Transcriptional activation from chromatin by nuclear receptors (NRs) requires multiple cofactors including CBP/p300, SWI/SNF and Mediator. How NRs recruit these multiple cofactors is not clear. Here we show that activation by androgen receptor and thyroid hormone receptor is associated with the promoter targeting of SRC family members, p300, SWI/SNF and the Mediator complex. We show that recruitment of SWI/ SNF leads to chromatin remodeling with altered DNA topology, and that both SWI/SNF and p300 histone acetylase activity are required for hormone-dependent activation. Importantly, we show that both the SWI/ SNF and Mediator complexes can be targeted to chromatin by p300, which itself is recruited through interaction with SRC coactivators. Furthermore, histone acetylation by CBP/p300 facilitates the recruitment of SWI/SNF and Mediator. Thus, our data indicate that multiple cofactors required for activation are not all recruited through their direct interactions with NRs and underscore a role of cofactor±cofactor interaction and histone modi®cation in coordinating the recruitment of multiple cofactors.

Previous studies have established an important role of histone acetylation in transcriptional control by nuclear hormone receptors. With chromatin immunoprecipitation assays, we have now investigated whether histone methylation and phosphorylation are also involved in transcriptional regulation by thyroid hormone receptor (TR). We found that repression by unliganded TR is associated with a substantial increase in methylation of H3 lysine 9 (H3-K9) and a decrease in methylation of H3 lysine 4 (H3-K4), methylation of H3 arginine 17 (H3-R17), and a dual modification of phosphorylation of H3 serine 10 and acetylation of lysine 14 (pS10/acK14). On the other hand, transcriptional activation by liganded TR is coupled with a substantial decrease in both H3-K4 and H3-K9 methylation and a robust increase in H3-R17 methylation and the dual modification of pS10/acK14. Trichostatin A treatment results in not only histone hyperacetylation but also an increase in methylation of H3-K4, increase in dual modification of pS10/acK14, and reduction in methylation of H3-K9, revealing an extensive interplay between histone acetylation, methylation, and phosphorylation. In an effort to understand the underlying mechanism for an increase in H3-K9 methylation during repression by unliganded TR, we demonstrated that TR interacts in vitro with an H3-K9-specific histone methyltransferase (HMT), SUV39H1. Functional analysis indicates that SUV39H1 can facilitate repression by unliganded TR and in so doing requires its HMT activity. Together, our data uncover a novel role of H3-K9 methylation in repression by unliganded TR and provide strong evidence for the involvement of multiple distinct histone covalent modifications (acetylation, methylation, and phosphorylation) in transcriptional control by nuclear hormone receptors.In eukaryotic cells, genomic DNA is complexed with histone and nonhistone proteins to form chromatin. The N-terminal tails of histone proteins are known to undergo a number of posttranslational covalent modifications, including acetylation, methylation, phosphorylation, ubiquitination, and ADP-ribosylation (55). Such posttranslational modifications have long been thought to play important roles in chromatin structure and function (50, 54). The identification and characterization of a large number of histone acetyltransferases and histone deacetylases (HDACs) over the last several years have firmly established the functional importance of histone acetylation in chromatin structure and function (13,40,46,60). First reported in 1964, histones have long been known to undergo methylation (33). Early studies have identified methylation in multiple lysine residues, including lysines 4, 9, 27, and 36 of H3 and lysine 20 in H4. In addition, histones can be methylated on arginine residues. The identification and characterization of several histone methyltransferases (HMTs) (8,36,39,44,47,52,53) have provided new insights into the role of histone methylation in chromatin function and gene transcription.Human (SUV39H1) and fission yeast...