title: Calmodulin-mediated activation of Akt regulates survival of c-Myc-overexpressing mouse mammary carcinoma cells.
abstract: c-Myc-overexpressing mammary epithelial cells are proapoptotic; their survival is strongly promoted by epidermal growth factor (EGF). We now demonstrate that EGF-induced Akt activation and survival in transgenic mouse mammary tumor virus-c-Myc mouse mammary carcinoma cells are both calcium/calmodulin-dependent. Akt activation is abolished by the phospholipase C-gamma inhibitor U-73122, by the intracellular calcium chelator BAPTA-AM, and by the specific calmodulin antagonist W-7. These results implicate calcium/calmodulin in the activation of Akt in these cells. In addition, Akt activation by serum and insulin is also inhibited by W-7. EGF-induced and calcium/calmodulin-mediated Akt activation occurs in both tumorigenic and non-tumorigenic mouse and human mammary epithelial cells, independent of their overexpression of c-Myc. These results imply that calcium/calmodulin may be a common regulator of Akt activation, irrespective of upstream receptor activator, mammalian species, and transformation status in mammary epithelial cells. However, only c-Myc-overexpressing mouse mammary carcinoma cells (but not normal mouse mammary epithelial cells) undergo apoptosis in the presence of the calmodulin antagonist W-7, indicating the vital selective role of calmodulin for survival of these cells. Calcium/calmodulin-regulated Akt activation is mediated directly by neither calmodulin kinases nor phosphatidylinositol 3-kinase (PI-3 kinase). Pharmacological inhibitors of calmodulin kinase kinase and calmodulin kinases II and III do not inhibit EGF-induced Akt activation, and calmodulin antagonist W-7 does not inhibit phosphotyrosine-associated PI-3 kinase activation. Akt is, however, co-immunoprecipitated with calmodulin in an EGF-dependent manner, which is inhibited by calmodulin antagonist W-7. We conclude that calmodulin may serve a vital regulatory function to direct the localization of Akt to the plasma membrane for its activation by PI-3 kinase.
authors.affiliation: Lombardi Comprehensive Cancer Center, Georgetown University Medical Center, Washington, DC 20057, USA.
authors.forename: Tushar B
authors.initials: TB
authors.lastname: Deb
authors.forename: Christine M
authors.initials: CM
authors.lastname: Coticchia
authors.forename: Robert B
authors.initials: RB
authors.lastname: Dickson
mesh_terms: D000818:Animals; D017209:Apoptosis; D015153:Blotting, Western; D002147:Calmodulin / Q000378:metabolism*; D045744:Cell Line, Tumor; D002470:Cell Survival; D002614:Chelating Agents / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004533:Egtazic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004963:Estrenes / Q000494:pharmacology; D006801:Humans; D051379:Mice; D008822:Mice, Transgenic; D008954:Models, Biological; D009474:Neurons / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D051966:Phospholipase C gamma; D011233:Precipitin Tests; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D021381:Protein Transport; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D016271:Proto-Oncogene Proteins c-myc / Q000378:metabolism*; D011760:Pyrrolidinones / Q000494:pharmacology; D015398:Signal Transduction; D013449:Sulfonamides / Q000494:pharmacology; D013997:Time Factors; D010738:Type C Phospholipases / Q000494:pharmacology
chemical_list: D002147:Calmodulin; D002614:Chelating Agents; D004533:Egtazic Acid; D004791:Enzyme Inhibitors; D004963:Estrenes; D019869:Phosphatidylinositol 3-Kinases; D010726:Phosphodiesterase Inhibitors; D051966:Phospholipase C gamma; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D016271:Proto-Oncogene Proteins c-myc; D011760:Pyrrolidinones; D013449:Sulfonamides; D010738:Type C Phospholipases; C060229:1-(6-((3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; C017967:W 7; C494918:AKT1 protein, human