Forkhead-box A1 (FOXA1) expression in breast cancer and its prognostic significance

FOXP1 and estrogen signaling in breast cancer

Breast cancers are considered to be primarily regulated by estrogen signaling pathways because estrogen-dependent proliferation is observed in the majority of breast cancer cases. Thus, hormone therapy using antiestrogen drugs such as tamoxifen is effective for breast cancers expressing estrogen receptor α (ERα). However, acquired resistance during the endocrine therapy is a critical unresolved problem in breast cancer. Recently, a forkhead transcription factor FOXA1 has been reported to play an important role in the regulation of ERα-mediated transcription and proliferation of breast cancer. Interestingly, immunohistochemical analysis of breast cancer specimens has revealed that nuclear immunoreactivities of FOXP1 as well as those of FOXA1 are positively correlated with hormone receptor status, including ERα and progesterone receptor. In particular, the double-positive immunoreactivities of FOXP1 and FOXA1 are significantly associated with a favorable prognosis for survival of breast cancer patients receiving adjuvant tamoxifen therapy. The functions of FOXP1 and FOXA1 have been characterized in cultured cells; further, similar to FOXA1, FOXP1 is assumed to be a critical transcription factor for ERα signaling, and both forkhead transcription factors can serve as predictive factors for acquired endocrine resistance in breast cancer.

Cooperating transcription factors mediate the function of estrogen receptor

Estrogen receptor (ER) is a hormone-regulated transcription factor that controls cell division and differentiation in the ovary, breast, and uterus. The expression of ER is a common feature of the majority of breast cancers, which is used as a therapeutic target. Recent genetic studies have shown that ER binding occurs in regions distant to the promoters of estrogen target genes. These studies have also demonstrated that ER binding is accompanied with the binding of other transcription factors, which regulate the function of ER and response to anti-estrogen therapies. In this review, we explain how these factors influence the interaction of ER to chromatin and their cooperation for ER transcriptional activity. Moreover, we describe how the expression of these factors dictates the response to anti-estrogen therapies. Finally, we discuss how cytoplasmatic signaling pathways may modulate the function of ER and its cooperating transcription factors.

Association of double-positive FOXA1 and FOXP1 immunoreactivities with favorable prognosis of tamoxifen-treated breast cancer patients

Breast cancer is primarily a hormone-dependent tumor that can be regulated by the status of the steroid hormones estrogen and progesterone. Forkhead box A1 (FOXA1) is a member of the forkhead box transcription factor family and functions as a pioneer factor of the estrogen receptor (ER) in breast cancer. In the present study, we demonstrate that FOXA1 mRNA was upregulated by estrogen and that estrogen receptor-α (ERα) recruitment to ER-binding sites in the vicinity of the FOXA1 gene was increased by estrogen in ERα-positive MCF-7 breast cancer cells. The estrogen-induced FOXA1 upregulation was repressed by 4-hydroxytamoxifen treatment. We also demonstrated that the proliferation and the migration of MCF-7 cells were decreased by FOXA1-specific small interfering RNA (siRNA; siFOXA1). Furthermore, siFOXA1 decreased the estrogen response element-driven transcription and the estrogen-dependent upregulation of ERα target genes in MCF-7 cells. Next, the immunohistochemical analyses of FOXA1 were performed using two groups of breast cancer specimens. The nuclear immunoreactivity of FOXA1 was detected in 80 (74%) of 108 human invasive breast cancers and was negatively correlated with tumor grade and positively correlated with hormone receptor status, including ERα and progesterone receptor, pathological tumor size, and immunoreactivity of FOXP1, another FOX family transcription factor. FOXA1 immunoreactivity was significantly elevated in the relapse-free breast cancer patients treated with tamoxifen. Notably, the double-positive immunoreactivities of FOXA1 and FOXP1 were significantly associated with a favorable prognosis for the relapse-free and overall survival of patients with tamoxifen-treated breast cancer, with lower P values compared with FOXA1 or FOXP1 immunoreactivity alone. These results suggest that FOXA1 plays an important role in the proliferation and migration of breast cancer cells by modulating estrogen signaling and that the double-positive immunoreactivities of FOXA1 and FOXP1 are associated with a favorable prognosis of tamoxifen-treated breast cancer.

