Overexpression of dominant negative PARP interferes with tumor formation of HeLa cells in nude mice: Evidence for increased tumor cell apoptosis in vivo

Poly(ADP-ribose) polymerase (PARP(4)) catalyzes the formation of ADP-ribose polymers covalently attached to proteins by using NAD(+) as substrate. PAR P is strongly activated by DNA single- or double-strand breaks and is thoug ht to be involved in cellular responses to DNA damage. We characterized a d ominant negative PARP mutant, i.e, the DNA-binding domain of this enzyme, w hose overexpression in cells leads to increased genetic instability followi ng DNA damage. In order to study whether PARP activity is also implicated i n the process of tumorigenesis, me generated stably transfected HeLa cell c lones with constitutive overexpression of dominant negative PARP and invest igated tumor formation of these clones in nude mice. We found that inhibiti on of PARP activity dramatically reduces tumor forming ability of HeLa cell s. Moreover, me provide strong evidence that the observed reduction in tumo r forming ability is due to increased tumor cell apoptosis in viva. Viewed together, our data and those from other groups show that inhibition of PARP enzyme activity interferes with DNA base excision repair and leads to incr eased genetic instability and recombination but, on the other hand, can sen sitize cells to apoptotic stimuli and by this mechanism may prevent tumor f ormation.