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.
Kast
R
R
Research Program Tumor Cell Regulation, German Cancer Research Center, Heidelberg.
Fürstenberger
G
G
Marks
F
F
D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism*; D001692:Biological Transport / Q000187:drug effects; D001920:Bradykinin / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D002384:Catalysis; D002460:Cell Line; D002462:Cell Membrane / Q000201:enzymology; D003600:Cytosol / Q000201:enzymology*; D015603:Keratinocytes / Q000378:metabolism*; D010741:Phospholipases A / Q000378:metabolism*; D054467:Phospholipases A2; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*
D016718:Arachidonic Acid; D010741:Phospholipases A; D054467:Phospholipases A2; D013755:Tetradecanoylphorbol Acetate; D001920:Bradykinin; D002118:Calcium