pp90rsk1 regulates estrogen receptor-mediated transcription through phosphorylation of Ser-167

Links between oestrogen receptor activation and proteolysis: relevance to hormone-regulated cancer therapy

Oestrogen receptor-α (ERα) is a master transcription factor that regulates cell proliferation and homeostasis in many tissues. Despite beneficial ERα functions, sustained oestrogenic exposure increases the risk and/or the progression of various cancers, including those of the breast, endometrium and ovary. Oestrogen–ERα interaction can trigger post-translational ERα modifications through crosstalk with signalling pathways to promote transcriptional activation and ubiquitin-mediated ERα proteolysis, with co-activators that have dual roles as ubiquitin ligases. These processes are reviewed herein. The elucidation of mechanisms whereby oestrogen drives both ERα transactivation and receptor proteolysis might have important therapeutic implications not only for breast cancer but also potentially for other hormone-regulated cancers.

The p90 ribosomal S6 kinase (RSK) inhibitor BI-D1870 prevents gamma irradiation-induced apoptosis and mediates senescence via RSK- and p53-independent accumulation of p21WAF1/CIP1

The p90 ribosomal S6 kinase (RSK) family is a group of highly conserved Ser/Thr kinases that promote cell proliferation, growth, motility and survival. As they are almost exclusively activated downstream of extracellular signal-regulated kinases 1 and 2 (ERK1/2), therapeutic intervention by RSK inhibition is less likely to produce such severe side effects as those observed following inhibition of the upstream master regulators Raf, MEK and ERK1/2. Here, we report that BI-D1870, a potent small molecule inhibitor of RSKs, induces apoptosis, although preferentially, in a p21-deficient background. On the other hand, BI-D1870 also induces a strong transcription- and p53-independent accumulation of p21 protein and protects cells from gamma irradiation (γIR)-induced apoptosis, driving them into senescence even in the absence of γIR. Although we identified p21 in in vitro kinase assays as a novel RSK substrate that specifically becomes phosphorylated by RSK1-3 at Ser116 and Ser146, RNA-interference, overexpression and co-immunoprecipitation studies as well as the use of SL0101, another specific RSK inhibitor, revealed that BI-D1870 mediates p21 accumulation via a yet unknown pathway that, besides its off-site targets polo-like kinase-1 and AuroraB, also does also not involve RSKs. Thus, this novel off-target effect of BI-D1870 should be taken into serious consideration in future studies investigating the role of RSKs in cellular signaling and tumorigenesis.

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.

MicroRNA-34a suppresses cell proliferation by targeting LMTK3 in human breast cancer mcf-7 cell line

Breast cancer remains the leading cause of cancer mortality in females, and about 70% of the primary breast cancer patients are diagnosed ERα-positive, which is the most common type of breast cancer. MicroRNA-34a (miR-34a) has been shown to be a master regulator of tumor suppression in many types of cancers including breast cancer. However, the role of miR-34a in ERα-positive breast cancer has not been elucidated. Here, we find that in MCF-7, which is an ERα-positive breast cancer cell line, miR-34a is remarkably downregulated after E2 treatment. Overexpression of miR-34a by lentivirus suppresses cell proliferation, S phase ratio, and tumor formation in an E2-dependent manner in vitro. According to the mRNA sequence, lemur tyrosine kinase 3 (LMTK3), which is an important regulator of estrogen receptor alpha (ERα), is a predicted target of miR-34a. This is confirmed by dual luciferase reporter assay and the decrease of LMTK3 mRNA and protein levels after overexpression of miR-34a. Moreover, miR-34a overexpression decreases AKT signaling pathway and increases ERα phosphorylation status. Taken together, these results suggest that miR-34a inhibits breast cancer proliferation by targeting LMTK3 and might be used as an anti-ERα agent in breast cancer therapy.

The Transactivating Function 2 (AF-2) of Estrogen Receptor (ER) α is Indispensable for ERα-mediated Physiological Responses and AF-1 Activity

Estrogen has various physiological functions and the estrogen receptor (ER) is a key regulator of those functions. ERα is a ligand-dependent transcription factor and that activity is mediated by the transactivating function-1 (AF-1) in the N-terminal domain and transactivating function-2 (AF-2) in the C-terminal ligand-binding domain. The functions of ERα AF-1 and AF-2 have been characterized by various in vitro experiments, however, there is still less information about the in vivo physiological functions of ERα AF-1 and AF-2. Recently, we established a genetically mutated ERα AF-2 knock-in mouse (AF2ERKI) that possesses L543A, L544A mutated-ERα. This AF-2 core mutation disrupted AF-2 function and resulted in ERα null phenotypes. This mouse model revealed that proper AF-2 core structure and function are indispensable for ERα-mediated physiological responses and AF-1 functionality. AF2ER mutation reverses the ERα antagonists to agonists and that activity is mediated by AF-1 solely. The pure antagonist, ICI182780/fulvestrant, activated several estrogen-mediated physiological responses in the AF2ERKI mouse. The AF2ERKI mouse model will be able to discern estrogen physiological functions which involve AF-1.

The human papillomavirus type 16 E7 oncoprotein induces a transcriptional repressor complex on the Toll-like receptor 9 promoter

HPV16-positive cervical cancer lesions contain NFκB–ERα nuclear complexes to repress the TLR9 promoter.

Human papillomavirus type 16 (HPV16) and other oncogenic viruses have been reported to deregulate immunity by suppressing the function of the double-stranded DNA innate sensor TLR9. However, the mechanisms leading to these events remain to be elucidated. We show that infection of human epithelial cells with HPV16 promotes the formation of an inhibitory transcriptional complex containing NF-κBp50–p65 and ERα induced by the E7 oncoprotein. The E7-mediated transcriptional complex also recruited the histone demethylase JARID1B and histone deacetylase HDAC1. The entire complex bound to a specific region on the TLR9 promoter, which resulted in decreased methylation and acetylation of histones upstream of the TLR9 transcriptional start site. The involvement of NF-κB and ERα in the TLR9 down-regulation by HPV16 E7 was fully confirmed in cervical tissues from human patients. Importantly, we present evidence that the HPV16-induced TLR9 down-regulation affects the interferon response which negatively regulates viral infection. Our studies highlight a novel HPV16-mediated mechanism that combines epigenetic and transcriptional events to suppress a key innate immune sensor.

