A fusion protein of the estrogen receptor (ER) and nuclear receptor corepressor (NCoR) strongly inhibits estrogen-dependent responses in breast cancer cells

SIAH ubiquitin ligases regulate breast cancer cell migration and invasion independent of the oxygen status

Seven-in-absentia homolog (SIAH) proteins are evolutionary conserved RING type E3 ubiquitin ligases responsible for the degradation of key molecules regulating DNA damage response, hypoxic adaptation, apoptosis, angiogenesis, and cell proliferation. Many studies suggest a tumorigenic role for SIAH2. In breast cancer patients SIAH2 expression levels correlate with cancer aggressiveness and overall patient survival. In addition, SIAH inhibition reduced metastasis in melanoma. The role of SIAH1 in breast cancer is still ambiguous; both tumorigenic and tumor suppressive functions have been reported. Other studies categorized SIAH ligases as either pro- or antimigratory, while the significance for metastasis is largely unknown. Here, we re-evaluated the effects of SIAH1 and SIAH2 depletion in breast cancer cell lines, focusing on migration and invasion. We successfully knocked down SIAH1 and SIAH2 in several breast cancer cell lines. In luminal type MCF7 cells, this led to stabilization of the SIAH substrate Prolyl Hydroxylase Domain protein 3 (PHD3) and reduced Hypoxia-Inducible Factor 1α (HIF1α) protein levels. Both the knockdown of SIAH1 or SIAH2 led to increased apoptosis and reduced proliferation, with comparable effects. These results point to a tumor promoting role for SIAH1 in breast cancer similar to SIAH2. In addition, depletion of SIAH1 or SIAH2 also led to decreased cell migration and invasion in breast cancer cells. SIAH knockdown also controlled microtubule dynamics by markedly decreasing the protein levels of stathmin, most likely via p27(Kip1). Collectively, these results suggest that both SIAH ligases promote a migratory cancer cell phenotype and could contribute to metastasis in breast cancer.

Gene therapy of benign gynecological diseases

Gene therapy is the introduction of genetic material into patient's cells to achieve therapeutic benefit. Advances in molecular biology techniques and better understanding of disease pathogenesis have validated the use of a variety of genes as potential molecular targets for gene therapy based approaches. Gene therapy strategies include: mutation compensation of dysregulated genes; replacement of defective tumor-suppressor genes; inactivation of oncogenes; introduction of suicide genes; immunogenic therapy and antiangiogenesis based approaches. Preclinical studies of gene therapy for various gynecological disorders have not only shown to be feasible, but also showed promising results in diseases such as uterine leiomyomas and endometriosis. In recent years, significant improvement in gene transfer technology has led to the development of targetable vectors, which have fewer side-effects without compromising their efficacy. This review provides an update on developing gene therapy approaches to treat common gynecological diseases such as uterine leiomyoma and endometriosis.

Transcriptional targeting of gene expression in breast cancer by the promoters of protein regulator of cytokinesis 1 and ribonuclease reductase 2

For cancer gene therapy, cancer-specific over- expression of a therapeutic gene is required to reduce side effects derived from expression of the gene in normal cells. To develop such an expression vector, we searched for genes over-expressed and/or specifically expressed in cancer cells using bioinformatics and have selected genes coding for protein regulator of cytokinesis 1 (PRC1) and ribonuclease reductase 2 (RRM2) as candidates. Their cancer-specific expressions were confirmed in both breast cancer cell lines and patient tissues. We compared each promoter's cancer-specific activity in the breast normal and cancer cell lines using the luciferase gene as a reporter and confirmed cancer-specific expression of both PRC1 and RRM2 promoters. To test activities of these promoters in viral vectors, the promoters were also cloned into an adeno-associated viral (AAV) vector containing green fluorescence protein (GFP) as the reporter. The GFP expression levels by these promoters were various depending on cell lines tested and, in MDA-MB-231 cells, GFP activities derived from the PRC1 and RRM2 promoters were as strong as that from the cytomegalovirus (CMV) promoter. Our result showed that a vector containing the PRC1 or RRM2 promoter could be used for breast cancer specific overexpression in gene therapy.

