Project description:MLL3 is a histone H3K4 methyltransferase which is frequently mutated in cancer, but the underlying molecular mechanisms remain elusive. Here, we found that MLL3 knockout by CRISPR/sgRNA did not elevate proliferation rate of cancer cells, but significantly enhanced cell migration. Through RNA-Seq and ChIP-Seq approaches, we identified TNS3 as the potential target gene for MLL3. MLL3 depletion caused down regulation of H3K4me1 and H3K27ac on an enhancer ~ 8 kb ahead of TNS3. 3C assay indicated the identified enhancer interacts with TNS3 promoter, and repression of enhancer with 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:MLL3 is a histone H3K4 methyltransferase which is frequently mutated in cancer, but the underlying molecular mechanisms remain elusive. Here, we found that MLL3 knockout by CRISPR/sgRNA did not elevate proliferation rate of cancer cells, but significantly enhanced cell migration. Through RNA-Seq and ChIP-Seq approaches, we identified TNS3 as the potential target gene for MLL3. MLL3 depletion caused down regulation of H3K4me1 and H3K27ac on an enhancer ~ 8 kb ahead of TNS3. 3C assay indicated the identified enhancer interacts with TNS3 promoter, and repression of enhancer with 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:a.Background Cancer resequencing studies have revealed epigenetic enzymes as common targets for recurrent mutations. The monomethyltransferase MLL3 is among the most recurrently mutated enzymes in ER+ breast cancer. The H3K4me1 marks created by MLL3 can define enhancers. In ER+ breast cancer, ERα genome binding sites are primarily distal enhancers. Thus, we hypothesize that mutation of MLL3 will alter the genomic binding and transcriptional regulatory activity of ERα. b.Methods We investigated the genomic consequences of knocking down MLL3 in an MLL3/PIK3CA WT ER+ breast cancer cell line. c. Results Loss of MLL3 led to large loss of H3K4me1 across the genome, and a shift in ERα binding sites, which was accompanied by a re-organization of the breast cancer transcriptome. Enrichment analyses of ERα binding sites in MLL3 KD identified endocrine therapy resistance terms, and we show that MLL3 KD cells are resistant to tamoxifen and fulvestrant. Many differentially expressed genes are controlled by new locations of H3K4me1 deposition and ERα binding, suggesting that loss of functional MLL3 leads to new transcriptional regulation of essential genes. Motif analysis of RNA-seq and ChIP-seq data highlighted SP1 as a critical transcription factor in the MLL3 KD cells. Loss of ERα binding is accompanied by a massive increase in SP1 binding at differentially expressed genes. d.Conclusions Our data show that loss of functional MLL3 leads to endocrine therapy resistance. This highlights the importance of genotyping patient tumor samples for MLL3 mutation upon initial resection, prior to deciding upon treatment plans.
Project description:FOXA1 is a pioneer factor that is important in hormone dependent cancer cells to stabilise nuclear receptors, such as estrogen receptor (ER) to chromatin. FOXA1 binds to enhancers regions that are enriched in H3K4mono- and dimethylation (H3K4me1, H3K4me2) histone marks and evidence suggests that these marks are requisite events for FOXA1 to associate with enhancers to initate subsequent gene expression events. However, exogenous expression of FOXA1 has been shown to induce H3K4me1 and H3K4me2 signal at enhancer elements and the order of events and the functional importance of these events is not clear. We performed a FOXA1 Rapid Immunoprecipitation Mass Spectrometry of Endogenous Proteins (RIME) screen in ERα-positive MCF-7 breast cancer cells in order to identify FOXA1 interacting partners and we found histone-lysine N-methyltransferase (MLL3) as the top FOXA1 interacting protein. MLL3 is typically thought to induce H3K4me3 at promoter regions, but recent findings suggest it may contribute to H3K4me1 deposition, in line with our observation that MLL3 associates with an enhancer specific protein. We performed MLL3 ChIP-seq in breast cancer cells and unexpectedly found that MLL3 binds mostly at non-promoter regions enhancers, in contrast to the prevailing hypothesis. MLL3 was shown to occupy regions marked by FOXA1 occupancy and as expected, H3K4me1 and H3K4me2. MLL3 binding was dependent on FOXA1, indicating that FOXA1 recruits MLL3 to chromatin. Motif analysis and subsequent genomic mapping revealed a role for Grainy head like protein-2 (GRHL2) which was shown to co-occupy regions of the chromatin with MLL3. Regions occupied by all three factors, namely FOXA1, MLL3 and GRHL2, were most enriched in H3K4me1. MLL3 silencing decreased H3K4me1 at enhancer elements, but had no appreciable impact on H3K4me3 at enhancer elements. We identify a complex relationship between FOXA1, MLL3 and H3K4me1 at enhancers in breast cancer and propose a mechanism whereby the pioneer factor FOXA1 can interact with a chromatin modifier MLL3, recruiting it to chromatin to facilitate the deposition of H3K4me1 histone marks, subsequently demarcating active enhancer elements.
Project description:Enhancers play a key role in regulating cell type-specific gene expression and are marked by histone modifications such as methylation and acetylation. Mono-methylation of lysine 4 on histone H3 (H3K4me1) initially primes enhancers, preceding enhancer activation via acetylation of lysine 27 on histone H3 (H3K27ac). MLL4 is a major enhancer H3K4 mono-methyltransferase with partial functional redundancy with MLL3. However, how H3K4me1 affects enhancer regulation in cell differentiation has remained unclear. By screening several lysine-to-methionine mutants of H3.3, we first found that depletion of H3K4 methylation by H3.3K4M mutation severely impairs adipogenesis in culture. Using tissue-specific expression of H3.3K4M in mice, we further demonstrate that H3.3K4M inhibits adipose tissue and muscle development in vivo. Mechanistically, H3.3K4M destabilizes MLL3/4 proteins but not other members of the mammalian Set1-like H3K4 methyltransferase family and prevents MLL3/4-mediated enhancer activation in adipogenesis. Using tissue-specific deletion of the enzymatic SET domain of MLL3/4 in mice, we also show that deletion of the SET domain prevents adipose tissue and muscle development in vivo and inhibits adipogenesis by destabilizing MLL3/4 in vitro. Notably, H3.3K4M expression mimics MLL3/4 SET domain deletion in preventing adipogenesis. Interestingly, H3.3K4M does not affect adipose tissue maintenance and function, suggesting that MLL3/4-mediated H3K4 methylation is dispensable for the maintenance and function of differentiated adipocytes. Together, our findings suggest that H3.3K4M targets MLL3/4 to prevent enhancer activation in adipogenesis.
Project description:To understand the interplay between cardiomyocyte and nonmyocyte cell types in human obstructive and non-obstructive hypertrophic cardiomyopathy, single nuclei RNA-sequencing was performed on 2 unused donor hearts, 1 obstructive HCM specimen, and 6 non-obstructive HCM specimens.
Project description:MLL3 inactivation mutations occurs frequently in human breast cancer. To understand the function of MLL3 inactivation, we compared the gene expression profiles of the vector control (WT) and Mll3-knockout MCF7 cells generated by CRISPR-CAS9. Affymetrix human Gene 2.0ST arrays were used for microarray.
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.