Background: The rate-limiting step in prostaglandin (PG) biosynthesis is catalyzed by phospholipase A2 (PLA2) enzymes which hydrolyze arachidonic acid from membrane phospholipids. Despite their importance in uterine PG production, little is known concerning the specific PLA2 enzymes that regulate arachidonic acid liberation in the uterine endometrium. The objectives of this study were to evaluate the expression and activities of calcium-independent Group VI and Group IVC PLA2 (PLA2G6 and PLA2G4C) and calcium-dependent Group IVA PLA2 (PLA2G4A) enzymes in the regulation of bovine uterine endometrial epithelial cell PG production.

Smoking is a major risk factor for endothelial cell injury and subsequent coronary artery disease. Epidemiological studies implicate the phospholipase A2/arachidonic acid cascade in the mechanism by which smoking causes heart disease. However, specific components of cigarette smoke that activate this pathway have not been identified. The purpose of this study was to investigate the effects of polycyclic aromatic hydrocarbons contained in cigarette smoke on phospholipase A2 (PLA2) activity and apoptosis of human coronary artery endothelial cells. 1-methylanthracene (1-MA), phenanthrene (PA), and benzo(a)pyrene (B(a)P) caused significant release of 3H-arachidonate from endothelial cells. 1-MA and PA, but not B(a)P, also caused significant release of 3H-linoleic acid. Release of fatty acids from membrane phospholipids preceded the onset of apoptosis. 3H-arachidonate release and apoptosis induced by 1-MA, B(a)P, and PA were inhibited by methylarachidonoyl-fluorophosphonate, an inhibitor of Groups IV and VI PLA2s. Bromoenol lactone, an inhibitor of Group VI enzymes, inhibited both 3H-arachidonate release and apoptosis induced by 1-MA and PA, but not B(a)P. MJ33, an inhibitor of the acidic calcium-independent PLA2, attenuated 3H-arachidonate release and apoptosis by PA, but not 1-MA or B(a)P. The presence of Groups IV and VI and the acidic iPLA2 in endothelial cells was demonstrated by reverse transcriptase-polymerase chain reaction and Western analysis. These data suggest that 1-MA, B(a)P and PA induce apoptosis of endothelial cells by a mechanism that involves activation of these three distinct isoforms of PLA2.

Background: Prostaglandins (PG), produced by the uterine endometrium, are key regulators of several reproductive events, including estrous cyclicity, implantation, pregnancy maintenance and parturition. Phospholipase A2 (PLA2) catalyzes the release of arachidonic acid from membrane phospholipids, the rate-limiting step in PG biosynthesis. The bovine endometrial (BEND) cell line has served as a model system for investigating regulation of signaling mechanisms involved in uterine PG production but information concerning the specific PLA2 enzymes involved and their role in regulation of this process is limited. The objectives of this investigation were to evaluate the expression and activities of calcium-dependent group IVA (PLA2G4A) and calciumindependent group VI (PLA2G6) enzymes in the regulation of BEND cell PG production.

Phospholipase A2 (PLA2) enzymes catalyze the rate-limiting step in eicosanoid production by liberating arachidonic acid from membrane phospholipids. There is limited information regarding the expression pattern and activity of uterine PLA2 enzymes during pregnancy. Polychlorinated biphenyls (PCBs) are a group of persistent environmental toxicants previously associated with decreased gestation length that are capable of activating PLA2. The purpose of the present study was to determine whether uterine sensitivity to PCB stimulation is dependent on PLA2 expression, comparing rat uterine PLA2 expression in Gestational Day (gd) 10 versus gd20. Western blot analysis revealed a significant increase in the expression of calcium-dependent PLA2G2A and a 50-kDa protein immunoreactive to calcium-independent PLA2G6 antibody in gd20 compared to gd10 rat uterine tissue. The increased expression of the 50-kDa PLA2G6 was associated with a gestational age-related increase in endometrial calcium-independent PLA2 activity that was sensitive to inhibition by bromoenol lactone (P < 0.05). Longitudinal uterine strips isolated from gd10 or gd20 rat were suspended in muscle baths to evaluate uterine contractions following exposure to the ortho substituted congener PCB 50. Exposure to 50 and 100 microM PCB 50 significantly increased the frequency of gd20, but not gd10, uteri compared to solvent (dimethyl sulfoxide) controls (P < 0.05). Pharmacologic inhibition of PLA2G6, but not PLA2G2A, attenuated PCB-induced stimulation of gd20 uterine contractions (P < 0.05). These data suggest that PCB 50 stimulates uterine contractions by activating endometrial PLA2G6. Furthermore, gestation age-related sensitivity to PCB is associated with an increase in the expression of a previously unidentified 50-kDa PLA2G6 in rat uterus.