Phosphorylation of human estrogen receptor-beta at serine 105 inhibits breast cancer cell migration and invasion

TNFR1/p38αMAPK signaling in Nex + supraspinal neurons regulates estrogen-dependent chronic neuropathic pain

Upregulation of soluble tumor necrosis factor (sTNF) cytokine signaling through TNF receptor 1 (TNFR1) and subsequent neuronal hyperexcitability are observed in both animal models and human chronic neuropathic pain (CNP). Previously, we have shown that estrogen modulates sTNF/TNFR1 signaling in CNP, which may contribute to female prevalence of CNP. The estrogen-dependent role of TNFR1-mediated supraspinal neuronal circuitry in CNP remains unknown. In this study, we interrogated the intersect between supraspinal TNFR1 mediated neuronal signaling and sex specificity by selectively removing TNFR1 in Nex + neurons in adult mice (NexCreERT2::TNFR1f/f). We determined that mechanical hypersensitivity induced by chronic constriction injury (CCI) decreases over time in males, but not in females. Subsequently, we investigated two downstream pathways, p38MAPK and NF-κB, important in TNFR1 signaling and injury response. We detected p38MAPK and NF-κB activation in male cortical tissue; however, p38MAPK phosphorylation was reduced in NexCreERT2::TNFR1f/f males. We observed a similar recovery from acute pain in male mice following CCI when p38αMAPK was knocked out of supraspinal Nex + neurons (NexCreERT2::p38αMAPKf/f), while chronic pain developed in female mice. To explore the intersection between estrogen and inflammation in CNP we used a combination therapy of an estrogen receptor β (ER β) inhibitor with a sTNF/TNFR1 or general p38MAPK inhibitor. We determined both combination therapies lends therapeutic relief to females following CCI comparable to the response evaluated in male mice. These data suggest that TNFR1/p38αMAPK signaling in Nex + neurons in CNP is male-specific and lack of therapeutic efficacy following sTNF inhibition in females is due to ER β interference. These studies highlight sex-specific differences in pathways important to pain chronification and elucidate potential therapeutic strategies that would be effective in both sexes.

Anticancer or carcinogenic? The role of estrogen receptor β in breast cancer progression

Estrogen receptor β (ERβ) is closely related to breast cancer (BC) progression. Traditional concepts regard ERβ as a tumor suppressor. As studies show the carcinogenic effect of ERβ, some people have come to a new conclusion that ERβ serves as a tumor suppressor in estrogen receptor α (ERα)-positive breast cancer, while it is a carcinogen in ERα-negative breast cancer. However, we re-examine the role of ERβ and find this conclusion to be misleading based on the last decade's research. A large number of studies have shown that ERβ plays an anticancer role in both ERα-positive and ERα-negative breast cancers, and its carcinogenicity does not depend solely on the presence of ERα. Herein, we review the anticancer and oncogenic effects of ERβ on breast cancer progression in the past ten years, discuss the mechanism respectively, analyze the main reasons for the inconsistency and update ERβ selective ligand library. We believe a detailed and continuously updated review will help correct the one-sided understanding of ERβ, promoting ERβ-targeted breast cancer therapy.

ERK1/2-RSK2 Signaling in Regulation of ERα-Mediated Responses

Signaling via extracellular regulated kinase 1/2 (ERK1/2) and p90 ribosomal S6 kinase (RSK), a downstream effector, mediates numerous processes. For example, ERK1/2-RSK signaling is essential for estrogen homeostasis in the mammary gland and uterus to maintain physiological responsiveness. This review will focus on the coordination of ERK1/2-RSK2 and estrogen signaling through estrogen receptor alpha (ERα). The interrelationship and the feedback mechanisms between these pathways occurs at the level of transcription, translation, and posttranslational modification. Identifying how ERK1/2-RSK2 and estrogen signaling cooperate in homeostasis and disease may lead to novel therapeutic approaches in estrogen-dependent disorders.

