NDF induces expression of a novel 46 kD protein in estrogen receptor positive breast cancer cells

Most human breast tumors start as estrogen-dependent, but during the course of the disease become refractory to hormone therapy. The transition of breast tumors from estrogen dependent to independent behavior may be regulated by autocrine and/or paracrine growth factor(s) that are independent of the estrogen receptor (ER). We have investigated the role(s) of NDF (neu-differentiation factor) in the biology of estrogen positive breast cancer cells by using MCF-7 cells as a model system. Treatment of MCF-7 cells with human recombinant NDF-β2 (NDF) inhibited the ER expression by 70% and this was associated with growth stimulation in an estrogen-independent manner. To explore the mechanism(s) of action of NDF in MCF-7 cells, we examined the expression of NDF-inducible gene products. We report here that NDF stimulated the levels of expression of a 46 kD protein (p46) (in addition to few minor proteins) in ER positive breast cancer cells including MCF-7, T-47-D, and ZR-75-R cells but not in ER negative breast cancer cells including MDA-231, SK-BP-3, and MDA-468 cells. This effect of NDF was due to induction in the rate of synthesis of new p46. The observed NDF-mediated induction of p46 expression was specific as there was no such effect by epidermal growth factor or 17-β-estradiol, and inclusion of actinomycin D partially inhibited the p46 induction elicited by NDF. NDF-inducible stimulation of p46 expression was an early event (2–6 h) which preceded the period of down-regulation of ER expression by NDF. These results support the existence of NDF-responsive specific cellular pathway(s) that may regulate ER, and these interactions could play a role(s) in hormone-independence of ER positive breast cancer cells. © 1996 Wiley-Liss, Inc.     

Proteomics profiling identify CAPS as a potential predictive marker of tamoxifen resistance in estrogen receptor positive breast cancer

Background

Despite the success of tamoxifen since its introduction, about one-third of patients with estrogen (ER) and/or progesterone receptor (PgR) - positive breast cancer (BC) do not benefit from therapy. Here, we aim to identify molecular mechanisms and protein biomarkers involved in tamoxifen resistance.

Results

Using iTRAQ and Immobilized pH gradient-isoelectric focusing (IPG-IEF) mass spectrometry based proteomics we compared tumors from 12 patients with early relapses (<2 years) and 12 responsive to therapy (relapse-free > 7 years). A panel of 13 proteins (TCEAL4, AZGP1, S100A10, ALDH6A1, AHNAK, FBP1, S100A4, HSP90AB1, PDXK, GFPT1, RAB21, MX1, CAPS) from the 3101 identified proteins, potentially separate relapse from non-relapse BC patients. The proteins in the panel are involved in processes such as calcium (Ca²⁺) signaling, metabolism, epithelial mesenchymal transition (EMT), metastasis and invasion. Validation of the highest expressed proteins in the relapse group identify high tumor levels of CAPS as predictive of tamoxifen response in a patient cohort receiving tamoxifen as only adjuvant therapy.

Conclusions

This data implicate CAPS in tamoxifen resistance and as a potential predictive marker.

Electronic supplementary material

The online version of this article (doi:10.1186/s12014-015-9080-y) contains supplementary material, which is available to authorized users.     

miR-142-3p is a tumor suppressor that inhibits estrogen receptor expression in ER-positive breast cancer

Estrogen receptors (ERs) are involved in the development of many types of malignant tumors, in particular, breast cancer. Among others, ERs affect cell growth, proliferation, and differentiation. The microRNA (miRNA) miR-142-3p has been shown to inhibit carcinogenesis by regulating various cellular processes, including cell cycle progression, cell migration, apoptosis, and invasion. It does so via targeting molecules involved in a range of signaling pathways. We surgically collected 20 ER-positive breast cancer samples, each with matched adjacent normal breast tissue, and measured the expression of miR-142-3p via quantitative real-time polymerase chain reaction (qRT-PCR). Bioinformatics methods, luciferase reporter assay, qRT-PCR, and western blot analysis were used to assess whether miR-142-3p could target ESR1, which encodes the estrogen receptor, in ER-positive breast cancer cells and patient samples. We also restored miRNA expression and performed cell viability, cytotoxicity, and colony formation assays. Western blot analysis and qRT-PCR were used to study the expression of apoptosis and stemness markers. We found that miR-142-3p is downregulated in ER-positive breast cancers. Restoration of miR-142-3p expression in ER-positive breast cancer cells reduced cell viability, induced apoptosis via the intrinsic pathway and decreased both colony formation and the expression of stem cell markers. Bioinformatic analysis predicted miR-142-3p could bind to 3′-untranslated region ESR1 messenger RNA (mRNA). Consistently, we demonstrated that miR-142-3p reduced luciferase activity in ER-positive breast cancer cells, and decreased ESR1 expression in both mRNA and protein levels. The results revealed miR-142-3p and ESR1 expression correlated negatively in ER-positive breast cancer samples. The results suggest miR-142-3p acts as a tumor suppressor via multiple mechanisms. Thus, restoration of miR-142-3p expression, for example, via miRNA replacement therapy, may represent an effective strategy for the treatment of ER-positive breast cancer patients.     

