REGULATION OF CELLULAR-RESPONSE TO CISPLATIN-INDUCED DNA-DAMAGE AND DNA-REPAIR IN CELLS OVEREXPRESSING P185(ERBB-2) IS DEPENDENT ON THE RASSIGNALING PATHWAY

We have examined the role of erbB-2 expression in the modulation of ce llular toxicity to cisplatin. We have demonstrated that treatment of N IH3T3-erbB-2 cells, which overexpress the p185(erbB-2) product of the human erbB-2 gene, with a monoclonal antibody directed against the ext racellular domain (TAb-250), results in enhanced cisplatin cytotoxicit y. A similar enhancement was obtained when cells were exposed to herbi mycin A and its analogue CP127 374, both of which inhibit tyrosine kin ase activity. Using the host cell. reactivation (HCR) of reporter gene expression from cisplatin-damaged plasmid and unscheduled DNA synthes is (UDS) following cisplatin treatment of cells, we have found that mo dulation of erbB-2 by TAb-250 was associated with inhibition of DNA re pair. TAb-250 alone, under conditions which modulate DNA repair, sligh tly reduces the S-phase of the cell cycle, while cisplatin induced arr est at S and G(2) phases. Combination of TAb-250 and cisplatin only sl ightly prevented cisplatin-induced S and G(2) blocks. Since the ras pa thway is one of the major signaling components coupled to erbB-2, we h ave examined the role of ras in DNA repair regulation. Transient expre ssion of a ras dominant negative mutant, Asn-17-ras(H), prevents DNA r epair modulation by TAb-250, suggesting that the erbB-2 receptor regul ates DNA repair mechanism(s), at least in part, through ras-coupled pa thway(s).