SELECTIVE INHIBITORS OF CYTOSOLIC OR SECRETORY PHOSPHOLIPASE A(2) BLOCK TNF-INDUCED ACTIVATION OF TRANSCRIPTION FACTOR NUCLEAR FACTOR-KAPPA-B AND EXPRESSION OF ICAM-1

TNF signaling mechanisms involved in activation of transcription facto r NF-kappa B were studied in the human keratinocyte cell line HaCaT. W e show that TNF-induced activation of NF-kappa B was inhibited by the well-known selective inhibitors of cytosolic phospholipase A(2) (cPLA( 2)): the trifluoromethyl ketone analogue of arachidonic acid (AACOCF3) and methyl arachidonyl fluorophosphate. The trifluoromethyl ketone an alogue of eicosapentaenoic acid (EPACOCP3) also suppressed TNF-induced NF-kappa B activation and inhibited in vitro cPLA(2) enzyme activity with a similar potency as AACOCF3. The arachidonyl methyl ketone analo gue (AACOCH3) and the eicosapentanoyl analogue (EPACHOHCF3), which bot h failed to inhibit cPLA(2) enzyme activity in vitro, had no effect on TNF-induced NR-kappa B activation. TNF-induced NF-kappa B activation was also strongly reduced in cells stimulated in the presence of the s ecretory PLA(2) (sPLA(2)) inhibitors 12-epi-scalaradial and LY311727. Addition of excess arachidonic acid suppressed the inhibitory effect o f 12-epi-scalaradial and LY311727. Moreover, both methyl arachidonyl f luorophosphate and 12-epi-scalaradial blocked TNF-mediated enhancement of expression of ICAM-1. Activation of NF-kappa B by IL-1 beta was ma rkedly less sensitive to both cPLA(2) and sPLA(2) inhibitors. The resu lts indicate that both cPLA(2) and sPLA(2) may be involved in the TNF signal transduction pathway leading to nuclear translocation of NF-kap pa B and to NF-kappa B-activated gene expression in HaCaT cells.