Interaction between IGF-IR and ER induced by E2 and IGF-I

Estrogen receptor (ER) is a nuclear receptor and the insulin-like growth factor-I (IGF-I) receptor (IGF-IR) is a transmembrane tyrosine kinase receptor. Estrogen and IGF-I are known to have synergistic effects on the growth of breast cancer cells. Recently, non-nuclear effects of ER have been under investigation. To study the mechanism involved in this process, we have used MCF-7 breast cancer cell lines transfected with IGF-IR anti-sense cDNA (SX13, MCF-7(SX13)) that resulted in 50% reduction of IGF-IR. In MCF-7 cells, estradiol (E2) and IGF-I induced the rapid association of ER to IGF-IR, however, the interaction was abrogated in MCF-7(SX13) cells. In addition, NWTB3 cells (NIH3T3 cells overexpressing IGF-IR) were transiently transfected with ERα, the ER-IGF-IR interaction was induced by both E2 and IGF-I. Moreover, ERα regulated the IGF-I signaling pathways through phosphorylation of ERK1/2 and Akt and the interaction of ER-IGF-IR potentiated the cell growth. Finally, E2 and IGF-I stimulated translocation of ER from the nucleus to the cytoplasm. Taken together, these findings reveal that the interaction of the ER and IGF-IR is important for the non-genomic effects of ER.

Tamoxifen resistance: from bench to bedside

Although tamoxifen is a classical example of a targeted drug, a substantial proportion of estrogen receptor alpha positive breast cancer patients does not benefit from the drug. Over the last few decades, many potential biomarkers have been discovered in cell biological studies that may aid in the prediction of tamoxifen sensitivity and guide in treatment selection. Nonetheless, the transition of such a biomarker from the scientific community towards a diagnostic test that can be used in daily clinical practice has been far from ideal, and such markers seldom face clinical introduction. From a large number of potential predictive biomarkers as described in cell biological literature, the clinical (translational) scientist has to make a decision which of these biomarkers should be tested in clinical material to determine their clinical validity. This problem is not trivial, since patient samples with clinical follow-up are a valuable asset that should therefore be cherished. In this review, we will describe a number of 'cell biological biomarkers' for tamoxifen resistance and their possible clinical implications. This may guide the clinical scientist in choosing what potential biomarkers to test on tumour samples, which may catalyse the translation of scientific discoveries into daily clinical practice of breast cancer medicine.

Brefeldin A is an estrogenic, Erk1/2-activating component in the extract of Agaricus blazei mycelia

We purified an Erk1/2-activating component in Agaricus blazei and identified it as brefeldin A (BFA). The extract of A. blazei mycelia (ABE) previously showed an estrogenic gene-expression profile and positive effects in patients with cardiovascular symptoms. Here, we demonstrate that BFA has estrogenic activity in reporter gene assays and stimulates an estrogen-receptor pathway revealed by activation of Erk1/2, although BFA had no growth-stimulating activity in breast cancer MCF-7 cells. The presence of estrogenic activity without any explicit growth-stimulating effect is unique to BFA, and such components are termed here "silent estrogens". To test this hypothesis, we examined the target-gene transcription and signaling pathways induced by BFA. Furthermore, BFA was found in the mycelium but not fruiting body of A. blazei, suggesting the potential use of ABE for therapeutics and its supplementary use in traditional medicines and functional foods.

Mechanisms of resistance to endocrine therapy in breast cancer: focus on signaling pathways, miRNAs and genetically based resistance

Breast cancer is the most frequent malignancy diagnosed in women. Approximately 70% of breast tumors express the estrogen receptor (ER). Tamoxifen and aromatase inhibitors (AIs) are the most common and effective therapies for patients with ERα-positive breast cancer. Alone or combined with chemotherapy, tamoxifen significantly reduces disease progression and is associated with more favorable impact on survival in patients. Unfortunately, endocrine resistance occurs, either de novo or acquired during the course of the treatment. The mechanisms that contribute to hormonal resistance include loss or modification in the ERα expression, regulation of signal transduction pathways, altered expression of specific microRNAs, balance of co-regulatory proteins, and genetic polymorphisms involved in tamoxifen metabolic activity. Because of the clinical consequences of endocrine resistance, new treatment strategies are arising to make the cells sensitive to tamoxifen. Here, we will review the current knowledge on mechanisms of endocrine resistance in breast cancer cells. In addition, we will discuss novel therapeutic strategies to overcome such resistance. Undoubtedly, circumventing endocrine resistance should help to improve therapy for the benefit of breast cancer patients.

Interactions between MAP kinase and oestrogen receptor in human breast cancer

PURPOSE

The oestrogen receptor (ERα) may be activated in a ligand-dependent manner, via oestrogen, or in a ligand-independent manner, via signal transduction pathways. Mitogen Activated Protein Kinase (MAPK) is known to directly phosphorylate ERα at serine 118 in a ligand-independent manner. This study investigated the interaction between MAPK and ERα in breast cancer.

MATERIALS & METHODS

Immunohistochemical experiments were undertaken to determine the expression of MAPK, pMAPK and pER(ser118) in breast tumours to determine their clinical relevance. Immunofluorescent experiments were performed, on MCF-7 breast cancer cells, to monitor the phosphorylation and localisation of MAPK and ERα in response to oestrogen, heregulin and a MAPK inhibitor.

RESULTS

Oestrogen and Heregulin stimulated phosphorylation of ERα and its nuclear translocation, but heregulin induced this at levels much lower than those observed with oestrogen. Following stimulation with heregulin, but not oestrogen, treatment with MAPK inhibitor reduced the levels of nuclear pER(ser118). In cells treated with both oestrogen and heregulin, nuclear pER(ser118) was visible; but at levels comparable with heregulin treatment alone.

CONCLUSION

This study confirms that ligand-mediated phosphorylation is associated with rapid nuclear localisation of ERα, due to oestrogen binding. ERα is phosphorylated at serine 118 in a ligand-independent manner. Preventing nuclear translocation of pMAPK reduced the levels of ligand-independent, but not ligand-dependent phosphorylation of ERα. Co-stimulation with both oestrogen and heregulin suggested that heregulin mediated signalling determines the subcellular localisation of ERα. Activation of ERα by direct phosphorylation may result in its rapid deactivation due to degradation or nuclear export.

Phosphorylation of p90RSK is associated with increased response to neoadjuvant chemotherapy in ER-positive breast cancer

Background

The clinical implication of Ras/Raf/ERK pathway activity in breast cancer tissue and its association with response to chemotherapy is controversial. We aimed to explore the value of p90RSK phosphorylation, a downstram molecule of the pathway, in predicting chemotherapy response in breast cancer.

Methods

The expression of phosphorylated p90RSK (phospho-p90RSK) and chemotherapy response was measured in 11 breast cancer cell lines and 21 breast cancer tissues. The predictive value of phospho-p90RSK was validated in core needle biopsy specimens of 112 locally advanced breast cancer patients who received anthracycline and taxane-based neoadjuvant chemotherapy.

