A novel leucine zipper targets AKAP15 and cyclic AMP-dependent protein kinase to the C terminus of the skeletal muscle Ca2+ channel and modulates its function.

Todd Scheuer,Stephen D. Hauschka,William A. Catterall,Misol Ahn,Joanne T. Hulme

doi:10.1074/jbc.m109814200

Abstract

In skeletal muscle, voltage-dependent potentiation of L-type Ca(2+) channel (Ca(V)1.1) activity requires phosphorylation by cyclic AMP-dependent protein kinase (PKA) anchored via an A kinase-anchoring protein (AKAP15). However, the mechanism by which AKAP15 targets PKA to L-type Ca(2+) channels has not been elucidated. Here we report that AKAP15 directly interacts with the C-terminal domain of the alpha(1) subunit of Ca(V)1.1 via a leucine zipper (LZ) motif. Disruption of the LZ interaction effectively inhibits voltage-dependent potentiation of L-type Ca(2+) channels in skeletal muscle cells. Our results reveal a novel mechanism whereby anchoring of PKA to Ca(2+) channels via LZ interactions ensures rapid and efficient phosphorylation of Ca(2+) channels in response to local signals such as cAMP and depolarization.

Highlights

The importance of protein kinase (PKA) anchoring through the association with AKAPs has recently been established in the regulation of L-type Ca2ϩ channels
We show that disruption of the leucine zipper (LZ) interaction between AKAP15 and the C-terminal domain of CaV1.1 effectively inhibits voltage-dependent potentiation of L-type Ca2ϩ channel activity in skeletal muscle cells
AKAP15 Directly Interacts with the C-terminal Domain of CaV1.1—Previous work has shown that AKAP15 co-immunoprecipitates and co-localizes with the skeletal muscle L-type Ca2ϩ channel in transverse tubule membranes [12, 16]

Summary

Channel and Modulates Its Function*

Trains of high frequency depolarizing stimuli that mimic action potentials or single long depolarizing pulses greatly increase the activity of these Ca2ϩ channels [4, 5] This “potentiation” of Ca2ϩ channel activity is strongly voltage-dependent and, in skeletal muscle, requires phosphorylation by PKA1 [4]. We show that disruption of the LZ interaction between AKAP15 and the C-terminal domain of CaV1.1 effectively inhibits voltage-dependent potentiation of L-type Ca2ϩ channel activity in skeletal muscle cells. Our results reveal a novel mechanism whereby anchoring of PKA to L-type Ca2ϩ channels via an LZ interaction ensures rapid and efficient phosphorylation of Ca2ϩ channels in response to local signals such as cAMP and depolarization. Of Pharmacology, Box 357280, University of Washington, Seattle, WA 981957280. Tel.: 206-543-1925; Fax: 206-543-3882, E-mail: wcatt@u. washington.edu

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION