MDC1 interacts with Rad51 and facilitates homologous recombination

Abstract

Mediator of DNA damage checkpoint protein-1 (MDC1) is a recently identified nuclear protein that participates in DNA-damage sensing and signaling. Here we report that knockdown of MDC1 by RNA interference results in cellular hypersensitivity to the DNA cross-linking agent mitomycin C and ionizing radiation and in impaired homology-mediated repair of double-strand breaks in DNA. MDC1 forms a complex with Rad51 through a direct interaction with the forkhead-associated domain of MDC1, not the BRCA1 C-terminal domain. Depletion of MDC1 results in impaired formation of Rad51 ionizing radiation-induced foci, reduced amounts of nuclear and chromatin-bound Rad51, and a corresponding increase in Rad51 protein degradation. Together, our findings suggest that MDC1 functions in Rad51-mediated homologous recombination by retaining Rad51 in chromatin.

The cellular response to DNA damage: A focus on MDC1 and its interacting proteins

“…Its binding to Rad51 does not seem to require phosphorylation 19 whereas its binding to ATM occurs via a phospho-Ser motif rather than an expected phospho-Thr motif. 58 Structural analysis coupled with oriented peptide library screening experiments based on both pSer and pThr peptides should help define the binding specificity of the FHA domain of MDC1.…”

“…Therefore, the main mechanism of action of MDC1 in HR is mediated by the regulation of Rad51 stability, which affects its recruitment to DSBs and subsequent repair. 19 It was discovered that there is an interaction between the FHA domain of MDC1 and Rad51. 19 The interaction between MDC1 and Rad51 is direct and constitutive, as it is not influenced by IR.…”

“…19 It was discovered that there is an interaction between the FHA domain of MDC1 and Rad51. 19 The interaction between MDC1 and Rad51 is direct and constitutive, as it is not influenced by IR. It also does not seem to require phosphorylation, a puzzling observation since FHA domains act as pThr-binding modules.…”

“…This hypothesis has been well substantiated by the large amount of data generated in recent years. Furthermore, additional roles have been ascribed to MDC1, including DNA repair via the non-homologous end joining (NHEJ) 18 and homologous recombination (HR) 19,20 pathways, activation of the decatenation checkpoint 21 and mitosis.…”

CTCF prevents genomic instability by promoting homologous recombination-directed DNA double-strand break repair

“…To determine how CTCF functions in the HR, we analyzed X-ray irradiation-induced Rad51 foci formation in the CTCF knockdown cells, since Rad51 is a key repair factor in HR (32)(33)(34), and aggregates into DNA repair foci after ionizing irradiation or DNA damage-inducing drug treatment (35,36). We found that the knockdown decreased the percentage of cells with five or more X-ray-induced Rad51 foci decreased from 42.13% to <10.17% (Fig.…”