title: RACK1, an insulin-like growth factor I (IGF-I) receptor-interacting protein, modulates IGF-I-dependent integrin signaling and promotes cell spreading and contact with extracellular matrix.
abstract: The insulin-like growth factor I (IGF-I) receptor (IGF-IR) is known to regulate a variety of cellular processes including cell proliferation, cell survival, cell differentiation, and cell transformation. IRS-1 and Shc, substrates of the IGF-IR, are known to mediate IGF-IR signaling pathways such as those of mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3K), which are believed to play important roles in some of the IGF-IR-dependent biological functions. We used the cytoplasmic domain of IGF-IR in a yeast two-hybrid interaction trap to identify IGF-IR-interacting molecules that may potentially mediate IGF-IR-regulated functions. We identified RACK1, a WD repeat family member and a Gbeta homologue, and demonstrated that RACK1 interacts with the IGF-IR but not with the closely related insulin receptor (IR). In several types of mammalian cells, RACK1 interacted with IGF-IR, protein kinase C, and beta1 integrin in response to IGF-I and phorbol 12-myristate 13-acetate stimulation. Whereas most of RACK1 resides in the cytoskeletal compartment of the cytoplasm, transformation of fibroblasts and epithelial cells by v-Src, oncogenic IR or oncogenic IGF-IR, but not by Ros or Ras, resulted in a significantly increased association of RACK1 with the membrane. We examined the role of RACK1 in IGF-IR-mediated functions by stably overexpressing RACK1 in NIH 3T3 cells that expressed an elevated level of IGF-IR. RACK1 overexpression resulted in reduced IGF-I-induced cell growth in both anchorage-dependent and anchorage-independent conditions. Overexpression of RACK1 also led to enhanced cell spreading, increased stress fibers, and increased focal adhesions, which were accompanied by increased tyrosine phosphorylation of focal adhesion kinase and paxillin. While IGF-I-induced activation of IRS-1, Shc, PI3K, and MAPK pathways was unaffected, IGF-I-inducible beta1 integrin-associated kinase activity and association of Crk with p130(CAS) were significantly inhibited by RACK1 overexpression. In RACK1-overexpressing cells, delayed cell cycle progression in G(1) or G(1)/S was correlated with retinoblastoma protein hypophophorylation, increased levels of p21(Cip1/WAF1) and p27(Kip1), and reduced IGF-I-inducible Cdk2 activity. Reduction of RACK1 protein expression by antisense oligonucleotides prevented cell spreading and suppressed IGF-I-dependent monolayer growth. Our data suggest that RACK1 is a novel IGF-IR signaling molecule that functions as a positive mediator of cell spreading and contact with extracellular matrix, possibly through a novel IGF-IR signaling pathway involving integrin and focal adhesion signaling molecules.
authors.affiliation: Department of Microbiology, Mount Sinai School of Medicine, New York, New York 10029, USA.
authors.forename: Ulrich
authors.initials: U
authors.lastname: Hermanto
authors.forename: Cong S
authors.initials: CS
authors.lastname: Zong
authors.forename: Weiqun
authors.initials: W
authors.lastname: Li
authors.forename: Lu-Hai
authors.initials: LH
authors.lastname: Wang
mesh_terms: D000818:Animals; D018797:Cell Cycle Proteins / Q000378:metabolism; D002455:Cell Division; D002460:Cell Line; D002461:Cell Line, Transformed; D048429:Cell Size / Q000187:drug effects; D002645:Chickens; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000378:metabolism; D003598:Cytoskeletal Proteins / Q000378:metabolism; D005109:Extracellular Matrix / Q000187:drug effects / Q000378:metabolism*; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; D022001:Focal Adhesions / Q000187:drug effects / Q000378:metabolism; D019204:GTP-Binding Proteins; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D019012:Integrin beta1 / Q000378:metabolism*; D051379:Mice; D009363:Neoplasm Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D009857:Oncogenes / Q000502:physiology; D051419:Paxillin; D010750:Phosphoproteins / Q000378:metabolism; D011485:Protein Binding / Q000187:drug effects; D011493:Protein Kinase C / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D017526:Receptor, IGF Type 1 / Q000378:metabolism*; D000075370:Receptors for Activated C Kinase; D011956:Receptors, Cell Surface; D015398:Signal Transduction / Q000187:drug effects*; D022502:Stress Fibers / Q000187:drug effects / Q000378:metabolism; D020798:Two-Hybrid System Techniques
chemical_list: C493956:CDKN1A protein, human; C493957:Cdkn1a protein, mouse; D018797:Cell Cycle Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D003598:Cytoskeletal Proteins; D019012:Integrin beta1; D009363:Neoplasm Proteins; C496061:PXN protein, human; D051419:Paxillin; D010750:Phosphoproteins; C496062:Pxn protein, mouse; C419368:RACK1 protein, human; D000075370:Receptors for Activated C Kinase; D011956:Receptors, Cell Surface; D007334:Insulin-Like Growth Factor I; D011505:Protein-Tyrosine Kinases; D017526:Receptor, IGF Type 1; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; C496050:PTK2 protein, human; C496051:Ptk2 protein, mouse; D011493:Protein Kinase C; D019204:GTP-Binding Proteins