Results

In 11 breast cancer cell lines, the relative expression of phospho-p90RSK was inversely correlated with cell survival after doxorubicin treatment (p = 0.021). Similar association was observed in fresh tissues from 21 breast cancer patients in terms of clinical response. In paraffin-embedded, formalin-fixed tissues from core needle biopsy tissues from 112 patients, positive phospho-p90RSK expression was associated with greater tumor shrinkage and smaller post-chemotherapy tumor size. The association between phospho-p90RSK expression and chemotherapy response was more evident in estrogen receptor(ER)-positive tumors. The expression of phosphor-p90RSK did not show a significant relationship with the incidence of pCR. P90RSK silencing using siRNA did not affect the cancer cell’s response to doxorubicin, and the expression of phospho-p90RSK was highly correlated with other Ras/Raf/ERK pathway activation.

Conclusion

Our results suggest that phospho-p90RSK expression, which reflects the tumor’s Ras/Raf/ERK/p90RSK pathway activation can be a potential predictive marker for chemotherapy response in ER-positive breast cancer which needs further independent validation.

Stable inhibition of specific estrogen receptor α (ERα) phosphorylation confers increased growth, migration/invasion, and disruption of estradiol signaling in MCF-7 breast cancer cells

Elevated phosphorylation of estrogen receptor α (ERα) at serines 118 (S118) and 167 (S167) is associated with favorable outcome for tamoxifen adjuvant therapy and may serve as surrogate markers for a functional ERα signaling pathway in breast cancer. It is possible that loss of phosphorylation at S118 and/or S167 could disrupt ERα signaling, resulting in aggressive ERα-independent breast cancer cells. To this end, MCF-7 breast cancer cells were stably transfected with an ERα-specific short hairpin RNA that reduced endogenous ERα. The resulting cell line was stably transfected with wild-type ERα (ER-AB cells), or ERα containing serine to alanine mutation at S118 or S167 (S118A cells and S167A cells, respectively). These stable cell lines expressed approximately equivalent ERα compared with parental MCF-7 cells and were evaluated for growth, morphology, migration/invasion, and ERα-regulated gene expression. S118A cells and S167A cells exhibited increased growth and migration/invasion in vitro. Forward- and side-scatter flow cytometry revealed that S167A cells were smaller in size, and both S118A and S167A cells exhibited less cellular complexity. S118A and S167A cells expressed pancytokeratin and membrane localization of β-catenin and did not express vimentin, indicating retention of epithelial lineage markers. Expression of ERα-target genes and other genes regulated by ERα signaling or involved in breast cancer were markedly altered in both S118A and S167A cells. In summary, attenuated phosphorylation of ERα at S118 and S167 significantly affected cellular physiology and behavior in MCF-7 breast cancer cells, resulting in increased growth, migration/invasion, compromised expression of ERα target genes, and markedly altered gene expression patterns.

Interactions of PI3K/Akt/mTOR and estrogen receptor signaling in breast cancer

SUMMARY Endocrine therapies are used to treat estrogen receptor-positive (ER+) breast cancer; however, patients develop resistance in some cases due to hormone-independent activation of ER signaling. Dysregulation of mTOR, a central hub for various signaling pathways regulated by hormones and growth factors, is a mechanism of endocrine therapy resistance. Activation of kinases in these pathways can cause ligand-independent ER signaling. Phosphorylation of ER regulates activity and predicts clinical outcome in ER+ breast cancer. PI3K/Akt/mTOR pathway activation in breast cancer is common and considered a therapeutic target. PI3K/Akt/mTOR signaling is complex and interacts with ER signaling. mTOR’s downstream target p70S6K negatively regulates Akt on one hand and can phosphorylate ER. Moreover, overexpressed p70S6K activates ER in breast cancer cells. An overall understanding of signaling events, especially those governed by mTOR, is important in deciding treatment protocols for ER+ breast cancers.

Can predictive biomarkers in breast cancer guide adjuvant endocrine therapy?

Personalized medicine for oestrogen receptor-α (ERα)-positive breast cancer requires predictive biomarkers for broad endocrine resistance as well as biomarkers capable of predicting resistance to a specific agent. In addition, biomarkers could be used to select patients that might benefit from the addition of treatments that do not target ERα. However, biomarker identification studies seem to be far from consistent and identified biomarkers seldom face an introduction into clinical practice. Importantly, most of the studies that seek to identify biomarkers have been performed using material from consecutive series of patients treated with tamoxifen (the most commonly prescribed ERα antagonist). Consequently, the predictive value of any biomarker identified is confounded by its prognostic value. Another important issue is the lack of differentiation between premenopausal and postmenopausal patients with breast cancer. The hormonal environment of a tumour in patients who are premenopausal is intrinsically distinct from those arising in postmenopausal women. Biomarkers of different biological mechanisms might enable the prediction of either broad endocrine resistance or resistance to a specific agent in each of these patient subtypes. Ultimately, improvements to study design are needed to establish the clinical validity of the most promising biomarkers to predict benefit from endocrine therapy.

Molecular cloning and characterization of estrogen receptor gene in the scallop Chlamys farreri: expression profiles in response to endocrine disrupting chemicals

In order to gain insights into the mechanism of sex steroid signaling in molluscs, the full-length cDNA of estrogen receptor (ER) was isolated and characterized from Chlamys farreri for the first time. The positions of cysteine residues and other residues around them that constitute the two zinc finger motifs and the P-box are conserved. Phylogenetic analysis revealed that the CfER is an ortholog of the other mollusk ERs. Tissue distribution analysis of the CfER mRNA revealed that the expression of ER mRNA was observed in various tissues, and highest in the gonad of males and females. C. farreri were exposed for 10 days to endocrine disrupting chemicals including Benzo(a)pyrene (B(a)p) and polybrominated diphenyl ethers (BDE-47). B(a)p exposure at 0.4 and 2 μg/L caused significant increase in mRNA expression of ER and VTG, but B(a)p at 10 μg/L down-regulated CfER and VTG mRNA expression compared to control. Varying increase of ER and VTG mRNA transcripts was resulted in by BDE-47 at 0.1, 1 and 10 μg/L. These results elucidate potential roles of CfER induced by xenobiotics in C. farreri and can be helpful for investigating the mechanism of sex steroid signaling in bivalve mollusks.

