AKT regulation of estrogen receptor beta transcriptional activity in breast cancer

Estrogen's sex-specific effects on ischemic cell death and estrogen receptor mRNA expression in rat cortical organotypic explants

Estrogens, such as the biologically active 17-β estradiol (E2), regulate not only reproductive behaviors in adults, but also influence neurodevelopment and neuroprotection in both females and males. E2, contingent upon the timing and concentration of the therapy, is neuroprotective in female and male rodent models of stroke. In Vivo studies suggest that E2 may partially mediate this neuroprotection, particularly in the cortex, via ERα. In Vitro studies, utilizing a chemically induced ischemic injury in cortical explants from both sexes, suggest that ERα or ERβ signaling is needed to mediate the E2 protection. Since we know that the timing and concentration of E2 therapy may be sex-specific, we examined if E2 (1 nM) mediates neuroprotection when female and male cortical explants are separately isolated from postnatal day (PND) 3-4 rat. Changes in basal levels ERα, ERβ, and AR mRNA expression are compared across early post-natal development in the intact cortex and the corresponding days in vitro (DIV) for cortical explants. Following ischemic injury at 7 DIV, cell death and ERα, ERβ and AR mRNA expression was compared in female and male cortical explants. We provide evidence that E2-mediated protection is maintained in isolated cortical explants from females, but not male rats. In female cortical explants, the E2-mediated protection at 24 h occurs secondarily to a blunted transient increase in ERα mRNA at 12 h. These results suggest that cortical E2-mediated protection is influenced by sex and supports data to differentially treat females and males following ischemic injury.

Oleuropein suppresses endometriosis progression and improves the fertility of mice with endometriosis

BACKGROUND

Endometriosis is an estrogen-dependent inflammatory reproductive disease. Therefore, systematic estrogen depletion and anti-inflammatory drugs are the current treatment for endometriosis. However, current endometriosis treatments have low efficacy and cause adverse effects in endometriosis patients. Consequently, alternative endometriosis treatments targeting endometriosis-specific factors are in demand. In this context, ERβ was selected as a druggable target for endometriosis due to its critical role in progression. Therefore, selective targeting of ERβ without inhibiting ERα activity would be a new paradigm for endometriosis treatment to overcome the low efficacy and adverse effects of hormonal endometriosis therapy.

METHODS

Cell-based ERβ and ERα activity assay systems were employed to define a selective ERβ-inhibiting chemical product from a library of natural products. A surgically induced endometriosis mouse model was used to determine whether an ERβ inhibitory drug suppressed endometriosis progression. Mice with endometriosis were randomly separated and then orally treated with vehicle or 25 mg/kg oleuropein (once a day for 21 days), an ERβ inhibitory drug. The volume of endometriotic lesions or luciferase activity of endometriotic lesions was examined to define the growth of ectopic lesions in mice with endometriosis. The metabolite and levels of metabolic enzymes of the liver and kidney were determined in the serum of female mice treated with vehicle and oleuropein (25 mg/kg, once a day for 21 days) to define the toxicity of oleuropein. The in vitro decidualization assay was conducted with normal human endometrial stromal cells and endometriotic stromal cells to determine whether oleuropein overcomes decidualization in endometriosis patients. The pregnancy rate and pup numbers of C57BL/6 J female mice with endometriosis treated with vehicle or oleuropein (n = 10/group) were determined after mating with male mice. The cytokine profile in endometriotic lesions treated with vehicle and oleuropein (25 mg/kg) was determined with a Mouse Cytokine Array Kit.

RESULTS

Among natural products, oleuropein selectively inhibited ERβ but not ERα activity in vitro. Oleuropein treatment inhibited the nuclear localization of ERβ in human endometrial cells upon estradiol treatment. Oleuropein (25 mg/kg) treatment suppressed the growth of mouse (6.6-fold) and human (sixfold) ectopic lesions in mice with endometriosis compared to the vehicle by inhibiting proliferation and activating apoptosis in endometriotic lesions. Oleuropein treatment did not cause reproductive toxicity in female mice. Additionally, mice with endometriosis subjected to oleuropein treatment had a higher pregnancy rate (100%) than vehicle-treated mice (70%). Furthermore, oleuropein treatment partially recovered the decidualization impact of human endometriotic stromal cells from endometriotic lesions compared to the vehicle. Oleuropein-treated mice with endometriosis exhibited significantly lower levels of cytokines directly regulated by ERβ in ectopic lesions than vehicle-treated mice, illustrating the improvement in the hyperinflammatory state of mice with endometriosis.

CONCLUSIONS

Oleuropein is a promising and novel nutraceutical product for nonhormonal therapy of endometriosis because it selectively inhibits ERβ, but not ERα, to suppress endometriosis progression and improve the fertility of mice with endometriosis.

