Abstract
Molecular mechanisms that mediate signal transduction by growth inhibitory cytokines are poorly understood. Type I (alpha and beta) interferons (IFNs) are potent growth inhibitory cytokines whose biological activities depend on induced changes in gene expression. IFN-alpha induced the transient activation of phospholipase A2 in 3T3 fibroblasts and rapid hydrolysis of [3H]arachidonic acid (AA) from prelabeled phospholipid pools. The phospholipase inhibitor, bromophenacyl bromide (BPB), specifically blocked IFN-induced binding of nuclear factors to a conserved, IFN-regulated enhancer element, the interferon-stimulated response element (ISRE). BPB also caused a dose-dependent inhibition of IFN-alpha-induced ISRE-dependent transcription in transient transfection assays. Specific inhibition of AA oxygenation by eicosatetraynoic acid prevented IFN-alpha induction of factor binding to the ISRE. Treatment of intact cells with inhibitors of fatty acid cyclooxygenase or lipoxygenase enzymes resulted in amplification of IFN-alpha-induced ISRE binding and gene expression. Thus, IFN-alpha receptor-coupled AA hydrolysis may function in activation of latent transcription factors by IFN-alpha and provides a system for studying the role of AA metabolism in transduction of growth inhibitory signals.
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