THE DIFFERENTIAL EXPRESSION OF CYTOKERATIN-18 IN CISPLATIN-SENSITIVE AND CISPLATIN-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 o f microtubules and intermediate filaments. It was found that the cispl atin-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 anal ysis of the DNA extracted from the two cell lines and then digested wi th HpaII and its methylation-sensitive isoschizomer, MspI, revealed no detectable differences in the methylation status of the cytokeratin g ene. Neither 5-azacytidine (5 mu m) nor retinoic acid (1 mu m) treatme nt enhanced the expression of cytokeratin 18 in the resistant cell lin e. However, transfection of full-length cytokeratin 18 cDNA into the c isplatin-resistant 2008/C13 cells resulted in clones with increased l evels of cytokeratin 18, which was accompanied in the majority of clon es by a marked increase in their sensitivity to cisplatin. These resul ts demonstrate that modulating the expression of an intermediate filam ent protein results in sensitization of a drug-resistant human ovarian cell line to cisplatin.