Structure, expression, and properties of an atypical protein kinase C (PKC3) from Caenorhabditis elegans. PKC3 is required for the normal progression of embryogenesis and viability of the organism.

Little is known about differential expression, functions, regulation, and targeting of "atypical" protein kinase C (aPKC) isoenzymes in vivo. We have cloned and characterized a novel cDNA that encodes a Caenorhabditis elegans aPKC (PKC3) composed of 597 amino acids. In post-embryonic animals, a 647-base pair segment of promoter/enhancer DNA directs transcription of the 3.6-kilobase pair pkc-3 gene and coordinates accumulation of PKC3 protein in approximately 85 muscle, epithelial, and hypodermal cells. These cells are incorporated into tissues involved in feeding, digestion, excretion, and reproduction. Mammalian aPKCs promote mitogenesis and survival of cultured cells. In contrast, C. elegans PKC3 accumulates in non-dividing, terminally differentiated cells that will not undergo apoptosis. Thus, aPKCs may control cell functions that are independent of cell cycle progression and programmed cell death. PKC3 is also expressed during embryogenesis. Ablation of PKC3 function by microinjection of antisense RNA into oocytes yields disorganized, developmentally arrested embryos. Thus, PKC3 is essential for viability. PKC3 is enriched in particulate fractions of disrupted embryos and larvae. Immunofluorescence microscopy revealed that PKC3 accumulates near cortical actin cytoskeleton/plasma membrane at the apical surface of intestinal cells and in embryonic cells. A candidate anchoring/targeting protein, which binds PKC3 in vitro, has been identified.