ERK1/2‐RSK regulation of oestrogen homeostasis

The molecular mechanisms regulating oestrogen homeostasis have been primarily studied in the mammary gland, which is the focus of this review. In the non-pregnant adult, the mammary gland undergoes repeated cycles of proliferation and apoptosis in response to the fluctuating levels of oestrogen that occur during the reproductive stage. Oestrogen actions are mediated through the steroid hormone receptors, oestrogen receptor α and β and through a G-protein coupled receptor. In the mammary gland, ERα is of particular importance and thus will be highlighted. Mechanisms regulating oestrogen-induced responses through ERα are necessary to maintain homeostasis given that the signalling pathways that are activated in response to ERα-mediated transcription can also induce transformation. ERK1/2 and its downstream effector, p90 ribosomal S6 kinase (RSK), control homeostasis in the mammary gland by limiting oestrogen-mediated ERα responsiveness. ERK1/2 drives degradation coupled ERα-mediated transcription, whereas RSK2 acts as a negative regulator of ERK1/2 activity to limit oestrogen responsiveness. Moreover, RSK2 acts as a positive regulator of translation. Thus, RSK2 provides both positive and negative signals to maintain oestrogen responsiveness. In addition to transmitting signals through tyrosine kinase receptors, ERK1/2-RSK engages with hedgehog signalling to maintain oestrogen levels and with the HIPPO pathway to regulate ERα-mediated transcription. Additionally, ERK1/2-RSK controls the progenitor populations within the mammary gland to maintain the ERα-positive population. RSK2 is involved in increased breast cancer risk in individuals taking oral contraceptives and in parity-induced protection against breast cancer. RSK2 and ERα may also co-operate in diseases in tissues outside of the mammary gland.

The interplay between estrogen receptor beta and protein kinase C, a crucial collaboration for medulloblastoma cell proliferation and invasion

Medulloblastoma (MB) is the most common and aggressive pediatric intracranial tumor. Estrogen receptor β (ERβ) expression correlates with MB development and its phosphorylation modifies its transcriptional activity in a ligand-dependent or independent manner. Using in silico tools, we have identified several residues in ERβ protein as potential targets of protein kinases C (PKCs) α and δ. Using Daoy cells, we observed that PKCα and PKCδ associate with ERβ and induce its phosphorylation. The activation of ERβ promotes MB cells proliferation and invasion, and PKCs downregulation dysregulates these steroid receptor mediated processes. Our data suggest that these kinases may play a crucial role in the regulation of the ERβ transcriptional activity. Overexpression of both PKCα and PKCδ in MB biopsies samples supports their relevance in MB progression.

Absolute Quantification of Phosphorylated ERβ Amino Acids in the Hippocampus of Women and in A Rat Model of Menopause

The rapid decline of circulating 17β-estradiol (E2) at menopause leads to negative neurological consequences, although hormone therapy paradoxically has both harmful and positive effects depending on the age at which it is delivered. The inconsistent response to E2 suggests unappreciated regulatory mechanisms for estrogen receptors (ERs), and we predicted it could be due to age-related differences in ERβ phosphorylation. We assessed ERβ phosphorylation using a sensitive mass spectrometry approach that provides absolute quantification (AQUA-MS) of individually phosphorylated residues. Specifically, we quantified phosphorylated ERβ in the hippocampus of women (aged 21-83 years) and in a rat model of menopause at 4 residues with conserved sequence homology between the 2 species: S105, S176, S200, and Y488. Phosphorylation at these sites, which spanned all domains of ERβ, were remarkably consistent between the 2 species, showing high levels of S105 phosphorylation (80%-100%) and low levels of S200 (20%-40%). Further, S200 phosphorylation decreased with aging in humans and loss of E2 in rats. Surprisingly, Y488 phosphorylation, which has been linked to ERβ ligand-independent actions, exhibited approximately 70% phosphorylation, unaltered by species, age, or E2, suggesting ERβ's primary mode of action may not require E2 binding. We further show phosphorylation at 2 sites directly altered ERβ DNA-binding efficiency, and thus could affect its transcription factor activity. These findings provide the first absolute quantification of ERβ phosphorylation in the human and rat brain, novel insights into ERβ regulation, and a critical foundation for providing more targeted therapeutic options for menopause in the future.

A Phosphotyrosine Switch in Estrogen Receptor β Is Required for Mouse Ovarian Function

The two homologous estrogen receptors ERα and ERβ exert distinct effects on their cognate tissues. Previous work from our laboratory identified an ERβ-specific phosphotyrosine residue that regulates ERβ transcriptional activity and antitumor function in breast cancer cells. To determine the physiological role of the ERβ phosphotyrosine residue in normal tissue development and function, we investigated a mutant mouse model (Y55F) whereby this particular tyrosine residue in endogenous mouse ERβ is mutated to phenylalanine. While grossly indistinguishable from their wild-type littermates, mutant female mice displayed reduced fertility, decreased ovarian follicular cell proliferation, and lower progesterone levels. Moreover, mutant ERβ from female mice during superovulation is defective in activating promoters of its target genes in ovarian tissues. Thus, our findings provide compelling genetic and molecular evidence for a role of isotype-specific ERβ phosphorylation in mouse ovarian development and function.

