Hypoxia increases methylated histones to prevent histone clipping and heterochromatin redistribution during Raf-induced senescence.
Abstract
Hypoxia enhances histone methylation by inhibiting oxygen- and α-ketoglutarate-dependent demethylases, resulting in increased methylated histones. This study reveals how hypoxia-induced methylation affects histone clipping and the reorganization of heterochromatin into senescence-associated heterochromatin foci (SAHF) during oncogene-induced senescence (OIS) in IMR90 human fibroblasts. Notably, using top-down proteomics, we discovered specific cleavage sites targeted by Cathepsin L (CTSL) in H3, H2B and H4 during Raf activation, identifying novel sites in H2B and H4. Hypoxia counteracts CTSL-mediated histone clipping by promoting methylation without affecting CTSL's activity. This increase in methylation under hypoxia protects against clipping, reshaping the epigenetic landscape and influencing chromatin accessibility, as shown by ATAC-seq analysis. These insights underscore the pivotal role of hypoxia-induced histone methylation in protecting chromatin from significant epigenetic shifts during cellular aging.
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Research summary
The paper explores the role of hypoxia-induced histone methylation in the context of oncogene-induced senescence, which is relevant to cellular aging mechanisms. It provides insights into how epigenetic modifications can influence chromatin dynamics during senescence, potentially linking to broader aging processes. However, while the findings are interesting and contribute to our understanding of epigenetic regulation in aging, they do not present a transformative breakthrough or directly address root causes of aging, limiting their overall impact.
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