Structural and functional analysis of K11-linked ubiquitin chains and the deubiquitinase Cezanne in the HIF signaling pathway and the cellular adaptation to hypoxia.

• Applicant: Dr. Anja Bremm
• Subject Area: Biochemistry
• Term: from 2011 to 2012
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 201210009

Protein ubiquitination is a versatile posttranslational modification that affects almost every cellular process. Its complexity arises from the ability of ubiquitin to form eight distinct polymers in which ubiquitin molecules are linked via one of seven lysine (K) residues or through the N-terminus. So far we know the cellular functions of K48-linked chains that mediate proteasomal degradation, and of K63-linked chains that have various non-proteolytic roles. K11-linked ubiquitin chains are also highly abundant, and emerged as key regulators of the cell cycle. I identified Cezanne as the first K11-specific deubiquitinating enzyme. This discovery provides a great entry point to reveal new roles of K11-linked ubiquitin chains in cells. Tumor hypoxia is a regulatory factor in cancer progression and is associated with poor prognosis and resistance to radiotherapy. The cellular responses to hypoxia are mediated by a key transcription factor, HIF-1. Factor inhibiting HIF (FIH-1) mediates HIF asparagine hydroxylation, which directly inhibits transcriptional activity. Interestingly, proteomic analysis identified FIH-1 as an interactor of Cezanne, suggesting a role of K11-linked ubiquitin chains in HIF signaling. Here I propose to study the role of Cezanne in hypoxia by understanding its interaction with FIH-1 biochemically, structurally and functionally. Preliminary analysis indeed identified Cezanne as a potent regulator of HIF transcriptional activity. I further established the interaction between Cezanne and FIH-1 at the endogenous level. I will now need to understand how Cezanne influences HIF activity, and if the observed effects are mediated via FIH-1. I will also need to identify K11-modified targets of Cezanne in the hypoxia signaling cascade. My work will reveal novel roles for K11-linked ubiquitin chains in cellular regulation, and open new avenues to understand and eventually interfere with a signaling pathway of highest medically importance.

• DFG Programme: Research Fellowships
• International Connection: United Kingdom
• Host: Professor David Komander, Ph.D.