Dicer regulates non-homologous end joining and is associated with chemosensitivity in colon cancer patients.

DNA double-strand break (DSB) repair is an important mechanism underlying chemotherapy resistance in human cancers. Dicer participates in DSB repair by facilitating homologous recombination. However, whether Dicer is involved in non-homologous end joining (NHEJ) remains unknown. Here, we addressed whether Dicer regulates NHEJ and chemosensitivity in colon cancer cells. Using our recently developed NHEJ assay, we found that DSB introduction by I-SceI cleavage leads to Dicer upregulation. Dicer knockdown increased SIRT7 binding and decreased the level of H3K18Ac (acetylated lysine 18 of histone H3) at DSB sites, thereby repressing the recruitment of NHEJ factors to DSB sites and inhibiting NHEJ. Dicer overexpression reduced SIRT7 binding and increased the level of H3K18Ac at DSB sites, promoting the recruitment of NHEJ factors to DSBs and moderately enhancing NHEJ. Dicer knockdown and overexpression increased and decreased, respectively, the chemosensitivity of colon cancer cells. Dicer protein expression in colon cancer tissues of patients was directly correlated with chemoresistance. Our findings revealed a function of Dicer in NHEJ-mediated DSB repair and the association of Dicer expression with chemoresistance in colon cancer patients.