FOXA1: a transcription factor with parallel functions in development and cancer

When aberrant, factors critical for organ morphogenesis are also commonly involved in disease progression. FOXA1 (forkhead box A1), also known as HNF3α (hepatocyte nuclear factor 3α), is required for postnatal survival due to its essential role in controlling pancreatic and renal function. In addition to regulating a variety of tissues during embryogenesis and early life, rescue experiments have revealed a specific role for FOXA1 in the postnatal development of the mammary gland and prostate. Activity of the nuclear hormone receptors ERα (oestrogen receptor α) and AR (androgen receptor) is also required for proper development of the mammary gland and prostate respectively. FOXA1 modulates ER and AR function in breast and prostate cancer cells, supporting the postulate that FOXA1 is involved in ER and AR signalling under normal conditions, and that some carcinogenic processes in these tissues stem from hormonally regulated developmental pathways gone awry. In addition to broadly reviewing the function of FOXA1 in various aspects of development and cancer, this review focuses on the interplay of FOXA1/ER and FOXA1/AR, in normal and cancerous mammary and prostate epithelial cells. Given the hormone dependency of both breast and prostate cancer, a thorough understanding of FOXA1's role in both cancer types is critical for battling hormone receptor-positive disease and acquired anti-hormone resistance.

Forkhead box transcription factor, forkhead box A1, shows negative association with lymph node status in endometrial cancer, and represses cell proliferation and migration of endometrial cancer cells

Endometrial cancer is the most common malignancy of the female genital tract and is associated with poor prognosis. It is primarily a hormone-dependent cancer that is regulated by steroid hormones, including estrogen and progesterone. Forkhead box A1 (FOXA1) is a member of the forkhead box transcription factor family and functions as a pioneer factor in estrogen receptor (ER)-positive breast cancer. In the present study, we investigated the expression of FOXA1 in endometrial cancers by immunohistochemical analysis. Nuclear immunoreactivity for FOXA1 was detected in 40 of 109 cases (37%), and was found to be negatively associated with lymph node status (P = 0.033). In ER-positive Ishikawa endometrial cancer cells, small interfering RNA-mediated downregulation of FOXA1 promoted cell proliferation and migration. Furthermore, exogenously introduced FOXA1 suppressed both proliferation and migration of Ishikawa cells. These results suggest that FOXA1 functions as a tumor suppressor through modulation of proliferation and migration of endometrial cancer cells.

Integrating Breast Cancer Genetics into Clinical Practice

Breast cancer prognosis and treatment is guided by traditional clinicopathological parameters and individual molecular markers. Despite the remarkable advances in our scientific understanding of breast cancer genetics, the impact of such information on medical care has, to date, been modest. Although the use of simple genetics is already in vogue in clinical practice, the concept of molecular profiling and multiparameter gene classifiers was raised after the introduction of the high-throughput gene expression microarrays. This technology, in addition to highlighting the molecular heterogeneity of breast cancer, has led to the development of prognostic and predictive gene signatures. Studies are underway to assess the clinical validity and clinical utility of these multigene assays and their incorporation into clinical practice. This article reviews the current status and projected future use of genetics and genomics in breast cancer management and their impact on the refinement of risk stratification to permit individualized and patient-tailored therapy. Limitations based on our current scientific understanding and realistic expectations are also explored.

