Journal of Biological Chemistry
Volume 272, Issue 51, 19 December 1997, Pages 32260-32266
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NUCLEIC ACIDS, PROTEIN SYNTHESIS, AND MOLECULAR GENETICS
Role of Estrogen Receptor Gene Demethylation and DNA Methyltransferase·DNA Adduct Formation in 5-Aza-2′deoxycytidine-induced Cytotoxicity In Human Breast Cancer Cells*

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The cytosine analog 5-aza-2′-deoxycytidine is a potent inhibitor of DNA methyltransferase. Its cytotoxicity has been attributed to several possible mechanisms including reexpression of growth suppressor genes and formation of covalent adducts between DNA methyltransferase and 5-aza-2′-deoxycytidine-substituted DNA which may lead to steric inhibition of DNA function. In this study, we use a panel of human breast cancer cell lines as a model system to examine the relative contribution of two mechanisms, gene reactivation and adduct formation. Estrogen receptor-negative cells, which have a hypermethylated estrogen receptor gene promoter, are more sensitive than estrogen receptor-positive cells and underwent apoptosis in response to 5-aza-2′-deoxycytidine. For the first time, we show that reactivation of a gene silenced by methylation, estrogen receptor, plays a major role in this toxicity in one estrogen receptor-negative cell line as treatment of the cells with anti-estrogen-blocked cell death. However, drug sensitivity of other tumor cell lines correlated best with increased levels of DNA methyltransferase activity and formation DNA·DNA methyltransferase adducts as analyzed in situ. Therefore, both reexpression of genes like estrogen receptor and formation of covalent enzyme· DNA adducts can play a role in 5-aza-2′-deoxycytidine toxicity in cancer cells.

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*

This work was supported by American Cancer Society Grants BE 237 (to N. E. D.) and PF 4231 (to A. T. F.), the Susan G. Komen Foundation (to N. E. D.), and National Institutes of Health Grants CA 43318 (to S. B. B.) and CA 16058, CA 63185, and CA 63653 (to M. T. M.).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

§

These authors contributed equally to this work.