Androgen regulation by the long terminal repeat of mouse mammary tumor virus

Enhancement of androgen transcriptional activation assay based on genome edited glucocorticoid knock out human prostate cancer cell line

Endocrine-disrupting chemicals (EDCs) interfere with the biological activity of hormones. Among EDC's, (anti-)androgenic compounds potentially cause several androgen-related diseases. To improve the accuracy of an in vitro transactivation assay (TA) for detection of (anti-)androgenic compounds, We established the glucocorticoid receptor (GR) knockout 22Rv1/MMTV cell line by using an RNA-guided engineered nuclease (RGEN)-derived CRISPR/Cas system. The 22Rv1/MMTV GRKO cell line was characterized and validated by androgen receptor (AR)-mediated TA assay compared with the AR-TA assay using 22Rv1/MMTV. In conclusion, the AR-TA assay with the 22Rv1/MMTV GRKO cell line was more accurate, excluding the misleading signals derived from glucocorticoids or equivalent chemicals, and might be an effective method for screening potential (anti-)androgenic compounds.

The role of androgens in experimental rodent mammary carcinogenesis

Breast cancer is currently the most frequent, fatal cancer of women in western countries. While estrogens have a widely understood involvement in breast cancer, a significant but not yet fully understood role for androgens has also been suggested. The principal androgen, testosterone, is the obligate steroidal precursor of estradiol, but can equally be metabolized into dihydrotestosterone, a more potent, pure androgen. Both androgens exert their distinctive biological effects via the androgen receptor, which is coexpressed with estrogen receptor alpha in 80 to 90% of breast cancers. The hormonal control of breast development and pathology has been examined experimentally through the use of animal models, notably mice and rats. This review summarizes the data from experimental rodent models on the effects of androgens in experimental breast cancer, aiming to address the importance of androgens and the androgen receptor in the origins and pathogenesis of breast cancers, as well as to discuss potential biomarker and therapeutic opportunities arising from novel insights based on the experimental research.

Long terminal repeats act as androgen-responsive enhancers for the PSA-kallikrein locus

The androgen receptor (AR) signaling pathway is a common therapeutic target for prostate cancer, because it is critical for the survival of both hormone-responsive and castrate-resistant tumor cells. Most of the detailed understanding that we have of AR transcriptional activation has been gained by studying classical target genes. For more than two decades, Kallikrein 3 (KLK3) (prostate-specific antigen) has been used as a prototypical AR target gene, because it is highly androgen responsive in prostate cancer cells. Three regions upstream of the KLK3 gene, including the distal enhancer, are known to contain consensus androgen-responsive elements required for AR-mediated transcriptional activation. Here, we show that KLK3 is one of a specific cluster of androgen-regulated genes at the centromeric end of the kallikrein locus with enhancers that evolved from the long terminal repeat (LTR) (LTR40a) of an endogenous retrovirus. Ligand-dependent recruitment of the AR to individual LTR-derived enhancers results in concurrent up-regulation of endogenous KLK2, KLK3, and KLKP1 expression in LNCaP prostate cancer cells. At the molecular level, a kallikrein-specific duplication within the LTR is required for maximal androgen responsiveness. Therefore, KLK3 represents a subset of target genes regulated by repetitive elements but is not typical of the whole spectrum of androgen-responsive transcripts. These data provide a novel and more detailed understanding of AR transcriptional activation and emphasize the importance of repetitive elements as functional regulatory units.

Impact of chromatin structure and dynamics on PR signaling. The initial steps in hormonal gene regulation

Gene regulation requires access of transcription factors to DNA sequences of target genes, which is limited by the compaction of DNA in chromatin. Based on our studies on the Progesterone receptor (PR)-dependent hormonal induction of mouse mammary tumor virus (MMTV) promoter we found that remodeling of the various levels of chromatin organization is a complex and necessary prerequisite for regulation. Two consecutive cycles are essential for transcriptional activation, both involving the collaboration between activated protein kinases, histone modifying enzymes and ATP-dependent chromatin remodelers. The first cycle ends with the displacement of histone H1 and decompaction of higher order chromatin structure. The second cycle leads to the displacement of dimers of histones H2A and H2B resulting in opening of nucleosomes. In both cases the hormone receptor recruits an ATP-dependent chromatin remodeler, whose binding to chromatin is stabilized by distinct histone modifications. The final result is to facilitate full occupancy of the cis regulatory sites and access for the basal transcription machinery. Thus, activation of PR-target genes involves a very rapid coordination of enzymatic activities via crosstalk with various kinase-signaling pathways.

Dexamethasone and mifepristone increase retroviral infectivity through different mechanisms

Using adapted retroviruses for gene delivery is a modern and powerful tool in biological research as well as a promising approach for gene therapy. An important limitation for the extensive use of retroviral vectors is the low infection rate in target cells such as pulmonary vascular endothelial cells due to the insufficient infectivity of standard retrovirus supernatants that can only be overcome by complicated methods of virus concentration. This paper describes two easy methods to augment target cell infectivity, first by increasing the retroviral titer in the medium collected from packaging cells by stimulation of viral propagation with dexamethasone, and second, by increasing target cell sensitivity to retroviral infection by the glucocorticoid receptor antagonist, mifepristone. Using this method, we increased the infectivity of pulmonary microvascular endothelial cells from 16% to 85%. We demonstrate that mifepristone increased the susceptibility of target cells to retroviruses without increasing the viral titer of the supernatant. Dexamethasone, but not mifepristone, increased expression of delivered proteins such as GFP that are important for early identification of infected cells. Each, or both step(s), may be included in a standard protocol for retrovirus propagation and infection of target cells.

