Insulin induces swelling-dependent activation of the epidermal growth factor receptor in rat liver.
The aim of the study was to analyze whether the proliferative effects of insulin in rat liver involve cross-signaling toward the epidermal growth factor receptor (EGFR) and whether this is mediated by insulin-induced hepatocyte swelling. Studies were performed in the perfused rat liver and in primary rat hepatocytes. Insulin (35 nmol/liter) induced phosphorylation of the EGFR at position Tyr(845) and Tyr(1173), but not at Tyr(1045), suggesting that EGF is not involved in insulin-induced EGFR activation. Insulin-induced EGFR phosphorylation and subsequent ERK1/2 phosphorylation were sensitive to bumetanide, indicating an involvement of insulin-induced hepatocyte swelling. In line with this, hypoosmotic (225 mosmol/liter) hepatocyte swelling also induced EGFR and ERK1/2 activation. Insulin- and hypoosmolarity-induced EGFR activation were sensitive to inhibition by an integrin-antagonistic RGD peptide, an integrin beta1 subtype-blocking antibody, and the c-Src inhibitor PP-2, indicating the involvement of the recently described integrin-dependent osmosensing/signaling pathway (Schliess, F., Reissmann, R., Reinehr, R., vom Dahl, S., and Häussinger, D. (2004) J. Biol. Chem. 279, 21294-21301). As shown by immunoprecipitation studies, insulin and hypoosmolarity induced a rapid, RGD peptide-, integrin beta1-blocking antibody and PP-2-sensitive association of c-Src with the EGFR. As for control, insulin-induced insulin receptor substrate-1 phosphorylation remained unaffected by the RGD peptide, PP-2, or inhibition of the EGFR tyrosine kinase activity by AG1478. Both insulin and hypoosmolarity induced a significant increase in BrdU uptake in primary rat hepatocytes, which was sensitive to RGD peptide-, integrin beta1-blocking antibody, PP-2, AG1478, and PD098059. It is concluded that insulin- or hypoosmolarity-induced hepatocyte swelling triggers an integrin- and c-Src kinase-dependent EGFR activation, which may explain the proliferative effects of insulin.
Reinehr
Roland
R
Clinic for Gastroenterology, Hepatology, and Infectious Diseases, Heinrich-Heine-University Düsseldorf, D-40225 Düsseldorf, Germany.
Sommerfeld
Annika
A
Häussinger
Dieter
D
D000818:Animals; D000081247:CSK Tyrosine-Protein Kinase; D049108:Cell Enlargement / Q000187:drug effects; D049109:Cell Proliferation; D066246:ErbB Receptors / Q000378:metabolism*; D022781:Hepatocytes / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D006529:Hepatomegaly / Q000139:chemically induced / Q000209:etiology; D007328:Insulin / Q000494:pharmacology*; D016023:Integrins / Q000378:metabolism; D008099:Liver / Q000378:metabolism* / Q000473:pathology; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D009842:Oligopeptides / Q000494:pharmacology; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D051381:Rats; D019061:src-Family Kinases
D007328:Insulin; D016023:Integrins; D009842:Oligopeptides; C047981:arginyl-glycyl-aspartic acid; D066246:ErbB Receptors; D011505:Protein-Tyrosine Kinases; D000081247:CSK Tyrosine-Protein Kinase; D019061:src-Family Kinases; D048052:Mitogen-Activated Protein Kinase 3