Estrogens and Progestogens in Triple Negative Breast Cancer: Do They Harm?

Triple-negative breast cancers (TNBC) occur more frequently in younger women and do not express estrogen receptor (ER) nor progesterone receptor (PR), and are therefore often considered hormone-insensitive. Treatment of premenopausal TNBC patients almost always includes chemotherapy, which may lead to premature ovarian insufficiency (POI) and can severely impact quality of life. Hormone replacement therapy (HRT) is contraindicated for patients with a history of hormone-sensitive breast cancer, but the data on safety for TNBC patients is inconclusive, with a few randomized trials showing increased risk-ratios with wide confidence intervals for recurrence after HRT. Here, we review the literature on alternative pathways from the classical ER/PR. We find that for both estrogens and progestogens, potential alternatives exist for exerting their effects on TNBC, ranging from receptor conversion, to alternative receptors capable of binding estrogens, as well as paracrine pathways, such as RANK/RANKL, which can cause progestogens to indirectly stimulate growth and metastasis of TNBC. Finally, HRT may also influence other hormones, such as androgens, and their effects on TNBCs expressing androgen receptors (AR). Concluding, the assumption that TNBC is completely hormone-insensitive is incorrect. However, the direction of the effects of the alternative pathways is not always clear, and will need to be investigated further.

Insights into the Role of Estrogen Receptor β in Triple-Negative Breast Cancer

Estrogen receptors (ERα and ERβ) are ligand-activated transcription factors that play different roles in gene regulation and show both overlapping and specific tissue distribution patterns. ERβ, contrary to the oncogenic ERα, has been shown to act as an oncosuppressor in several instances. However, while the tumor-promoting actions of ERα are well-known, the exact role of ERβ in carcinogenesis and tumor progression is not yet fully understood. Indeed, to date, highly variable and even opposite effects have been ascribed to ERβ in cancer, including for example both proliferative and growth-inhibitory actions. Recently ERβ has been proposed as a potential target for cancer therapy, since it is expressed in a variety of breast cancers (BCs), including triple-negative ones (TNBCs). Because of the dependence of TNBCs on active cellular signaling, numerous studies have attempted to unravel the mechanism(s) behind ERβ-regulated gene expression programs but the scenario has not been fully revealed. We comprehensively reviewed the current state of knowledge concerning ERβ role in TNBC biology, focusing on the different signaling pathways and cellular processes regulated by this transcription factor, as they could be useful in identifying new diagnostic and therapeutic approaches for TNBC.

Possible roles for glucocorticoid signalling in breast cancer

Our understanding of breast cancer biology, and our ability to manipulate breast cancers have grown exponentially in the last 20 years. Much of that expansion has focused on the roles of steroids in driving these neoplasms. Initially this research focused on estrogens and progesterone receptors, and more recently on androgen actions in breast cancers. This review aims to make the case for glucocorticoids as the next essential steroid subclass that contributes significantly to our understanding of steroidogenic regulation of these neoplasms. Glucocorticoids have the potential to play multiple roles in the regulation of breast cancers including their control of cellular differentiation, apoptosis and proliferation. Beyond this they also act as a master integrator of organ homeostats in relation to such as circadian rhythms and stress responses. Therefore a better understanding of glucocorticoids and breast cancer could help to explain some of the epidemiological links between circadian disruption and/or stress and breast cancer development. Finally glucocorticoids are currently used during chemotherapeutic treatment in breast cancer therapy and yet results of various studies suggest that this may have an adverse impact on treatment success. This review aims to summarise the current evidence for glucocorticoids as actors in breast cancer and then suggest future essential approaches in order to determine the roles of glucocorticoids in this disease.

AKT Signaling Pathway in Invasive Ductal Carcinoma of the Breast: Correlation with ERα, ERβ and HER-2 Expression

Aims and background

Estradiol exerts most of its effects by direct binding to the estrogen receptor in breast carcinoma, ERβ expression is a useful biomarker for breast cancer in a manner that is independent of ERα expression. However, studies evaluating ERβ expression with certain tumor variables, such as tumor grade and disease-free survival, had produced conflicting results. The Akt signaling pathway currently attracts considerable attention as a new target for effective therapeutic strategies. The current study attempted to compare the relative associations of variables including ERα, ERβ, HER-2/neu and AKT staining with the presence of metastases or survival.

Methods and study design

Immunohistochemical staining was employed to determine the expression of ERα, ERβ, pAkt and HER-2/neu in 110 cases of primary breast carcinoma.

Results

Positive ERα, ERβ, pAkt and HER-2/neu expressions were respectively observed in 46.4% (51/110), 59.1% (65/110), 40.9% (45/110) and 31.8% (35/110) of the tumors. pAkt was significantly associated with HER-2/neu overexpression (P <0.005) and axillary lymph node metastasis (P <0.05). However, there was no significant relationship between pAkt and ERα, ERβ, p53 (P >0.05) expressions. Survival analysis showed that pAkt positivity was associated with poor disease-free survival of the patients.

