Homologous recombination (HR) mediated repair of DNA double-strand break (DSB)s is restricted to the post-replicative phases of the cell cycle. Initiation of HR in the G1 phase blocks non-homologous end joining (NHEJ) impairing DSB repair. Execution of HR in G1 cells can lead to the loss-of-heterozygosity (LOH) which is potentially carcinogenic. We conducted a gain-of-function screen to systematically identify miRNAs that regulate HR-mediated DSB repair, and of these miRNAs, miR-1255b, miR-148b*and miR-193b* specifically suppress the HR-pathway in the G1 phase by targeting BRCA1, BRCA2 and RAD51. miR-1255b, miR-148b*and miR-193b* associate with the transcripts of these HR factors via non-canonical binding sites. Mutations in the miRNA binding sites restore the levels of BRCA1, BRCA2 and RAD51 and neutralize the phenotype induced by over-expressing the miRNAs. Inhibiting miR-1255b, miR-148b* and miR-193b* leads to an ectopic increase in expression of BRCA1, BRCA2 and RAD51 specifically in the G1 phase and impedes DSB repair through the initiation of HR. Depletion of CtIP, a BRCA1-associated DNA end resection protein, rescues this phenotype. Furthermore, deletion of miR-1255b or miR-148b* or miR-193b* in independent cohorts of ovarian tumors correlates with significant increase in LOH events/ chromosomal aberrations and BRCA1 expression.
All Science Journal Classification (ASJC) codes
- Immunology and Microbiology(all)
- Biochemistry, Genetics and Molecular Biology(all)