Estradiol receptors in breast cancer cells: associated co-factors as targets for new therapeutic approaches

Calycosin suppresses colorectal cancer progression by targeting ERβ, upregulating PTEN, and inhibiting PI3K/Akt signal pathway

High intake of phytoestrogen has been reported to be associated with the prevention of colorectal cancer (CRC). Calycosin belongs to the phytoestrogen that has been shown to suppress CRC cells in our previous study. However, its anticancer activity and molecular mechanisms have not been elucidated. In this study, we analyzed the effect of calycosin on the viability and apoptosis of human CRC HCT116 and SW480 cells via MTT assay, flow cytometry assay, and caspase-3/7 activity assay. The protein expressions of estrogen receptor β (ERβ), PTEN, and PI3K/Akt signal pathways were determined by Western blot analysis. And then, the alterations of biological behavior in CRC cells transfected with ERβ siRNA were analyzed. Mouse xenograft models were further performed to detect the antitumor effect in vivo. The results show that calycosin reduces CRC cell viability, induces cell apoptosis, and suppresses xenograft tumor growth. The protein expressions of ERβ and PTEN are significantly upregulated following calycosin treatment, whereas p-AKT/AKT ratio and Bcl-2 level are downregulated. Suppressing ERβ with siRNA partially attenuates the reduction in viability and apoptosis induced by calycosin. Our results indicate that calycosin shows inhibitory effects on CRC cells, which might be obtained by targeting ERβ, upregulating PTEN, and inhibiting the PI3K/Akt signal pathway.

β-Estradiol Induces Mitochondrial Apoptosis in Cervical Cancer Through the Suppression of AKT/NF-κB Signaling Pathway

BACKGROUND

Cervical cancer is the fourth most prevalent gynecological cancer worldwide, which threatens women's health and causes cancer-related mortality. In the search for effective anticervical cancer drugs, we discovered that β-estradiol (E2), a patent drug for estrogen deficiency syndrome treatment, displays the most potent cytotoxicity against HeLa cells.

OBJECTIVE

This study aims to evaluate the growth inhibitory effect of β-estradiol on HeLa cells and explore its underlying mechanisms.

METHODS

CCK-8 assay was used to evaluate the cytotoxicity of 6 compounds against HeLa cells. Flow cytometric analysis and Hoechst 33258 staining assay were performed to detect cell cycle arrest and apoptosis induction. The collapse of the mitochondrial potential was observed by the JC-1 staining assay. The expression levels of proteins were examined by western blotting.

RESULTS

β-Estradiol, at high concentration, displays potent cytotoxicity against HeLa cells with an IC50 value of 18.71 ± 1.57 μM for 72 h treatment. β-Estradiol induces G2/M cell cycle arrest through downregulating Cyclin B1 and p-CDK1. In addition, β-estradiol-induced apoptosis is accompanied by the loss of mitochondrial potential, activation of the Caspase family, and altered Bax/Bcl-2 ratio. β-Estradiol markedly decreased the expression level of p-AKT and p-NF-κB.

CONCLUSION

This study demonstrated that β-estradiol induces mitochondrial apoptosis in cervical cancer through the suppression of the AKT/NF-κB signaling pathway, indicating that β-estradiol may serve as a potential agent for cervical cancer treatment.

Heat Shock Factor 1 (HSF1) cooperates with estrogen receptor α (ERα) in the regulation of estrogen action in breast cancer cells

