Ionizing radiation triggers chromatin-bound kin17 complex formation in human cells

The human DNA-binding (HSA)kin17 protein cross-reacts with antibodies raised against the stress-activated Escherichia coli RecA protein. We show here that HSAkin17 protein is directly associated with chromosomal DNA as judged by cross-linking experiments on living cells. We detected increased amounts of DNA-bound HSAkin17 protein 24 h after gamma irradiation, with 2.6-fold more (HSA)kin17 molecules after 6 Gy of irradiation (46,000-117,000 molecules). At this time we observed that highly proliferating RKO cells displayed the concentration and co-localization of (HSA)kin17 and replication protein A in nucleoplasmic foci. Our results suggest that 24 h post-irradiation HSAkin17 protein may localize at the sites of unrepaired DNA damages. RKO clones expressing an (HSA)KIN17 antisense transcript (RASK.5 and RASK.13 cells) revealed that reduced (HSA)kin17 protein levels are correlated with a decrease in clonogenic cell growth and cell proliferation, as well as an accumulation of cells in early and mid-S phase. Taken together our observations support the idea that HSAkin17 protein is a DNA maintenance protein involved in the cellular response to the presence of DNA damage and suggest that it helps to overcome the perturbation of DNA replication produced by unrepaired lesions.