This study investigates the mechanism by which 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase inhibitors, such as mevastatin, increase endothelial nitric oxide synthase (eNOS) expression. The authors found that mevastatin treatment increased eNOS mRNA and protein levels in human endothelial cells. Co-treatment with geranylgeranylpyrophosphate (GGPP), but not farnesylpyrophosphate (FPP) or low-density lipoprotein (LDL), reversed these effects. Further investigation revealed that mevastatin inhibited Rho GTPase membrane translocation and GTP binding activity, which were reversed by GGPP. Inhibition of Rho by Clostridium botulinum C3 transferase or overexpression of a dominant-negative RhoA mutant increased eNOS expression, while activation of Rho by Escherichia coli cytotoxic necrotizing factor-1 decreased eNOS expression. These findings suggest that Rho negatively regulates eNOS expression and that HMG-CoA reductase inhibitors up-regulate eNOS expression by blocking Rho geranylgeranylation, which is necessary for its membrane-associated activity. The study also highlights the potential therapeutic benefits of selectively inhibiting endothelial Rho activity in cardiovascular diseases.This study investigates the mechanism by which 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase inhibitors, such as mevastatin, increase endothelial nitric oxide synthase (eNOS) expression. The authors found that mevastatin treatment increased eNOS mRNA and protein levels in human endothelial cells. Co-treatment with geranylgeranylpyrophosphate (GGPP), but not farnesylpyrophosphate (FPP) or low-density lipoprotein (LDL), reversed these effects. Further investigation revealed that mevastatin inhibited Rho GTPase membrane translocation and GTP binding activity, which were reversed by GGPP. Inhibition of Rho by Clostridium botulinum C3 transferase or overexpression of a dominant-negative RhoA mutant increased eNOS expression, while activation of Rho by Escherichia coli cytotoxic necrotizing factor-1 decreased eNOS expression. These findings suggest that Rho negatively regulates eNOS expression and that HMG-CoA reductase inhibitors up-regulate eNOS expression by blocking Rho geranylgeranylation, which is necessary for its membrane-associated activity. The study also highlights the potential therapeutic benefits of selectively inhibiting endothelial Rho activity in cardiovascular diseases.