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Molecular and Cellular Biology, September 2006, p. 6395-6402, Vol. 26, No. 17
0270-7306/06/$08.00+0 doi:10.1128/MCB.00723-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.
Mohamed-Ali Hakimi,
Neil Cooch,
and
Ramin Shiekhattar*
The Wistar Institute, 3601 Spruce Street, Philadelphia, Pennsylvania 19104
Received 26 April 2006/ Returned for modification 30 May 2006/ Accepted 7 June 2006
| ABSTRACT |
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| INTRODUCTION |
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In particular, histone methylation was considered irreversible. However, recent studies have revealed that histone methylation can be reversed by several histone demethylases, including PAD4/PADI4, BHC110/LSD1, and JmjC domain-containing demethylases (6, 24, 31, 34-36). PAD4/PADI4 has been reported to convert monomethyl arginine to citrulline by demethylimination. The JmjC domain-containing demethylases contain a JmjC domain responsible for their enzymatic activity and demethylate mono-, di- or trimethylated lysines by a hydroxylation-based mechanism (31, 35, 36). BHC110 demethylates mono- and dimethyl histone H3 lysine 4 (H3K4) and belongs to a family of FAD-dependent polyamine oxidases which use molecular oxygen as an electron acceptor to oxidize an amine group (24). In addition, we and others have shown that CoREST, the corepressor of REST (RE1-silencing transcription factor) protein, mediates nucleosomal demethylation by BHC110 (18, 26). Surprisingly, androgen receptor was recently reported to alter BHC110 enzymatic activity, leading to the demethylation of histone H3 lysine 9 (20).
BHC110 has been isolated as a component of many multiprotein complexes (1, 9, 12, 14, 15, 25, 30). One such complex, termed BHC (BRAF-HDAC complex), mediates the repression of neuron-specific genes (1, 12). Importantly, we have shown that such corepressor complexes share two enzymatic core subunits: histone deacetylase (HDAC1/2) and BHC110 (13). Here we provide evidence that the enzymatic activities of the histone demethylase and the deacetylase are intimately linked. Such cross talk between the two enzymes is seen only when nucleosomal substrates are used and is mediated through different domains of the CoREST protein. Importantly, we show that due to such functional connections, HDAC inhibitors diminish histone demethylation. Given that some HDAC inhibitors have reached clinical trials (21), these findings not only reveal a second mechanism of action for HDAC inhibitors but also point to the future potential of histones demethylase inhibitors as therapeutics for cancer.
| MATERIALS AND METHODS |
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ELM2, FLAG-
SANT2, FLAG-
SANT1, and FLAG-ELM2) were generated using pFLAG-CMV2 or p3xFLAG-CMV14 (Sigma). Anti-dimethyl K4 H3 antibodies (12-460), anti-acetyl (K9/K14) H3 antibodies (06-599), and sodium butyrate were purchased from Upstate. Anti-H3 (ab1791) and anti-HDAC2 (34-6400) antibodies were from Abcam Ltd. (Cambridge, United Kingdom) and Zymed laboratories, respectively. Anti-FLAG antibody (F3165) and trichostatin A (TSA; T8552) were from Sigma. Affinity purification of the BHC110 complex and recombinant proteins. BHC110 and its mutant complexes were purified from 150- to 200-mg nuclear extracts isolated from stable cell lines using anti-FLAG M2 affinity resin as previously described (18). Baculoviral recombinant proteins (FLAG-BHC110, FLAG-HDAC1, and FLAG-CoREST-His6) were purified from Sf21 insect cells infected by recombinant viruses using anti-FLAG M2 affinity resin (Sigma) as previously described (18). Bacterial recombinant proteins (FLAG-CoREST and FLAG-ELM2) were purified from BL21 cells. BHC110-associated proteins were identified and described previously (12, 13, 18). The amount of BHC110 in complexes was determined by silver staining, and amounts of recombinant proteins were determined by colloidal staining compared with known amounts of bovine serum albumin.
Demethylation and deacetylation assay. Demethylation and deacetylation assays were performed as previously described (18).
Coimmunoprecipitation.
HEK-293 cells were transiently transfected with mammalian expression plasmids encoding FLAG-CoREST and its mutants (FLAG-
ELM2, FLAG-
SANT2, FLAG-
SANT1, and FLAG-ELM2) and harvested 36 h after transfection. Whole-cell extracts were prepared using a lysis buffer (20 mM Tris [pH 8.0], 137 mM NaCl, 1.5 mM MgCl, 1% Triton X-100, 10% glycerol, 0.2 mM phenylmethylsulfonyl fluoride [PMSF], and 1 mM dithiothreitol [DTT]) and immunoprecipitated with anti-FLAG M2 resin. The beads were washed extensively with a wash buffer (20 mM Tris-HCl [pH 8.0], 250 mM KCl, 0.2 mM EDTA, 0.1% NP-40, 10% glycerol, 0.2 mM PMSF, and 1 mM DTT) and eluted with phosphate-buffered saline containing 0.5 µg/ml FLAG peptide. The eluates were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), followed by Western blotting using anti-BHC110, anti-HDAC2, and anti-FLAG antibodies.