Heat shock factor 1 (HSF1), a key regulator of transcriptional responses to proteotoxic stress, was linked to estrogen (E2) signaling through estrogen receptor α (ERα). We found that an HSF1 deficiency may decrease ERα level, attenuate the mitogenic action of E2, counteract E2-stimulated cell scattering, and reduce adhesion to collagens and cell motility in ER-positive breast cancer cells. The stimulatory effect of E2 on the transcriptome is largely weaker in HSF1-deficient cells, in part due to the higher basal expression of E2-dependent genes, which correlates with the enhanced binding of unliganded ERα to chromatin in such cells. HSF1 and ERα can cooperate directly in E2-stimulated regulation of transcription, and HSF1 potentiates the action of ERα through a mechanism involving chromatin reorganization. Furthermore, HSF1 deficiency may increase the sensitivity to hormonal therapy (4-hydroxytamoxifen) or CDK4/6 inhibitors (palbociclib). Analyses of data from The Cancer Genome Atlas database indicate that HSF1 increases the transcriptome disparity in ER-positive breast cancer and can enhance the genomic action of ERα. Moreover, only in ER-positive cancers an elevated HSF1 level is associated with metastatic disease.

About 70% of breast cancers rely on supplies of a hormone called estrogen – which is the main hormone responsible for female physical characteristics – to grow. Breast cancer cells that are sensitive to estrogen possess proteins known as estrogen receptors and are classified as estrogen-receptor positive. When estrogen interacts with its receptor in a cancer cell, it stimulates the cell to grow and migrate to other parts of the body. Therefore, therapies that decrease the amount of estrogen the body produces, or inhibit the receptor itself, are widely used to treat patients with estrogen receptor-positive breast cancers.

When estrogen interacts with an estrogen receptor known as ERα it can also activate a protein called HSF1, which helps cells to survive under stress. In turn, HSF1 regulates several other proteins that are necessary for ERα and other estrogen receptors to work properly. Previous studies have suggested that high levels of HSF1 may worsen the outcomes for patients with estrogen receptor-positive breast cancers, but it remains unclear how HSF1 acts in breast cancer cells.

Vydra, Janus, Kuś et al. used genetics and bioinformatics approaches to study HSF1 in human breast cancer cells. The experiments revealed that breast cancer cells with lower levels of HSF1 also had lower levels of ERα and responded less well to estrogen than cells with higher levels of HSF1. Further experiments suggested that in the absence of estrogen, HSF1 helps to keep ERα inactive. However, when estrogen is present, HSF1 cooperates with ERα and enhances its activity to help cells grow and migrate. Vydra, Janus, Kuś et al. also found that cells with higher levels of HSF1 were less sensitive to two drug therapies that are commonly used to treat estrogen receptor-positive breast cancers.

These findings reveal that the effect HSF1 has on ERα activity depends on the presence of estrogen. Therefore, cancer therapies that decrease the amount of estrogen a patient produces may have a different effect on estrogen receptor-positive tumors with high HSF1 levels than tumors with low HSF1 levels.

Nuclear role for human Argonaute-1 as an estrogen-dependent transcription coactivator

In mammals, argonaute (AGO) proteins have been characterized for their roles in small RNA-mediated posttranscriptional and also in transcriptional gene silencing. Here, we report a different role for AGO1 in estradiol-triggered transcriptional activation in human cells. We show that in MCF-7 mammary gland cells, AGO1 associates with transcriptional enhancers of estrogen receptor α (ERα) and that this association is up-regulated by treating the cells with estrogen (E2), displaying a positive correlation with the activation of these enhancers. Moreover, we show that AGO1 interacts with ERα and that this interaction is also increased by E2 treatment, but occurs in the absence of RNA. We show that AGO1 acts positively as a coactivator in estradiol-triggered transcription regulation by promoting ERα binding to its enhancers. Consistently, AGO1 depletion decreases long-range contacts between ERα enhancers and their target promoters. Our results point to a role of AGO1 in transcriptional regulation in human cells that is independent from small RNA binding.

