title: Ca(2+)/calmodulin directly interacts with the pleckstrin homology domain of AKT1.
abstract: AKT kinase, also known as protein kinase B, is a key regulator of cell growth, proliferation, and metabolism. The activation of the AKT signaling pathway is one of the most frequent molecular alterations in a wide variety of human cancers. Dickson and coworkers recently observed that Ca(2+).calmodulin (Ca(2+).CaM) may be a common regulator of AKT1 activation (Deb, T. B., Coticchia, C. M., and Dickson, R. B. (2004) J. Biol. Chem. 279, 38903-38911). In our efforts to scan the mRNA-displayed proteome libraries for Ca(2+).CaM-binding proteins, we found that both human and Caenorhabditis elegans AKT1 kinases bound to CaM in a Ca(2+)-dependent manner (Shen, X., Valencia, C. A., Szostak, J., Dong, B., and Liu, R. (2005) Proc. Natl. Acad. Sci. U. S. A. 102, 5969-5974 and Shen, X., Valencia, C. A., Gao, W., Cotten, S. W., Dong, B., Chen, M., and Liu, R. (2007) submitted for publication). Here we demonstrate that Ca(2+).CaM and human AKT1 were efficiently co-immunoprecipitated, and their interaction was direct rather than mediated by other proteins. The binding is in part attributed to the first 42 residues of the pleckstrin homology (PH) domain, a region that is critical for the recognition of its lipid ligands. The PH domain of human AKT1 can disrupt the complex of the full-length AKT1 with Ca(2+).CaM. In addition, Ca(2+).CaM competes with phosphatidylinositol 3,4,5-trisphophate for interaction with the PH domain of human AKT1. Our findings suggest that Ca(2+).CaM is directly involved in regulating the functions of AKT1, presumably by releasing the activated AKT1 from the plasma membrane and/or prohibiting it from re-association with phosphoinositides on plasma membrane.
authors.affiliation: School of Pharmacy and Carolina Center for Genome Sciences, University of North Carolina, Chapel Hill, North Carolina 27599, USA.
authors.forename: Biao
authors.initials: B
authors.lastname: Dong
authors.forename: C Alexander
authors.initials: CA
authors.lastname: Valencia
authors.forename: Rihe
authors.initials: R
authors.lastname: Liu
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001667:Binding, Competitive; D001798:Blood Proteins / Q000737:chemistry*; D017173:Caenorhabditis elegans; D002118:Calcium / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D049109:Cell Proliferation; D006367:HeLa Cells; D006801:Humans; D008969:Molecular Sequence Data; D010750:Phosphoproteins / Q000737:chemistry*; D011485:Protein Binding; D051057:Proto-Oncogene Proteins c-akt / Q000737:chemistry* / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
chemical_list: D001798:Blood Proteins; D002147:Calmodulin; D010750:Phosphoproteins; C039077:platelet protein P47; C494918:AKT1 protein, human; D051057:Proto-Oncogene Proteins c-akt; D002118:Calcium