Protein kinase-C stimulatory activity in human amnion cytosol

Cytosolic preparations from human amnions at term were tested for the presence of endogenous modulators of protein kinase-C (PKC) activity. Tissues were obtained from 14 patients undergoing cesarean section (CS) and 14 patients after spontaneous delivery (SL). PKC activity was significantly greater in cytosols from CS than SL amnion (1.65 +/- 0.04 vs 0.73 +/- 0.2 pmol/min, respectively; mean +/- SE; n = 14 CS; n = 14 SL; P < 0.05). When amnion cytosols were mixed with a control preparation of PKC (rat brain cytosol partially purified on diethylaminoethyl), PKC activity was significantly increased compared to the control value (control, 12.81 +/- 2.1; control + CS, 22.19 +/- 1.5; control + SL, 21.98 +/- 0.7 pmol/min). The stimulation of PKC was dose dependent. The PKC stimulatory factor in amnion cytosol was stable to heat treatment at 80-90 C for 2 min (control + heat-treated CS, 23.20 +/- 1.2; control + heat-treated SL, 24.49 +/- 1.0 pmol/min) and substituted for phosphatidylserine and diacylglycerol in the PKC assay (control, no lipids, 0.05 +/- 0.04 pmol/min; control + amnion cytosol, no lipids, 9.60 +/- 1.06 pmol/min). The PKC stimulatory factor was calcium dependent, was not extractable in organic solvents, and was greater then 100,000 mol wt. Thus, the human amnion contains a PKC stimulatory factor which may modify or mediate the cellular response to extracellular stimulators of the PKC pathway.