FOXA1 Promotes Tumor Progression in Prostate Cancer and Represents a Novel Hallmark of Castration-Resistant Prostate Cancer

FOXA1 mutations in hormone-dependent cancers

The forkhead protein, FOXA1, is a critical interacting partner of the nuclear hormone receptors, oestrogen receptor-α (ER) and androgen receptor (AR), which are major drivers of the two most common cancers, namely breast and prostate cancer. Over the past few years, progress has been made in our understanding of how FOXA1 influences nuclear receptor function, with both common and distinct roles in the regulation of ER or AR. Recently, another level of regulation has been described, with the discovery that FOXA1 is mutated in 1.8% of breast and 3–5% prostate cancers. In addition, a subset of both cancer types exhibit amplification of the genomic region encompassing the FOXA1 gene. Furthermore, there is evidence of somatic changes that influence the DNA sequence under FOXA1 binding regions, which may indirectly influence FOXA1-mediated regulation of ER and AR activity. These recent observations provide insight into the heterogeneity observed in ER and AR driven cancers.

FoxA1 corrupts the antiandrogenic effect of bicalutamide but only weakly attenuates the effect of MDV3100 (Enzalutamide™)

Prostate cancer growth depends on androgens. Synthetic antiandrogens are used in the cancer treatment. However, antiandrogens, such as bicalutamide (BIC), have a mixed agonist/antagonist activity. Here we compare the antiandrogenic capacity of BIC to a new antiandrogen, MDV3100 (MDV) or Enzalutamide™. By reconstitution of a hormone-regulated enhancer in Xenopus oocytes we show that both antagonists trigger the androgen receptor (AR) translocation to the nucleus, albeit with a reduced efficiency for MDV. Once in the nucleus, both AR-antagonist complexes can bind sequence specifically to DNA in vivo. The forkhead box transcription factor A (FoxA1) is a negative prognostic indicator for prostate cancer disease. FoxA1 expression presets the enhancer chromatin and makes the DNA more accessible for AR binding. In this context the BIC-AR antiandrogenic effect is seriously compromised as demonstrated by a significant chromatin remodeling and induction of a robust MMTV transcription whereas the MDV-AR complex displays a more persistent antagonistic character.

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.

FOXA1 promotes tumor progression in prostate cancer via the insulin-like growth factor binding protein 3 pathway

Fork-head box protein A1 (FOXA1) is a "pioneer factor" that is known to bind to the androgen receptor (AR) and regulate the transcription of AR-specific genes. However, the precise role of FOXA1 in prostate cancer (PC) remains unknown. In this study, we report that FOXA1 plays a critical role in PC cell proliferation. The expression of FOXA1 was higher in PC than in normal prostate tissues (P = 0.0002), and, using immunohistochemical analysis, we found that FOXA1 was localized in the nucleus. FOXA1 expression levels were significantly correlated with both PSA and Gleason scores (P = 0.016 and P = 0.031, respectively). Moreover, FOXA1 up-regulation was a significant factor in PSA failure (P = 0.011). Depletion of FOXA1 in a prostate cancer cell line (LNCaP) using small interfering RNA (siRNA) significantly inhibited AR activity, led to cell-growth suppression, and induced G0/G1 arrest. The anti-proliferative effect of FOXA1 siRNA was mediated through insulin-like growth factor binding protein 3 (IGFBP-3). An increase in IGFBP-3, mediated by depletion of FOXA1, inhibited phosphorylation of MAPK and Akt, and increased expression of the cell cycle regulators p21 and p27. We also found that the anti-proliferative effect of FOXA1 depletion was significantly reversed by simultaneous siRNA depletion of IGFBP-3. These findings provide direct physiological and molecular evidence for a role of FOXA1 in controlling cell proliferation through the regulation of IGFBP-3 expression in PC.

FoxA1 is a key mediator of hormonal response in breast and prostate cancer

Hormonally regulated breast and prostate cancers are the most common cause of cancer in females and males respectively. FoxA1 acts as a pioneer factor for both androgen receptor (AR) and estrogen receptor-α (ER), dictating the binding location, and therefore function of these transcription factors. It is an essential protein for the transcriptional activity of both ER and AR, yet it has distinct roles with the two different nuclear receptors. In both malignancies, FoxA1 plays a pivotal role from early stage cancer through to drug resistant and metastatic disease. Due to this key role in mediating ER and AR function, FoxA1 is not only an attractive therapeutic target but could potentially function as a novel biomarker.