Estrogen stimulates transcription from the human prolactin distal promoter through AP1 and estrogen responsive elements in T47D human breast cancer cells

The immunotoxin targeting PRLR increases tamoxifen sensitivity and enhances the efficacy of chemotherapy in breast cancer

BACKGROUND

Though tamoxifen achieves success in treating estrogen receptor α (ERα)-positive breast cancer, the followed development of tamoxifen resistance is a common challenge in clinic. Signals downstream of prolactin receptor (PRLR) could synergize with ERα in breast cancer progression. However, the potential effect of targeting PRL-PRLR axis combined with tamoxifen has not been thoroughly investigated.

METHODS

High-throughput RNA-seq data obtained from TCGA, Metabric and GEO datasets were analyzed to explore PRLR expression in breast cancer cell and the association of PRLR expression with tamoxifen treatment. Exogenous or PRL overexpression cell models were employed to investigate the role of activated PRLR pathway in mediating tamoxifen insensitivity. Immunotoxin targeting PRLR (N8-PE24) was constructed with splicing-intein technique, and the efficacy of N8-PE24 against breast cancer was evaluated using in vitro and in vivo methods, including analysis of cells growth or apoptosis, 3D spheroids culture, and animal xenografts.

RESULTS

PRLR pathway activated by PRL could significantly decrease sensitivity of ERα-positive breast cancer cells to tamoxifen. Tamoxifen treatment upregulated transcription of PRLR and could induce significant accumulation of PRLR protein in breast cancer cells by alkalizing lysosomes. Meanwhile, tamoxifen-resistant MCF7 achieved by long-term tamoxifen pressure exhibited both upregulated transcription and protein level of PRLR. Immunotoxin N8-PE24 enhanced sensitivity of breast cancer cells to tamoxifen both in vitro and in vivo. In xenograft models, N8-PE24 significantly enhanced the efficacy of tamoxifen and paclitaxel when treating PRLR-positive triple-negative breast cancer.

CONCLUSIONS

PRL-PRLR axis potentially associates with tamoxifen insensitivity in ERα-positive breast cancer cells. N8-PE24 could inhibit cell growth of the breast cancers and promote drug sensitivity of PRLR-positive breast cancer cells to tamoxifen and paclitaxel. Our study provides a new perspective for targeting PRLR to treat breast cancer.

Potent Estrogen Receptor β Agonists with Inhibitory Activity In Vitro , Fail to Suppress Xenografts of Endocrine-Resistant Cyclin-dependent Kinase 4/6 inhibitor-Resistant Breast Cancer Cells

Objective

Seventy percent of newly diagnosed breast cancers are estrogen receptor-α positive and HER2/neu negative [1]. First-line treatments incorporate endocrine therapy and cyclin-dependent kinase 4/6 inhibitors [2]. However, therapy resistance occurs in most patients [3-5]. Hence, there is an urgent need for effective second-line treatments. We previously showed that the potent estrogen receptor-β agonists, OSU-ERb-12 and LY500307, synergized with the selective estrogen receptor modulator, tamoxifen, in vitro. Furthermore, we showed that these compounds inhibited endocrine-resistant and cyclin-dependent kinase 4/6-inhibitor-resistant estrogen receptor α-positive cell lines in vitro [6]. Here, we used fulvestrant- and abemaciclib-resistant T47D-derived cell line xenografts to determine the efficacy of the combination of OSU-ERb-12 and LY500307 with tamoxifen in vivo.

Results

Despite efficacy in vitro, treatments failed to reduce xenograft tumor volumes. Hence, we conclude that this treatment strategy lacks direct cancer cell-intrinsic cytotoxic efficacy in vivo.

miR-19b-3p regulated by estrogen controls lipid synthesis through targeting MSMO1 and ELOVL5 in LMH cells

miR-19b-3p is reported to undertake various biological role, while its function and action mechanism in chicken hepatic lipid metabolism is unclear. Conservation analysis and tissue expression pattern of miR-19b-3p and its target gene were evaluated, respectively. Dual luciferase reporter system and Western blot technologies were adopted to validate miR-19b-3p target gene. Overexpression and knockdown assays were done to explore the biological functions of miR-19b-3p and target gene in Leghorn Male Hepatoma cell line (LMH). Regulatory approaches of estrogen on miR-19b-3p and target gene expressions are analyzed through site-directed mutation combined with estrogen receptors antagonist treatment assays. The results showed that chicken miR-19b-3p mature sequences are highly conserved among Capra hircus, Columba livia, Rattus norvegicus, Mus musculus, Cricetulus griseus, Danio rerio, Danio novaehollandiae, Orycodylus porosus, Crocodylus porosus, Gadus morhua, and widely expressed in lung, ovary, spleen, duodenum, kidney, heart, liver, leg muscle, and pectoral muscle tissues. miR-19b-3p could significantly increase intracellular triglyceride (TG) content and decrease intracellular cholesterol (TC) content via targeting methylsterol monooxygenase 1 (MSMO1) and elongase of very long chain fatty acids 5 (ELOVL5), which are highly conserved among species, in both mRNA and protein levels. Estrogen could inhibit miR-19b-3p expression, but directly promoted MSMO1 transcription via estrogen receptor α (ERα) and indirectly regulated ELOVL5 expression at the transcription level. Meanwhile, estrogen could also upregulate MSMO1 and ELOVL5 expression through inhibiting miR-19b-3p expression at the post-transcription level. Taken together, these results highlight the role and regulatory mechanism of miR-19b-3p in hepatic lipid metabolism in chicken, and might produce useful comparative information for human obesity studies and biomedical research.