Regulation and function of the RSK family of protein kinases

The RSK (90 kDa ribosomal S6 kinase) family comprises a group of highly related serine/threonine kinases that regulate diverse cellular processes, including cell growth, proliferation, survival and motility. This family includes four vertebrate isoforms (RSK1, RSK2, RSK3 and RSK4), and single family member orthologues are also present in Drosophila and Caenorhabditis elegans. The RSK isoforms are downstream effectors of the Ras/ERK (extracellular-signal-regulated kinase) signalling pathway. Significant advances in the field of RSK signalling have occurred in the past few years, including several new functions ascribed to the RSK isoforms, the discovery of novel protein substrates and the implication of different RSK isoforms in cancer. Collectively, these new findings increase the diversity of biological functions regulated by RSK, and highlight potential new directions of research. In the present paper, we review the structure, expression and activation mechanisms of the RSK isoforms, and discuss their physiological roles on the basis of established substrates and recent discoveries.

Breaking the cycle: An insight into the role of ERα in eukaryotic cell cycles

There have been numerous reviews written to date on estrogen receptor (ER), focusing on topics such as its role in the etiology of breast cancer, its mode of regulation, its role as a transcriptional activator and how to target it therapeutically, just to name a few. One reason for so much attention on this nuclear receptor is that it acts not only as a prognostic marker, but also as a target for therapy. However, a relatively undiscovered area in the literature regarding ER is how its activity in the presence and absence of ligand affects its role in proliferation and cell cycle transition. In this review, we provide a brief overview of ER signaling, ligand dependent and independent, genomic and non-genomic, and how these signaling events affect the role of ER in the mammalian cell cycle.

Cracking the estrogen receptor's posttranslational code in breast tumors

Estrogen signaling pathways, because of their central role in regulating the growth and survival of breast tumor cells, have been identified as suitable and efficient targets for cancer therapies. Agents blocking estrogen activity are already widely used clinically, and many new molecules have entered clinical trials, but intrinsic or acquired resistance to treatment limits their efficacy. The basic molecular studies underlying estrogen signaling have defined the critical role of estrogen receptors (ER) in many aspects of breast tumorigenesis. However, important knowledge gaps remain about the role of posttranslational modifications (PTM) of ER in initiation and progression of breast carcinogenesis. Whereas major attention has been focused on the phosphorylation of ER, many other PTM (such as acetylation, ubiquitination, sumoylation, methylation, and palmitoylation) have been identified as events modifying ER expression and stability, subcellular localization, and sensitivity to hormonal response. This article will provide an overview of the current and emerging knowledge on ER PTM, with a particular focus on their deregulation in breast cancer. We also discuss their clinical relevance and the functional relationship between PTM. A thorough understanding of the complete picture of these modifications in ER carcinogenesis might not only open new avenues for identifying new markers for prognosis or prediction of response to endocrine therapy but also could promote the development of novel therapeutic strategies.

Sustained activation of the HER1-ERK1/2-RSK signaling pathway controls myoepithelial cell fate in human mammary tissue

Human mammary glands arise from multipotent progenitor cells, which likely respond both to cell-autonomous and to extrinsic cues. However, the identity of these cues and how they might act remain unclear. We analyzed HER1 ligand effects on mammary morphogenesis using a three-dimensional organoid model generated from human breast tissue that recapitulates both qualitatively and quantitatively the normal ductal network in situ. Strikingly, different HER1 ligands generate distinct patterns of cell fate. Epidermal growth factor (EGF) causes a massive expansion of the myoepithelial lineage. Amphiregulin, in contrast, enables normal ductal development. These differences cannot be ascribed to preferential apoptosis or proliferation of differentiated cell populations, but are dependent on HER1 signal intensity. Inhibition of the extracellular signal-regulated kinase 1/2 (ERK1/2) effector RSK prevents the EGF-induced myoepithelial expansion. Notably, mouse mammary organoids are much less responsive to HER1 ligands. Little is known about the myoepithelial lineage or about growth factor effects on mammary progenitor differentiation, and our studies provide an important window into human mammary development that reveals unexpected differences from the mouse model.

ER-α36, a novel variant of estrogen receptor α, is involved in EGFR-related carcinogenesis in endometrial cancer

OBJECTIVE

To explore the role of estrogen receptor-α36 (ER-α36) in epidermal growth factor receptor (EGFR)-related carcinogenesis in endometrial cancer.

STUDY DESIGN

The expression of ER-α36, EGFR, and phospho-extracellular signal-regulated kinase was analyzed using immunohistochemistry in endometrial cancer samples. The cellular localization of ER-α36 and EGFR was determined using immunofluorescence in the endometrial cancer Hec1A cells. The level of phospho-extracellular signal-regulated kinase of Hec1A cells was determined using Western blotting after treatment with epidermal growth factor.

RESULTS

Positive rate of ER-α36 was increased in high-stage (P = .03) and high-grade (P = .224) endometrial cancer; expression of ER-α36 and EGFR exhibited a significant positive correlation (r = 0.334, P = .025) and they showed substantial colocalization on the plasma membrane of glandular cells; phospho-extracellular signal-regulated kinase positive rate in ER-α36 positive group and EGFR positive group was higher than that of ER-α36 negative group (P = .014) and EGFR negative group (P = .016); finally, ER-α36 mediated epidermal growth factor-stimulated extracellular signal-regulated kinase activation in Hec1A cells.

CONCLUSION

ER-α36 mediates EGFR-related extracellular signal-regulated kinase activation in endometrial cancer.

A role for estrogen receptor phosphorylation in the resistance to tamoxifen

About two thirds of all human breast cancer cases are estrogen receptor positive. The drug of first choice for these patients is tamoxifen. However, about half of the recurrences after removal of the primary tumor are or become resistant to this drug. While many mechanisms have been identified for tamoxifen resistance in the lab, at present only a few have been translated to the clinic. This paper highlights the role in tamoxifen resistance of phosphorylation by different kinases on different sites of the estrogen receptor. We will discuss the molecular pathways and kinases that are involved in phosphorylation of ERα and how these affect tamoxifen resistance. Finally, we will elaborate on the clinical translation of these observations and the possibility to predict tamoxifen responses in patient tumor samples before treatment onset. The findings made originally on the bench may translate into a better and personalized treatment of breast cancer patients using an old and safe anticancer drug: tamoxifen.

New and translational perspectives of oestrogen deprivation in breast cancer

Over the last 20 years, aromatase inhibitors have been developed to become a highly effective treatment strategy for treatment of hormone receptor positive breast cancer. Despite their success, poor response and resistance limit the effectiveness of these agents in up to 50% of patients. In recent years, studies using highly sensitive hormone assays have provided insight into the source of oestrogen production for the stimulation of oestrogen receptor positive breast cancer growth, suggesting that uptake from the circulation is likely to make a significant contribution to intratumoural oestradiol. To obtain insight into how tumours become resistant to oestrogen after aromatase inhibition, long term oestrogen deprivation of cultured cells has been used to mimic acquired resistance to aromatase inhibitors. This work has aided the selection of agents to rationally combine with aromatase inhibitors to combat resistance. Molecular profiling using genome-wide approaches has shed new light on the heterogeneity of responses to oestrogen deprivation and predictors of resistance in vivo. Testing new agents and combinations in short-term pre-surgical studies using biomarkers such as Ki67 is critical for increasing the rate at which new rational combinations can be assessed for efficacy.

