Low-density lipoprotein receptors play an important role in the inhibition of prostate cancer cell proliferation by statins

Abstract

Background: There are some reports about the antitumor effects of statins in these days. Statins decrease the level of cholesterol in the blood by inhibiting 3-hydroxy-3-methylglutaryl-coenzyme A reductase. Inhibition of this enzyme decreases intracellular cholesterol synthesis. Thus, the expression of low-density lipoprotein receptor (LDLr) is increased to import more cholesterol from the bloodstream. In this study, we assessed the effects of statins on the proliferation of prostate cancer cells, and studied the relationship between the expression of LDLr and the effects of statins.

Methods: Simvastatin was used in the experiments. We studied the effect of simvastatin on PC-3 and LNCaP cell proliferation using the MTS assay, and evaluated the expression of LDLr after administration of simvastatin by quantitative polymerase chain reaction and Western blotting. Intracellular cholesterol levels in the prostate cancer cells were measured after administration of simvastatin. Furthermore, small interfering RNA (siRNA) was used to knockdown the gene expression of LDLr.

Results: In PC-3 cells, simvastatin inhibited cell proliferation. In LNCaP cells, only a high concentration of simvastatin (100μM) inhibited cell proliferation. In LNCaP cells, the protein level of LDLr was increased by simvastatin. In PC-3 cells, the protein levels of LDLr were unregulated. In PC-3 cells, but not in LNCaP cells, intracellular cholesterol levels were significantly decreased by simvastatin. After knocking down LDLr expression by siRNA, intracellular cholesterol levels were decreased, and cell proliferation was inhibited by simvastatin in LNCaP cells.

Conclusion: Simvastatin inhibited prostate cancer cell growth by decreasing cellular cholesterol and could be more effective in androgen-independent prostate cancer, where there is loss of regulation of LDLr expression. LDLr was shown to play an important role in the statin-induced inhibition of prostate cancer cell proliferation. These results suggest that future studies evaluating the cholesterol-lowering effects of statin may lead to new approaches to the prevention and treatment of prostate cancer.

Keywords: Cholesterol; Low-density lipoprotein receptor; Prostate cancer; Statins.

Fig. 1

Effects of simvastatin on prostate cancer cell proliferations. (A, B) Cells were incubated with simvastatin-containing media. The inhibitor effects of simvastatin on cell proliferation were evaluated at 48 hours with MTS assay. Data are expressed as mean ± SD (n = 4). ^a)P < 0.01 versus simvastatin 0μM.

Fig. 2

Low-density lipoprotein receptor (LDLr) expression levels in prostate cancer cells after treatment with simvastatin. (A, B) Cells were incubated with simvastatin-containing media. RNA samples were extracted and assayed by quantitative real-time polymerase chain reaction. Data are expressed as means ± SD (n = 5). ^a)P < 0.01 versus 0μM. (C, D) Cells were incubated in simvastatin simvastatin-containing media for 48 hours and analyzed for LDLr protein levels by Western blotting. Beta-actin protein levels were used as the internal control. Sim, simvastatin.

Fig. 3

Total cholesterol mass after 72-hour treatment with various concentrations of simvastatin. (A, B) Data are expressed as means ± SD (n = 3). ^a)P < 0.01, versus 0μM.

Fig. 4

Effect of low-density lipoprotein receptor (LDLr) knockdown on LNCaP cells treated with simvastatin. (A) Transfection of LNCaP cells with LDLr small interfering RNA (siRNA) or negative siRNA was performed as described in the “Materials and Methods” section. After transfection, the cells were incubated for 48 hours before harvesting for Western blotting. Negative siRNA-transfected cells were used as controls. (B) After transfection, the cells were incubated with simvastatin-containing media. The total cholesterol mass was evaluated after 72 hours of treatment with various concentrations of simvastatin. Values are expressed as the means ± SD (n = 3). ^a)P < 0.01, vs. 0μM. (C) After transfection, the cells were incubated with simvastatin-containing media. The number of viable cells was evaluated using MTS assay after 48 hours of treatment with various concentrations of simvastatin. Values are expressed as means ± SD (n = 3). ^a)P < 0.05 versus 0μM. ^b)P < 0.01 versus 0μM.