Lipid-independent activation of a muscle-specific PKCa splicing variant

Protein kinase C -a (PKCa) plays a major role in a diverse range of cellular processes. Studies to date have defined the regulatory controls and function of PKCa entirely based upon the previously annotated ubiquitously expressed prototypical isoform. From RNA-seq-based transcriptome analysis in murine heart, we identified a previously unannotated PKCa variant produced by alter-native RNA splicing. This PKCa transcript variant, which we named PKCa-novel exon (PKCa-NE), contains an extra exon between exon 16 and exon 17, and is specifically detected in adult mouse cardiac and skeletal muscle, but not other tissues; it is also detected in human hearts. This transcript variant yields a PKCa isoform with additional 16 amino acids inserted in its COOH-terminal variable region. Although the canonical PKCa enzyme is a lipid-dependent kinase, in vitro kinase assays show that PKCa-NE displays a high level of basal lipid-independent catalytic activity. Our unbiased proteomic analysis identified a specific interaction between PKCa-NE and eukaryotic elongation factor-1a (eEF1A1). Studies in cardiomyocytes link PKCa-NE expression to an increase in eEF1A1 phosphorylation and elevated protein synthesis. In summary, we have identified a previously uncharacterized muscle-specific PKCa splicing variant, PKCa-NE, with distinct biochemical properties that plays a unique role in the control of the protein synthesis machin-ery in cardiomyocytes. NEW & NOTEWORTHY PKCa is an important signaling molecule extensively studied in many cellular processes. However, no isoforms have been reported for PKCa except one prototypic isoform. Alternative mRNA splicing of Prkca gene was detected for the first time in rodent and human cardiac tissue, which can produce a previously unknown PKCa-novel exon (NE) isoform. The biochemistry and molecular effects of PKCa-NE are markedly different from PKCa wild type, suggesting potential functional di-versity of PKCa signaling in muscle.

Automated summary

Protein kinase C-alpha (PKCa) is a signaling molecule that plays a major role in various cellular processes. A previously unannotated PKCa variant, PKCa-novel exon (PKCa-NE), was identified through RNA-seq-based transcriptome analysis in mouse and human cardiac tissue. PKCa-NE has distinct biochemical properties and plays a unique role in regulating protein synthesis in cardiomyocytes.