Feline XRCC4 undergoes rapid Ku‐dependent recruitment to DNA damage sites

Abstract

Radiation and chemotherapy resistance remain some of the greatest challenges in human and veterinary cancer therapies. XRCC4, an essential molecule for nonhomologous end joining repair, is a promising target for radiosensitizers. Genetic variants and mutations of XRCC4 contribute to cancer susceptibility, and XRCC4 is also the causative gene of microcephalic primordial dwarfism (MPD) in humans. The development of clinically effective molecular‐targeted drugs requires accurate understanding of the functions and regulatory mechanisms of XRCC4. In this study, we cloned and sequenced the cDNA of feline XRCC4. Comparative analysis indicated that sequences and post‐translational modification sites that are predicted to be involved in regulating the localization of human XRCC4, including the nuclear localization signal, are mostly conserved in feline XRCC4. All examined target amino acids responsible for human MPD are completely conserved in feline XRCC4. Furthermore, we found that the localization of feline XRCC4 dynamically changes during the cell cycle. Soon after irradiation, feline XRCC4 accumulated at laser‐induced DNA double‐strand break (DSB) sites in both the interphase and mitotic phase, and this accumulation was dependent on the presence of Ku. Additionally, XRCC4 superfamily proteins XLF and PAXX accumulated at the DSB sites. Collectively, these findings suggest that mechanisms regulating the spatiotemporal localization of XRCC4 are crucial for XRCC4 function in humans and cats. Our findings contribute to elucidating the functions of XRCC4 and the role of abnormal XRCC4 in diseases, including cancers and MPD, and may help in developing XRCC4‐targeted drugs, such as radiosensitizers, for humans and cats.

DNA double-strand break genetic variants in patients with premature ovarian insufficiency

“…In a recent report, Li et al performed whole-exome sequencing of a family with three generations of POI patients and identified a rare heterozygous natural loss-of-function mutation located in NHEJ1 [ 113 ]. NHEJ1 binds XRCC4-LIG4 complex, stabilises and enhances the ligating activity of the complex and may also mediate the recruitment of other NHEJ components, such as Ku and DNA-PKcs [ 194 , 195 ]. Mice with the same mutation have remarkably fewer follicles and a 50% reduction in ovarian size compared to wild-type mice Breeding tests illustrated that mice with the Nhej1 mutation take longer to complete their first birth, demonstrating that the mutation causes reduced fertility.…”