High-throughput cell-based screening reveals a role for ZNF131 as a repressor of ERalpha signaling

BACKGROUND

Estrogen receptor alpha (ERalpha) is a transcription factor whose activity is affected by multiple regulatory cofactors. In an effort to identify the human genes involved in the regulation of ERalpha, we constructed a high-throughput, cell-based, functional screening platform by linking a response element (ERE) with a reporter gene. This allowed the cellular activity of ERalpha, in cells cotransfected with the candidate gene, to be quantified in the presence or absence of its cognate ligand E2.

RESULTS

From a library of 570 human cDNA clones, we identified zinc finger protein 131 (ZNF131) as a repressor of ERalpha mediated transactivation. ZNF131 is a typical member of the BTB/POZ family of transcription factors, and shows both ubiquitous expression and a high degree of sequence conservation. The luciferase reporter gene assay revealed that ZNF131 inhibits ligand-dependent transactivation by ERalpha in a dose-dependent manner. Electrophoretic mobility shift assay clearly demonstrated that the interaction between ZNF131 and ERalpha interrupts or prevents ERalpha binding to the estrogen response element (ERE). In addition, ZNF131 was able to suppress the expression of pS2, an ERalpha target gene.

CONCLUSION

We suggest that the functional screening platform we constructed can be applied for high-throughput genomic screening candidate ERalpha-related genes. This in turn may provide new insights into the underlying molecular mechanisms of ERalpha regulation in mammalian cells.

Interaction of the tumor metastasis suppressor nonmetastatic protein 23 homologue H1 and estrogen receptor alpha alters estrogen-responsive gene expression

Metastasis of cancer cells from the primary tumor is associated with poor prognosis and decreased overall survival. One protein implicated in inhibiting metastasis is the tumor metastasis suppressor nonmetastatic protein 23 homologue 1 (NM23-H1). NM23-H1 is a multifunctional protein, which, in addition to limiting metastasis, has DNase and histidine protein kinase activities. We have identified new functions for NM23-H1 in influencing estrogen receptor alpha (ER alpha)-mediated gene expression. Using a battery of molecular and biochemical techniques, we show that NM23-H1 interacts with ER alpha and increases the ER alpha-estrogen response element (ERE) interaction. When NM23-H1 expression is increased in U2 osteosarcoma and MDA-MB-231 breast cancer cells, transcription of a transiently transfected, estrogen-responsive reporter plasmid is decreased. More importantly, when endogenous NM23-H1 expression is knocked down in MCF-7 human breast cancer cells using small interfering RNA, estrogen responsiveness of the progesterone receptor (PR), Bcl-2, cathepsin D, and cyclin D1 genes, but not the pS2 gene, is enhanced. Furthermore, NM23-H1 associates with the region of the PR gene containing the +90 activator protein 1 site, but not with the ERE-containing region of the pS2 gene, indicating that NM23-H1 mediates gene-specific effects by association with endogenous chromatin. Our studies suggest that the capacity of NM23-H1 to limit the expression of estrogen-responsive genes such as cathepsin D and Bcl-2, which are involved in cell migration, apoptosis, and angiogenesis, may help to explain the metastasis-suppressive effects of this protein. The complementary abilities of ER alpha and NM23-H1 together to influence gene expression, cell migration, and apoptosis could be key factors in helping to determine tumor cell fate.

Environmental risk factors for prevention and molecular intervention of cervical cancer

Cervical cancer (CC) is potentially the most preventable and treatable cancer in human but it is a leading cause for cancer morbidity and mortality in women around the world. Therefore, more innovative prevention and treatment protocols need to be developed and implemented. With better understanding of the etiology of the disease, specific prevention protocols that involve life-style modifications to minimize the impact of environmental risk factors can be developed. It may be necessary to implement unique modification protocols for different countries. In addition, antiviral vaccine is a highly promising prevention approach. With respect to therapy, the development of more specific protocols that have fewer side effects is needed. With the availability of sophisticated molecular techniques, a new generation of targeted approach that has the potential to generate outstanding efficacy is being tested. Using the siRNA technology against the expression of human papillomavirus oncogenes, specific biological pathways that are essential to the growth and survival of the CC cells can be interrupted. Another promising approach is the molecular intervention of the estrogen pathway by blocking the expression of estrogen receptors. These molecular techniques may work by reactivating endogenous regulatory processes, e.g., the core apoptotic machinery, that can cause self-destruction of the CC cells, thus providing potentially effective molecular therapy. These topics are discussed in this review.

