Endothelin-1–Induced Interleukin-8 Production in Human Brain-Derived Endothelial Cells Is Mediated by the Protein Kinase C and Protein Tyrosine Kinase Pathways

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We have previously demonstrated that endothelin-1 (Et-1) induces human central nervous system-derived endothelial cells (CNS-EC) to produce and secrete the chemokine interleukin 8 (IL-8). In the present study, we use specific inhibitors and activators to elucidate the signal transduction pathways involved in this process. Et-1–induced IL-8 production was blocked by ETA receptor antagonist BQ610, but not by ETB receptor antagonist BQ788, demonstrating that CNS-EC activation is initiated by Et-1 binding to the ETA receptor. IL-8 mRNA expression is blocked by the protein kinase C inhibitor bisindolylmaleimide or protein tyrosine kinase inhibitors, genestein and geldanamycin, establishing the involvement of the protein kinase C and protein tyrosine kinase pathways in the activation process. The transcription factor, NF-κB, is involved in Et-1 activation as determined by specific inhibitors of translocation and direct analysis of DNA-binding proteins. Neither inhibition nor activation of cAMP-dependent protein kinase affected IL-8 production in the absence or presence of Et-1. Similarly, no effect was observed upon inhibition of protein phosphatases by okadaic acid. Thus, the signal transduction process induced by Et-1 in CNS-EC, leading to increased mRNA IL-8 expression, is initiated by Et-1 binding to ETA receptor followed by subsequent activation of protein kinase C, protein tyrosine kinase, and NF-κB. Because increased expression of Et-1 is associated with hypertension and stroke and IL-8 is likely to be involved in the accumulation of neutrophils causing tissue damage in ischemic/reperfusion injury, identification of the mechanism involved in the Et-1–induced increase in IL-8 production may have significant therapeutic value.