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?IV-Spectrin and CaMKII facilitate Kir6.2 regulation in pancreatic beta cells.

ABSTRACT: Identified over a dozen years ago in the brain and pancreatic islet, ?IV-spectrin is critical for the local organization of protein complexes throughout the nervous system. ?IV-Spectrin targets ion channels and adapter proteins to axon initial segments and nodes of Ranvier in neurons, and ?IV-spectrin dysfunction underlies ataxia and early death in mice. Despite advances in ?IV-spectrin research in the nervous system, its role in pancreatic islet biology is unknown. Here, we report that ?IV-spectrin serves as a multifunctional structural and signaling platform in the pancreatic islet. We report that ?IV-spectrin directly associates with and targets the calcium/calmodulin-dependent protein kinase II (CaMKII) in pancreatic islets. In parallel, ?IV-spectrin targets ankyrin-B and the ATP-sensitive potassium channel. Consistent with these findings, ?IV-spectrin mutant mice lacking CaMKII- or ankyrin-binding motifs display selective loss of expression and targeting of key protein components, including CaMKII?. ?IV-Spectrin-targeted CaMKII directly phosphorylates the inwardly-rectifying potassium channel, Kir6.2 (alpha subunit of KATP channel complex), and we identify the specific residue, Kir6.2 T224, responsible for CaMKII-dependent regulation of KATP channel function. CaMKII-dependent phosphorylation alters channel regulation resulting in KATP channel inhibition, a cellular phenotype consistent with aberrant insulin regulation. Finally, we demonstrate aberrant KATP channel phosphorylation in ?IV-spectrin mutant mice. In summary, our findings establish a broader role for ?IV-spectrin in regulation of cell membrane excitability in the pancreatic islet, define the pathway for CaMKII local control in pancreatic beta cells, and identify the mechanism for CaMKII-dependent regulation of KATP channels.

SUBMITTER: Kline CF

PROVIDER: S-EPMC3808601 | biostudies-literature | 2013 Oct

REPOSITORIES: biostudies-literature

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βIV-Spectrin and CaMKII facilitate Kir6.2 regulation in pancreatic beta cells.

Kline Crystal F CF Wright Patrick J PJ Koval Olha M OM Zmuda Erik J EJ Johnson Benjamin L BL Anderson Mark E ME Hai Tsonwin T Hund Thomas J TJ Mohler Peter J PJ

Proceedings of the National Academy of Sciences of the United States of America 20131007 43

Identified over a dozen years ago in the brain and pancreatic islet, βIV-spectrin is critical for the local organization of protein complexes throughout the nervous system. βIV-Spectrin targets ion channels and adapter proteins to axon initial segments and nodes of Ranvier in neurons, and βIV-spectrin dysfunction underlies ataxia and early death in mice. Despite advances in βIV-spectrin research in the nervous system, its role in pancreatic islet biology is unknown. Here, we report that βIV-spec ...[more]

PMID: 24101510

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Project description:Fibrosis is a pronounced feature of heart disease and the result of dysregulated activation of resident cardiac fibroblasts (CFs). Recent work identified stress-induced degradation of the cytoskeletal protein βIV-spectrin as an important step in CF activation and cardiac fibrosis. Furthermore, loss of βIV-spectrin was found to depend on Ca2+/calmodulin-dependent kinase II (CaMKII). Therefore, we sought to determine the mechanism for CaMKII-dependent regulation of βIV-spectrin and CF activity. Computational screening and MS revealed a critical serine residue (S2250 in mouse and S2254 in human) in βIV-spectrin phosphorylated by CaMKII. Disruption of βIV-spectrin/CaMKII interaction or alanine substitution of βIV-spectrin Ser2250 (βIV-S2254A) prevented CaMKII-induced degradation, whereas a phosphomimetic construct (βIV-spectrin with glutamic acid substitution at serine 2254 [βIV-S2254E]) showed accelerated degradation in the absence of CaMKII. To assess the physiological significance of this phosphorylation event, we expressed exogenous βIV-S2254A and βIV-S2254E constructs in βIV-spectrin-deficient CFs, which have increased proliferation and fibrotic gene expression compared with WT CFs. βIV-S2254A but not βIV-S2254E normalized CF proliferation, gene expression, and contractility. Pathophysiological targeting of βIV-spectrin phosphorylation and subsequent degradation was identified in CFs activated with the profibrotic ligand angiotensin II, resulting in increased proliferation and signal transducer and activation of transcription 3 nuclear accumulation. While therapeutic delivery of exogenous WT βIV-spectrin partially reversed these trends, βIV-S2254A completely negated increased CF proliferation and signal transducer and activation of transcription 3 translocation. Moreover, we observed βIV-spectrin phosphorylation and associated loss in total protein within human heart tissue following heart failure. Together, these data illustrate a considerable role for the βIV-spectrin/CaMKII interaction in activating profibrotic signaling.

Dataset Information

?IV-Spectrin and CaMKII facilitate Kir6.2 regulation in pancreatic beta cells.

Publications

βIV-Spectrin and CaMKII facilitate Kir6.2 regulation in pancreatic beta cells.

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