Hypoxia, or decreased oxygen availability, is an important stimulus for physiological processes such as embryo development but importantly plays a role in the pathology of numerous human diseases. Furthermore, hypoxia is associated with treatment resistance. As such, understanding the mechanisms controlling the cellular responses to hypoxia is of great importance.
In response to hypoxia, cells activate a transcriptional programme aiming to restore oxygen homeostasis. To this end, the Hypoxia Inducible Factor (HIF) family of transcription factors (HIF-1a, HIF-2a and HIF-3a) is the main regulator of this process. Oxygen-mediated control of these transcription factors is achieved by the action of a class of dioxygenases encompassing prolyl-hydroxylases (PHDs) and Factor Inhibiting HIF (FIH), an asparagine hydroxylase. Hydroxylation by PHDs creates a high affinity binding site for the tumour suppressor von Hippel Lindau (VHL), which promotes ubiquitination and rapid proteasomal degradation of HIF-a in normal oxygen tensions.
Research in the Rocha lab focuses on investigating additional mechanisms controlling the HIF system in cells, both in normoxia and hypoxia. We have made important contributions identifying an intricate crosstalk between HIF and a major transcription factor family involved in the response to inflammation, NF-kB.
In addition to NF-kB, we have identified Cezanne (OTUD7b) as a novel regulator of the HIF system. Cezanne is a Lysine 11-ubiquitin specific de-ubiquinase, and our data indicated that HIF-1a is lysine 11-ubiquitin modified. Cezanne inhibition leads to reduced HIF-1a expression independent of transcription and proteasomal degradation, but seems to result in increased HIF-1a degradation by autophagy. We have also found that Cezanne regulates HIF-2a, however, in this case, the mechanism is indirect, through the control of the transcription factor E2F1. We have found that E2F1 is a direct regulator of the HIF-2a promoter, indicating that HIF-2a is cell cycle regulated.
Given that PHDs are the main regulators of HIF, we investigated if PHDs had other functions in the cell. We have found that PHD1 and PHD2 are important regulators of the cell cycle. We have identified the first non-HIF related target for PHD1, in the centrosomal protein Cep192. We have identified a CDK-mediated phosphorylation site in PHD1 that controls its substrate specificity in cells, without affecting its intrinsic hydroxylase activity. Projects in any of these areas are available for PhD students with interests in mechanisms underpinning human diseases such as cancer, inflammatory diseases, cardiovascular diseases amongst others.
PHD1 links Cell-Cycle progression to oxygen sensing through hydroxylation of the centrosomal protein Cep192. Moser S, Bensaddek D, Ortmann B, Maure JF, Mudie S, Blow JJ, Lamond AI, Swedlow JR, and Rocha S. (2013) Dev. Cell. 26, 381-192.
HIF-1alpha restricts NF-kappaB-dependent gene expression to control innate immunity signals. Bandarra, D., Biddlestone, J., Mudie, S., Muller, H. A., and Rocha, S. (2015). Dis. Models and Mech. 8, 169-181.
Cezanne (OTUD7B) regulates HIF-1alpha homeostasis in a proteasome-independent manner. Bremm, A., Moniz, S., Mader, J., Rocha, S., and Komander, D. (2014). EMBO Rep. 15, 1268-1277