Estrogen Receptor Beta (ERβ): A Ligand Activated Tumor Suppressor

Estrogen receptor alpha (ERα) and estrogen receptor beta (ERβ) belong to a superfamily of nuclear receptors called steroid hormone receptors, which, upon binding ligand, dimerize and translocate to the nucleus where they activate or repress the transcription of a large number of genes, thus modulating critical physiologic processes. ERβ has multiple isoforms that show differing association with prognosis. Expression levels of the full length ERβ1 isoform are often lower in aggressive cancers as compared to normal tissue. High ERβ1 expression is associated with improved overall survival in women with breast cancer. The promise of ERβ activation, as a potential targeted therapy, is based on concurrent activation of multiple tumor suppressor pathways with few side effects compared to chemotherapy. Thus, ERβ is a nuclear receptor with broad-spectrum tumor suppressor activity, which could serve as a potential treatment target in a variety of human cancers including breast cancer. Further development of highly selective agonists that lack ERα agonist activity, will be necessary to fully harness the potential of ERβ.

The role of estrogen receptor beta in breast cancer

Breast cancer, a malignant tumor originating from mammary epithelial tissue, is the most common cancer among women worldwide. Challenges facing the diagnosis and treatment of breast cancer necessitate the search for new mechanisms and drugs to improve outcomes. Estrogen receptor (ER) is considered to be important for determining the diagnosis and treatment strategy. The discovery of the second estrogen receptor, ERβ, provides an opportunity to understand estrogen action. The emergence of ERβ can be traced back to 1996. Over the past 20 years, an increasing body of evidence has implicated the vital effect of ERβ in breast cancer. Although there is controversy among scholars, ERβ is generally thought to have antiproliferative effects in disease progression. This review summarizes available evidence regarding the involvement of ERβ in the clinical treatment and prognosis of breast cancer and describes signaling pathways associated with ERβ. We hope to highlight the potential of ERβ as a therapeutic target.

Sex-specific regulation of collagen I and III expression by 17β-Estradiol in cardiac fibroblasts: role of estrogen receptors

Aims

Sex differences in cardiac fibrosis point to the regulatory role of 17β-Estradiol (E2) in cardiac fibroblasts (CF). We, therefore, asked whether male and female CF in rodent and human models are differentially susceptible to E2, and whether this is related to sex-specific activation of estrogen receptor alpha (ERα) and beta (ERβ).

Methods and results

In female rat CF (rCF), 24 h E2-treatment (10-8  M) led to a significant down-regulation of collagen I and III expression, whereas both collagens were up-regulated in male rCF. E2-induced sex-specific collagen regulation was also detected in human CF, indicating that this regulation is conserved across species. Using specific ERα- and ERβ-agonists (10-7 M) for 24 h, we identified ERα as repressive and ERβ as inducing factor in female and male rCF, respectively. In addition, E2-induced ERα phosphorylation at Ser118 only in female rCF, whereas Ser105 phosphorylation of ERβ was exclusively found in male rCF. Further, in female rCF we found both ER bound to the collagen I and III promoters using chromatin immunoprecipitation assays. In contrast, in male rCF only ERβ bound to both promoters. In engineered connective tissues (ECT) from rCF, collagen I and III mRNA were down-regulated in female ECT and up-regulated in male ECT by E2. This was accompanied by an impaired condensation of female ECT, whereas male ECT showed an increased condensation and stiffness upon E2-treatment, analysed by rheological measurements. Finally, we confirmed the E2-effect on both collagens in an in vivo mouse model with ovariectomy for E2 depletion, E2 substitution, and pressure overload by transverse aortic constriction.

Conclusion

The mechanism underlying the sex-specific regulation of collagen I and III in the heart appears to involve E2-mediated differential ERα and ERβ signaling in CFs.

