Epidemiologic studies reported that the prevalence of hereditary non-polyposis colon cancer (HNPCC) in male is about 1.5-fold higher than that in female. Decreases in circulatory estrogen (E2) have been reported to downregulate the expression of E2 receptor (ER) and significantly increase the risk of colorectal cancer. Patients that received E2 replacement therapy were found to have a reduction in the incidence of colon adenoma and carcinoma. Furthermore, significant decreases in the expression of ER have been found in colorectal cancer specimens. Evidences strongly suggest the protective roles of E2 and ER against colorectal cancer. However, the mechanisms of ERα effects on colorectal cancer cells remained un-clear. LoVo cells were transient transfected to overexpress ERα, DNA fragmentation and the activated caspases measurements were performed to evaluate apoptotic effects. Western blotting was used to evaluate protein levels, and luciferase activity assay to measure the Htnf-a promoter activity. The results clearly demonstrated that overexpressed ERα with or without E2 (10-8 M) treatment could activate caspase -8, -9, and 3 and induce DNA fragmentation in LoVo cell. At the same time, overexpressed ERα plus E2 significantly increases the expression and promoter activity of hTNF-α and the DNA fragmentation effect induced by E2 plus ERα were reduced by the addition of hTNF antibody (0.1 ng(ml). In addition, E2 plus ERα significantly upregulated p21 and p27 levels and downregulated the β-catenin and its target genes, cyclin D1 and Rb, which regulate the cell cycle and cell proliferation. The results indicate that E2 plus overexpressed ERα induce LoVo cell apoptosis might mediate through the increase of hTNF-α gene expression, which in turn activate caspase-8, -9 and caspase-3 and lead to the DNA fragmentation and apoptosis. E2 plus ERα also showed the downregulation of β-catenin signalings implicating the suppression of proliferation and metastasis of colorectal cells. Efforts aiming at enhancing ERα expression and(or activity may be proved to be an alternative therapy against colorectal cancer.
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