Protein Kinase A, Ca²⁺/Calmodulin-Dependent Kinase II, and Calcineurin Regulate the Intracellular Trafficking of Myopodin between the Z-Disc and the Nucleus of Cardiac Myocytes

Abstract

Spatial and temporal resolution of intracellular signaling can be achieved by compartmentalizing transduction units. Myopodin is a dual-compartment, actin-bundling protein that shuttles between the nucleus and the Z-disc of myocytes in a differentiation- and stress-dependent fashion. Importin α binding and nuclear import of myopodin are regulated by serine/threonine phosphorylation-dependent binding of myopodin to 14-3-3. Here we show that in the heart myopodin forms a Z-disc signaling complex with α-actinin, calcineurin, Ca²⁺/calmodulin-dependent kinase II (CaMKII), muscle-specific A-kinase anchoring protein, and myomegalin. Phosphorylation of myopodin by protein kinase A (PKA) or CaMKII mediates 14-3-3 binding and nuclear import in myoblasts. Dephosphorylation of myopodin by calcineurin abrogates 14-3-3β binding. Activation of PKA or inhibition of calcineurin in adult cardiac myocytes releases myopodin from the Z-disc and induces its nuclear import. The identification of myopodin as a direct target of PKA, CaMKII, and calcineurin defines a novel intracellular signaling pathway whereby changes in Z-disc dynamics may translate into compartmentalized signal transduction in the heart.

We thank Mary Donnelly, Celine Chiu, Eric Chan, Frank Graner, and Svetlana Ratner for excellent technical assistance, Hoon Young Choi for help with statistical analysis, and Stefan Hüttelmaier, University of Halle-Wittenberg, Halle, Germany, for advice on the phosphorylation assays. We also thank Norbert Frey, University of Heidelberg, Heidelberg, Germany, and Eric N. Olson, University of Texas, Southwestern Medical Center, Dallas, as well as Thomas R. Soderling and John D. Scott, The Vollum Institute, Oregon Health & Science University, Portland, for providing cDNA constructs.

This work was supported by National Institutes of Health grants DA18886, DK57683, and DK062472 to P.M. and HL73458 to A.D.S.