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- W4248731539 abstract "In previous studies, we showed that pretreatment of rat FRTL-5 thyroid cells with TSH, or other agents that increased intracellular cAMP, markedly potentiated DNA synthesis in response to insulin-like growth factor-I (IGF-I). In addition, we found that TSH pretreatment caused an increase in tyrosine phosphorylation of intracellular proteins including an unidentified 125-kDa protein that was well correlated with the TSH-potentiating effect on DNA synthesis induced by IGF-I. These results suggested that cAMP amplified IGF-I-dependent signals for cell growth through changes of cAMP-dependent tyrosine phosphorylation. The present studies were undertaken to determine how tyrosine kinase activation followed by an increase in tyrosine phosphorylation is required for cAMP-dependent potentiation of DNA synthesis induced by IGF-I in this cell line. First of all, we measured tyrosine kinase or protein-tyrosine phosphatase activities in the cell lysates by the in vitro assay. Chronic treatment with TSH or (Bu)2-cAMP stimulated tyrosine kinase activity in the particulate fraction and protein-tyrosine phosphatase activity in the soluble fraction, suggesting that tyrosine kinase plays more important roles for a cAMP-dependent increase in tyrosine phosphorylation of intracellular proteins. The increased tyrosine kinase activity was sensitive to genistein, a potent tyrosine kinase inhibitor. Genistein abolished both the cAMP-dependent increase in tyrosine phosphorylation of the 125-kDa protein and the enhanced DNA synthesis induced by IGF-I in a similar concentration-dependent manner. The only tyrosine-phosphorylated protein associated with the p85 regulatory subunit of phosphatidylinositol (PI) 3-kinase in response to cAMP was 125 kDa. In addition, we found that PI 3-kinase activity bound to p85 subunit significantly increased after (Bu)2cAMP treatment. These results suggested that cAMP stimulates PI 3-kinase through tyrosine phosphorylation of the 125-kDa protein. We then measured DNA synthesis in cells pretreated for 24 h with TSH or (Bu)2cAMP in the absence or presence of LY294002, a PI 3-kinase inhibitor, followed by treatment with IGF-I for 24 h. Presence of LY294002 during TSH or (Bu)2cAMP pretreatment completely abolished cAMP-dependent potentiation of DNA synthesis induced by IGF-I. These results suggest that in FRTL-5 cells cAMP activates genistein-sensitive tyrosine kinases that in turn activate PI 3-kinase activity. These mechanisms appear to be necessary for cAMP-dependent potentiation of the DNA synthesis induced by IGF-I." @default.
- W4248731539 created "2022-05-12" @default.
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- W4248731539 date "2000-07-01" @default.
- W4248731539 modified "2023-10-03" @default.
- W4248731539 title "Tyrosine Kinase and Phosphatidylinositol 3-Kinase Activation Are Required for Cyclic Adenosine 3',5'-Monophosphate-Dependent Potentiation of Deoxyribonucleic Acid Synthesis Induced by Insulin-Like Growth Factor-I in FRTL-5 Cells" @default.
- W4248731539 doi "https://doi.org/10.1210/en.141.7.2429" @default.
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