Abstract 287: Identification of a Novel PKCα Isoform in Heart Transcriptome via RNA Deep Sequencing

Abstract

The Protein kinase C (PKC) family of Ca2+ and /or lipid-activated AGC kinases are important regulators of multiple cellular responses including cell growth and programmed cell death. Among these, PKCα is the predominant conventional PKC isoform in heart and has been implicated to have a major impact on cardiac function, hypertrophic response and heart failure. Earlier studies have revealed that the conserved AGC-C-terminal tail containing active site cleft is responsible for regulating AGC kinase activity. The phosphorylation events in AGC-C-terminal tail mediate the activity of kinase by regulating kinase maturation, translocation and substrate interaction. In a genome-wide RNA-Seq analysis in mouse heart, we have identified a novel isoform of PKCα-- due to the insertion of a novel exon in its C-terminal tail. This novel exon has a highly conserved sequence from mouse to human, suggesting a conserved role in PKCα regulation. Tissue analysis showed that this PKCα isoform with Novel Exon (PKCαNE) has enriched expression in heart and skeletal muscle, indicating the involvement of a muscle specific alternative splicing event. The insertion of this novel exon lies between the kinase C-Lobe Tether and Active Site Tether. Biochemistry study in cells showed that both PKCα and PKCαNE were activated and translocated from cytosol to membrane and nucleus in response to PMA. However, upon IGF-1 treatment, PKCαNE showed no activation and could not translocate to either membrane or nucleus in contrast to PKCα. To further explore the mechanism for PKCαNE activation, we have determined the phosphorylation events of this novel isoform. Interestingly, the PKCαNE showed a decreased phosphorylation level at the Turn Motif , which could directly impact its activation and maturation. In summary, we have identified a novel isoform of PKCα that is enriched in heart and skeletal muscle. The PKCαNE isoform has different activation profile and its biological significance in cell signaling in physiology and diseases remains to be further explored.