Project description:MYC is an oncogenic driver that regulates transcriptional activation and repression, yet molecular mechanisms of MYC transformation remain unclear. We demonstrate that MYC interacts with the G9a H3K9-methyltransferase complex to control transcriptional repression. Inhibiting G9a hinders MYC chromatin binding at MYC-repressed genes and de-represses gene expression to antagonize cellular transformation. By identifying the MYC Box II region as essential for MYC-G9a interaction, a long-standing missing link between MYC transformation and gene repression is unveiled. In breast cancer, anti-proliferative sensitivity to G9a pharmacological inhibition associates with MYC sensitivity and the basal subtype. Inhibiting G9a in vivo suppresses MYC-dependent basal breast tumor growth. Our findings reveal G9a as an epigenetic regulator of MYC-mediated transcriptional repression and a therapeutic vulnerability in MYC-driven cancers.
Project description:MYC is a master regulator of transcriptional activation and repression that mediates diverse physiological and disease functions, including hematopoiesis, aging, and oncogenesis, yet its essential co-regulators remain unclear. We demonstrate that MYC interacts with and regulates the G9a H3K9 methyltransferase complex to control transcriptional repression in cancer. Inhibiting G9a hinders MYC binding, shifts repressive epigenetic locales to an active state, and de-represses gene expression to antagonize MYC-dependent cellular processes. MYC requires MYC Box II region for its interaction with G9a, providing a mechanism for this region essential for transcriptional repression. In treatment models of MYC-dependent basal breast cancer, genetically inhibiting G9a decreases tumour growth. Anti-proliferative sensitivity to G9a small molecule inhibitors correlates with sensitivity to MYC knockdown and associates with the basal subtype. Our findings illustrate an epigenetic model of MYC-mediated transcriptional repression in driving oncogenesis and establishes G9a as a therapeutic vulnerability in MYC-driven cancers.
Project description:We report a novel translation-regulatory function of G9a, a histone methyltransferase and well-understood transcriptional repressor, in promoting hyperinflammation and lymphopenia; two hallmarks of endotoxin tolerance (ET)-associated chronic inflammatory complications. Using multiple approaches, we demonstrate that G9a interacts with multiple translation regulators during ET, particularly the N6-methyladenosine (m6A) RNA methyltransferase METTL3, to co-upregulate expression of certain m6A-modified mRNAs that encode immune-checkpoint and anti-inflammatory proteins. Mechanistically, G9a promotes m6A methyltransferase activity of METTL3 at translational/post-translational level by regulating its expression, its methylation, and its cytosolic localization during ET. Additionally, from a broader view extended from the G9a-METTL3-m6A translation regulatory axis, our translatome proteomics approach identified numerous “G9a-translated” proteins that unite the networks associated with inflammation dysregulation, T cell dysfunction, and systemic cytokine response. In sum, we identified a previously unrecognized function of G9a in protein-specific translation that can be leveraged to treat ET-related chronic inflammatory diseases.
Project description:Posttranslational modifications of histone N-terminal tails influence the status of chromatin and eventually control the transcriptional outcome of a particular gene. As a histone H3K9 methyltransferase (HMTase) in higher eukaryotes, G9a-mediated transcriptional repression is the major epigenetic silencing machinery. UHRF1 (ubiquitin-like with PHD and ring finger domains I) binds to hemi-methylated DNA and plays essential role in maintenance of DNA methylation by recruiting DNMT1. Here, we provide evidence that UHRF1 is transcriptionally downregulated by H3K9 HMTase G9a. We found that increased expression of G9a along with transcription factor YY1 specifically represses UHRF1 transcription. We uncovered showed that G9a regulates UHRF1-mediated H3K23 ubiquitylation and proper DNA replication maintenance by FACS analysis and propose that H3K9 HMTase G9a is a specific epigenetic regulator of UHRF1.
Project description:Cocaine-mediated repression of the histone methyltransferase (HMT) G9a has recently been implicated in transcriptional, morphological, and behavioral responses to chronic cocaine administration. Here, using a ribosomal affinity purification approach, we find that G9a repression by cocaine occurs in both Drd1 (striatonigral)- and Drd2 (striatopallidal)-expressing medium spiny neurons (MSNs). Conditional knockout and overexpression of G9a within these distinct cell types, however, reveals divergent behavioral phenotypes in response to repeated cocaine treatment. Our studies further indicate that such developmental deletion of G9a selectively in Drd2 neurons results in the unsilencing of transcriptional programs normally specific to striatonigral neurons, and the acquisition of Drd1-associated projection and electrophysiological properties. This partial striatopallidal to striatonigral ‘switching’ phenotype in mice indicates a novel role for G9a in contributing to neuronal subtype identity, and suggests a critical function for cell-type specific histone methylation patterns in the regulation of behavioral responses to environmental stimuli.
