CXXC5 deletion enhances tumorigenesis by impairing DNA damage responses in CRC

Abstract

CXXC5 (RINF) is a CpG-binding epigenetic regulator implicated in transcriptional control and cellular stress responses; however, its role in epithelial DNA damage repair and colorectal tumorigenesis remains incompletely understood. Because maintenance of genomic stability in the intestinal epithelium relies heavily on efficient double-strand break (DSB) repair, we investigated whether CXXC5 contributes to non-homologous end joining (NHEJ) and influences APC-driven colorectal tumor development.Analysis of publicly available colorectal cancer datasets revealed that CXXC5 expression is elevated in tumor tissues compared with normal counterparts. Consistent with this observation, APCmin/+ mice exhibited increased Cxxc5 protein levels in tumor regions relative to adjacent non-tumor intestine. To examine the epithelial-specific function of CXXC5 in vivo, we generated intestinal epithelium–specific Cxxc5 knockout mice using Villin-Cre, with or without the APCmin/+ background, and confirmed efficient depletion of CXXC5 in the intestinal epithelium by Western blotting and immunohistochemistry.Functionally, epithelial loss of Cxxc5 was associated with earlier clinical decline and increased colorectal tumor burden in APCmin/+ mice. These changes were accompanied by increased colon weight without additional shortening of colon length, as well as enhanced tumor multiplicity, larger tumor size, and more severe histopathological abnormalities. To explore a potential link to DNA repair, chromatin fractionation assays performed in SW620 colorectal cancer cells showed reduced chromatin recruitment of Ku70 and DNA-PKcs, along with sustained γH2AX accumulation following DNA damage, suggesting impaired resolution of DSBs via the NHEJ pathway.Together, these findings indicate that CXXC5 contributes to DNA damage responses in intestinal epithelial cells and that its loss is associated with defective recruitment of specific NHEJ factors and enhanced APC-driven colorectal tumor development. This study suggests a role for CXXC5 in epithelial genome maintenance under conditions of chronic genomic stress.