Epigenetic mechanisms of drug resistance: drug-induced DNA hypermethylation and drug resistance.

ECU Author/Contributor (non-ECU co-authors, if there are any, appear on document)

Dawn Canupp (Creator)

Sherry Leonard (Creator)

Jonathan Nyce (Creator)

Stefan Schulz (Creator)

So Wong (Creator)

Institution

East Carolina University (ECU )

Web Site: http://www.ecu.edu/lib/

Abstract: In a model system employing Chinese hamster V-79 cells the DNA synthesis inhibitor 3'-azido-3'- deoxythymidine (BW A509U AZT) was shown to induce genome-wide DNA hypermethylation low-frequency silencing of thymidine kinase (TK; EC 2.7.1.21) gene expression and resistance to AZT. Twenty-four hours of exposure of V-79 cells to 150 uM AZT led to >2-fold enhancement of genomic 5-methylcytosine levels and produced TK- epimutants at a rate -43-fold above background. Such AZT-induced TK- epimutants were shown to be severely reduced in their capacity to activate AZT to its proximate antiviral form AZT 5'- monophosphate as compared with the TK+ parental cell line from which they were derived. TK- clones isolated under these conditions were shown to be 9- to 24-fold more resistant to the cytotoxic effects of AZT than the parental TK+ cell line and showed collateral resistance to 5-fluoro-2'-deoxyuridine. Three of four TK- epimutants could be reactivated at very high frequency (8-73%) to the TK+ AZT-sensitive phenotype by 24 hr of exposure to the demethylating agent 5-azadeoxycytidine (5-azadC) implying that drug-induced DNA hypermethylation rather than classical mutation was involved in the original gene-silencing event in these three clones. These 5-azadC-induced TK+ revertants concomitantly regained the ability to metabolize AZT to its 5'-monophosphate. RNA slot blot analyses indicated that the four AZT-induced TK- clones expressed 8.9% 15.6% 17.8% and 11.1% of the parental level ofTK mRNA. The three clones that were reactivatable by 5-azadC showed reexpression of TK mRNA to levels 84.4% 51.1% and 80.0% that of the TK+ parental cell line. These experiments show that one potential mechanism of drug resistance involves drug-induced DNA hypermethylation and resulting transcriptional inactivation of cellular genes whose products are required for drug activation. Originally published Proceedings of the National Academy of Science Vol. 90 No. 7 Apr 1993

Additional Information

Publication

Other

Proceedings of the National Academy of Sciences. 90:7(April 1993) p. 2960-2964.

Language: English

Date: 2011

Keywords

DNA methylation, epimutants, 3'-azido-3'-deoxythymidine, 5-fluoro-2'-deoxyuridine, gene silencing

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