Comparison of prostate cancer cell lines for androgen receptor-mediated reporter gene assays

In order to select a better prostate cancer cell model for androgen receptor (AR)-mediated reporter gene assays, we assessed the androgen response characteristics of three cell lines, LNCaP, PC3/AR(+) and 22Rv1, in this study. Both the mRNA and the proteins of AR and glucocorticoid receptor (GR) were expressed in all three cell lines. Among the three cell lines, only in LNCaP cells, DHT concentration-dependently stimulated proliferation. DHT induced the luciferase activity in three cell lines which were transiently transfected with pMMTV-Luc, in a concentration-dependent manner. The maximum induction was 24.0-fold and 13.4-fold in 22Rv1 and in the LNCaP respectively. PC3/AR(+) were more sensitive to respond to DHT at a minimal concentration of 10(-12)M by 14.0-fold induction. The transcriptional activity induced with 10(-8)M DHT was inhibited about 50-75% in the PC3/AR(+) and 22Rv1, and 98% in the LNCaP, by vinclozolin. Dexamethasone concentration-dependently induced the luciferase activity in PC3 and 22Rv1, but not in the LNCaP. However, the response to dexamethasone in 22Rv1 was very weak compared to DHT. The (anti)androgencity of seven pyrethroids was assessed via an AR-mediated luciferase reporter assay. None of them showed the androgenic action in all three cell lines. Permethrin inhibited the DHT induced luciferase activity about 22%, 35.8% and 75.5% in 22Rv1, PC3/AR(+) and LNCaP, respectively. Based on results from in this study and cell line character, 22Rv1 cells seemed to be an appropriate model for the screening of androgenic endocrine disruptors, although it needs further studies with other steroid receptor and thyroid receptor.

Expression and function of human steroid receptor RNA activator in prostate cancer cells: role of endogenous hSRA protein in androgen receptor-mediated transcription

Steroid receptor RNA activator (SRA) was first isolated as a steroid receptor co-activator that functioned as an RNA transcript. Later, we demonstrated that SRA needs to be translated in order to co-activate androgen receptor (AR). Here, we showed that three isoforms of human SRA enhanced AR activities. Small interfering RNA against SRA suppressed AR activities in PC-3 cells transfected with pSG5AR and in LNCaP cells that have an endogenous mutated-AR. Western blot showed that SRA protein was expressed at a higher level in PC-3 than in LNCaP cells, suggesting that SRA may be related to hormone-independent growth of prostate cancer.

Androgen inducibility ofFgf8 in Shionogi carcinoma 115 cells correlates with an adjacent t(5;19) translocation

Fgf8 (fibroblast growth factor 8) was initially cloned from a mouse mammary tumor cell line derived from the androgen-dependent Shionogi carcinoma 115. The androgen-inducible expression of Fgf8 in this tumor controls its androgen-dependent phenotype, thus stimulating interest in this gene as a possible factor in human prostate cancer and other androgen-sensitive cancers. However, apart from Shionogi carcinoma 115, the androgen inducibility of Fgf8 is controversial. In the present study, having not detected androgen-inducible expression of Fgf8 in other mouse mammary cell lines or mouse prostate, we examined the Shionogi carcinoma 115-derived S115 cell line for mouse mammary tumor virus (MMTV) insertions or other nearby DNA rearrangements that might explain the androgen inducibility of Fgf8 in these cells. Southern blotting did not detect MMTV insertions near Fgf8 but did reveal a specific DNA rearrangement 3.7 kb upstream of Fgf8 in S115 cells and in other cells (SC115) independently derived from Shionogi carcinoma 115. Spectral karyotyping of S115 cells and sequencing of the cloned rearrangement junctions indicate that Fgf8 is involved in a t(5;19) translocation. The chromosome 5 sequence joined to Fgf8 is immediately adjacent to Smr2 (submaxillary gland androgen-regulated protein 2) and includes Muc10 (mucin 10), two genes that we show are testosterone inducible in S115 cells, suggesting that the androgen-dependent expression of Fgf8 in Shionogi carcinoma 115 and derivative cells results from this translocation. Together, these results suggest that androgen inducibility is not an inherent property of the Fgf8 gene, which has implications regarding this gene's proposed role in the etiology of hormone-responsive cancers.

Androgen regulates follicle-stimulating hormone beta gene expression in an activin-dependent manner in immortalized gonadotropes

Little is known about the molecular mechanisms of androgen regulation of the FSHbeta gene; however, studies suggest that it consists of a complex feedback loop that involves multiple mechanisms acting at both the level of the hypothalamus and the pituitary. In the present study, we address androgen regulation of the FSHbeta gene in immortalized gonadotrope cells and investigate the roles of activin and GnRH in androgen action. Using transient transfection assays in the FSHbeta-expressing mouse gonadotrope cell line, LbetaT2, we demonstrate that androgens stimulate expression of an ovine FSHbeta reporter gene in a dose-dependent manner. Mutation of either of two conserved androgen response elements at -245/-231 and -153/-139 within the proximal region of the ovine FSHbeta gene promoter abolishes this stimulation, and androgen receptor binds directly to the -244 ARE in vitro. Androgen induction of the FSHbeta reporter gene is also dependent upon the activin autocrine loop present in the LbetaT2 cells, as well as an activin-response element at -138/-124 of the FSHbeta gene. However, activin regulation of other genes remains unaffected by androgens. In addition, androgens stimulate expression of a mouse GnRH receptor reporter gene, and thus may indirectly augment the response of the FSHbeta gene to GnRH. Taken together, these data demonstrate that, in mouse gonadotropes, androgens act directly on the ovine FSHbeta gene to stimulate expression by a mechanism that is dependent upon activin, as well as acting indirectly, potentially through a second mechanism that may be dependent upon induction of GnRH receptor.

