Cell cycle-specific reactivation of an inactive X-chromosome locus by 5-azadeoxycytidine

P. A. Jones, S. M. Taylor, T. Mohandas, L. J. Shapiro

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    Three cytidine analogs containing modifications in the 5-position of the cytosine ring (5-azacytidine, 5-aza-2'-deoxycytidine and pseudoisocytidine) induced the expression of human hypoxanthine/guanine phosphoribosyltransferase (IMP:pyrophosphate phosphoribosyltransferase, EC gene (HPRT) from a structurally normal inactive human X chromosome retained in a mouse-human somatic cell hybrid. Between 0.1% and 8% of the cells surviving treatment with these analogs were able to form colonies in selective medium (hypoxanthine/aminopterin/thymidine/glycine medium), but two other analogs, 5-fluoro-2'-deoxycytidine and 5,6-dihydro-5-azacytidine, did not induce HPRT expression. The inactive X chromosome present in the hybrid was found to be late replicating, and experiments with synchronized cells showed that the induction of HPRT expression by 5-aza-2'-deoxycytidine occurred maximally in cells treated in the latter half of the S phase. Two division cycles were required after analog treatment for the highest frequency of expression of the induced gene. Because these analogs are powerful inhibitors of the methylation of cytosine residues in DNA, the results imply that demethylation of specific DNA sequences may be required for the reexpression of human HPRT.

    Original languageEnglish
    Pages (from-to)1215-1219
    Number of pages5
    JournalProceedings of the National Academy of Sciences of the United States of America
    Issue number4 I
    StatePublished - 1982


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