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PubMed1997

Transcriptional up-regulation of the human androgen receptor by androgen in bone cells.

Androgen regulation of androgen receptor (AR) expression has been observed in a variety of tissues, generally as inhibition, and is thought to attenuate cellular responses to androgen. AR is expressed in osteoblasts, the bone-forming cell, suggesting direct actions of androgens on bone. Here we characterized the effect of androgen exposure on AR gene expression in human osteoblastic SaOS-2 and U-2 OS cells. Treatment of osteoblastic cells with the nonaromatizable androgen 5alpha-dihydrotestosterone increased AR steady state messenger RNA levels in a time- and dose-dependent fashion. Reporter assays with 2.3 kilobases of the proximal 5'-flanking region of the human AR promoter linked to the chloramphenicol acetyltransferase gene in transfected cultures showed that up-regulation of AR promoter activity by androgen was time and dose dependent. Treatment with other steroid hormones, including progesterone, 17beta-estradiol, and dexamethasone, was without effect. The antiandrogen hydroxyflutamide completely antagonized androgen up-regulation. Thus, in contrast to many other androgen target tissues, androgen exposure increases steady state AR messenger RNA levels in osteoblasts. This regulation occurs at least partially at the level of transcription, is mediated by the 5'-promoter region of the AR gene, and is dependent on functional AR. These results suggest that physiological concentrations of androgens have significant effects on AR expression in skeletal tissue.

Bone Neoplasms↗
PubMed2003

The androgen receptor in hormone-refractory prostate cancer: relevance of different mechanisms of androgen receptor signaling (Review).

The last decade has brought increased awareness to prostate cancer as a significant health problem. Prostate cancer is very heterogeneous in its etiology and progression, but androgen signaling appears to be a common key element in its development and progression. Blocking of androgen signaling results in a decrease in tumor volume as well as a decline in serum PSA in the majority of patients with prostate cancer. Today, endocrine therapy involves androgen depletion by orchiectomy or by treatment with LHRH-analoga as well as blockade of the androgen receptor (AR) with anti-androgens. However, during these treatments almost all tumors relapse to a hormone-insensitive state. The mechanisms that lead from initially androgen-sensitive to androgen-unresponsive tumor cell growth have been partly elucidated by new insights into the molecular mechanisms of androgen receptor signaling over the past several years. In addition to androgen receptor mutations that broaden the ligand-specificity of the AR, androgen-independent transactivation of the AR by peptide growth factors such as epidermal growth factor and insulin-like growth factor-I has been discovered. Furthermore, analysis of proteins that interact with the AR led to the isolation of coactivator proteins that mediate transcriptional activation by the AR. The following review will discuss the elements involved in androgen receptor signaling and summarize the present knowledge of their biological and clinical relevance in advanced prostate cancer.

Cell Division↗
PubMed1987

Partial androgen resistance due to a distinctive qualitative defect of the androgen receptor.

Using whole genital skin fibroblasts, we have characterized a novel androgen receptor mutation in a family with partial androgen resistance. The proposita was born with bilateral labioscrotal folds and a single perineal urogenital orifice. Her similarly affected maternal aunt was raised as a female with the support of gonadectomy and vaginoplasty. The mutant androgen receptor has a normal maximum binding capacity (Bmax), but an increased apparent equilibrium dissociation constant (Kd) with 5 alpha-dihydrotestosterone (DHT) and 2 synthetic androgens, methyltrienolone (MT) and mibolerone (MB). Preformed mutant DHT-receptor complexes dissociate (k) at a near-normal rate, but their MT and MB counterparts dissociate twice as quickly as normal. The native free mutant receptor is not more thermolabile than normal, but its recently dissociated counterpart is. Prolonged incubation of the cells with each of the 3 androgens causes the mutant receptor to acquire a normal increment of increased androgen-receptor activity. This androgen-sensitive pattern of misbehavior of the present mutant receptor distinguishes it from those responsible for 3 other families with partial androgen resistance studied previously. These differences will help to identify structure-function domains on the androgen receptor protein, particularly in conjunction with the use of DNA probes to analyze mutations at the X-linked androgen receptor locus.