PBX1 genomic pioneer function drives ERα signaling underlying progression in breast cancer

Altered transcriptional programs are a hallmark of diseases, yet how these are established is still ill-defined. PBX1 is a TALE homeodomain protein involved in the development of different types of cancers. The estrogen receptor alpha (ERα) is central to the development of two-thirds of all breast cancers. Here we demonstrate that PBX1 acts as a pioneer factor and is essential for the ERα-mediated transcriptional response driving aggressive tumors in breast cancer. Indeed, PBX1 expression correlates with ERα in primary breast tumors, and breast cancer cells depleted of PBX1 no longer proliferate following estrogen stimulation. Profiling PBX1 recruitment and chromatin accessibility across the genome of breast cancer cells through ChIP-seq and FAIRE-seq reveals that PBX1 is loaded and promotes chromatin openness at specific genomic locations through its capacity to read specific epigenetic signatures. Accordingly, PBX1 guides ERα recruitment to a specific subset of sites. Expression profiling studies demonstrate that PBX1 controls over 70% of the estrogen response. More importantly, the PBX1-dependent transcriptional program is associated with poor-outcome in breast cancer patients. Correspondingly, PBX1 expression alone can discriminate a priori the outcome in ERα-positive breast cancer patients. These features are markedly different from the previously characterized ERα-associated pioneer factor FoxA1. Indeed, PBX1 is the only pioneer factor identified to date that discriminates outcome such as metastasis in ERα-positive breast cancer patients. Together our results reveal that PBX1 is a novel pioneer factor defining aggressive ERα-positive breast tumors, as it guides ERα genomic activity to unique genomic regions promoting a transcriptional program favorable to breast cancer progression.

Subtype and pathway specific responses to anticancer compounds in breast cancer

Breast cancers are comprised of molecularly distinct subtypes that may respond differently to pathway-targeted therapies now under development. Collections of breast cancer cell lines mirror many of the molecular subtypes and pathways found in tumors, suggesting that treatment of cell lines with candidate therapeutic compounds can guide identification of associations between molecular subtypes, pathways, and drug response. In a test of 77 therapeutic compounds, nearly all drugs showed differential responses across these cell lines, and approximately one third showed subtype-, pathway-, and/or genomic aberration-specific responses. These observations suggest mechanisms of response and resistance and may inform efforts to develop molecular assays that predict clinical response.

FOXO3a nuclear localisation is associated with good prognosis in luminal-like breast cancer

Oestrogen receptor (ER)-positive breast cancer (BC) constitutes a heterogeneous group of tumours with regard to outcome and response to therapy. Accurate stratification of ER-positive BC according to risk of relapse and response to therapy will be achieved through an improved understanding of ER and ER-related biological pathways. Recent studies have identified Forkhead box O3a (FOXO3a) transcription factor as an intracellular mediator of ERα expression and as an important downstream target of the Akt/PI3K pathway indicating a biological and potential clinical role for FOXO3a in ER-positive BC. In this study, we investigated the clinical relevance and biological associations of FOXO3a protein expression, using tissue microarrays and immunohistochemistry, in a large series of patients with invasive breast cancer. FOXO3a protein expression showed both nuclear and/or cytoplasmic staining patterns. FOXO3a predominant nuclear expression was positively associated with biomarkers of good prognosis including PgR, FOXA1 and p27 expression. There was an inverse association with mitotic counts, MIB1 growth fraction, C-MYC and PIK3CA expression. With respect to patient outcome, FOXO3a nuclear localisation was associated with longer BC specific survival (P < 0.001) and longer distant metastasis free interval (P = 0.001), independently of the well-established breast cancer prognostic factors. In conclusion, our results demonstrate the biological and prognostic role of FOXO3a protein expression and its subcellular localisation in ER-positive/luminal-like BC possibly through its involvement in controlling cell proliferation.

Alpha- and beta-adrenergic receptor (AR) protein expression is associated with poor clinical outcome in breast cancer: an immunohistochemical study

