O-GlcNAcylation of NONO mediates alternative splicing of SETMAR and facilitates NHEJ repair.

BACKGROUND: The NONO protein plays a crucial role in RNA metabolism and DNA repair. It undergoes various post-translational modifications, including phosphorylation, ubiquitination, acetylation and methylation, all of which regulate its diverse cellular functions. However, the role of O-GlcNAcylation in regulating NONO's function in DNA damage repair is not well understood. RESULTS: This study demonstrates that O-GlcNAcylation of NONO at Serine 147 (Ser147) is essential for its recruitment to DNA damage sites. Specifically, O-GlcNAcylation at Ser147 reduces NONO ubiquitination and stabilizes its interaction with SFPQ, regulating the alternative splicing of the histone methyltransferase SETMAR. A deficiency in O-GlcNAcylation at Ser 147 impairs NONO's binding to SETMAR pre-mRNA, leading to an increased production of the truncated isoform of SETMAR (SETMAR-S). The resulting SETMAR-S suppresses the generation of H3K36me2 and inhibits the recruitment of Ku70 at DNA damage sites, ultimately impairing non-homologous end joining (NHEJ) repair. Furthermore, the disruption of O-GlcNAcylation at Ser147 sensitizes liver cancer cells to ionizing radiation treatment, both in vitro and in vivo. CONCLUSIONS: O-GlcNAcylation at Ser 147 of NONO mediates the alternative splicing of SETMAR and facilitates NHEJ repair. Collectively, our findings suggest that targeting NONO O-GlcNAcylation may provide a novel therapeutic strategy for cancer treatment.