title: A distinct mechanism for coactivator versus corepressor function by histone methyltransferase G9a in transcriptional regulation.
abstract: Histone methyltransferase G9a has been understood primarily as a corepressor of gene expression, but we showed previously that G9a positively regulates nuclear receptor-mediated transcription in reporter gene assays. Here, we show that endogenous G9a contributes to the estradiol (E(2))-dependent induction of some endogenous target genes of estrogen receptor (ER)α in MCF-7 breast cancer cells while simultaneously limiting the E(2)-induced expression of other ERα target genes. Thus, G9a has a dual and selective role as a coregulator for ERα target genes. The ERα binding regions associated with the pS2 gene, which requires G9a for E(2)-induced expression, are transiently occupied by G9a at 15 min after beginning E(2) treatment, suggesting that G9a coactivator function is by direct interaction with ERα target genes. Transient reporter gene assays with deletion mutants of G9a demonstrated that domains previously associated with the corepressor functions of G9a (C-terminal methyltransferase domain, ankyrin repeat domain, and cysteine-rich domain) were unnecessary for G9a coactivator function in ERα-mediated transcription. In contrast, the N-terminal domain of G9a was necessary and sufficient for enhancement of ERα-mediated transcription and for E(2)-induced occupancy of G9a on ERα binding sites associated with endogenous target genes of ERα. In addition to a previously identified activation domain, this region contains a previously uncharacterized ligand-dependent ERα binding function, indicating how G9a is recruited to the target genes. Therefore, the coactivator and corepressor functions of G9a involve different G9a domains and different molecular mechanisms.
authors: Department of Biochemistry and Molecular Biology, Norris Comprehensive Cancer Center, University of Southern California, Los Angeles, California 90089-9176.
authors: Daniel J
authors: DJ
authors: Purcell
authors: Department of Biochemistry and Molecular Biology, Norris Comprehensive Cancer Center, University of Southern California, Los Angeles, California 90089-9176.
authors: Kwang Won
authors: KW
authors: Jeong
authors: Department of Biochemistry and Molecular Biology, Norris Comprehensive Cancer Center, University of Southern California, Los Angeles, California 90089-9176.
authors: Danielle
authors: D
authors: Bittencourt
authors: Department of Biochemistry and Molecular Biology, Norris Comprehensive Cancer Center, University of Southern California, Los Angeles, California 90089-9176.
authors: Daniel S
authors: DS
authors: Gerke
authors: Department of Biochemistry and Molecular Biology, Norris Comprehensive Cancer Center, University of Southern California, Los Angeles, California 90089-9176. Electronic address: stallcup@usc.edu.
authors: Michael R
authors: MR
authors: Stallcup
mesh_terms: D000818:Animals; D019556:COS Cells; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism; D002522:Chlorocebus aethiops; D047369:Chromatin Immunoprecipitation; D004967:Estrogens / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic; D005982:Glutathione Transferase / Q000378:metabolism; D006649:Histocompatibility Antigens / Q000235:genetics / Q000502:physiology*; D011495:Histone-Lysine N-Methyltransferase / Q000235:genetics / Q000502:physiology*; D006657:Histones / Q000737:chemistry; D006801:Humans; D008745:Methylation; D051379:Mice; D017434:Protein Structure, Tertiary; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism; D011960:Receptors, Estrogen / Q000378:metabolism; D014158:Transcription, Genetic
chemical_list: D004967:Estrogens; D006649:Histocompatibility Antigens; D006657:Histones; D018160:Receptors, Cytoplasmic and Nuclear; D011960:Receptors, Estrogen; C445405:EHMT2 protein, human; C533711:G9a protein, mouse; D011495:Histone-Lysine N-Methyltransferase; D005982:Glutathione Transferase