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 arachido nic acid and subsequent production of eicosanoids, which play an impor tant role in a variety of biological processes, including mitogenic si gnalling by epidermal growth factor (EGF). In a previous study [Spaarg aren, M. et al. (1992) Biochem J. 287, 37-43] we identified the EGF-ac tivated PLA(2) as being similar to the recently cloned high-molecular- mass cytosolic phospholipase A(2) (cPLA(2)). In the present study we d emonstrate a rapid transient EGF-induced activation of this cPLA(2) an d an EGF-induced increase in phosphorylation of the cPLA(2). The EGF-i nduced activation of cPLA(2) is reversed upon phosphatase treatment sh owing phosphorylation-dependent activation of the cPLA(2). No direct a ssociation of the cPLA(2) to the EGF receptor was detected under condi tions where such an association with phospholipase C-gamma was demonst rated. Phosphoamino acid analysis of this cPLA(2) showed that EGF indu ced an increase in serine phosphorylation exclusively, no tyrosine pho sphorylation being observed. EGF treatment of the cells resulted in a Ca2+-dependent translocation of the cPLA(2) from the cytosol to the me mbrane 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 cPL A(2) to membranes does not require accessory membrane molecules.