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Lookup NU author(s): Dr Gordon Strathdee
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Experimental evidence from several sources has identified a link between mismatch repair deficiency and cytotoxic drug resistance. Selection for cisplatin resistance in the human ovarian cancer cell line A2780, results in loss of expression of the mismatch repair protein hMLH1 in most (90%) of the resultant cisplatin-resistant cell lines. Here we demonstrate that the cisplatin sensitive parental cell line displays methylation of the promoter of only one hMLH1 allele, but that the resistant cell lines all exhibit hyper-methylation of the promoters of both hMLH1 alleles. Full methylation of all sites tested was found to be invariably associated with loss of hMLH1 expression, whereas a partial increase in methylation appears compatible with either loss or maintenance of expression. In addition treatment of two of the resistant cell lines with 5-azacytidine, a known inhibitor of methylation, results in re-expression of hMLH1. Clonogenic assays demonstrate that the 5-azacytidine treated cells show increased sensitivity to cisplatin. Furthermore, 12.5% (3/ 24) of ovarian tumours show hypermethylation of the hMLH1 promoter. Expression of hMLH1 is absent in the tumours that are hypermethylated, while all the unmethylated tumours still express the protein. This analysis suggests that methylation of the hMLH1 promoter may be a common mechanism for loss of hMLH1 expression, and possibly for cisplatin-resistance, in ovarian cancer.
Author(s): Strathdee G, MacKean MJ, Illand M, Brown R
Publication type: Article
Publication status: Published
Journal: Oncogene
Year: 1999
Volume: 18
Issue: 14
Pages: 2335-41
Print publication date: 08/04/1999
ISSN (print): 0950-9232
ISSN (electronic): 1476-5594
Publisher: Nature Publishing Group
URL: http://dx.doi.org/10.1038/sj.onc.1202540
DOI: 10.1038/sj.onc.1202540
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