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HMGA1 causes a global shift in chromatin architecture linked to transcriptional changes [Hi-C]

ABSTRACT: High Mobility Group A1 (HMGA1) is an architectural chromatin-binding protein that regulates gene expression in various biological contexts, including differentiation and cancer. While previous studies show that HMGA1 acts by binding specific gene promoters or by contributing to the enhanceosome, its global effect on transcription remains unclear. HMGA1 is also critical for the formation of senescence-associated heterochromatic foci (SAHF) in oncogene-induced senescence (OIS), a stable form of cell cycle arrest with a pro-inflammatory phenotype. This link between the two roles of HMGA1, gene regulation and chromatin organisation, has not been fully explained. Here, we used graph theory and data integration from high-throughput assays to investigate how HMGA1 binding impacts the chromatin interactions network. Our results demonstrate that HMGA1 profoundly remodels the global chromatin network during OIS and contributes to stronger compartmentalization. This remodelling goes beyond SAHF, leading to substantial gene repositioning and differential gene expression, highlighting a novel role for HMGA1 in altering chromatin environments. The HMGA1 effects of gene expression go beyond senescence and appear to be relevant in other contexts, such as lung cancer.

ORGANISM(S): Homo sapiens

PROVIDER: GSE245804 | GEO | 2024/07/08

REPOSITORIES: GEO

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Project description:Hypoxia in stem cell niches and inner core of solid tumors contributes to cellular senescence and differentiation inhibition. It directly increases histone methylationby inhibiting the activities of O2-and α-ketoglutarate (α-KG)-dependent histone lysine demethylases. This study is the first to demonstrate how the hypoxic increment of methylated histones cross-talks with other epigenetic changes, such as histone clipping and heterochromatin redistribution, named senescence-associated heterochromatin foci (SAHF), which are found during oncogene-induced senescence (OIS). This study showed that Raf activation in primary human fibroblasts IMR90 increases mature cathepsin L (CTSL)-mediated cleavage of H3, H2B, and H4. Hypoxia prevented H3 cleavage not by inhibiting CTSL but by increasing H3K18me3 and H3K23me3 nearby cleaved site of H3. Forced expression of cleaved H3 in IMR90 cells induced senescence even under hypoxia, suggesting that hypoxia breaks this positive feedback senescence driving circle by increasing methylated histones. The decrease in methylated histones is necessary for OIS to trigger histone clipping and SAHFs, but hypoxia maintains methylated histones to prevent both. Forced reduction of methylated histones in hypoxic cells using inhibitors of methyl-transferases makes hypoxic conditions unable to prevent OIS from inducing both histone clipping and SAHFs. Reversely forced enhancement of methylated histones in normoxic cells using inhibitors of histone demethylases protected histones from clipping during OIS but failed to block SAHFs. Altogether, the maintenance of methylated histones, especially H3K23me3 and H3K18me3, is sufficient to protect histones from clipping during OIS, but not for inhibiting SAHFs, suggesting that besides inhibiting KDMs, hypoxia adopts other methods to inhibit SAHFs. These findings provide a novel mechanism by which hypoxia affects cell fate by increasing methylated histones that protect histones and chromatin from dramatic epigenetic changes.

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HMGA1 causes a global shift in chromatin architecture linked to transcriptional changes [Hi-C]

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