Myospryn Is a Direct Transcriptional Target for MEF2A That Encodes a Striated Muscle, α-Actinin-interacting, Costamere-localized Protein

Abstract

The full repertoire of proteins that comprise the striated muscle Z-disc and peripheral structures, such as the costamere, have yet to be discovered. Recent studies suggest that this elaborate protein network, which acts as a structural and signaling center for striated muscle, harbors factors that function as mechanosensors to ensure coordinated contractile activity. Mutations in genes whose products reside in this region often result in skeletal and cardio myopathies, demonstrating the importance of this macromolecular complex in muscle structure and function. Here, we describe the characterization of a direct, downstream target gene for the MEF2A transcription factor encoding a large, muscle-specific protein that localizes to the costamere in striated muscle. This gene, called myospryn, was identified by microarray analysis as a transcript downregulated in MEF2A knock-out mice. MEF2A knock-out mice develop cardiac failure during the perinatal period with mutant hearts exhibiting several cardiac abnormalities including myofibrillar disarray. Myospryn is the mouse ortholog of a partial human cDNA of unknown function named cardiomyopathy-associated gene 5 (CMYA5). Myospryn is expressed as a single, large transcript of ϳ12 kilobases in adult heart and skeletal muscle with an open reading frame of 3739 amino acids. This protein, belonging to the tripartite motif superfamily of proteins, contains a B-box coiled-coil (BBC), two fibronectin type III (FN3) repeats, and SPRY domains and interacts with the sarcomeric Z-disc protein, ␣-actinin-2. Our findings demonstrate that myospryn functions directly downstream of MEF2A at the costamere in striated muscle potentially playing a role in myofibrillogenesis.

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

“…This is in accordance with the predominantly subsarcolemmal localization of myospryn (21). As myospryn has been reported to associate with costameres (23,24), the interaction of titin with myospryn could provide a link between the peripheral myofibrils and the costamere-like structures present at the M-band level (39). The nature of this interaction could be either structural or regulatory.…”

“…1C) (21). Myospryn is specifically expressed in striated muscle (21,22), where it has been suggested to associate with sarcoplasmic reticulum (SR) and costameres (23,24).…”

Deregulated Protein Kinase A Signaling and Myospryn Expression in Muscular Dystrophy

“…As depicted in Fig. 1B, immunostaining of adult wild type hind limb muscle detected myospryn along the myofiber periphery (see WT-myospryn, upper middle panel) as previously published by our group and others (28,31,32). In striking contrast, mdx muscle exhibited a discontinuous localization of myospryn at the myofiber periphery with extensive regions devoid of myospryn ( Fig.…”

“…For myospryn analysis in wild type and mdx muscle, extracts were separated by SDS-PAGE electrophoresis, electroblotted, and probed with anti-myospryn antibodies at 1:2,000 (28).…”

Myomaxin Is a Novel Transcriptional Target of MEF2A That Encodes a Xin-related α-Actinin-interacting Protein

“…We recently reported that the myospryn gene is directly regulated by MEF2A (16). myospryn encodes an ␣-actinin-and dysbindin-interacting protein localized to the peripheral Z-disc region of striated muscle known as the costamere (16,17).…”