Inhibition of growth of cervical cancer cells using a dominant negative estrogen receptor gene

OBJECTIVE

Estrogen stimulates human papilloma virus oncogene expression, promotes cervical cancer (CC) cell proliferation and prevents apoptosis. Therefore, blockage of estrogen function may have therapeutic application to CC.

METHODS

CasKi CC cells were transfected with an adenovirus expressing a dominant negative estrogen receptor gene (Ad-ER-DN) and their responses were investigated by RT-PCR, Flow Cytometry and Western blot assays.

RESULT

Transfected cells showed disturbance of cell colony morphology, reduced HPV E6 and E7 mRNA, interruption of cell proliferation, reduced cyclin D1 protein and expression of apoptosis.

CONCLUSION

We report, for the first time, the use of Ad-ER-DN to block estrogen receptors which led to dramatic changes in CC cells that are consistent with the possible reactivation of cellular p53 and Rb function. Their reactivation most likely allowed the recognition of existing chromosome abnormalities as a serious stress signal and the initiation of a cascade of cellular events in response to the stress, including the activation of the core apoptotic machinery which led to self-destruction of the CC cells.

Expression of steroid receptor coactivators and corepressors in human endometrial hyperplasia and carcinoma with relevance to steroid receptors and Ki-67 expression

BACKGROUND

To examine the steroid hormone dependent growth mechanism of human endometrial hyperplasia and carcinoma, expression levels of steroid receptor cofactors, such as coactivators (steroid receptor coactivator 1 [SRC-1] and p300/cyclic AMP-response element-binding protein (p300/CBP]) and corepressors (nuclear receptor corepressor [NCoR] and silencing mediator for retinoid and thyroid-hormone receptors [SMRT]), were investigated.

METHODS

The expression levels of cofactors were examined immunohistochemically using 20 samples of normal endometria, 36 samples of hyperplastic endometria, and 58 of malignant endometria and were compared with the expression levels of estrogen receptor (ER), progesterone receptor (PR), and a proliferation marker, Ki-67.

RESULTS

In samples of normal endometria, the expression of coactivators was observed diffusely in glandular cells in the proliferative phase, with a mean positivity index (PI) of 81.8 for SRC-1 and 91.3 for p300/CBP, whereas expression levels decreased in endometrial hyperplasia (PI: SRC-1, 58.9; p300/CBP, 83.8) and endometrial carcinoma (PI: SRC-1, 45.0; p300/CBP, 55.4). In endometrial hyperplasia, there was a significant correlation between the expression of ER and SRC-1 or p300/CBP. In contrast, there were no significant statistical or topologic correlations between the expression of coactivators and the expression of ER/PR in endometrial carcinoma. The expression of corepressors generally was limited, except for elevated expression of NCoR in endometrial hyperplasia (PI, 23.8).

CONCLUSIONS

The current study showed that expression levels of the steroid receptor coactivators SRC-1 and p300/CBP were reduced in endometrial carcinoma compared with normal and hyperplastic endometrium. In addition, topologic coexpression of both coactivators and ER/PR was lost in endometrial carcinoma. Accordingly, limited response to sex steroids in patients with endometrial carcinoma may be ascribed to the dissociation of cofactors and ER/PR.

Expression of sex steroid receptors and their co-factors in normal and malignant breast tissue: AIB1 is a carcinoma-specific co-activator

The differential expression pattern of estrogen receptor alpha (ER-alpha), estrogen receptor beta (ER-beta) and their co-activator/co-repressor proteins is thought to modulate estrogenic action and to be present already during the early stages of tumorigenesis. It has therefore been postulated that certain co-activator and co-repressor proteins contribute to the development of breast cancer. There are some reports providing information on gene amplification and mRNA over-expression of certain co-factors in breast cancer, but to date there is only limited knowledge about their respective protein expressions. The aim of this study was to examine the expression of four steroid receptor co-activators (steroid receptor co-activator 1 (SRC-1), transcription intermediary factor 2 (TIF 2), protein 300 kDa/CREB binding protein (p300/CBP), amplified in breast cancer 1 (AIB1)), and of the co-repressor nuclear receptor co-repressor (NCoR), in malignant breast tissues and in matching normal breast biopsies of the same individuals. Protein expression was analyzed by immunohistochemistry and was compared to prognostic parameters such as lymph node involvement, tumor grading and receptor status. All members of the co-regulatory protein family were detected in both, benign and matching malignant tissue samples, except for AIB1, which was found to be expressed exclusively in malignant epithelium. AIB1 was preferentially present in carcinomas with high tumor grade (r = 0.48, p = 0.014), and was co-expressed with p300/CBP (r = 0.54, p = 0.006). TIF 2 correlated significantly to nodal status (r = 0.46, p = 0.025). Furthermore, protein levels of ER-beta p300/CBP and AIB1 were higher in invasive ductal carcinomas than in normal mammary tissue. The tumoral ER-alpha protein expression was significantly correlated with that of PgR (r = 0.61, p = 0.001) and NCoR (r = 0.4, p = 0.043), whereas ER-beta expression was associated with SRC-1 (r = 0.68, p < or = .001), TIF 2 (r = 0.64, p = 0.001) and NCoR (r = 0.48, p = 0.014) protein levels in malignant specimens. In our hands, 20% of ER-beta positive tumors did not express ER-alpha protein, thereby suggesting that a substantial fraction of ER-beta positive tumors is falsely considered to be 'estrogen receptor negative' if only ER-alpha specific antibodies are employed in the histological assessment of the ER status.