An estrogen receptor (ER)‐related signature in predicting prognosis of ER‐positive breast cancer following endocrine treatment

Quite a few estrogen receptor (ER)‐positive breast cancer patients receiving endocrine therapy are at risk of disease recurrence and death. ER‐related genes are involved in the progression and chemoresistance of breast cancer. In this study, we identified an ER‐related gene signature that can predict the prognosis of ER‐positive breast cancer patient receiving endocrine therapy. We collected RNA expression profiling from Gene Expression Omnibus database. An ER‐related signature was developed to separate patients into high‐risk and low‐risk groups. Patients in the low‐risk group had significantly better survival than those in the high‐risk group. ROC analysis indicated that this signature exhibited good diagnostic efficiency for the 1‐, 3‐ and 5‐year disease‐relapse events. Moreover, multivariate Cox regression analysis demonstrated that the ER‐related signature was an independent risk factor when adjusting for several clinical signatures. The prognostic value of this signature was validated in the validation sets. In addition, a nomogram was built and the calibration plots analysis indicated the good performance of this nomogram. In conclusion, combining with ER status, our results demonstrated that the ER‐related prognostic signature is a promising method for predicting the prognosis of ER‐positive breast cancer patients receiving endocrine therapy.     

DNA methylation in breast cancers: Differences based on estrogen receptor status and recurrence

DNA methylation plays a role in the etiology of primary breast cancers. We analyzed paired primary and second breast tumors to elucidate the role of methylation in recurrence. Methylation profiles from paired primary and second breast tumors of 23 women were assessed using the HumanMethylation450 BeadChip. Twelve women had estrogen receptor positive (ERpos) primary and second tumors, five had estrogen receptor negative (ERneg) primary and second tumors, and six had an ERpos primary tumor but an ERneg second tumor. Stratifying tumors by occurrence revealed that the greater methylation previously associated with ERpos tumors, is more pronounced in primary tumors than in second tumors. Further, ERneg second tumors are more methylated than ERpos second tumors among women who had ERpos primary tumors. Pathway analyses using gene lists generated from comparisons of methylation in ERpos primary tumors from the paired sets with ERpos tumors from six women without recurrences, identified differences between groups based on the ER status of the second tumor. Hypermethylated genes of significantly enriched pathways were differentially associated with survival. DNA methylation profiles of ERpos primary breast tumors support the development and use of tumor methylation profiles for stratifying women with breast cancer both for prognosis and therapy.     

雌激素受体信号通路在乳腺癌发生和治疗中的作用

雌激素受体信号通路在调控乳腺细胞增殖和凋亡等生理机能中发挥重要功能,该通路出现调控异常时可导致乳腺癌发生。雌激素受体在乳腺癌发生中的作用机制包括核受体介导的基因组信号通路和膜受体介导的非基因组信号通路以及二者的相互作用。基于雌激素受体信号通路及其关键信号分子的靶向治疗是开展乳腺癌治疗的重要策略与有效途径。对雌激素受体结构以及雌激素受体信号通路在乳腺癌发生和治疗中的作用作一综述。     

Environmental magnetic fields inhibit the antiproliferative action of tamoxifen and melatonin in a human breast cancer cell line

