PLATELET-ACTIVATING-FACTOR INDUCTION OF ACTIVATOR PROTEIN-1 SIGNALINGIN BRONCHIAL EPITHELIAL-CELLS

Platelet-activating factor (PAF) has been implicated in the pathogenes is of allergic and inflammatory events in the airway. In the present s tudy, we sought to determine if PAF receptors are present on human bro nchial epithelial cells and whether PAF binding to these receptors lea ds to activation of activator protein-1 (AP-l)-mediated transcription. Radioligand binding studies demonstrated specific binding sites for t he PAF antagonist [H-3]WEB 2086 yl)-9-methyl-6H-thieno[3,2-f]-[1,2,4]t riazolo[4,3- 1,4]diazepine-2-yl]-1-(4-morpholinyl)-1-propanone) on pri mary bronchial epithelial cells with an equilibrium dissociation const ant (K-d) = 9.8 nM and maximal density of binding sites (B-max), = 42. 4 fmol/mg of protein. The expression of PAF receptors in these cells w as further confirmed by reverse transcriptase-polymerase chain reactio n, which revealed amplification products derived from PAF receptor mRN A corresponding to transcripts 1 and 2. In the bronchial epithelial ce ll line BEAS-2B transfected with an expression plasmid for the human P AF receptor, PAF stimulation increased AP-1 DNA binding activity as de termined by electrophoretic mobility shift assays. The Fos and Jun fam ily proteins were identified as components of the DNA-protein complexe s by anti-peptide antibodies in gel supershift assays. Additionally, P AF significantly induced AP-I mediated transcription which was depende nt on the expression of PAF receptors. The PAF antagonist WEB 2086 blo cked the PAF effect but not that induced by 12-O-tetradecanoyl phorbol -13-acetate, indicating the specificity of the PAF response. These res ults indicate that activation of airway epithelial cells through stimu lation of PAF receptors includes up-regulation of the nuclear transcri ption factor AP-1 and AP-I transcriptional activity.