EPIDERMAL GROWTH-FACTOR (EGF) INDUCES SERINE PHOSPHORYLATION-DEPENDENT ACTIVATION AND CALCIUM-DEPENDENT TRANSLOCATION OF THE CYTOSOLIC PHOSPHOLIPASE A(2)

Phospholipase A(2) (PLA(2)) is a key enzyme in the release of arachidonic acid and subsequent production of eicosanoids, which play an important role in a variety of biological processes, including mitogenic signalling by epidermal growth factor (EGF). In a previous study [Spaargaren, M. et al. (1992) Biochem J. 287, 37-43] we identified the EGF-activated PLA(2) as being similar to the recently cloned high-molecular-mass cytosolic phospholipase A(2) (cPLA(2)). In the present study we demonstrate a rapid transient EGF-induced activation of this cPLA(2) and an EGF-induced increase in phosphorylation of the cPLA(2). The EGF-induced activation of cPLA(2) is reversed upon phosphatase treatment showing phosphorylation-dependent activation of the cPLA(2). No direct association of the cPLA(2) to the EGF receptor was detected under conditions where such an association with phospholipase C-gamma was demonstrated. Phosphoamino acid analysis of this cPLA(2) showed that EGF induced an increase in serine phosphorylation exclusively, no tyrosine phosphorylation being observed. EGF treatment of the cells resulted in a Ca2+-dependent translocation of the cPLA(2) from the cytosol to the membrane fraction. This is due to an EGF-induced [Ca2+](i) rise which is dependent on the influx of extracellular Ca2+ via voltage-independent Ca2+ channels. It is shown that the Ca2+-dependent association of cPLA(2) to membranes does not require accessory membrane molecules.