Prolactin peptide (pPRL) induces anti-prolactin antibodies, ROS and cortisol but suppresses specific immune responses in rainbow trout

Prolactin has several immune functions in fish however, the effects on innate and specific components of rainbow trout immunity are currently unknown. Therefore in this study, prolactin peptide (pPRL) injection in rainbow trout generated anti-PRL antibodies that were confirmed through Western blot assays of fish brain tissue extract. At the same time, this group of fish was immunized with a viral antigen (VP2) and the specific antibody titer generated by the rainbow trout was subsequently determined, as well as the sero-neutralizing capacity of the antibodies. Interestingly, this group of fish (pPRL-VP2) generated approximately 150% less antibodies compared with fish immunized only with the viral antigen (VP2), and pPRL-VP2 fish increased their cortisol level by 4 times compared to the control. Additionally, through qPCR assay, we determined that the pPRL-VP2 fish group decreased pro-inflammatory transcript expression, and the serum of these (pPRL-VP2) fish stimulated ROS production in untreated fish leukocytes, a phenomenon that was blocked by the pharmacological cortisol receptor inhibitor (RU486). Collectively, this is the first report that indicates that pPRL could modulate both components of immunity in rainbow trout.

Genome-Wide Analysis of the FABP Gene Family in Liver of Chicken (Gallus gallus): Identification,Dynamic Expression Profile, and RegulatoryMechanism

The fatty acid-binding protein (FABP) gene family, which encodes a group of fatty acid-trafficking molecules that affect cellular functions, has been studied extensively in mammals. However, little is known about the gene structure, expression profile, and regulatory mechanism of the gene family in chickens. In the present study, bioinformatics-based methods were used to identify the family members and investigate their evolutionary history and features of gene structure. Real-time PCR combined with in vivo and in vitro experiments were used to examine the spatiotemporal expression pattern, and explore the regulatory mechanism of FABP genes. The results show that nine members of the FABP gene family, which branched into two clusters and shared a conserved FATTYACIDBP domain, exist in the genome of chickens. Of these, seven FABP genes, including FABP1, FABP3-7, and FABP10 were abundantly expressed in the liver of hens. The expression levels of FABP1, FABP3, and FABP10 were significantly increased, FABP5 and FABP7 were significantly decreased, and FABP4 and FABP6 remained unchanged in hens at the peak laying stage in comparison to those at the pre-laying stage. Transcription of FABP1 and FABP3 were activated by estrogen via estrogen receptor (ER) α, whilst FABP10 was activated by estrogen via ERβ. Meanwhile, the expression of FABP1 was regulated by peroxisome proliferator activated receptor (PPAR) isoforms, of which tested PPARα and PPARβ agonists significantly inhibited the expression of FABP1, while tested PPARγ agonists significantly increased the expression of FABP1, but downregulated it when the concentration of the PPARγ agonist reached 100 nM. The expression of FABP3 was upregulated via tested PPARβ and PPARγ agonists, and the expression of FABP7 was selectively promoted via PPARγ. The expression of FABP10 was activated by all of the three tested PPAR agonists, but the expression of FABP4-6 was not affected by any of the PPAR agonists. In conclusion, members of the FABP gene family in chickens shared similar functional domains, gene structures, and evolutionary histories with mammalian species, but exhibited varying expression profiles and regulatory mechanisms. The results provide a valuable resource for better understanding the biological functions of individual FABP genes in chickens.

Interaction between 17β-estradiol, prolactin and human papillomavirus induce E6/E7 transcript and modulate the expression and localization of hormonal receptors

Background

Cervical cancer (CC) is the second most common cancer in less developed countries and the second leading cause of death by cancer in women worldwide. The 99% of CC patients are infected with the Human Papilloma Virus (HPV), being HPV16 and HPV18 infection the most frequent. Even though HPV is considered to be a necessary factor for the development of CC, it is not enough, as it requires the participation of other factors such as the hormonal ones. Several studies have demonstrated the requirement of estrogen and its receptors (ERα, ERβ, and GPER) in the precursor lesions progress towards CC. Also, prolactin (PRL) and its receptor (PRLR) have been associated with CC. The molecular mechanisms underlying the cooperation of these hormones with the viral oncoproteins are not well elucidated. For this reason, this study focused on analyzing the contribution of 17β-estradiol (E2), PRL, and HPV on the expression and localization of hormone receptors, as well as to evaluate whether these hormones may promote greater expression of HPV oncogenes and contribute to tumor progression.

Methods

qPCR was used to evaluate the effect of E2 and PRL on the expression of E6 and E7 oncoproteins in HeLa and SiHa cervical cancer cells lines. HaCaT cells were transduced with the viral oncogenes E6 and E7 from HPV 16 and 18. ERα, ERβ, GPER, and PRLR expression and localization were evaluated by qPCR, Western blot and immunofluorescence.

