title: Localized calcineurin confers Ca2+-dependent inactivation on neuronal L-type Ca2+ channels.
abstract: Excitation-driven entry of Ca(2+) through L-type voltage-gated Ca(2+) channels controls gene expression in neurons and a variety of fundamental activities in other kinds of excitable cells. The probability of opening of Ca(V)1.2 L-type channels is subject to pronounced enhancement by cAMP-dependent protein kinase (PKA), which is scaffolded to Ca(V)1.2 channels by A-kinase anchoring proteins (AKAPs). Ca(V)1.2 channels also undergo negative autoregulation via Ca(2+)-dependent inactivation (CDI), which strongly limits Ca(2+) entry. An abundance of evidence indicates that CDI relies upon binding of Ca(2+)/calmodulin (CaM) to an isoleucine-glutamine motif in the carboxy tail of Ca(V)1.2 L-type channels, a molecular mechanism seemingly unrelated to phosphorylation-mediated channel enhancement. But our work reveals, in cultured hippocampal neurons and a heterologous expression system, that the Ca(2+)/CaM-activated phosphatase calcineurin (CaN) is scaffolded to Ca(V)1.2 channels by the neuronal anchoring protein AKAP79/150, and that overexpression of an AKAP79/150 mutant incapable of binding CaN (ΔPIX; CaN-binding PXIXIT motif deleted) impedes CDI. Interventions that suppress CaN activity-mutation in its catalytic site, antagonism with cyclosporine A or FK506, or intracellular perfusion with a peptide mimicking the sequence of the phosphatase's autoinhibitory domain-interfere with normal CDI. In cultured hippocampal neurons from a ΔPIX knock-in mouse, CDI is absent. Results of experiments with the adenylyl cyclase stimulator forskolin and with the PKA inhibitor PKI suggest that Ca(2+)/CaM-activated CaN promotes CDI by reversing channel enhancement effectuated by kinases such as PKA. Hence, our investigation of AKAP79/150-anchored CaN reconciles the CaM-based model of CDI with an earlier, seemingly contradictory model based on dephosphorylation signaling.
authors.affiliation: Department of Pharmacology, University of Colorado School of Medicine, Aurora, Colorado 80045, USA.
authors.forename: Seth F
authors.initials: SF
authors.lastname: Oliveria
authors.forename: Philip J
authors.initials: PJ
authors.lastname: Dittmer
authors.forename: Dong-ho
authors.initials: DH
authors.lastname: Youn
authors.forename: Mark L
authors.initials: ML
authors.lastname: Dell'Acqua
authors.forename: William A
authors.initials: WA
authors.lastname: Sather
mesh_terms: D054758:A Kinase Anchor Proteins / Q000235:genetics / Q000378:metabolism; D000818:Animals; D030801:Animals, Genetically Modified; D001464:Barium / Q000494:pharmacology; D019703:Calcineurin / Q000502:physiology*; D002118:Calcium / Q000502:physiology*; D020746:Calcium Channels, L-Type / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D020013:Calcium Signaling / Q000502:physiology*; D002147:Calmodulin / Q000378:metabolism; D002478:Cells, Cultured; D017868:Cyclic AMP-Dependent Protein Kinases / Q000502:physiology; D031541:Fluorescence Resonance Energy Transfer; D005470:Fluorometry; D006624:Hippocampus / Q000166:cytology / Q000502:physiology; D051379:Mice; D009474:Neurons / Q000502:physiology*; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D018408:Patch-Clamp Techniques; D017966:Pyramidal Cells / Q000502:physiology; D014162:Transfection
chemical_list: D054758:A Kinase Anchor Proteins; C520665:Akap5 protein, mouse; C513988:Akap8 protein, mouse; C514350:CACNA1C protein, mouse; D020746:Calcium Channels, L-Type; D002147:Calmodulin; D009687:Nuclear Proteins; D001464:Barium; D017868:Cyclic AMP-Dependent Protein Kinases; D019703:Calcineurin; D002118:Calcium