Valosin-containing Protein (VCP)/p97 Segregase Mediates Proteolytic Processing of Cockayne Syndrome Group B (CSB) in Damaged Chromatin.

Cockayne syndrome group A and B (CSB) proteins act in transcription-coupled repair, a subpathway of nucleotide excision repair. Here we demonstrate that valosin-containing protein (VCP)/p97 segregase functions in ultraviolet radiation (UVR)-induced ubiquitin-mediated CSB degradation. We show that VCP/p97 inhibition and siRNA-mediated ablation of VCP/p97 and its cofactors UFD1 and UBXD7 impair CSB degradation. VCP/p97 inhibition also results in the accumulation of CSB in chromatin. Moreover, VCP/p97 interacts with both native and ubiquitin-conjugated forms of CSB. The localized cellular UVR exposures lead to VCP/p97 accumulation at DNA damage spots, forming distinct UVR-induced foci. However, manifestation of VCP/p97 foci is independent of CSB and UBXD7. Furthermore, VCP/p97 and UBXD7 associate with the Cockayne syndrome group A-DDB1-Cul4A complex, an E3 ligase responsible for CSB ubiquitination. Compromising proteasome and VCP/p97 function allows accumulation of both native and ubiquitinated CSB and results in an increase of UBXD7, proteasomal RPN2, and Sug1 in the chromatin compartment. Surprisingly, both biochemical inhibition and genetic defect of VCP/p97 enhance the recovery of RNA synthesis following UVR, whereas both VCP/p97 and proteasome inhibitions decrease cell viability. Our findings reveal a new role of VCP/p97 segregase in the timely processing of ubiquitinated CSB from damaged chromatin.