Calycosin induces apoptosis in osteosarcoma cell line via ERβ‑mediated PI3K/Akt signaling pathways

Previous studies have shown that calycosin, a natural phytoestrogen which is structurally similar to estrogen, inhibits proliferation and induces apoptosis in estrogen-dependent cancer types via the estrogen receptor (ER)β-induced inhibition of PI3K/Akt. Therefore, the aims of the present study were to investigate the effects of calycosin on human osteosarcoma (OS), and to examine the molecular mechanisms associated with ERβ. Human OS MG-63 cells were treated with various concentrations of calycosin, and MTT and flow cytometry assays were used to assess the effects of calycosin on cellular proliferation and apoptosis. In addition, protein expression levels of ERβ, phosphorylated (p)-PI3K, p-Akt, cleaved poly (ADP-ribose) polymerase 1 (PARP) and cleaved caspase-3 were evaluated by western blot analysis. The present results suggested that calycosin inhibited proliferation and induced apoptosis in MG-63 cells. Furthermore, increased ERβ expression was detected in OS MG-63 cells treated with calycosin, and an ERβ inhibitor (PHTPP) reversed calycosin-induced cytotoxicity and apoptosis. Moreover, phosphorylation levels of PI3K and Akt were significantly downregulated after calycosin treatment, whereas PHTPP reversed their phosphorylation. ERβ-mediated PI3K/Akt downstream signaling pathways were found to influence the activity of poly (ADP-ribose) polymerase 1 and caspase-3. Thus, the present results indicated that calycosin inhibited proliferation and induced apoptosis in OS MG-63 cells, and that these effects were mediated by ERβ-dependent inhibition of the PI3K/Akt pathways.

17β-Estradiol Activates HSF1 via MAPK Signaling in ERα-Positive Breast Cancer Cells

Heat Shock Factor 1 (HSF1) is a key regulator of gene expression during acute environmental stress that enables the cell survival, which is also involved in different cancer-related processes. A high level of HSF1 in estrogen receptor (ER)-positive breast cancer patients correlated with a worse prognosis. Here we demonstrated that 17β-estradiol (E2), as well as xenoestrogen bisphenol A and ERα agonist propyl pyrazole triol, led to HSF1 phosphorylation on S326 in ERα positive but not in ERα-negative mammary breast cancer cells. Furthermore, we showed that MAPK signaling (via MEK1/2) but not mTOR signaling was involved in E2/ERα-dependent activation of HSF1. E2-activated HSF1 was transcriptionally potent and several genes essential for breast cancer cells growth and/or ERα action, including HSPB8, LHX4, PRKCE, WWC1, and GREB1, were activated by E2 in a HSF1-dependent manner. Our findings suggest a hypothetical positive feedback loop between E2/ERα and HSF1 signaling, which may support the growth of estrogen-dependent tumors.

Selection of a GPER1 Ligand via Ligand-based Virtual Screening Coupled to Molecular Dynamics Simulations and Its Anti-proliferative Effects on Breast Cancer Cells

BACKGROUND

Recent reports have demonstrated the role of the G Protein-Coupled Estrogen Receptor 1 (GPER1) on the proliferation of breast cancer. The coupling of GPER1 to estrogen triggers cellular signaling pathways related to cell proliferation.

OBJECTIVE

Develop new therapeutic strategies against breast cancer.

METHOD

We performed in silico studies to explore the binding mechanism of a set of G15 /G1 analogue compounds. We included a carboxyl group instead of the acetyl group from G1 to form amides with several moieties to increase affinity on GPER1. The designed ligands were submitted to ligand-based and structure-based virtual screening to get insights into the binding mechanism of the best designed compound and phenol red on GPER1.

RESULTS

According to the in silico studies, the best molecule was named G1-PABA ((3aS,4R,9bR)-4-(6- bromobenzo[d][1,3]dioxol-5-yl)-3a,4,5,9b-tetrahydro-3H-cyclopenta[c]quinoline-8-carboxylic acid). It was synthesized and assayed in vitro in breast cancer (MCF-7 and MDA-MB-231) and normal (MCF-10A) cell lines. Experimental studies showed that the target compound was able to decrease cell proliferation, IC50 values of 15.93 µM, 52.92 µM and 32.45 µM in the MCF-7, MDA-MB-231 and MCF-10A cell lines, respectively, after 72 h of treatment. The compound showed better IC50 values without phenol red, suggesting that phenol red interfere with the G1-PABA action at GPER1, as observed through in silico studies, which is present in MCF-7 cells according to PCR studies and explains the cell proliferation effects.

