RAD52 and ERCC6L/PICH have a compensatory relationship for genome stability in mitosis.

Mammalian RAD52 is a DNA repair factor with strand annealing and recombination mediator activities that appear important in both interphase and mitotic cells. Nonetheless, RAD52 is dispensable for cell viability. To query RAD52 synthetic lethal relationships, we performed genome-wide CRISPR knock-out screens and identified hundreds of candidate synthetic lethal interactions. We then performed secondary screening and identified genes for which depletion causes reduced viability and elevated genome instability (increased 53BP1 nuclear foci) in RAD52-deficient cells. One such factor was ERCC6L, which marks DNA bridges during anaphase, and hence is important for genome stability in mitosis. Thus, we investigated the functional interrelationship between RAD52 and ERCC6L. We found that RAD52 deficiency increases ERCC6L-coated anaphase ultrafine bridges, and that ERCC6L depletion causes elevated RAD52 foci in prometaphase and interphase cells. These effects were enhanced with replication stress (i.e. hydroxyurea) and topoisomerase IIα inhibition (ICRF-193), where post-treatment effect timings were consistent with defects in addressing stress in mitosis. Altogether, we suggest that RAD52 and ERCC6L co-compensate to protect genome stability in mitosis. Author summary: Mammalian RAD52 is a protein that protects DNA integrity through its roles in DNA repair and replication, and is being developed as a target for cancer treatment. To identify factors that influence dependence on RAD52 to maintain cell viability, we performed screens to identify genes that negatively impact cell viability and increase genome instability when disrupted in cells that also lack RAD52. Through these screens, we identified ERCC6L/PICH, a protein that helps resolve ultrafine DNA bridges, which can disrupt the segregation of sister chromatids during anaphase of mitosis. In characterizing the relationship between ERCC6L and RAD52, we found that RAD52 loss increases the number of DNA bridges marked by ERCC6L. Likewise, we discovered that ERCC6L depletion causes RAD52 to accumulate into foci in both mitosis and interphase. These effects were enhanced when loss of each protein was combined with agents that induce additional genotoxic stress (e.g., DNA replication stress). Our findings point to a model where RAD52 compensates for genotoxic stress caused by ERCC6L loss, and vice versa. [ABSTRACT FROM AUTHOR]