RACK1 is an insulin-like growth factor 1 (IGF-1) receptor-interacting protein that can regulate IGF-1-mediated Akt activation and protection from cell death.
The insulin receptor and insulin-like growth factor 1 receptor (IGF-1R), activated by their ligands, control metabolism, cell survival, and proliferation. Although the signaling pathways activated by these receptors are well characterized, regulation of their activity is poorly understood. To identify regulatory proteins we undertook a two-hybrid screen using the IGF-1R beta-chain as bait. This screen identified Receptor for Activated C Kinases (RACK1) as an IGF-1R-interacting protein. RACK1 also interacted with the IGF-1R in fibroblasts and MCF-7 cells and with endogenous insulin receptor in COS cells. Interaction with the IGF-1R did not require tyrosine kinase activity or receptor autophosphorylation but did require serine 1248 in the C terminus. Overexpression of RACK1 in either R+ fibroblasts or MCF-7 cells inhibited IGF-1-induced phosphorylation of Akt, whereas it enhanced phosphorylation of Erks and Jnks. Src, the p85 subunit of phosphatidylinositol 3-kinase, and SHP-2 were all associated with RACK1 in these cells. Interestingly, the proliferation of MCF-7 cells was enhanced by overexpression of RACK1, whereas IGF-1-mediated protection from etoposide killing was greatly reduced. Altogether the data indicate that RACK1 is an IGF-1R-interacting protein that can modulate receptor signaling and suggest that RACK1 has a particular role in regulating Akt activation and cell survival.
Kiely
Patrick A
PA
Cell Biology Laboratory, Department of Biochemistry and Bioscience Institute, National University of Ireland, Lee Maltings Cork, Ireland.
Sant
Anagha
A
O'Connor
Rosemary
R
D000409:Alanine / Q000737:chemistry; D000818:Animals; D015153:Blotting, Western; D019556:COS Cells; D016923:Cell Death; D002455:Cell Division; D002470:Cell Survival; D003001:Cloning, Molecular; D004789:Enzyme Activation; D005347:Fibroblasts / Q000378:metabolism; D019204:GTP-Binding Proteins; D006801:Humans; D009154:Mutation; D009363:Neoplasm Proteins / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation; D011233:Precipitin Tests; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases; D017434:Protein Structure, Tertiary; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D017526:Receptor, IGF Type 1 / Q000378:metabolism*; D000075370:Receptors for Activated C Kinase; D011956:Receptors, Cell Surface; D011994:Recombinant Proteins / Q000378:metabolism; D012694:Serine / Q000737:chemistry; D013997:Time Factors; D014162:Transfection; D014407:Tumor Cells, Cultured; D020798:Two-Hybrid System Techniques
D000409:Alanine; D019204:GTP-Binding Proteins; D009363:Neoplasm Proteins; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D017526:Receptor, IGF Type 1; D000075370:Receptors for Activated C Kinase; D011956:Receptors, Cell Surface; D011994:Recombinant Proteins; D012694:Serine; C419368:RACK1 protein, human; C494918:AKT1 protein, human