We have previously reported that environmental-level magnetic fields (1.2 μT [12 milligauss], 60 Hz) block the growth inhibition of the hormone melatonin (10⁻⁹ M) on MCF-7 human breast cancer cells in vitro. We now report that the same 1.2 μT, 60 Hz magnetic fields significantly block the growth inhibitory action of pharmacological levels of tamoxifen (10⁻⁷ M). In biophysical studies we have taken advantage of Faraday's Law of Current Induction and tested whether the 1.2 μT magnetic field or the associated induced electric field is responsible for this field effect on melatonin and tamoxifen. We observe that the magnetic field component is associated with the field blocking effect on melatonin and tamoxifen function. To our knowledge the tamoxifen studies represent the first experimental evidence for an environmental-level magnetic field modification of drug interaction with human breast cancer cells. Together, these findings provide support to the theory that environmental-level magnetic fields can act to modify the action of a drug or hormone on regulation of cell proliferation. Melatonin and tamoxifen may act through different biological pathways to down-regulate cell growth, and further studies are required to identify a specific biological site of interaction for the 1.2 μT magnetic field. Bioelectromagnetics 18:555–562, 1997. Published 1997 Wiley-Liss, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

Differential expression of estrogen receptor alpha (ERalpha) protein in MCF-7 breast cancer cells chronically exposed to TCDD

Estrogens play a key role in the development and evolution of breast cancer tumors. Estrogen receptor alpha (ERalpha) mediates many of the biological activities of estrogens, and its expression is associated with low invasiveness and good prognosis. Recent epidemiological reports suggest that long-term exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is implicated in the increased incidence of breast cancer in exposed women. TCDD interferes with the expression of some ERalpha-dependent genes and inhibits estradiol (E2)- dependent growth of breast cancer cells in vitro. However, E2-dependent xenographs of MCF-7 human breast cancer cells resumed growth after a 2-week exposure to TCDD. The mechanisms involved in the resumption of cell growth are not completely understood. In this study, we show that short term-exposure (16 days) to 1 nM TCDD results in the suppression of ERalpha protein expression, while chronic exposure for more than 1 year (LTDX cells) results in the partial re-expression of the receptor. Immunocytochemistry studies showed that re-expression of ERalpha in LTDX cells occurred in some of the cells. Analysis by Western immunoblots indicated that four out of five LTDX clones expressed ERalpha at levels comparable to those in unexposed MCF-7 cells. Removal of TCDD treatment for 16 days restored the expression of ERalpha in the ERalpha-negative clonal cells. These results suggest that MCF-7 cells chronically exposed to TCDD contain at least two cell subpopulations that may respond differently to the ERalpha-mediated effects of TCDD.     

Estrogen receptor alpha/beta isoforms, but not betacx, modulate unique patterns of gene expression and cell proliferation in Hs578T cells

The actions of 17beta-estradiol (E2) and selective estrogen receptor modulators (SERMs) have been extensively investigated regarding their ability to act through estrogen receptor-alpha (ERalpha) to perturb estrogen receptor positive (ER+) breast cancer (BC) growth. However, many BCs also express ERbeta, along with multiple estrogen receptor (ER) splice variants such as ERbetacx, an ERbeta splice variant incapable of binding ligand. To gain a more comprehensive understanding of ER action in BC cells, we stably expressed ERalpha, ERbeta, or ERbetacx under doxycycline (Dox) control in Hs578T cells. Microarrays performed on E2 or 4OH-tamoxifen (4HT) treated Hs578T ERalpha and ERbeta cells revealed distinct ligand and receptor-dependent patterns of gene regulation, while the induction of ERbetacx did not alter gene expression patterns. E2 stimulation of Hs578T ERbeta cells resulted in a 27% decrease in cellular proliferation, however, no significant change in proliferation was observed following the exposure of Hs578T ERalpha or ERbeta cells to 4HT. Expression of ERbetacx in Hs578T cells did not effect cellular proliferation. Flow cytometry assays revealed a 50% decrease in E2-stimulated Hs578T ERbeta cells entering S-phase, along with a 17% increase in G0/G1 cell-cycle arrest. We demonstrate here that ERalpha and ERbeta regulate unique gene expression patterns in Hs578T cells, and such regulation likely is responsible for the observed isoform-specific changes in cell proliferation. Hs578T ER expressing cell-lines provide a unique BC model system, permitting the comparison of ERalpha, ERbeta, and ERbetacx actions in the same cell-line.     