Project description:We report a novel translation-regulatory function of G9a, a histone methyltransferase and well-understood transcriptional repressor, in promoting hyperinflammation and lymphopenia; two hallmarks of endotoxin tolerance (ET)-associated chronic inflammatory complications. Using multiple approaches, we demonstrate that G9a interacts with multiple translation regulators during ET, particularly the N6-methyladenosine (m6A) RNA methyltransferase METTL3, to co-upregulate expression of certain m6A-modified mRNAs that encode immune-checkpoint and anti-inflammatory proteins. Mechanistically, G9a promotes m6A methyltransferase activity of METTL3 at translational/post-translational level by regulating its expression, its methylation, and its cytosolic localization during ET. Additionally, from a broader view extended from the G9a-METTL3-m6A translation regulatory axis, our translatome proteomics approach identified numerous “G9a-translated” proteins that unite the networks associated with inflammation dysregulation, T cell dysfunction, and systemic cytokine response. In sum, we identified a previously unrecognized function of G9a in protein-specific translation that can be leveraged to treat ET-related chronic inflammatory diseases.
Project description:Increased activation of the serine-glycine biosynthetic pathway is an integral part of cancer metabolism that drives macromolecule synthesis needed for cell proliferation. Whether this pathway is under epigenetic control is unknown. Here we show that the histone H3 lysine 9 (H3K9) methyltransferase G9A is required for maintaining the pathway enzyme genes in an active state marked by H3K9 monomethylation and for the transcriptional activation of this pathway in response to serine deprivation. G9A inactivation depletes serine and its downstream metabolites, triggering cell death with autophagy in cancer cell lines of different tissue origins. Higher G9A expression, which is observed in various cancers and is associated with greater mortality in cancer patients, increases serine production and enhances the proliferation and tumorigenicity of cancer cells. These findings identify a G9A-dependent epigenetic program in the control of cancer metabolism, providing a rationale for G9A inhibition as a therapeutic strategy for cancer. Affymetrix microarray assays were performed according to the manufacturer's directions on total RNA isolated from three independent samples of BE(2)-C cells treated either with 0.05% DMSO or with 5 M-BM-5M BIX01294 (B9311, Sigma-Aldrich) for 24 hours.
Project description:Increased activation of the serine-glycine biosynthetic pathway is an integral part of cancer metabolism that drives macromolecule synthesis needed for cell proliferation. Whether this pathway is under epigenetic control is unknown. Here we show that the histone H3 lysine 9 (H3K9) methyltransferase G9A is required for maintaining the pathway enzyme genes in an active state marked by H3K9 monomethylation and for the transcriptional activation of this pathway in response to serine deprivation. G9A inactivation depletes serine and its downstream metabolites, triggering cell death with autophagy in cancer cell lines of different tissue origins. Higher G9A expression, which is observed in various cancers and is associated with greater mortality in cancer patients, increases serine production and enhances the proliferation and tumorigenicity of cancer cells. These findings identify a G9A-dependent epigenetic program in the control of cancer metabolism, providing a rationale for G9A inhibition as a therapeutic strategy for cancer.
Project description:PALI1 is a newly identified accessory protein of the Polycomb Repressive Complex 2 (PRC2) that catalyzes H3K27 methylation. However, the roles of PALI1 in cancer are yet to be defined. Here we report that PALI1 is upregulated in advanced prostate cancer (PCa) and competes with JARID2 for binding to PRC2 core subunit SUZ12. PALI1 further interacts with the H3K9 methyltransferase G9A, bridging the formation of a unique G9A-PALI1-PRC2 super-complex that occupies a subset of G9A-target genes to mediate dual H3K9/K27 methylation and gene repression. Many of these genes are developmental regulators induced upon cell differentiation, and their loss in PCa predicts poor prognosis. Accordingly, PALI1 and G9A drive PCa cell proliferation and invasion in vitro and xenograft tumor growth in vivo. Collectively, our study shows that PALI1 harnesses two central epigenetic mechanisms to suppress cellular differentiation and promote tumorigenesis, which can be targeted by dual EZH2 and G9A inhibition.