Results

E2 and PRL induce E6/E7 oncogenes expression in HeLa and SiHa cells. E6 and E7 oncogenes of HPV16/18 significantly increased the protein expression of ERα, GPER, and PRLR. ERβ was positively regulated only by E6 oncogenes of HPV16/18. Besides, some of these oncogenes modify the location of PRLR toward cytoplasm, and ERα, ERβ, and GPER mainly to the nucleus.

Conclusion

Our studies suggest that the mutual regulation between E2, PRL, and HPV oncogenes could cooperate with the carcinogenesis process in CC.

Mechanisms for estrogen receptor expression in human cancer

Estrogen is a steroid hormone that has critical roles in reproductive development, bone homeostasis, cardiovascular remodeling and brain functions. However, estrogen also promotes mammary, ovarian and endometrial tumorigenesis. Estrogen antagonists and drugs that reduce estrogen biosynthesis have become highly successful therapeutic agents for breast cancer patients. The effects of estrogen are largely mediated by estrogen receptor (ER) α and ERβ, which are members of the nuclear receptor superfamily of transcription factors. The mechanisms underlying the aberrant expression of ER in breast cancer and other types of human tumors are complex, involving considerable alternative splicing of ERα and ERβ, transcription factors, epigenetic and post-transcriptional regulation of ER expression. Elucidation of mechanisms for ER expression may not only help understand cancer progression and evolution, but also shed light on overcoming endocrine therapy resistance. Herein, we review the complex mechanisms for regulating ER expression in human cancer.

Dynamic Expression Profile, Regulatory Mechanism and Correlation with Egg-laying Performance of ACSF Gene Family in Chicken (Gallus gallus)

Acyl-CoA synthetases (ACSs) are responsible for acyl-CoA synthesis from nonpolar hydrophilic fatty acids and play a vital role in many metabolic processes. As a category of ACS isozymes, members of ACS family (ACSF1-3) participate in lipid metabolism; however, their expression patterns, regulatory mechanisms and effects on egg-laying performance in chicken are poorly understood. Our in vivo and in vitro studies showed that ACSF1-3 genes were extensively expressed, and their expression levels changed dynamically in the liver among different development stages. Moreover, ACSF1 expression was upregulated and ACSF2 expression was downregulated by estrogen, but ACSF3 showed no response to estrogen treatment. The regulatory effect of estrogen on ACSF1 expression was mediated via ERα. The ACSF2 was highly expressed in the liver in peak-laying hens compared with pre-laying and late-laying hens, and also highly expressed in the liver continued egg-laying hens compared with inactive egg-laying hens. It is suggested that hepatic ACSF2 expression level might relate to egg-laying performance in chicken. In conclusion, the expression of ACSF1 was upregulated by estrogen via ERα, and the expression of ACSF2 was downregulated by estrogen and might be related to egg-laying performance in chicken.

Involvement of miR-106b in tumorigenic actions of both prolactin and estradiol

Prolactin promotes a variety of cancers by an array of different mechanisms. Here, we have investigated prolactin's inhibitory effect on expression of the cell cycle-regulating protein, p21. Using a miRNA array, we identified a number of miRNAs upregulated by prolactin treatment, but one in particular that was strongly induced by prolactin and predicted to bind to the 3′UTR of p21 mRNA, miR-106b. By creating a p21 mRNA 3′UTR-luciferase mRNA construct, we demonstrated degradation of the construct in response to prolactin in human breast, prostate and ovarian cancer cell lines. Increased expression of miR-106b replicated, and anti-miR-106b counteracted, the effects of prolactin on degradation of the 3′UTR construct, p21 mRNA levels, and cell proliferation in breast (T47D) and prostate (PC3) cancer cells. Increased expression of miR-106b also stimulated migration of the very epithelioid T47D cell line. By contrast, anti-miR-106b dramatically decreased expression of the mesenchymal markers, SNAIL-2, TWIST-2, VIMENTIN, and FIBRONECTIN. Using signaling pathway inhibitors and the 3′UTR construct, induction of miR-106b by prolactin was determined to be mediated through the MAPK/ERK and PI3K/Akt pathways and not through Jak2/Stat5 in both T47D and PC3 cells. Prolactin activation of MAPK/ERK and PI3K/Akt also activates ERα in the absence of an ERα ligand. 17β-estradiol promoted degradation of the construct in both cell lines and pre-incubation in the estrogen antagonist, Fulvestrant, blocked the ability of both prolactin and 17β-estradiol to induce the construct-degrading activity. Together, these data support a convergence of the prolactin and 17β-estradiol miR-106b-elevating signaling pathways at ERα.

Grass Carp Prolactin Gene: Structural Characterization and Signal Transduction for PACAP-induced Prolactin Promoter Activity

