title: The xeroderma pigmentosum group E gene product DDB2 activates nucleotide excision repair by regulating the level of p21Waf1/Cip1.
abstract: The xeroderma pigmentosum group E gene product DDB2, a protein involved in nucleotide excision repair (NER), associates with the E3 ubiquitin ligase complex Cul4A-DDB1. But the precise role of these interactions in the NER activity of DDB2 is unclear. Several models, including DDB2-mediated ubiquitination of histones in UV-irradiated cells, have been proposed. But those models lack clear genetic evidence. Here we show that DDB2 participates in NER by regulating the cellular levels of p21(Waf1/Cip1). We show that DDB2 enhances nuclear accumulation of DDB1, which binds to a modified form of p53 containing phosphorylation at Ser18 (p53(S18P)) and targets it for degradation in low-dose-UV-irradiated cells. DDB2(-/-) mouse embryonic fibroblasts (MEFs), unlike wild-type MEFs, are deficient in the proteolysis of p53(S18P). Accumulation of p53(S18P) in DDB2(-/-) MEFs causes higher expression p21(Waf1/Cip1). We show that the increased expression of p21(Waf1/Cip1) is the cause NER deficiency in DDB2(-/-) cells because deletion or knockdown of p21(Waf1/Cip1) reverses their NER-deficient phenotype. p21(Waf1/Cip1) was shown to bind PCNA, which is required for both DNA replication and NER. Moreover, an increased level of p21(Waf1/Cip1) was shown to inhibit NER both in vitro and in vivo. Our results provide genetic evidence linking the regulation of p21(Waf1/Cip1) to the NER activity of DDB2.
authors.affiliation: Department of Biochemistry and Molecular Genetics (M/C 669), University of Illinois at Chicago, 900 South Ashland Avenue, Chicago, IL 60607, USA.
authors.forename: Tanya
authors.initials: T
authors.lastname: Stoyanova
authors.forename: Taewon
authors.initials: T
authors.lastname: Yoon
authors.forename: Dragana
authors.initials: D
authors.lastname: Kopanja
authors.forename: Margalit B
authors.initials: MB
authors.lastname: Mokyr
authors.forename: Pradip
authors.initials: P
authors.lastname: Raychaudhuri
mesh_terms: D000818:Animals; D002460:Cell Line; D044842:Cullin Proteins / Q000378:metabolism; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D004247:DNA / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004260:DNA Repair; D004268:DNA-Binding Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D009711:Nucleotides / Q000235:genetics*; D011485:Protein Binding; D015398:Signal Transduction / Q000528:radiation effects; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism; D014466:Ultraviolet Rays; D014983:Xeroderma Pigmentosum / Q000235:genetics / Q000378:metabolism*
chemical_list: C493957:Cdkn1a protein, mouse; C491940:Cul4a protein, mouse; D044842:Cullin Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; C117669:DDB2 protein, human; D004268:DNA-Binding Proteins; C490415:Ddb1 protein, mouse; C496850:Ddb2 protein, mouse; D009711:Nucleotides; D016159:Tumor Suppressor Protein p53; D004247:DNA