Intracellular calcium signals regulating cytosolic phospholipase A2 translocation to internal membranes.

Increased intracellular Ca(2+) concentrations ([Ca(2+)](i)) promote cytosolic phospholipase A(2) (cPLA(2)) translocation to intracellular membranes. The specific membranes to which cPLA(2) translocates and the [Ca(2+)](i) signals required were investigated. Plasmids of EGFP fused to full-length cPLA(2) (EGFP-FL) or to the cPLA(2) C2 domain (EGFP-C2) were used in Ca(2+)/EGFP imaging experiments of cells treated with [Ca(2+)](i)-mobilizing agonists. EGFP-FL and -C2 translocated to Golgi in response to sustained [Ca(2+)](i) greater than approximately 100-125 nm and to Golgi, ER, and perinuclear membranes (PNM) at [Ca(2+)](i) greater than approximately 210-280 nm. In response to short duration [Ca(2+)](i) transients, EGFP-C2 translocated to Golgi, ER, and PNM, but EGFP-FL translocation was restricted to Golgi. However, EGFP-FL translocated to Golgi, ER, and PNM in response to long duration transients. In response to declining [Ca(2+)](i), EGFP-C2 readily dissociated from Golgi, but EGFP-FL dissociation was delayed. Agonist-induced arachidonic acid release was proportional to the [Ca(2+)](i) and to the extent of cPLA(2) translocation. In summary, we find that the differential translocation of cPLA(2) to Golgi or to ER and PNM is a function of [Ca(2+)](i) amplitude and duration. These results suggest that the cPLA(2) C2 domain regulates differential, Ca(2+)-dependent membrane targeting and that the catalytic domain regulates both the rate of translocation and enzyme residence.