Systematic review of p38 mitogen-activated kinase and its functional role in reproductive tissues

Oxidative stress (OS) plays a role in uterine tissue remodeling during pregnancy and parturition. While p38 MAPK is an OS-response kinase, a precise functional role is unknown. Therefore, we conducted a systematic review of literature on p38 MAPK expression, activation, and function in reproductive tissues throughout pregnancy and parturition, published between January 1980 and August 2017, using four electronic databases (Web of Science, PubMed, Medline, and CoCHRANE). We identified 418 reports; 108 were selected for full-text evaluation and 74 were included in final review. p38 MAPK was investigated using feto-maternal primary or immortalized cells, tissue explants, and animal models. Western blot was most commonly used to report phosphorylated (active) p38 MAPK. Human placenta (27), chorioamniotic membranes (14), myometrium (13), decidua (8), and cervix (1) were the studied tissues. p38 MAPK's functions were tissue and gestational age dependent. Isoform specificity was hardly reported. p38 MAPK activity was induced by ROS or proinflammatory cytokines to promote cell signaling linked to cell fate, primed uterus, ripened cervix, and proinflammatory cytokine/chemokine production. In 35 years, reports on p38 MAPK's role during pregnancy and parturition are scarce and current literature is insufficient to provide a comprehensive description of p38 MAPK's mechanistic role during pregnancy and parturition.

Tyrosine phosphorylation regulates ERβ ubiquitination, protein turnover, and inhibition of breast cancer

Unlike estrogen receptor α (ERα) that predominantly promotes hormone-dependent breast tumor growth, ERβ exhibits antitumor effects in a variety of cancer types. We recently identified a phosphotyrosine residue in ERβ, but not ERα, that dictates ERβ transcriptional activity and antitumor function. We show here that this ER isotype-specific phosphotyrosine switch is important for regulating ERβ activity in cell proliferation, migration, and invasion. At the mechanistic level, phosphorylated ERβ, which recruits transcriptional coactivator p300, is in turn targeted by p300 for ubiquitination and proteasome-dependent protein turnover. Furthermore, ERβ-specific agonists such as S-equol enhance ERβ phosphorylation, suggesting a crosstalk between ligand- and posttranslational modification-dependent ERβ activation. Inhibition of xenograft tumor growth by S-equol is associated with reduced tumor Ki-67 expression and elevated ERβ tyrosine phosphorylation. Taken together, our data support the notion that phosphotyrosine-dependent ERβ signaling is an attractive target for anticancer treatment.

Phosphorylation of interleukin (IL)-24 is required for mediating its anti-cancer activity

Interleukin (IL)-24 is a tumor suppressor/cytokine gene that undergoes post-translational modifications (PTMs). Glycosylation and ubiquitination are important for IL-24 protein stabilization and degradation respectively. Little is known about IL-24 protein phosphorylation and its role in IL-24-mediated anti-tumor activities. In this study we conducted molecular studies to determine whether IL-24 phosphorylation is important for IL-24-mediated anti-cancer activity.

Human H1299 lung tumor cell line that was stably transfected with a doxycycline (DOX)-inducible (Tet-on) plasmid vector carrying the cDNA of IL-24-wild-type (IL-24^wt) or IL-24 with all five phosphorylation sites replaced (IL-24^mt) was used in the present study. Inhibition of tumor cell proliferation, cell migration and invasion, and induction of G2/M cell cycle arrest was observed in DOX-induced IL-24^wt-expressing cells but not in IL-24^mt-expressing cells. Secretion of IL-24^mt protein was greatly reduced compared to IL-24^wt protein. Further, IL-24^wt and IL-24^mt proteins markedly differed in their subcellular organelle localization. IL-24^wt but not IL-24^mt inhibited the AKT/mTOR signaling pathway. SiRNA-mediated AKT knockdown and overexpression of myristolyated AKT protein confirmed that IL-24^wt but not IL-24^mt mediated its anti-cancer activity by inhibiting the AKT signaling pathway.

Our results demonstrate that IL-24 phosphorylation is required for inhibiting the AKT/mTOR signaling pathway and exerting its anti-cancer activities.

Are all regions of folded proteins that undergo ligand-dependent order-disorder transitions targets for allosteric peptide mimetics?

Although the classical view of how proteins function relied on well folded structures, it is now recognized that the functions of many proteins are dependent on being intrinsically disordered. The primary consideration in this work is the intermediate group of proteins that are overall well folded, but which contain small regions that undergo order-disorder transitions. In particular, the current focus is on those order-disorder transitions that are energetically coupled to ligand binding. As exemplified by the case of human liver pyruvate kinase (hL-PYK), peptides that mimic the sequence of the order-disorder region can be used as allosteric regulators of the enzyme. On the basis of this example and others reported in the literature, we propose that a similar use of peptides that mimic protein regions that experience ligand-dependent order-disorder transitions can be a generalized initiation point for the development of allosteric drugs.