Androgen-Insensitivity Syndrome↗
PubMed1996

Androgen receptor mediated growth control of breast cancer and endometrial cancer modulated by antiandrogen- and androgen-like steroids.

Androgens are involved in many regulatory processes in mammary and endometrial epithelium, but their role in the development and progression of breast and endometrial carcinoma is poorly understood. Androgen receptors (AR) are found in normal epithelium as well as in more than 50% of specimen from both tumor types. The occurrence of AR is correlated with estrogen and progesterone receptors. Androgen receptor positive cell lines were established during the last few years in our laboratory from malignant mammary (MFM-223) and endometrial (MFE-296) tumors supplementing the small number of androgen-responsive cell lines published so far. In this paper some aspects of the role of androgens in these two types of hormone responsive female cancers are presented. The proliferation of ZR-75-1, MFM-223 and MFE-296 cells is inhibited by androgens. The progestin medroxyprogesterone acetate inhibits the proliferation of estrogen- and progesterone receptor negative MFM-223 cells via the androgen receptor. Some steroid metabolites with distinct estrogenic properties like androst-5-ene-3 beta,17 beta-diol possess androgenic properties in this model system. Androgens stimulate the in vitro secretion of gross cystic disease fluid proteins by human mammary cancer cells. These proteins are normally found in benign breast cysts in vivo. The occurrence of gross cystic disease is correlated with an increased risk of breast cancer. The AR is autoregulated in MFM-223 mammary cancer cells on the protein and mRNA level. In MFE-296 cells with endometrial origin AR protein was increased after incubation with androgens.

Androgen Antagonists↗
PubMed2004

Role of the androgen receptor in skeletal homeostasis: the androgen-resistant testicular feminized male mouse model.

UNLABELLED: The role of androgen receptor-mediated androgen action on bone was investigated in testicular feminized male (Tfm) mice. Cortical bone was found to be unresponsive to testosterone (T) in orchidectomized Tfm mice, whereas cortical thickness as well as trabecular BMD and structure were fully maintained by T in the corresponding Tabby control mice. These data show an essential role for androgen receptor-mediated androgen action in periosteal bone formation. INTRODUCTION: Androgens can affect the male skeleton both directly-through activation of the androgen receptor (AR)-and indirectly-through stimulation of estrogen receptors after aromatization. We assessed the importance of AR-mediated androgen action on bone in a mouse model of androgen resistance. MATERIALS AND METHODS: Eight-week-old androgen-resistant testicular feminized male (Tfm) and Tabby control mice were orchidectomized (ORX) and treated for 4 weeks with a slow-release testosterone (T) pellet (delivering 167 microg/day) or a placebo pellet. A comprehensive analysis of the skeletal effects of androgen deficiency and replacement was performed using histomorphometry, QCT, and biochemical assessment of bone turnover. RESULTS: As expected, T increased trabecular BMD, volume, number, and width in ORX Tabby mice. In ORX Tfm mice, however, T had less effect on trabecular BMD and no effect on trabecular bone structure. T action on trabecular bone was associated with opposite changes in bone turnover: trabecular and endocortical bone turnover and serum levels of osteocalcin were all reduced by T in ORX Tabby mice, but not in ORX Tfm mice. T also increased cortical thickness (+16%), area, and density in ORX Tabby mice, but not in Tfm mice, resulting in greater bone strength in the Tabby control strain. The positive effects of T on cortical bone reflected a stimulatory effect on periosteal bone formation (+137%), which was again absent in Tfm mice. CONCLUSIONS: These data show that, in male mice, AR-mediated T action is essential for periosteal bone formation and contributes to trabecular bone maintenance.

