Project description:Heterozygous missense mutations in EZH2 cause Weaver syndrome (WS), a developmental disorder characterized by intellectual disability and overgrowth. EZH2encodes the enzymatic subunit of Polycomb Repressive Complex 2 (PRC2), which mediates mono-, di-, and tri-methylation of histone H3 lysine 27 (H3K27me1/2/3). Most WS-associated EZH2 variants lack functional characterization but are presumed loss of function. However, the lack of early truncating mutations in EZH2 led us to hypothesise a dominant-negative mechanism for WS, which was supported by our structural analysis of all known WS-associated EZH2 variants. We isogenically modelled 10 representative variants in embryonic stem cells and showed they reduce global H3K27me2/3 with concomitant increases in H3K27ac and chromatin decompaction. Notably, the pattern of H3K27me2/3 reductions indicated dominant-negative interference on PRC2 activity, even when WS-variants were expressed atlow levels. RNA-seq identified weakly Polycomb-bound genes that lose canonical PRC1 (cPRC1) occupancy and become derepressed, including several phenotypically relevant growth control genes. Comparative analysis of a gain-of-function EZH2 variant causing growth restriction revealed reciprocal chromatin and transcriptional changes compared to WS-associated variants. Taken together, our findings support a model where EZH2 variants associated with opposing developmental growth syndromes affect not only H3K27me3, but also intergenic H3K27me2, chromatin architecture, and cPRC1 recruitment.
Project description:Heterozygous missense mutations in EZH2 cause Weaver syndrome (WS), a developmental disorder characterized by intellectual disability and overgrowth. EZH2 encodes the enzymatic subunit of Polycomb Repressive Complex 2 (PRC2), which mediates mono-, di-, and tri-methylation of histone H3 lysine 27 (H3K27me1/2/3). Most WS-associated EZH2 variants lack functional characterization but are presumed loss of function. However, the lack of early truncating mutations in EZH2 led us to hypothesise a dominant-negative mechanism for WS, which was supported by our structural analysis of all known WS-associated EZH2 variants. We isogenically modelled 10 representative variants in embryonic stem cells and showed they reduce global H3K27me2/3 with concomitant increases in H3K27ac and chromatin decompaction. Notably, the pattern of H3K27me2/3 reductions indicated dominant- negative interference on PRC2 activity, even when WS-variants were expressed at low levels. RNA-seq identified weakly Polycomb-bound genes that lose canonical PRC1 (cPRC1) occupancy and become derepressed, including several phenotypically relevant growth control genes. Comparative analysis of a gain-of-function EZH2 variant causing growth restriction revealed reciprocal chromatin and transcriptional changes compared to WS-associated variants. Taken together, our findings support a model where EZH2 variants associated with opposing developmental growth syndromes affect not only H3K27me3, but also intergenic H3K27me2, chromatin architecture, and cPRC1 recruitment.
Project description:EHMT1 and EHMT2 genes encode human euchromatin histone lysine methyltransferase 1 and 2 (EHMT1 alias GLP; EHMT2 alias G9a) that form heteromeric GLP/G9a complexes with essential roles in epigenetic regulation of gene expression. While EHMT1 haploinsufficiency has been established as the cause of Kleefstra syndrome 1, the pathogenesis of G9a dysfunction in human disease remains largely unknown. We identified seven de novo EHMT2 variants in patients with clinical presentation, episignatures, histone modifications and transcriptomic profiles similar to those of Kleefstra syndrome 1. In vitro studies revealed that these variants encode for structurally stable G9a proteins that are catalytically incompetent due to aberrant interactions either with histone H3 tail or with S-adenosylmethionine. Heterozygous mice carrying a patient-derived variant exhibited growth retardation, facial/skull dysmorphia and aberrant behavior. Here we report pathogenic EHMT2 variants that likely exert dominant-negative effect on GLP/G9a complexes and thus genocopy the EHMT1 haploinsufficiency via a distinct molecular mechanism.
Project description:Overexpression of EZH2 in estrogen receptor negative (ER-) breast cancer promotes metastasis. EZH2 has been mainly studied as the catalytic component of the Polycomb Repressive Complex 2 (PRC2) that mediates gene repression by trimethylating histone H3 at lysine 27 (H3K27me3). However, how EZH2 drives metastasis despite the low H3K27me3 levels observed in ER- breast cancer is unknown. We have shown that in human invasive carcinomas and distant metastases, cytoplasmic EZH2 phosphorylated at T367 is significantly associated with ER- disease and low H3K27me3 levels. Here, we explore the interactome of EZH2 and of a phosphodeficient mutant EZH2_T367A. We identified novel interactors of EZH2, and identified interactions that are dependent on the phosphorylation and cellular localization of EZH2 that may play a role in EZH2 dependent metastatic progression.
Project description:A dominant-negative gene therapy approach has been proposed and tested on proto-oncogene KRAS, wherein the oncogenic activity (and cell proliferation) of KRAS can be suppressed by introducing a dominant-negative KRAS allele (S17N). We employed REPLACE to conduct continuous evolution on KRAS (S17N) and examined its potential pathways for conferring resistance in this gene therapy methodology.