Dose-dependent effects of histone methyltransferase NSD2 on site-specific double-strand break repair

Histone modifications are catalyzed and recognized by specific proteins to regulate dynamic DNA metabolism processes. NSD2 is a histone H3 lysine 36 (H3K36)-specific methyltransferase that associates both with various transcription regulators and DNA repair factors. Specifically, it has been implicated in the repair of DNA double-strand breaks (DSBs); however, the role of NSD2 during DSB repair remains enigmatic. Here, we show that NSD2 does not accumulate at DSB sites and that the localization of NSD2 at chromatin is maintained even after DSB formation. Using three different DSB repair reporter systems, which contained the endonuclease site in the active thymidine kinase gene ( TK ) locus, we demonstrated separate dose-dependent effects of NSD2 on HR, canonical-NHEJ (c-NHEJ), and non-canonical-NHEJ (non-c-NHEJ). Endogenous NSD2 has a role in repressing non-c-NHEJ, without affecting DSB repair efficiency by HR or total NHEJ. Furthermore, overexpression of NSD2 promotes c-NHEJ repair suppressing HR repair. Therefore, we propose that NSD2 has functions in chromatin integrity at the active regions during DSB repair.