Therapeutic Levels of the Hydroxmethylglutaryl-Coenzyme A Reductase Inhibitor Lovastatin Activate Ras Signaling via Phospholipase D2

Abstract

Hydroxmethylglutaryl (HMG)-coenzyme A (CoA) reductase inhibitors (statins) lower serum cholesterol but exhibit pleiotropic biological effects that are difficult to ascribe solely to cholesterol depletion. Here, we investigated the effect of lovastatin on protein prenylation and cell signaling. We show that high concentrations (50 M) of lovastatin inhibit Ras, Rho, and Rap prenylation but that therapeutic levels of lovastatin (50 nM to 500 nM) do not. In contrast, depletion of cellular cholesterol by therapeutic levels of lovastatin increased Ras GTP loading and mitogen-activated protein kinase (MAPK) activation in human umbilical vein endothelial cells and rodent fibroblasts. Elevated Ras signaling was not seen in statin-treated cells if cholesterol levels were maintained by supplementation. Activation of Ras-MAPK signaling was a consequence of, and dependent on, activation of phospholipase D2 (PLD2). Expression of dominant interfering PLD2 or biochemical inhibition of PLD2 abrogated Ras and MAPK activation induced by lovastatin. In contrast, ectopic expression of wild-type PLD2 enhanced Ras and MAPK activation in response to therapeutic levels of lovastatin. Statin-induced cholesterol depletion also modestly activated the epidermal growth factor receptor (EGFR), resulting in downregulation of EGFR expression. These results suggest that statins modulate key cell signaling pathways as a direct consequence of cholesterol depletion and identify the EGFR-PLD2-Ras-MAPK axis as an important statin target.Hydroxmethylglutaryl (HMG)-coenzyme A (CoA) reductase inhibitors (statins) are widely used for the treatment of hypercholesterolemia (39). These drugs block the conversion of HMG-CoA to mevalonate, a rate-limiting step in the cholesterol biosynthesis pathway (15). In addition to the cholesterol-lowering effect, there is extensive evidence for additional clinical effects. Statins improve endothelial function, promote vascular relaxation, and inhibit platelet aggregation in part by driving increased synthesis of nitric oxide (NO) (36). Statins therefore correct the reduced synthesis, release, and activity of endothelium-derived NO observed in hypercholesterolemic patients (39). Statins also promote atherosclerotic plaque stability (58), have anti-inflammatory effects (3, 60), and are associated with a reduced risk of Alzheimer's disease (39). Nevertheless, it has been difficult to mechanistically link many of these beneficial clinical effects directly to reduced cellular and serum cholesterol levels.One class of signaling molecules that has been identified as putative cholesterol-independent targets of statin action are prenylated small GTPases (16,17,39,42). Ras and Rho GTPases act as molecular switches to regulate cell proliferation, differentiation, apoptosis, and cytoskeletal reorganization (26, 31). The biological activity of these GTPases requires farnesylation or geranylgeranylation of C-terminal CAAX motifs (where C is Cys, A is aliphatic amino acid, and X is Ser or Met in Ras or Leu in Rho) (27). High concentra...

A Review of Statin Use and Prostate Cancer

“…It has been demonstrated that radiation therapy can increase inflammation during therapy [45,46], but it is not clear if these effects may lead to increased risk of recurrence. Future research needs to be done on the mechanistic effects of statins as anticancer agents; however, studies should be performed using concentrations more likely to be seen in vivo to give them a more sound basis [15,17]. Perhaps, another research angle would be to discover a way to deliver in vitro concentrations of statins to the cancer site safely and effectively [47].…”

“…One study demonstrated that a 40-or 80-mg dose of lovastatin led to a serum concentration of about 50 nM 6 h later [16]. However, most studies that demonstrate statin-mediated inhibitions in Ras protein isoprenylation use statin concentrations that are significantly higher [15]. Therefore, it remains to be seen if these promising effects in vitro will be realized in vivo.…”

“…Therefore, it remains to be seen if these promising effects in vitro will be realized in vivo. In fact, one study using more physiologic concentrations of lovastatin (50-500 nM) demonstrated an increase in Ras signaling [15]. More research needs to be performed in this area to better elucidate the relationship between the effects of statins on Ras function.…”

“…However, one criticism of this mechanism is that the concentrations of statins used in in vitro studies are much higher than one would see in the bloodstream with usual doses of statin therapy [15]. One study demonstrated that a 40-or 80-mg dose of lovastatin led to a serum concentration of about 50 nM 6 h later [16].…”

Synergistic Effect of Simvastatin Plus Radiation in Gastric Cancer and Colorectal Cancer: Implications of BIRC5 and Connective Tissue Growth Factor

“…There is a report that high concentrations (50 mM) of lovastatin inhibit the Ras signaling pathway (4). These antiproliferative and pro-apoptotic properties suggest that statins could also inhibit carcinogenesis, thereby impacting cancer outcomes (5).…”