CBP recruitment and histone acetylation in differential gene induction by glucocorticoids and progestins

We have analyzed histone acetylation at the steroid-responsive mouse mammary tumor virus (MMTV) promoter in five separate cell lines that express functional glucocorticoid and/or progesterone receptors. Chromatin immunoprecipitation assays reveal that glucocorticoid and progesterone receptors bind the MMTV promoter after hormone addition but that receptor binding is not associated with an increase in acetylation of histone H3 or H4. We have, however, found one exception to this rule. Previously we described a cell line [T47D(C&L)] that displayed a remarkable differential induction of MMTV by glucocorticoids and progestins. At one chromosomal locus (MMTV-luciferase), MMTV is preferentially induced by glucocorticoids, whereas at another locus within the same cell (MMTV-CAT), MMTV is activated by both glucocorticoids and progestins. Here we show that the glucocorticoid-mediated induction of MMTV-luciferase is accompanied by increased recruitment of CBP to the promoter and increased histone H3 and H4 acetylation, whereas the hormonal induction of MMTV-CAT in the same cell exhibits a more modest CBP recruitment without any increase in histone acetylation. These studies suggest that increased histone acetylation may serve a potentiating function for MMTV promoter activation at certain loci. However, increased histone acetylation is not requisite for steroid-mediated induction of transcription at all genes.

A glucocorticoid response element in the LTR U3 region of Friend murine leukaemia virus variant FIS-2 enhances virus production in vitro and is a major determinant for sex differences in susceptibility to FIS-2 infection in vivo

The nucleotide sequence of the Friend murine leukaemia virus variant FIS-2 LTR has high identity with the closely related Friend murine leukaemia virus (F-MuLV) LTR, except for the deletion of one direct repeat, a few point mutations and the generation of a glucocorticoid response element (GRE) in the U3 region. The GRE can mediate gene induction by glucocorticoids, mineral corticoids, progesterone and androgens, and it has been shown that incorporation of a GRE(s) within the LTR can increase the transcriptional activity of retroviral enhancers. We have previously reported an increased early virus replication in male mice compared with female mice when infected with a virus containing the FIS-2 LTR and have proposed that the GRE might contribute to this sex difference. In the present study, we introduced a single point mutation in the GRE and performed comparative studies in NIH 3T3 cells and in young adult male and female NMRI mice. We found that significantly more virus was produced from NIH 3T3 cells infected with wt FIS-2 than from cells infected with the FIS-2 GRE mutant and that this difference was further augmented by glucocorticoids. The glucocorticoid antagonist RU486 inhibited virus production in a dose-dependent manner. The wt FIS-2 disseminated significantly faster than the FIS-2 GRE mutant in both male and female mice. There was no significant difference in the dissemination rate between male and female mice infected with the FIS-2 GRE mutant. Hence, the GRE in the FIS-2 LTR is one determinant of the significant sex difference in susceptibility to FIS-2 infection.

Ectopic expression of FGF-3 results in abnormal prostate and Wolffian duct development

To evaluate the effects of FGF-3 expression in the prostate and male reproductive tract, we employed a bitransgenic system to target FGF-3 to these organs. We present a first study that ectopic FGF-3 expression resulted in exuberant hyperplasia of all bigenic prostatic lobes typified by epithelial stratification, cribiform structures and papillary tufts. These cells displayed increased nuclear-to-cytoplasmic ratios and bromodeoxyuridine (BrdU) proliferative index but retained relatively uniform nuclear androgen receptor (AR) and the tumor suppressor C-CAM1 staining. Furthermore, the dysmorphogenic prostatic cells also resembled PIN (prostatic intraepithelial neoplasia)-like lesions but did not appear to have invaded the basal lamina. In addition to these phenotypes, profound disorders of the bigenic Wolffian duct derivatives were observed. The bigenic ampullary glands and vas deferens were extremely cystic, hypertrophic and hyperplastic; the enlarged epididymi showed a reduction of spermatozoa and the seminal vesicles exhibited a dramatic reduction of seminal secretions. Because of these severe abnormalities, these infertile males presented with diaphragmatic hernias, hemoperitoneum and many secondary abnormalities at sacrifice. Taken together, we show that ectopic FGF-3 expression severely perturbs normal prostate development and our system should be useful for the analyses of early changes in prostatic hyperplasia.

A G577R mutation in the human AR P box results in selective decreases in DNA binding and in partial androgen insensitivity syndrome

We have characterized a novel mutation of the human AR, G577R, associated with partial androgen insensitivity syndrome. G577 is the first amino acid of the P box, a region crucial for the selectivity of receptor/DNA interaction. Although the equivalent amino acid in the GR (also Gly) is not involved in DNA interaction, the residue at the same position in the ER (Glu) interacts with the two central base pairs in the PuGGTCA motif. Using a panel of 16 palindromic probes that differ in these base pairs (PuGNNCA) in gel shift experiments with either the AR DNA-binding domain or the full length receptor, we observed that the G577R mutation does not induce binding to probes that are not recognized by the wild-type AR. However, binding to the four PuGNACA elements recognized by the wild-type AR was affected to different degrees, resulting in an altered selectivity of DNA response element recognition. In particular, AR-G577R did not interact with PuGGACA palindromes. Modeling of the complex between mutant AR and PuGNACA motifs indicates that the destabilizing effect of the mutation is attributable to a steric clash between the C beta of Arg at position 1 of the P box and the methyl group of the second thymine residue in the TGTTCPy arm of the palindrome. In addition, the Arg side chain can interact with G or T at the next position (PuGCACA and PuGAACA elements, respectively). The presence of C is not favorable, however, because of incompatible charges, abrogating binding to the PuGGACA element. Transactivation of several natural or synthetic promoters containing PuGGACA motifs was drastically reduced by the G577R mutation. These data suggest that androgen target genes may be differentially affected by the G577R mutation, the first natural mutation characterized that alters the selectivity of the AR/DNA interaction. This type of mutation may thus contribute to the diversity of phenotypes associated with partial androgen insensitivity syndrome.

Gender-related differences in susceptibility, early virus dissemination and immunosuppression in mice infected with Friend murine leukaemia virus variant FIS-2

An emerging amount of data indicates a correlation between gender-related factors and regulation of virus infection and supports what is known in clinical circles, that these topics are of great importance in many infectious diseases. In the present study we found that young adult NMRI male mice are more susceptible to infection by a variant of Friend murine leukaemia virus, FIS-2, than are female mice. We observed that the level of virus in serum, bone marrow and spleen was initially higher in male mice. Male mice were also more susceptible to FIS-2-induced immunosuppression. These results indicate a more efficient virus replication and dissemination in male mice. Studies with recombinant viruses between FIS-2 and the prototype Friend murine leukaemia virus revealed that FIS-2 LTR is one major factor contributing to the observed gender differences. A possible sex hormone influence on FIS-2 transcription due to the presence of a glucocorticoid response element in FIS-2 LTR is discussed.

