Project description:Mutations in genes encoding epigenetic regulators are among the most frequent somatic events in human cancers. For example, missense and truncating mutations in the MLL3 (KTM2C) histone H3K4-methyltransferase gene can be found in several tumor types. MLL3 is a member of the mixed lineage leukemia gene family and component of the mammalian COMPASS/like complex that promotes gene expression by establishing chromatin modifications favoring gene activation. While Mll3 loss of function promotes tumorigenesis in mice, the molecular targets and biological processes underlying its anti-neoplastic effects remain unknown. Here we combine powerful genetic, genomic, and animal modeling approaches to demonstrate that Mll3 suppresses hepatocellular carcinoma (HCC) by promoting activation of the Cdkn2a (Ink4a/Arf) locus. Hence, disruption of Mll3 using CRISPR/Cas9-mediated genome editing or by RNA interference using short hairpin RNAs cooperates with the Myc oncogene to drive tumorigenesis, producing tumors with reduced H3K4 methylation at multiple gene regulatory elements and low levels of p16Ink4a and p19Arf expression. These results place MLL3 in an established tumor suppressor network and reveal how disruption of a conserved mechanism of epigenetic regulation can alter CDKN2A action and cancer development.
Project description:Mutations in genes encoding epigenetic regulators are among the most frequent somatic events in human cancers. For example, missense and truncating mutations in the MLL3 (KTM2C) histone H3K4-methyltransferase gene can be found in several tumor types. MLL3 is a member of the mixed lineage leukemia gene family and component of the mammalian COMPASS/like complex that promotes gene expression by establishing chromatin modifications favoring gene activation. While Mll3 loss of function promotes tumorigenesis in mice, the molecular targets and biological processes underlying its anti-neoplastic effects remain unknown. Here we combine powerful genetic, genomic, and animal modeling approaches to demonstrate that Mll3 suppresses hepatocellular carcinoma (HCC) by promoting activation of the Cdkn2a (Ink4a/Arf) locus. Hence, disruption of Mll3 using CRISPR/Cas9-mediated genome editing or by RNA interference using short hairpin RNAs cooperates with the Myc oncogene to drive tumorigenesis, producing tumors with reduced H3K4 methylation at multiple gene regulatory elements and low levels of p16Ink4a and p19Arf expression. These results place MLL3 in an established tumor suppressor network and reveal how disruption of a conserved mechanism of epigenetic regulation can alter CDKN2A action and cancer development.
Project description:MLL3 is a histone H3K4 methyltransferase that is frequently mutated in cancer, but the underlying molecular mechanisms remain elusive. Here, we found that MLL3 depletion by CRISPR/sgRNA significantly enhanced cell migration, but did not elevate the proliferation rate of cancer cells. Through RNA-Seq and ChIP-Seq approaches, we identified TNS3 as the potential target gene for MLL3. MLL3 depletion caused downregulation of H3K4me1 and H3K27ac on an enhancer ~ 7 kb ahead of TNS3. 3C assay indicated the identified enhancer interacts with TNS3 promoter and repression of enhancer activity by dCas9-KRAB system impaired TNS3 expression. Exogenous expression of TNS3 in MLL3 deficient cells completely blocked the enhanced cell migration phenotype. Taken together, our study revealed a novel mechanism for MLL3 in suppressing cancer, which may provide novel targets for diagnosis or drug development.
Project description:The histone H3 demethylase Not dead yet-1 (Ndy1/KDM2B) is a physiological inhibitor of senescence. Here, we show that Ndy1 is down-regulated during senescence in mouse embryonic fibroblasts (MEFs) and that it represses the Ink4a/Arf locus. Ndy1 counteracts the senescence-associated down-regulation of Ezh2, a component of polycomb-repressive complex (PRC) 2, via a JmjC domain-dependent process leading to the global and Ink4a/Arf locus-specific up-regulation of histone H3K27 trimethylation. The latter promotes the Ink4a/Arf locus-specific binding of Bmi1, a component of PRC1. Ndy1, which interacts with Ezh2, also binds the Ink4a/Arf locus and demethylates the locus-associated histone H3K36me2 and histone H3K4me3. The combination of histone modifications driven by Ndy1 interferes with the binding of RNA Polymerase II, resulting in the transcriptional silencing of the Ink4a/Arf locus and contributing to the Ndy1 immortalization phenotype. Other studies show that, in addition to inhibiting replicative senescence, Ndy1 inhibits Ras oncogene-induced senescence via a similar molecular mechanism.
Project description:By functionally dissecting densest enhancer cluster in the gene desert at 9P21 locus, we identified a non-redundant inter-dependent enhancer network that functions over long distances, the perturbation in any enhancer in the network results in the complete collapse of entire enhancer cluster and target genes activity. The enhancer network can be targeted to regulate INK4a/ARF locus in associated pathophysiologies and cancers.
Project description:Genetic alterations in the INK4a/ARF (or CDKN2A) locus have been reported in many cancer types, including melanoma; head and neck squamous cell carcinomas; lung, breast, and pancreatic cancers. In melanoma, loss of function CDKN2A alterations have been identified in approximately 50% of primary melanomas, in over 75% of metastatic melanomas, and in the germline of 40% of families with a predisposition to cutaneous melanoma. The CDKN2A locus encodes two critical tumor suppressor proteins, the cyclin-dependent kinase inhibitor p16INK4a and the p53 regulator p14ARF. The majority of CDKN2A alterations in melanoma selectively target p16INK4a or affect the coding sequence of both p16INK4a and p14ARF. There is also a subset of less common somatic and germline INK4a/ARF alterations that affect p14ARF, while not altering the syntenic p16INK4a coding regions. In this review, we describe the frequency and types of somatic alterations affecting the CDKN2A locus in melanoma and germline CDKN2A alterations in familial melanoma, and their functional consequences in melanoma development. We discuss the clinical implications of CDKN2A inactivating alterations and their influence on treatment response and resistance.