Molecular cloning, characterization and expression profiles of three estrogen receptors in protogynous hermaphroditic orange-spotted grouper (Epinephelus coioides)

Estrogen plays key roles in vertebrate reproductive system via estrogen receptors (ERs) as mediating pathways. In the present study, three full-length ERs cDNA sequences were isolated from a protogynous teleost, the orange-spotted grouper (Epinephelus coioides), and were 2235bp for gERα, 1967bp for gERβ1 and 2158bp for gERβ2, respectively. Phylogenetic and amino acid alignment analyses showed that each gER was clustered in the corresponding taxonomic groups of the perciformes and exhibited high evolutional conservation in functional domains. RT-PCR revealed that gERs expressed at different levels in all the obtained tissues. gERα highly expressed in mature ovaries, gERβ1 mainly expressed in immature ovaries and gERβ2 varied greatly during ovarian development. During female to male sex reversal induced by 17α-methyltestosterone (MT) implantation, gERα decreased gradually, gERβ1 increased gradually, and gERβ2 decreased firstly and recovered subsequently in male stage. The present study speculated the potential roles of gERs during female maturation and female to male sex reversal induced by MT in the protogynous grouper E. coioides.

Activation and function of the MAPKs and their substrates, the MAPK-activated protein kinases

The mitogen-activated protein kinases (MAPKs) regulate diverse cellular programs by relaying extracellular signals to intracellular responses. In mammals, there are more than a dozen MAPK enzymes that coordinately regulate cell proliferation, differentiation, motility, and survival. The best known are the conventional MAPKs, which include the extracellular signal-regulated kinases 1 and 2 (ERK1/2), c-Jun amino-terminal kinases 1 to 3 (JNK1 to -3), p38 (α, β, γ, and δ), and ERK5 families. There are additional, atypical MAPK enzymes, including ERK3/4, ERK7/8, and Nemo-like kinase (NLK), which have distinct regulation and functions. Together, the MAPKs regulate a large number of substrates, including members of a family of protein Ser/Thr kinases termed MAPK-activated protein kinases (MAPKAPKs). The MAPKAPKs are related enzymes that respond to extracellular stimulation through direct MAPK-dependent activation loop phosphorylation and kinase activation. There are five MAPKAPK subfamilies: the p90 ribosomal S6 kinase (RSK), the mitogen- and stress-activated kinase (MSK), the MAPK-interacting kinase (MNK), the MAPK-activated protein kinase 2/3 (MK2/3), and MK5 (also known as p38-regulated/activated protein kinase [PRAK]). These enzymes have diverse biological functions, including regulation of nucleosome and gene expression, mRNA stability and translation, and cell proliferation and survival. Here we review the mechanisms of MAPKAPK activation by the different MAPKs and discuss their physiological roles based on established substrates and recent discoveries.

Gender-specific interplay of signaling through β-catenin and CAR in the regulation of xenobiotic-induced hepatocyte proliferation

Aberrant signaling through the Wnt/β-catenin pathway is a critical determinant in human and rodent liver carcinogenesis and generally accepted to be a potent driver of proliferation. Xenobiotic agonists of the constitutive androstane receptor (CAR) induce massive acute hyperplasia of mouse liver and facilitate the outgrowth of hepatocellular carcinomas with activated β-catenin. In the present study, the interplay of β-catenin-dependent and CAR-dependent signaling in the liver and its effect on hepatocyte proliferation were analyzed in transgenic mice with hepatocyte-specific knockout of Ctnnb1 (encoding β-catenin) following treatment with two CAR agonists, 1,4-bis[2-(3,5-dichloropyridyloxy)]-benzene (TCPOBOP) and phenobarbital. Hepatocyte-specific knockout of β-catenin inhibited CAR agonists-induced hepatocyte proliferation in male mice. By contrast, the proliferative effect of CAR agonists was strongly augmented in female β-catenin knockout animals. This was due to prolonged proliferation of the knockout hepatocytes. CAR-mediated hepatocyte proliferation was, at least in part, dependent on estrogen signaling and was associated with enhanced expression of FoxM1 and elevated activity of the PDK1/p90RSK pathway. In conclusion, our study shows that gender-specific factors determine whether β-catenin signaling plays a pro- or an antiproliferative role in the regulation of mouse hepatocyte proliferation induced by CAR agonists.

The Ras-ERK and PI3K-mTOR pathways: cross-talk and compensation

The Ras-extracellular signal-regulated kinase (Ras-ERK) and phosphatidylinositol 3-kinase-mammalian target of rapamycin (PI3K-mTOR) signaling pathways are the chief mechanisms for controlling cell survival, differentiation, proliferation, metabolism, and motility in response to extracellular cues. Components of these pathways were among the first to be discovered when scientists began cloning proto-oncogenes and purifying cellular kinase activities in the 1980s. Ras-ERK and PI3K-mTOR were originally modeled as linear signaling conduits activated by different stimuli, yet even early experiments hinted that they might intersect to regulate each other and co-regulate downstream functions. The extent of this cross-talk and its significance in cancer therapeutics are now becoming clear.

Activation and Function of the MAPKs and Their Substrates, the MAPK-Activated Protein Kinases

The mitogen-activated protein kinases (MAPKs) regulate diverse cellular programs by relaying extracellular signals to intracellular responses. In mammals, there are more than a dozen MAPK enzymes that coordinately regulate cell proliferation, differentiation, motility, and survival. The best known are the conventional MAPKs, which include the extracellular signal-regulated kinases 1 and 2 (ERK1/2), c-Jun amino-terminal kinases 1 to 3 (JNK1 to -3), p38 (α, β, γ, and δ), and ERK5 families. There are additional, atypical MAPK enzymes, including ERK3/4, ERK7/8, and Nemo-like kinase (NLK), which have distinct regulation and functions. Together, the MAPKs regulate a large number of substrates, including members of a family of protein Ser/Thr kinases termed MAPK-activated protein kinases (MAPKAPKs). The MAPKAPKs are related enzymes that respond to extracellular stimulation through direct MAPK-dependent activation loop phosphorylation and kinase activation. There are five MAPKAPK subfamilies: the p90 ribosomal S6 kinase (RSK), the mitogen- and stress-activated kinase (MSK), the MAPK-interacting kinase (MNK), the MAPK-activated protein kinase 2/3 (MK2/3), and MK5 (also known as p38-regulated/activated protein kinase [PRAK]). These enzymes have diverse biological functions, including regulation of nucleosome and gene expression, mRNA stability and translation, and cell proliferation and survival. Here we review the mechanisms of MAPKAPK activation by the different MAPKs and discuss their physiological roles based on established substrates and recent discoveries.

