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-
spectrin serves as a multifunctional structural and signaling platform in the pancreatic islet. We report that βIV-
spectrin directly associates with and targets the
calcium/calmodulin-dependent protein kinase II (
CaMKII) in pancreatic islets. In parallel, βIV-
spectrin targets
ankyrin-B and the
ATP-sensitive potassium channel. Consistent with these findings, βIV-
spectrin mutant mice lacking
CaMKII- or
ankyrin-binding motifs display selective loss of expression and targeting of key
protein components, including CaMKIIδ. βIV-
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 βIV-
spectrin mutant mice. In summary, our findings establish a broader role for βIV-
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.