Role of the JNK pathway in thrombin-induced ICAM-1 expression in endothelial cells

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Abstract
Objective: Thrombin induces leukocyte adherence to endothelial cells via increased expression of intercellular adhesion molecule-1 (ICAM-1). Although ICAM-1 expression is regulated by NF-κB, recent studies have suggested that additional signaling mechanisms may also be involved. The goal of this study was to determine whether mitogen-activated protein (MAP) kinases, including extracellular signal-regulated kinase 1/2 (ERK1/2), c-Jun N-terminal kinase (JNK), and p38 MAP kinase (p38), mediate thrombin-induced ICAM-1 expression in endothelial cells. Methods: Western blot analysis using anti-ICAM-1 antibody and luciferase assays were performed in cultured endothelial cells after addition of signal transduction inhibitors or transfection of various gene constructs. JNK kinase activity was determined by a kinase assay using c-Jun as a substrate or by Western blot analysis with anti-phospho-JNK antibody. Results: Treatment of endothelial cells with the JNK-specific inhibitors, SP600125 or JNK inhibitory peptide 1 (JNKI1), resulted in a significant decrease in thrombin-induced ICAM-1 expression as demonstrated by Western blot analysis (67 ± 3% and 72 ± 7%, respectively). In contrast, inhibitors of MEK and p38 had only minimal effect. The combination of SP600125 and the NF-κB inhibitor, BAY11-7082, resulted in complete inhibition of thrombin-induced ICAM-1 expression. The Gαq inhibitor, YM-254890, inhibited thrombin-induced JNK activation and ICAM-1 expression. Dominant-negative Ras and Rac1, but not Rho, inhibited thrombin-induced JNK activation and ICAM-1 promoter activity. Finally, thrombin-induced JNK activation and ICAM-1 promoter activity were inhibited by βARK1ct (a Gβγ subunit scavenger) and Csk. Conclusions: These data suggest that, in concert with NF-κB, JNK regulates thrombin-induced ICAM-1 expression by a mechanism that is dependent on Gαq, Gβγ, Ras, Rac1 and the Src kinase family.

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