title: Distinct modes of activation of phosphatidylinositol 3-kinase in response to cyclic adenosine 3', 5'-monophosphate or insulin-like growth factor I play different roles in regulation of cyclin D1 and p27Kip1 in FRTL-5 cells.
abstract: Bioactivities of IGFs in various cells are often potentiated in the presence of other hormones. In previous studies we showed that pretreatment of rat FRTL-5 thyroid cells with TSH or other cAMP-generating agents markedly potentiated DNA synthesis induced by IGF-I. Under these conditions we found that phosphatidylinositol (PI) 3-kinase was activated in response to either cAMP or IGF stimulus, and both activation modes were indispensable for the potentiation of DNA synthesis. The present studies were undertaken to elucidate how cAMP and/or IGF-I stimulus regulated the G1 cyclin-cyclin dependent kinase (CDK)-inhibitor system, and to determine the roles of PI 3-kinase activation by cAMP or IGF-I stimulus in this system. We found that cAMP pretreatment enhanced IGF-I-dependent increases in cyclin D1, due to synergistic increases in mRNA and elevation of translation rates. Furthermore, cAMP pretreatment enhanced IGF-I-induced protein degradation of the CDK inhibitor, p27(Kip1). These changes well explained an increase in cyclin E, leading to marked activation of G1 CDKs, followed by retinoblastoma protein phosphorylation. Our results using a PI 3-kinase inhibitor showed that cAMP-dependent PI 3-kinase activation plays an important role in the increase in cyclin D1 translation. In contrast, IGF-I-dependent PI 3-kinase activation was required for the increase in cyclin D1 mRNA levels and degradation of p27(Kip1). Together, the present study elucidates the role of cAMP and IGF-I in differentially activating PI 3-kinase as a mediator of multiple molecular events. These events converge in the regulation of cyclin D1 and p27(Kip1), leading to cAMP-dependent potentiation of IGF-I-dependent CDK activation and DNA synthesis.
authors.affiliation: Laboratory of Cell Regulation, Departments of Animal Sciences and Applied Biological Chemistry, Graduate School of Agriculture and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, Japan.
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Fukushima
authors.forename: Taku
authors.initials: T
authors.lastname: Nedachi
authors.forename: Hidenori
authors.initials: H
authors.lastname: Akizawa
authors.forename: Masakazu
authors.initials: M
authors.lastname: Akahori
authors.forename: Fumihiko
authors.initials: F
authors.lastname: Hakuno
authors.forename: Shin-Ichiro
authors.initials: S
authors.lastname: Takahashi
mesh_terms: D000818:Animals; D015152:Blotting, Northern; D002453:Cell Cycle / Q000187:drug effects; D002460:Cell Line; D000242:Cyclic AMP / Q000494:pharmacology*; D019938:Cyclin D1 / Q000235:genetics / Q000378:metabolism*; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000378:metabolism*; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D004261:DNA Replication / Q000187:drug effects; D004789:Enzyme Activation / Q000187:drug effects; D005786:Gene Expression Regulation / Q000187:drug effects; D015151:Immunoblotting; D047468:Immunoprecipitation; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats
chemical_list: D012333:RNA, Messenger; D019938:Cyclin D1; D050760:Cyclin-Dependent Kinase Inhibitor p27; D007334:Insulin-Like Growth Factor I; D000242:Cyclic AMP; D019869:Phosphatidylinositol 3-Kinases; D018844:Cyclin-Dependent Kinases