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Originally published online as doi:10.1189/jlb.0907652 on April 24, 2008

Published online before print April 24, 2008
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(Journal of Leukocyte Biology. 2008;84:215-223.)
© 2008 by Society for Leukocyte Biology

Thrombin-induced expression of endothelial CX3CL1 potentiates monocyte CCL2 production and transendothelial migration

Milan Popovic1, Yves Laumonnier1, Ladislav Burysek, Tatiana Syrovets and Thomas Simmet2

Institute of Pharmacology of Natural Products and Clinical Pharmacology, Ulm University, Ulm, Germany

2Correspondence: Institute of Pharmacology of Natural Products and Clinical Pharmacology, Ulm University, Helmholtzstr. 20, D-89081 Ulm, Germany. E-mail: thomas.simmet{at}uni-ulm.de

CX3CL1 (fractalkine, neurotactin) is the sole CX3C chemokine. It induces monocyte locomotion in its cleaved form, but in its membrane-anchored form, it also acts as an adhesion molecule. The expression of CX3CL1 is up-regulated in endothelial cells by proinflammatory cytokines such as IL-1 or TNF-{alpha}. Here, we studied the effect of the serine protease thrombin on endothelial CX3CL1 induction and its putative relevance for monocyte function. In HUVEC, thrombin triggered a time- and concentration-dependent expression of CX3CL1 at the mRNA and the protein level as shown by RT-PCR, Western immunoblotting, and flow cytometric analysis. Thrombin induced CX3CL1 by activating protease-activated receptor 1 (PAR1) as demonstrated by the use of PAR1-activating peptide and the PAR1-specific antagonist SCH 79797. The thrombin-induced CX3CL1 expression was NF-{kappa}B-dependent, as shown by EMSA, ELISA, and by inhibition of the NF-{kappa}B signaling pathway by the I{kappa}B kinase inhibitor acety-11-keto-β-boswellic acid or by transient overexpression of a transdominant-negative form of I{kappa}B{alpha}. Upon cocultivation of human monocytes with HUVEC, the thrombin-dependent induction of membrane-anchored CX3CL1 in HUVEC triggered monocyte adhesion and an enhanced release of the MCP-1/CCL2 by monocytes and potentiated the monocyte transendothelial migration. Accordingly, the recombinant extracellular domain of CX3CL1 induced CCL2 release by monocytes. Thus, the thrombin-induced monocyte/endothelial cell cross-talk mediated by increased CX3CL1 expression potentiates the CCL2 chemokine generation that might contribute to the recruitment of monocytes into inflamed areas.

Key Words: Mono-Mac-6 • HUVEC • chemokine • protease-activated receptor 1 • coculture






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