Androgen-Insensitivity Syndrome↗
PubMed1994

Cooperative binding of androgen receptors to two DNA sequences is required for androgen induction of the probasin gene.

The functional and structural interactions of two androgen receptor-binding sites in the 5'-flanking DNA of the rat probasin gene were determined. Deletion mapping and DNase I footprinting analysis had previously identified two androgen receptor-binding sites (ARBS) necessary for androgen induction of the probasin gene: ARBS-1, which resembled a glucocorticoid-responsive element, and ARBS-2, which had a unique sequence. In this study, maximal androgen induction in transient transfection studies only occurred when both sites were present. Neither binding site functioned independently, and deletion of the DNA sequence between the sites resulted in a 60% loss of androgen inducibility. Moreover, point mutations in either ARBS-1 or ARBS-2 led to > 90% loss in activity. Scatchard analysis indicated that ARBS-1 and ARBS-2 bound a synthetic androgen receptor, AR2, with Kd values of 20.0 and 6.7 nM, respectively. Consistent with the higher affinity, ARBS-2 bound AR2 at half the threshold concentration (200 ng) of that required in reciprocal DNase I footprinting experiments with ARBS-1. By comparison, protection occurred at a much lower threshold concentration of AR2 (60 ng) and to the same extent over each site when both sites were present, suggesting a cooperative interaction between the two sites. The cooperative effect was further substantiated when a point mutation in ARBS-1 blocked AR2 binding not only to ARBS-1, but also to ARBS-2. Similarly, a point mutation in ARBS-2 also prevented receptor binding to both sites. Androgen-specific regulation of probasin gene transcription therefore required an androgen-responsive region (positions -286 and +28) containing two androgen receptor-binding sites, where the binding of the androgen receptor to both sites occurred in a cooperative, mutually dependent manner.

Androgen-Binding Protein↗
PubMed2005

Expression of androgen receptor coactivator ARA70/ELE1 in androgenic alopecia.

BACKGROUND: Androgens have been implicated in androgenic alopecia as evidenced by the increased cutaneous expression of androgen receptor (AR), 5alpha-reductase, and decreased aromatase. Abnormalities of the AR-signal transduction pathway probably participate in the development of androgenic alopecia. ARA70/ELE1 is an AR coactivator with two isoforms, one full-length form (ARA70alpha/ELE1alpha), and an internally deleted form (ARA70beta/ELE1beta). We decided to examine the cutaneous expression of both isoforms in male androgenic alopecia. METHODS: Formalin-fixed, paraffin-embedded tissue sections from seven subjects with androgenic alopecia with matched punch biopsies from non-balding and balding areas were examined by in situ hybridization. RESULTS: Expression of at least one of the two probes for ARA70/ELE1 was present in all phases of the hair-growth cycle in all epithelial hair structures except for the inner root sheath. The dermal papilla and hair bulb expressed only the short (beta) but not the long (alpha) form of ARA70/ELE1. In situ labeling for ARA70beta/ELE1beta was weaker in the dermal papilla of balding recipient areas than those from donor ones. CONCLUSIONS: Our data further support that the hair growth is regulated by androgens. The differential expression pattern of ARA70/ELE1 suggests that this key androgen receptor coactivator is involved in androgenic alopecia. Lee P, Zhu C-C, Sadick NS, Diwan AH, Zhang PS, Liu JS, Prieto VG. Expression of androgen receptor coactivator ARA70/ELE1 in androgenic alopecia.

Alopecia↗
PubMedDate not supplied

Apoptosis in androgen-independent mouse mammary tumor cells induced by 5-fluorodeoxyuridine but not by androgen withdrawal.