Breast cancer mortality is frequently associated with metastatic disease. Metastasis models have shown adrenoceptor (AR) stimulation induces cell migration which is inhibited by adrenoceptor antagonist drugs. We investigated adrenoceptor protein expression in clinical breast tumours and its association with disease progression and prognosis. Immunohistochemistry on tissue microarrays was used to characterise α1b, α2c and β(2)2 adrenoceptor protein expression in operable breast tumours. Associations with tumour-relevant biological markers and clinical outcome were statistically assessed. Strong α1b expression occurred in large high grade (P < 0.0001), HER2+ (P < 0.0001) or basal-like (CK5/6, P = 0.0005; CK14, P = 0.0001; EGFR, P = 0.003) cancers, showing increased proliferation (Mib1, P = 0.002), decreased apoptosis (Bcl2, P < 0.0001) and poor NPI membership (P = 0.001). α1b expression correlated with poor cancer-specific survival (LR = 7.628, P = 0.022) and tumour recurrence (LR = 6.128, P = 0.047). Strong α2c was over-expressed in high grade (P = 0.007), HER3+ (P = 0.002) and HER4+ (P < 0.0001) cancers with borderline increase in EGFR, p53 and MIB1 proteins, and inverse association with hormonal (PgR, P = 0.002) phenotype. In contrast, strong β(2) expression occurred in small-size, luminal-like (ER+, P < 0.001) tumours of low grade (P < 0.001) and lymph node stage (P = 0.027) that showed poor prognosis when hormonal treatment was withheld. Adrenoceptors were not found to be independent predictors of clinical outcome. Alpha1b and α2c AR is over-expressed in basal-like breast tumours of poor prognosis. Strong β(2) adrenoceptor expression is seen in patients with a luminal (ER+) tumour phenotype and good prognosis, due to benefits derived from hormonal therapy. These findings suggest a possible role for targeted therapy using adrenoceptor antagonists.

RERG (Ras-like, oestrogen-regulated, growth-inhibitor) expression in breast cancer: a marker of ER-positive luminal-like subtype

Global gene expression profiling studies have classified breast cancer into a number of distinct biological and molecular classes with clinical relevance. The heterogeneous luminal group, which is largely characterised by oestrogen receptor (ER) expression, appears to contain distinct subgroups with differing behaviour. In this study, we analysed 47,293 gene transcripts in 128 invasive breast carcinomas (BC) using Artificial Neural Networks and a cross-validation analysis in combination with an ensemble sample classification to identify genes that can be used to subclassify ER+ luminal tumours. The results were validated using immunohistochemistry on TMAs containing 1,140 invasive breast cancers. Our results showed that the RERG gene is one of the highest ranked genes to differentiate between ER+ luminal-like and ER- non-luminal cancers based on a 10-fold external cross-validation analysis with an average classification accuracy of 89%. This was confirmed in our protein expression studies that showed RERG positive associations with markers of luminal differentiation including ER, luminal cytokeratins (CK19, CK18 and CK7/8) and FOXA1 (P = 0.004) and other markers of good prognosis in BC including small size, lower histologic grade and positive expression of androgen receptor, nuclear BRCA1, FHIT and cell cycle inhibitors p27 and p21. RERG expression was inversely associated with the proliferation marker MIB1 (P = 0.005) and p53. Strong RERG expression showed an association with longer breast cancer specific survival and distant metastasis free interval in the whole series as well as in the ER+ luminal group and these associations were independent of other prognostic variables. In conclusion, we used novel bioinformatics methods to identify candidate genes to characterise ER+ luminal-like breast cancer. RERG gene is a key marker of the luminal BC class and can be used to separate distinct prognostic subgroups.

FOXA1 is an essential determinant of ERalpha expression and mammary ductal morphogenesis

FOXA1, estrogen receptor alpha (ERalpha) and GATA3 independently predict favorable outcome in breast cancer patients, and their expression correlates with a differentiated, luminal tumor subtype. As transcription factors, each functions in the morphogenesis of various organs, with ERalpha and GATA3 being established regulators of mammary gland development. Interdependency between these three factors in breast cancer and normal mammary development has been suggested, but the specific role for FOXA1 is not known. Herein, we report that Foxa1 deficiency causes a defect in hormone-induced mammary ductal invasion associated with a loss of terminal end bud formation and ERalpha expression. By contrast, Foxa1 null glands maintain GATA3 expression. Unlike ERalpha and GATA3 deficiency, Foxa1 null glands form milk-producing alveoli, indicating that the defect is restricted to expansion of the ductal epithelium, further emphasizing the novel role for FOXA1 in mammary morphogenesis. Using breast cancer cell lines, we also demonstrate that FOXA1 regulates ERalpha expression, but not GATA3. These data reveal that FOXA1 is necessary for hormonal responsiveness in the developing mammary gland and ERalpha-positive breast cancers, at least in part, through its control of ERalpha expression.