Acquired resistance to selective estrogen receptor modulators (SERMs) in clinical practice (tamoxifen & raloxifene) by selection pressure in breast cancer cell populations

Tamoxifen, a pioneering selective estrogen receptor modulator (SERM), has long been a therapeutic choice for all stages of estrogen receptor (ER)-positive breast cancer. The clinical application of long-term adjuvant antihormone therapy for the breast cancer has significantly improved breast cancer survival. However, acquired resistance to SERM remains a significant challenge in breast cancer treatment. The evolution of acquired resistance to SERMs treatment was primarily discovered using MCF-7 tumors transplanted in athymic mice to mimic years of adjuvant treatment in patients. Acquired resistance to tamoxifen is unique because the growth of resistant tumors is dependent on SERMs. It appears that acquired resistance to SERM is initially able to utilize either E₂ or a SERM as the growth stimulus in the SERM-resistant breast tumors. Mechanistic studies reveal that SERMs continuously suppress nuclear ER-target genes even during resistance, whereas they function as agonists to activate multiple membrane-associated molecules to promote cell growth. Laboratory observations in vivo further show that three phases of acquired SERM-resistance exists, depending on the length of SERMs exposure. Tumors with Phase I resistance are stimulated by both SERMs and estrogen. Tumors with Phase II resistance are stimulated by SERMs, but are inhibited by estrogen due to apoptosis. The laboratory models suggest a new treatment strategy, in which limited-duration, low-dose estrogen can be used to purge Phase II-resistant breast cancer cells. This discovery provides an invaluable insight into the evolution of drug resistance to SERMs, and this knowledge is now being used to justify clinical trials of estrogen therapy following long-term antihormone therapy. All of these results suggest that cell populations that have acquired resistance are in constant evolution depending upon selection pressure. The limited availability of growth stimuli in any new environment enhances population plasticity in the trial and error search for survival.     

RANK links senescence to stemness in the mammary epithelia,delaying tumor onset but increasing tumor aggressiveness

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Sex hormone-binding globulin, its membrane receptor, and breast cancer: a new approach to the modulation of estradiol action in neoplastic cells

The role of human Sex Hormone-Binding Globulin (SHBG), the plasma carrier of sex steroids, and its membrane receptor, SHBG-R, in estrogen-dependent breast cancer has been investigated in our laboratory in the past few years. SHBG-R is expressed in MCF-10 A cells (not neoplastic mammary cells), MCF-7 cells (breast cancer, ER positive) and in tissue samples from patients affected with ER positive breast cancer, but not in estrogen-insensitive MDA-MB 231 cells. The SHBG/SHBG-R interaction, followed by the binding of estradiol to the complex protein/receptor, causes a significant increase of the intracellular levels of cAMP, but does not modify the amount of estradiol entering MCF-7 cells. The estradiol-induced proliferation of MCF-7 cells is inhibited by SHBG, through SHBG-R, cAMP and PKA. Similarly, the proliferation rate of tissue samples positive for SHBG-R was significantly lower than the proliferation rate of negative samples. SHBG and SHBG-R could thus trigger a ‘biologic’ anti-estrogenic pathway. In order to get a more detailed knowledge of this system, we first examined the frequence of the reported mutated form of SHBG in 255 breast cancer patients. The mutated SHBG is characterized by a point mutation (Asp 327→Asn) causing an additional N-glycosylation site, which does not affect the binding of steroids to SHBG. The frequence of the mutation was significantly higher (24.5%) in estrogen-dependent breast cancers than in healthy control subjects (11.6%). This observation confirms the close relationship between SHBG and estrogen-dependent breast cancer and suggests that the mutation could modify SHBG activity at cell site. Lastly, the possibility of using SHBG to modulate the estradiol action in breast cancer was further studied by transfecting MCF-7 cells with an expression vector carrying the SHBG cDNA (study in collaboration with G.L. Hammond). Transfected cells are able to produce significant amount of SHBG in their medium, but their SHBG-R is reduced to undetectable levels. The SHBG produced by transfected MCF-7 cells is, however, able to inhibit estradiol-induced proliferation of MCF-7 cells expressing a functional receptor. Thus, the local production of SHBG obtained with transfection could be a useful tool to control cell growth in estrogen-dependent breast cancer.     