Androgen-dependent tumors eventually progress to independent tumors after androgen withdrawal. Androgen-dependent SC 115 cells could not grow in serum free culture without testosterone. Androgen-independent CS 2 cells, however, could grow whether androgen was present in the media or not. Based upon the temporal sequence of DNA fragmentation, morphological changes and loss of cell viability, androgen withdrawal did not induce the programmed cell death (apoptosis) of CS 2 cells in serum free culture. However, CS 2 cells as well as SC 115 cells retained the ability to undergo apoptosis with 5-fluorodeoxyuridine (FUdR) treatment. Northern blot analysis was used to identify a series of genes and whether the expressions of these per cell changed during apoptotic pathway (i.e. testosterone repressed prostatic message-2; TRPM-2, transforming growth factor-beta 1; TGF-beta 1, glucose regulated 78 kilodalton protein; GRP-78). Although the expression of these genes was increased in SC 115 cells after androgen depletion, none of the genes were induced by androgen withdrawal in CS 2 cells. During the apoptotic process induced by FUdR, mRNA expression of these genes was increased in CS 2 cells as well as in SC 115 cells. These results demonstrate that androgen-independent CS 2 cells do not undergo apoptosis induced by androgen withdrawal, but retain the ability to undergo apoptosis by FUdR. The apoptotic pathway is same whether the cells are androgen-dependent or independent.

Animals↗
PubMed1996

Androgen spares androgen-insensitive motoneurons from apoptosis in the spinal nucleus of the bulbocavernosus in rats.

The spinal nucleus of the bulbocavernosus (SNB) is a sexually dimorphic motor nucleus in the rat lumbar spinal cord. The sex difference arises through the androgenic sparing of the motoneurons and their target muscles from ontogenetic cell death. Indirect evidence suggests that androgen acts on the target muscles rather than directly on SNB motoneurons to spare them from death. The testicular feminization mutation (Tfm), a defect in the androgen receptor (AR), blocks androgenic sparing of SNB motoneurons and their targets. The pattern of AR immunocytochemistry was previously found to be different in adult Tfm and wild-type rats: immunostaining was nuclear in most SNB cells of wild-type rats, but very few SNB cells display nuclear AR immunostaining in affected Tfm rats. Because the Tfm mutation is carried on the X chromosome, random X inactivation during development makes female carriers of Tfm (+/Tfm) genetic mosaics for androgen sensitivity. Tfm carriers, their wild-type sisters, and affected Tfm males were treated with perinatal testosterone and immunocytochemistry was used to detect androgen receptor in the SNB when the rats reached adulthood. Mosaic females could be distinguished from their wild-type sisters by external morphology. In such perinatally androgenized mosaics, adult SNB cells were equally divided between wild-type and Tfm genotype, as indicated by AR immunocytochemistry. In contrast, the pattern of AR immunocytochemistry in target muscles of mosaics appeared similar to that of wild-type females. These results indicate that early androgen spared both androgen-sensitive and -insensitive motoneurons from cell death, confirming a site of androgen action other than the motoneurons themselves.

Androgens↗
PubMed2006

Development of a stickleback kidney cell culture assay for the screening of androgenic and anti-androgenic endocrine disrupters.

Issues raised by the presence in the environment of chemicals able to mimic or antagonize the action of androgenic hormones are of growing concern. Here we report the development of a novel in vitro test for the screening of (anti-)androgenic chemicals, based on primary cultures of stickleback kidney cells that produce a protein, the spiggin, in response to androgenic stimulation. Cell spiggin content was measured by ELISA. Comparison between cell cultures from quiescent males, photoperiodically stimulated males, control females and dihydrotestosterone (DHT)-primed females led to the selection of cell cultures from DHT-primed females for the development of a standardized protocol. 48h of treatment with androgens proved to be sufficient to induce concentration-dependent increase in spiggin cell content with a high sensitivity. DHT induced a significant spiggin increase at 10(-12)M, while testosterone (T) and the teleost specific androgen 11-ketotestosterone (11-KT) had a significant effect at 10(-10)M. Maximal responses were obtained with 10(-8)M DHT and 10(-6)M T and 11-KT. This indicates a higher sensitivity to DHT than to T and 11-KT, in agreement with previous data on stickleback kidney androgen receptor affinity. No effect was observed with other steroids or thyroid hormone, indicating the androgen specificity of the test. The anabolic steroid 17beta-Trenbolone (TB) was able to stimulate spiggin synthesis in a concentration-dependent manner with a significant effect at a concentration as low as 10(-10)M, and a maximal effect at 10(-6)M. The synthetic human androgen receptor antagonist, flutamide had no effect alone, but concentration-dependently inhibited the stimulatory effect of 10(-8)M 11-KT with a complete inhibition at 10(-6)M flutamide. This cell culture system provides an innovative tool for the rapid and sensitive screening of androgenic and anti-androgenic properties of environmental contaminants.

