farnesyl-pyrophosphate and Colonic-Neoplasms

3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (HRIs) are widely used to reduce serum cholesterol in patients with hypercholesterolemia. Previous studies have shown that HRIs can induce apoptosis in colon cancer cells. In this study, we investigated the mechanisms underlying the apoptosis-inducing effect of HRIs in greater detail. The HRI lovastatin induced apoptosis in the human colon cancer cell line SW480 by blocking the cholesterol synthesis pathway. Immunoblot analysis of antiapoptotic molecules, including survivin, XIAP, cIAP-1, cIAP-2, Bcl-2, and Bcl-X(L), revealed that only survivin expression was decreased by lovastatin. Survivin down-regulation by RNA interference induced apoptosis, and survivin overexpression rendered the cells resistant to lovastatin-induced growth inhibition. These results indicate that survivin down-regulation contributes substantially to the proapoptotic properties of lovastatin. Farnesyl pyrophosphate and geranylgeranyl pyrophosphate, two downstream intermediates in the cholesterol synthesis pathway, simultaneously reversed survivin down-regulation and the blocking of Ras isoprenylation by lovastatin. Ras isoprenylation is important for the activation of Ras-mediated signaling, including the activation of the phosphatidylinositol 3-kinase (PI3-kinase)/Akt pathway. The PI3-kinase inhibitor down-regulated survivin in SW480 cells. In addition, lovastatin blocked Ras activation and Akt phosphorylation. We conclude that survivin down-regulation is crucial in lovastatin-induced apoptosis in cancer cells and that lovastatin decreases survivin expression by inhibiting Ras-mediated PI3-kinase activation via the blocking of Ras isoprenylation.

Topics: Apoptosis; Apoptosis Regulatory Proteins; Cell Line, Tumor; Cholesterol; Colonic Neoplasms; Diterpenes; Down-Regulation; Humans; Hydroxymethylglutaryl-CoA Reductase Inhibitors; Hydroxymethylglutaryl-CoA-Reductases, NADP-dependent; Hypercholesterolemia; Inhibitor of Apoptosis Proteins; Lovastatin; Microtubule-Associated Proteins; Neoplasm Proteins; Phosphorylation; Polyisoprenyl Phosphates; Protein Prenylation; RNA Interference; Sesquiterpenes; Signal Transduction; Survivin

Beta-hydroxy-beta-methylglutaryl coA reductase inhibitors (HRIs) inhibit isoprenylation of several members of the Ras superfamily of proteins and therefore have important cellular effects, including the reduction of proliferation and increasing apoptosis. Significant toxicity at high doses has precluded the use of HRIs as a monotherapy for cancers. We therefore studied whether combinations of the HRI lovastatin with standard chemotherapeutic agents would augment apoptosis in colon cancer cells. In the colon cancer cell lines SW480, HCT116, LoVo, and HT29, lovastatin induced apoptosis with differing sensitivity. Pretreatment with lovastatin significantly increased apoptosis induced by 5-fluorouracil (5-FU) or cisplatin in all four cell lines. Lovastatin treatment resulted in decreased expression of the antiapoptotic protein bcl-2 and increased the expression of the proapoptotic protein bax. The addition of geranylgeranylpyrophospate (10 microM) prevented lovastatin-induced augmentation of 5-FU and cisplatin-induced apoptosis; mevalonate (100 microM) was partially effective, whereas cotreatment with farnesyl pyrophosphate (100 microM) had no effect. These data imply that lovastatin acts by inhibiting geranylgeranylation and not farnesylation of target protein(s). Our data suggest that lovastatin may potentially be combined with 5-FU or cisplatin as chemotherapy for colon cancers.

Topics: Antineoplastic Agents; Apoptosis; bcl-2-Associated X Protein; Cell Division; Cisplatin; Colonic Neoplasms; Dose-Response Relationship, Drug; Drug Therapy, Combination; Flow Cytometry; Fluorouracil; Humans; Hydroxymethylglutaryl-CoA Reductase Inhibitors; In Situ Nick-End Labeling; Lovastatin; Mevalonic Acid; Microscopy, Electron; Polyisoprenyl Phosphates; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-bcl-2; Sesquiterpenes; Tumor Cells, Cultured