Overexpression of hepatocyte nuclear factor-3alpha induces apoptosis through the upregulation and accumulation of cytoplasmic p53 in prostate cancer cells

BACKGROUND

Hepatocyte nuclear factor-3alpha (HNF-3alpha) has been known to act as a repressor in the pathogenesis of many cancers. Herein, we investigated the effect of HNF-3alpha overexpression in prostate cancer cells.

METHODS

HNF-3alpha was overexpressed in prostate cancer cells using an adenovirus recombinant expressing wild-type HNF-3alpha. The apoptosis of prostate cancer cells was determined by TUNEL, FACS, and caspase activity analyses.

RESULTS

Adenovirus-mediated overexpression of HNF-3alpha caused cell death in prostate cancer cells as assessed by changes in cellular and nuclear morphology, TUNEL analysis, and caspase activations. Furthermore, FACS analysis showed an increased sub-G1 phase of cell cycle as well as the G2/M phase with a corresponding decrease in S phases. HNF-3alpha overexpression caused the upregulation of p53 protein and its accumulation, together with HNF-3alpha, in the cytoplasm. It also causes Bax protein to localize to the mitochondria-enriched fraction. These findings suggest that multiple apoptotic pathways seem to be involved in the HNF-3alpha-induced cell death: pathways involving the accumulation of p53 protein in the cytoplasm and subsequent cytochrome c release, and other pathways involving death receptor signaling and caspase-8 activation.

CONCLUSIONS

The results of the current study suggest a novel function of HNF-3alpha as a killer of malignant prostate cancer cells, which reveals HNF-3alpha as a promising therapeutic molecule for prostate cancers.

Investigating AP-2 and YY1 protein expression as a cause of high HER2 gene transcription in breast cancers with discordant HER2 gene amplification

Introduction

Candidacy for anti-HER2 adjuvant therapy in breast cancer is assessed using tumour HER2 status but recently it has been proposed that the transcription factors AP-2α and YY1 may cause Her2 protein overexpression independently of gene amplification.

Methods

We characterised AP-2α/β, AP-2α and YY1 with HER2 gene and protein expression, other relevant biomarkers, and clinical outcome using tissue microarrays (TMAs) and immunohistochemistry in a large (n = 1,176) clinically annotated series of early stage operable breast cancer. The associations and prognostic independence of AP-2 and YY1 was assessed in all patients and an oestrogen receptor negative subgroup.

Results

Nuclear expression of AP-2α/β, AP-2α and YY1 was detected in 23%, 44% and 33% of cases respectively. AP-2α/β significantly correlated with YY1 and both markers were increased in luminal oestrogen receptor (ER) positive tumours of small size and low grade but only AP-2α/β correlated with good prognosis breast cancer specific survival and disease free interval (BCSS and DFI). These characteristics were lost in oestrogen receptor negative patients. AP-2α also correlated with luminal-type tumours but not with YY1 expression or good prognosis. AP-2α and YY1 showed a significant correlation with Her2 protein expression and in addition, YY1 correlated with HER2 gene expression. Discordant HER2 gene and protein expression was identified in six cases (0.71% of the study group) with four of these showing AP-2α but absence of AP-2α/β and YY1 expression.

Conclusions

AP-2α/β and YY1 are markers of good prognosis principally due to their association with oestrogen receptor but are not independent predictors. Discordant HER2 protein/gene expression is a rare event that is not always explained by the actions of AP-2 and YY1.

Gene expression meta-analysis supports existence of molecular apocrine breast cancer with a role for androgen receptor and implies interactions with ErbB family

Background

Pathway discovery from gene expression data can provide important insight into the relationship between signaling networks and cancer biology. Oncogenic signaling pathways are commonly inferred by comparison with signatures derived from cell lines. We use the Molecular Apocrine subtype of breast cancer to demonstrate our ability to infer pathways directly from patients' gene expression data with pattern analysis algorithms.