Conclusions

The current study suggested that activity of the Akt signaling pathway may indicate a poor prognosis in patients with breast carcinoma. The results implied that estrogen can activate the PI3K-Akt pathway through ERα and ERβ-independent mechanisms in breast cancer.

MicroRNA-3127 promotes cell proliferation and tumorigenicity in hepatocellular carcinoma by disrupting of PI3K/AKT negative regulation

Recent studies have shown that multiple phosphatases deactivate the PI3K/AKT signaling pathway. Here we demonstrated that, by suppressing multiple phosphatases, miR-3127 promotes growth of hepatocellular carcinoma (HCC). Our study also reveals clinical significance of miR-3127 expression in HCC patients. MiR-3127 expression was markedly upregulated in HCC tissues and cells. Furthermore, high miR-3127 expression was associated with an aggressive phenotype and poor prognosis. MiR-3127 overexpression promoted HCC cell proliferation in vitro and tumor growth in vivo. Also, miR-3127 accelerated G1-S transition by activating AKT/ FOXO1 signaling, by directly targeting the 3' untranslated regions (3`UTR) of pleckstrin homology domain leucine-rich repeat protein phosphatase 1/2 (PHLPP1/2), inositol polyphosphate phosphatase 4A (INPP4A), and inositol polyphosphate-5-phosphatase J (INPP5J) mRNA, repressing their expression. In agreement, the miRNA antagonist antagomir-3127 suppressed HCC cell proliferation and tumor growth by inhibiting the AKT/FOXO1 signaling. Taken together, these findings suggest that silencing miR-3127 might be a potential therapeutic strategy.

ERβ1 inversely correlates with PTEN/PI3K/AKT pathway and predicts a favorable prognosis in triple-negative breast cancer

In contrast to the well-established role of estrogen receptor alpha (ERα) in breast cancer, the significance of estrogen receptor beta (ERβ) remains controversial, especially in triple-negative breast cancer (TNBC). We sought to investigate the clinical importance of wild-type ERβ (ERβ1) in TNBC based on a large population, and to explore the potential molecular pathways involved in. A total of 571 patients with invasive TNBC undergoing curative surgery were included in this study. Immunohistochemical staining for ERβ1, pAKT, PTEN, pERK, β-catenin, EGFR, p53, and E-cadherin was performed on tissue microarrays. Prognostic determinants for overall survival (OS) and disease-free survival (DFS), as well as the risk factors for distant metastasis-free survival (DMFS) and locoregional recurrence-free survival, were evaluated in univariate and multivariate analyses. Overexpression of ERβ1 was detected in 30.4% of tumor samples. Patients with ERβ1 tended to be postmenopausal, and less likely to develop lymphatic metastasis. Multivariate analysis demonstrated that ERβ1 predicted a better OS, DFS, and DMFS independently. Regarding other biomarkers, only pAKT was identified as an independent negative predictor for survival. Additionally, ERβ1 expression was inversely associated with pAKT and the loss of PTEN. Notably, further survival analysis according to status of ERβ1/pAKT indicated that ERβ1(+)/pAKT(-) predicted the most favorable prognosis for TNBC. On the contrary, ERβ1(-)/pAKT(+) was associated with the worst outcomes. In summary, our findings indicate that ERβ1 independently predicts a better prognosis for TNBC and potentially interacts with the PTEN/PI3K/pAKT pathway. The role of ERβ1-specific agonists combined with the inhibitors of pAKT merits further investigation.

KSHV microRNAs mediate cellular transformation and tumorigenesis by redundantly targeting cell growth and survival pathways

Kaposi's sarcoma-associated herpesvirus (KSHV) is causally linked to several human cancers, including Kaposi's sarcoma, primary effusion lymphoma and multicentric Castleman's disease, malignancies commonly found in HIV-infected patients. While KSHV encodes diverse functional products, its mechanism of oncogenesis remains unknown. In this study, we determined the roles KSHV microRNAs (miRs) in cellular transformation and tumorigenesis using a recently developed KSHV-induced cellular transformation system of primary rat mesenchymal precursor cells. A mutant with a cluster of 10 precursor miRs (pre-miRs) deleted failed to transform primary cells, and instead, caused cell cycle arrest and apoptosis. Remarkably, the oncogenicity of the mutant virus was fully restored by genetic complementation with the miR cluster or several individual pre-miRs, which rescued cell cycle progression and inhibited apoptosis in part by redundantly targeting IκBα and the NF-κB pathway. Genomic analysis identified common targets of KSHV miRs in diverse pathways with several cancer-related pathways preferentially targeted. These works define for the first time an essential viral determinant for KSHV-induced oncogenesis and identify NF-κB as a critical pathway targeted by the viral miRs. Our results illustrate a common theme of shared functions with hierarchical order among the KSHV miRs.