Dominant negative ER induces apoptosis in GH(4) pituitary lactotrope cells and inhibits tumor growth in nude mice

The ER plays an important role in the proliferation and differentiation of lactotrope tumor cells. GH(4) cells were infected with adenoviral vectors (AdL540Q and Ad1-536) to investigate the ability of dominant negative ER mutants to affect the regulation of gene expression and cell growth by endogenous ER. The dominant negative mutants suppressed estradiol stimulation of an estrogen-responsive reporter gene and the PRL promoter in these cells. AdL540Q or Ad1--536 infection also inhibited GH(4) cell growth and induced apoptosis, increasing the expression of the proapoptotic Bax protein and decreasing the expression of antiapoptotic Bcl-2. AdwtER-infected cells also showed decreased Bcl-2 protein. E2-induced activation of p38 MAPK, an enzyme that may participate in apoptosis, was observed in cells infected with AdwtER, AdL540Q, and Ad1--536. Consistent with the apoptotic effects in vitro, infection of GH(4) cells with AdL540Q or Ad1--536 inhibited the ability of the cells to form tumors in nude mice. These results indicate that dominant negative ER mutants induce apoptosis of GH(4) cells and suppress tumor formation and development. The delivery of dominant negative ERs by adenoviral vectors may provide an alternative modality for the targeted therapy of pituitary lactotrope adenomas and other estrogen-responsive tumors.

Estrogen receptor binding to DNA is not required for its activity through the nonclassical AP1 pathway

In the classical signaling pathway, the estrogen receptor (ER) binds directly to estrogen response elements (EREs) to regulate gene transcription. To test the hypothesis that the nonclassical pathway involves ER interactions with other proteins rather than direct binding to DNA, mutations were introduced into the DNA binding domain (DBD) of the mouse ERalpha. The effects of these DBD mutations were examined in DNA binding assays using reporter constructs containing either EREs (classical) or AP1 (nonclassical) response elements. Using the AP1 reporter, there was a reversal of ER action relative to that seen with the ERE reporter. Estradiol induced suppression, and the antiestrogen ICI 182,780 stimulated transcription of the AP1 reporter. DBD mutations in the proximal (P-box) of the first zinc finger of the ER (E207A/G208A and E207G/G208S) eliminated ERE binding. These mutants were inactive using the ERE reporter but retained partial or full activity with the AP1 reporter. The DBD mutant ERs interacted with Jun when tested in mammalian cell two-hybrid assays. Two mutations (K366D and I362R) in the ER ligand binding domain known to alter coactivator interactions impaired transcriptional responses using either the ERE or AP1 reporters. We concluded that ER action through the AP1 response element involves interactions with other promoter-bound proteins instead of, or in addition to, direct binding to DNA. Interactions with coactivators were required for both pathways. These data supported a model in which ER-mediated transcriptional activation or repression is dependent on the ligand and the nature of the response element in the target gene.