Methods

We combine data from two studies that propose the existence of the Molecular Apocrine phenotype. We use quantile normalization and XPN to minimize institutional bias in the data. We use hierarchical clustering, principal components analysis, and comparison of gene signatures derived from Significance Analysis of Microarrays to establish the existence of the Molecular Apocrine subtype and the equivalence of its molecular phenotype across both institutions. Statistical significance was computed using the Fasano & Franceschini test for separation of principal components and the hypergeometric probability formula for significance of overlap in gene signatures. We perform pathway analysis using LeFEminer and Backward Chaining Rule Induction to identify a signaling network that differentiates the subset. We identify a larger cohort of samples in the public domain, and use Gene Shaving and Robust Bayesian Network Analysis to detect pathways that interact with the defining signal.

Results

We demonstrate that the two separately introduced ER^- breast cancer subsets represent the same tumor type, called Molecular Apocrine breast cancer. LeFEminer and Backward Chaining Rule Induction support a role for AR signaling as a pathway that differentiates this subset from others. Gene Shaving and Robust Bayesian Network Analysis detect interactions between the AR pathway, EGFR trafficking signals, and ErbB2.

Conclusion

We propose criteria for meta-analysis that are able to demonstrate statistical significance in establishing molecular equivalence of subsets across institutions. Data mining strategies used here provide an alternative method to comparison with cell lines for discovering seminal pathways and interactions between signaling networks. Analysis of Molecular Apocrine breast cancer implies that therapies targeting AR might be hampered if interactions with ErbB family members are not addressed.

Expression of FOXA1 and GATA-3 in breast cancer: the prognostic significance in hormone receptor-negative tumours

Introduction

The expression of additional genes, other than oestrogen receptor (ER), may be important to the hormone-responsive phenotype of breast cancer. Microarray analyses have revealed that forkhead box A1 (FOXA1) and GATA binding protein 3 (GATA-3) are expressed in close association with ERα, both encoding for transcription factors with a potential involvement in the ERα-mediated action in breast cancer. The purpose of this study was to explore if the expression of FOXA1 and GATA-3 may provide an opportunity to stratify subsets of patients that could have better outcome, among the ERα-negative/poor prognosis breast cancer group.

Methods

We evaluate FOXA1 and GATA-3 expression in 249 breast carcinomas by immunohistochemistry, associating it with breast cancer molecular markers, clinicopathological features and patient's survival. The clinicopathological features and immunohistochemical markers of the tumours were compared using the chi-square test and ANOVA. Disease-free survival was analysed through Kaplan–Meier survival curves and Cox regression.

Results

FOXA1 expression was demonstrated in 42% of invasive carcinomas, while GATA-3 was detected in 48% of the cases. FOXA1 expression was inversely associated with tumour size, Nottingham Prognostic Index, histological grade, lymph vascular invasion, lymph node stage and human epidermal growth factor receptor-2 (HER-2) overexpression, while GATA-3 expression showed inverse association with histological grade and HER-2. Both FOXA1 and GATA-3 were directly associated with ERα and progesterone receptor. Among FOXA1-positive tumours, 83.1% are comprised in the luminal A subtype, similar to GATA-3 where 87.7% of positive tumours were classified within this molecular subtype. In the subset of ERα-negative patients, those who were FOXA1-negative had a 3.61-fold increased risk of breast cancer recurrence when compared with the FOXA1-positive.

Conclusions

FOXA1 was a significant predictor of good outcome in breast cancer, whereas GATA-3 was an important luminal marker. The expression of FOXA1 may be used for risk stratification among ERα-negative patients.

