PKCð regulates chromatin remodeling and DNA repair through SIRT6.

Irradiation (IR) is a highly effective cancer therapy, however, IR damage to tumor-adjacent healthy tissues can result in significant co-morbidities and potentially limit the course of therapy. We have previously shown that protein kinase C delta (PKCð) is required for IR-induced apoptosis and that inhibition of PKCð activity provides radioprotection in vivo. Here we show that PKCð regulates histone modification, chromatin accessibility, and double stranded break (DSB) repair through a mechanism that requires SIRT6. Overexpression of PKCð promotes genomic instability and increases DNA damage and apoptosis. Conversely, depletion of PKCð increases DNA repair via non-homologous end joining (NHEJ) and homologous recombination (HR) as evidenced by increased formation of DNA damage foci, increased expression of DNA repair proteins, and increased repair of NHEJ and HR fluorescent reporter constructs. Nuclease sensitivity indicates that PKCð depletion is associated with more open chromatin, while overexpression of PKCð reduces chromatin accessibility. Epiproteome analysis reveals increased chromatin associated H3K36me2 in PKCð-depleted cells which is accompanied by chromatin disassociation of KDM2A. We identify SIRT6 as a downstream mediator of PKCð. PKCð-depleted cells have increased SIRT6 expression, and depletion of SIRT6 reverses changes in chromatin accessibility, histone modification and DSB repair in PKCð-depleted cells. Furthermore, depletion of SIRT6 reverses radioprotection in PKCð-depleted cells. Our studies describe a novel pathway whereby PKCð orchestrates SIRT6-dependent changes in chromatin accessibility to regulate DNA repair, and define a mechanism for regulation of radiation-induced apoptosis by PKCð. Implications: PKCð controls sensitivity to irradiation by regulating DNA repair.