Kaposi's sarcoma-associated herpesvirus (KSHV) is the causal agent of several human cancers. KSHV encodes over two dozen genes that regulate diverse cellular pathways. However, the molecular mechanism of KSHV-induced oncogenesis remains unknown. In this study, we determined the roles of KSHV microRNAs (miRs) in KSHV-induced oncogenesis using a recently developed KSHV cellular transformation system of primary rat mesenchymal precursor cells. A KSHV mutant with a cluster of 10 precursor miRs (pre-miRs) deleted failed to transform primary cells, and instead, caused cell cycle arrest and apoptosis. Expression of the miR cluster or several pre-miRs was sufficient to restore the oncogenicity of the mutant virus. KSHV miRs regulated cell cycle progression and inhibited apoptosis in part by redundantly targeting IκBα and the NF-κB pathway. By integrating gene expression profiling and target prediction, we identified common targets of KSHV miRs in diverse pathways. Importantly, several cancer-related pathways were preferentially targeted by KSHV miRs. These works have demonstrated for the first time the important roles of KSHV miRs in oncogenesis and identified NF-κB as a critical pathway targeted by the miRs. Our results reveal that shared function is a common theme of KSHV miRs, which manifest functional hierarchical order.

MEK5/ERK5 signaling suppresses estrogen receptor expression and promotes hormone-independent tumorigenesis

Endocrine resistance and metastatic progression are primary causes of treatment failure in breast cancer. While mitogen activated protein kinases (MAPKs) are known to promote ligand-independent cell growth, the role of the MEK5-ERK5 pathway in the progression of clinical breast carcinoma remains poorly understood. Here, we demonstrated increased ERK5 activation in 30 of 39 (76.9%) clinical tumor samples, as well as across breast cancer cell systems. Overexpression of MEK5 in MCF-7 cells promoted both hormone-dependent and hormone-independent tumorigenesis in vitro and in vivo and conferred endocrine therapy resistance to previously sensitive breast cancer cells. Expression of MEK5 suppressed estrogen receptor (ER)α, but not ER-β protein levels, and abrogated downstream estrogen response element (ERE) transcriptional activity and ER-mediated gene transcription. Global gene expression changes associated with upregulation of MEK5 included increased activation of ER-α independent growth signaling pathways and promotion of epithelial-to-mesenchymal transition (EMT) markers. Taken together, our findings show that the MEK5-ERK5 pathway mediates progression to an ER(-), mesenchymal and endocrine therapy resistant phenotype. Given the need for new clinical therapeutic targets, our results demonstrate the therapeutic potential of targeting the MEK5-ERK5 pathway in breast cancer.

Malignant transformation of rat kidney induced by environmental substances and estrogen

The use of organophosphorous insecticides in agricultural environments and in urban settings has increased significantly. The aim of the present study was to analyze morphological alterations induced by malathion and 17β-estradiol (estrogen) in rat kidney tissues. There were four groups of animals: control, malathion, estrogen and combination of both substances. The animals were injected for five days and sacrificed 30, 124 and 240 days after treatments. Kidney tissues were analyzed for histomorphological and immunocytochemical alterations. Morphometric analysis indicated that malathion plus estrogen-treated animals showed a significantly (p < 0.05) higher grade of glomerular hypertrophy, signs of tubular damage, atypical proliferation in cortical and hilium zone than malathion or estrogen alone-treated and control animals after 240 days. Results indicated that MFG, ER-α, ER-β, PgR, CYP1A1, Neu/ErbB2, PCNA, vimentin and Thrombospondin 1 (THB) protein expression was increased in convoluted tubules of animals treated with combination of malathion and estrogen after 240 days of 5 day treatment. Malignant proliferation was observed in the hilium zone. In summary, the combination of malathion and estrogen induced pathological lesions in glomeruli, convoluted tubules, atypical cell proliferation and malignant proliferation in hilium zone and immunocytochemical alterations in comparison to control animals or animals treated with either substance alone. It can be concluded that an increased risk of kidney malignant transformation can be induced by exposure to environmental and endogenous substances.

Nuclear receptor coactivators: structural and functional biochemistry

Transcription of eukaryotic cell is a multistep process tightly controlled by concerted action of macromolecules. Nuclear receptors are ligand-activated sequence-specific transcription factors that bind DNA and activate (or repress) transcription of specific sets of nuclear target genes. Successful activation of transcription by nuclear receptors and most other transcription factors requires "coregulators" of transcription. Coregulators make up a diverse family of proteins that physically interact with and modulate the activity of transcription factors and other components of the gene expression machinery via multiple biochemical mechanisms. The coregulators include coactivators that accomplish reactions required for activation of transcription and corepressors that suppress transcription. This review summarizes our current knowledge of nuclear receptor coactivators with an emphasis on their biochemical mechanisms of action and means of regulation.

