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, 0.3-1mM), there is a rapid (1 less than or equal toh) ac tivation (100% above unexposed control) of the DNA repair enzyme DNA ligase I (130 kD) followed by a first-order decay (1-5 h), The DNA ligase activat ion is accompanied by a time-dependent (0.5-4 h) and significant DNA repair . Inhibition of another putative DNA repair enzyme, poly(ADP-ribose) polyme rase (PARP), by using 3-amino benzamide does not affect DNA ligase activati on following HD exposure, but increases the half-life of the activated enzy me threefold, To examine the role of PARP in HD-induced DNA Ligase activati on and subsequent DNA repair, we conducted studies using cultured keratinoc ytes 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 thes e cells, there was no stimulation of DNA ligase up to 3 h, and a small stim ulation (ca. 30% above unexposed control at 5-6 h after HD exposure, A time -course (0.5-6 h) study of DNA repair in HD-exposed PARP-deficient keratino cytes 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 DNA repair in mammalian cells, and also indicate that modulation of PARP-media ted mechanisms may provide a useful approach in preventing HD toxicity. Pub lished in 2000 by John Wiley & Sons, Ltd.