Cell type-specific roles of histone deacetylase in TR ligand-independent transcriptional repression

Abstract

Recent evidence indicates that corepressor protein with histone deacetylase (HDAC) activity mediates thyroid hormone receptor (TR) transcriptional repression. In order to examine the physiological relevance of HDAC in ligand-independent TR-mediated repression, we studied the effect of trichostatin A (TSA), a specific HDAC inhibitor, in transient transfection studies with natural reporters, and assessed the expression of TR-regulated endogenous genes. Luciferase-coupled DR4-, F2-, PAL- or GH-TREs and TRβ1 expression vectors were cotransfected in CV-1 and GH3 cells. We did not observe any effect of TSA on TR-induced basal repression in CV-1 cells. Instead, TSA was able to induce an increase in transcription without T3 on all TREs tested in GH3 cells. This increase was >7-fold on F2-, >4-fold on DR4-, and 3-fold on GH-TREs. The cotransfection of a TRβ1 mutant that exhibits decreased affinity with N-CoR (AHT) reduced the TSA effect in GH3 cells, demonstrating a primary role for TR/N-CoR/Sin3/HDAC complex. Next, we examined the effects of TSA on endogenous GH mRNA production in GH3 cells by Northern blot analysis. We observed an increase of 50-70% of GH mRNA in cells treated with TSA in hypothyroid medium, and an increase of GH mRNA in T3-treated cells after TSA treatment. Our results show that TSA can increase the expression of endogenous genes that are susceptible to TR regulation. These results support an active role of HDAC in transcriptional repression by ligand-independent TR. Copyright © 2001 Elsevier Science Ireland Ltd.