Involvement of a serine esterase in oxidant-mediated activation of phospholipase A2 in pulmonary endothelium

Exposure of bovine pulmonary arterial endothelial cells to 1 mM H2O2 stimulated associated TAME-esterase and PLA2 activities. Pretreatment with the serine esterase inhibitors: PMSF (1 mM), DFP (1 mM), and alpha 1-PI (1 mg/ml) inhibited H2O2-induced stimulation of TAME-esterase and PLA2 activities. The TAME-esterase and PLA2 activities under H2O2 exposure were determined to be linearly correlated. Affinity labelling of the endothelial cell membrane with 3H]DFP demonstrated that the serine esterase resides in a protein having molecular weight of 29,000 daltons (29 kDa) which is similar to that of elastase. Treatment of the endothelial cell homogenate with trypsin (1 microgram/ml) also stimulated PLA2 activity.