title: Akt increases sarcoplasmic reticulum Ca2+ cycling by direct phosphorylation of phospholamban at Thr17.
abstract: Cardiomyocytes adapt to physical stress by increasing their size while maintaining cell function. The serine/threonine kinase Akt plays a critical role in this process of adaptation. We previously reported that transgenic overexpression of an active form of Akt (Akt-E40K) in mice results in increased cardiac contractility and cell size, as well as improved sarcoplasmic reticulum (SR) Ca(2+) handling. Because it is not fully elucidated, we decided to study the molecular mechanism by which Akt-E40K overexpression improves SR Ca(2+) handling. To this end, SR Ca(2+) uptake and the phosphorylation status of phospholamban (PLN) were evaluated in heart extracts from wild-type and Akt-E40K mice and mice harboring inducible and cardiac specific knock-out of phosphatidylinositol-dependent kinase-1, the upstream activator of Akt. Moreover, the effect of Akt was assessed in vitro by overexpressing a mutant Akt targeted preferentially to the SR, and by biochemical assays to evaluate potential interaction with PLN. We found that when activated, Akt interacts with and phosphorylates PLN at Thr(17), the Ca(2+)-calmodulin-dependent kinase IIdelta site, whereas silencing Akt signaling, through the knock-out of phosphatidylinositol-dependent kinase-1, resulted in reduced phosphorylation of PLN at Thr(17). Furthermore, overexpression of SR-targeted Akt in cardiomyocytes improved Ca(2+) handling without affecting cell size. Thus, we describe here a new mechanism whereby the preferential translocation of Akt to the SR is responsible for enhancement of contractility without stimulation of hypertrophy.
authors.affiliation: Istituto di Ricovero e Cura a Carattere Scientifico Multimedica, Milan 20138, Italy; Istituto Tecnologie Biomediche, Consiglio Nazionale delle Ricerche, Segrate, Milan 20090, Italy; Division of Cardiology, Department of Medicine, University of California, San Diego, La Jolla, California 92093. Electronic address: daniele.catalucci@itb.cnr.it.
authors.forename: Daniele
authors.initials: D
authors.lastname: Catalucci
authors.affiliation: Istituto di Ricovero e Cura a Carattere Scientifico Multimedica, Milan 20138, Italy.
authors.forename: Michael V G
authors.initials: MVG
authors.lastname: Latronico
authors.affiliation: Istituto di Ricovero e Cura a Carattere Scientifico Multimedica, Milan 20138, Italy.
authors.forename: Marcello
authors.initials: M
authors.lastname: Ceci
authors.affiliation: Istituto di Ricovero e Cura a Carattere Scientifico Multimedica, Milan 20138, Italy; Istituto Tecnologie Biomediche, Consiglio Nazionale delle Ricerche, Segrate, Milan 20090, Italy.
authors.forename: Francesca
authors.initials: F
authors.lastname: Rusconi
authors.affiliation: Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada.
authors.forename: Howard S
authors.initials: HS
authors.lastname: Young
authors.affiliation: Istituto di Ricovero e Cura a Carattere Scientifico Multimedica, Milan 20138, Italy.
authors.forename: Paolo
authors.initials: P
authors.lastname: Gallo
authors.affiliation: Istituto di Ricovero e Cura a Carattere Scientifico Multimedica, Milan 20138, Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Santonastasi
authors.affiliation: Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111.
authors.forename: Alfonso
authors.initials: A
authors.lastname: Bellacosa
authors.affiliation: Department of Pharmacology, University of California, San Diego, La Jolla, California 92093.
authors.forename: Joan Heller
authors.initials: JH
authors.lastname: Brown
authors.affiliation: Istituto di Ricovero e Cura a Carattere Scientifico Multimedica, Milan 20138, Italy; Division of Cardiology, Department of Medicine, University of California, San Diego, La Jolla, California 92093; Istituto Tecnologie Biomediche, Consiglio Nazionale delle Ricerche, Segrate, Milan 20090, Italy. Electronic address: gcondorelli@ucsd.edu.
authors.forename: Gianluigi
authors.initials: G
authors.lastname: Condorelli
mesh_terms: D064413:3-Phosphoinositide-Dependent Protein Kinases; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2 / Q000235:genetics / Q000378:metabolism; D002478:Cells, Cultured; D051379:Mice; D008822:Mice, Transgenic; D032383:Myocytes, Cardiac / Q000166:cytology / Q000378:metabolism; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*; D013912:Threonine / Q000378:metabolism*; D000099211:Phospholamban
chemical_list: D064413:3-Phosphoinositide-Dependent Protein Kinases; D002118:Calcium; D002135:Calcium-Binding Proteins; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D013912:Threonine; D000099211:Phospholamban
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