Regulation of ERalpha-mediated transcription of Bcl-2 by PI3K-AKT crosstalk: implications for breast cancer cell survival

Both estrogen, through the estrogen receptor (ER), and growth factors, through the phosphatidylinositol-3-kinase (PI3K)-AKT pathway, have been shown to independently promote cell survival. Here, we investigated the role of ER/PI3K-AKT crosstalk in the regulation of cell survival in MCF-7 breast carcinoma cells. The ER inhibitor ICI 182,780 was used to determine the requirement of the ER for estrogen in the suppression of tumor necrosis factor-alpha (TNFalpha) induced apoptosis. Gene reporter assays and Western blot analyses were used to determine the involvement of the pro-survival factor Bcl-2 and the coactivator GRIP1 in this survival crosstalk. We demonstrated that an intact ER signaling pathway was required for estrogen to suppress apoptosis induced by TNFalpha. Our gene reporter assays revealed that ERalpha, not ERbeta, was targeted by AKT, resulting in transcriptional potentiation of the full-length Bcl-2 promoter, ultimately leading to increased Bcl-2 protein levels. AKT targeted both activation function (AF) domains of the ERalpha for maximal induction of Bcl-2 reporter activity, although the AF-II domain was predominately targeted. In addition, AKT also caused an upregulation of GRIP1 protein levels. Finally, AKT and GRIP1 cooperated to increase Bcl-2 protein expression to a greater level than either factor alone. Collectively, our study suggests a role for ER/PI3K-AKT crosstalk in cell survival and documents the ability of AKT to regulate Bcl-2 expression via differential activation of ERalpha and ERbeta as well as regulation of GRIP1.

Antiestrogenic effects of the novel sphingosine kinase-2 inhibitor ABC294640

Alterations in sphingolipid metabolism have been shown to contribute to the development of endocrine resistance and breast cancer tumor survival. Sphingosine kinase (SK), in particular, is overexpressed in breast cancer and is a promising target for breast cancer drug development. In this study, we used the novel SK inhibitor ABC294640 as a tool to explore the relationship between SK and estrogen (E2) receptor (ER) signaling in breast cancer cells. Treatment with ABC294640 decreased E2-stimulated ERE-luciferase activity in both MCF-7 and ER-transfected HEK293 cells. Furthermore, the inhibitor reduced E2-mediated transcription of the ER-regulated genes progesterone receptor and SDF-1. Competitive receptor-binding assays revealed that ABC294640 binds in the antagonist ligand-binding domain of the ER, acting as a partial antagonist similar to tamoxifen. Finally, treatment with ABC294640 inhibited ER-positive breast cancer tumor formation in vivo. After 15 d of treatment with ABC294640, tumor volume was reduced by 68.4% (P < 0.05; n = 5) compared with control tumors, with no marked weight loss or illness. Taken together, these results provide strong evidence that this novel SK inhibitor, which had not previously been known to interact with E2 signaling pathways, has therapeutic potential in treating ER-positive breast cancer via inhibition of both SK and ER signaling.

Minireview: Estrogen receptor-beta: mechanistic insights from recent studies

The discovery of estrogen receptor-beta (ERbeta) in 1996 stimulated great interest in the physiological roles and molecular mechanisms of ERbeta action. We now know that ERbeta plays a major role in mediating estrogen action in several tissues and organ systems, including the ovary, cardiovascular system, brain, and the immune system, and that ERbeta and ERalpha generally play distinct physiological roles in the body. Although significant progress has been made toward understanding the molecular mechanisms of ERbeta action, particularly in vitro, there remains a large gap in our understanding of the mechanisms by which ERbeta elicits its biological functions in a true physiological context.

Estrogen receptor alpha/beta, AIB1, and TIF2 in colorectal carcinogenesis: do coregulators have prognostic significance?

PURPOSE

Estrogen receptor beta (ER beta) is abundantly expressed in colorectal tissue, but its role in colorectal carcinogenesis remains elusive. Estrogen receptor coregulators, amplified in breast cancer 1 (AIB1) and transcription intermediary factor 2 (TIF2), have been well-characterized, but their expression in colorectal carcinomas has not been investigated.

MATERIALS AND METHODS

Estrogen receptor alpha (ER alpha), ER beta, AIB1, and TIF2 protein expression were evaluated by immunohistochemistry in colorectal normal mucosa, adenomas, and adenocarcinomas from 110 patients with colorectal cancer.

