DNA double-strand break-induced phosphorylation of Drosophila histone variant H2Av helps prevent radiation-induced apoptosis

Abstract

The response of eukaryotic cells to the formation of a double‐strand break (DSB) in chromosomal DNA is highly conserved. One of the earliest responses to DSB formation is phosphorylation of the C‐terminal tail of H2A histones located in nucleosomes near the break. Histone variant H2AX and core histone H2A are phosphorylated in mammals and budding yeast, respectively. We demonstrate the DSB‐induced phosphorylation of histone variant H2Av in Drosophilamelanogaster . H2Av is a member of the H2AZ family of histone variants. Ser137 within an SQ motif located near the C‐ terminus of H2Av was phosphorylated in response to γ‐irradiation in both tissue culture cells and larvae. Phosphorylation was detected within 1 min of irradiation and detectable after only 0.3 Gy of radiation exposure. Photochemically induced DSBs, but not general oxidative damage or UV‐induced nicking of DNA, caused H2Av phosphorylation, suggesting that phosphorylation is DSB specific. Imaginal disc cells from Drosophila expressing a mutant allele of H2Av with its C‐terminal tail deleted, and therefore unable to be phosphorylated, were more sensitive to radiation‐induced apoptosis than were wildtype controls, suggesting that phosphorylation of H2Av is important for repair of radiation‐induced DSBs. These observations suggest that in addition to providing the function of an H2AZ histone, H2Av is also the functional homolog in Drosophila of H2AX.