RACK1-mediated integration of adhesion and insulin-like growth factor I (IGF-I) signaling and cell migration are defective in cells expressing an IGF-I receptor mutated at tyrosines 1250 and 1251.
The scaffolding protein receptor for activated C kinase (RACK1) has been proposed to mediate the integration of insulin-like growth factor I receptor (IGF-IR) and adhesion signaling. Here we investigated the mechanism of this integration of signaling, by using an IGF-IR mutant (Y1250F/Y1251F) that is deficient in anti-apoptotic and transforming function. RACK1 was found to associate with the IGF-IR only in adherent cells and did not associate with the IGF-IR in nonadherent cells, lymphocytic cells, or cells expressing the Y1250F/Y1251F mutant. In R- cells transiently expressing the Y1250F/Y1251F mutant RACK1 became constitutively associated with beta1 integrin and did not associate with Shc, Src, or Shp2. This was accompanied by the loss of formation of a complex containing the IGF-IR, RACK1, and beta1 integrin; loss of migratory capacity; enhanced Src and FAK activity; enhanced Akt phosphorylation; and decreased p38 mitogen-activated protein kinase activity. Shc was not phosphorylated in response to IGF-I in cells expressing the Y1250F/Y1251F mutant and remained associated with protein phosphatase 2A. Similar alterations in signaling were observed in cells that were stimulated with IGF-I in nonadherent cultures. Our data suggest that disruption of RACK1 scaffolding function in cells expressing the Y1250F/Y1251F mutant results in the loss of adhesion signals that are necessary to regulate Akt activity and to promote turnover of focal adhesions and cell migration.
Kiely
Patrick A
PA
Cell Biology Laboratory, Department of Biochemistry, BioSciences Institute, National University of Ireland, Cork, Ireland.
Leahy
Madeline
M
O'Gorman
Denise
D
O'Connor
Rosemary
R
D000818:Animals; D015153:Blotting, Western; D002448:Cell Adhesion; D002460:Cell Line; D045744:Cell Line, Tumor; D002465:Cell Movement; D005353:Fibronectins / Q000378:metabolism; D019204:GTP-Binding Proteins; D006801:Humans; D047468:Immunoprecipitation; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D019012:Integrin beta1 / Q000378:metabolism; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D051379:Mice; D008954:Models, Biological; D009154:Mutation; D009363:Neoplasm Proteins / Q000378:metabolism*; D010749:Phosphoprotein Phosphatases / Q000737:chemistry / Q000378:metabolism; D010766:Phosphorylation; D011485:Protein Binding; D054648:Protein Phosphatase 2; D000075370:Receptors for Activated C Kinase; D011956:Receptors, Cell Surface; D011994:Recombinant Proteins / Q000737:chemistry; D015398:Signal Transduction; D013997:Time Factors; D014443:Tyrosine / Q000737:chemistry*; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
D005353:Fibronectins; D019012:Integrin beta1; D009363:Neoplasm Proteins; C419368:RACK1 protein, human; D000075370:Receptors for Activated C Kinase; D011956:Receptors, Cell Surface; D011994:Recombinant Proteins; D014443:Tyrosine; D007334:Insulin-Like Growth Factor I; D048031:JNK Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2; D019204:GTP-Binding Proteins