RESUMO
The Polycomb repressive complex 2 (PRC2) mediates epigenetic maintenance of gene silencing in eukaryotes via methylation of histone H3 at lysine 27 (H3K27). Accessory factors define two distinct subtypes, PRC2.1 and PRC2.2, with different actions and chromatin-targeting mechanisms. The mechanisms orchestrating PRC2 assembly are not fully understood. Here, we report that alternative splicing (AS) of PRC2 core component SUZ12 generates an uncharacterized isoform SUZ12-S, which co-exists with the canonical SUZ12-L isoform in virtually all tissues and developmental stages. SUZ12-S drives PRC2.1 formation and favors PRC2 dimerization. While SUZ12-S is necessary and sufficient for the repression of target genes via promoter-proximal H3K27me3 deposition, SUZ12-L maintains global H3K27 methylation levels. Mouse embryonic stem cells (ESCs) lacking either isoform exit pluripotency more slowly and fail to acquire neuronal cell identity. Our findings reveal a physiological mechanism regulating PRC2 assembly and higher-order interactions in eutherians, with impacts on H3K27 methylation and gene repression.
Assuntos
Processamento Alternativo , Complexo Repressor Polycomb 2 , Animais , Camundongos , Complexo Repressor Polycomb 2/genética , Complexo Repressor Polycomb 2/metabolismo , Histonas/genética , Histonas/metabolismo , Cromatina/genética , Isoformas de Proteínas/genéticaRESUMO
Cell cycle progression is linked to transcriptome dynamics and variations in the response of pluripotent cells to differentiation cues, mostly through unknown determinants. Here, we characterized the cell-cycle-associated transcriptome and proteome of mouse embryonic stem cells (mESCs) in naive ground state. We found that the thymine DNA glycosylase (TDG) is a cell-cycle-regulated co-factor of the tumor suppressor p53. Furthermore, TDG and p53 co-bind ESC-specific cis-regulatory elements and thereby control transcription of p53-dependent genes during self-renewal. We determined that the dynamic expression of TDG is required to promote the cell-cycle-associated transcriptional heterogeneity. Moreover, we demonstrated that transient depletion of TDG influences cell fate decisions during the early differentiation of mESCs. Our findings reveal an unanticipated role of TDG in promoting molecular heterogeneity during the cell cycle and highlight the central role of protein dynamics for the temporal control of cell fate during development.
Assuntos
Timina DNA Glicosilase , Proteína Supressora de Tumor p53 , Animais , Camundongos , Ciclo Celular/genética , Linhagem Celular , Regulação da Expressão Gênica , Timina DNA Glicosilase/genética , Timina DNA Glicosilase/metabolismo , Proteína Supressora de Tumor p53/genética , Proteína Supressora de Tumor p53/metabolismoRESUMO
Polycomb repressive complex 2 (PRC2) is a key epigenetic multiprotein complex involved in the regulation of gene expression in metazoans. PRC2 is formed by a tetrameric core that endows the complex with histone methyltransferase activity, allowing it to mono-, di- and tri-methylate histone H3 on lysine 27 (H3K27me1/2/3); H3K27me3 is a hallmark of facultative heterochromatin. The core complex of PRC2 is bound by several associated factors that are responsible for modulating its targeting specificity and enzymatic activity. Depletion and/or mutation of the subunits of this complex can result in severe developmental defects, or even lethality. Furthermore, mutations of these proteins in somatic cells can be drivers of tumorigenesis, by altering the transcriptional regulation of key tumour suppressors or oncogenes. In this review, we present the latest results from structural studies that have characterised PRC2 composition and function. We compare this information with data and literature for both gain-of function and loss-of-function missense mutations in cancers to provide an overview of the impact of these mutations on PRC2 activity.
Assuntos
Cromatina/metabolismo , Regulação Neoplásica da Expressão Gênica/genética , Código das Histonas/genética , Neoplasias/genética , Complexo Repressor Polycomb 2/genética , Animais , Proteína Potenciadora do Homólogo 2 de Zeste/genética , Proteína Potenciadora do Homólogo 2 de Zeste/metabolismo , Proteína Potenciadora do Homólogo 2 de Zeste/ultraestrutura , Mutação com Ganho de Função , Humanos , Mutação com Perda de Função , Camundongos , Proteínas de Neoplasias , Complexo Repressor Polycomb 2/metabolismo , Complexo Repressor Polycomb 2/ultraestrutura , Domínios Proteicos , Estrutura Quaternária de Proteína , Estrutura Terciária de Proteína , Subunidades Proteicas , Relação Estrutura-Atividade , Fatores de TranscriçãoRESUMO
Epigenetic mechanisms are crucial for sustaining cell type-specific transcription programs. Among the distinct factors, Polycomb group (PcG) proteins are major negative regulators of gene expression in mammals. These proteins play key roles in regulating the proliferation, self-renewal, and differentiation of stem cells. During hematopoietic differentiation, many PcG proteins are fundamental for proper lineage commitment, as highlighted by the fact that a lack of distinct PcG proteins results in embryonic lethality accompanied by differentiation biases. Correspondingly, proteins of these complexes are frequently dysregulated in hematological diseases. In this review, we present an overview of the role of PcG proteins in normal and malignant hematopoiesis, focusing on the compositional complexity of PcG complexes, and we briefly discuss the ongoing clinical trials for drugs targeting these factors.
Assuntos
Epigênese Genética , Neoplasias Hematológicas/genética , Hematopoese/genética , Células-Tronco Hematopoéticas/metabolismo , Proteínas do Grupo Polycomb/genética , Animais , Diferenciação Celular , Proliferação de Células , Proteínas de Drosophila/genética , Proteínas de Drosophila/metabolismo , Drosophila melanogaster/genética , Drosophila melanogaster/metabolismo , Neoplasias Hematológicas/metabolismo , Neoplasias Hematológicas/patologia , Células-Tronco Hematopoéticas/patologia , Humanos , Proteínas do Grupo Polycomb/classificação , Proteínas do Grupo Polycomb/metabolismo , Transcrição GênicaRESUMO
JARID1B/KDM5B histone demethylase's mRNA is markedly overexpressed in breast cancer tissues and cell lines and the protein has been shown to have a prominent role in cancer cell proliferation and DNA repair. However, the mechanism of its post-transcriptional regulation in cancer cells remains elusive. We performed a computational analysis of transcriptomic data from a set of 103 breast cancer patients, which, along with JARID1B upregulation, showed a strong downregulation of 2 microRNAs (miRNAs), mir-381 and mir-486, potentially targeting its mRNA. We showed that both miRNAs can target JARID1B 3'UTR and reduce luciferase's activity in a complementarity-driven repression assay. Moreover, MCF7 breast cancer cells overexpressing JARID1B showed a strong protein reduction when transfected with mir-486. This protein's decrease is accompanied by accumulation of DNA damage, enhanced radiosensitivity and increase of BRCA1 mRNA, 3 features previously correlated with JARID1B silencing. These results enlighten an important role of a miRNA's circuit in regulating JARID1B's activity and suggest new perspectives for epigenetic therapies.
