Role of poly(ADP-ribose) polymerase (PARP) in DNA repair in sulfur mustard-exposed normal human epidermal keratinocytes (NHEK)

We previously reported that, in normal human epidermal keratinocytes (NHEK) cultures exposed to the alkylating compound sulfur mustard (bis-(2-chloroe thyl) sulfide, HD, 0.3-1 mM), there is a rapid (less than or equal to1 h) a ctivation (100% above unexposed control) of the DNA repair enzyme DNA ligas e I (130 kD) followed by a first-order decay (1-5 h), The DNA ligase activa tion is accompanied by a time-dependent (0.5-4 h) and significant DNA repai r. Inhibition of another putative DNA repair enzyme, poly(ADP-ribose) polym erase (PARP), by using 3-amino benzamide does not affect DNA ligase activat ion following HD exposure, but increases the half-life of the activated enz yme threefold. To examine the role of PARP in HD-induced DNA ligase activat ion and subsequent DNA repair, we conducted studies using cultured keratino cytes in which the level of PARP had been selectively lowered (greater than or equal to 85%) by the use of induced expression of antisense RNA. In the se cells, there was no stimulation of DNA ligase up to 3 h, and a small sti mulation (ca, 30% above unexposed control at 5-6 h after HD exposure. A tim e-course (0.5-6 h) study of DNA repair in HD-exposed PARP-deficient keratin ocytes revealed a much slower rate of repair compared with HD-exposed NHEK. The results suggest an active role of PARP in DNA ligase activation and DN A repair in mammalian cells, and also indicate that modulation of PARP-medi ated mechanisms may provide a useful approach in preventing HD toxicity.