Prostate cancer and the androgen receptor: strategies for the development of novel therapeutics

The early demonstrations that prostate cancer was hormone-sensitive initiated a therapeutic strategy of hormone ablation that is still in use today. Although chemical or surgical castration reduces androgen stimulation of the androgen receptor (AR) and produces tumor regression, little survival benefit is achieved. Patients with metastatic cancer eventually relapse as their tumors progress to hormone independence. The AR is a member of the steroid receptor family; however, it manifests many unique features including: N-terminal, C-terminal interactions and antiparallel dimerization, unique N-terminal domains for co-factor recruitment, AR-specific co-activators and upstream promoter/enhancer response elements that amplify AR-mediated responses. The AR is regulated by phosphorylation and cross-talk with several signaling pathways, including MAP kinases, PKA and PKC. Non-genomic effects of AR to regulate transcription factors elk-1 and -2 have also been demonstrated. These unique features suggest mechanisms by which novel therapeutics might target and influence AR-mediated actions. Progress in this direction has been realized with the recent synthesis of non-steroidal androgen agonists that may have tissue-selective effects.

Steroid-selective initiation of chromatin remodeling and transcriptional activation of the mouse mammary tumor virus promoter is controlled by the site of promoter integration

The mouse mammary tumor virus (MMTV) promoter has target sequences recognized by several steroid receptors. We present evidence for a novel mechanism that confers hormone specificity to this promoter. We show that remodeling of MMTV chromatin and the concomitant activation of the MMTV promoter are induced equally by glucocorticoids and progestins in one chromosomal context but are selective for glucocorticoids in another. Furthermore, increased histone acetylation modulates MMTV promoter regulation disparately at the two chromosomal locations. Together, these data indicate that chromosomal architecture commands a crucial role in gene regulation, imposing locus-specific selectivity between regulators with similar sequence recognition.

Enlargement of the ampullary gland and seminal vesicle, but not the prostate in int-2/Fgf-3 transgenic mice

Expression of the int2/Fgf-3 gene occurs during normal embryonic development and is associated with mammary cancer in mice. Overexpression of this gene under the control of the mouse mammary tumor virus long terminal repeat (MMTV-LTR) in males was reported to result in prostatic enlargement. In this report male Fgf-3-overexpressing mice were shown to have enlarged ampullary glands, seminal vesicles, and ductus deferens; there was extensive epithelial hyperplasia in the ampullary glands and seminal vesicles. The prostates of these animals were of normal size and histology. The transgene was expressed in all of the enlarged organs, which are derived exclusively from the Wolffian duct. Male secondary sex organs derived from the urogenital sinus, e.g., the ventral prostate, coagulating gland, and bulbourethral glands, were normal and did not express the MMTV-LTR-driven Fgf-3 transgene. A dorsolateral prostate was also morphologically normal but did express the transgene. This study underscores the importance of careful organ identification in transgenic models in which gross organ enlargement or distortion occurs. It also highlights the heterogeneity of the response to Fgf-3 among the secondary sex organs and even within the prostate itself.

Differential activity of progesterone and glucocorticoid receptors on mouse mammary tumor virus templates differing in chromatin structure

In vivo, transcription factors interact with promoters having complex nucleoprotein structures. The transiently expressed progesterone receptor (PR) efficiently activates a transfected mouse mammary tumor virus (MMTV) promoter but is a poor activator of the MMTV promoter when it acquires an ordered chromatin structure as an endogenous, replicating gene. We show that the deficiency in PR activity is not due to insufficient expression of either B or A isoforms or competition between the two types of MMTV templates. Rather, this deficiency reflects an inability to induce the chromatin remodeling event that is required for activation of the replicated MMTV template. To determine whether this characteristic is common to transiently expressed steroid receptors or specific to the PR, we examined the activity of transiently expressed glucocorticoid (GR) receptor. Unlike the PR, the transiently expressed GR is an effective activator of both MMTV templates and efficiently induces the necessary chromatin remodeling event at the replicated template. These results indicate that the GR and PR have unique requirements for activation of promoters with ordered chromatin structure. These differences may provide a mechanism for establishing target gene specificity in vivo for steroid receptors that recognize and bind to identical DNA sequences.

Characterization of an androgen response element within the promoter of the epididymis-specific murine glutathione peroxidase 5 gene

We have shown in earlier studies, using a mouse model, that the expression of the glutathione peroxidase 5 protein (GPX5) is restricted to the epididymis and that the accumulation of its corresponding mRNA is hormonally, spatially and temporally regulated throughout postnatal development. We report here, using run-on assays, transient expression experiments as well as gel-shift and footprinting analyses on the findings that at least part of the androgenic control of the GPX5 expression is exerted at the transcriptional level via an androgen response element localized in the distal promoter region of the GPX5 gene. The gpx5 androgen response element (ARE) is found to be consistent with the consensus palindromic steroid-receptor target sequence 5'-AGWACWnnnTGTYCT-3' but exhibits a quite weak conservation in the left half site. The data presented here further expand the diversity of sequence able to confer androgen responsiveness.

