Serum stimulation of phospholipase A2 and prostaglandin release in 3T3 cells is associated with platelet-derived growth-promoting activity.

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Abstract
Sera from mouse, rat and calf sources stimulate cellular phospholipase A2 activity (PLase; phosphatide 2-acrylhydrolase, EC 3.1.1.4) and prostanglandin synthesis in 3T3 Swiss mouse fibroblasts, releasing up to 33% of biosynthetically incorporated [3H]arachidonic acid as hydrolysis products in 1 h. The PLase stimulated by mouse serum exhibits specificity for arachidonic acid residues on phospholipids. It is stimulated 2.5-fold by 1.8 mM Ca2+ in the presence of 5 .mu.M divalent cation ionophore A23187, consistent with a Ca2+-dependent enzyme possessing a cytoplasmic Ca2+ binding site. The percentage maximal PLase- and growth-stimulating activities of the 3 sera exhibit similar concentration dependencies, with the homologous (mouse) serum exhibiting the highest specific activities. Confluent 3T3 cells deplete PLase-stimulating activity from medium containing calf serum at a rate similar to the depletion of cell growth-stimulating activity. The PLase-stimulating activity in rat and mouse sera is derived from the leukocyte fraction of blood, presumably from platelets. In rat leukocyte lysates the PLase-stimulating activity exhibits properties similar to those reported for platelet-derived cell growth factors from rat and human sources, i.e., stability to exposure to 100.degree. C for 2 min or to pH 2 or pH 11 and cationic properties. Purified preparations of human platelet-derived growth factor also exhibit 3T3 PLase-stimulating activity.

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