ABSTRACT: Rhabdomyosarcoma (RMS) is a pediatric soft tissue sarcoma, wherein the malignant tumors arise from the myoblast like cells due to the perturbations in growth and differentiation. Alveolar rhabdomyosarcoma (ARMS) is one of the two major histological subtypes which exhibits high metastatic potential and tumor recurrence culminating in poor prognosis. In the recent past, understanding the epigenetic modifications in these tumors with less genetic alterations has shed light on the process of tumor pathogenesis and development of potential epi-drugs for the effective treatment strategies. Epigenetic regulator, Euchromatin histone lysine methyltransferase 1 (EHMT1)/G9A-like protein (GLP) and its homolog Euchromatin histone lysine methyltransferase 1 (EHMT2)/G9A has been shown to promote proliferation and inhibit differentiation in the mouse myoblast cells, independently. Also, previous study from our lab reported the overexpression of EHMT2 and molecular mechanism associated with the oncogenic phenotype in ARMS. However, expression pattern and functional role of EHMT1 in ARMS is unknown. Herein, we investigated the role of EHMT1 in ARMS. Our preliminary data indicated the overexpression of EHMT1 and the associated oncogenic phenotypes in ARMS. Although EHMT1 has shown to be upregulated and correlated with the increased disease severity in several cancers including gastric, esophagus, squamous cell carcinoma, ovarian and breast cancer, the mechanism involved in the EHMT1 mediated tumorigenesis was unclear. Therefore, through our current study we aimed to understand the expression pattern and the mechanism through which EHMT1 regulated cancer phenotypes in ARMS, for this we performed whole transcriptomic analysis in ARMS cell lines upon EHMT1 knockdown for the first time. In addition, we also compared the expression levels of EHMT1 between Human skeletal muscle myoblasts (HSMM) and ARMS patient samples (obtained from St Jude cloud database).
Project description:EHMT1 (also known as GLP) is a multifunctional protein, best known for its role as an H3K9me1 and H3K9me2 methyltransferase through its reportedly obligatory dimerization with EHMT2 (also known as G9A). Here, we investigated the role of EHMT1 in the oocyte in comparison to EHMT2 using oocyte-specific conditional knockout mouse models (Ehmt2 cKO, Ehmt1cKO, Ehmt1/2 cDKO), with ablation from the early phase of oocyte growth. Loss of EHMT1 in Ehmt1 cKO and Ehmt1/2 cDKO oocytes recapitulated meiotic defects observed in the Ehmt2 cKO; however, there was a significant impairment in oocyte maturation and developmental competence in Ehmt1 cKO and Ehmt1/2 cDKO oocytes beyond that observed in the Ehmt2cKO. Consequently, loss of EHMT1 in oogenesis results, upon fertilization, in mid-gestation embryonic lethality. To identify H3K9 methylation and other meaningful biological changes in each mutant to explore the molecular functions of EHMT1 and EHMT2, we performed immunofluorescence imaging, multi-omics sequencing, and mass spectrometry (MS)–based proteome analyses in cKO oocytes. Although H3K9me1 was depleted only upon loss of EHMT1, H3K9me2 was decreased, and H3K9me2-enriched domains were eliminated equally upon loss of EHMT1 or EHMT2. Furthermore, there were more significant changes in the transcriptome, DNA methylome, and proteome in Ehmt1/2 cDKO than Ehmt2 cKO oocytes, withtranscriptional derepression leading to increased protein abundance and local changes in genic DNA methylation in Ehmt1/2 cDKO oocytes. Together, our findings suggest that EHMT1 contributes to local transcriptional repression in the oocyte, partially independent of EHMT2, and is critical for oogenesis and oocyte developmental competence
Project description:Rhabdomyosarcoma (RMS) is the most common soft-tissue sarcoma of childhood characterized by the inability to exit the proliferative myoblast-like stage. Here, we identified the DEAD box RNA helicase 5 (DDX5) as a potential therapeutic target to inhibit alveolar rhabdomyosarcoma (ARMS) growth. We show that DDX5 is overexpressed in alveolar RMS cells, demonstrating that its depletion drastically decreases ARMS viability and slows tumor growth in xenograft models. Mechanistically, we provide evidence that DDX5 functions upstream the G9a/AKT survival signalling pathway, by modulating G9a protein stability
Project description:Rhabdomyosarcoma (RMS) is the most common soft-tissue sarcoma of childhood characterized by the inability to exit the proliferative myoblast-like stage. Here, we identified the DEAD box RNA helicase 5 (DDX5) as a potential therapeutic target to inhibit alveolar rhabdomyosarcoma (ARMS) growth. We show that DDX5 is overexpressed in alveolar RMS cells, demonstrating that its depletion drastically decreases ARMS viability and slows tumor growth in xenograft models. Mechanistically, we provide evidence that DDX5 functions upstream the G9a/AKT survival signalling pathway, by modulating G9a protein stability
Project description:G9a (EHMT2) and the G9a-like protein GLP (EHMT1) form a stable G9a/GLP heterodimer in embryonic stem cells and function cooperatively to establish and maintain the abundant repressive H3K9me2 modification, in addition to modifying several non-histone proteins. The G9a-dependent H3K9me2 is implicated in lineage-specific gene silencing and covers large chromosomal domains. While the mechanism of H3K9me2maintenance by G9a/GLP is known, how new patterns of this modification are established is not well understood. With this in mind, we used FLAG affinity purification of G9a under two different stringency conditions (150 and 300 mM NaCl) coupled with mass spectrometry to identify proteins stably associated with G9a/GLP, which could serve as potential recruiters of the complex to unmodified chromatin.
