Serum stimulation of phospholipase A2 and prostaglandin release in 3T3 cells is associated with platelet-derived growth-promoting activity.
Sera from mouse, rat, and calf sources stimulate cellular phospholipase A2 activity (PLase; phosphatide 2-acylhydrolase, EC 3.1.1.4) and prostaglandin synthesis in 3T3 Swiss mouse fibroblasts, releasing up to 33% of biosynthetically incorporated [3H]arachidonic acid as hydrolysis products in 1 hr. 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 microM 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 three 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-stimulus 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 degrees 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.
D000818:Animals; D001792:Blood Platelets / Q000502:physiology*; D002478:Cells, Cultured; D004789:Enzyme Activation / Q000187:drug effects; D005227:Fatty Acids / Q000378:metabolism; D006133:Growth Substances / Q000097:blood / Q000494:pharmacology*; D006801:Humans; D051379:Mice; D010740:Phospholipases / Q000378:metabolism*; D010741:Phospholipases A / Q000378:metabolism*; D054467:Phospholipases A2; D011453:Prostaglandins / Q000378:metabolism*; D051381:Rats; D013379:Substrate Specificity
D005227:Fatty Acids; D006133:Growth Substances; D011453:Prostaglandins; D010740:Phospholipases; D010741:Phospholipases A; D054467:Phospholipases A2