Chromatin structure of the MMTV promoter and its changes during hormonal induction

1. The packaging of nuclear DNA in chromatin determines the conversion of the genetic information into a defined phenotype by influencing the availability of DNA sequences for interactions with regulatory proteins and transcription factors. 2. We have studied the influence of the first level of chromatin organization, the nucleosome, on the activity of the mouse mammary tumor virus (MMTV) promoter. The MMTV promoter is strongly transcribed in response to steroid hormones but is virtually silent in the absence of hormonal stimuli. Full hormonal induction requires binding of the hormone receptors to four hormone-responsive elements (HREs), as well as binding of nuclear factor I (NFI) and the octamer transcription factor 1 (OTF-1 or Oct-1) to sites located between the HREs and the TATA box. A full loading with transcription factors cannot be achieved on free DNA due to steric hindrance between hormone receptor and NFI and between NFI and OTF-1. 3. The low basal activity of the MMTV promoter is most likely due to its organization in a positioned nucleosome. In the intact cell, as well in reconstituted chromatin, the regulatory region of the MMTV promoter is wrapped around a histone octamer in a precise rotational orientation, which permits access of the hormone receptors to only two of the four HREs, while precluding binding of NFI and OTF-1 to their respective sites. Upon hormone induction, the nucleosome is remodeled and the path of its DNA altered in a way which makes the nucleosomal dyad axis more accessible to DNase I and enables occupancy of all relevant sites: the four HREs, as well as the binding sites for NFI and OTF-1. 4. These results suggest that the nucleosomal organization of the MMTV promoter not only is responsible for the low activity prior to hormone treatment, but also may be a prerequisite for full loading with transcription factors after hormone induction. We conclude that the DNA contains topological information which modulates the expression of the genetic program.

Inverse PCR-mediated cloning of the promoter for the rat vasopressin V2 receptor gene

The adenylyl cyclase-coupled vasopressin V2 receptor has been cloned recently and shown, in rats, to be produced from the predominant form of two alternate spliced variants. To begin to unravel the transcriptional regulation of this receptor, we have isolated the 5' flanking region of the rat vasopressin V2 receptor gene and characterized its promoter sequence. The method of inverse polymerase chain reaction (PCR), which allows the amplification of DNA fragments adjacent to a segment of known sequence, was used as an alternative approach to genomic DNA library screening. Using a probe encompassing part of the coding region, first we identified by Southern blot analysis, a single BstX I hybridizing fragment of 2.3 kilobases (kb). This size predicted a BstX I restriction site 1.5 kb upstream to the gene coding region. Cloning of this fragment was accomplished through circularization of BstX I restriction digests and inverse PCR-mediated amplification. Sequence analysis of the gene 5' flanking domain enabled the design of oligonucleotide primers with the usual forward/reverse orientation, and additional clones were generated from native genomic DNA using a high fidelity thermoresistant DNA polymerase. Reverse transcription-PCR (RT-PCR) and primer extension analysis mapped the major transcription start site 422 nucleotides upstream to the translation initiation codon. The promoter region lacks a TATA box but contains a CAAT box and a consensus binding site for transcription factor Sp1. Multiple potential binding sites for the transcription factor PEA3 are clustered in two DNA portions located 0.6 kb and 1 kb upstream to the coding region. In addition, sequences homologous to glucocorticoid response elements are present and might be responsible for the regulation by adrenal steroids of vasopressin-dependent adenylyl cyclase activity in the kidney.

Gene ecology: a cis-acting gene-to-gene interaction due to the spatial arrangement of genes in chromosomes affects neighbouring transfected c-H-ras expression

A cis-acting interference between gene activities, which occurs when two genes lie on the same DNA strand and have an intergenic distance less than a defined length, was previously deduced when chromosomal organizations of various higher eukaryote nuclear genes in clusters were compared. In order to investigate such an interference due to arrangement of genes along chromosomes, we have isolated a few cell lines which possessed (i) human mutated c-H-ras fused with the mouse mammary tumour virus long terminal repeat and (ii) the E. coli xanthine-guanine phosphoribosyltransferase (gpt) gene with the SV40 promoter, on the same or on different DNA strands, separated by a short intergenic distance or unlinked. Since the cancerous phenotype of a cell can be readily identified due to c-H-ras expression, we examined in these cell lines whether continuous c-H-ras expression, induced by dexamethasone, is disturbed through a cis-acting gene-to-gene interaction when the expression of the neighbouring gpt gene is enforced and as a result, the cancerous state of a cell is converted to the 'normal' state. The enforced expression of the neighbouring gpt gene was shown to alter c-H-ras expression, and thus reversible conversion of a cell between cancerous and normal states occurred only when the cell possessed an optimum number of the gene pair, in which both c-H-ras and the gpt gene were on the same DNA strand. This implies that the spatial arrangement of genes in chromosomes plays an important role in the regulation of gene expression in a cluster.

Antiandrogens inhibit human androgen receptor-dependent gene transcription activation in the human prostate cancer cells LNCaP

Human androgen receptor (hAR) is a ligand-dependent transcription factor that mediates androgen-induced actions on target tissues. Transfection studies in the human prostate cancer cell line LNCaP examine the ability of dihydrotestosterone (DHT), hydroxyflutamide (HO-FLU), cyproterone acetate (Cypro.A), and RU 23908-10 to stimulate or to inhibit the transcription activation of mouse mammary tumor virus-bacterial chloramphenicol acetyltransferase (MMTV-CAT). DHT stimulated transcription activation of MMTV-CAT gene in LNCaP cells in a dose-dependent manner. HO-FLU, Cypro.A, and RU 23908-10, though only partially, also stimulated the transcription activation of MMTV-CAT. Despite this, 100- to 1,000-fold molar excess of all antiandrogens inhibited the agonistic activity of 10 nM DHT in this system. Receptor binding assays confirmed that HO-FLU, Cypro.A, and RU 23908-10 competed with DHT for AR binding in LNCaP cells. Western blot analysis using AR antipeptide antibodies raised in rabbits revealed the presence of two AR protein bands in LNCaP cells, following treatment with antiandrogens. Increasing doses of HO-FLU stimulated the expression of the 114-kDa AR by 2.5-fold, but did not affect the 108-kDa AR. Increasing doses of Cypro.A and RU 23908-10 decreased the levels of both the 114-kDa and the 108-kDa AR. Although the exact nature of 108-kDa and 114-kDa AR in LNCaP cells is still unknown, these data suggest that the regulatory actions of each individual antiandrogen on AR expression in LNCaP cells may be different.