RESULTS

ER alpha expression was rare in colorectal tissue and its expression does not appear to be associated with colorectal carcinogenesis. ER beta, AIB1, and TIF2 were detected in the nucleus of epithelial, endothelial, inflammatory, smooth muscle cells, and myofibroblasts. The expression of the three proteins was significantly increased in epithelial cells of carcinomas compared to normal mucosa. In carcinomas, a significant correlation between the levels of expression of AIB1 and TIF2 was noted. Although AIB1 overexpression was associated with local tumor invasion, it was also found to correlate independently with prolonged overall survival.

CONCLUSIONS

ER beta, AIB1, and TIF2 appear to be involved in colorectal tumorigenesis and might have prognostic significance.

Association of MDM2 SNP309, age of onset, and gender in cutaneous melanoma

PURPOSE

In certain cancers, MDM2 SNP309 has been associated with early tumor onset in women. In melanoma, incidence rates are higher in women than in men among individuals less than 40 years of age, but among those older than 50 years of age, melanoma is more frequent in men than in women. To investigate this difference, we examined the association among MDM2 SNP309, age at diagnosis, and gender among melanoma patients.

EXPERIMENTAL DESIGN

Prospectively enrolled melanoma patients (N = 227) were evaluated for MDM2 SNP309 and the related polymorphism, p53 Arg72Pro. DNA was isolated from patient blood samples, and genotypes were analyzed by PCR-restriction fragment length polymorphism. Associations among MDM2 SNP309, p53 Arg72Pro, age at diagnosis, and clinicopathologic features of melanoma were analyzed.

RESULTS

The median age at diagnosis was 13 years earlier among women with a SNP309 GG genotype (46 years) compared with women with TG+TT genotypes (59 years; P = 0.19). Analyses using age dichotomized at each decade indicated that women with a GG genotype had significantly higher risks of being diagnosed with melanoma at ages <50 years compared with women >or=50 years, but not when the comparison was made between women <60 and >or=60 years. At ages <50 years, women with a GG genotype had a 3.89 times greater chance of being diagnosed compared with women with TG+TT genotypes (P = 0.01). Similar observations were not seen among men.

CONCLUSIONS

Our data suggest that MDM2 may play an important role in the development of melanoma in women. The MDM2 SNP309 genotype may help identify women at risk of developing melanoma at a young age.

Estrogen receptor beta functions through nongenomic mechanisms in lung cancer cells

Recent studies have shown that estrogens promote the growth of lung cancer cells and may potentially be responsible for increased susceptibility to lung cancer in women. These observations raise the possibility of using antiestrogens in treating and preventing lung cancer. However, it is not clear how estrogen receptors (ERs) modulate the growth of non-small cell lung cancer (NSCLC) cells. Our Western blotting and real-time PCR analysis showed that NSCLC cells expressed ERbeta, but not ERalpha. In addition, ERbeta-specific ligands, but not ERalpha-specific ligands, promoted the growth of lung cancer cells. Furthermore, knockdown of ERbeta by short hairpin RNA constructs resulted in loss of estrogen-dependent growth of lung cancer cells. Interestingly, endogenous ERbeta failed to transcriptionally activate estrogen response element (ERE)-luciferase constructs in NSCLC cells, suggesting a lack of genomic function. Upon further investigation, ERbeta was found to be in the cytoplasm in all lung cancer cells and failed to translocate to the nucleus in the presence of estrogen, as observed by biochemical, ArrayScan, and confocal microscopy experiments. Nonetheless, estrogen caused rapid activation of cAMP, Akt, and MAPK signaling pathways in lung cancer cells. Immunohistochemical analysis of lung tumor biopsies showed strong ERbeta staining in the cytoplasm, whereas no staining was observed for ERalpha. In conclusion, our results suggest that that proliferative effects of estrogen in lung cancer cells is mediated primarily, if not exclusively, by the nongenomic action of ERbeta.

Steroid receptor coactivator 2: an essential coregulator of progestin-induced uterine and mammary morphogenesis

The importance of the progesterone receptor (PR) in transducing the progestin signal is firmly established in female reproductive and mammary gland biology; however, the coregulators preferentially recruited by PR in these systems have yet to be comprehensively investigated. Using an innovative genetic approach, which ablates gene function specifically in murine cell-lineages that express PR, steroid receptor coactivator 2 (SRC-2, also known as TIF-2 or GRIP-1) was shown to exert potent coregulator properties in progestin-dependent responses in the uterus and mammary gland. Uterine cells positive for PR (but devoid of SRC-2) led to an early block in embryo implantation, a phenotype not shared by knockouts for SRC-1 or SRC-3. In the case of the mammary gland, progestin-dependent branching morphogenesis and alveologenesis failed to occur in the absence of SRC-2, thereby establishing a critical coactivator role for SRC-2 in cellular proliferative programs initiated by progestins in this tissue. Importantly, the recent detection of SRC-2 in both human endometrium and breast suggests that this coregulator may provide a new clinical target for the future management of female reproductive health and/or breast cancer.