The prognostic significance of PELP1 expression in invasive breast cancer with emphasis on the ER-positive luminal-like subtype

The transcription functions of oestrogen receptors (ER) are influenced by several coregulators such as PELP1 (proline, glutamate and leucine rich protein 1). The aim of the present study, which uses tissue microarrays and immunohistochemistry, is to explore the clinical and biological relevance of PELP1 protein expression in a large series of consecutive patients (1,162 patients) with invasive breast cancers with particular emphasis on its role in the ER-positive/luminal-like class of tumours. Our results showed that increased PELP1 expression is associated with tumours of larger size, higher histological grade, higher mitotic count, and with positive expression of basal cytokeratins (CK) (CK14; P = 0.018 and CK5/6; P = 0.029), P-cadherin (P = 0.002), p53 and MIB1 (P = 0.018). There was an inverse association between PELP1 expression and ER (P = 0.002), progesterone (PgR) (P = 0.004), androgen (AR) receptor (P < 0.001), and luminal CK (CK18; P = 0.027) expression. A significant association between PELP1 expression and shorter breast cancer specific survival (BCSS) (P = 0.002) and disease-free survival (DFI) (P = 0.006) was found. Multivariate Cox hazard analysis showed that PELP1 expression was an independent predictor of shorter BCSS (Hazard ratio (HR) = 1.349, P = 0.006) and shorter DFI (HR = 1.255, P = 0.011). In the ER-positive/luminal-like group (n = 768), PELP1 expression showed similar association with other clinicopathological variables and was an independent predictor of shorter DFI (HR = 1.256, P = 0.036). In conclusion, PELP1 protein expression is an independent prognostic predictor of shorter BCSS and DFI in breast cancer and its elevated expression is positively associated with markers of poor outcome. PELP1 appears to have a potential application in assessing the clinical outcome of patients with ER-positive breast cancer.

FOXA1 in breast cancer

Breast cancer is a heterogeneous disease and classification is important for clinical management. At least five subtypes can be identified based on unique gene expression patterns; this subtype classification is distinct from the histopathological classification. The transcription factor network(s) required for the specific gene expression signature in each of these subtypes is currently being elucidated. The transcription factor network composed of the oestrogen (estrogen) receptor alpha (ERalpha), FOXA1 and GATA3 may control the gene expression pattern in luminal subtype A breast cancers. Breast cancers that are dependent on this network correspond to well-differentiated and hormone-therapy-responsive tumours with good prognosis. In this review, we discuss the interplay between these transcription factors with a particular emphasis on FOXA1 structure and function, and its ability to control ERalpha function. Additionally, we discuss modulators of FOXA1 function, ERalpha-FOXA1-GATA3 downstream targets, and potential therapeutic agents that may increase differentiation through FOXA1.

Transferrin receptor (CD71) is a marker of poor prognosis in breast cancer and can predict response to tamoxifen

Transferrin receptor (CD71) is involved in the cellular uptake of iron and is expressed on cells with high proliferation. It may be implicated in promoting the growth of endocrine resistant phenotypes within ER+/luminal-like breast cancer. We used a panel of in vitro cell models of acquired resistance to tamoxifen (TAMR), Faslodex (FASR) or severe oestrogen deprivation (MCF-7X) and the ER+ luminal MCF-7 parental line to determine CD71 mRNA expression and to study transferrin (Tf) effects on in vitro tumour growth and its inhibition. Furthermore, CD71 protein expression was assessed in a well-characterized series of patients with invasive breast carcinoma using tissue microarrays. Our results demonstrated a striking elevation of CD71 in all cell models of acquired resistance. Exogenous Tf significantly promoted growth in MCF-7-X and MCF-7 cells but more so in MCF-7-X; this growth was significantly reduced by Faslodex (FAS) or a phosphoinositide-3 kinase inhibitor (LY294002). Increased CD71 expression was associated with poor NPI score, tumour proliferation, basal CKs, p53, EGFR, HER2, steroid receptor negativity and shortened breast cancer specific survival (P < 0.001). On multivariate analysis, CD71 was found to be an independent prognostic factor in the ER+ cohort of patients. In conclusion, therapies of current interest in breast cancer (e.g. FAS, PI3K-inhibitors) appear able to partially impact on transferrin/CD71-promoted growth, but further investigation of this important mitogenic mechanism may assist in designing new therapeutic strategies to target highly proliferative, endocrine resistant breast cancers. CD71 appears to be a candidate marker of a subgroup of ER+/luminal-like breast cancer characterised by poor outcome and resistance to tamoxifen.