Rho proteins and the p38-MAPK pathway are important mediators for LPS-induced interleukin-8 expression in human endothelial cells

Bacterial endotoxin (lipopolysaccharide, or LPS) has potent proinflammatory properties by acting on many cell types, including endothelial cells. Secr etion of the CXC-chemokine interleukin-8 (IL-8) by LPS-activated endothelia l cells contributes substantially to the inflammatory response. Using human umbilical vein endothelial cells (HUVECs), we analyzed the role of small G TP-binding Rho proteins and p38 mitogen-activated protein kinase (MAPK) for LPS-dependent IL-8 expression in endothelial cells. Specific inactivation of RhoA/Cdc42/Rac1 by Clostridium difficile toxin B-10463 (TcdB-10463) redu ced LPS-induced tyrosine phosphorylation, nuclear factor (NF)-kappa B-depen dent gene expression, IL-8 messenger RNA, and IL-8 protein accumulation but showed no effect on LPS-dependent p38 MAPK activation. Inhibition of p38 M APK by SE 202190 also blocked LPS-induced NF-kappa B activation and IL-8 sy nthesis. Furthermore, selective activation of the p38 MARK pathway by trans ient expression of a constitutively active form of MAPK kinase (MKK)6, the upstream activator of p38, was as effective as LPS with respect to IL-8 exp ression in HUVECs. In summary, our data suggest that LPS-induced NF-kappa B activation and IL-8 synthesis in HUVECs are regulated by both a Rho-depend ent signaling pathway and the MKK6/p38 kinase cascade. (C) 2000 by The Amer ican Society of Hematology.