Group Ramadan

Background: Unrepaired DNA double strand breaks (DSB) are the cause of genetic instability that may lead to malignant transformation or cell death. Cells respond to DSB with the ordered recruitment of signaling and repair proteins to the site of lesion to orchestrate the repair of damaged DNA. This complex mechanism is called the DNA damage response (DDR). In recent years ubiquitin and SUMO emerged as necessary factors in the regulation of signaling and repair cascades, but how ubiquitination and sumoylation coordinate DDR is still poorly understood. Upon DSB E3 ubiquitin ubiquitin ligase RNF8 creates monoubiquitination on histones, which serves as a recruiting platform for the engagement of the second E3 ubiqutin ligase RNF168. RNF168 further creates Lys(K)63 polyubiquitinated chains on histones, which serves as the main signal to recruit downstream factors such as BRCA1 and 53BP1 to finally orchestrate DNA repair and cell cycle regulation. 53BP1 and BRCA1 are two crucial proteins for genome maintenance and cell survival. Until now this cascade was considered to be the main ubiquitin signaling pathway at the sites of DSB. Recently, we have discovered that Valosin-containing protein (VCP) or p97, a central element of the ubiquitin-proteasome system (UPS) is a crucial factor in DDR after DSB. Our finding opens a new paradigm in the orchestration of the ubiqutin cascade at sites of DSB.

Goal: Our aim is to understand the molecular details of how p97 orchestrates DSB. This is of the fundamental biological and medical interest, because only accurate and precise functioning of DDR can protect cells from cancer. Using the cell- biological and biochemical methods in human cell lines and Xenopus laevis egg extract we want to address:
a) mechanistic insight of p97 function in DSB
b) implication of p97 in anti-cancer therapy

General impact: Given the essential functions of DDR proteins in coordination of the DSB repair pathways, NHEJ and HR, p97 may qualify as a potential drug target for the anti cancer therapy. In addition, our results will also tremendously contribute to the understanding the, so far unknown, molecular function of the proteasome inhibitor bortezomib (Velcade, Millennium Pharmaceuticals), which is currently used as a successful drug for the treatments of multiple myeloma and mantle-cell lymphoma.