Role of Phosphorylation Sites and the C2 Domain in Regulation of Cytosolic Phospholipase A(2)

Cytosolic phospholipase A(2) (cPLA(2)) mediates agonist-induced arachidonic acid release, the first step in eicosanoid production. cPLA(2) is regulated by phosphorylation and by calcium, which binds to a C2 domain and induces its translocation to membrane. The functional roles of phosphorylation sites and the C2 domain of cPLA(2) were investigated. In Sf9 insect cells expressing cPLA(2), okadaic acid, and the calcium-mobilizing agonists A23187 and CryIC toxin induce arachidonic acid release and translocation of green fluorescent protein (GFP)-cPLA(2) to the nuclear envelope. cPLA(2) is phosphorylated on multiple sites in Sf9 cells; however, only S505 phosphorylation partially contributes to cPLA(2) activation. Although okadaic acid does not increase calcium, mutating the calcium-binding residues D43 and D93 prevents arachidonic acid release and translocation of cPLA(2), demonstrating the requirement for a functional C2 domain. However, the D93N mutant is fully functional with A23187, whereas the D43N mutant is nearly inactive. The C2 domain of cPLA(2) linked to GFP translocates to the nuclear envelope with calcium-mobilizing agonists but not with okadaic acid. Consequently, the C2 domain is necessary and sufficient for translocation of cPLA(2) to the nuclear envelope when calcium is increased; however, it is required but not sufficient with okadaic acid.