Phorbol ester TPA- and bradykinin-induced arachidonic acid release from keratinocytes is catalyzed by a cytosolic phospholipase A2 (cPLA2).

In a previous paper, we have shown that bradykinin (Bk) and the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) stimulate arachidonic acid release from HEL-30 keratinocytes along a Bk-B2 receptor G-protein-coupled pathway or a protein kinase C-dependent mechanism, respectively. Here we show a cytosolic PLA2 (cPLA2) to be responsible for this effect. This enzyme exhibited a marked acyl-group specificity towards arachidonic acid. It was activated by Ca++ in micromolar concentrations and partially translocated from the cytoplasmic to the membrane fraction upon Ca++ treatment. Translocation was also observed upon treatment of cells with either Bk or TPA. However, only with Bk was a corresponding increase of the cytoplasmic Ca++ level observed, whereas TPA-induced translocation occurred at basal Ca++ concentrations. Indirect evidence for a G protein to be involved in Bk- but not TPA-dependent cPLA2 activation was provided using non-hydrolyzable GTP derivatives. It is concluded that keratinocyte cPLA2 plays a critical role in the initiation by exogenous and endogenous factors of the eicosanoid cascade in skin.