Cyclic AMP blocks bacterial lipopolysaccharide-induced myosin light chain phosphorylation in endothelial cells through inhibition of Rho/Rho kinase signaling

During Gram-negative sepsis bacterial LPS induces endothelial cell contract ion, actin reorganization, and loss of endothelial integrity by an unknown signal mechanism, In this study, we provide evidence that LPS-stimulation o f endothelial cells (HUVEC) decreases myosin light chain (MLC) phosphatase, resulting in an increase in MLC phosphorylation followed by cell contracti on. All of these LPS effects could be blocked by the Rho-GTPase inhibitor C 3 transferase from Clostridium botulinum or the Rho kinase inhibitor Y-2763 2, These data suggest that LPS induces MLC phosphorylation via Rho/Rho kina se-mediated inhibition of MLC phosphatase in HUVEC. Furthermore, we observe d that cAMP-elevating drugs, known to exert a vasoprotective function, mimi cked the effects of C3 transferase and Y-27632, i.e., inhibited LPS-induced MLC phosphatase inactivation and MLC phosphorylation, cAMP elevation did n ot inhibit myosin phosphorylation induced by constitutively active V14Rho o r the MLC phosphatase inhibitor calyculin and did not induce phosphorylatio n of RhoA in HUVEC, indicating inhibition of an upstream regulator of Rho/R ho kinase, Taken together, Rho/Rho kinase appears to be a central target fo r inflammatory mediators causing endothelial cell contraction such as bacte rial toxins, but also for vasoprotective molecules elevating intracellular cAMP.