title: Histone modifications in senescence-associated resistance to apoptosis by oxidative stress.
abstract: Aging and age-related diseases are associated with cellular senescence that results in variable apoptosis susceptibility to oxidative stress. Although fibroblast senescence has been associated with apoptosis resistance, mechanisms for this have not been well defined. In this report, we studied epigenetic mechanisms involving histone modifications that confer apoptosis resistance to senescent human diploid fibroblasts (HDFs). HDFs that undergo replicative senescence display typical morphological features, express senescence-associated β-galactosidase, and increased levels of the tumor suppressor genes, p16, p21, and caveolin-1. Senescent HDFs are more resistant to oxidative stress (exogenous H2O2)-induced apoptosis in comparison to non-senescent (control) HDFs; this is associated with constitutively high levels of the anti-apoptotic gene, Bcl-2, and low expression of the pro-apoptotic gene, Bax. Cellular senescence is characterized by global increases in H4K20 trimethylation and decreases in H4K16 acetylation in association with increased activity of Suv420h2 histone methyltransferase (which targets H4K20), decreased activity of the histone acetyltransferase, Mof (which targets H4K16), as well as decreased total histone acetyltransferase activity. In contrast to Bax gene, chromatin immunoprecipitation studies demonstrate marked enrichment of the Bcl-2 gene with H4K16Ac, and depletion with H4K20Me3, predicting active transcription of this gene in senescent HDFs. These data indicate that both global and locus-specific histone modifications of chromatin regulate altered Bcl-2:Bax gene expression in senescent fibroblasts, contributing to its apoptosis-resistant phenotype.
authors.affiliation: Division of Pulmonary, Allergy and Critical Care Medicine, Department of Medicine University of Alabama at Birmingham, Birmingham, AL, 35294, USA.
authors.forename: Yan Y
authors.initials: YY
authors.lastname: Sanders
authors.forename: Hui
authors.initials: H
authors.lastname: Liu
authors.forename: Xiangyu
authors.initials: X
authors.lastname: Zhang
authors.forename: Louise
authors.initials: L
authors.lastname: Hecker
authors.forename: Karen
authors.initials: K
authors.lastname: Bernard
authors.forename: Leena
authors.initials: L
authors.lastname: Desai
authors.forename: Gang
authors.initials: G
authors.lastname: Liu
authors.forename: Victor J
authors.initials: VJ
authors.lastname: Thannickal
mesh_terms: D017209:Apoptosis; D002478:Cells, Cultured; D016922:Cellular Senescence / Q000187:drug effects; D044127:Epigenesis, Genetic / Q000187:drug effects*; D005347:Fibroblasts / Q000187:drug effects* / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000187:drug effects*; D006657:Histones / Q000378:metabolism*; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D018384:Oxidative Stress / Q000187:drug effects; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism; D051028:bcl-2-Associated X Protein / Q000235:genetics / Q000378:metabolism
chemical_list: C494826:BAX protein, human; D006657:Histones; D019253:Proto-Oncogene Proteins c-bcl-2; D051028:bcl-2-Associated X Protein; D006861:Hydrogen Peroxide
keywords: Aging; Apoptosis; Epigenetics; Fibrosis; Histone modifications
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