Prostate Cancer Expression Profiles of Cytoplasmic ERβ1 and Nuclear ERβ2 are Associated with Poor Outcomes following Radical Prostatectomy

PURPOSE

Existing data regarding the expression of estrogen receptors (ERs) and prostate cancer outcomes have been limited. We evaluated the relationship of expression profiles of ERβ subtypes and the ER GPR30 (G-protein-coupled receptor-30) with patient factors at diagnosis and outcomes following radical prostatectomy.

MATERIALS AND METHODS

Tissue microarrays constructed using samples from 566 men with long-term clinical followup were analyzed by immunohistochemistry targeting ERβ1, ERβ2, ERβ5 and GPR30. An experienced pathologist scored receptor distribution and staining intensity. Tumor staining characteristics were evaluated for associations with patient characteristics, recurrence-free survival and prostate cancer specific mortality following radical prostatectomy.

RESULTS

Prostate cancer cells had unique receptor subtype staining patterns. ERβ1 demonstrated predominantly nuclear localization while ERβ2, ERβ5 and GPR30 were predominantly cytoplasmic. After controlling for patient factors intense cytoplasmic ERβ1 staining was independently associated with time to recurrence (HR 1.7, 95% CI 1.1-2.6, p = 0.01) and prostate cancer specific mortality (HR 6.6, 95% CI 1.8-24.9, p = 0.01). Intense nuclear ERβ2 staining was similarly independently associated with prostate cancer specific mortality (HR 3.9, 95% CI 1.1-13.4, p = 0.03). Patients with cytoplasmic ERβ1 and nuclear ERβ2 co-staining had significantly worse 15-year prostate cancer specific mortality than patients with expression of only cytoplasmic ERβ1, only nuclear ERβ2 and neither ER (16.4%, 4.3%, 0.0% and 2.0 %, respectively, p = 0.001).

CONCLUSIONS

Increased cytoplasmic ERβ1 and nuclear ERβ2 expression is associated with worse cancer specific outcomes following radical prostatectomy. These findings suggest that tumor ERβ1 and ERβ2 staining patterns provide prognostic information on patients treated with radical prostatectomy.

Phosphorylation Alters Oestrogen Receptor β-Mediated Transcription in Neurones

Nuclear steroid hormone receptors are ubiquitously expressed transcription factors whose activity can be altered by post-translational modifications, such as phosphorylation. The consequences of post-translational modifications have been described for several members of the nuclear steroid hormone receptor superfamily; however, little is known about the effects of oestrogen receptor (ER)β phosphorylation in the brain. Moreover, to our knowledge, the presence of phosphorylated ERβ has not been detected in the brain of any species to date. Oestrogen receptor β is highly expressed in several regions of the brain and in vitro studies have demonstrated that it can be phosphorylated at two serine residues (S87 and S105) in the N-terminal AF-1 region. The present study aimed to determine whether phosphorylated ERβ is detectable in the hippocampus of aged female rats, as well as the functional consequences of ERβ S87 and S105 phosphorylation on transcriptional activity in neuronal cells. First, we used a novel PhosTag(™) approach to detect phosphorylated forms of ERβ in the dorsal hippocampus of aged female rats. The data obtained demonstrated abundant forms of phosphorylated ERβ in the dorsal hippocampus, suggesting that this post-translational modification might be an important regulator of ERβ function. To assess the functional consequences of ERβ phosphorylation in neuronal cells, we created phospho-mimetic (S87E, S105E) and phospho-null (S87A, S105A) ERβ receptors that were transiently transfected in a hippocampal-derived cell line. Collectively, our results showed that phosphorylation of S87 and S105 altered both ligand-independent and ligand-dependent ERβ transcriptional regulation. Overall, these data demonstrate that phosphorylated forms of ERβ are present in the brain of aged female rats and that phosphorylation of ERβ could differentially alter ERβ-mediated gene expression.

Critical role of CDK11(p58) in human breast cancer growth and angiogenesis

Background

A capillary network is needed in cancer growth and metastasis. Induction of angiogenesis represents one of the major hallmarks of cancer. CDK11^p58, a Ser/Thr kinase that belongs to the Cell Division Cycle 2-like 1 (CDC2L1) subfamily is associated with cell cycle progression, tumorigenesis, sister chromatid cohesion and apoptotic signaling. However, its role in breast cancer proliferation and angiogenesis remains unclear.

