Increased poly(ADP-ribosyl)ation in intact cells by cisplatin treatment

Cisplatin (DDP) is a clinically important antitumor drug that induces the formation of DNA-DNA and DNA-protein crosslinks. We have studied whether poly(ADP-ribosyl)ation, a post-translational modification of nuclear proteins that is drastically increased by the presence of DNA strand breaks and plays a role in DNA repair, is induced following DDP treatment of cell cultures. By using an immunofluorescence technique for the in situ detection of poly(ADP-ribose) in intact cells, we found spotty nuclear signals after DDP treatment of O-342 rat ovarian tumor cells or CV-1 monkey cells, but not in untreated control cells, nor in DDP-treated cells postincubated with the ADP-ribosylation inhibitor 3-aminobenzamide. Our results thus provide direct evidence for an involvement of poly(ADP-ribosyl)ation in the cell's response to DDP treatment and, more generally, illustrate the versatility of this rapid in situ method for the detection of increased poly(ADP-ribosyl)ation in living cells.