Journal Article

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

Johnson, Benjamin L., Anderson, Mark E., Kline, Crystal F., Hai, Tsonwin, Wright, Patrick J., Zmuda, Erik J., Hund, Thomas J., Mohler, Peter J., Koval, Olha M.

2013

Overview

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.

• Publisher: National Academy of Sciences,NATIONAL ACADEMY OF SCIENCES,National Acad Sciences
• Subject: adenosine triphosphate / Animals / Ankyrins / Ankyrins - metabolism / ataxia (disorder) / Beta cells / Binding Sites - genetics / Biological Sciences / brain / Calcium-Calmodulin-Dependent Protein Kinase Type 2 - genetics / Calcium-Calmodulin-Dependent Protein Kinase Type 2 - metabolism / cell membranes / Cells, Cultured / Cercopithecus aethiops / COS Cells / death / Diabetes / Gene expression regulation / Immunoblotting / Immunohistochemistry / Insulin / Insulin-Secreting Cells - metabolism / Islets of Langerhans / Male / Membrane Potentials - genetics / Membrane Potentials - physiology / mice / Mice, Inbred C57BL / Mice, Knockout / Microscopy, Confocal / mutants / Mutation / neurons / Pancreas / phenotype / Phosphorylation / Physiological regulation / potassium channels / Potassium Channels, Inwardly Rectifying - genetics / Potassium Channels, Inwardly Rectifying - metabolism / Potassium Channels, Inwardly Rectifying - physiology / Protein Binding / Proteins / Spectrin - genetics / Spectrin - metabolism