title: Activation of a keratinocyte phospholipase A2 by bradykinin and 4 beta-phorbol 12-myristate 13-acetate. Evidence for a receptor-GTP-binding protein versus a protein-kinase-C mediated mechanism.
abstract: The release of arachidonic acid from cellular phospholipids and its subsequent conversion to eicosanoids is the common early response of skin keratinocytes to a wide variety of exogenous or endogenous agonists including irritant skin mitogens such as the phorbol ester, 4 beta-phorbol 12-myristate 13-acetate (PMA) or the inflammatory peptide bradykinin. In mouse keratinocytes labeled with [14C]arachidonic acid, both PMA and bradykinin induced the release of the fatty acid in a  dose-dependent and time-dependent manner. Three lines of evidence indicate phospholipase A2 activity to be involved in arachidonic acid release: (a) its inhibition by mepacrine, (b) the concomitant generation of lysophosphatidylcholine from [3H]choline-labeled cells and (c) an increase in arachidonic acid release from 14C-labeled phosphatidylcholine in particulate fractions from PMA-treated and bradykinin-treated keratinocytes. Inhibition or down regulation of protein kinase C (PKC) led to a suppression of PMA-induced but not bradykinin-induced arachidonic acid release, indicating a critical involvement of this kinase in phorbol-ester-induced activation of epidermal phospholipase A2 activity. Bradykinin-induced activation of phospholipase A2 was however, shown to be mediated by specific B2 receptors coupled to GTP-binding proteins (G protein). In support of this mechanism it was demonstrated that the bradykinin-induced phospholipase A2 activity was increased in the presence of non-hydrolysable GTP but decreased upon addition of non-hydrolysable GDP analogues. Moreover, cholera toxin stimulated both basal and bradykinin-induced phospholipase A2 activity in a cAMP-independent manner, whereas pertussis toxin was found to be inactive in this respect. The data suggest that epidermal phospholipase A2 activity can be stimulated by bradykinin via a B2 receptor-G-protein-dependent pathway, which is independent of PKC and a PKC-dependent pathway which is activated by phorbol esters such as PMA.
authors.affiliation: Institute of Biochemistry, German Cancer Research Center, Heidelberg.
authors.forename: R
authors.initials: R
authors.lastname: Kast
authors.forename: G
authors.initials: G
authors.lastname: Fürstenberger
authors.forename: F
authors.initials: F
authors.lastname: Marks
mesh_terms: D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism; D001920:Bradykinin / Q000031:analogs & derivatives / Q000494:pharmacology*; D002250:Carbon Radioisotopes; D002460:Cell Line; D002772:Cholera Toxin / Q000494:pharmacology; D004789:Enzyme Activation; D019204:GTP-Binding Proteins / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D007295:Inositol Phosphates / Q000378:metabolism; D015603:Keratinocytes / Q000187:drug effects / Q000201:enzymology*; D007700:Kinetics; D008244:Lysophosphatidylcholines / Q000302:isolation & purification / Q000378:metabolism; D051379:Mice; D009243:NAD / Q000378:metabolism; D037342:Pertussis Toxin; D010741:Phospholipases A / Q000378:metabolism*; D054467:Phospholipases A2; D011493:Protein Kinase C / Q000378:metabolism*; D018002:Receptors, Bradykinin; D017981:Receptors, Neurotransmitter / Q000187:drug effects / Q000378:metabolism*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
chemical_list: D002250:Carbon Radioisotopes; D007295:Inositol Phosphates; D008244:Lysophosphatidylcholines; D018002:Receptors, Bradykinin; D017981:Receptors, Neurotransmitter; D010566:Virulence Factors, Bordetella; D009243:NAD; D016718:Arachidonic Acid; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D002772:Cholera Toxin; D037342:Pertussis Toxin; D011493:Protein Kinase C; D010741:Phospholipases A; D054467:Phospholipases A2; D019204:GTP-Binding Proteins; D013755:Tetradecanoylphorbol Acetate; D001920:Bradykinin