Methods

Tumorigenicity assays and blood vessel assessment in athymic mice were used to assess the function of CDK11^p58 in tumor proliferation and angiogenesis. CCK-8 assay was used to detect breast cancer cell growth. Immunohistochemistry was used to detect the expression of vascular endothelial growth factor (VEGF), CD31 and CD34 in CDK11 positive patient breast cancer tissues. Dual-Luciferase array was used to analyze the function of CDK11^p58 in the regulation of VEGF promoter activity. Western blot was used to detect related protein expression levels.

Results

CDK11^p58 inhibited breast cancer growth and angiogenesis in breast cancer cells and in nude mice transplanted with tumors. Immunohistochemistry confirmed that CDK11^p58 was negatively associated with angiogenesis-related proteins such as VEGF, CD31 and CD34 in breast cancer patients. Real-time PCR and dual-luciferase assay showed CDK11^p58 inhibited the mRNA levels of VEGF and the promoter activity of VEGF. As CDK11^p58 is a Ser/Thr kinase, the kinase-dead mutant failed to inhibit VEGF mRNA and promoter activity. Western blot analysis showed the same pattern of related protein expression. The data suggested angiogenesis inhibition was dependent on CDK11^p58 kinase activity.

Conclusion

This study indicates that CDK11^p58 inhibits the growth and angiogenesis of breast cancer dependent on its kinase activity.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1698-7) contains supplementary material, which is available to authorized users.

Genistein increases estrogen receptor beta expression in prostate cancer via reducing its promoter methylation

Genistein has protective effects against prostate cancer (PCa) but whether this protection involves an estrogen receptor (ER) β dependent mechanism has yet to be elucidated. ER-β has a tumor suppressor role in PCa and its levels decline with cancer progression which was linked to ER-β promoter hypermethylation. Genistein has been suggested to have demethylating activities in cancer. However, the ability of genistein to reverse ER-β promoter hypermethylation in PCa has not been studied. In addition, there are great discrepancies among studies that examined the effect of genistein on ER-β gene expression. Therefore, we sought to explore effects of genistein on ER-β promoter methylation as a mechanism of modulating ER-β expression using three PCa cell lines, LNCaP, LAPC-4 and PC-3. We also examined the role of ER-β in mediating the preventive action of genistein. Our data demonstrated that genistein at physiological ranges (0.5-10 μmol/L) reduced ER-β promoter methylation significantly with corresponding dose-dependent increases in ER-β expression in LNCaP and LAPC-4 but not in PC-3 cells, which could be attributed to the low basal levels of ER-β promoter methylation in PC-3 cell line. Genistein induced phosphorylation, nuclear translocation and transcriptional activity of ER-β in all three PCa cell lines. Inhibitory effects of genistein on LAPC-4 and PC-3 cell proliferation were diminished using a specific ER-β antagonist. In conclusion, genistein and ER-β act together to prevent PCa cell proliferation; genistein increases ER-β levels via reducing its promoter methylation and ER-β, in turn, mediates the preventive action of genistein.

Mnk kinase pathway: Cellular functions and biological outcomes

The mitogen-activated protein kinase (MAPK) interacting protein kinases 1 and 2 (Mnk1 and Mnk2) play important roles in controlling signals involved in mRNA translation. In addition to the MAPKs (p38 or Erk), multiple studies suggest that the Mnk kinases can be regulated by other known kinases such as Pak2 and/or other unidentified kinases by phosphorylation of residues distinct from the sites phosphorylated by the MAPKs. Several studies have established multiple Mnk protein targets, including PSF, heterogenous nuclear ribonucleoprotein A1, Sprouty 2 and have lead to the identification of distinct biological functions and substrate specificity for the Mnk kinases. In this review we discuss the pathways regulating the Mnk kinases, their known substrates as well as the functional consequences of engagement of pathways controlled by Mnk kinases. These kinases play an important role in mRNA translation via their regulation of eukaryotic initiation factor 4E (eIF4E) and their functions have important implications in tumor biology as well as the regulation of drug resistance to anti-oncogenic therapies. Other studies have identified a role for the Mnk kinases in cap-independent mRNA translation, suggesting that the Mnk kinases can exert important functional effects independently of the phosphorylation of eIF4E. The role of Mnk kinases in inflammation and inflammation-induced malignancies is also discussed.

