#3032 The p160 coactivators AIB1 and SRC-1 are known to play a critical role in modulating transcription in breast cancer cells in conjunction with ligand-bound estrogen receptor. The interactions of the p160 proteins with this nuclear receptor are also important in the development of resistance to endocrine treatments. Using quantitative coassociation immunofluorescent microscopy, the colocalisation of the p160s and ERα was increased in the LY2 endocrine resistant cell line following treatment with the anti-estrogen tamoxifen in comparison to the endocrine sensitive MCF-7 cell line. In cell cultures derived from patient tumours at the time of primary surgery prior to treatment, there was an increase in association of the coactivators with ERα following treatment with estrogen but dissociation was evident in the presence of tamoxifen. Immunohistochemical staining of a tissue microarray, constructed from 560 breast cancer patients, revealed that SRC-1 was a strong predictor of reduced disease-free survival, both in patients receiving adjuvant tamoxifen treatment and untreated patients (p<0.0001 and p=0.0111 respectively). AIB1 was not a significant independent predictor of disease recurrence. SRC-1 was assigned a hazard ratio of 2.12 when survival analysis using a Cox proportional hazards model was applied. Quantitative coassociation analysis of the p160 coactivators with ERα in the patient TMA revealed significantly stronger colocalisation of SRC-1 and ERα in patients who are known to have relapsed than those patients who did not recur (p=0.00001). This data suggests SRC-1 is pivotal in tumour aggressiveness and is a powerful predictor of progression of disease in breast cancer patients. Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 3032.

#2056 The invasive potential of cancer cells is mediated in part through the action of matrix metalloproteinases (MMP), which degrade the extra-cellular membrane and promote metastasis. The transcription regulatory region of MMP genes contains binding sites for Ets transcription factors. While the underlying mechanism of MMP regulation is unclear, the Ets transcription factor PEA3 has been shown to be involved. We have previously reported that expression of PEA-3 is associated with the co-activator AIB-1, HER2 positivity, metastasis, and reduced disease free survival. Furthermore, an AIB-1 knockout mouse exhibited PEA-3 dependant MMP production, resulting in reduced metastatic potential. In this study we combined translational and molecular approaches to study the role of PEA-3 and AIB-1 in the transcriptional regulation of MMPs in breast cancer.
 The expression of PEA-3, AIB-1, and MMP-9 was assessed in a tissue microarray of breast cancer patients (n=560). Strong associations were observed between both PEA-3, AIB-1, and their target gene MMP-9 (p= 0.007, p= 0.0016 respectively). In HER2 positive patients PEA-3, but not AIB-1 or MMP-9, was associated with reduced disease free survival (p<0.0044, p= 0.4491, and p= 0.0666 respectively). A stable breast cancer cell line over-expressing PEA-3 was created. Upregulation of the growth factor pathway in this cell line resulted in the increased expression of MMP-9. Furthermore, silencing AIB-1 resulted in reduced MMP-9 production in breast cancer cells in vitro.
 Ets transcription factors are important mediators of breast tumour invasion. This data supports a role for the transcription factor PEA-3 and its co-activator AIB-1 in the production of MMPs in breast cancer. Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 2056.