The IGF pathway regulates ERα through a S6K1-dependent mechanism in breast cancer cells

The IGF pathway stimulates malignant behavior of breast cancer cells. Herein we identify the mammalian target of rapamycin (mTOR)/S6 kinase 1 (S6K1) axis as a critical component of IGF and estrogen receptor (ER)α cross talk. The insulin receptor substrate (IRS) adaptor molecules function downstream of IGF-I receptor and dictate a specific biological response, in which IRS-1 drives proliferation and IRS-2 is linked to motility. Although rapamycin-induced mTOR inhibition has been shown to block IGF-induced IRS degradation, we reveal differential effects on motility (up-regulation) and proliferation (down-regulation). Because a positive correlation between IRS-1 and ERα expression is thought to play a central role in the IGF growth response, we investigated the potential role of ERα as a downstream mTOR target. Small molecule inhibition and targeted knockdown of S6K1 blocked the IGF-induced ERα(S167) phosphorylation and did not influence ligand-dependent ERα(S118) phosphorylation. Inhibition of S6K1 kinase activity consequently ablated IGF-stimulated S6K1/ERα association, estrogen response element promoter binding and ERα target gene transcription. Moreover, site-specific ERα(S167) mutation reduced ERα target gene transcription and blocked IGF-induced colony formation. These findings support a novel link between the IGF pathway and ERα, in which the translation factor S6K1 affects transcription of ERα-regulated genes.

Growth factor stimulation induces a distinct ER(alpha) cistrome underlying breast cancer endocrine resistance

Estrogen receptor α (ERα) expression in breast cancer is predictive of response to endocrine therapy; however, resistance is common in ERα-positive tumors that overexpress the growth factor receptor ERBB2. Even in the absence of estrogen, ERα can be activated by growth factors, including the epidermal growth factor (EGF). EGF induces a transcriptional program distinct from estrogen; however, the mechanism of the stimulus-specific response is unknown. Here we show that the EGF-induced ERα genomic targets, its cistromes, are distinct from those induced by estrogen in a process dependent on the transcription factor AP-1. The EGF-induced ERα cistrome specifically regulates genes found overexpressed in ERBB2-positive human breast cancers. This provides a potential molecular explanation for the endocrine therapy resistance seen in ERα-positive breast cancers that overexpress ERBB2. These results suggest a central role for ERα in hormone-refractory breast tumors dependent on growth factor pathway activation and favors the development of therapeutic strategies completely antagonizing ERα, as opposed to blocking its estrogen responsiveness alone.

Targeting the receptor tyrosine kinase RET sensitizes breast cancer cells to tamoxifen treatment and reveals a role for RET in endocrine resistance

Endocrine therapy is the main therapeutic option for patients with estrogen receptor (ERalpha)-positive breast cancer. Resistance to this treatment is often associated with estrogen-independent activation of ERalpha. In this study, we show that in ERalpha-positive breast cancer cells, activation of the receptor tyrosine kinase RET (REarranged during Transfection) by its ligand GDNF results in increased ERalpha phosphorylation on Ser118 and Ser167 and estrogen-independent activation of ERalpha transcriptional activity. Further, we identify mTOR as a key component in this downstream signaling pathway. In tamoxifen response experiments, RET downregulation resulted in 6.2-fold increase in sensitivity of MCF7 cells to antiproliferative effects of tamoxifen, whereas GDNF stimulation had a protective effect against the drug. In tamoxifen-resistant (TAM(R)-1) MCF7 cells, targeting RET restored tamoxifen sensitivity. Finally, examination of two independent tissue microarrays of primary human breast cancers revealed that expression of RET protein was significantly associated with ERalpha-positive tumors and that in primary tumors from patients who subsequently developed invasive recurrence after adjuvant tamoxifen treatment, there was a twofold increase in the number of RET-positive tumors. Together these findings identify RET as a potentially important therapeutic target in ERalpha-positive breast cancers and in particular in tamoxifen-resistant tumors.

Targeting tumour-initiating cells to improve the cure rates for triple-negative breast cancer

Tumour recurrence is one of the biggest challenges in breast cancer management because it affects 25-30% of women with breast cancer and the tumours are often incurable. Women with triple-negative breast cancer (TNBC--lacking expression of the oestrogen receptor, progesterone receptor and the receptor HER2/ERBB2) have the highest rates of early recurrence relative to other breast cancer subtypes. Early recurrence might be due to tumour-initiating cells (TICs), which are resistant to conventional therapies, can remain dormant and can subsequently give rise to secondary tumours. In breast cancer, TICs are identified by the cell-surface markers CD44+/CD24-/EpCAM+ and/or possess ALDH1 enzyme activity. This subpopulation has the ability to self-renew, grow as mammospheres and initiate tumour formation. Fuelling the problem of relapse is the fact that chemotherapy and radiation can induce or select for TICs; this was reported in preclinical models and more recently in women being treated for breast cancer. Thus, new therapeutic agents for TNBC are presently being sought to overcome this problem. Here we review the roles of receptor tyrosine kinases, signalling intermediates and transcription factors in sustaining the TIC subpopulation. Particular emphasis is placed on targeting these molecules in order to eliminate and/or prevent the induction of TICs and ultimately reduce the frequency of TNBC recurrence.

Identification of Insulin-Like Growth Factor-I Receptor (IGF-IR) Gene Promoter-Binding Proteins in Estrogen Receptor (ER)-Positive and ER-Depleted Breast Cancer Cells

The insulin-like growth factor I receptor (IGF-IR) has been implicated in the etiology of breast cancer. Overexpression of the IGF-IR gene is a typical feature of most primary breast cancers, whereas low IGF-IR levels are seen at advanced stages. Hence, evaluation of IGF-IR levels might be important for assessing prognosis. In the present study, we employed a proteomic approach based on DNA affinity chromatography followed either by mass spectroscopy (MS) or Western blot analysis to identify transcription factors that may associate with the IGF-IR promoter in estrogen receptor (ER)-positive and ER-depleted breast cancer cells. A biotinylated IGF-IR promoter fragment was bound to streptavidin magnetic beads and incubated with nuclear extracts of breast cancer cells. IGF-IR promoter-binding proteins were eluted with high salt and analyzed by MS and Western blots. Among the proteins that were found to bind to the IGF-IR promoter we identified zinc finger transcription factors Sp1 and KLF6, ER-α, p53, c-jun, and poly (ADP-ribosylation) polymerase. Furthermore, chromatin immune-precipitation (ChIP) analysis confirmed the direct in vivo binding of some of these transcription factors to IGF-IR promoter DNA. The functional relevance of binding data was assessed by cotransfection experiments with specific expression vectors along with an IGF-IR promoter reporter. In summary, we identified nuclear proteins that are potentially responsible for the differential expression of the IGF-IR gene in ER-positive and ER-depleted breast cancer cells.