Anabolic Agents↗
PubMed2002

Anabolic steroids, testosterone-precursors and virilizing androgens induce distinct activation profiles of androgen responsive promoter constructs.

Different androgens, e.g. virilizing androgens such as testosterone and its precursors as well as synthetic anabolic steroids, respectively, induce diverse biological effects. The molecular basis for this variety in biological actions, however, is not well understood. We hypothesized that this variability of actions may be due to steroid-specific target gene expression profiles following androgen receptor (AR)-activation. Therefore, we investigated androgen receptor dependent transactivation of three structurally different androgen responsive promoter constructs ((ARE)(2)TATA-luc, MMTV-luc, GRE-OCT-luc) in co-transfected Chinese hamster ovary (CHO)-cells as an artificial model simulating different natural target genes. Three virilizing androgens (dihydrotestosterone, testosterone, methyltrienolone), three anabolic steroids (oxandrolone, stanozolol, nandrolone) and two testosterone-precursors of gonadal and adrenal origin (dehydroepiandrosterone, androstenedione) were used as ligands (0.001-100 nM). All steroids proved to be potent activators of the AR. Remarkably, anabolic steroids and testosterone-precursors showed characteristic promoter activation profiles distinct from virilizing androgens with significantly lower (ARE)(2)TATA-luc activation. Hierarchical clustering based on similarity of activation profiles lead to a dendrogram with two major branches: first virilizing androgens, and second anabolics/testosterone-precursors. We conclude that steroid-specific differences in gene transcription profiles due to androgen receptor activation could contribute to differences in biological actions of androgens.

Adjuvants, Immunologic↗
PubMed1997

5alpha-reduction of norethisterone enhances its binding affinity for androgen receptors but diminishes its androgenic potency.

Norethisterone (NET), a 19-nor synthetic progestin, undergoes enzyme-mediated 5alpha-reduction and exerts potent androgenic effects in target organs. To investigate its mode of androgenic action we examined, in a comparative manner, the in vitro metabolism of NET and testosterone (T), as well as the binding affinities to androgen receptors (AR) and the androgenic potency of NET, T, and their 5alpha-reduced derivatives. Bioconversion of [3H]-NET and [3H]-T was studied in rat prostate homogenates, AR binding affinity was assessed in rat ventral prostates using [3H]-mibolerone as the radioligand, and the androgenic potency was evaluated by the increase of beta-glucuronidase activity in the mouse kidney, and by the growth of accessory sex organs in castrated male rats. The results demonstrated that 5alpha-NET displayed a higher AR binding affinity but a significantly lower androgenic potency than unchanged NET. The bioconversion studies indicated that the metabolism of NET was similar to that of T, although to a lesser extent, thus ruling out the possibility that the synthetic progestin metabolizes rapidly into less active derivatives. To investigate the nature of the paradoxical effect of 5alpha-reduction upon the NET molecule, the interaction with AR and the androgenic potency of T, 19-nortestosterone (19norT), 17alpha-ethynyl testosterone (ET) and their 5alpha-reduced derivatives were examined. The results of AR binding studies revealed that 5alpha-reduction of T and ET significantly enhanced their affinities, and that the 5alpha-derivative of 19norT displayed a similar binding affinity to that exhibited by 19norT. In terms of biological activity, the results showed that 5alpha-reduction of T and 19norT significantly increased their androgenic potency, whereas 5alpha-reduction of ET resulted in a significant diminution of its androgenicity in a manner similar to that observed with the 5alpha-reduction of NET. When NET and 19norT were simultaneously administered with 5alpha-dihydrotestosterone they exhibited a potent synandrogenic activity, an effect that was cancelled by their 5alpha-reduction. Interestingly, ET displayed an antiandrogenic activity, an effect that was also suppressed by its 5alpha-reduction. The overall results demonstrated a distinctive, paradoxical effect of 5alpha-reduction upon the NET molecule, which was different from that seen in naturally occurring androgens, and which suggests that the presence of the 17alpha-ethynyl group plays a key role in this phenomenon. The data provided further evidence that the metabolism of synthetic contraceptive progestins modulates the expression of their hormone-like actions.

