756 ATR kinase activity promotes the viability and proliferative capacity of quiescent human keratinocytes exposed to UVB radiation

Abstract

The ATR protein kinase plays well-described roles during the DNA synthesis phase of the cell cycle in maintaining genomic integrity in response to DNA damage induced by UV radiation and other genotoxic agents. However, the function and activation mechanism of ATR in cells that are not actively replicating DNA remains largely unexplored but is physiologically important and relevant to understanding the fate of quiescent and stem cell populations exposed to DNA damaging agents. Using HaCaT and telomerase-immortalized normal human keratinocytes maintained in a confluent, non-replicating state in vitro, we show that the ATR kinase is rapidly activated in response to UVB radiation in a manner dependent on the DNA translocase XPB. Inhibition of ATR kinase activity has modest effects on acute cell survival but more severely abrogates the ability of UVB-irradiated keratinocytes to proliferate upon stimulation with growth factors. Furthermore, ATR kinase inhibition in quiescent HaCaT keratinocytes potentiates UVB mutagenesis at the HPRT locus but does not impact the rate of removal of cyclobutane pyrimidine dimers from genomic DNA. These results indicate that the ATR kinase plays important roles in limiting mutagenesis and promoting cell viability and proliferation following UVB exposure even in cells that are not actively synthesizing DNA.