Steroid receptor coactivator 2 is required for female fertility and mammary morphogenesis: insights from the mouse, relevance to the human

Although the importance of the progesterone receptor (PR) to female reproductive and mammary gland biology is firmly established, the coregulators selectively co-opted by PR in these systems have not been clearly delineated. A selective gene-knockout approach applied to the mouse, which abrogates gene function only in cell types that express PR, recently disclosed steroid receptor coactivator 2 (SRC-2, also known as TIF-2 or GRIP-1) to be an indispensable coregulator for uterine and mammary gland responses that require progesterone. Uterine cells positive for PR (but devoid of SRC-2) were found to be incapable of facilitating embryo implantation, a necessary first step toward the establishment of the materno-fetal interface. Importantly, such an implantation defect is not exhibited by knockouts for SRC-1 or SRC-3, underscoring the unique coregulator importance of SRC-2 in peri-implantation biology. Moreover, despite normal levels of PR, SRC-1 and SRC-3, progesterone-dependent branching morphogenesis and alveologenesis fails to occur in the murine mammary gland in the absence of SRC-2, thereby establishing a critical coregulator role for SRC-2 in signaling cascades that mediate progesterone-induced mammary epithelial proliferation. Finally, the recent detection of SRC-2 in the human endometrium and breast suggests that this coregulator may represent a new clinical target for the future management of female reproductive health and/or breast cancer.

Akt plays an important role in breast cancer cell chemotaxis to CXCL12

The chemokine receptor CXCR4 is functionally expressed on the cell surface of various cancer cells, and plays a role in cell proliferation and migration of these cells. Specifically, in breast cancer cells the CXCR4/CXCL12 axis has been implicated in cell migration in vitro and in metastasis in vivo, but the underlying signaling mechanisms are incompletely understood. The xenograft-derived MDA-MB-231 breast cancer cell line (231mfp), which was shown previously to grow more aggressively than the parent cells, showed increased CXCR4 expression at the mRNA, total protein and cell surface expression level. This correlated with an enhanced response to CXCL12, specifically in augmented and prolonged Akt activation in a G(i), Src family kinase and PI-3 kinase dependent fashion. 231mfp cells migrated towards CXCL12--in contrast to the parent cell line--and this chemotaxis was blocked by inhibition of G(i), Src family kinases, PI-3 kinase and interestingly, Akt itself, as could be shown with two pharmacological inhibitors, a dominant negative Akt construct and with Akt shRNA. Collectively, we have demonstrated that prolonged Akt activation is an important signaling pathway for breast cancer cells expressing CXCR4 and is necessary for CXCL12-dependent cell migration.

Direct involvement of breast tumor fibroblasts in the modulation of tamoxifen sensitivity

Using contact-dependent three-dimensional coculture systems and serum-free conditions, we compared the ability of estrogen receptor (ER)-alpha(+) tamoxifen-sensitive premalignant (EIII8) or tumorigenic (MCF-7), ER-alpha(+) tamoxifen-resistant (EIII8-TAM(R)) or ER-alpha(-) MDA-MB-231 breast cancer cells to interact and undergo epithelial morphogenesis on association with breast tumor-derived fibroblasts. Although all breast cancer cell lines interacted with tumor fibroblasts, EIII8 and its intrinsically tamoxifen-resistant counterpart EIII8-TAM(R) cells were most receptive and responded with dramatic, albeit, aberrant epithelial morphogenesis. EIII8 cells underwent epithelial morphogenesis when cocultured with fibroblasts from ER-alpha(-)/PgR(-) or ER-alpha(+)/PgR(+) breast tumors; however, EIII8 cells cocultured with ER-alpha(-)/PgR(-) tumor-derived fibroblasts exhibited decreased tamoxifen sensitivity compared with cells cocultured with ER-alpha(+)/PgR(+) tumor fibroblasts. Fibroblast-induced tamoxifen resistance was accompanied by mitogen-activated protein kinase and Akt hyperactivation, reduced sensitivity to U0126 or LY294002, and ER-alpha hyperphosphorylation in the activation function-1 domain. The intrinsic tamoxifen resistance of EIII8-Tam(R) cells correlated with constitutive ER-alpha hyperphosphorylation that was unaffected by the tumor fibroblasts. Our results suggest that tumor fibroblast-induced tamoxifen resistance of EIII8 cells is not mediated by epidermal growth factor receptor or insulin-like growth factor (IGF)-1R axes because no correlation was found between expression levels of IGF-1, IGF-2, phosphorylated IGF-1R, or epidermal growth factor receptor, and tamoxifen sensitivity of EIII8 fibroblast cultures.