Androgens↗
PubMed1993

Androgen induction of a human prostate-specific kallikrein, hKLK2: characterization of an androgen response element in the 5' promoter region of the gene.

The human prostate-specific kallikreins, human glandular kallikrein-1 (hKLK2) and prostate-specific antigen (hKLK3), have been shown to be regulated by androgens. To determine whether the androgen induction of these genes is transcriptionally regulated via an androgen response element, an hKLK2 promoter DNA fragment was linked to a promoterless chloramphenicol acetyltransferase (CAT) reporter gene and cotransfected with an androgen receptor expression vector in an androgen receptor-less human prostate cell line, PC-3. Dose response and steroid specificity experiments showed that the hKLK2 promoter confers androgen receptor-mediated gene induction in a ligand-specific manner. Moreover, 5' deletion constructs of the hKLK2 promoter DNA and internal deletion constructs devoid of the 5' half-site of the putative androgen responsive element (ARE) were used to show that the putative ARE is indeed acting as a functional ARE in prostate cells. In addition, multiple AREs from both hKLK2 and hKLK3 were able to reconstitute androgenic induction, further strengthening the argument that the AREs are functional. Although previous studies have shown that hKLK3 mRNA is expressed at a higher level than that of hKLK2, our results suggest that the hKLK2 ARE may have higher androgenic inducibility than the hKLK3 ARE. These results suggest that other cis-acting elements may be involved in coordinating in vivo androgenic induction of hKLK2 and hKLK3 genes.

Androgens↗
PubMed2000

Glucocorticoids can promote androgen-independent growth of prostate cancer cells through a mutated androgen receptor.

The androgen receptor (AR) is involved in the development, growth and progression of prostate cancer (CaP). CaP often progresses from an androgen-dependent to an androgen-independent tumor, making androgen ablation therapy ineffective. However, the mechanisms for the development of androgen-independent CaP are unclear. More than 80% of clinically androgen-independent prostate tumors show high levels of AR expression. In some CaPs, AR levels are increased because of gene amplification and/or overexpression, whereas in others, the AR is mutated. Nonetheless, the involvement of the AR in the transition of CaP to androgen-independent growth and the subsequent failure of endocrine therapy are not fully understood. Here we show that in CaP cells from a patient who failed androgen ablation therapy, a doubly mutated AR functioned as a high-affinity cortisol/cortisone receptor (ARccr). Cortisol, the main circulating glucocorticoid, and its metabolite, cortisone, both equally stimulate the growth of these CaP cells and increase the secretion of prostate-specific antigen in the absence of androgens. The physiological concentrations of free cortisol and total cortisone in men greatly exceed the binding affinity of the ARccr and would activate the receptor, promoting CaP cell proliferation. Our data demonstrate a previously unknown mechanism for the androgen-independent growth of advanced CaP. Understanding this mechanism and recognizing the presence of glucocorticoid-responsive AR mutants are important for the development of new forms of therapy for the treatment of this subset of CaP.