RSK in tumorigenesis: connections to steroid signaling

The Ser/Thr kinase family, RSK, has been implicated in numerous types of hormone-dependent and -independent cancers. However, there has been little consideration of RSKs as downstream mediators of steroid hormone non-genomic effects or of their ability to facilitate steroid receptor-mediated gene expression. Steroid hormone signaling can directly stimulate the MEK/ERK/RSK pathway to regulate cellular proliferation and survival in transformed cells. To date, multiple mechanisms of RSK and steroid hormone receptor-mediated proliferation/survival have been elucidated. For example, RSK enhances proliferation of breast and prostate cancer cells via its ability to control the levels of the estrogen receptor co-activator, cyclin D1. While in lung and other tumors RSK may control apoptosis via estrogen-mediated regulation of mitochondrial integrity. Thus the RSKs could be important anti-cancer therapeutic targets in many different transformed tissues. The recent discovery of RSK-specific inhibitors will advance our current understanding of RSK in transformation and drive these studies into animal and clinical models. In this review we explore the mechanisms associated with RSK in tumorigenesis and their relationship to steroid hormone signaling.

mTOR/S6K1 and MAPK/RSK signaling pathways coordinately regulate estrogen receptor alpha serine 167 phosphorylation

Resistance to anti-estrogen therapy is a major clinical concern in treatment of breast cancer. Estrogen-independent phosphorylation of estrogen receptor alpha, specifically on Ser167, is one of the contributing causes to development of resistance, and a prognostic marker for the disease. Here, we dissect the signaling pathways responsible for Ser167 phosphorylation. We report that the mTOR/S6K1 and MAPK/RSK contribute non-overlapping inputs into ERalpha activation via Ser167 phosphorylation. This cooperation may be targeted in breast cancer treatment by a combination of mTOR and MAPK inhibitors.

Identification of four novel phosphorylation sites in estrogen receptor alpha: impact on receptor-dependent gene expression and phosphorylation by protein kinase CK2

Background

Estrogen receptor α (ERα) phosphorylation is important for estrogen-dependent transcription of ER-dependent genes, ligand-independent receptor activation and endocrine therapy response in breast cancer. However ERα phosphorylation at the previously identified sites does not fully account for these receptor functions. To determine if additional ERα phosphorylation sites exist, COS-1 cells expressing human ERα were labeled with [³²P]H₃PO₄ in vivo and ERα tryptic phosphopeptides were isolated to identify phosphorylation sites.

Results

Previously uncharacterized phosphorylation sites at serines 46/47, 282, 294, and 559 were identified by manual Edman degradation and phosphoamino acid analysis and confirmed by mutagenesis and phospho-specific antibodies. Antibodies detected phosphorylation of endogenous ERα in MCF-7, MCF-7-LCC2, and Ishikawa cancer cell lines by immunoblot. Mutation of Ser-282 and Ser-559 to alanine (S282A, S559A) resulted in ligand independent activation of ERα as determined by both ERE-driven reporter gene assays and endogenous pS2 gene expression in transiently transfected HeLa cells. Mutation of Ser-46/47 or Ser-294 to alanine markedly reduced estradiol dependent reporter activation. Additionally protein kinase CK2 was identified as a kinase that phosphorylated ERα at S282 and S559 using motif analysis, in vitro kinase assays, and incubation of cells with CK2 kinase inhibitor.

Conclusion

These novel ERα phosphorylation sites represent new means for modulation of ERα activity. S559 represents the first phosphorylation site identified in the extreme C-terminus (F domain) of a steroid receptor.

IKKepsilon phosphorylation of estrogen receptor alpha Ser-167 and contribution to tamoxifen resistance in breast cancer

IKKepsilon has recently been identified as a breast cancer oncogene. Elevated levels of IKKepsilon are associated with cell survival and growth. Here, we show that IKKepsilon interacts with and phosphorylates estrogen receptor alpha (ERalpha) on serine 167 in vitro and in vivo. As a result, IKKepsilon induces ERalpha transactivation activity and enhances ERalpha binding to DNA. Cyclin D1, a major target of ERalpha, is transcriptionally up-regulated by IKKepsilon in a phospho-ERalpha-Ser-167-dependent manner. Further, overexpression of IKKepsilon induces tamoxifen resistance, whereas knockdown of IKKepsilon sensitizes cells to tamoxifen-induced cell death. These data suggest that ERalpha is a bona fide substrate of IKKepsilon and IKKepsilon plays an important role in tamoxifen resistance. Thus, IKKepsilon represents a critical therapeutic target in breast cancer.

Steroid receptor phosphorylation: Assigning function to site-specific phosphorylation

Steroid receptors (SRs) are hormone-activated transcription factors important for a wide variety of cellular functions. Post-translational modifications of SRs, including phosphorylation, ubiquitination, acetylation, and sumoylation regulate their expression and function. The remarkable number of phosphorylation sites in these receptors and the wide variety of kinases shown to modulate phosphorylation influence the integration between cell-signaling pathways and SR action. These phosphorylation sites have been identified in all of the functional domains with the majority being located within the amino-terminal portions of the receptors. The regulation of function is receptor specific, site specific, and often dependent on the cellular context. Numerous roles for site-specific phosphorylation have been elucidated including sensitivity of hormone response, DNA binding, expression, stability, subcellular localization, dimerization, and protein-protein interactions that can determine the regulation of specific target genes. This review summarizes the current knowledge regarding receptor site-specific phosphorylation and regulation of function. As functional assays become more sophisticated, it is likely that additional roles for phosphorylation in receptor function will be identified.

