Simvastatin Potentiates TNF-α-Induced Apoptosis through the Down-Regulation of NF-κB-Dependent Antiapoptotic Gene Products: Role of IκBα Kinase and TGF-β-Activated Kinase-1

Abstract

Numerous recent reports suggest that statins (hydroxy-3-methylglutaryl-CoA reductase inhibitors) exhibit potential to suppress tumorigenesis through a mechanism that is not fully understood. Therefore, in this article, we investigated the effects of simvastatin on TNF-α-induced cell signaling. We found that simvastatin potentiated the apoptosis induced by TNF-α as indicated by intracellular esterase activity, caspase activation, TUNEL, and annexin V staining. This effect of simvastatin correlated with down-regulation of various gene products that mediate cell proliferation (cyclin D1 and cyclooxygenase-2), cell survival (Bcl-2, Bcl-xL, cellular FLIP, inhibitor of apoptosis protein 1, inhibitor of apoptosis protein 2, and survivin), invasion (matrix mellatoproteinase-9 and ICAM-1), and angiogenesis (vascular endothelial growth factor); all known to be regulated by the NF-κB. We found that simvastatin inhibited TNF-α-induced NF-κB activation, and l-mevalonate reversed the suppressive effect, indicating the role of hydroxy-3-methylglutaryl-CoA reductase. Simvastatin suppressed not only the inducible but also the constitutive NF-κB activation. Simvastatin inhibited TNF-α-induced IκBα kinase activation, which led to inhibition of IκBα phosphorylation and degradation, suppression of p65 phosphorylation, and translocation to the nucleus. NF-κB-dependent reporter gene expression induced by TNF-α, TNFR1, TNFR-associated death domain protein, TNFR-associated factor 2, TGF-β-activated kinase 1, receptor-interacting protein, NF-κB-inducing kinase, and IκB kinase β was abolished by simvastatin. Overall, our results provide novel insight into the role of simvastatin in potentially preventing and treating cancer through modulation of IκB kinase and NF-κB-regulated gene products.