CONCLUSION

Concentration-dependent inhibition of cell proliferation occurred with G1-PABA in the assayed cell lines and could be due to its action on GPER1.

Biological Actions of the Hsp90-binding Immunophilins FKBP51 and FKBP52

Immunophilins are a family of proteins whose signature domain is the peptidylprolyl-isomerase domain. High molecular weight immunophilins are characterized by the additional presence of tetratricopeptide-repeats (TPR) through which they bind to the 90-kDa heat-shock protein (Hsp90), and via this chaperone, immunophilins contribute to the regulation of the biological functions of several client-proteins. Among these Hsp90-binding immunophilins, there are two highly homologous members named FKBP51 and FKBP52 (FK506-binding protein of 51-kDa and 52-kDa, respectively) that were first characterized as components of the Hsp90-based heterocomplex associated to steroid receptors. Afterwards, they emerged as likely contributors to a variety of other hormone-dependent diseases, stress-related pathologies, psychiatric disorders, cancer, and other syndromes characterized by misfolded proteins. The differential biological actions of these immunophilins have been assigned to the structurally similar, but functionally divergent enzymatic domain. Nonetheless, they also require the complementary input of the TPR domain, most likely due to their dependence with the association to Hsp90 as a functional unit. FKBP51 and FKBP52 regulate a variety of biological processes such as steroid receptor action, transcriptional activity, protein conformation, protein trafficking, cell differentiation, apoptosis, cancer progression, telomerase activity, cytoskeleton architecture, etc. In this article we discuss the biology of these events and some mechanistic aspects.

UXT Is a LOX-PP Interacting Protein That Modulates Estrogen Receptor Alpha Activity in Breast Cancer Cells

The lysyl oxidase proenzyme propeptide region (LOX-PP) is a tumor suppressor protein whose mechanism of action is not completely understood. Here, the Ubiquitously expressed Transcript (UXT) was identified in a yeast two-hybrid assay with LOX-PP as bait and confirmed as a novel LOX-PP associating protein. UXT, a prefoldin-like protein, is ubiquitous in human and mouse. Since UXT modulates androgen receptor transcriptional activity in prostate cancer, we studied its role in breast cancer. Breast tumors and derived cell lines overexpressed UXT. UXT was able to associate with the estrogen receptor alpha (ER) and decrease its transcriptional activity and target gene expression. Conversely, UXT knockdown increased ER element-dependent transcriptional activity. Ectopic LOX-PP relocalized UXT to the cytoplasm and decreased its stability. UXT ubiquitination and depletion in the presence of LOX-PP was rescued by a proteasomal inhibitor. In summary, proteasome-mediated turnover of UXT upon interaction with LOX-PP releases repression of ER transcriptional activity. J. Cell. Biochem. 118: 2347-2356, 2017. © 2017 Wiley Periodicals, Inc.

Unusual Suspects in the Twilight Zone Between the Hsp90 Interactome and Carcinogenesis

The molecular chaperone Hsp90 has attracted a lot of interest in cancer research ever since cancer cells were found to be more sensitive to Hsp90 inhibition than normal cells. Why that is has remained a matter of debate and is still unclear. In addition to increased Hsp90 dependence for some mutant cancer proteins and modifications of the Hsp90 machinery itself, a number of other characteristics of cancer cells probably contribute to this phenomenon; these include aneuploidy and overall increased numbers and levels of defective and mutant proteins, which all contribute to perturbed proteostasis. Work over the last two decades has demonstrated that many cancer-related proteins are Hsp90 clients, and yet only few of them have been extensively investigated, selected either on the basis of their obvious function as cancer drivers or because they proved to be convenient biomarkers for monitoring the effects of Hsp90 inhibitors. The purpose of our review is to go beyond these "usual suspects." We established a workflow to select poorly studied proteins that are related to cancer processes and qualify as Hsp90 clients. By discussing and taking a fresh look at these "unusual suspects," we hope to stimulate others to revisit them as novel therapeutic targets or diagnostic markers.

