Phosphorylation of heterogeneous ribonucleoprotein A1 in human diploid fibroblasts: Implications for p38 MAP kinase.
Item
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Title
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Phosphorylation of heterogeneous ribonucleoprotein A1 in human diploid fibroblasts: Implications for p38 MAP kinase.
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Identifier
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AAI3287106
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identifier
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3287106
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Creator
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Rios, Ileana.
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Contributor
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Adviser: Karen Hubbard
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Date
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2005
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Language
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English
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Publisher
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City University of New York.
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Subject
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Biology, Molecular
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Abstract
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Heterogeneous nuclear ribonucleoproteins (hnRNP's) are several classes of RNA binding proteins which are important in the biogenesis of mature RNA (mRNA). We have previously found that hnRNP protein A1 has diminished protein levels in senescent human diploid fibroblasts (HDF). This RNA binding protein modulates splice site usage, general splicing factors, polyadenylation, and cleavage efficiency. hnRNP A1 has also been implicated in mRNA stability and transport from the nucleus. Thus, the alteration in activity of the hnRNP A1 protein may affect the level of expression of mature mRNA's and contribute to the senescent phenotype.;Protein levels of hnRNP A1 decrease in senescent HDF and this decrease parallels the observed alteration of nucleic acid binding properties. We have previously shown that in young HDF's hnRNP A1 accumulates in the nucleus while in senescent HDF hnRNP A1 disperses to the cytoplasm in a punctate pattern, the mechanism underlying this localization pattern is unknown.;In this study we have examined the phosphorylation status of hnRNP A1 in young and senescent fibroblasts and have found that in senescent fibroblasts the phosphorylation of hnRNP A1 increases relative to its total albeit diminished protein levels.;Recent studies have implicated p38 MAP in the modulation of oncogenic rasinduced premature senescence. Other studies have shown that post-translational modification by phosphorylation is necessary and sufficient for hnRNP A1 cytoplasmic accumulation. The p38 MAP kinase pathway has been shown to induce hnRNP A1 cytoplasmic accumulation during osmotic shock. Thus, this pathway was examined as a putative modulator of hnRNP A1 protein levels.;Our findings suggest that both p38 MAP kinase levels and activity are elevated in senescent fibroblasts consistent with that reported in other fibroblast systems. We have shown that hnRNP A1 co-immunoprecipitates with phosphorylated p38 MAP kinase which suggests an in vivo interaction. We have also demonstrated that inhibition of p38 MAP kinase activity modulates total protein levels of hnRNP A1. Since phosphorylation is known to have an important role in the regulation of protein binding to nucleic acids, the phosphorylation status of hnRNP A1 in addition to its differential nucleo/cytoplasmic protein levels may have a critical effect in its RNA binding activity and localization with ultimate consequences for gene expression during senescence.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
