BRCA1 overexpression sensitizes cancer cells to lovastatin via regulation of cyclin D1-CDK4-p21WAF1/CIP1 pathway: analyses using a breast cancer cell line and tumoral xenograft model.

It is well established that statins display potent anticancer activity in several types of proliferating tumor cells. However, how to promote the sensitivity of statins to mammary cancer is yet to be completely deciphered. The purpose of this study was to investigate whether breast cancer susceptibility gene 1 (BRCA1) overexpression sensitizes mammary cancer cells to statins. MCF-7 cells, which have only one wild-type BRCA1 allele, were transfected with pcDNA3-beta-HA-hsBRCA1 plasmids via liposomes to reconstitute BRCA1 overexpression human breast cancer cell line, and tumoral xenografts with BRCA1 overexpression were subsequently established in BALB/c nude mice. Then, the inhibitory activity of lovastatin on cancer cells and tumoral xenografts, and the underlying mechanism involving in cell-cycle regulatory proteins were analyzed. The proliferative ability of MCF-7 cells treated with lovastatin was reduced compared to normal, and further decreased in the presence of excess BRCA1, detected by methyl thiazolyl tetrazolium and flow cytometry techniques in vitro or by 5-bromodeoxyuridine incorporation in vivo. Additionally, the mRNA and protein expression of cyclin D1, cyclin-dependent kinase 4 (CDK4) and retinoblastoma protein (pRb), was further down-regulated under exposure to lovastatin in condition of BRCA1 overexpression, but the expression of p21WAF1/CIP1, a cyclin-dependent kinase inhibitor (CDKI), was further up-regulated, both in vitro and in vivo detected with quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot analysis. Moreover, we found the further reduced volume of tumoral xenografts treated with lovastatin in the presence of BRCA1 overexpression. Our results suggest that BRCA1 overexpression sensitizes cancer cells to lovastatin via regulation of cyclin D1-CDK4-p21WAF1/CIP1 pathway, which will provide an innovative experimental framework to study control of breast cancer cell proliferation.

[Effects of lovastatin on cell cycle distribution in MCF-7 cells transfected with BRCA1].

BACKGROUND & OBJECTIVE: The breast and ovarian cancer susceptibility gene BRCA1 acts as a tumor suppressor gene, its product expresses in a cell cycle-dependent manner. Inheritance of a mutant allele of BRCA1 leads to increased risk of developing breast,and ovarian cancers. Lovastatin, as a potent inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-CoA reductase),is the main rate-limiting enzyme of endogenous cholesterol biosynthesis pathway. This study was to evaluate the effect and mechanism of combined application of BRCA1 and lovastatin on cell cycle distribution of MCF-7 cells. METHODS: MCF-7 cells were transfected with expression vector pcDNA3-beta-HA-hsBRCA1 containing full-length BRCA1, and named MCF-7BRCA1 cells. The expression of BRCA1 gene was examined with reverse transcription polymerase chain reaction (RT-PCR) and Western blot analysis. After cultured with 8 micromol/L lovastatin, growth curve and MTT assay were used to determine cell proliferation capacity; the cell cycle distribution was measured with flow cytometry (FCM). Meanwhile,the protein expression of Cyclin D1 and retinoblastoma (Rb) were analyzed by Western blot analysis. RESULTS: The pcDNA3-beta-HA-hsBRCA1 plasmids were successfully transfected into MCF-7 cells and expressed stably. The growth curve and MTT assay results showed that cell proliferation capacity decreased in the cells cultured with lovastatin for 4 days. FCM showed that S phase, and G2/M phase of BRCA1-infected cells decreased,while G0/G1 phase increased after cultured with lovastatin, the cells were blocked in G0/G1 phase at 72 h post-treatment by lovastatin. Ectopic expression of BRCA1 leads to decrease of the Rb protein and Cyclin D1 protein. Overall data showed that the effects of Lovastatin were more obviously in MCF-7BRCA1 cells than MCF-7 cells. CONCLUSIONS: Overexpression of BRCA1 protein may amplify sensibility of breast cancer to lovastatin,and enhance the anti-tumor effect of lovastatin.