Simvastatin modulates angiotensin II signaling pathway by preventing Rac1-mediated upregulation of p27

Recent experimental observations have suggested that statins may exert modulatory effects on a number of pathobiological processes beyond their cholesterol-lowering properties. Some of the pleiotropic effects of statins seem to be mediated by their ability to block the synthesis of isoprenoid intermediates, which serve as important lipid attachments required for the proper function and activation of the small GTP-binding proteins. The current study explored the modulatory effects of simvastatin (SMV) on the angiotensin II (Ang II)-induced Racl-mediated, upregulation of cyclin-dependent kinase inhibitor p27. Ang II (100 nM) stimulation of rat mesangial cells induced a significant increase in p27 protein expression. Co-treatment of cells with SMV (1 μM) inhibited Ang II-induced upregulation of p27 protein. Addition of mevalonate (200 μM) or geranylgeranyl pyrophosphate (5 μM) reversed the inhibitory effect of SMV on p27 protein expression, suggesting that the effect of SMV is geranylgeranyl dependent. This study also provides evidence for a sequential link between Ang II stimulation and downstream activation of Rac1, intracellular H₂O₂ production, and Akt kinase leading to upregulation of p27 protein in mesangial cells. It was also shown that SMV, by inhibiting Racl activity, reversed Ang II-induced increase in intracellular H₂O₂ production, Akt activation, and p27 protein expression. The data presented in this study not only elucidate Ang II-mediated signaling cascade in mesangial cells but also demonstrate for the first time the modulatory effects of SMV on Ang II-induced signaling pathway at the cell cycle level.