Heat shock protein 90 inhibitors: new mode of therapy to overcome endocrine resistance

Aromatase inhibitors are important drugs to treat estrogen receptor alpha (ERalpha)-positive postmenopausal breast cancer patients. However, development of resistance to aromatase inhibitors has been observed. We examined whether the heat shock protein 90 (HSP90) inhibitor 17-(dimethylaminoethylamino)-17-demethoxygeldanamycin (17-DMAG) can inhibit the growth of aromatase inhibitor-resistant breast cancers and the mechanisms by which 17-DMAG affects proliferation. Aromatase inhibitor-responsive MCF-7aro and aromatase inhibitor-resistant LTEDaro breast epithelial cells were used in this study. We observed that 17-DMAG inhibited proliferation in both MCF-7aro and LTEDaro cells in a dose-dependent manner. 17-DMAG induced apoptosis and G(2) cell cycle arrest in both cell lines. Although inhibition of HSP90 decreased the levels of ERalpha, the ERalpha transcriptional activity was not affected when cells were treated with 17-DMAG together with estradiol. Moreover, detailed mechanistic studies suggested that 17-DMAG inhibits cell growth via degradation of HSP90 client proteins AKT and HER2. Collectively, results from this study provide data to support that HSP90 inhibitors may be an effective therapy to treat aromatase inhibitor-resistant breast cancers and that improved efficacy can be achieved by combined use of a HSP90 inhibitor and an AKT inhibitor.

Estrogen and progesterone receptors: from molecular structures to clinical targets

Research involving estrogen and progesterone receptors (ER and PR) have greatly contributed to our understanding of cell signaling and transcriptional regulation. In addition to the classical ER and PR nuclear actions, new signaling pathways have recently been identified due to ER and PR association with cell membranes and signal transduction proteins. Bio-informatics has unveiled how ER and PR recognize their ligands, selective modulators and co-factors, which has helped to implement them as key targets in the treatment of benign and malignant tumors. Knowledge regarding ER and PR is vast and complex; therefore, this review will focus on their isoforms, signaling pathways, co-activators and co-repressors, which lead to target gene regulation. Moreover it will highlight ER and PR involvement in benign and malignant diseases as well as pharmacological substances influencing cell signaling and provide established and new structural insights into the mechanism of activation and inhibition of these receptors.

Epidermal growth factor receptor cross-talks with ligand-occupied estrogen receptor-alpha to modulate both lactotroph proliferation and prolactin gene expression

Both estrogen (E2) and EGF regulate lactotrophs, and we recently demonstrated that EGF phosphorylates S118 on estrogen receptor-alpha (ERalpha) and requires ERalpha to stimulate prolactin (PRL) release. However, the interactions between ligand-occupied ERalpha and activated ErbB1 and its impact on lactotroph function are unknown. Using rat GH3 lactotrophs, we found that both E2 and EGF independently stimulated proliferation and PRL gene expression. Furthermore, their combination resulted in an enhanced stimulatory effect on both cell proliferation and PRL gene expression. Inhibitors of ER as well as ErbB1 blocked the combined effects of E2 and EGF. Pretreatment with UO126 abolished the combined effects, demonstrating Erk1/2 requirement. Although bidirectionality in ER-ErbB1 cross-talk is a well-accepted paradigm, interestingly in lactotrophs, ErbB1 kinase inhibitor failed to block the effect of E2 on proliferation and stimulation of PRL gene expression, suggesting that ER does not require ErbB1 to mediate its effects. Furthermore, E2 did not affect the ability of EGF to induce c-Fos expression or modulate AP-1 activity. However, both E2 and EGF combine to enhance S118 phosphorylation of ERalpha, leading to enhanced E2-mediated estrogen response element transactivation. Taken together, our results suggest that, in lactotrophs, activated ErbB1 phosphorylates ERalpha to enhance the stimulatory effect of E2, thereby providing the molecular basis by which EGF amplifies the response of E2.

Clinical and molecular overview of inherited disorders resulting from epigenomic dysregulation

Epigenetics is the study of heritable changes in gene expression that occur without a change in the DNA sequence. Most constitutional defects in genes encoding components of the machinery that regulates the epigenome lead to embryonic death. Hypomorphic mutations may be compatible with life, but lead to severe developmental disorders. Their study is of great importance to our understanding of epigenetics and may clarify the interplay between different epigenetic mechanisms. This review will briefly introduce DNA methylation, post-translational histone modifications, and non-coding small RNA transcription, which are the best known epigenetic mechanisms. Then it will describe five human disorders (RETT, ATRX, ICF, Coffin-Lowry, and Rubinstein-Taybi) resulting from mutations in genes responsible for DNA methylation and in genes involved in chromatin remodeling. Finally, it will discuss how research in medical genetics can elucidate fundamental epigenetic processes.

Expression of the K303R estrogen receptor-alpha breast cancer mutation induces resistance to an aromatase inhibitor via addiction to the PI3K/Akt kinase pathway

Aromatase inhibitors (AI) are rapidly becoming the first choice for hormonal treatment of estrogen receptor-alpha (ERalpha)-positive breast cancer in postmenopausal women. However, de novo and acquired resistance frequently occurs. We have previously identified a lysine to arginine transition at residue 303 (K303R) in ERalpha in premalignant breast lesions and invasive breast cancers, which confers estrogen hypersensitivity and resistance to tamoxifen treatment. Thus, we questioned whether resistance to AIs could arise in breast cancer cells expressing the ERalpha mutation. As preclinical models to directly test this possibility, we generated K303R-overexpressing MCF-7 cells stably transfected with an aromatase expression vector. Cells were stimulated with the aromatase substrate, androstenedione, with or without the AI anastrozole (Ana). We found that Ana decreased androstenedione-stimulated growth of wild-type cells, whereas K303R-expressing cells were resistant to the inhibitory effect of Ana on growth. We propose that a mechanism of resistance involves an increased binding between the mutant receptor and the p85alpha regulatory subunit of phosphatidylinositol-3-OH kinase (PI3K), leading to increased PI3K activity and activation of protein kinase B/Akt survival pathways. Inhibition of the selective "addiction" to the PI3K/Akt pathway reversed AI resistance associated with expression of the mutant receptor. Our findings suggest that the K303R ERalpha mutation might be a new predictive marker of response to AIs in mutation-positive breast tumors, and that targeting the PI3K/Akt pathway may be a useful strategy for treating patients with tumors resistant to hormone therapy.

E-cadherin mediates the aggregation of breast cancer cells induced by tamoxifen and epidermal growth factor

In the present study, we evaluated the ability of 4-hydroxytamoxifen (OHT) and epidermal growth factor (EGF) to regulate homotypic adhesion in MCF7 breast cancer cells. Our results demonstrate that OHT and EGF activate the E-cadherin promoter, increase E-cadherin mRNA and protein expression and enhance homotypic aggregation of MCF7 cells. Interestingly, an ERalpha and EGFR cross-talk is involved in the E-cadherin expression by OHT and EGF, as demonstrated by knocking down either receptor. On the basis of our findings, the well-established cross-talk between ERalpha and EGFR could be extended to the modulation of E-cadherin expression by OHT and EGF. Thus, the potential ability of tamoxifen to induce cell-cell aggregation may contribute to the biologic response of pharmacologic intervention in patients with breast cancer.