Defective resolution of pH2AX foci and enhanced DNA breakage in ionizing radiation-treated cockayne syndrome B cells

Abstract

We have previously shown that DNA repair of oxidized bases (either purines or pyrimidines) is inefficient in cells from patients with Cockayne syndrome (cs), a rare developmental and neurological genetic disorder. Here, we show for the first time that resolution of ionizing radiation (IR)-induced pH2AX foci, an indicator of DNA double-strand breaks, is significantly delayed in IR-treated cells belonging to the B complementation group of cs (csb). Using alkaline single-cell gel electrophoresis, which predominantly detects single-strand breaks, we further demonstrate elevated DNA breakage in csb cells early after irradiation. Both the delayed resolution of pH2AX foci and the early DNA breakage of csb cells were partially complemented by expression of wild-type CSB protein. Hence, the csb mutation impairs resolution of pH2AX foci and causes DNA fragility, broadening the spectrum of lesions whose processing is altered in this syndrome.