SEMA6D Expression and Patient Survival in Breast Invasive Carcinoma

Breast cancer (BC) is the second most common cancer diagnosed in American women and is also the second leading cause of cancer death in women. Research has focused heavily on BC metastasis. Multiple signaling pathways have been implicated in regulating BC metastasis. Our knowledge of regulation of BC metastasis is, however, far from complete. Identification of new factors during metastasis is an essential step towards future therapy. Our labs have focused on Semaphorin 6D (SEMA6D), which was implicated in immune responses, heart development, and neurogenesis. It will be interesting to know SEMA6D-related genomic expression profile and its implications in clinical outcome. In this study, we examined the public datasets of breast invasive carcinoma from The Cancer Genome Atlas (TCGA). We analyzed the expression of SEMA6D along with its related genes, their functions, pathways, and potential as copredictors for BC patients' survival. We found 6-gene expression profile that can be used as such predictors. Our study provides evidences for the first time that breast invasive carcinoma may contain a subtype based on SEMA6D expression. The expression of SEMA6D gene may play an important role in promoting patient survival, especially among triple negative breast cancer patients.

Biotransformed soybean extract induces cell death of estrogen-dependent breast cancer cells by modulation of apoptotic proteins

The process of soybean biotransformation increases the quantity of isoflavones (daidzein and genistein), which besides being considered an alternative to estroprogestive hormone replacement therapy (HRT), are able of hindering the growth and development of tumor cells. We investigated the effects of soybean extract biotransformed by fungus on estrogen-dependent (MCF-7) and nondependent (SK-BR-3) breast cell lines. Cells were treated with different concentrations of biotransformed (BSE) and nonbiotransformed soybean extract (SE), or daidzein (D) and genistein (G) patterns isolated and in combination (D + G). Afterwards, we analyzed cell viability by MTT assay, phosphatidylserine exposure and cell permeability by flow cytometry; expression of apoptotic proteins by Western blotting. BSE promoted reduction in cell viability and increase in DNA degradation in both cell lines. In addition, we verified increase in cell permeability and in the expression of phosphatidylserine, as well as modulation in the expression of apoptotic proteins in MCF-7 cells. The cells did not show any signs of cell death when incubated with the controls (D, G, and D + G). Unknown components found in the BSE induce cell death by apoptosis and necrosis, mainly in MCF-7 cells. These processes depend on the activation of caspase-3 and involve an increase in the expression of proapoptotic molecules.

Expression of P450arom and Estrogen Receptor Alpha in the Oviduct of Chinese Brown Frog (Rana dybowskii) during Prehibernation

One specific physiological phenomenon of Chinese brown frog (Rana dybowskii) is that its oviduct expands prior to hibernation instead of expanding during the breeding period. In this study, we investigated the expression of P450arom and estrogen receptors α and β (ERα and ERβ) in the oviduct of Rana dybowskii during the breeding period and prehibernation. The results of the present study showed that there were significant differences in both oviductal weight and size with values markedly higher in prehibernation than in the breeding period. P450arom was observed in stromal tissue in both the breeding period and prehibernation. ERα was expressed in stromal tissue and epithelial cells in both periods, whereas ERβ could not be detected. The mean protein and mRNA levels of P450arom and ERα were significantly higher in prehibernation as compared to the breeding period. Besides, oviductal content of 17β-estradiol was also higher in prehibernation than in the breeding period. These results suggested that estrogen may play autocrine/paracrine roles mediated by ERα in regulating the oviductal hypertrophy during prehibernation.