Interaction of antiandrogen-androgen receptor complexes with DNA and transcription activation

Human androgen receptor (hAR) is a ligand-dependent transcription factor that mediates androgen-induced actions on target tissues. Transfection studies in receptor deficient monkey kidney cells CV-1 in culture examine the ability of dihydrotestosterone (DHT) and of the antiandrogens hydroxylflutamide (HO-FLU), cyproterone acetate (Cypro.A) and RU 23908-10 to stimulate or to inhibit the transcription activation of mouse mammary tumor virus-bacterial chloramphenicol acetyltransferase (MMTV-CAT). CV-1 cells cotransfected with wild type hAR (hAR1-910) and MMTV-CAT, were treated with varying concentrations of DHT. DHT stimulated transcription activation of MMTV-CAT gene in a dose-dependent fashion. Cypro.A though only partially, also stimulated the transcription activation of MMTV-CAT. In the absence of steroids, HO-FLU induced the MMTV-CAT transcription in transfectants only 4% above the basal level. RU 23908-10 revealed the least agonistic activity at concentrations between 10 nM and 1 microM. Despite this, 100- to 1000-fold molar excess of all antiandrogens inhibited the agonistic activity of 10 nM DHT in this system. Receptor binding assays confirmed that HO-FLU, Cypro.A and RU 23908-10 competed with [3H]DHT for AR binding with hAR expressed in CV-1 cells. Western blot analysis using AR antipeptide antibodies raised in rabbits revealed the presence of two AR protein bands in extracts prepared from hAR1-910 transfected CV-1 cells. Incubation of labeled synthetic palindromic androgen responsive element (ARE) with the hAR containing CV-1 cell extracts followed by u.v. cross-linking demonstrated the specificity of AR-DNA interaction. Analysis by gel mobility shift assays showed that the interaction of AR-antiandrogen complexes with labeled ARE was specific.

Antiandrogen action in the development of androgen insensitivity in S115 mouse mammary tumour cells

Endocrine therapy for steroid-sensitive tumours often involves administration of steroid antagonists which are designed to bind to the steroid receptor and block steroid action. However, the clinical problem remains the temporary nature of the tumour regression. Since in vitro models suggest that steroid ablation itself can result in loss of steroid sensitivity of tumour cells, these studies aimed to investigate the influence of the antiandrogen ICI 141,307 on this progression. This antiandrogen exhibits both agonist and antagonist actions on androgen-regulated cellular and molecular parameters of S115 mouse mammary tumour cells in culture. Its ability to regulate mouse mammary tumour virus (MMTV) RNA production in these cells confirms that the antiandrogen-receptor complex can not only bind to the steroid response element (SRE) in the MMTV DNA sequences but also activate gene transcription. Despite these molecular abilities of this antiandrogen, it was still unable to maintain androgen sensitivity in the long term. It was able to delay progression to insensitivity of the various steroid-regulated parameters, although the different parameters were delayed for different lengths of time, but ultimately the antiandrogen was unable to prevent loss of any parameters. It is thus concluded that the nature of the ligand is critical for maintenance of steroid sensitivity: only androgen and not antiandrogen will maintain long-term response. Previous molecular models for loss of steroid response suggest that it could result from inactivation of SRE in the genome when no receptor complex is bound. However, loss of response occurred in these experiments even in the presence of an activated receptor complex capable of binding to the SRE. Possible molecular mechanisms and the clinical implications are discussed.

Benign prostatic hyperplasia in a transgenic mouse: a new hormonally sensitive investigatory model

Recent advances in molecular biology have enabled incorporation of proto-oncogenes into the mouse germline. In this study we use a transgenic mouse line that overexpresses the fibroblastic growth factor (FGF) family member, int-2, under the control of mouse mammary tumor virus (MMTV) regulatory elements. One of the tissues targeted by MMTV is the mouse prostate. Expression of the MMTV-int-2 transgene in male transgenic mouse carriers results in a dramatic enlargement of the prostate gland which on histologic examination closely resembles the epithelial/glandular BPH observed in human and canine models. Pre- and postpubertal transgenic (NR) and wild-type (WT) FVB/N male mice were evaluated for the effects of hormonal manipulation by orchiectomy and orchiectomy followed by androgen replacement. Orchiectomy results in a significant decrease in size of the prostate in both NR and WT mice (p < 0.05), regardless of sexual maturity. Exogenous hormonal replacement with testosterone or dihydrotestosterone following orchiectomy results in significant regrowth of the prostate in both NR and WT mice. Flutamide, a potent nonsteroidal anti-androgen, resulted in a 55% reduction in size of the NR prostate (p < 0.002) and a similar 44% reduction in size of the WT prostate. Similarly, treatment of both NR and WT mice with leuprolide, a GnRH agonist, resulted in a significant decrease in prostate size (p < 0.05). Treatment of both NR and WT mice with finasteride (MK-906), a 5-alpha reductase inhibitor, failed to produce any significant regression in prostatic tissue. Based upon these data, we conclude that this transgenic mouse model, expressing int-2, produces an epithelial BPH histologically similar to other animal models. This transgenic model is hormonally sensitive and appears to represent a unique model for the investigation of BPH and growth factor induced epithelial cell hyperplasia.

Interaction of androgen and glucocorticoid receptor DNA-binding domains with their response elements

Fusion proteins containing the glucocorticoid and the androgen receptor DNA-binding domain (ARF1 and GRF1) were produced in Escherichia coli. DNAse I footprinting was used to compare the interaction of these proteins with responsive elements (REs) in a typically glucocorticoid-responsive gene (mouse mammary tumour virus (MMTV)) and in an androgen-responsive gene (the C3(1) gene of rat prostatic binding protein). It is demonstrated that response elements which most closely resemble the consensus sequence show identical footprinting patterns for ARF1 and GRF1. The protected regions suggest that these sequences are occupied by two DNA-binding domains (DBDs) forming a dimer. Regions that constitute imperfect RE sequences, however, are apparently recognized by only one DBD, which mainly protects the TGTTCT motif. At these REs, the protection patterns produced by ARF1 and GRF1 are not identical. In the long terminal repeat (LTR) of MMTV but not in C3(1), a mechanism other than classical dimer formation seems to increase the affinity of ARF1 and GFR1 for these imperfect REs.