In this study, structural analysis of grass carp prolactin (PRL) gene was performed and the signaling mechanisms for pituitary adenylate cyclase-activating peptide (PACAP) regulation of PRL promoter activity were investigated. In αT3-1 cells, PRL promoter activity could be induced by oPACAP₃₈ which was blocked by PACAP antagonist but not the VIP antagonist. The stimulatory effect of oPACAP₃₈ was mimicked by activation of AC/cAMP and voltage-sensitive Ca²⁺ channel (VSCC) signaling, or induction of Ca²⁺ entry. In parallel, PACAP-induced PRL promoter activity was negated or inhibited by suppressing cAMP production, inhibiting PKA activity, removal of extracellular Ca²⁺, VSCC blockade, calmodulin (CaM) antagonism, and inactivation of CaM kinase II. Similar sensitivity to L-type VSCC, CaM and CaM kinase II inhibition were also observed by substituting cAMP analog for oPACAP₃₈ as the stimulant for PRL promoter activity. Moreover, PACAP-induced PRL promoter activity was also blocked by inhibition of PLC signaling, attenuation of [Ca²⁺]i immobilization via IP3 receptors, and blockade of PI3K/P₇₀^S6K pathway. The PACAP-induced PRL promoter activation may involve transactivation of the transcription factor CREB. These results suggest that PACAP can stimulate PRL promoter activation by PAC1 mediated functional coupling of the Ca²⁺/CaM/CaM kinase II cascades with the AC/cAMP/PKA pathway. Apparently, other signaling pathways, including PLC/IP3 and PI3K/P₇₀^S6K cascades, may also be involved in PACAP induction of PRL gene transcription.

An integrative method to decode regulatory logics in gene transcription

Modeling of transcriptional regulatory networks (TRNs) has been increasingly used to dissect the nature of gene regulation. Inference of regulatory relationships among transcription factors (TFs) and genes, especially among multiple TFs, is still challenging. In this study, we introduced an integrative method, LogicTRN, to decode TF–TF interactions that form TF logics in regulating target genes. By combining cis-regulatory logics and transcriptional kinetics into one single model framework, LogicTRN can naturally integrate dynamic gene expression data and TF-DNA-binding signals in order to identify the TF logics and to reconstruct the underlying TRNs. We evaluated the newly developed methodology using simulation, comparison and application studies, and the results not only show their consistence with existing knowledge, but also demonstrate its ability to accurately reconstruct TRNs in biological complex systems.

Existing transcriptional regulatory networks models fall short of deciphering the cooperation between multiple transcription factors on dynamic gene expression. Here the authors develop an integrative method that combines gene expression and transcription factor-DNA binding data to decode transcription regulatory logics.

Role of Estrogen Response Element in the Human Prolactin Gene: Transcriptional Response and Timing

The use of bacterial artificial chromosome (BAC) reporter constructs in molecular physiology enables the inclusion of large sections of flanking DNA, likely to contain regulatory elements and enhancers regions that contribute to the transcriptional output of a gene. Using BAC recombineering, we have manipulated a 160-kb human prolactin luciferase (hPRL-Luc) BAC construct and mutated the previously defined proximal estrogen response element (ERE) located -1189 bp relative to the transcription start site, to assess its involvement in the estrogen responsiveness of the entire hPRL locus. We found that GH3 cell lines stably expressing Luc under control of the ERE-mutated hPRL promoter (ERE-Mut) displayed a dramatically reduced transcriptional response to 17β-estradiol (E2) treatment compared with cells expressing Luc from the wild-type (WT) ERE hPRL-Luc promoter (ERE-WT). The -1189 ERE controls not only the response to E2 treatment but also the acute transcriptional response to TNFα, which was abolished in ERE-Mut cells. ERE-WT cells displayed a biphasic transcriptional response after TNFα treatment, the acute phase of which was blocked after treatment with the estrogen receptor antagonist 4-hydroxy-tamoxifen. Unexpectedly, we show the oscillatory characteristics of hPRL promoter activity in individual living cells were unaffected by disruption of this crucial response element, real-time bioluminescence imaging showed that transcription cycles were maintained, with similar cycle lengths, in ERE-WT and ERE-Mut cells. These data suggest the -1189 ERE is the dominant response element involved in the hPRL transcriptional response to both E2 and TNFα and, crucially, that cycles of hPRL promoter activity are independent of estrogen receptor binding.

Estrogen receptorβ2 regulates interlukin-12 receptorβ2 expression via p38 mitogen-activated protein kinase signaling and inhibits non-small-cell lung cancer proliferation and invasion

Lung cancer is one of the most common types of cancer and is the leading cause of cancer-related mortality worldwide. Estrogens are known to be involved in the development and progression of non-small-cell lung cancer (NSCLC). These effects are initially mediated through binding of estrogen to estrogen receptors (ERs), in particular ERβ2. Our preliminary studies demonstrated that ERβ2 and interleukin-12 receptorβ2 (IL-12Rβ2) expression are correlated in NSCLC. The present study investigated the expression of these proteins in NSCLC cells and how changes in their expression affected cell proliferation and invasion. In addition, it aimed to explore whether p38 mitogen-activated protein kinase (p38MAPK) is involved in the regulation of IL-12Rβ2 expression by ERβ2. An immunocytochemical array was used to observe the distribution of ERβ2 and IL-12Rβ2. Co-immuoprecipitation was employed to observe the interaction between p38MAPK and IL-12Rβ2, by varying the expression of ERβ2 and p38MAPK. Western-blot analysis and reverse transcription-polymerase chain reaction assays were used to investigate the mechanism underlying ERβ2 regulation of IL-12Rβ2 expression. 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, scratch wound healing and Transwell assays were used to investigate the impact of ERβ2 on proliferative, invasive and migratory abilities of NSCLC cells. ERβ2 was predominantly found in the cytoplasm and nucleus, whilst IL-12Rβ2 was largely confined to the cytoplasm, although a degree of expression was observed in the nucleus. Compared with normal bronchial epithelial cells, IL-12Rβ2 and ERβ2 were overexpressed in the NSCLC cell groups. Coimmuoprecipitation demonstrated an interaction between p38MAPK and IL-12Rβ2. ERβ2 appeared to upregulate IL-12Rβ2 expression and inhibition of p38MAPK attenuated this effect. ERβ2 and IL-12Rβ2 expression inhibited the proliferation, metastasis and invasion of NSCLC cell lines, but knockout of IL-12Rβ2, even in the presence of ERβ2, led to an increase in NSCLC cell proliferation and invasiveness. In conclusion, to the best of our knowledge this study is the first to demonstrate that IL-12Rβ2 may be important in the mechanisms underlying ERβ2 inhibition of NSCLC development, and that this interaction may be mediated via p38MAPK.

