The catalytic domain limits the translocation of protein kinase C alpha in response to increases in Ca2+ and diacylglycerol.

Translocation of protein kinase C (PKC) alpha, beta II, delta and epsilon fused to enhanced green fluorescent protein (EGFP) was studied in living neuroblastoma cells by confocal microscopy. Exposure to carbachol elicited transient translocation of PKC alpha-EGFP and beta II-EGFP in most of the cells, PKC delta-EGFP in a few cells and induced sustained translocation of PKC epsilon-EGFP. To monitor levels of Ca(2+) and diacylglycerol and the translocation of PKC in the same cell, the Ca(2+)-sensitive C2 domain, diacylglycerol-sensitive C1 domains and full-length PKC were fused to red, cyan and yellow fluorescent proteins respectively. PKC alpha was translocated a few seconds after the C2 domain, which represents an increase in Ca(2+). This delay was insensitive to removal of the pseudosubstrate in PKC alpha, but the isolated regulatory domain translocated simultaneously with the C2 domain. Translocation of PKC epsilon coincided with the increase in diacylglycerol. Ionomycin induced translocation of PKC alpha and the C2 domain, whereas 1,2-dioctanoylglycerol caused translocation of the C1 domains and PKC epsilon, but not PKC alpha. Experiments with individual C1 domains showed that treatment with carbachol or phorbol 12,13-dibutyrate elicited translocation of PKC alpha C1a, PKC epsilon C1a and PKC epsilon C1b, whereas PKC alpha C1b was largely insensitive to these agents. In contrast with full-length PKC alpha, the regulatory domain of PKC alpha and pseudosubstrate-devoid PKC alpha responded to the carbachol-stimulated increase in diacylglycerol.