Interplay of steroid hormone receptors and transcription factors on the mouse mammary tumor virus promoter

The mouse mammary tumor virus (MMTV) promoter, that responds to glucocorticoids and progestins, contains a complex hormone response element (HRE) in the long terminal repeat (LTR) region covered by a phased nucleosome. Hormone treatment leads to alterations in chromatin structure that make the HRE region more accessible to digestion by DNase I and permit binding of transcription factors, including nuclear factor I (NFI), immediately downstream of the HRE. NFI acts as a basal transcription factor on the MMTV promoter in vitro but competes with the hormone receptors in terms of binding to free DNA. In uninduced chromatin, the precise positioning of the DNA double helix on the surface of the histone octamer precludes binding of NFI to its cognate sequence while still allowing recognition of the HRE by the hormone receptors. We postulate that receptor binding to the nucleosomally organized MMTV promoter disrupts the chromatin structure enabling NFI binding and subsequent formation of a stable transcription complex. Whether the receptor remains bound to DNA during induction or is displaced by NFI is not conclusively known, but our evidence supports a "hit and run" mechanism. NFI is not the only factor involved in hormonally induced transcription of the MMTV promoter. Two degenerated octamer motifs located immediately upstream of the TATA box are recognized by the ubiquitous transcription factor OTF-1 (Oct-1, NFIII), and are also important. In vitro, mutations in these motifs do not influence basal transcription, but completely abolish the stimulatory effect of purified progesterone receptor. Progesterone receptor bound to the HRE facilitates binding of OTF-1 to the two octamer motifs. Thus, OTF-1 is a natural mediator of progesterone induction of the MMTV promoter and acts through cooperation with the hormone receptor for binding to DNA.

Testosterone and 5 alpha-dihydrotestosterone interact differently with the androgen receptor to enhance transcription of the MMTV-CAT reporter gene

Testosterone and its 5 alpha-reduced derivative 5 alpha-dihydrotestosterone exert different actions in the male during embryogenesis and in postnatal life. Nevertheless the two hormones bind to the same intracellular androgen receptor, and genetic and endocrinological studies in the Tfm mouse suggest that the actions of both hormones are mediated by this single receptor. Previous studies indicate that dihydrotestosterone binds more tightly to the androgen receptor but that the Bmax of binding of the two hormones is the same. To determine whether these differences in binding parameters could explain the mechanism by which the two hormones exert different physiological actions via the same receptor, we introduced a plasmid encoding the androgen receptor cDNA and a reporter plasmid encoding MMTV-CAT into Chinese hamster ovary cells. These cells do not express endogenous androgen receptor and do not convert testosterone to dihydrotestosterone. Therefore, it was possible to examine the relation between the concentration of each of the steroids and reporter gene expression. Both hormones enhanced CAT activity, but dihydrotestosterone was approximately 10 times as potent (half maximal of 0.018 nM) as testosterone (half maximal of 0.2 nM); the maximal activity achieved was the same for the two androgens. These findings are nearly identical to the apparent Kd values for the interaction of the two hormones with the androgen receptor. Although testosterone and dihydrotestosterone may influence the expression of other genes differently, these findings are compatible with a model system in which the differential effects can be explained as a consequence of different binding affinities to the receptor.(ABSTRACT TRUNCATED AT 250 WORDS)

Stable transfection of androgen receptor and MMTV-CAT into mammalian cells: inhibition of cat expression by anti-androgens

A hormone-inducible transcriptional system has been established, based on the stable transfection of the rat androgen receptor (rAR) and a reporter plasmid containing the mouse mammary tumour virus promoter linked to the chloramphenicol acetyltransferase gene (pMMTV-CAT) into steroid receptor-negative CV-1 cells. First, the rAR was stably introduced into CV-1 cells. Single clones were tested for stable expression of functionally active AR by analysing the effect of dihydrotestosterone on induction of transiently transfected pMMTV-CAT. Stable transfection and the expression of AR was confirmed by steroid-binding assays. In a second step, a clone expressing physiological amounts of AR protein (30 fmol/mg protein) was stably transfected with pMMTV-CAT to yield a permanent cell line that stably expresses functional AR and MMTV-CAT sequences. This cell line provides a powerful tool for the efficient and accurate determination and quantification of the effects of androgens and anti-androgens on reporter gene transcription. This was demonstrated by investigating the action of the three anti-androgens hydroxyflutamide, casodex and cyproterone acetate. The three compounds were shown to reverse the effects of the androgen R1881 on gene expression but were themselves devoid of agonistic activity.

Identification of a novel mammary cell line-specific enhancer element in the long terminal repeat of mouse mammary tumor virus, which interacts with its hormone-responsive element

We analyzed the long terminal repeat (LTR) of mouse mammary tumor virus for sequences that influence its promoter activity by using the chloramphenicol acetyltransferase assay. A series of LTR deletion mutants and recombinants between LTR and simian virus 40 regulatory sequences were used for these studies. Through transfection experiments in three different human cell lines (T47D, MCF-7, and HeLa), we identified a novel mammary cell line-specific enhancer element on a 98-bp BanII fragment (from position -1075 to -978 upstream of the start site of transcription) which interacts with the hormone-responsive element of LTR. We also identified nuclear factors that specifically interacted with this BanII fragment in the nuclear extract from the mammary tumor cell line, T47D, but not from the HeLa cell line.

