Protein kinases of the human placental microvillous membrane. Their potential role in intrasyncytial communication

Protein phosphorylation has been shown to alter various plasma membrane functions. To investigate the role of phosphorylation in human placental trophoblast, microvillous membrane vesicles were incubated with gamma-32-P]ATP and the phosphorylation of endogenous and exogenous protein substrates was measured. The microvillous membrane was shown to possess both adenosine 3',5'-cyclic monophosphate (cAMP)-independent and cAMP-dependent kinases. Both endogenous proteins and exogenous proteins were phosphorylated and these processes were enhanced by the presence of Triton or the ionophore alamethicin. The phosphorylation of histone and of endogenous peptides of molecular weights (MW) 147 000, 97 000 and 53 000 was increased by the addition of cAMP. cAMP stimulation required the presence of Triton or alamethicin. The cAMP-dependent kinases are apparently located at the internal (cytoplasmic) surface of the membrane. This location would allow stimulation by cAMP produced by the basal (fetal-facing) plasma membrane. cAMP-stimulated protein phosphorylation may serve as a means of communication between the syncytial plasma membranes facing the fetal and maternal surfaces.