title: RACK1 regulates G1/S progression by suppressing Src kinase activity.
abstract: Cancer genes exert their greatest influence on the cell cycle by targeting regulators of a critical checkpoint in late G(1). Once cells pass this checkpoint, they are fated to replicate DNA and divide. Cancer cells subvert controls at work at this restriction point and remain in cycle. Previously, we showed that RACK1 inhibits the oncogenic Src tyrosine kinase and NIH 3T3 cell growth. RACK1 inhibits cell growth, in part, by prolonging G(0)/G(1). Here we show that RACK1 overexpression induces a partial G(1) arrest by suppressing Src activity at the G(1) checkpoint. RACK1 works through Src to inhibit Vav2, Rho GTPases, Stat3, and Myc. Consequently, cyclin D1 and cyclin-dependent kinases 4 and 2 (CDK4 and CDK2, respectively) are suppressed, CDK inhibitor p27 and retinoblastoma protein are activated, E2F1 is sequestered, and G(1)/S progression is delayed. Conversely, downregulation of RACK1 by short interference RNA activates Src-mediated signaling, induces Myc and cyclin D1, and accelerates G(1)/S progression. RACK1 suppresses Src- but not mitogen-activated protein kinase-dependent platelet-derived growth factor signaling. We also show that Stat3 is required for Rac1 induction of Myc. Our results reveal a novel mechanism of cell cycle control in late G(1) that works via an endogenous inhibitor of the Src kinase.
authors.affiliation: Stanford University School of Medicine, 300 Pasteur Drive, Stanford, CA 94305-5187, USA.
authors.forename: Vidya
authors.initials: V
authors.lastname: Mamidipudi
authors.forename: Jian
authors.initials: J
authors.lastname: Zhang
authors.forename: Kelly C
authors.initials: KC
authors.lastname: Lee
authors.forename: Christine A
authors.initials: CA
authors.lastname: Cartwright
mesh_terms: D000818:Animals; D042846:CDC2-CDC28 Kinases / Q000378:metabolism; D002453:Cell Cycle; D002455:Cell Division; D019938:Cyclin D1 / Q000378:metabolism; D051357:Cyclin-Dependent Kinase 2; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D005434:Flow Cytometry; D016193:G1 Phase; D019204:GTP-Binding Proteins; D017930:Genes, Reporter; D006801:Humans; D015151:Immunoblotting; D051379:Mice; D008840:Microfilament Proteins / Q000378:metabolism; D008856:Microscopy, Fluorescence; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D008954:Models, Biological; D009124:Muscle Proteins; D041681:NIH 3T3 Cells; D009363:Neoplasm Proteins / Q000502:physiology*; D009369:Neoplasms / Q000378:metabolism; D015513:Oncogene Proteins / Q000378:metabolism; D010957:Plasmids / Q000378:metabolism; D011518:Proto-Oncogene Proteins; D016271:Proto-Oncogene Proteins c-myc / Q000378:metabolism; D051567:Proto-Oncogene Proteins c-vav; D000075370:Receptors for Activated C Kinase; D011956:Receptors, Cell Surface; D016160:Retinoblastoma Protein / Q000378:metabolism; D016196:S Phase; D015398:Signal Transduction; D014162:Transfection; D019061:src-Family Kinases / Q000378:metabolism*
chemical_list: D008840:Microfilament Proteins; D009124:Muscle Proteins; D009363:Neoplasm Proteins; D015513:Oncogene Proteins; D011518:Proto-Oncogene Proteins; D016271:Proto-Oncogene Proteins c-myc; D051567:Proto-Oncogene Proteins c-vav; C419368:RACK1 protein, human; D000075370:Receptors for Activated C Kinase; D011956:Receptors, Cell Surface; D016160:Retinoblastoma Protein; C058992:Tagln protein, mouse; C093651:VAV2 protein, human; C490565:Vav2 protein, mouse; D019938:Cyclin D1; D019061:src-Family Kinases; D042846:CDC2-CDC28 Kinases; C495894:CDK2 protein, human; C495900:CDK4 protein, human; C495893:Cdk2 protein, mouse; C495902:Cdk4 protein, mouse; D051357:Cyclin-Dependent Kinase 2; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases; D020928:Mitogen-Activated Protein Kinases; D019204:GTP-Binding Proteins