Project description:Eukaryotic nuclei encase the genome and differentially package it for the various needs of distinct cell types. Tuning of genome structure and function is accomplished by chromatin binding proteins, which are responsive to cellular stress, determining the transcriptome and phenotype of the cell. We sought to investigate the connection between extracellular stress and chromatin structure to regulate cellular stiffness. We demonstrate that the linker histone H1.0, which compacts nucleosomes into higher order chromatin fibers, controls genome structure and cellular response to stress. Histone H1.0 has privileged expression in tension-responsive fibroblasts across tissue types in mouse and humans, and is necessary and sufficient to mount a myofibroblast phenotype in these cells. Loss of histone H1.0 prevents transforming growth factor beta (TGF-b)-induced fibroblast contraction, proliferation and migration in an isoform-specific manner via inhibition of a transcriptome targeting extracellular matrix molecules. Histone H1.0 is associated with local regulation of gene expression by chromatin fiber compaction and histone acetylation, rendering the nucleus and cell stiffer in response to cytokine stimulation. Knockdown of H1.0 decreased levels of HDAC1 and the chromatin reader BRD4, thereby preventing transcription of a fibrotic gene program. Transient depletion of histone H1.0 in vivo decompacts chromatin and prevents fibrosis in cardiac muscle, lung, and kidney, thereby linking chromatin structure with fibroblast phenotype in response to extracellular stress. Our work identifies an unexpected role of linker histones to sense and respond to cellular stress, directly coupling cellular tension, nuclear organization and gene transcription.
Project description:Eukaryotic nuclei encase the genome and differentially package it for the various needs of distinct cell types. Tuning of genome structure and function is accomplished by chromatin binding proteins, which are responsive to cellular stress, determining the transcriptome and phenotype of the cell. We sought to investigate the connection between extracellular stress and chromatin structure to regulate cellular stiffness. We demonstrate that the linker histone H1.0, which compacts nucleosomes into higher order chromatin fibers, controls genome structure and cellular response to stress. Histone H1.0 has privileged expression in tension-responsive fibroblasts across tissue types in mouse and humans, and is necessary and sufficient to mount a myofibroblast phenotype in these cells. Loss of histone H1.0 prevents transforming growth factor beta (TGF-b)-induced fibroblast contraction, proliferation and migration in an isoform-specific manner via inhibition of a transcriptome targeting extracellular matrix molecules. Histone H1.0 is associated with local regulation of gene expression by chromatin fiber compaction and histone acetylation, rendering the nucleus and cell stiffer in response to cytokine stimulation. Knockdown of H1.0 decreased levels of HDAC1 and the chromatin reader BRD4, thereby preventing transcription of a fibrotic gene program. Transient depletion of histone H1.0 in vivo decompacts chromatin and prevents fibrosis in cardiac muscle, lung, and kidney, thereby linking chromatin structure with fibroblast phenotype in response to extracellular stress. Our work identifies an unexpected role of linker histones to sense and respond to cellular stress, directly coupling cellular tension, nuclear organization and gene transcription.
Project description:Tumors comprise functionally diverse subpopulations of cells with distinct proliferative potential. Here, we show that dynamic epigenetic states defined by the linker histone H1.0 determine which cells within a tumor can sustain the long-term cancer growth. Numerous cancer types exhibit high inter- and intratumor heterogeneity of H1.0, with H1.0 levels correlating with tumor differentiation status, patient survival, and, at the single-cell level, cancer stem cell markers. Silencing of H1.0 promotes maintenance of self-renewing cells by inducing derepression of megabase-sized gene domains harboring downstream effectors of oncogenic pathways. Self-renewing epigenetic states are not stable, and reexpression of H1.0 in subsets of tumor cells establishes transcriptional programs that restrict cancer cells' long-term proliferative potential and drive their differentiation. Our results uncover epigenetic determinants of tumor-maintaining cells.
Project description:Previous studies suggested that MeCP2 competes with linker histone H1, but this hypothesis has never been tested in vivo. Here, we performed chromatin immunoprecipitation followed by sequencing (ChIP-seq) of Flag-tagged-H1.0 in mouse forebrain excitatory neurons. Unexpectedly, Flag-H1.0 and MeCP2 occupied similar genomic regions and the Flag-H1.0 binding was not changed upon MeCP2 depletion. Furthermore, mild overexpression of H1.0 did not alter MeCP2 binding, suggesting that the functional binding of MeCP2 and H1.0 are largely independent.
Project description:Extracellular vesicles (EVs) are now recognized as a fundamental way for cell-to-cell horizontal transfer of properties, in both physiological and pathological conditions. Most of EV-mediated cross-talk among cells depend on the exchange of proteins, and nucleic acids, among which mRNAs, and non-coding RNAs such as different species of miRNAs. Cancer cells, in particular, use EVs to discard molecules which could be dangerous to them (for example differentiation-inducing proteins such as histone H1.0, or antitumor drugs), to transfer molecules which, after entering the surrounding cells, are able to transform their phenotype, and even to secrete factors, which allow escaping from immune surveillance. Herein we report that melanoma cells not only secrete EVs which contain a modified form of H1.0 histone, but also transport the corresponding mRNA. Given the already known role in tumorigenesis of some RNA binding proteins (RBPs), we also searched for proteins of this class in EVs. This study revealed the presence in A375 melanoma cells of at least three RBPs, with apparent MW of about 65, 45 and 38 kDa, which are able to bind H1.0 mRNA. Moreover, we purified one of these proteins, which by MALDI-TOF mass spectrometry was identified as the already known transcription factor MYEF2.