Calycosin suppresses breast cancer cell growth via ERβ-dependent regulation of IGF-1R, p38 MAPK and PI3K/Akt pathways

We previously reported that calycosin, a natural phytoestrogen structurally similar to estrogen, successfully triggered apoptosis of estrogen receptor (ER)-positive breast cancer cell line, MCF-7. To better understand the antitumor activities of calycosin against breast cancer, besides MCF-7 cells, another ER-positive cell line T-47D was analyzed here, with ER-negative cell lines (MDA-231, MDA-435) as control. Notably, calycosin led to inhibited cell proliferation and apoptosis only in ER-positive cells, particularly in MCF-7 cells, whereas no such effect was observed in ER-negative cells. Then we investigated whether regulation of ERβ, a subtype of ER, contributed to calycosin-induced apoptosis in breast cancer cells. The results showed that incubation of calycosin resulted in enhanced expression ERβ in MCF-7 and T-47D cells, rather than MDA-231 and MDA-435 cells. Moreover, with the upregulation of ERβ, successive changes in downstream signaling pathways were found, including inactivation of insulin-like growth factor 1 receptor (IGF-1R), then stimulation of p38 MAPK and suppression of the serine/threonine kinase (Akt), and finally poly(ADP-ribose) polymerase 1 (PARP-1) cleavage. However, the other two members of the mitogen-activated protein kinase (MAPK) family, extracellular signal-regulated kinase (ERK) 1/2 and c-Jun N-terminal kinase (JNK), were not consequently regulated by downregulated IGF-1R, indicating ERK 1/2 and JNK pathways were not necessary to allow proliferation inhibition by calycosin. Taken together, our results indicate that calycosin tends to inhibit growth and induce apoptosis in ER-positive breast cancer cells, which is mediated by ERβ-induced inhibition of IGF-1R, along with the selective regulation of MAPK and phosphatidylinositol 3-kinase (PI3K)/Akt pathways.

Activation of ERα signaling differentially modulates IFN-γ induced HLA-class II expression in breast cancer cells

The coordinate regulation of HLA class II (HLA-II) is controlled by the class II transactivator, CIITA, and is crucial for the development of anti-tumor immunity. HLA-II in breast carcinoma is associated with increased IFN-γ levels, reduced expression of the estrogen receptor (ER) and reduced age at diagnosis. Here, we tested the hypothesis that estradiol (E₂) and ERα signaling contribute to the regulation of IFN-γ inducible HLA-II in breast cancer cells. Using a panel of established ER⁻ and ER⁺ breast cancer cell lines, we showed that E₂ attenuated HLA-DR in two ER⁺ lines (MCF-7 and BT-474), but not in T47D, while it augmented expression in ER⁻ lines, SK-BR-3 and MDA-MB-231. To further study the mechanism(s), we used paired transfectants: ERα⁺ MC2 (MDA-MB-231 c10A transfected with the wild type ERα gene) and ERα⁻ VC5 (MDA-MB-231 c10A transfected with the empty vector), treated or not with E₂ and IFN-γ. HLA-II and CIITA were severely reduced in MC2 compared to VC5 and were further exacerbated by E₂ treatment. Reduced expression occurred at the level of the IFN-γ inducible CIITA promoter IV. The anti-estrogen ICI 182,780 and gene silencing with ESR1 siRNA reversed the E₂ inhibitory effects, signifying an antagonistic role for activated ERα on CIITA pIV activity. Moreover, STAT1 signaling, necessary for CIITA pIV activation, and selected STAT1 regulated genes were variably downregulated by E₂ in transfected and endogenous ERα positive breast cancer cells, whereas STAT1 signaling was noticeably augmented in ERα⁻ breast cancer cells. Collectively, these results imply immune escape mechanisms in ERα⁺ breast cancer may be facilitated through an ERα suppressive mechanism on IFN-γ signaling.

