title: The involvement of the docking protein Gab1 in mitogenic signalling induced by EGF and HGF in rat hepatocytes.
abstract: Grb2-associated binder (Gab) family proteins are docking molecules that can interact with receptor tyrosine kinases (RTKs) and cytokine receptors and bind several downstream signalling proteins. Studies in several cell types have shown that Gab1 may have a role in signalling mediated by the two RTKs epidermal growth factor (EGF) receptor (EGFR) and Met, the receptor for hepatocyte growth factor (HGF), but the involvement of Gab1 in EGFR and Met signalling has not been directly compared in the same cell. We have studied mechanisms of activation and role in mitogenic signalling of Gab1 in response to EGF and HGF in cultured rat hepatocytes. Gab1, but not Gab2, was expressed in the hepatocytes and was phosphorylated upon stimulation with EGF or HGF. Depletion of Gab1, using siRNA, decreased the ERK and Akt activation, cyclin D1 expression, and DNA synthesis in response to both EGF and HGF. Studies of mechanisms of recruitment to the receptors showed that HGF induced co-precipitation of Gab1 and Met while EGF induced binding of Gab1 to Grb2 but not to EGFR. Gab1 activation in response to both EGF and HGF was dependent on PI3K. While EGF activated Gab1 and Shc equally, within the same concentration range, HGF very potently and almost exclusively activated Gab1, having only a minimal effect on Shc. Collectively, our results strongly suggest that although Gab1 interacts differently with EGFR and Met, it is involved in mitogenic signalling mediated by both these growth factor receptors in hepatocytes.
authors.affiliation: Department of Pharmacology, Institute of Clinical Medicine, University of Oslo and Oslo University Hospital, P.O. Box 1057, Blindern, 0316 Oslo, Norway. Electronic address: monica.aasrum@medisin.uio.no.
authors.forename: Monica
authors.initials: M
authors.lastname: Aasrum
authors.affiliation: Department of Pharmacology, Institute of Clinical Medicine, University of Oslo and Oslo University Hospital, P.O. Box 1057, Blindern, 0316 Oslo, Norway.
authors.forename: John
authors.initials: J
authors.lastname: Ødegård
authors.affiliation: Department of Pharmacology, Institute of Clinical Medicine, University of Oslo and Oslo University Hospital, P.O. Box 1057, Blindern, 0316 Oslo, Norway.
authors.forename: Dagny
authors.initials: D
authors.lastname: Sandnes
authors.affiliation: Department of Pharmacology, Institute of Clinical Medicine, University of Oslo and Oslo University Hospital, P.O. Box 1057, Blindern, 0316 Oslo, Norway.
authors.forename: Thoralf
authors.initials: T
authors.lastname: Christoffersen
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D019938:Cyclin D1 / Q000378:metabolism; D004247:DNA / Q000096:biosynthesis; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D017228:Hepatocyte Growth Factor / Q000494:pharmacology*; D022781:Hepatocytes / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D006801:Humans; D008297:Male; D051379:Mice; D008934:Mitogens / Q000494:pharmacology*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D055765:Shc Signaling Adaptor Proteins / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D013997:Time Factors
chemical_list: C490896:Gab1 protein, rat; D008934:Mitogens; D010750:Phosphoproteins; D055765:Shc Signaling Adaptor Proteins; D019938:Cyclin D1; D004815:Epidermal Growth Factor; D017228:Hepatocyte Growth Factor; D004247:DNA; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D048049:Extracellular Signal-Regulated MAP Kinases
keywords: EGF; EGFR; ERK; GAPDH; Gab1; Grb2; Grb2-associated binding protein 1; HGF; Hepatocytes; Met; PH; PI3K; PIP3; Proliferation; RTK; epidermal growth factor; epidermal growth factor receptor; extracellular-signal-regulated kinase; glyceraldehyde 3-phosphate dehydrogenase; growth factor receptor-bound protein 2; hepatocyte growth factor; phosphatidylinositol (3,4,5)-trisphosphate; phosphatidylinositol-3-kinase; pleckstrin homology; receptor tyrosine kinase