Nucleotide excision repair (NER) is the DNA repair pathway by which cisplatin-induced damage is removed from DNA in human cells. ERCC-1 is one of the essential proteins in NER, and is essential for life. Enhanced ERCC-1 expression has been associated with clinical and cellular resistance to cisplatin. We therefore carried out this study to investigate the effect of cisplatin on ERCC-1 protein expression in A2780/CP70 human ovarian cancer cells. Western blot analysis showed that ERCC-1 protein levels were increased to more than 3 times control after a 1 h cisplatin exposure to A2780/CP70 cells in culture. This increase was time- and concentration-dependent. The effect of cisplatin was maximal at 40 mM and peaked 24-48 h after exposure to the drug. These results extend our previous observations that ERCC-1 mRNA expression is induced by cisplatin in this system. TPA, a known AP-1 activator and tumor-promoting phorbol ester, also induced ERCC-1 protein to the same extent as cisplatin, but did not synergize with cisplatin in this regard. These findings suggest that ERCC-1 gene up-regulation in these cells can result through a DNA damage-response pathway, or through the induction of AP-1 activity, independent of the occurrence of DNA damage.