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: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.
Project description:Heterozygous in-frame mutations in coding regions of human STAT3 underlie the only known autosomal dominant form of hy- per IgE syndrome (AD HIES). About 5% of familial cases remain unexplained. The mutant proteins are loss-of-function and dominant-negative when tested following overproduction in re- cipient cells. However, the production of mutant proteins has not been detected and quantified in the cells of heterozygous pa- tients. We report a deep intronic heterozygous STAT3 mutation, c.1282-89C>T, in 7 relatives with AD HIES. This mutation creates a new exon in the STAT3 complementary DNA, which, when over- expressed, generates a mutant STAT3 protein (D427ins17) that is loss-of-function and dominant-negative in terms of tyrosine phos- phorylation, DNA binding, and transcriptional activity. In immor- talized B cells from these patients, the D427ins17 protein was 2 kDa larger and 4-fold less abundant than wild-type STAT3, on mass spectrometry. The patients’ primary B and T lymphocytes responded poorly to STAT3-dependent cytokines. These findings are reminiscent of the impaired responses of leukocytes from other patients with AD HIES due to typical STAT3 coding muta- tions, providing further evidence for the dominance of the mutant intronic allele. These findings highlight the importance of sequenc- ing STAT3 introns in patients with HIES without candidate variants in coding regions and essential splice sites. They also show that AD HIES-causing STAT3 mutant alleles can be dominant-negative even if the encoded protein is produced in significantly smaller amounts than wild-type STAT3.
Project description:Dominant negative mutatons in nuclear receptors can repress target gene expression, thus having stronger effects than simple loss of gene function. We sought to characterise the effects of a dominant negative mutant (p.W443R) in the hepatoma cell line HepG2 using cell lines stably transfected with wild type and mutant LXR isoforms.