Blockade of estrogen-stimulated proliferation by a constitutively-active prolactin receptor having lower expression in invasive ductal carcinoma

A comprehensive understanding of prolactin's (PRL's) role in breast cancer is complicated by disparate roles for alternatively-spliced PRL receptors (PRLR) and crosstalk between PRL and estrogen signaling. Among PRLRs, the short form 1b (SF1b) inhibits PRL-stimulated cell proliferation. In addition to ligand-dependent PRLRs, constitutively-active varieties, missing the S2 region of the extracellular domain (ΔS2), naturally occur. Expression analysis of the ΔS2 version of SF1b (ΔS2SF1b) showed higher expression in histologically-normal contiguous tissue versus invasive ductal carcinoma. To determine the function of ΔS2SF1b, a T47D breast cancer line with inducible expression was produced. Induction of ΔS2SF1b blocked estrogen-stimulated cell proliferation. Unlike intact SF1b, induction of ΔS2SF1b had no effect on PRL-mediated activation of Stat5a. However induction inhibited estrogen's stimulatory effects on serine-118 phosphorylation of estrogen receptor α, serine-473 phosphorylation of Akt, serine-9 phosphorylation of GSK3β, and c-myc expression. In addition, induction of ΔS2SF1b increased expression of the cell cycle-inhibiting protein, p21. Thus, increased expression of ΔS2SF1b, such as we demonstrate occurs with the selective PRLR modulator, S179D PRL, would create a physiological state in which estrogen-stimulated proliferation was inhibited, but differentiative responses to PRL were maintained.

Estrogen increases the transcription of human α2-Heremans-Schmid-glycoprotein by an interplay of estrogen receptor α and activator protein-1

The expression of α2-Heremans-Schmid-glycoprotein (AHSG) was estrogen responsive in oophorectomized (OVX) osteopenic rats and HepG2 cells. Estrogen receptor α (ERα) interacted with the c-Jun/c-Fos heterodimer and indirectly associated with the -1488/-1482 activator protein-1 (AP-1) motif of the AHSG promoter. Estrogen increased c-Jun/c-Fos expression via the mitogen-activated protein kinase (MAPK) pathway.

INTRODUCTION

AHSG is a hepatic secretory protein implicated in the regulation of bone homeostasis. Serum AHSG in women has been reported to decrease after menopause and increase with estrogen therapy. The detailed regulatory mechanism of estrogen on AHSG is unclear.

METHODS

A postmenopausal osteoporosis model was generated in OVX rats. Skeletal parameters were determined by automatic biochemical analysis and dual X-ray absorptiometry. The expression of AHSG was evaluated by ELISA, real-time PCR, and Western blot. The 1.5-kb 5'-promoter region of AHSG was analyzed by serial truncation and luciferase assays. The putative -1488/-1482 AP-1 responsive element was identified by electrophoresis mobility shift assay (EMSA). Chromatin immunoprecipitation (ChIP), re-ChIP, and co-immunoprecipitation (Co-IP) were used to characterize the interaction of ERα and AP-1 at the -1488/-1482 AP-1 binding site. The MAPK pathway was evaluated using a specific inhibitor and active transfection.

RESULTS

The expression of AHSG was estrogen responsive in both OVX rats and estradiol (E2)/ERα-treated HepG2 cells. E2/ERα most prominently increased luciferase activity of a construct with a putative -1488/-1482 AP-1 binding element. ERα interacted with the c-Jun/c-Fos heterodimer and indirectly associated with the -1488/-1482 AP-1 motif of the AHSG promoter. c-Jun/c-Fos expression was increased via the MAPK pathway by E2/ERα.

CONCLUSION

Estrogen activated the transcription of AHSG through an indirect binding of ERα to the -1488/-1482 AP-1 binding element, with the c-Jun/c-Fos heterodimers.

Calcitriol restores antiestrogen responsiveness in estrogen receptor negative breast cancer cells: a potential new therapeutic approach

BACKGROUND

Approximately 30% of breast tumors do not express the estrogen receptor (ER) α, which is necessary for endocrine therapy approaches. Studies are ongoing in order to restore ERα expression in ERα-negative breast cancer. The aim of the present study was to determine if calcitriol induces ERα expression in ER-negative breast cancer cells, thus restoring antiestrogen responses.

