thromboplastin and geranylgeranyl-pyrophosphate

Low density lipoprotein (LDL) internalized in the vascular wall and modified by binding to extracellular matrix-proteoglycans (ECM) becomes aggregated (agLDL). AgLDL induces tissue factor (TF) expression and activity in human vascular smooth muscle cells (VSMC). TF expression in vascular cells promotes the prothrombotic transformation of the vascular wall. However, the mechanisms by which agLDL induces TF are not known. The aim of this study was to investigate the mechanisms involved in TF activation by extracellular matrix-modified LDL in human VSMC.. AgLDL significantly induces TF expression (real time PCR and Western blot analysis) and procoagulant activity (factor Xa generation test) in human VSMC. HMG-CoA reductase inhibition completely prevents agLDL-induced TF expression and partially inhibits agLDL-TF activation. These effects are reverted by geranylgeranyl pyrophosphate (GGPP) but not by farnesyl pyrophosphate (FPP), suggesting the involvement of a geranylated protein in agLDL-TF induction. AgLDL increases Rho A translocation (2-fold) from the cytoplasm to the cell membrane in control but not in simvastatin-treated VSMC. Exoenzyme C3, a specific Rho A inhibitor, completely prevents agLDL-induced TF overexpression and partially agLDL-TF activation. Blocking LRP1, the receptor of agLDL, with anti-LRP1 antibodies or inhibiting LRP1 expression by small interference RNA treatment (siRNA-LRP1) impairs agLDL-induced TF overexpression and activation.. These results demonstrate that TF induction by agLDL depends on LRP1 expression and requires Rho A translocation to the cellular membrane.

Topics: ADP Ribose Transferases; Antibodies, Monoclonal; Biological Transport; Blotting, Western; Botulinum Toxins; Cell Membrane; Cells, Cultured; Coronary Vessels; Cytoplasm; Humans; Hydroxymethylglutaryl-CoA Reductase Inhibitors; Immunohistochemistry; Lipoproteins, LDL; Low Density Lipoprotein Receptor-Related Protein-1; Muscle, Smooth, Vascular; Myocytes, Smooth Muscle; Polyisoprenyl Phosphates; rac1 GTP-Binding Protein; Reverse Transcriptase Polymerase Chain Reaction; rhoA GTP-Binding Protein; Sesquiterpenes; Simvastatin; Thromboplastin

3-hydroxyl-3-methyl coenzyme A reductase inhibitors (statins) can function to protect the vasculature in a manner that is independent of their lipid-lowering activity. The main feature of the antithrombotic properties of endothelial cells is an increase in the expression of thrombomodulin (TM) without induction of tissue factor (TF) expression. We investigated the effect of statins on the expression of TM and TF by endothelial cells.. The incubation of endothelial cells with pitavastatin led to a concentration- and time-dependent increase in cellular TM antigen and mRNA levels. In contrast, the expression of TF mRNA was not induced under the same conditions. A nuclear run-on study revealed that pitavastatin accelerates TM transcription rate. The stimulation of TM expression by pitavastatin was prevented by either mevalonate or geranylgeranylpyrophosphate. Specific inhibition of geranylgeranyltransferase-I and Rac/Cdc42 by GGTI-286 and Clostridium sordellii lethal toxin, respectively, enhanced TM expression, whereas inactivation of Rho by Clostridium botulinum C3 exoenzyme was ineffective.. Statins regulate TM expression via inhibition of small G proteins of the Rho family; Rac/Cdc42. A statin-mediated increase in TM expression by endothelial cells may contribute to the beneficial effects of statins on endothelial function.

Topics: Bacterial Proteins; Bacterial Toxins; Cells, Cultured; Endothelium, Vascular; Humans; Hydroxymethylglutaryl-CoA Reductase Inhibitors; Leucine; Mevalonic Acid; Monomeric GTP-Binding Proteins; Polyisoprenyl Phosphates; Quinolines; RNA, Messenger; Thrombomodulin; Thromboplastin; Umbilical Veins; Up-Regulation