title: Feedback regulation of mitogen-activated protein kinase kinase kinase activity of c-Raf-1 by insulin and phorbol ester stimulation.
abstract: Recently, it has been reported that Raf-1 kinase (Raf-1) has mitogen-activated protein kinase kinase kinase (MAPKKK) activity in various cells, although Raf-1 and MAP kinase kinase (MAPKK) can be phosphorylated by MAP kinase (MAPK) in vitro. Here we show that the maximal hyperphosphorylation of Raf-1 and MAPKK (10 min) was substantially achieved after the maximal activation of MAPKKK of Raf-1, MAPKK (2-5 min), and MAPK in Chinese hamster ovary cells overexpressing human insulin receptor (CHO-HIR cells) treated with insulin or 12-O-tetradecanoylphorbol-13-acetate (TPA). Moreover, we show that overexpression of MAPK in CHO-HIR cells resulted in enhanced hyperphosphorylation of Raf-1, MAPKK, and mammalian homolog of son of sevenless (mSos) after insulin or TPA stimulation as compared with parental cells. Furthermore, the maximal hyperphosphorylation of Raf-1 appears to be accompanied by a significant decrease in MAPKKK activity. These results suggest that 1) signals initiated by insulin and TPA converge on Raf-1 and activate its MAPKKK activity and 2) Raf-1, MAPKK, and mSos not only lie upstream of MAPK but also are phosphorylated by MAPK, directly or indirectly, and at least Raf-1 kinase activity might be down-regulated by this feedback mechanism.
authors.affiliation: Third Department of Internal Medicine, Faculty of Medicine, University of Tokyo, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Ueki
authors.forename: S
authors.initials: S
authors.lastname: Matsuda
authors.forename: K
authors.initials: K
authors.lastname: Tobe
authors.forename: Y
authors.initials: Y
authors.lastname: Gotoh
authors.forename: H
authors.initials: H
authors.lastname: Tamemoto
authors.forename: M
authors.initials: M
authors.lastname: Yachi
authors.forename: Y
authors.initials: Y
authors.lastname: Akanuma
authors.forename: Y
authors.initials: Y
authors.lastname: Yazaki
authors.forename: E
authors.initials: E
authors.lastname: Nishida
authors.forename: T
authors.initials: T
authors.lastname: Kadowaki
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D016466:CHO Cells; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D006224:Cricetinae; D017931:DNA Primers; D005246:Feedback; D006801:Humans; D007328:Insulin / Q000494:pharmacology*; D020930:MAP Kinase Kinase Kinases; D020929:Mitogen-Activated Protein Kinase Kinases; D008969:Molecular Sequence Data; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D019908:Proto-Oncogene Proteins c-raf; D011972:Receptor, Insulin / Q000096:biosynthesis / Q000187:drug effects / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000378:metabolism; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D014162:Transfection
chemical_list: D017931:DNA Primers; D007328:Insulin; D011518:Proto-Oncogene Proteins; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins; D011494:Protein Kinases; D011972:Receptor, Insulin; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D020930:MAP Kinase Kinase Kinases; D020929:Mitogen-Activated Protein Kinase Kinases; D013755:Tetradecanoylphorbol Acetate