Ubiquitin-specific protease 7 regulates nucleotide excision repair through deubiquinating XPC and preventing XPC from UV-induced and VCP/p97-regulated proteolysis [Cell Biology]
August 12th, 2014 by He, J., Zhu, Q., Wani, G., Sharma, N., Han, C., Qian, J., Pentz, K., Wang, Q., Wani, A. A.
Ubiquitin specific protease 7 (USP7), is a known deubiquinating enzyme for tumor suppressor p53 and its downstream regulator E3 ubiquitin-ligase Mdm2. Here, we report that USP7 regulates nucleotide excision repair (NER) via deubiquitinating Xeroderma pigmentosum complementation group C (XPC) protein, a critical damage recognition factor which binds to helix-distorting DNA lesions and initiates NER. XPC is ubiquitinated during early stage of NER of ultraviolet light (UV)-induced DNA lesions. We demonstrate that transiently compromising cellular USP7 by siRNA and chemical inhibition leads to accumulation of ubiquitinated forms of XPC, while complete USP7 deficiency leads a rapid ubiquitin-mediated XPC degradation upon UV irradiation. We show that USP7 physically interacts with XPC in vitro and in vivo. Overexpression of wild-type USP7, but not its catalytically inactive or interaction-defective mutants, reduces ubiquitinated forms of XPC. Importantly, USP7 efficiently deubiquitinates XPC-ubiquitin conjugates in deubiquitination assays in vitro. We further showed that valosin-containing protein (VCP)/p97 is involved in UV-induced XPC degradation in USP7-deficient cells. VCP/p97 is readily recruited to DNA damage sites and co-localizes with XPC. Chemical inhibition of VCP/p97 ATPase activity causes an increase in ubiquitinated XPC on DNA damaged chromatin. Moreover, USP7 deficiency severely impairs the repair of cyclobutane pyrimidine dimers (CPD) and, to a lesser extent, affects the repair of 6-4 photoproducts (6-4PP). Taken together, our findings have uncovered an important role of USP7 in regulating NER via deubiquitinating XPC and by preventing its VCP/p97-regulated proteolysis.