title: Osmotic regulation of insulin-induced mitogen-activated protein kinase phosphatase (MKP-1) expression in H4IIE rat hepatoma cells.
abstract: A contribution of intracellular dehydration to insulin resistance has been established in human subjects and in different experimental systems. Here the effect of hyperosmolarity (405 mosmol/l) on insulin-induced mitogen-activated protein (MAP) kinase phosphatase (MKP)-1 expression was studied in H4IIE rat hepatoma cells. Insulin induces robust MKP-1 expression which correlates with a vanadate-sensitive decay of extracellular-signal-regulated kinase (Erk-1/Erk-2) activity. Hyperosmolarity delays MKP-1 accumulation by insulin and this corresponds to impaired MKP-1 synthesis, whereas MKP-1 degradation remains unaffected by hyperosmolarity. Rapamycin, which inhibits signalling downstream from the mammalian target of rapamycin (mTOR) and a peptide inhibiting protein kinase C (PKC) zeta/lambda abolish insulin-induced MKP-1 protein but not mRNA expression, suggesting the involvement of the p70 ribosomal S6 protein kinase (p70S6-kinase) and/or the eukaryotic initiation factor 4E-binding proteins (4E-BPs) as well as atypical PKCs in MKP-1 translation. Hyperosmolarity induces sustained suppression of p70S6-kinase and 4E-BP1 hyperphosphorylation by insulin, whereas insulin-induced tyrosine phosphorylation of the insulin receptor (IR) beta subunit and the IR substrates IRS1 and IRS2, recruitment of the phosphoinositide 3-kinase (PI 3-kinase) regulatory subunit p85 to the receptor substrates as well as PI 3-kinase activation, and Ser-473 phosphorylation of protein kinase B and Thr-410/403 phosphorylation of PKC zeta/lambda are largely unaffected under hyperosmotic conditions. The hyperosmotic impairment of both, MKP-1 expression and p70S6-kinase hyperphosphorylation by insulin is insensitive to K(2)CrO(4), calyculin A and vanadate, and inhibition of the Erk-1/Erk-2 and p38 pathways. The suppression of MKP-1 may further contribute to insulin resistance under dehydrating conditions by allowing unbalanced MAP kinase activation.
authors.affiliation: Medizinische Einrichtungen der Heinrich-Heine Universität, Klinik für Gastroenterologie, Hepatologie und Infektiologie, Moorenstrasse 5, D-40225 Düsseldorf, Germany.
authors.forename: Mohammad Reza
authors.initials: MR
authors.lastname: Lornejad-Schäfer
authors.forename: Christine
authors.initials: C
authors.lastname: Schäfer
authors.forename: Dirk
authors.initials: D
authors.lastname: Graf
authors.forename: Dieter
authors.initials: D
authors.lastname: Häussinger
authors.forename: Freimut
authors.initials: F
authors.lastname: Schliess
mesh_terms: D000818:Animals; D006528:Carcinoma, Hepatocellular; D018797:Cell Cycle Proteins; D054638:Dual Specificity Phosphatase 1; D004790:Enzyme Induction / Q000187:drug effects; D015971:Gene Expression Regulation, Enzymologic; D015972:Gene Expression Regulation, Neoplastic / Q000502:physiology*; D017874:Immediate-Early Proteins / Q000096:biosynthesis / Q000235:genetics*; D007328:Insulin / Q000494:pharmacology*; D007700:Kinetics; D008113:Liver Neoplasms; D020935:MAP Kinase Signaling System; D009994:Osmolar Concentration; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; D017027:Protein Tyrosine Phosphatases / Q000096:biosynthesis / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured
chemical_list: D018797:Cell Cycle Proteins; D017874:Immediate-Early Proteins; D007328:Insulin; D012333:RNA, Messenger; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; C517019:DUSP1 protein, human; D054638:Dual Specificity Phosphatase 1; C517021:Dusp1 protein, rat; D017027:Protein Tyrosine Phosphatases