Simvastatin inhibits T‐cell activation by selectively impairing the function of Ras superfamily GTPases

Abstract

Statins are widely used hypocholesterolemic drugs that inhibit 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase, a rate-limiting enzyme of the mevalonate pathway whose biosynthetic end product is cholesterol. In addition to lowering circulating cholesterol, statins perturb the composition of cell membranes, resulting in disruption of lipid rafts, which function as signaling platforms in immunoreceptor signaling. Furthermore, by inhibiting protein prenylation, a process also dependent on mevalonate, statins block membrane targeting and hence activity of small GTPases, which control multiple pathways triggered by these receptors. T-cell activation is crucially dependent on Ras, Rho and Rab GTPases. Furthermore TCR signaling is orchestrated at lipid rafts, identifying T-cells as potential cellular targets of statins. Here we report that simvastatin suppresses T-cell activation and proliferation as the result of its capacity to inhibit HMG-CoA reductase. T-cell treatment with simvastatin does not affect intracellular cholesterol levels or raft integrity nor, accordingly, the initial tyrosine phosphorylation-dependent cascade. Conversely, inhibition of protein prenylation by simvastatin results in a dramatic impairment in the pathways regulated by small GTPases, including the Ras/MAP kinase pathway, the Rac/stress kinase pathway, and the Rab-dependent pathway of receptor endocytosis. The results identify Ras superfamily GTPases as strategic molecular targets in T-cell immunosuppression by statins.

A chemical biology screen reveals a role for Rab21-mediated control of actomyosin contractility in fibroblast-driven cancer invasion

“…This finding is striking because geranylgeranyl-pyrophosphate is not an intermediate between HMG-CoA reductase and cholesterol synthesis but is largely used to modify small G proteins and enable their interaction with cellular membranes. Furthermore, previous reports have documented defects in small G-protein targeting after statin treatment (Laezza et al, 1998;Kusama et al, 2001;Holstein et al, 2002;Ghittoni et al, 2005;Walker and Olson, 2005). In agreement with these findings, simvastatin and lovastatin both affected the subcellular localisation of a range of small G proteins in CAFs ( Figure 3A and B).…”

Inhibition of 3-Hydroxy-3-Methylglutaryl Coenzyme A (HMG CoA) Reductase Blunts Factor VIIa/Tissue Factor and Prothrombinase Activities via Effects on Membrane Phosphatidylserine

“…Other studies have used short-term exposure of cells to cytotoxic concentrations of statins (2 to 100 mol/L). [35][36][37] Conclusions from these studies are limited by undefined effects on cell viability. Our conditions used concentrations of statins that would realistically be achieved in the circulation, but on the other hand used serum containing far less cholesterol than is found in human serum.…”

p66SHC promotes T cell apoptosis by inducing mitochondrial dysfunction and impaired Ca2+ homeostasis

“…38 Post-mitochondrial supernatants were obtained by cell fractionation using a modification of the protocol described by Liang et al 39 Briefly, 30 Â 10 6 cells/sample were washed twice with PBS, resuspended in 450 ml buffer A (20 mM Hepes pH 7.0, 10 mM KCl, 1.5 mM MgCl 2 , 1 mM EDTA, 1 mM EGTA, 1 mM DTT, 0.1 mM PMSF, 250 mM sucrose), incubated 10 min on ice and broken in a Dounce homogenizer (25 strokes). The homogenate was centrifuged at 41C for 10 min at 600 Â g, and the supernatant was subjected to a second centrifugation at 41C for 10 min at 700 Â g. The latter supernatant was then centrifuged at 41C for 10 min at 7000 Â g. The pellet, enriched in mitochondria, was discarded, whereas the post-mitochondrial supernatant was used for immunoblot analysis of cytochrome c release.…”