Identification and mapping of protein kinase A binding sites in the costameric protein myospryn

Abstract

Recently we identified a novel target gene of MEF2A named myospryn that encodes a large, muscle-specific, costamere-restricted alpha-actinin binding protein. Myospryn belongs to the tripartite motif (TRIM) superfamily of proteins and was independently identified as a dysbindin-interacting protein. Dysbindin is associated with alpha-dystrobrevin, a component of the dystrophin-glycoprotein complex (DGC) in muscle. Apart from these initial findings little else is known regarding the potential function of myospryn in striated muscle. Here we reveal that myospryn is an anchoring protein for protein kinase A (PKA) (or AKAP) whose closest homolog is AKAP12, also known as gravin/AKAP250/SSeCKS. We demonstrate that myospryn co-localizes with RII alpha, a type II regulatory subunit of PKA, at the peripheral Z-disc/costameric region in striated muscle. Myospryn interacts with RII alpha and this scaffolding function has been evolutionarily conserved as the zebrafish ortholog also interacts with PKA. Moreover, myospryn serves as a substrate for PKA. These findings point to localized PKA signaling at the muscle costamere.

cAMP signaling in skeletal muscle adaptation: hypertrophy, metabolism, and regeneration

“…PKA catalyzes phosphorylation on serine and threonine residues in numerous proteins. In skeletal muscle, these include metabolic enzymes (213), ion channels (204,205), transcription factors (74), and structural proteins (187) (Fig. 2).…”

“…1B). The prominent AKAP isoforms expressed in skeletal muscle include AKAP15 (AKAP7) (78), AKAP-100/mAKAP (AKAP6) (159), Yotiao (AKAP9) (144), D-AKAP1 (AKAP1) (107) and D-AKAP2 (AKAP10) (29,106), and myospryn (CMYA5) (187), which localize PKA to sites of excitationcontraction coupling, the SR, the NMJ, mitochondria, the nucleus, and costameres, respectively (Table 3). Of the AKAPs listed above, only mAkap (161), D-Akap1 (Akap1) (174) and Fig.…”

A-kinase anchoring proteins: scaffolding proteins in the heart

“…ezrin (36), sphingosine kinase type 1-interacting protein (61,96), gravin (81), synemin (95), myospryn (92), troponin T (109), and the phosphoinositide 3-kinase p110␥ (90) have been shown to be expressed in cardiac tissues (Table 1). In this context, it is now clear that in the heart, AKAP-based transduction complexes play a crucial role in coordinating signaling pathways that control physiological functions such as Ca 2ϩ cycling, cardiac contractility, and action potential duration, as well as pathophysiological processes including arrhythmias, cardiomyocyte hypertrophy, heart failure, and the adaptive response to hypoxia.…”

Interactions with M-band Titin and Calpain 3 Link Myospryn (CMYA5) to Tibial and Limb-girdle Muscular Dystrophies

“…The nature of this interaction could be either structural or regulatory. Partial localization of the PKA RII subunits to the M-band level (26) suggests that the role of myospryn there could be related to its protein kinase A-anchoring protein function.…”

“…25). It binds the regulatory RII␣ subunit of PKA and functions as an protein kinase A-anchoring protein regulating the spatial specificity of cAMP-PKA signaling (26). A role in vesicular trafficking or protein sorting is implied by the interaction of myospryn with dysbindin-1, a subunit of BLOC-1 (biogenesis of lysosome-related organelles complex 1) (21), and evidence exists for myospryn participating in lysosomal biogenesis and positioning (24).…”