Phosphatidylinositol 3-kinase/AKT-mediated activation of estrogen receptor alpha: a new model for anti-estrogen resistance

Estrogen receptors (ERs) mediate most of the biological effects of estrogen in mammary and uterine epithelial cells by binding to estrogen response elements in the promoter region of target genes or through protein-protein interactions. Anti-estrogens such as tamoxifen inhibit the growth of ER-positive breast cancers by reducing the expression of estrogen-regulated genes. However, anti-estrogen-resistant growth of ER-positive tumors remains a significant clinical problem. Here we show that phosphatidylinositol (PI) 3-kinase and AKT activate ERalpha in the absence of estrogen. Although PI 3-kinase increased the activity of both estrogen-independent activation function 1 (AF-1) and estrogen-dependent activation function 2 (AF-2) of ERalpha, AKT increased the activity of only AF-1. PTEN and a catalytically inactive AKT decreased PI 3-kinase-induced AF-1 activity, suggesting that PI 3-kinase utilizes AKT-dependent and AKT-independent pathways in activating ERalpha. The consensus AKT phosphorylation site Ser-167 of ERalpha is required for phosphorylation and activation by AKT. In addition, LY294002, a specific inhibitor of the PI 3-kinase/AKT pathway, reduced phosphorylation of ERalpha in vivo. Moreover, AKT overexpression led to up-regulation of estrogen-regulated pS2 gene, Bcl-2, and macrophage inhibitory cytokine 1. We demonstrate that AKT protects breast cancer cells from tamoxifen-induced apoptosis. Taken together, these results define a molecular link between activation of the PI 3-kinase/AKT survival pathways, hormone-independent activation of ERalpha, and inhibition of tamoxifen-induced apoptotic regression.

Ligand- and coactivator-mediated transactivation function (AF2) of the androgen receptor ligand-binding domain is inhibited by the cognate hinge region

Transactivation functions (AF2) in the ligand-binding domains (LBD) of many steroid receptors are well characterized, but there is little evidence to support such a function for the LBD of the androgen receptor (AR). We report a mutant AR, with residues 628-646 in the hinge region deleted, which exhibited transactivation activity that was more than double that of the wild type (WT) AR. Although no androgen-dependent AF2 activity could be observed for the WT ARLBD fused to a heterologous DNA-binding domain, the mutant ARLBD(Delta628-646) was 30-40 times more active than the WT ARLBD. In the presence of the p160 coactivator TIF2, AR(Delta628-646) was significantly more active than similarly treated WT AR. Deletion of residues 628-646 also enhanced TIF2-ARLBD activity 8-fold, an effect not present when the LBD-interacting LXXLL motifs of TIF2 were mutated, suggesting that the negative modulatory activity of residues 628-646 were exerted via coactivator pathways. Although the AP-1 (c-Jun/c-Fos) system and NcoR have been reported to interact with and repress the activity of some steroid receptors, c-Jun, c-Fos, c-Jun/c-Fos, nor NcoR function was consistently affected by the absence or presence of residues 628-646, implying that the AR hinge region exerts its silencing effects in a manner independent of these corepressors. Our data provide evidence for the novel finding that strong androgen-dependent AF2 exists in the ARLBD and is the first report of a negative regulatory domain in the AR. Because mutations in this region are commonly associated with prostate cancer, it is important to characterize the mechanisms by which the hinge region exerts its repressor effect on ligand-activated and coactivator-mediated AF2 activity of the ARLBD.

Estrogen receptor-KRAB chimeras are potent ligand-dependent repressors of estrogen-regulated gene expression

As an approach to targeted repression of genes of interest, we describe the development of human estrogen receptor (ER) alpha-KRAB repressor domain chimeras that are potent ligand-dependent repressors of the transcription of estrogen response element (ERE)-containing promoters and analyze their mechanisms of action. Repression by the KRAB domain was dominant over transactivation mediated by ER AF1 and AF2. An ERE and an ER ligand (estrogen or antiestrogen) were required for repression. Studies with several promoters and cell lines demonstrated that the presence of EREs, rather than the capacity for estrogen induction, determines the potential for repression of a gene by the KRAB-ERalpha-KRAB (KERK) chimera. A single consensus ERE was sufficient for repression, but the KERK chimera was unable to suppress transcription from the imperfect ERE in the native pS2 promoter. We recently reported mutations that enhance binding of a steroid receptor DNA-binding domain to the ERE. Introducing these mutations into wild-type ER enhanced transactivation from the pS2 ERE. Insertion of these mutations into KERK created the novel repressor KERK-3M, which is a potent repressor of both ER-induced and basal transcription on a promoter containing the pS2 ERE. These modified ER-KRAB chimeras should prove useful as new tools for the functional analysis and repression of ER-regulated genes.