title: SFPQ•NONO and XLF function separately and together to promote DNA double-strand break repair via canonical nonhomologous end joining.
abstract: A complex of two related mammalian proteins, SFPQ and NONO, promotes DNA double-strand break repair via the canonical nonhomologous end joining (c-NHEJ) pathway. However, its mechanism of action is not fully understood. Here we describe an improved SFPQ•NONO-dependent in vitro end joining assay. We use this system to demonstrate that the SFPQ•NONO complex substitutes in vitro for the core c-NHEJ factor, XLF. Results are consistent with a model where SFPQ•NONO promotes sequence-independent pairing of DNA substrates, albeit in a way that differs in detail from XLF. Although SFPQ•NONO and XLF function redundantly in vitro, shRNA-mediated knockdown experiments indicate that NONO and XLF are both required for efficient end joining and radioresistance in cell-based assays. In addition, knockdown of NONO sensitizes cells to the interstrand crosslinking agent, cisplatin, whereas knockdown of XLF does not, and indeed suppresses the effect of NONO deficiency. These findings suggest that each protein has one or more unique activities, in addition to the DNA pairing revealed in vitro, that contribute to DNA repair in the more complex cellular milieu. The SFPQ•NONO complex contains an RNA binding domain, and prior work has demonstrated diverse roles in RNA metabolism. It is thus plausible that the additional repair function of NONO, revealed in cell-based assays, could involve RNA interaction.
authors.affiliation: Departments of Radiation Oncology and Biochemistry, Emory University, Atlanta, GA 30322, USA.
authors.forename: Lahcen
authors.initials: L
authors.lastname: Jaafar
authors.affiliation: Departments of Radiation Oncology and Biochemistry, Emory University, Atlanta, GA 30322, USA.
authors.forename: Zhentian
authors.initials: Z
authors.lastname: Li
authors.affiliation: Departments of Radiation Oncology and Biochemistry, Emory University, Atlanta, GA 30322, USA.
authors.forename: Shuyi
authors.initials: S
authors.lastname: Li
authors.affiliation: Departments of Radiation Oncology and Biochemistry, Emory University, Atlanta, GA 30322, USA.
authors.forename: William S
authors.initials: WS
authors.lastname: Dynan
mesh_terms: D002460:Cell Line; D002470:Cell Survival / Q000235:genetics; D053903:DNA Breaks, Double-Stranded; D059766:DNA End-Joining Repair; D004260:DNA Repair; D045643:DNA Repair Enzymes / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D004843:Epistasis, Genetic; D006801:Humans; D034521:Nuclear Matrix-Associated Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D050810:Octamer Transcription Factors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000072670:PTB-Associated Splicing Factor / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs; D016601:RNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D004268:DNA-Binding Proteins; C508551:NHEJ1 protein, human; C083214:NONO protein, human; D034521:Nuclear Matrix-Associated Proteins; D050810:Octamer Transcription Factors; D000072670:PTB-Associated Splicing Factor; D016601:RNA-Binding Proteins; D045643:DNA Repair Enzymes