The differential expression of cytokeratin 18 in cisplatin-sensitive and -resistant human ovarian adenocarcinoma cells and its association with drug sensitivity.

DNA is the primary target of cis-diamminedichloroplatinum (cisplatin), but the drug also interacts with the cellular cytoskeleton composed of microtubules and intermediate filaments. It was found that the cisplatin-resistant 2008/C13* cell line contained markedly lower levels (6-fold) of cytokeratin 18, when compared to the cisplatin-sensitive 2008 cell line. Northern blot analysis revealed a markedly decreased level of cytokeratin 18 mRNA in the resistant cell line. Southern blot analysis of the DNA extracted from the two cell lines and then digested with HpaII and its methylation-sensitive isoschizomer, MspI, revealed no detectable differences in the methylation status of the cytokeratin gene. Neither 5-azacytidine (5 microM) nor retinoic acid (1 microM) treatment enhanced the expression of cytokeratin 18 in the resistant cell line. However, transfection of full-length cytokeratin 18 cDNA into the cisplatin-resistant 2008/C13* cells resulted in clones with increased levels of cytokeratin 18, which was accompanied in the majority of clones by a marked increase in their sensitivity to cisplatin. These results demonstrate that modulating the expression of an intermediate filament protein results in sensitization of a drug-resistant human ovarian cell line to cisplatin.