Expression of Poly (ADP-ribose) Polymerase During Apoptosis Induced by Ultraviolet Radiation in HeLa S₃ Cells

Induction of apoptosis allows the organism to get rid of abnormal cells and also of tumor cells. Understanding the mechanism involved in Ultraviolet radiation (UV) induced apoptosis may improve its therapeutic efficacy. In this study, we present expression of poly (ADP-ribose) polymerase (PARP) during apoptosis induced by UV in HeLa S₃ cells. Four different assays were performed in this study: morphological assessment of apoptotic cells and cell viability, DNA fragmentation analysis by agarose gel electrophoresis, quantitative assay of fragmented DNA, and expression of PARP by the western blot analysis. The percentages of apoptotic HeLa S3 cells irradiated with 75 J/㎡ UV was increased continuously from 3 hrs incubation. DNA ladder pattern was appeared at 6 hrs. The amount of nucleosomal DNA fragments in cells treated UV increased from 3 to 12 hrs incubation and gradually decreased. The cleavage of PARP in HeLa S₃ cells irradiated with UV was induced, and the cleavage of PARP was more delayed in the cells pretreated with 5 J/㎡ UV and subsequently irradiated with 75 J/㎡ UV than that in the cells only irradiated with 75 J/㎡ UV. Thus these data suggest that the cleavage of PARP relates with DNA fragmentation associated with apoptosis.