Role of INT6/EIF3E in DSB repair

Unrepaired DNA double-strand breaks (DSBs) are the most destructive chromosomal lesions driving genomic instability, a core hallmark of cancer. Here, we identify the anti-oncogenic breast cancer factor INT6/EIF3E as an essential regulator of DSB repair that promotes homologous recombination (HR)-mediated repair and, to a lesser extent, non-homologous end joining repair. INT6 silencing impaired the accrual of the ubiquitin ligase RNF8 at DSBs and the formation of ubiquitin conjugates at DSB sites, especially Lys63-linked polyubiquitin chains, resulting in impaired recruitment of BRCA1, BRCA2 and RAD51, which are all involved in HR repair. In contrast, INT6 deficiency did not affect the accumulation of RNF168, 53BP1, or RPA at DSBs. In INT6-silenced cells, there was also an alteration in DNA damage-induced localization of MDC1, a key target for ATM phosphorylation, which is a pre-requisite for RNF8 recruitment. The attenuated DNA damage-localization of RNF8 resulting from INT6 depletion could be attributed to the defective retention of ATM previously reported by us. Our findings deepen insights into how INT6 protects against breast cancer by showing how it functions in DSB repair, with potential clinical implications for cancer therapy.

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