METHODS

Cultured cells derived from ERα-negative breast tumors and an ERα-negative breast cancer cell line (SUM-229PE) were treated with calcitriol and ERα expression was assessed by real time PCR and western blots. The ERα functionality was evaluated by prolactin gene expression analysis. In addition, the effects of antiestrogens were assessed by growth assay using the XTT method. Gene expression of cyclin D1 (CCND1), and Ether-à-go-go 1 (EAG1) was also evaluated in cells treated with calcitriol alone or in combination with estradiol or ICI-182,780. Statistical analyses were determined by one-way ANOVA.

RESULTS

Calcitriol was able to induce the expression of a functional ERα in ER-negative breast cancer cells. This effect was mediated through the vitamin D receptor (VDR), since it was abrogated by a VDR antagonist. Interestingly, the calcitriol-induced ERα restored the response to antiestrogens by inhibiting cell proliferation. In addition, calcitriol-treated cells in the presence of ICI-182,780 resulted in a significant reduction of two important cell proliferation regulators CCND1 and EAG1.

CONCLUSIONS

Calcitriol induced the expression of ERα and restored the response to antiestrogens in ERα-negative breast cancer cells. The combined treatment with calcitriol and antiestrogens could represent a new therapeutic strategy in ERα-negative breast cancer patients.

Prolactin expression in the cochlea of aged BALB/c mice is gender biased and correlates to loss of bone mineral density and hearing loss

Prolactin is a versatile hormone with over 300 known functions and predominantly expressed in the pituitary. However, its expression has additionally been found in a number of extrapituitary organs. Recently, we described the expression of prolactin in the inner ear of mice, where it was correlated to age. Previous research has shown prolactin to be linked to abnormal bone metabolism and hearing loss due to changes in morphology of the bony otic capsule. Here we further investigated the relationship between prolactin, hearing loss and cochlea bone metabolism. BALB/c mice were tested for hearing using ABR at 6 and 12 months of age. Bone mineral density of the cochlea was evaluated using microCT scanning. Prolactin expression was calculated using quantitative real time PCR. Expression of the key regulators of bone metabolism, osteoprotegerin and receptor activator of nuclear factor-kappaB ligand were also determined. We found that prolactin expression was exclusive to the female mice. This also correlated to a greater threshold shift in hearing for the females between 6 and 12 months of age. Analyses of the cochlea also show that the bone mineral density was lower in females compared to males. However, no gender differences in expression of osteoprotegerin or receptor activator of nuclear factor-kappaB ligand could be found. Further analysis of cochlea histological sections revealed larger ostocyte lacunae in the females. These results provide a possible mechanism for an age related hearing loss sub-type that is associated with gender and provides clues as to how this gender bias in hearing loss develops. In addition, it has the potential to lead to treatment for this specific type of hearing loss.

Prolactin--to be reconsidered in canine mammary tumourigenesis?

Mammary tumours represent the most common neoplastic disease of the female dog, and the incidence in female dogs is much higher than in women. Whereas the influence of sexual steroids on breast cancer (BC) development in dogs has been studied, very little is known about the role of prolactin (PRL). New studies show that until recently, the importance of PRL in human BC development and progression has been highly underestimated. PRL plays a role in promoting benign as well as malignant neoplastic cell growth in BC in vitro and in vivo. Sporadic publications proposed a tumour promotor role in the dog. The goal of this review is to summarize our knowledge about PRL and human BC as well as canine mammary tumourigenesis, and propose future research in this area.

Genetic variation in PRL and PRLR, and relationships with serum prolactin levels and breast cancer risk: results from a population-based case-control study in Poland

Introduction

Studies suggest that high circulating levels of prolactin increase breast cancer risk. It is unclear if genetic variations in prolactin (PRL) or prolactin receptor (PRLR) genes also play a role. Thus, we examined the relationship between single nucleotide polymorphisms (SNPs) in PRL and PRLR, serum prolactin levels and breast cancer risk in a population-based case-control study.

Methods

We genotyped 8 PRL and 20 PRLR tag SNPs in 1965 breast cancer cases and 2229 matched controls, aged 20-74, and living in Warsaw or Łódź, Poland. Serum prolactin levels were measured by immunoassay in a subset of 773 controls. Odds ratios (ORs) and 95% confidence intervals (CIs) for genotype associations with breast cancer risk were estimated using unconditional logistic regression, adjusted for age and study site. Geometric mean prolactin levels were estimated using linear regression models adjusted for age, study site, blood collection time, and menstrual cycle day (premenopausal women).

Results

Three SNPs were associated with breast cancer risk: in premenopausal women, PRLR rs249537 (T vs. C per-allele OR 1.39, 95% CI 1.07 - 1.80, P = 0.01); and in postmenopausal women, PRLR rs7718468 (C vs. T per-allele OR 1.16, 95% CI 1.03 - 1.30, P = 0.01) and PRLR rs13436213 (A vs. G per-allele OR 1.13 95% CI 1.01 - 1.26, P = 0.04). However, mean serum prolactin levels for these SNPs did not vary by genotype (P-trend > 0.05). Other SNPs were associated with serum prolactin levels: PRLR rs62355518 (P-trend = 0.01), PRLR rs10941235 (P-trend = 0.01), PRLR rs1610218 (P-trend = 0.01), PRLR rs34024951 (P-trend = 0.02), and PRLR rs9292575 (P-trend = 0.03) in premenopausal controls and PRL rs849872 (P-trend = 0.01) in postmenopausal controls.