Pathways to tamoxifen resistance

Therapies that target the synthesis of estrogen or the function of estrogen receptor(s) have been developed to treat breast cancer. While these approaches have proven to be beneficial to a large number of patients, both de novo and acquired resistance to these drugs is a significant problem. Recent advances in our understanding of the molecular mechanisms that contribute to resistance have provided a means to begin to predict patient responses to these drugs and develop rational approaches for combining therapeutic agents to circumvent or desensitize the resistant phenotype. Here, we review common mechanisms of antiestrogen resistance and discuss the implications for prediction of response and design of effective combinatorial treatments.

Estrogen Receptor β2 Negatively Regulates the Transactivation of Estrogen Receptor α in Human Breast Cancer Cells

Estrogens, by binding to and activating two estrogen receptors (ERalpha and ERbeta), are critically involved in the development of the mammary gland and breast cancer. An isoform of ERbeta, ERbeta2 (also called ERbetacx), with an altered COOH-terminal region, is coexpressed with ERalpha in many human breast cancers. In this study, we generated a stable cell line from MCF7 breast cancer cells expressing an inducible version of ERbeta2, along with endogenous ERalpha, and examined the effects of ERbeta2 on the ERalpha protein levels and function. We showed that ERbeta2 inhibited ERalpha-mediated transactivation via estrogen response element and activator protein-1 sites of reporter constructs as well as the endogenous genes pS2 and MMP-1. Chromatin immunoprecipitation assays revealed that ERbeta2 expression caused a significant reduction in the recruitment of ERalpha to both the pS2 and MMP-1 promoters. Furthermore, ERbeta2 expression induced proteasome-dependent degradation of ERalpha. The inhibitory effects of ERbeta2 on ERalpha activity were further confirmed in HEK293 cells that lack functional endogenous ERs. We also showed that ERbeta2 can interact with ERalpha both in vitro and in mammalian cells, which is compatible with a model where ERbeta2/ERalpha heterodimers are targeted to the proteasome. Finally, in human breast cancer samples, we observed that expression of ERbeta2 significantly correlated with ERalpha-negative phenotype. Our data suggest that ERbeta2 could influence ERalpha-mediated effects relevant for breast cancer development, including hormone responsiveness.

Regulation of SRC family coactivators by post-translational modifications

Initially identified as a group of auxiliary protein factors involved in transcriptional regulation by steroid hormone receptors as well as by other members of the nuclear receptor superfamily, the steroid receptor coactivators (SRCs) have since then been implicated in the transcriptional regulation of other transcription factors which are important components of very different signaling pathways. Members of the SRC family have been shown to interact with myogenin, MEF-2, transcriptional enhancer factor (TEF), NF-kappaB, AP-1, STAT, p53, and E2F1, suggesting that SRC coactivators participate in diverse cellular processes. Recent evidence indicates that various post-translational modifications play critical roles in determining the final transcriptional output and specificity of SRC coactivators. In this review, we summarized the current knowledge concerning post-translational modifications, dynamic interplay between different modifications, and patho-physiological relevance of the modifications of SRC proteins.

Mice expressing myrAKT1 in the mammary gland develop carcinogen-induced ER-positive mammary tumors that mimic human breast cancer

AKT1/PKB is a serine/threonine protein kinase that regulates biological processes such as proliferation, apoptosis and growth in a variety of cell types. To assess the oncogenic capability of an activated form of AKT in vivo we have generated several transgenic mouse lines that overexpress in the mammary epithelium the murine Akt1 gene modified with a myristoylation signal, which renders active this protein by localizing it to the plasma membrane. We demonstrate that expression of myristoylated AKT in the mammary glands increases the susceptibility of these mice to the induction of mammary tumors of epithelial origin by the carcinogen 9,10-dimethyl-1,2 benzanthracene (DMBA). We have found that while carcinogen-treated wild-type mice show mostly mammary tumors of sarcomatous origin, AKT transgenic mice treated with DMBA developed mainly adenocarcinoma or adenosquamous tumors, all of them displaying activated AKT. We analyzed other possible molecular alterations cooperating with AKT and found that neither Ras nor beta-catenin/Wnt pathways seemed altered nor p53 mutated. We have found that 100% of mammary DMBA-induced tumors and benign lesions in myrAKT mice are estrogen receptor (ERalpha)-positive and are more frequent than in wild-type littermates. These data show that AKT activation cooperates with deregulation of the estrogen receptor in the DMBA-induced mammary tumorigenesis model and recapitulate two characteristics of some human breast tumors. Thus, our model might provide a preclinical relevant model system to study the role of AKT and ERalpha in breast tumorigenesis and the response of mammary gland tumors to chemotherapeutics.