A phosphotyrosine switch determines the antitumor activity of ERβ

Estrogen receptors ERα and ERβ share considerable sequence homology yet exert opposite effects on breast cancer cell proliferation. While the proliferative role of ERα in breast tumors is well characterized, it is not clear whether the antitumor activity of ERβ can be mobilized in breast cancer cells. Here, we have shown that phosphorylation of a tyrosine residue (Y36) present in ERβ, but not in ERα, dictates ERβ-specific activation of transcription and is required for ERβ-dependent inhibition of cancer cell growth in culture and in murine xenografts. Additionally, the c-ABL tyrosine kinase and EYA2 phosphatase directly and diametrically controlled the phosphorylation status of Y36 and subsequent ERβ function. A nonphosphorylatable, transcriptionally active ERβ mutant retained antitumor activity but circumvented control by upstream regulators. Phosphorylation of Y36 was required for ERβ-mediated coactivator recruitment to ERβ target promoters. In human breast cancer samples, elevated phosphorylation of Y36 in ERβ correlated with high levels of c-ABL but low EYA2 levels. Furthermore, compared with total ERβ, the presence of phosphorylated Y36-specific ERβ was strongly associated with both disease-free and overall survival in patients with stage II and III disease. Together, these data identify a signaling circuitry that regulates ERβ-specific antitumor activity and has potential as both a prognostic tool and a molecular target for cancer therapy.

Support of a bi-faceted role of estrogen receptor β (ERβ) in ERα-positive breast cancer cells

The expression of estrogen receptor α (ERα) in breast cancer identifies patients most likely to respond to endocrine treatment. The second ER, ERβ, is also expressed in breast tumors, but its function and therapeutic potential need further study. Although in vitro studies have established that ERβ opposes transcriptional and proliferative functions of ERα, several clinical studies report its correlation with proliferative markers and poorer prognosis. The data demonstrate that ERβ opposes ERα are primarily based on transient expression of ERβ. Here, we explored the functions of constitutively expressed ERβ in ERα-positive breast cancer lines MCF7 and T47D. We found that ERβ, under these conditions heterodimerized with ERα in the presence and absence of 17β-estradiol, and induced genome-wide transcriptional changes. Widespread anti-ERα signaling was, however, not observed and ERβ was not antiproliferative. Tamoxifen antagonized proliferation and ER-mediated gene regulation both in the presence and absence of ERβ. In conclusion, ERβ's role in cells adapted to its expression appears to differ from its role in cells with transient expression. Our study is important because it provides a deeper understanding of ERβ's role in breast tumors that coexpress both receptors and supports an emerging bi-faceted role of ERβ.

Prognostic role of lemur tyrosine kinase-3 germline polymorphisms in adjuvant gastric cancer in Japan and the United States

Lemur tyrosine kinase-3 (LMTK3) was recently identified as an estrogen receptor (ER)-α modulator related to endocrine therapy resistance, and its polymorphisms rs9989661 (T>C) T/T genotype and rs8108419 (G>A) G/G or A/G genotype predicted improved outcomes in breast cancer. Because different predominant ER distributions link to breast and gastric cancer and little is known of the prognostic role of LMTK3 in gastric cancer, this study was carried out to clarify the prognostic role of these polymorphisms in gastric cancer. One-hundred and sixty-nine Japanese and 137 U.S. patients with localized gastric adenocarcinoma were enrolled. Genomic DNA was extracted from blood or tissue, and all samples were analyzed by PCR-based direct DNA sequencing. Overall, these polymorphisms were not associated with survival in both cohorts. When gender was considered, in multivariate analysis, harboring rs9989661 T/T genotype was associated with disease-free survival [HR, 4.37; 95% confidence interval (CI), 2.08-9.18; P < 0.0001] and overall survival (OS; HR, 3.69; 95% CI, 1.65-8.24; P = 0.0014) in the Japanese males and time to recurrence (HR, 7.29; 95% CI, 1.07-49.80; P = 0.043) in the U.S. females. Meanwhile, harboring rs8108419 G/G genotype was associated with OS in the Japanese females (HR, 3.04; 95% CI, 1.08-8.56; P = 0.035) and the U.S. males (HR, 3.39; 95% CI, 1.31-8.80; P = 0.012). The prognostic role of these polymorphisms may be negative in gastric cancer. These findings suggest that the estrogen pathway may play a prognostic role in patients with gastric cancer but this may be dependent on the regional differences both in physiology and genetic alterations of gastric cancer.

Phosphorylation: a fundamental regulator of steroid receptor action

Steroid hormone receptors (SHRs) are hormone-activated transcription factors involved in numerous cellular functions and in health and disease. Their activities depend on the cellular level of the receptor, the presence of coregulator proteins, and the cell signaling pathways that are active in the cell. SHRs and their coregulators are phosphorylated on multiple sites by a wide variety of kinases. Each site may contribute to multiple functions and the net effect of an individual phosphorylation depends on the activating kinase. Here we discuss functions of known SHR phosphorylation sites, kinase regulation, evidence of translational relevance, and crosstalk between SHRs and cell signaling pathways. Understanding how cell signaling pathways regulate SHRs might yield novel therapeutic targets for multiple human diseases.