Conclusions

Our data provide limited support for an association between common variations in PRLR and breast cancer risk. Altered serum prolactin levels were not associated with breast cancer risk-associated variants, suggesting that common genetic variation is not a strong predictor of prolactin-associated breast cancer risk in this population.

Progesterone induces expression of the prolactin receptor gene through cooperative action of Sp1 and C/EBP

Prolactin (Prl) and progesterone (P) cooperate synergistically during mammary gland development and tumorigenesis. We hypothesized that one mechanism for these effects may be through mutual induction of receptors (R). EpH4 mouse mammary epithelial cells stably transfected with PR-A express elevated levels of PrlR mRNA and protein compared to control EpH4 cells that lack the PR. Likewise, T47D human breast cancer cells treated with P overexpress the PrlR and activate PrlR promoter III. PrlR promoter III does not contain a classical P response element but contains several binding sites for transcription proteins, including C/EBP, Sp1 and AP1, which may also interact with the PR. Using promoter deletion and site directed mutagenesis analyses as well as gel shift assays, cooperative activation of the C/EBP and adjacent Sp1A, but not the Sp1B or AP1, sites by P is shown to confer P responsiveness leading to increased PrlR transcription.

Estrogen regulation of human with-no-lysine (K) kinase-4 gene expression involves AP-1 transcription factor

With-no-lysine (K) kinase-4 (WNK4) is a serine/threonine protein kinase and plays a crucial role in the regulation of blood pressure and electrolyte homeostasis. Whether or not estrogen, an important regulator of physiologic functions, modulates human WNK4 (hWNK4) gene expression is unknown. In the current study, real-time PCR assay showed that 17β-estradiol (E(2)) with estrogen receptor alpha (ERα) suppressed the level of hWNK4 mRNA in cultured human embryo kidney 293 cells (HEK293). Luciferase activity analysis of the truncated hWNK4 promoters indicated that a regulatory region from -216 to -202 is essential for the basal transcriptional activity and response to E(2)/ERα. Using an electrophoresis mobility shift assay and a chromatin immunoprecipitation assay, we identified an activator protein-1 (AP-1) element at position -215/-205, to which AP-1 binding was enhanced by E(2)/ERα. Accordingly, AP-1 protein was increased by E(2)/ERα using Western blot analysis. Moreover, re-chromatin-immunoprecipitation and co-immunoprecipitation assays showed a direct interaction between ERα and AP-1 in HEK293 cells. In summary, these data document that E(2)/ERα regulates hWNK4 expression partly through AP-1 binding to the hWNK4 promoter.

Proteome analysis and genome-wide regulatory motif prediction identify novel potentially sex-hormone regulated proteins in rat efferent ducts

The efferent ducts are a series of tubules that conduct sperm from the rete testis to the epididymis. They absorb most fluid and proteins originating from the rete testis during concentration of spermatozoa prior to their entry into the epididymis. Proteome analysis of micro-dissected efferent duct samples from adult rats was combined with genome-wide computational prediction of conserved hormone response elements to identify factors likely regulated by oestrogens and androgens. We identified 165 proteins and found subsets of the promoters controlling their corresponding genes to contain androgen- and oestrogen response elements (ARE/EREs) at similar frequencies. Moreover, EREs were significantly enriched among the loci identified compared with their genome-wide occurrence. The expression and localization of Anxa6, Ckb, Krt19, Park7, Pdzk1 and Tpt1 in the efferent ducts and other related hormone controlled tissues was further validated at the RNA or protein level. This study identifies many novel proteins predicted to play roles in sperm maturation and male fertility and provides significant computational evidence that the efferent ducts express genes transcriptionally controlled by sex hormones.

Prolactin serum levels and breast cancer: relationships with risk factors and tumour characteristics among pre- and postmenopausal women in a population-based case-control study from Poland

Background:

Previous prospective studies have found an association between prolactin (PRL) levels and increased risk of breast cancer. Using data from a population-based breast cancer case–control study conducted in two cities in Poland (2000–2003), we examined the association of PRL levels with breast cancer risk factors among controls and with tumour characteristics among the cases.

Methods:

We analysed PRL serum levels among 773 controls without breast cancer matched on age and residence to 776 invasive breast cancer cases with available pretreatment serum. Tumours were centrally reviewed and prepared as tissue microarrays for immunohistochemical analysis. Breast cancer risk factors, assessed by interview, were related to serum PRL levels among controls using analysis of variance. Mean serum PRL levels by tumour characteristics are reported. These associations also were evaluated using polytomous logistic regression.

Results:

Prolactin levels were associated with nulliparity in premenopausal (P=0.05) but not in postmenopausal women. Associations in postmenopausal women included an inverse association with increasing body mass index (P=0.0008) and direct association with use of recent/current hormone therapy (P=0.0006). In case-only analyses, higher PRL levels were more strongly associated with lobular compared with ductal carcinoma among postmenopausal women (P=0.02). Levels were not different by tumour size, grade, node involvement or oestrogen receptor, progesterone receptor, or human epidermal growth factor receptor 2 status.

Conclusions:

Our analysis demonstrates that PRL levels are higher among premenopausal nulliparous as compared with parous women. Among postmenopausal women, levels were higher among hormone users and lower among obese women. These results may have value in understanding the mechanisms underlying several breast cancer risk factor associations.