Role of receptor occupancy in the transition from responsive to unresponsive states in cultured breast tumor cells

Progression from a steroid sensitive to insensitive state is characteristic of breast tumors, but little is known about the molecular mechanisms involved. Changes in steroid receptor can be associated with the progression. This paper reviews the cell culture data pertaining to loss of response and concludes that loss of receptor is a consequence rather than a cause of insensitivity. This view is based on evidence that loss of all response parameters occurs despite the presence of fully functional receptors as determined by transfection experiments. The postreceptor defect appears to be at the level of the hormone response element of the responsive genes and may involve DNA methylation. The implications of the model for human breast cancer biology are discussed.     

Stabilization of MORC2 by estrogen and antiestrogens through GPER1- PRKACA-CMA pathway contributes to estrogen-induced proliferation and endocrine resistance of breast cancer cells

ABSTRACT

Aberrant activation of estrogen signaling through three ESR (estrogen receptor) subtypes, termed ESR1/ERα, ESR2/ERβ, and GPER1 (G protein-coupled estrogen receptor 1), is implicated in breast cancer pathogenesis and progression. Antiestrogens tamoxifen (TAM) and fulvestrant (FUL) are effective for treatment of ESR1-positive breast tumors, but development of resistance represents a major clinical challenge. However, the molecular mechanisms behind these events remain largely unknown. Here, we report that 17β-estradiol (E2), TAM, and FUL stabilize MORC2 (MORC family CW-type zinc finger 2), an emerging oncoprotein in human cancer, in a GPER1-dependent manner. Mechanistically, GPER1 activates PRKACA (protein kinase cAMP-activated catalytic subunit alpha), which in turn phosphorylates MORC2 at threonine 582 (T582). Phosphorylated MORC2 decreases its interaction with HSPA8 (heat shock protein family A [Hsp70] member 8) and LAMP2A (lysosomal associated membrane protein 2A), two core components of the chaperone-mediated autophagy (CMA) machinery, thus protecting MORC2 from lysosomal degradation by CMA. Functionally, knockdown of MORC2 attenuates E2-induced cell proliferation and enhances cellular sensitivity to TAM and FUL. Moreover, introduction of wild-type MORC2, but not its phosphorylation-lacking mutant (T582A), in MORC2-depleted cells restores resistance to antiestrogens. Clinically, the phosphorylation levels of MORC2 at T582 are elevated in breast tumors from patients undergoing recurrence after TAM treatment. Together, these findings delineate a phosphorylation-dependent mechanism for MORC2 stabilization in response to estrogen and antiestrogens via blocking CMA-mediated lysosomal degradation and uncover a dual role for MORC2 in both estrogen-induced proliferation and resistance to antiestrogen therapies of breast cancer cells.     

Nuclear estrogen receptor targeted photodynamic therapy: selective uptake and killing of MCF-7 breast cancer cells by a C17alpha-alkynylestradiol-porphyrin conjugate

We hypothesized that over-expression of estrogen receptor (ER) in hormone-sensitive breast cancer could be harnessed synergistically with the tumor-migrating effect of porphyrins to selectively deliver estrogen-porphyrin conjugates into breast tumor cells, and preferentially kill the tumor cells upon exposure to red light. In the present work we synthesized four (4) conjugates of C17-alpha-alkynylestradiol and chlorin e6-dimethyl ester with varying tether lengths, and showed that all these conjugates specifically bound to recombinant ER alpha. In a cellular uptake assay with ER-positive MCF-7 and ER-negative MDA-MB 231 human breast cancer cell-lines, we observed that one such conjugate (E17-POR, XIV) was selectively taken up in a dose-dependent and saturable manner by MCF-7 cells, but not by MDA-MB 231 cells. Furthermore, MCF-7 cells, but not MDA-MB 231 cells, were selectively and efficiently killed by exposure to red light after incubation with E17-POR. Therefore, the combination approach, including drug and process modalities has the potential to be applied clinically for hormone-sensitive cancers in organs where ER is significantly expressed. This could potentially be carried out either as monotherapy involving a photo-induced selective destruction of tumor cells and/or adjuvant therapy in post-surgical treatment for the destruction of residual cancer cells in tissues surrounding the tumor.     

