Mechanism of Regulation of Group IVA Phospholipase A2 Activity by Ser727 Phosphorylation

Although group IVA cytosolic phospholipase A2 (cPLA2α) has been reported to be phosphorylated at multiple Ser residues, the mechanisms by which phosphorylation at different sites regulates cPLA2α activities are not fully understood. To explore the possibility that phosphorylation of Ser727 modulates cellular protein-protein interactions, we measured the effect of Ser727 mutations on the interaction of cPLA2α with a reported cPLA2α-binding protein, p11. In vitro activity assays and membrane binding measurements by surface plasmon resonance analysis showed that a heterotetramer (A2t) of p11 and annexin A2, but not p11 or annexin A2 alone, directly binds cPLA2α via Ser727, which keeps the enzyme from binding the membrane and catalyzing the phospholipid hydrolysis. Phosphorylation of Ser727 disrupts this inhibitory cPLA2α-A2t interaction, thereby activating cPLA2α. Subcellular translocation and activity measurements in HEK293 cells cotransfected with cPLA2α and p11 also showed that p11, in the form of A2t, inhibits cPLA2α by the same mechanism and that phosphorylation of Ser727 activates cPLA2α by interfering with the inhibitory cPLA2α-A2t interaction. Collectively, these studies provide new insight into the regulatory mechanism of cPLA2α through Ser727 phosphorylation.