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

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 110; no. 43; pp. 17576 - 17581
• Main Authors: Kline, Crystal F., Wright, Patrick J., Koval, Olha M., Zmuda, Erik J., Johnson, Benjamin L., Anderson, Mark E., Hai, Tsonwin, Hund, Thomas J., Mohler, Peter J.
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 22.10.2013; NATIONAL ACADEMY OF SCIENCES; National Acad Sciences
• Subjects: Animals; Ankyrins; Ankyrins - metabolism; Beta cells; Binding Sites - genetics; Biological Sciences; Calcium-Calmodulin-Dependent Protein Kinase Type 2 - genetics; Calcium-Calmodulin-Dependent Protein Kinase Type 2 - metabolism; Cells, Cultured; Cercopithecus aethiops; COS Cells; Diabetes; Gene expression regulation; Immunoblotting; Immunohistochemistry; Insulin; Insulin-Secreting Cells - metabolism; Islets of Langerhans; Male; Membrane Potentials - genetics; Membrane Potentials - physiology; Mice, Inbred C57BL; Mice, Knockout; Microscopy, Confocal; Mutation; Pancreas; Phosphorylation; Physiological regulation; Potassium Channels, Inwardly Rectifying - genetics; Potassium Channels, Inwardly Rectifying - metabolism; Potassium Channels, Inwardly Rectifying - physiology; Protein Binding; Proteins; Spectrin - genetics; Spectrin - metabolism; local regulation; trafficking
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1314195110

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