Estrogen regulated expression of the p21 Waf1/Cip1 gene in estrogen receptor positive human breast cancer cells

The cyclin-dependent kinase inhibitor protein p21(Waf1/Cip1) is a potent tumor suppressor. Here, we demonstrate that estradiol regulates the p21(Waf1/Cip1) gene. Estradiol induces p21(Waf1/Cip1) mRNA expression within 30-60 min independent of new protein synthesis in the estrogen receptor alpha (ER alpha) positive human breast cancer cell line MCF-7. Similar to other estradiol responsive promoters, the p21(Waf1/Cip1) upstream promoter region has several estrogen response element (ERE) half-sites nestled in AP-1 binding sites, which are positioned upstream to Sp1 binding sites. Using the chromatin immunoprecipitation (ChIP) assay, we show that estradiol stimulation resulted in the recruitment of transcription factors ER alpha, Sp1, and Sp3 to the p21(Waf1/Cip1) upstream promoter element. The Sp1 inhibitor mithramycin A abrogated Sp1, and to a lesser extent Sp3 binding, and markedly reduced the estradiol stimulated p21(Waf1/Cip1) gene expression. However, ER alpha binding was not affected in the mithramycin A and estradiol treated cells. On closer examination of the half-site ERE/AP-1 sites upstream to the Sp1 sites in a separate ChIP experiment, we found a pronounced association of ER alpha upon estradiol treatment compared to almost negligible binding of Sp1 or Sp3. Together these studies provide evidence that ER alpha is recruited to the half-site ERE/AP-1 sites in the p21(Waf1/Cip1) upstream promoter element. Although Sp1/Sp3 is not involved in the recruitment of ER alpha to the promoter, Sp1 is necessary for estrogen-induced p21(Waf1/Cip1) promoter activity.

Complex prolactin crosstalk in breast cancer: new therapeutic implications

The contributions of prolactin (PRL) to breast cancer are becoming increasingly recognized. To better understand the role for PRL in this disease, its interactions with other oncogenic growth factors and hormones must be characterized. Here, we review our current understanding of PRL crosstalk with other mammary oncogenic factors, including estrogen, epidermal growth factor (EGF) family members, and insulin-like growth factor-I (IGF-I). The ability of PRL to potentiate the actions of these targets of highly successful endocrine and molecular therapies suggests that PRL and/or its receptor (PRLR) may be an attractive therapeutic target(s). We discuss the potential benefit of PRL/PRLR-targeted therapy in combination with established therapies and implications for de novo and acquired resistance to treatment.

Non-classical genomic estrogen receptor (ER)/specificity protein and ER/activating protein-1 signaling pathways

17beta-estradiol binds to the estrogen receptor (ER) to activate gene expression or repression and this involves both genomic (nuclear) and non-genomic (extranuclear) pathways. Genomic pathways include the classical interactions of ligand-bound ER dimers with estrogen-responsive elements in target gene promoters. ER-dependent activation of gene expression also involves DNA-bound ER that subsequently interacts with other DNA-bound transcriptions factors and direct ER-transcription factor (protein-protein) interactions where ER does not bind promoter DNA. Ligand-induced activation of ER/specificity protein (Sp) and ER/activating protein-1 [(AP-1); consisting of jun/fos] complexes are important pathways for modulating expression of a large number of genes. This review summarizes some of the characteristics of ER/Sp- and ER/AP-1-mediated transactivation, which are dependent on ligand structure, cell context, ER-subtype (ERalpha and ERbeta), and Sp protein (SP1, SP3, and SP4) and demonstrates that this non-classical genomic pathway is also functional in vivo.

Mammary tumor development from T47-D human breast cancer cells in obese ovariectomized mice with and without estradiol supplements

Obesity is a risk factor for postmenopausal breast cancer, particularly for development of estrogen-receptor (ER)-positive tumors. Additionally, obesity is implicated in breast cancer progression. However, few studies address mechanisms of action of how obesity mediates these responses. Our goal was to address how obesity and/or elevated serum leptin affects tumor formation from ER-positive T47-D cells. In Study 1 ovariectomized CD-1 nude female mice were injected with goldthioglucose (GTG) at 0.5 mg/g body weight in saline or the vehicle at 6 weeks of age. At 10 weeks of age mice were inoculated with T47-D cells and implanted with estrogen pellets. In Study 2 mice were injected with 0.3 mg/g GTG or the vehicle. At 10 weeks of age cells were inoculated and mice were implanted with estrogen or placebo pellets. Mice were followed until 30 weeks of age. Some GTG mice became obese and others were non-responders. In Study 1 no mice developed tumors. In Study 2 mice with placebo pellets developed more tumors than mice with estrogen pellets, 50% vs. 13%. GTG-obese mice with placebo pellets had a 100% tumor incidence compared to 50% and 20% for GTG-lean and controls without estrogen. Serum leptin was higher in obese compared to lean mice and adiponectin was not affected by body weight. Adiponectin:leptin ratio was significantly reduced in obese compared to lean mice. Leptin, leptin receptor and signaling protein expression were determined in mammary and tumor tissue. Leptin and STAT3 were most abundant in tumors. These findings suggest that in vivo estrogen suppressed proliferation of T47-D cells but without supplemental estrogen obesity enhanced tumor development. The exact reason for this is not presently clear.