DIFFERENTIAL EXPRESSION OF PROTEIN-KINASE-C ISOFORMS IN THE HUMAN PLACENTA

The extensive role played by protein kinase C (PKC) in signal transduc tion prompted this study of the expression and localization of PKC iso forms in human placental syncytiotrophoblast. Membranes prepared from these cells and samples of villous tissue were analysed by immunoblott ing and immunocytochemistry using isoform-specific antibodies. PKC bet a 2, gamma, epsilon and zeta were found to be present in both microvil lous and basal membranes from term placenta. The alpha isoform was obs erved only on the basal membrane while the beta 1 isoform was confined to the microvillous membrane. The basal : microvillous ratios for bet a 2, gamma, epsilon and zeta ranged between 0.3 and 0.5, demonstrating a substantial asymmetry in plasma membrane localization. Immunocytoch emistry 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 me mbranes, in contrast to the other villous cell types. Immunoblotting e xperiments demonstrated significant increases in PKC beta 2 and a on t he microvillous membrane and PKC gamma and epsilon on the basal membra ne between 16 and 40 of weeks gestation. This is the first detailed ma pping of PKC isoform distribution in an epithelial cell type and demon strates the potential for selectivity in signal transduction through p hosphorylation of isoform-specific and spatially-separated substrates. (C) 1996 W. B. Saunders Company Ltd