The Role and Regulatory Mechanism of 14-3-3 Sigma in Human Breast Cancer / 한국유방암학회지

ABSTRACT

PURPOSE: 14-3-3 sigma (sigma) is considered to be an important tumor suppressor and decreased expression of the same has been reported in many malignant tumors by hypermethylation at its promoter or ubiquitin-mediated proteolysis by estrogen-responsive ring finger protein (Efp). In this study, we investigated the significance of 14-3-3 sigma expression in human breast cancer and its regulatory mechanism. METHODS: Efp was silenced using small interfering RNA (siRNA) in the MCF-7 breast cancer cell line in order to examine its influence on the level of 14-3-3 sigma protein. The methylation status of the 14-3-3 sigma promoter was also evaluated by methylation-specific polymerase chain reaction (PCR). The expression of Efp and 14-3-3 sigma in 220 human breast carcinoma tissues was assessed by immunohistochemistry. Other clinicopathological parameters were also evaluated. RESULTS: Silencing Efp in the MCF-7 breast cancer cell line resulted in increased expression of 14-3-3 sigma. The Efp-positive human breast cancers were more frequently 14-3-3 sigma-negative (60.5% vs. 39.5%). Hypermethylation of 14-3-3 sigma was common (64.9%) and had an inverse association with 14-3-3 sigma positivity (p=0.072). Positive 14-3-3 sigma expression was significantly correlated with poor prognosis disease-free survival (p=0.008) and disease-specific survival (p=0.009). CONCLUSION: Our data suggests that in human breast cancer, the regulation of 14-3-3 sigma may involve two mechanisms ubiquitin-mediated proteolysis by Efp and downregulation by hypermethylation. However, the inactivation of 14-3-3 sigma is probably achieved mainly by hypermethylation. Interestingly, 14-3-3 sigma turned out to be a very significant poor prognostic indicator, which is in contrast to its previously known function as a tumor suppressor, suggesting a different role of 14-3-3 sigma in breast cancer.