Cdt2-mediated XPG degradation promotes gap-filling DNA synthesis in nucleotide excision repair.
Xeroderma pigmentosum group G (XPG) protein is a structure-specific repair endonuclease, which cleaves DNA strands on the 3' side of the DNA damage during nucleotide excision repair (NER). XPG also plays a crucial role in initiating DNA repair synthesis through recruitment of PCNA to the repair sites. However, the fate of XPG protein subsequent to the excision of DNA damage has remained unresolved. Here, we show that XPG, following its action on bulky lesions resulting from exposures to UV irradiation and cisplatin, is subjected to proteasome-mediated proteolytic degradation. Productive NER processing is required for XPG degradation as both UV and cisplatin treatment-induced XPG degradation is compromised in NER-deficient XP-A, XP-B, XP-C, and XP-F cells. In addition, the NER-related XPG degradation requires Cdt2, a component of an E3 ubiquitin ligase, CRL4(Cdt2). Micropore local UV irradiation and in situ Proximity Ligation assays demonstrated that Cdt2 is recruited to the UV-damage sites and interacts with XPG in the presence of PCNA. Importantly, Cdt2-mediated XPG degradation is crucial to the subsequent recruitment of DNA polymerase δ and DNA repair synthesis. Collectively, our data support the idea of PCNA recruitment to damage sites which occurs in conjunction with XPG, recognition of the PCNA-bound XPG by CRL4(Cdt2) for specific ubiquitylation and finally the protein degradation. In essence, XPG elimination from DNA damage sites clears the chromatin space needed for the subsequent recruitment of DNA polymerase δ to the damage site and completion of gap-filling DNA synthesis during the final stage of NER.
['Han|Chunhua|C|', 'Wani|Gulzar|G|', 'Zhao|Ran|R|', 'Qian|Jiang|J|', 'Sharma|Nidhi|N|', 'He|Jinshan|J|', 'Zhu|Qianzheng|Q|', 'Wang|Qi-En|QE|', 'Wani|Altaf A|AA|']
D002945:Cisplatin D004249:DNA Damage D004258:DNA Polymerase III D004260:DNA Repair D004268:DNA-Binding Proteins D004720:Endonucleases D006367:HeLa Cells D006801:Humans D007976:Leupeptins D009687:Nuclear Proteins D018809:Proliferating Cell Nuclear Antigen D046988:Proteasome Endopeptidase Complex D061988:Proteasome Inhibitors D059748:Proteolysis D014157:Transcription Factors D044767:Ubiquitin-Protein Ligases D054875:Ubiquitination
XPG gap-filling DNA synthesis nucleotide excision repair PCNA Cdt2 ubiquitylation protein degradation CRL4