Identification of a 42-kDa Group IV cPLA2-activating protein, cPLAPγ, as a GTP-binding protein in the bovine brain

Brain tissue contains multiple forms of Phospholipase A(2) (PLA(2)) whose activities are involved in intracellular and intercellular signalling related to normal functions such as long-term potentiation, neurotransmitter release, cell growth and differentiation. Among them, we focused on regulatory mechanism of cPLA(2)alpha (Group IVA cytosolic PLA(2)) in brain tissue. In the present study, we report the identification of a cPLA(2)-activating protein (cPLAP) in the bovine brain. cPLAP activity appeared as two major peaks with molecular masses of 200 and 42 kDa in a Superose 12 gel filtration FPLC column. The 42-kDa form of cPLAP, designated cPLAP gamma, was further purified using a Mono S FPLC column to near homogeneity and characterized to as a GTP-binding protein (G protein). Metabolic labelling and immunoprecipitation studies revealed that cPLAP gamma associates with cPLA(2) in vitro and co-immunoprecipitates with [S-35]-cPLA(2). Notably, cPLAP gamma rendered cPLA(2) fully activated at submicromolar concentrations of Ca2+. These results suggest that cPLAP gamma may act as a G protein, activating cPLA(2)alpha prior to reaching full intracellular Ca2+ concentrations.