title: Insulin enhances growth hormone induction of the MEK/ERK signaling pathway.
abstract: Growth hormone (GH) plays an important role in growth and metabolism by signaling via at least three major pathways, including STATs, ERK1/2, and phosphatidylinositol 3-kinase/Akt. Physiological concentrations of insulin promote growth probably by modulating liver GH receptor (GHR) levels in vivo, but the possible effects of insulin on GH-induced post-GHR signaling have yet to be studied. We hypothesized that short-term insulin, similar to the fluctuations that occur following feeding, affects GH-induced post-GHR signaling. Our present studies suggest that, in rat H4IIE hepatoma cells, insulin (4 h or less) selectively enhanced GH-induced phosphorylation of MEK1/2 and ERK1/2, but not GH-induced activation of STAT5 and Akt. Although insulin pretreatment altered GH-induced formation of Shc.Grb2.SOS complex, it did not significantly affect GH-induced activation of other signaling intermediates upstream of MEK/ERK, including JAK2, Ras, and Raf-1. Immunofluorescent staining indicated that insulin pretreatment facilitated GH-induced cell membrane translocation of MEK1/2. Insulin pretreatment also increased the amount of MEK association with its scaffolding protein, KSR. In summary, short-term insulin treatment of cultured, liver-derived cells selectively sensitized GH-induced MEK/ERK phosphorylation independent of JAK2, Ras, and Raf-1, but likely resulted from increased cell membrane translocation of MEK1/2. These findings suggest that insulin may be necessary for sensitization of cells to GH-induced ERK1/2 activation and provides a potential cellular mechanism by which insulin promotes growth.
authors.affiliation: Department of Pathology, Division of Molecular and Cellular Pathology, University of Alabama at Birmingham, 35294, USA.
authors.forename: Jie
authors.initials: J
authors.lastname: Xu
authors.forename: Adam B
authors.initials: AB
authors.lastname: Keeton
authors.forename: John L
authors.initials: JL
authors.lastname: Franklin
authors.forename: Xin
authors.initials: X
authors.lastname: Li
authors.forename: Derwei Y
authors.initials: DY
authors.lastname: Venable
authors.forename: Stuart J
authors.initials: SJ
authors.lastname: Frank
authors.forename: Joseph L
authors.initials: JL
authors.lastname: Messina
mesh_terms: D000818:Animals; D001692:Biological Transport; D006528:Carcinoma, Hepatocellular / Q000378:metabolism; D002417:Cattle; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D003720:Densitometry; D005419:Flavonoids / Q000494:pharmacology; D013006:Growth Hormone / Q000378:metabolism*; D006160:Guanosine Triphosphate / Q000378:metabolism; D015151:Immunoblotting; D047468:Immunoprecipitation; D007328:Insulin / Q000378:metabolism*; D008099:Liver / Q000378:metabolism; D048369:MAP Kinase Kinase 1 / Q000378:metabolism; D048370:MAP Kinase Kinase 2 / Q000378:metabolism; D020935:MAP Kinase Signaling System; D008856:Microscopy, Fluorescence; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D010766:Phosphorylation; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism; D051381:Rats; D050799:STAT5 Transcription Factor / Q000378:metabolism; D015398:Signal Transduction; D013997:Time Factors; D014443:Tyrosine / Q000378:metabolism; D018631:ras Proteins / Q000378:metabolism
chemical_list: D005419:Flavonoids; D007328:Insulin; D050799:STAT5 Transcription Factor; D014443:Tyrosine; D006160:Guanosine Triphosphate; D013006:Growth Hormone; C482128:MAP2K2 protein, human; D019908:Proto-Oncogene Proteins c-raf; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D048369:MAP Kinase Kinase 1; D048370:MAP Kinase Kinase 2; C482125:MAP2K1 protein, human; D018631:ras Proteins; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one