title: A UVR-induced G2-phase checkpoint response to ssDNA gaps produced by replication fork bypass of unrepaired lesions is defective in melanoma.
abstract: UVR is a major environmental risk factor for the development of melanoma. Here we describe a coupled DNA-damage tolerance (DDT) mechanism and G2-phase cell cycle checkpoint induced in response to suberythemal doses of UVR that is commonly defective in melanomas. This coupled response is triggered by a small number of UVR-induced DNA lesions incurred during G1 phase that are not repaired by nucleotide excision repair (NER). These lesions are detected during S phase, but rather than stalling replication, they trigger the DDT-dependent formation of single-stranded DNA (ssDNA) gaps. The ssDNA attracts replication protein A (RPA), which initiates ATR-Chk1 (ataxia telangiectasia and Rad3-related/checkpoint kinase 1) G2-phase checkpoint signaling, and colocalizes with components of the RAD18 and RAD51 postreplication repair pathways. We demonstrate that depletion of RAD18 delays both the resolution of RPA foci and exit from the G2-phase arrest, indicating the involvement of RAD18-dependent postreplication repair in ssDNA gap repair during G2 phase. Moreover, the presence of RAD51 and BRCA1 suggests that an error-free mechanism may also contribute to repair. Loss of the UVR-induced G2-phase checkpoint results in increased UVR signature mutations after exposure to suberythemal UVR. We propose that defects in the UVR-induced G2-phase checkpoint and repair mechanism are likely to contribute to melanoma development.
authors.affiliation: University of Queensland Diamantina Institute, Princess Alexandra Hospital, Brisbane, Queensland, Australia.
authors.forename: Matthew
authors.initials: M
authors.lastname: Wigan
authors.forename: Alex
authors.initials: A
authors.lastname: Pinder
authors.forename: Nichole
authors.initials: N
authors.lastname: Giles
authors.forename: Sandra
authors.initials: S
authors.lastname: Pavey
authors.forename: Andrew
authors.initials: A
authors.lastname: Burgess
authors.forename: Shushyan
authors.initials: S
authors.lastname: Wong
authors.forename: Rick A
authors.initials: RA
authors.lastname: Sturm
authors.forename: Brian
authors.initials: B
authors.lastname: Gabrielli
mesh_terms: D016203:CDC2 Protein Kinase / Q000378:metabolism; D059447:Cell Cycle Checkpoints / Q000235:genetics / Q000528:radiation effects; D045744:Cell Line, Tumor; D056744:Cyclin B1 / Q000378:metabolism; D004261:DNA Replication / Q000235:genetics* / Q000528:radiation effects; D004277:DNA, Single-Stranded / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000502:physiology; D000078404:Epidermal Cells; D004817:Epidermis / Q000528:radiation effects; D016193:G1 Phase / Q000235:genetics / Q000528:radiation effects; D016195:G2 Phase / Q000235:genetics / Q000528:radiation effects*; D006801:Humans; D008545:Melanoma / Q000235:genetics / Q000473:pathology*; D009154:Mutation / Q000235:genetics / Q000528:radiation effects; D016196:S Phase / Q000235:genetics / Q000528:radiation effects; D012878:Skin Neoplasms / Q000235:genetics / Q000473:pathology*; D014466:Ultraviolet Rays / Q000009:adverse effects
chemical_list: C534700:Ccnb1 protein, mouse; D056744:Cyclin B1; D004277:DNA, Single-Stranded; D004268:DNA-Binding Proteins; C485953:Rad18 protein, mouse; D016203:CDC2 Protein Kinase