title: ING1a expression increases during replicative senescence and induces a senescent phenotype.
abstract: The ING family of tumor suppressor proteins affects cell growth, apoptosis and response to DNA damage by modulating chromatin structure through association with different HAT and HDAC complexes. The major splicing isoforms of the ING1 locus are ING1a and INGlb. While INGlb plays a role in inducing apoptosis, the function of ING1a is currently unknown. Here we show that alternative splicing of the ING1 message alters the INGla:INGlb ratio by approximately 30-fold in senescent compared to low passage primary fibroblasts. INGla antagonizes INGlb function in apoptosis, induces the formation of structures resembling senescence-associated heterochromatic foci containing heterochromatin protein 1 gamma, the accumulation of senescence-associated beta-galactosidase activity and promotes senescent cell morphology and cell cycle arrest. Phenotypic effects may result from differential effects on gene expression since ING1a increases levels of both retinoblastoma and the p16 cyclin-dependent kinase inhibitor and ING1a and ING1b have opposite effects on the expression of proliferating nuclear cell antigen (PCNA), which is required for cell growth. Gene expression appears to be altered by targeting of HDAC complexes to gene promoters since INGla associates with several-fold higher levels of HDAC1 in senescent, compared to replication-competent cells and ING1 is found on the PCNA promoter by chromatin immunoprecipitation analysis. These data demonstrate a novel role for the ING1 proteins in differentially regulating senescence-associated chromatin remodeling vs. apoptosis and support the idea that altered ratios of the ING1 splicing isoforms may contribute to establishing the senescent phenotype through HDAC and HAT complex-mediated effects on chromatin structure.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Calgary, Calgary, Alberta, Canada.
authors.forename: Mohamed A
authors.initials: MA
authors.lastname: Soliman
authors.forename: Philip
authors.initials: P
authors.lastname: Berardi
authors.forename: Svitlana
authors.initials: S
authors.lastname: Pastyryeva
authors.forename: Paul
authors.initials: P
authors.lastname: Bonnefin
authors.forename: Xiaolan
authors.initials: X
authors.lastname: Feng
authors.forename: Ana
authors.initials: A
authors.lastname: Colina
authors.forename: Dallan
authors.initials: D
authors.lastname: Young
authors.forename: Karl
authors.initials: K
authors.lastname: Riabowol
mesh_terms: D017398:Alternative Splicing / Q000502:physiology; D002455:Cell Division / Q000235:genetics; D002460:Cell Line; D016922:Cellular Senescence / Q000502:physiology*; D042002:Chromatin Assembly and Disassembly / Q000502:physiology; D005786:Gene Expression Regulation / Q000502:physiology; D006655:Histone Deacetylases / Q000378:metabolism; D006801:Humans; D000076023:Inhibitor of Growth Protein 1; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics*; D009687:Nuclear Proteins / Q000096:biosynthesis / Q000235:genetics*; D010641:Phenotype; D020033:Protein Isoforms / Q000096:biosynthesis / Q000235:genetics; D025521:Tumor Suppressor Proteins / Q000096:biosynthesis / Q000235:genetics*
chemical_list: C501503:ING1 protein, human; D000076023:Inhibitor of Growth Protein 1; D047908:Intracellular Signaling Peptides and Proteins; D009687:Nuclear Proteins; D020033:Protein Isoforms; D025521:Tumor Suppressor Proteins; D006655:Histone Deacetylases