Phosphorylation of Estrogen Receptor β at Serine 105 in Primary Breast Cancer

Background: Estrogen receptor (ER) α predicts response to hormonal therapy in breast carcinoma. The role of ERβ is less well understood. ER activities can be modulated by post-translational modifications including phosphorylation and phosphorylated ERα has been correlated with patient outcome. We investigated whether ERβ phosphorylated at Serine 105 (P-S105-ERβ) is expressed in breast carcinoma and assessed its potential clinical implications.Material and Methods: Tissue microarrays comprising 427 breast tumours (23% grade 1, 43% grade 2, 34% grade 3) with median follow up 118 months and 106 endocrine resistant breast tumours (15% grade 1, 41% grade 2, 44% grade 3) with median follow up 71 months were used in this study. Expression of P-S105-ERβ was studied by immunohistochemistry and analysed against clinical data. Regulation of P-S105-ERβ in vitro was assessed by immunofluorescence and Western blotting.Results: Expression of P-S105-ERβ was mainly nuclear and could be abolished by phosphatase pre-incubation, indicating specificity. In the first cohort Allred scoring ranged from 0 to 8 (median 6). Nuclear speckling was observed in 45% of cases. P-S105-ERβ correlated with ERβ1 (Allred score ≥ 3) and was associated with better overall survival (OS) and disease free survival (DFS) (p=0.028 and p=0.027, respectively). In a multivariate Cox hazard analysis, P-S105-ERβ overexpression was a significant predictor of better survival independent of tumor grade, lymph node status, size or ERα. In the endocrine resistant cohort Allred scoring ranged from 0 to 8 (median of 4) and the overexpression of P-S105-ERβ was also associated with improved OS and DFS (p=0.044 and p=0.033, respectively). Nuclear speckling was present in only 11% of cases. The difference in expression of P-S105-ERβ and association with survival outcome between the two cohorts was statistically significant. P-S105-ERβ was expressed in MCF-7 cells and in response to 17β-estradiol (E2); levels were raised within 30 min, and sustained for 24 hours. ERβ1 expression was unaffected by this treatment. Nuclear speckling was also observed and was markedly increased at 24 hours following E2 but not Tamoxifen.Conclusion: This is the first time to our knowledge that the expression of P-S105-ERβ in breast carcinoma has been investigated. Its presence in breast carcinoma and association with improved survival suggest P-S105-ERβ might be a useful additional prognostic marker in breast cancer.

Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 4141.

Yes-associated protein (YAP) functions as a tumor suppressor in breast

Yes-associated protein (YAP) has been shown to positively regulate p53 family members and to be negatively regulated by the AKT proto-oncogene product in promoting apoptosis. On the basis of this function and its location at 11q22.2, a site of frequent loss of heterozygosity (LOH) in breast cancer, we investigated whether YAP is a tumor suppressor in breast. Examination of tumors by immunohistochemistry demonstrated significant loss of YAP protein. LOH analysis revealed that protein loss correlates with specific deletion of the YAP gene locus. Functionally, short hairpin RNA knockdown of YAP in breast cell lines suppressed anoikis, increased migration and invasiveness, inhibited the response to taxol and enhanced tumor growth in nude mice. This is the first report indicating YAP as a tumor suppressor, revealing its decreased expression in breast cancer as well as demonstrating the functional implications of YAP loss in several aspects of cancer signaling.