Cell transformation and signal transduction of an oncogenic human insulin-like growth factor-I receptor.
Item
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Title
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Cell transformation and signal transduction of an oncogenic human insulin-like growth factor-I receptor.
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Identifier
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AAI9720100
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identifier
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9720100
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Creator
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Jiang, Yixing.
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Contributor
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Adviser: Lu-Hai Wang
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Date
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1997
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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 | Health Sciences, Oncology
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Abstract
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An oncogenic human insulin-like growth factor I receptor was constructed previously in our laboratory by truncating its EC domain and fusing to retroviral gag sequence resulting in a gag-IGFR fusion receptor. In this study, tyrosine residues in the cytoplasmic domain of gag-IGFR were systematically mutated to phenylalanines to investigate their role in the enzymatic and biological function of this fusion receptor. 19 mutants including two deletion mutants were constructed. Tyrosine residues 1131, 1135, and 1136 are important for the receptor PTK activity. Y1221, Y1095 and Y1183 have significant effect on the in vitro kinase activity but not on the in vivo autophosphorylation. Mutation of Y1136 (F1136) only slightly affects the kinase activity but dramatically reduced the transforming activity. Tyrosines 943 and 950 play important roles in autophosphorylation of the gag-IGFR. Mutation of either of the two tyrosine residues results in significantly reduced phosphorylation of the receptor but not on its PTK activity or transforming ability. Mutation of Y950 from the most oncogenic gag-IGFR produces little effect on the phosphorylation of insulin receptor substrate 1 (IRS-1), association of IRS-1 with PI3 kinase or cell transforming activity. Deletion of 13 amino acids surrounding Y950, however, results in a significant reduction of IRS1-associated PI3 kinase and transforming activity. Deletion of 19 amino acids (dS2) in this region dramatically reduces transforming activity but not its kinase activity. However, mutation of Y950 from a moderate transforming gag-IGFR results in reduced IRS1-associated PI3 kinase and transforming activity. The most carboxyl tyrosine residue Y1316 is involved in tyrosine phosphorylation of PLC{dollar}\gamma,{dollar} which is, however, not important for cell transforming activity.;Since, dS2 and F1136 retain kinase activity but have greatly reduced transforming ability, their downstream was further analyzed. The pathway other than MAP kinase is essential for the mitogenic activity and is impaired in the mutants. Nevertheless, MAP kinase also plays certain role in cell growth and transformation since a dominant negative mutant of MEK-1 only inhibits the transforming activity of the wild type gag-IGFR by 2 to 3 folds.;To further explore the pathways that are defective in those two mutants, the role of RhoA, Rac1 and Cdc42 were assessed. The results indicate that RhoA and Cdc42 play important roles and have differential effect in gag-IGFR induced cell transformation. Activation of each pathway alone is not sufficient to support the full transforming activity of gag-IGFR. This is supported by the observation that a dominant negative RhoA significantly but not completely inhibits gag-IGFR-induced cell transformation suggesting that pathways other than RhoA are also involved.;Overall, this study has identified several tyrosine residues of IGFR important for its PTK activity and substrate interaction. The transforming potential of the gag-IGFR correlates well with its ability to phosphorylate cellular substrates in general and to activate PI3 kinase via IRS1 in particular. MAP kinase, RhoA, and Rac1/Cdc42-mediated pathways play certain role in the transforming activity of gag-IGFR. Activation of each pathway alone is insufficient for the gag-IGFR-induced cell growth and transformation. It appears that RhoA is involved in regulating contact inhibition and anchorage independent growth while Rac1 and Cdc42 are more involved in regulating the latter activity. (Abstract shortened by UMI.).
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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.
