title: Characterization of the intracellular signalling pathways that underlie growth-factor-stimulated glucose transport in Xenopus oocytes: evidence for ras- and rho-dependent pathways of phosphatidylinositol 3-kinase activation.
abstract: The stimulation of glucose transport is one of the early cellular responses to growth factors and is essential for cell proliferation, yet the molecular processes that underlie this response are poorly defined. The aim of this study was to characterize the role of the low-molecular-mass G-proteins, Ras and Rho, and their downstream targets, Raf protein kinase and phosphatidylinositol 3-kinase, in the regulation of glucose transport in Xenopus oocytes by two distinct growth-factor receptors: the insulin-like growth factor I (IGF-I) tyrosine kinase receptor and the heterotrimeric G-protein-coupled lysophosphatidic acid (LPA) receptor. Microinjection of a neutralizing anti-Ras antibody partially blocked IGF-I-stimulated deoxyglucose uptake but was without effect on LPA-stimulated deoxyglucose uptake. In contrast, microinjection of the C3 coenzyme of botulinum toxin, which selectively ADP-ribosylates and inactivates Rho, inhibited LPA-stimulated, but not IGF-I-stimulated, deoxyglucose uptake. Similarly, LPA- but not IGF-I-stimulated deoxyglucose uptake was attenuated in oocytes expressing a dominant negative rho construct. Cells expressing a dominant negative mutant of Raf protein kinase exhibited markedly reduced sensitivity to both LPA and IGF-I, consistent with a role for endogenous Raf in glucose uptake by both growth factors. Furthermore, expression of a constitutively activated form of raf-1 resulted in a growth-factor-independent increase in deoxyglucose uptake. Measurements of phosphatidylinositol 3-kinase activity in microinjected cells support the hypothesis that the IGF-I receptor stimulates glucose transport by a Ras-dependent activation of phosphatidylinositol 3-kinase, whereas the G-protein-coupled LPA receptor controls this response by a pathway that involves Rho-dependent activation of a distinct phosphatidylinositol 3-kinase. Thus we provide evidence for clear differences in the signalling pathways that control glucose transport by G-protein-coupled and tyrosine kinase growth-factor receptors. Furthermore this is the first demonstration that active Rho is involved in the signalling pathways that regulate glucose uptake in response to some growth factors.
authors.affiliation: Division of Biochemistry and Molecular Biology, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow G12 8QQ, Scotland, U.K.
authors.forename: F J
authors.initials: FJ
authors.lastname: Thomson
authors.forename: T J
authors.initials: TJ
authors.lastname: Jess
authors.forename: C
authors.initials: C
authors.lastname: Moyes
authors.forename: R
authors.initials: R
authors.lastname: Plevin
authors.forename: G W
authors.initials: GW
authors.lastname: Gould
mesh_terms: D000818:Animals; D001692:Biological Transport; D004789:Enzyme Activation; D005260:Female; D019204:GTP-Binding Proteins / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism*; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D008246:Lysophospholipids / Q000494:pharmacology*; D009865:Oocytes / Q000187:drug effects* / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D019908:Proto-Oncogene Proteins c-raf; D015398:Signal Transduction; D014982:Xenopus laevis
chemical_list: D019204:GTP-Binding Proteins; D005947:Glucose; D007334:Insulin-Like Growth Factor I; D008246:Lysophospholipids; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor); D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D019908:Proto-Oncogene Proteins c-raf