Abstract A68: The role of estrogen-responsive finger protein (Efp) and 14-3-3 sigma (σ) in breast carcinogenesis and their prognostic implication

Abstract

Abstract Background: 14-3-3 sigma (σ) is a negative regulator of the cell cycle and contributes to G2/M arrest. In many malignant tumors, the 14-3-3 σ is considered to be an important tumor suppressor of which the decreased expression has been reported. The level of the 14-3-3 σ was reported to be decreased either by hypermethylation at its promoter site or ubiquitin-mediated proteolysis by the estrogen-responsive ring finger protein (Efp). In this study, we tried to investigate which mechanism plays more important role in the 14-3-3 σ regulation, how the change of the 14-3-3 σ expression affect the biology of human breast cancer, and hence to extend our understanding of the role of the 14-3-3 σ in human breast cancer. Materials and Methods: In order to examine the role of ubiquitin-associated proteolysis by the Efp, we examined the change of the level of 14-3-3 σ protein after Efp silencing using siRNA in MCF-7 breast cancer cell line. We also examined the Efp and 14-3-3 σ expression in 220 human breast carcinoma tissues by immunohistochemistry. To investigate the role of methylation in regulation of 14-3-3 σ, we examined the methylation status of 14-3-3 σ promoter in human breast carcinoma tissue by methylation-specific polymerase chain reaction. Other clinicopathological variables were also evaluated together with the follow-up data to assess the prognostic significance of those two molecules. Results: Silencing of the Efp with siRNA in a MCF-7 breast cancer cell line resulted in increased expression of the 14-3-3 σ. Expression of the Efp and 14-3-3 σ in human breast cancer tissue was not very common with 19.8% and 20.7% of the total cases being positive, respectively. The Efp-positive cases were more frequently 14-3-3 sigma-negative. Hypermethylation of the 14-3-3 σ was common in breast cancer (64.9%) and had a tendency of negative association with the 14-3-3 σ positivity. The Efp expression was negatively associated with axillary lymph node metastasis (p=0.021) or positive p53 status (p=0.009). The 14-3-3 σ expression was positively associated with increasing histologic and nuclear grade (p=0.012 and p=0.033), and positive p53 (p=0.001). The 14-3-3 σ was negatively correlated with ER or PR expression (p=0.020 and p=0.032) and hypermethylation (p=0.072). Positive 14-3-3 σ expression was significantly correlated with poor prognosis. A multivariate analyses of disease-free survival (p=0.008) and disease-specific survival (p=0.009) showed that the 14-3-3 σ was a independent prognostic marker. Conclusion: Our data clearly demonstrated that 14-3-3 σ expression was negatively correlated with Efp expression in vitro and excised breast cancer tissues demonstrated similar tendency. 14-3-3 σ was also negatively correlated with hypermethylation in human breast cancer tissue. These results suggest that 14-3-3 σ may be regulated by both mechanisms i.e. ubiquitin-mediated proteolysis by Efp and down-regulation by hypermethylation in human breast cancers. Interestingly, 14-3-3 σ turned out to be a significant poor prognostic indicator in breast cancer, suggesting a hither to unrecognized role of 14-3-3 σ in breast cancer in addition to a well established role as tumor suppressor. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):A68.