Single-dose UV-C irradiation induces the formation of gamma-H2AX foci in the human cell line (MCF7) that are not resolved after 2 and 24 hours of recovery as determined by immunofluorescence microscopy

Abstract

 The integrity of the genome is of utmost importance for proper functioning existence of all living systems. Genotoxic insults, such as UV-C radiation, may exert adverse effects on genomic integrity. Cells have developed a number of highly conserved repair mechanism to counteract the variety of mutagenic and cytotoxic DNA lesions induced by genotoxic agents. Phosphorylation of gamma-histone H2AX is a known DNA-repair signaling response to double- stranded breaks (DSBs); however, the formation of DSB by UV-C radiation is reported to be rare. We sought to determine whether a single dose of UV-C radiation (0.31 J/cm2, 254nm) can induce the formation of gamma-H2AX foci in the human cell line (MCF7) and determine the amount of DNA damage present after a recovery period of two and 24 hours by immunofluorescence microscopy. We also exposed cells to 50 nM of camptothecin (CPT), a DNA damaging agent, as a positive control. We found that similar to CPT, human cells exposed to UV-C radiation (0.31 J/cm2) showed upregulated gamma-H2AX foci at both 2 h and 24 h after the genotoxic insult. Cells exposed to this single dose showed significantly higher gamma-H2AX from non- treated cells and the extent of DNA damage remained the same between 2 and 24 h. Our results indicate that UV-C radiation is capable of inducing the formation of the DSB signaling foci gamma-H2AX and that cells are unable to repair the genotoxic insult within 24 h of recovery. This further indicates that human cell line (MCF7) may require longer than 24 hours to noticeably repair the extent of DNA damage induced by (0.31 J/cm2) of UV-C light.