Structure and expression of the Caenorhabditis elegans protein kinase C2 gene. Origins and regulated expression of a family of Ca²⁺ -activated protein kinase C isoforms

The molecular and cellular basis for concerted Ca²⁺/lipid signaling in Caenorhabditis elegans was investigated. A unique gene (pkc-2) and cognate cDNAs that encode six Ca²⁺/diacylglycerol-stimulated PKC2 isoenzymes were characterized. PKC2 polypeptides (680-717 amino acid residues) share identical catalytic, Ca²⁺ binding, diacylglycerol-activation and pseudosubstrate domains. However, sequences of the N- and C-terminal regions of the kinases diverge. PKC2 diversity is partly due to differential activation of transcription by distinct promoters. Each promoter precedes an adjacent exon that encodes 5'-untranslated RNA, an initiator AUG codon and a unique open reading frame. PKC2 mRNAs also incorporate one of two 3'- terminal exons via alternative splicing. Cells that are capable of receiving and propagating signals carried by Ca²⁺/diacylglyceroI were identified by assessing activities of pkc-2 gene promoters in transgenie C. elegans and visualizing the distribution of PKC2 polypeptides via immunofluorescence. Highly-selective expression of certain PKC2 isoforms was observed in distinct subsets of neurons, intestinal and muscle cells. A low level of PKC2 isoforms is observed in embryos. When L1 larvae hatch and interact with the external environment PKC2 content increases 10-fold. Although 77- and 78-kDa PKC2 isoforms are evident throughout post-embryonic development, an 81-kDa isoform appears to be adapted for function in L1 and L2 larvae.