Development and evolution of therapies targeted to the estrogen receptor for the treatment and prevention of breast cancer

This article describes the origins and evolution of "antiestrogenic" medicines for the treatment and prevention of breast cancer. Developing drugs that target the estrogen receptor (ER) either directly (tamoxifen) or indirectly (aromatase inhibitors) has improved the prognosis of breast cancer and significantly advanced healthcare. The development of the principles for treatment and the success of the concept, in practice, has become a model for molecular medicine and presaged the current testing of numerous targeted therapies for all forms of cancer. The translational research with tamoxifen to target the ER with the appropriate duration (5 years) of adjuvant therapy has contributed to the falling national death rates from breast cancer. Additionally, exploration of the endocrine pharmacology of tamoxifen and related nonsteroidal antiestrogen (e.g. keoxifene now known as raloxifene) resulted in the laboratory recognition of selective ER modulation and the translation of the concept to use raloxifene for the prevention of osteoporosis and breast cancer. However, the extensive evaluation of tamoxifen treatment revealed small but significant side effects such as endometrial cancer, blood clots and the development of acquired resistance. The solution was to develop drugs that targeted the aromatase enzyme specifically to prevent the conversion of androstenedione to estrone and subsequently estradiol. The successful translational research with the suicide inhibitor 4-hydroxyandrostenedione (known as formestane) pioneered the development of a range of oral aromatase inhibitors that are either suicide inhibitors (exemestane) or competitive inhibitors (letrozole and anastrozole) of the aromatase enzyme. Treatment with aromatase inhibitors is proving effective and is associated with reduction in the incidence of endometrial cancer and blood clots when compared with tamoxifen and there is also limited cross resistance so treatment can be sequential. Current clinical trials are addressing the value of aromatase inhibitors as chemopreventive agents for postmenopausal women.     

A mutation in β‐tubulin and a sustained dependence on androgen receptor signalling in a newly established docetaxel‐resistant prostate cancer cell line

The mechanisms of docetaxel resistance in PC (prostate cancer) are unclear because of the lack of suitable experimental models, and no effective treatment exists for docetaxel‐resistant PC. We established a docetaxel‐resistant cell line, LNDCr, from an androgen‐refractory PC cell line, LNCaP‐hr, by intermittent exposure to docetaxel in vitro. The LNDCr cells harboured an F270I mutation in class I β‐tubulin, and demonstrated impaired tubulin polymerization by docetaxel. AR signalling was sustained in LNDCr cells, and AR knockdown suppressed the growth of LNDCr cells. These results suggest that an acquired mutation in β‐tubulin is associated with docetaxel resistance in PC and that a novel AR‐targeted therapy is effective for docetaxel‐resistant PC.     

High FOXA1 levels induce ER transcriptional reprogramming,a pro-metastatic secretome,and metastasis in endocrine-resistant breast cancer

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Protein kinase D1 regulates ERα‐positive breast cancer cell growth response to 17β‐estradiol and contributes to poor prognosis in patients

About 70% of human breast cancers express and are dependent for growth on estrogen receptor α (ERα), and therefore are sensitive to antiestrogen therapies. However, progression to an advanced, more aggressive phenotype is associated with acquisition of resistance to antiestrogens and/or invasive potential. In this study, we highlight the role of the serine/threonine‐protein kinase D1 (PKD1) in ERα‐positive breast cancers. Growth of ERα‐positive MCF‐7 and MDA‐MB‐415 human breast cancer cells was assayed in adherent or anchorage‐independent conditions in cells overexpressing or depleted for PKD1. PKD1 induces cell growth through both an ERα‐dependent manner, by increasing ERα expression and cell sensitivity to 17β‐estradiol, and an ERα‐independent manner, by reducing cell dependence to estrogens and conferring partial resistance to antiestrogen ICI 182,780. PKD1 knockdown in MDA‐MB‐415 cells strongly reduced estrogen‐dependent and independent invasion. Quantification of PKD1 mRNA levels in 38 cancerous and non‐cancerous breast cell lines and in 152 ERα‐positive breast tumours from patients treated with adjuvant tamoxifen showed an association between PKD1 and ERα expression in 76.3% (29/38) of the breast cell lines tested and a strong correlation between PKD1 expression and invasiveness (P < 0.0001). In tamoxifen‐treated patients, tumours with high PKD1 mRNA levels (n = 77, 50.66%) were significantly associated with less metastasis‐free survival than tumours with low PKD1 mRNA expression (n = 75, 49.34%; P = 0.031). Moreover, PKD1 mRNA levels are strongly positively associated with EGFR and vimentin levels (P < 0.0000001). Thus, our study defines PKD1 as a novel attractive prognostic factor and a potential therapeutic target in breast cancer.