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Department of Biochemistry (W.R., R.S., J.D., A.A., E.H., S.M.) and Institute of Research in Immunology and in Cancer (W.R., J.D., E.H., S.M.), Université de Montréal, Montréal, Canada; Montréal Center for Experimental Therapeutics in Cancer, Jewish General Hospital, Montréal, Canada (W.R., J.D., E.H., J.H.W., S.M.); and Departments of Physiology (J.H.W.) and Medicine (J.H.W., S.M.), McGill University, Montréal, Canada
Histone deacetylase inhibitors (HDACi), which have emerged as a new class of anticancer agents, act by modulating expression of genes controlling apoptosis or cell proliferation. Here, we compared the effect of HDACi on transcriptional activation by estrogen or glucocorticoid receptors (ER and GR, respectively), two members of the steroid receptor family with cell growth regulatory properties. Like other transcription factors, steroid receptors modulate histone acetylation on target promoters. Using episomal reporter vectors containing minimal promoters to avoid promoter-specific effects, we observed that long-term (24-h) incubation with HDACi strongly stimulated GR-dependent but markedly repressed ER-dependent signaling in ER+/GR+ human endometrial carcinoma Ishikawa cells. These effects were reproduced on endogenous target genes and required incubation periods with HDACi substantially longer than necessary to increase global histone acetylation. Repression of estrogen signaling was due to direct inhibition of transcription from multiple ER
promoters and correlated with decreased histone acetylation of these promoters. In contrast, the strong HDACi stimulation of GR-dependent gene regulation was not accounted for by increased GR expression, but it was mimicked by overexpression of the histone acetyltransferase complex component transcriptional intermediary factor 2. Together, our results demonstrate striking and opposite effects of HDACi on ER and GR signaling that involve regulatory events independent of histone hyperacetylation on receptor target promoters.
Address correspondence to: Dr. Sylvie Mader, Département de Biochimie, Université de Montréal, CP 6128 Succursale Centre-Ville, Montréal, Québec H3C 3J7, Canada. E-mail: sylvie.mader{at}umontreal.ca
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