Quantitative chromatin immunoprecipitation. HEK 293 cells were transiently transfected with plasmids expressing BHC110 or its mutant (K661A) for 14 to 16 h using Fugene (Roche). For trichostatin A treatment, HEK 293 cells were treated with 100 ng/ml trichostatin A for 14 to 16 h. Dimethyl K4 H3 and acetyl H3 levels on synapsin promoters were measured by quantitative chromatin immunoprecipitation assay as previously described (12) and expressed as the increase (-fold) over the control. Quantitative PCR was performed with a Finnzymes DyNAmo HS SYBR Green qPCR kit using Opticon2 (MJ Research). Data are presented as means and standard errors of the means.
| RESULTS |
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HDAC inhibitors diminish H3 K4 demethylation. To assess whether the enhancement of demethylation by HDAC1 is due to its catalytic activity, we used HDAC inhibitors to silence histone deacetylation. Inhibition of deacetylase activity by the HDAC inhibitors sodium butyrate and TSA decreased nucleosomal demethylation (Fig. 4A to E). Importantly, the effect of HDAC inhibitors is observed only when nucleosomes are used as substrates for the deacetylation reactions (Fig. 4A, B, and D). Moreover, treatment of the BHC110 complex with increasing concentrations of TSA resulted in similar magnitudes of inhibition of HDAC and histone demethylase activities, attesting to the functional interconnection of the two enzymes (Fig. 4F).
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The ELM2 domain of CoREST mediates nucleosomal deacetylation. We recently showed that the SANT domains of CoREST are required for nucleosomal demethylation (18). Since CoREST was also required for nucleosomal deacetylation by HDAC1, we mapped the domain in CoREST mediating HDAC1 association (Fig. 5A). These experiments revealed that in contrast to BHC110, which is associated through CoREST SANT domains, HDAC1 association requires the ELM2 domain of CoREST (Fig. 5B). The ELM2 domain was previously shown to associate with HDAC1 in other transcription factors (7, 27). Importantly, not only is the ELM2 domain of CoREST sufficient for HDAC1 association, but also it could confer nucleosomal deacetylation to recombinant HDAC1 (Fig. 5B and C). However, the ELM2 domain alone in the absence of CoREST SANT domains is unable to recruit BHC110 and consequently confer the enhanced deacetylation mediated through BHC110 (Fig. 5B and C). Collectively, these results indicate that different domains of CoREST are required for mediating deacetylation and demethylation and that the cross talk between the two enzymes requires both the ELM2 and the SANT domains of CoREST.
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| DISCUSSION |
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Since both dimethyl H3K4 and acetyl H3K9/K14 marks are often associated with gene activation in mammalian cells, the repressive function of the BHC110 complex may be enhanced by removing both marks through a synergistic interplay between histone demethylase and acetylase enzymes. Similar cross talks between histone modifications have previously been reported to modulate gene expression in eukaryotic cells. Rad6-mediated ubiquitination of H2B lysine 123 is required for H3K4 methylation by COMPASS and H3K79 methylation by Dot1, leading to telomeric gene silencing in Saccharomyces cerevisiae (8, 23, 29). In contrast, phosphorylation of histone H3 serine 10 by Snf1 unidirectionally facilitates acetylation of H3K14 by Gcn5 to activate gene transcription (19).
Importantly, the two enzymes in the BHC110 complex are linked when nucleosomes but not core histones are used as substrates, reflecting differences in how histone tails are packaged in nucleosomes. These results are consistent with our previous observations that inhibition of histone deacetylation by HDAC inhibitors in experiments using the three-subunit complex (BHC110/CoREST/HDAC1) had no significant effect on core histone demethylation (18). Moreover, we show that while recombinant HDAC1 fails to deacetylate nucleosomal substrates, addition of the ELM2 domain of CoREST is sufficient to confer nucleosomal deacetylation in recombinant HDAC1. The ELM2 domain is also required for the association of HDAC1 with CoREST (Fig. 5B and C). Previously, it has been shown that BHC110 interacts with the SANT domains of CoREST and requires either of these domains for its enzymatic activity for nucleosomes (18). Therefore, although both histone deacetylase and demethylase require CoREST for their nucleosomal activities, they may have different strategies in unmasking the nucleosomal histone tails. Since the minimal complex of the two enzymes and CoREST is sufficient to display enzymatic activities found in the native complex, we speculate that the other components of the complex may have other roles, such as recruitment of the corepressor to specific genomic loci or regulation of the complex's enzymatic activities.
How does CoREST mediate the synergy between the two enzymes and confer nucleosomal deacetylation and demethylation? A likely scenario for the action of CoREST entails its role as a bridge between the two enzymes and the nucleosome. Each enzyme is associated with a different domain of CoREST and through this interaction could influence the activity of the other enzyme. Moreover, such interactions with CoREST may increase nucleosomal accessibility of BHC110 and HDAC1 by inducing conformational changes in both enzymes. Structural studies will be required to unravel the exact mechanism by which the two enzymes are coupled.
Histone deacetylase inhibitors are in phase I clinical trials and show promise as a new generation of anticancer therapeutics (21). Although HDAC inhibitors can cause growth arrest of cancer cells by increasing the expression of tumor suppressor proteins such as p21 (5, 22, 28), the downstream effects of these inhibitors are not entirely clear. In this study, we found that HDAC inhibitors diminish H3 K4 demethylation due to the functional link between HDAC activity and BHC110 activity, providing another mechanism of action for HDAC inhibitors. Whether inhibition of histone demethylation is an important component of the antitumor activity of these drugs is not known. Future studies aimed at identifying in vivo inhibitors of H3K4 demethylation should be able to address these questions and may reveal a new class of anticancer agents.
| ACKNOWLEDGMENTS |
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R.S. was supported by NIH grant R01 GM 61204.
| FOOTNOTES |
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Present address: The University of Michigan, 3301E MSRB III, 1150 W. Medical Center Drive, Ann Arbor, MI 48109-0606. ![]()
Present address: CNRS, UMR5163, Université Joseph Fourier, 38700 La Tronche, France. ![]()
Present address: N3108, Wyeth Pharmaceuticals and Research Headquarters, 500 Arcola Road, Collegeville, PA 19426. ![]()
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