Effects of Transforming Growth Factor β and Interleukin-1β on Expression of Cyclooxygenase 1 and 2 and Phospholipase A2 mRNA in Lung Fibroblasts and Endothelial Cells in Culture

Experiments were conducted to determine the roles of the rate limiting enzymes, cyclooxygenase 1 and 2 (COX1 and COX2) and cytoplasmic phospholipase A2 (PLA2), in transforming growth factor beta (TGF-β) and interleukin-1 (IL-1β) activated prostaglandin synthesis. Results show that TGF-β increases steady state levels of COX1 mRNA in both human embryo lung fibroblasts (IMR90) and calf pulmonary artery endothelial cells (BPAEC). Temporal experiments show that TGF-β increases, within 2hrs, a 5.5kb COX1 in IMR90 and the 2.7kb COX1 mRNA in BPAEC. IL-1β increases COX1 mRNA only in IMR90, not BPAEC. COX2 mRNA, under basal conditions, is not detected in BPAEC and is expressed only marginally in IMR90. TGF-β or IL-1β have no effect on expression of COX2 gene in either cell type. IL-1β increases steady state levels of PLA2 mRNA in both IMR90 and BPAEC while TGF-β increases expression of the PLA2 gene only in BPAEC. Time experiments with TGF-β show induction of PLA2 mRNA within 1hr, peaking at 4hrs. PG synthesis in response to the cytokines was determined in IMR90 and BPAEC to further assess the significance of the above results. TGF-β increases the synthesis of prostacyclin in BPAEC in a time related fashion peaking at 8hrs at 13 fold above basal. To focus on the action of COX1 and bypass the action of PLA2, exogenous arachidonic acid was used as substrate for PG synthesis. In these experiments IL-1β increases PGE2 synthesis 8 fold in IMR90 while IL-1β and TGF-β added simultaneously increases PGE2 synthesis 25 fold. These results in sum illustrate that the cytokines, TGF-β and IL-1β, regulate both COX1 and PLA2 rnRNA levels. Furthermore, this regulation appears coordinated to bring about elevation of prostaglandin synthesis.