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-chloroethyl) sulfide, HD, 0.3-1mM), there is a rapid (1 less than or equal toh) activation (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 activation is accompanied by a time-dependent (0.5-4 h) and significant DNA repair. Inhibition of another putative DNA repair enzyme, poly(ADP-ribose) polymerase (PARP), by using 3-amino benzamide does not affect DNA ligase activation following HD exposure, but increases the half-life of the activated enzyme threefold, To examine the role of PARP in HD-induced DNA Ligase activation and subsequent DNA repair, we conducted studies using cultured keratinocytes 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 these cells, there was no stimulation of DNA ligase up to 3 h, and a small stimulation (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 keratinocytes 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-mediated mechanisms may provide a useful approach in preventing HD toxicity. Published in 2000 by John Wiley & Sons, Ltd.