PLATELET-ACTIVATING-FACTOR INDUCES NF-KAPPA-B ACTIVATION THROUGH A G-PROTEIN-COUPLED PATHWAY

The capability of platelet activating factor (PAF) to induce transcrip tion factor activation was examined. In stably transfected Chinese ham ster ovary cells expressing the PAF receptor (CHO PAFR), PAF stimulati on resulted in the nuclear expression of a DNA binding activity with s pecificity to the kappa B sequence. The p50 and p65 proteins, constitu ents of the prototypic nuclear factor kappa B (NF-kappa B), were ident ified as components of the DNA . protein complexes by antipeptide anti bodies in gel supershift as well as UV cross-linking experiments. PAF induced an initial decrease and subsequent increase of cytoplasmic I k appa B alpha levels, accompanied by up-regulation of the I kappa B alp ha messenger RNA, a feature of NF-kappa B activation. PAF-induced kapp a B binding activity was detected within 15 min after agonist stimulat ion, peaked at 30-40 min, and remained detectable by 2.5 h. SR 27417, a PAF receptor antagonist, blocked PAF-induced kappa B binding activit y but not that induced by tumor necrosis factor-alpha (TNF alpha). Cho lera toxin treatment markedly reduced PAF-induced kappa B binding acti vity, whereas pertussis toxin had no significant inhibitory effect. Ne ither of the two toxins affected the kappa B binding activity induced by TNF alpha in the same cells. In addition to the CHO-PAFR cells, PAF stimulated kappa B binding activity in the murine P388D(1) macrophage and the human ASK.0 B cell lines that express endogenous PAF receptor s. These results imply a potential role of PAF in the regulation of ge ne expression through a G protein-coupled transcription factor activat ion pathway.