Differential expression of protein kinase C isoforms in the human placenta

The extensive role played by protein kinase C (PKC) in signal transduction prompted this study of the expression and localization of PKC isoforms in human placental syncytiotrophoblast. Membranes prepared from these cells and samples of villous tissue were analysed by immunoblotting and immunocytochemistry using isoform-specific antibodies. PKC beta 2, gamma, epsilon and zeta were found to be present in both microvillous and basal membranes from term placenta. The alpha isoform was observed only on the basal membrane while the beta 1 isoform was confined to the microvillous membrane. The basal microvillous ratios for beta 2, gamma, epsilon and zeta ranged between 0.3 and 0.5, demonstrating a substantial asymmetry in plasma membrane localization. Immunocytochemistry supported the isoform identification and localization observed in the immunoblotting experiments. Moreover the cellular distribution showed that the majority of syncytical PKC was bound to the plasma membranes, in contrast to the other villous cell types. Immunoblotting experiments demonstrated significant increases in PKC beta 2 and epsilon on the microvillous membrane and PKC gamma and epsilon on the basal membrane between 16 and 40 of weeks gestation. This is the first detailed mapping of PKC isoform distribution in an epithelial cell type and demonstrates the potential for selectivity in signal transduction through phosphorylation of isoform specific and spatially-separated substrates.