Chromatin and epigenetic determinants of estrogen receptor alpha (ESR1) signaling

The oestrogen receptor alpha (ESR1) is a transcription factor that potentiates the response to diverse stimuli, including oestrogen and growth factors, in various tissue types. Its recruitment to the DNA is directly regulated by the chromatin landscape, inclusive of chromatin compaction and epigenetic modifications. In this review we discuss our current understanding of the interplay between ESR1 signaling and the chromatin landscape. We present how the chromatin landscape primes the lineage-specific response and contributes to stimuli-specific signaling. Finally, we discuss recent efforts to decipher the relationship between genetic and epigenetic as it relates to ESR1 signaling in breast cancer.

Systematic nucleo-cytoplasmic trafficking of proteins following exposure of MCF7 breast cancer cells to estradiol

We have used a proteomics subcellular spatial razor approach to look at changes in total protein abundance and in protein distribution between the nucleus and cytoplasm following exposure of MCF7 breast cancer cells to estradiol. The dominant response of MCF7 cells to estrogen stimulation involves dynamic changes in protein subcellular spatial distribution rather than changes in total protein abundance. Of the 3604 quantitatively monitored proteins, only about 2% show substantial changes in total abundance (>2-fold), whereas about 20% of the proteins show substantial changes in local abundance and/or redistribution of their subcellular location, with up to 16-fold changes in their local concentration in the nucleus or the cytoplasm. We propose that dynamic redistribution of the subcellular location of multiple proteins in response to stimuli is a fundamental characteristic of cells and suggest that perturbation of cellular spatial control may be an important feature of cancer.

Harmful effect of ERβ on BCRP-mediated drug resistance and cell proliferation in ERα/PR-negative breast cancer

The role of estrogen receptor β (ERβ) in breast cancer is still under investigation. Various studies have provided evidence that ERβ behaves as a tumor suppressor in breast cancer, whereas some studies of estrogen receptor α (ERα) negative breast cancer reported a positive correlation between high ERβ expression and poor prognostic phenotypes, such as induced proliferation, invasion and metastasis. In the present immunohistochemistry study of 99 ERα/progesterone receptor (PR)-negative breast cancer samples, nuclear expression of ERβ was positively associated with membranous expression of breast cancer resistance protein (BCRP), Ki67 (proliferation marker) and tumor size. Moreover, both endogenous and exogenous ERβ upregulated BCRP expression which induced BCRP-mediated drug resistance and enhanced proliferation of ERα-/PR- breast cancer cells in the presence of 17β-estradiol, whereas these effects were reversed by additional use of tamoxifen (TAM). In addition, the regulation of BCRP via specific binding between ERβ and estrogen response element (ERE) was demonstrated in an electrophoretic mobility shift assay. Overall, our findings manifest that ERβ might act as a tumor promoter of cell proliferation and BCRP-mediated drug resistance in ERα-/PR- breast cancer. TAM routinely used for patients with ERα+/PR+, ERα+/PR- and ERα-/PR+ breast cancer might also be effective in ERα-/PR- but ERβ+ breast cancer. Therefore, the detection of ERβ in clinic is valuable and should not be neglected in breast cancer, especially for the ERα-/PR- phenotype.

Hsp90-binding immunophilins as a potential new platform for drug treatment

Immunophilins are proteins that contain a PPIase domain as a family signature. Low-molecular-weight immunophilins were first described associated to immunosuppressive action and protein folding. Recent studies of other members of the family have led to the identification of their participation in basic processes such as protein-protein interactions, signal transduction cascades, cell differentiation, cell cycle progression, metabolic activity, apoptosis mechanisms, microorganisms infection, cancer, neurotrophism and neuroprotection, among several other physiological and pathophysiological processes. Due to all these emerging features, the development of specific ligands for immunophilins appears to have promising perspectives, in particular in the fields of cancer biology and neuroregeneration fields. We review the emerging role of immunophilins in protein transport, transcription regulation, malignancies development and neurotrophic action, in addition to a number of biological properties that transform these proteins in potential targets for novel therapeutic strategies.