Effects of protein kinase CK2, extracellular signal-regulated kinase 2, and protein phosphatase 2A on a phosphatidic acid-preferring phospholipase A1

A soluble, phosphatidic acid-preferring phospholipase A1, expressed in matu re bovine testes but not in newborn calf testes, may contribute to the form ation or function of sperm. Here we incubated a recombinant preparation of the phospholipase in vitro with several enzymes including protein kinase CK 2 (CK2), extracellular signal-regulated kinase 2 (ERK2), and protein phosph atase 2A (PP2A) to identify effects that might be of regulatory importance in vivo. Major findings were that 1) CK2 phosphorylated the phospholipase o n serines 93, 105, and 716; 2) ERK2 phosphorylated the enzyme on serine 730 ; 3) there was cross-antagonism between the reactions that phosphorylated s erines 716 and 730; 4) PP2A selectively hydrolyzed phosphate groups that we re esterified to serines 716 and 730; 5) CK2 alpha formed a stable, MgATP/M gGTP-dependent complex with the phospholipase by a novel mechanism; and 6) the complex showed reduced phospholipase activity and resembled a complex i dentified in homogenates of macaque testis. These results provide the first available information about the effects of reactions of phosphorylation an d dephosphorylation on the behavior of the phospholipase, shed Light on pro perties of CK2 alpha that may be required for the formation of complexes wi th its substrates, and raise the possibility that a complex containing CK2 alpha and the phospholipase may play a special biological role in the testi s.