Site-specific S-nitrosylation of integrin α6 increases the extent of prostate cancer cell migration by enhancing integrin β1 association and weakening adherence to laminin-1

The increased mortality in prostate cancer is usually the result of metastatic progression of the disease from the organ-confined location. Among the major events in this progression cascade are enhanced cell migration and loss of adhesion. Moreover, elevated levels of nitric oxide (NO) and inducible nitric oxide synthase (iNOS) found within the tumor microenvironment are hallmarks of progression of this cancer. To understand the role of nitrosative stress in prostate cancer progression, we investigated the effects of NO and iNOS on prostate cancer cell migration and adhesion. Our results indicate that ectopic expression of iNOS in prostate cancer cells increased the extent of cell migration, which could be blocked by selective ITGα6 blocking antibody or iNOS inhibitors. Furthermore, iNOS was found to cause S-nitrosylation of ITGα6 at Cys86 in prostate cancer cells. By comparing the activities of wild-type ITGα6 and a Cys86 mutant, we showed that treatment of prostate cancer cells with NO increased the level of ITGα6 heterodimerization with ITGβ1 but not with ITGβ4. Finally, S-nitrosylation of ITGα6 weakened its binding to laminin-β1 and weakened the adhesion of prostate cancer cells to laminin-1. In conclusion, S-nitrosylation of ITGα6 increased the extent of prostate cancer cell migration, which could be a potential mechanism of NO- and iNOS-induced enhancement of prostate cancer metastasis.

Characterisation of human oestrogen receptor beta (ERβ) splice variants in neuronal cells

Oestrogen receptor (ER)α and ERβ are members of the ligand-activated superfamily of nuclear receptors and mediate most facets of oestrogen signalling. Several naturally occurring splice variants of each ER have been identified in the human brain, yet the biological significance of these splice variants in the brain remains unknown. In the present study, we exploit the unique structural differences of the human ERβ splice variants to determine the functional significance of individual ER domains in the brain. We previously established that full-length rodent ERβ (i.e. rERβ1) has constitutive transcriptional activity in neuronal cells in the absence of ligand. By contrast to the rodent splice variants, the human ERβ splice variants used in the present study contain varying length truncations of exon 8, which encodes for the E/F domains. Our results reveal that, in neuronal cells, each human-specific ERβ splice variant constitutively activated promoters mediated by a canonical oestrogen response element and repressed promoters mediated by activator protein-1 sites via p38 activity. From these data, we conclude that the C-terminus, encoding the AF-2 region and F domain, is not essential for the constitutive properties of human ERβ. Taken together, these studies show that human-specific ERβ variants are constitutively active and also provide novel insight into the contributions of the functional domains of ERβ towards mediating constitutive transcription at various promoters in neuronal cells.

Estrogen receptor-beta and breast cancer: translating biology into clinical practice

Estrogen receptor (ER) β was discovered over a decade ago. The design of most studies on this receptor was based on knowledge of its predecessor, ERα. Although breast cancer (BCa) has been a main focus of ERβ research, its precise roles in breast carcinogenesis remain elusive. Data from in vitro models have not always matched those from observational or clinical studies. Several inherent factors may contribute to these discrepancies: (a) several ERβ spliced variants are expressed at the protein level, and isoform-specific antibodies are unavailable for some variants; (b) post-translational modifications of the receptor regulate receptor functions; (c) the role of the receptor differs significantly depending on the type of ligands, cis-elements, and co-regulators that interact with the receptor; and (d) the diversity of distribution of the receptor among intracellular organelles of BCa cells. This review addresses the gaps in knowledge in ERβ research as it pertains to BCa regarding the following questions: (1) is ERβ a tumor suppressor in BCa?; (2) do ERβ isoforms play differential roles in breast carcinogenesis?; (3) do nuclear signaling and extranuclear ERβ signaling differ in BCa?; (4) what are the consequences of post-translational modifications of ERβ in BCa?; (5) how do co-regulators and interacting proteins increase functional diversity of ERβ?; and (6) how do the types of ligand and regulatory cis-elements affect the action of ERβ in BCa?. Insights gained from these key questions in ERβ research should help in prevention, diagnosis/prognosis, and treatment of BCa.