Purpose:This study investigates the role of the p160 coactivators AIB1and SRC-1independently, and their interactions with the estrogen receptor, in the development of resistance to endocrine treatments. Experimental Design: The expression of the p160s and the estrogen receptor, and their interactions, was analyzed by immunohistochemistry and quantitative coassociation immunofluorescent microscopy, using cell lines, primary breast tumor cell cultures, and a tissue microarray with breast cancer samples from 560 patients. Results: Coassociation of the p160s and estrogen receptor a was increased in the LY2 endocrine-resistant cell line following treatment with tamoxifen in comparison with endocrinesensitive MCF-7 cells. In primary cultures, there was an increase in association of the coactivators with estrogen receptor a following estrogen treatment but dissociation was evident with tamoxifen. Immunohistochemical staining of the tissue microarray revealed that SRC-1 was a strong predictor of reduced disease-free survival (DFS), both in patients receiving adjuvant tamoxifen treatment and untreated patients (P < 0.0001 and P = 0.0111, respectively). SRC-1 was assigned a hazard ratio of 2.12 using a Cox proportional hazards model. Endocrine-treated patients who coexpressed AIB1with human epidermal growth factor receptor 2 had a significantly shorter DFS compared with all other patients (P = 0.03). Quantitative coassociation analysis in the patient tissue microarray revealed significantly stronger colocalization of AIB1and SRC-1with estrogen receptor a in patients who have relapsed in comparison with those patients who did not recur (P = 0.026 and P = 0.00001, respectively). Conclusions: SRC-1is a strong independent predictor of reduced DFS, whereas the interactions of the p160 proteins with estrogen receptor a can predict the response of patients to endocrine treatment.Adjuvant endocrine therapy offers substantial benefit in terms of reduction in risk of tumor recurrence in women with estrogen receptor -positive tumors. However, although most patients initially respond to tamoxifen, in 30% to 40% of cases these tumors recur within 5 years. This precipitates cessation of the regime and the initiation of second-line therapy. However, despite new targeted treatments for breast cancer, the vast majority of patients still depend on endocrine manipulation for management of their breast cancer.The magnitude of estrogen receptor gene regulation is influenced not only by the ligand but also by the presence of specific coregulatory proteins, present at rate-limiting levels, which modulate transcription. Over the past 10 years a number of nuclear receptor -interacting proteins have been isolated using various screening strategies. These include the p160 family coactivator proteins -steroid receptor coactivator-1 (SRC-1/NCoA-1), SRC-2 (TIF2/GRIP1), and SRC-3 (AIB1/ pCIP/RAC3/ACTR). The coactivator proteins drive nuclear receptor transcriptional activity by doing the significant reactions required for control of enhancer-d...

In breast cancer (BrCa), overexpression of the nuclear co-activator NCOA1 (SRC-1) is associated with disease recurrence and resistance to endocrine therapy. To examine the impact of NCOA1 overexpression on morphogenesis and carcinogenesis in the mammary gland (MG), we generated MMTV-hNCOA1 transgenic [Tg(NCOA1)] mice. In the context of two distinct transgenic models of breast cancer, NCOA1 overexpression did not affect the morphology or tumor forming capability of MG epithelial cells. However, NCOA1 overexpression increased the number of circulating BrCa cells and the efficiency of lung metastasis. Mechanistic investigations showed that NCOA1 and c-Fos were recruited to a functional AP-1 site in the macrophage attractant CSF1 promoter, directly upregulating CSF1 expression to enhance macrophage recruitment and metastasis. Conversely, silencing NCOA1 reduced CSF1 expression and decreased macrophage recruitment and BrCa cell metastasis. In a cohort of 453 human breast tumors, NCOA1 and CSF1 levels correlated positively with disease recurrence, higher tumor grade and poor prognosis. Together, our results define an NCOA1/AP-1/CSF1 regulatory axis that promotes BrCa metastasis, offering a novel therapeutic target for impeding this process.

The molecular events and transcriptional plasticity driving brain metastasis in clinically relevant breast tumor subtypes has not been determined. Here we comprehensively dissect genomic, transcriptomic and clinical data in patient-matched longitudinal tumor samples, and unravel distinct transcriptional programs enriched in brain metastasis. We report on subtype specific hub genes and functional processes, central to disease-affected networks in brain metastasis. Importantly, in luminal brain metastases we identify homologous recombination deficiency operative in transcriptomic and genomic data with recurrent breast mutational signatures A, F and K, associated with mismatch repair defects, TP53 mutations and homologous recombination deficiency (HRD) respectively. Utilizing PARP inhibition in patient-derived brain metastatic tumor explants we functionally validate HRD as a key vulnerability. Here, we demonstrate a functionally relevant HRD evident at genomic and transcriptomic levels pointing to genomic instability in breast cancer brain metastasis which is of potential translational significance.

Purpose: The use of aromatase inhibitors (AI) in the treatment of estrogen receptor (ER)-positive, postmenopausal breast cancer has proven efficacy. However, inappropriate activation of ER target genes has been implicated in the development of resistant tumors. The ER coactivator protein AIB1 has previously been associated with initiation of breast cancer and resistance to endocrine therapy.Experimental Design: Here, we investigated the role of AIB1 in the deregulation of ER target genes occurring as a consequence of AI resistance using tissue microarrays of patients with breast cancer and cell line models of resistance to the AI letrozole.Results: Expression of AIB1 associated with disease recurrence (P ¼ 0.025) and reduced disease-free survival time (P ¼ 0.0471) in patients treated with an AI as first-line therapy. In a cell line model of resistance to letrozole (LetR), we found ERa/AIB1 promoter recruitment and subsequent expression of the classic ER target genes pS2 and Myc to be constitutively upregulated in the presence of both androstenedione and letrozole. In contrast, the recruitment of the ERa/AIB1 transcriptional complex to the nonclassic ER target cyclin D1 and its subsequent expression remained sensitive to steroid treatment and could be inhibited by treatment with letrozole. Molecular studies revealed that this may be due in part to direct steroid regulation of c-jun-NH 2 -kinase (JNK), signaling to Jun and Fos at the cyclin D1 promoter.Conclusion: This study establishes a role for AIB1 in AI-resistant breast cancer and describes a new mechanism of ERa/AIB1 gene regulation which could contribute to the development of an aggressive tumor phenotype.