ICAM-1 SIGNALING PATHWAYS ASSOCIATED WITH RHO-ACTIVATION IN MICROVASCULAR BRAIN ENDOTHELIAL-CELLS

Endothelium of the cerebral blood vessels, which constitutes the blood -brain barrier, controls leukocyte adhesion and trafficking to the bra in. Investigating signaling pathways triggered by the engagement of ad hesion molecules expressed on brain endothelial cells, we report here that ICAM-1 cross-linking induces tyrosine phosphorylation of three cy toskeleton-associated proteins: focal adhesion kinase, paxillin, and p 130(Cas) (Cas), which are found to associate as complexes. Tyrosine-ph osphorylated Cas associates with the adaptor protein Crk and the GTP e xchange factor C3G. In the same conditions the small G protein Rho was activated, as shown by the increase in its GTP loading. In addition, tyrosine phosphorylation of focal adhesion kinase, paxillin, and Cas a s web as triggering of the Crk signaling pathway are blocked by pretre atment of the cells with the exoenzyme C3, a specific Rho inhibitor. C 3-sensitive activation of the c-Jun N-terminal kinase in response to I CAM-1 cross-linking is also observed, whereas no significant activatio n of Ras or of the extracellular signal-regulated kinase was detected. In conclusion, these results suggest that through coupling to Rho act ivation and phosphorylation of cytoskeletal proteins and transcription factors, ICAM-1 cross-linking participates in the cell shape changes and gene regulation that may accompany lymphocyte migration through th e blood-brain barrier.