage. Middle-aged mice—8 months old—showed only partial recovery of blood flow and many of the mice developed soft-tissue necrosis or the loss of one or more toes. Old mice—20 months old—showed little recovery of blood flow and many of the mice lost their entire foot due to inadequate perfusion. We also performed the experiments with mice that were heterozygous for a knockout allele at the HIF-1α locus and, at every age, they had a more severe phenotype then their wild-type littermates. Next, we looked at the expression of HIF-1α in the ischaemic limb. In the young wild-type mice, there was a robust induction of HIF-1α protein in the limb 3 days after femoral artery ligation; in the middle-aged mice, the induction was not as robust; and in the old mice, there was very little induction at all. These results suggested that aging impaired the induction of HIF-1α in response to hypoxia/ischaemia. We then provided replacement therapy in the form of an adenovirus that we had engineered to encode a stable form of HIF-1α. When the adenovirus was injected into the ischaemic limb of middle-aged mice immediately after femoral artery ligation, they recovered blood flow at the rate observed in the young mice and were protected from the development of tissue injury. Thus, we were able to overcome the age-dependent impairment of HIF-1α expression in response to ischaemia. In other studies, we showed that HIFs play a critical role in the phenomenon of ischaemic preconditioning of the myocardium. In contrast to these protective roles in ischaemic cardiovascular disease, HIFs are induced by hypoxia within tumours and many studies have demonstrated that HIFs contribute to critical aspects of cancer progression, including angiogenesis, cancer stem-cell specification, invasion and metastasis, metabolic reprogramming and, most recently, immune evasion. Inhibition of HIF activity, through genetic or pharmacological strategies, blocks these processes.
As the C. Michael Armstrong professor at John Hopkins University, you manage a top-level research centre. Where do your current research interests lie? What are your priorities in terms of basic and clinical research?
From a basic science standpoint, we continue to investigate the molecular mechanisms by which increased expression of HIFs leads to increased transcriptional activation of target genes in response to hypoxia. We are also interested in genetic disorders in which HIF activity is altered. From a clinical standpoint, the major goal of the lab is to identify chemical compounds that inhibit HIF activity and block cancer progression. We have identified a compound, which we have designated 32–134D, that inhibits HIF transcriptional activity in Hep3B hepatocellular carcinoma xenografts by causing degradation of HIF-1α and HIF-2α, thereby inhibiting the expression of multiple angiogenic factors and impairing tumour vascularization. In a Hepa1–6 syngeneic mouse model of hepatocellular carcinoma, HIF inhibition by administration of 32–134D reprogrammes the tumour immune microenvironment by increasing the recruitment of CD8+ T cells and natural killer cells, which mediate antitumour immunity, and by decreasing the number myeloid-derived suppressor cells and tumour-associated macrophages, which mediate immunosuppression. When administered as monotherapy, anti-PD1 immunotherapy resulted in tumour eradication in 25% of the mice, whereas co-administration of 32–134D with anti-PD1 therapy increased the tumour eradication rate to 67%. Our efforts to develop novel HIF inhibitors as anticancer agents would not be possible without the generous support of Mike Armstrong, who is a three-time cancer survivor.
What role does communication play for a scientist? Can you suggest any strategies to raise public awareness of the relevance of scientific research and the need to invest in it more?
Scientists communicate with one another through publications and presentations at scientific meetings. Communication with the public is not as frequent because the media give less attention to scientific discoveries than they do to baseball games. At the same time, a large industry has developed to discredit scientific research and scientific advances that improve public health. Shutting down these social media platforms, which propagate lies and misinformation in a cynical effort to enrich themselves at the expense of public health, would be an important step. Publicizing basic science discoveries which have led directly or indirectly to therapies that advance public health would help the average citizen to connect the dots from basic research to improved patient outcomes. How many people know who discovered oxygen? For that matter, how many scientists know? It is a great story filled with inspiration, folly, and deceit.
What role did mentorship have in your career and what makes a good mentor? You have trained many young researchers; any special advice for them?
I was fortunate to have strong mentors at every step of my career and my achievements would have been impossible without them. As a mentor, I try to help my trainees reach their chosen goals regardless of what career path they decide to follow.
To conclude, the prestigious awards you have received are the result of exceptional tenacity and intense work. Every achievement requires sacrifices. Were there any barriers that you had to overcome to achieve such extraordinary results?
First, I would say that it is not always necessary or even proper to invoke exceptionalism: sometimes ordinary scientists perform ordinary experiments and obtain results that over time have extraordinary significance. Second, all scientists encounter challenges that must be overcome, and this is one of the appealing features of biomedical research. Third, we all make decisions on how we choose to live our lives, which we understand involve taking the good with the bad. For the most part, I have found a career in biomedical research to be both challenging and fulfilling.
Data availability
No new data were generated or analysed in support of this research.
References
Author notes
Conflict of interest: None declared.
