Proliferative effect of phospholipase A2 in rat chondrocyte via its specific binding sites

We studied the presence of specific binding sites for pancreatic-type group I phospholipase A2 (PLA2-I), EC 3.1.1.4, and a PLA2-I action on the DNA synthesis of rat chondrocytes. Rat chondrocytes, derived from the xiphisternum of adult rats, had a single class of PLA2-I binding site with an equilibrium binding constant value of 0.9 nM and a maximum binding capacity of 53.9 fmol/10(6) cells. PLA2-I alone did not show any proliferative effect, however, PLA2-I dose-dependently stimulated thymidine incorporation in DNA in the presence of basic fibroblast growth factor (bFGF). The mammalian mature type of PLA2s-I specifically recognized the binding sites in these cells and had a synergistic effect on DNA synthesis with bFGF, whereas its inactive zymogen and group II PLA2 showed much lesser activities. The type-specific action of PLA2s implicated the involvement of PLA2-I specific binding sites in this activation process.