Transition of human breast cancer cells from an oestrogen responsive to unresponsive state

An in vitro model system is described for studying the problem of loss of steroid sensitivity in breast cancer cells. Growth of cloned oestrogen-sensitive human breast cancer cells in the long-term absence of steroid gives rise to a population of oestrogen-insensitive cells. In ZR-75-1 cells, the effect is clonal but occurs at high frequency suggesting a mechanism affecting a wide proportion of the cell population synchronously. This does not involve any reduction in oestrogen receptor number. Furthermore, there is no coordinated loss of oestrogen-sensitive molecular markers, showing that oestrogen receptors remain not only present but functional. These growth changes are not accompanied by any loss of growth inhibition by antioestrogen. Although steroid deprivation does not result in loss of oestrogen-sensitive markers, this does not hold true for other steroids. There was a reduction in progestin, androgen and glucocorticoid regulation on transfected LTRs. Loss of steroid-sensitive growth was accompanied by changes in response to exogenous growth factors and altered endogenous growth factor mRNA production. Steroid-deprived T-47-D cells acquire sensitivity to stimulation by TGF beta and have raised TGF beta 1 and TGF beta 2 mRNA levels. ZR-75-1 cells are growth inhibited by TGF beta and have reduced TGF beta 1 mRNA levels. In MCF-7 cells, increased IGFII mRNA, following transfection, can result in an increased basal cell growth rate in the absence of steroid. These findings are discussed in relation to possible autocrine mechanisms in the loss of steroid sensitivity of breast cancer cells.

Oestrogen enhances the responsiveness of the MMTV-LTR to glucocorticoid in ZR-75-1 human breast cancer cells

Treatment of ZR-75-1 human breast cancer cells with oestrogen has no direct effect on the expression of a transfected MMTV-LTR but enhances its inducibility in response to glucocorticoid treatment. This effect which can be produced with both oestradiol and diethylstilbestrol is specific to induction of the MMTV-LTR, no effect of the treatment on expression driven by the RSV-LTR being observed. The effect can be observed in cells pre-treated with oestrogen prior to removal of DNA and glucocorticoid addition but not in cells where oestrogen is added after removal of the DNA. The possible mechanisms of these effects and their relationship to the induction of oestrogen-responsive genes by this hormone are discussed.

Identification of a glucocorticoid-responsive element in Epstein-Barr virus

Immortalization of B lymphocytes by Epstein-Barr virus (EBV) is complex and poorly understood. However, some evidence suggests that glucocorticoids influence this process. We identified a glucocorticoid-responsive element in the BamHI C fragment of EBV which we call ES-1. In glucocorticoid-treated cells, ES-1 enhanced chloramphenicol acetyltransferase gene expression from the herpes simplex virus thymidine kinase promoter, as well as the EBV Bam-C promoter, from which several latent viral gene products are transcribed. By Northern blot analysis, glucocorticoid treatment enhanced transcription from the Bam-C promoter in Jijoye cells, a Burkitt's lymphoma cell line. In addition, the DNA-binding domain of the glucocorticoid receptor bound specifically to the ES-1 region. These glucocorticoid effects on the Bam-C promoter region may provide some insight into the process of EBV immortalization.

Temperature-sensitive mutants for steroid-sensitive growth of S115 mouse mammary tumor cells

We have generated temperature-sensitive (ts) mutants for steroid-regulated anchorage-independent cell growth. Androgen-responsive S115+A mouse mammary tumor cells were mutagenized with ethyl methane sulfonate and the variants which were growth-arrested in suspension at the nonpermissive temperature of 41 degrees C were selected by killing dividing wild-type cells with the DNA synthesis inhibitors 5-fluoro-2'-deoxyuridine or cytosine arabinoside. Fifteen clones were isolated and characterized for morphology and growth properties. Three (ts21, ts27, ts33) of the phenotypic variants were ts for androgen-maintained anchorage-independent growth, two of them (ts27 and ts33) also for growth in monolayer. Growth arrest at 41 degrees C was not due to a defect in androgen receptor function in any of the mutant cell lines as shown by steroid binding assays and by the androgen-stimulated expression of both endogenous MMTV RNA and the transiently transfected LTR-CAT gene at the nonpermissive temperature. It remains to be determined for clone ts33 whether the defect is in postreceptor events of steroid action or in genes affecting general mechanisms of cell growth. However, since in clones ts21 and ts27 general cell growth remains functional at 41 degrees C under serum stimulation, defects may be in postreceptor steroid-related pathways. It is hoped that these mutants will provide a useful tool for study of steroid regulation of cell growth and in particular of the property of anchorage-independent growth.

Mapping contacts between unpurified human progesterone receptor and the hormone response element of mouse mammary tumor virus

Binding of steroid hormone receptors to specific recognition sites of hormone-inducible genes is one of the events required for hormonal regulation of gene transcription. We have employed an immunoprecipitation assay to map the interaction between unpurified human progesterone receptors from crude nuclear extracts of T47D cells and the hormone response element of the mouse mammary tumor virus (MMTV). DNase I footprints and methylation interference patterns are similar to those reported with highly purified rabbit progesterone receptors, suggesting that both human and rabbit receptors recognize similar features in the hormone response element. More importantly, these patterns suggest that if other factors are associated with unpurified nuclear receptor, they do not alter the contacts made by receptor nor do they make contacts themselves with MMTV DNA in a manner detected by DNase I or methylation interference assays. The sites of interaction of receptors bound with the clinically important progestin antagonist, RU 486, are comparable to those observed with an agonist-receptor complex. These results suggest that the antagonist prevents receptor action at a step after its recognition and binding to specific sites on a hormone-responsive enhancer element.

Functional characterization of an androgen response element in the first intron of the C3(1) gene of prostatic binding protein

We demonstrate that the 204 bp intronic gene fragment of C3(1), which has a specific in vitro affinity for the androgen receptor, is able to confer androgen responsiveness to a heterologous promoter. This characteristic is completely destroyed by a single G----T substitution, affecting a 5'-TGTTCT-3' element that closely resembles the consensus sequence of the glucocorticoid and progesterone response elements (GRE/PRE). In fact we could show that this androgen response element (ARE) also acts as a similarly weak GRE or PRE in T-47D cells.