Project description:The euchromatin histone methyltransferase 2 (EHMT2, aka G9a) methylates histone H3K9 to repress gene expression, but it also acts as a coactivator for some nuclear receptors. The molecular mechanisms underlying this activation remain elusive. Here we show that G9a functions as a bona fide coactivator of the endogenous estrogen receptor α (ERα) in breast cancer cells in a histone methylation-independent manner. G9a dimethylates ERα protein at lysine 235 both in vitro and in cells. Dimethylation of ERαK235 (ERαK235me2) is recognized by the Tudor domain of PHF20, which in turn recruits the MOF histone acetyltransferase (HAT) complex to ERα target gene promoters to deposit histone H4K16 acetylation promoting active transcription. Together, our in vitro and in vivo data establish the molecular mechanism by which G9a functions as an ERα coactivator. Along with the PHF20/MOF complex, G9a links the crosstalk between ERα methylation and histone acetylation governing the epigenetic regulation of hormonal gene expression.
Project description:Kleefstra syndrome (KS, also known as 9q.34.3 deletion syndrome) is a rare genetic disorder characterized by a developmental delay, abnormal behaviors and autism-like features. This syndrome is caused by haplo-insufficiency of the euchromatin histone methyltransferase 1 gene (EHMT1/GLP/KDM1D). This gene product, GLP is a methyltransferase responsible for mono- and di-methylation of lysine 9 on histone H3 N-terminal tail, which modulates epigenetic information. Ehmt1 heterozygous mutant (Ehmt1∆/+) mice show KS-like abnormal behavioral phenotypes and utilized as KS model mice. Here, we isolated nuclei from adult Ehmt1∆/+ mice cortex and analysed gene expression precisely by single nucleus RNA-seq analysis. It showed that many genes were up or down regulated in different cell types of Ehmt1∆/+ mice brain. Among them, inflammation associating genes are up-regulated in Ehmt1∆/+ mice neuronal cells. And this up-regulation was reversed by postnatal supply of GLP in post-mitotic neuron of Ehmt1∆/+ mice brain.
Project description:Alveolar Rhabdomyosarcoma (ARMS) is the most aggressive subtype mainly caused by the expression of PAX3/7-FOXO1 oncoproteins Here, we show that G9a interacts with PAX3-FOXO1 and regulates its activity. In line with this, transcriptomic analysis by RNA-seq revealed that G9a depletion in RH41 cells induced transcriptional changes inversely correlated by those imposed by PAX3-FOXO1 expression. Overall, our results indicate that G9a promotes PAX3-FOXO1 stability, thus sustaining ARMS myoblastic state.
Project description:The methylation of histone 3 at lysine 9 (H3K9) is widely regarded as a major roadblock for cellular reprogramming and interference with associated methyltransferases such as EHMT1 and EHMT2 (also known as GLP and G9A) facilitates the derivation of induced pluripotent stem cells (iPSCs). In addition, activation of demethylases by ascorbic acid (AA) has become a common approach to facilitate the extensive epigenetic remodeling required for iPSC formation. The functional interaction between the H3K9 methylation machinery and AA-stimulated enzymes, and consequences of interfering with these pathways, remain insufficiently explored. Here, we show that reduction of EHMT1/2 activity paradoxically counteracts iPSC formation in an optimized reprogramming system in the presence of AA. At the cellular and molecular level, EHMT1/2 activity is required for efficient downregulation of somatic genes and transition into an epithelial state. Genetic interference with the demethylase KDM3B partially rescues the adverse effect of EHMT1/2 inhibition on iPSC formation. Transient inhibition of EHMT1/2 during reprogramming yields iPSCs that fail to efficiently give rise to viable mice, suggesting persistent molecular defects in these cells. Together, our observations document a more nuanced function of H3K9 methyltransferases during iPSC formation and suggest that the balancing of AA-stimulated enzymes by EHMT1/2 is required for efficient and error-free reprogramming to pluripotency.
Project description:GLP (EHMT1) functions as an H3K9me1 and H3K9me2 methyltransferase through its reportedly obligatory dimerization with G9A (EHMT2). Here, we investigated the role of GLP in oocyte and embryo development in comparison to G9A using oocyte-specific conditional knockout mouse models (G9a cKO, Glp cKO, G9a-Glp cDKO). Loss of GLP in oogenesis severely impairs oocyte maturation, fertilization and embryo development, resulting in lethality before embryonic day E12.5. In contrast, loss of G9A has a milder effect with a proportion of embryos producing viable offspring. The Glp cKO also showed loss of G9A protein and, hence, was phenotypically very similar to the G9a-Glp cDKO. H3K9me2 was equally depleted in all cKO genotypes, whereas H3K9me1 was decreased only in Glp cKO and G9a-Glp cDKO oocytes. Furthermore, the transcriptome, DNA methylome and proteome were markedly more affected in G9a-Glp cDKO than G9a cKO oocytes, demonstrating that in the absence of GLP there are widespread epigenetic and gene expression changes in the oocyte independent of H3K9me2. Gene dysregulation with coupled changes in DNA methylation suggest localised loss of chromatin repression, resulting in upregulated protein expression. Together, our findings demonstrate that GLP can function independently of G9A in the oocyte and is required for oocyte developmental competence.