Abstract
Three members of phosphoinositide-3-kinase-like protein kinase (PIKK) family, ATM, ATR and DNA-PKcs, play distinct but sometimes redundant roles in regulating DNA damage response. Histone H2AX is one of the well-known substrates and is phosphorylated at Ser139 in response to double strand break (DSB) as well as stalled DNA replication forks or their collapse. We previously reported that histone H2AX is also phosphorylated in serum-starved quiescent cells exposed to UV in a nucleotide excision repair (NER)-dependent manner. Recently, we found that this phosphorylation is mediated not only by ATR in response to ssDNA gap formation but also by ATM possibly activated by DSB formation.
In this study, we focused on detecting DSB in G0-arrested cells following UV irradiation and analyzing a biological role of ATM signaling under this condition. A neutral comet assay revealed that longer comet tails were detected in G0-arrested normal cells but not in XP cells following UV irradiation, demonstrating NER-dependent DSB formation. The time course of DSB formation was correlated well with that of ATM signaling activation. Moreover, under G0-arrested condition, AT cells were found to be more sensitive to UV than normal cells, indicating the significant contribution of ATM signaling pathway to UV response in G0-arrested cells. We will also discuss more detailed mechanism of NER-dependent DSB formation.