Aldosterone↗
PubMed2004

Applicability of the SHBG androgen sensitivity test in the differential diagnosis of 46,XY gonadal dysgenesis, true hermaphroditism, and androgen insensitivity syndrome.

The sex hormone-binding globulin (SHBG) androgen sensitivity test has been used as a simple method to assess androgen receptor function in vivo. After a short term oral administration of the anabolic-androgenic steroid stanozolol the mean nadir serum concentration of SHBG is used as a measure of androgen response. We performed this test in order to evaluate its applicability in 16 patients with intersexual genital status: eleven with 46,XY gonadal dysgenesis and three with true hermaphroditism (group I), and in two patients with androgen insensitivity syndrome (AIS, group II). Ten healthy adult volunteers served as controls. In the two patients with AIS (group II) we found a diminished decrease of serum SHBG to 80.1 % and 80.7 %, respectively, indicating slight residual androgen responsiveness. In eleven patients of group I who were not on hormone replacement therapy, a mean nadir level of 51.7 +/- 8.7 % was found. In the controls the mean nadir serum SHBG level was significantly higher (62.7 +/- 5.2 %), probably due to interference of endogenous androgens and contraceptive medication with the stanozolol-induced SHBG decrease. In three gonadectomised patients who were on hormone replacement therapy the initial SHBG concentration was increased (513.5 +/- 239.1 nmol/l); the mean nadir SHBG concentration of 45.6 +/- 9.8 % of the initial level indicates an increased sensitivity of the test in patients in whom the counteracting ovarian androgens are absent. Our findings confirm that under standard test conditions the SHBG androgen sensitivity test is a simple diagnostic tool for the detection of androgen receptor malfunction.

Adolescent↗
PubMed2006

Ligand-independent androgen receptor activity is activation function-2-independent and resistant to antiandrogens in androgen refractory prostate cancer cells.

Androgen ablation inhibits androgen receptor (AR) activity and is as an effective treatment for advanced prostate cancer (PCa). Invariably, PCa relapses in a form resistant to further hormonal manipulations. Although this stage of the disease is androgen-refractory, or androgen depletion-independent (ADI), most tumors remain AR-dependent through aberrant mechanisms of AR activation. We employed the LNCaP/C4-2 model of PCa progression to study AR activity in androgen-dependent and ADI PCa cells. In this report, we show that the AR is transcriptionally inactive in androgen-dependent LNCaP cells in the absence of androgens. However, in ADI C4-2 cells, the AR displays a high level of constitutive, androgen-independent transcriptional activity. To study the mechanisms of ligand-dependent and ligand-independent AR activation in these AR-expressing cells, we generated a reporter system based on swapping the DNA binding domain of the AR with the DNA binding domain of the yeast Gal4 transcription factor. In androgen-dependent PCa cells, the well characterized C-terminal AR activation function-2 (AF-2) domain was critical for strong, ligand-dependent activity. Conversely, in ADI PCa cells, constitutive, ligand-independent AR activity was AF-2-independent but instead dependent on N-terminal AR domains. Importantly, the ligand- and AF-2-independent mode of AR activation observed in ADI PCa cells was completely resistant to the antiandrogen, bicalutamide. Our data thus demonstrate that the AR can inappropriately activate transcription in ADI PCa cells via mechanisms that are resistant to castration and AR antagonism, the two modes of androgen ablation used to treat advanced PCa.

Androgen Antagonists↗
PubMed1999

Prostate cancer cell cycle regulators: response to androgen withdrawal and development of androgen independence.

BACKGROUND: Androgen withdrawal is a standard therapy for prostate cancer that results in a decrease in tumor volume and a decline in serum prostate-specific antigen in the majority of patients. To understand the factors associated with regression of prostate cancers after androgen withdrawal, we studied cell cycle regulator changes in the CWR22 human prostate cancer xenograft model. METHODS: Established tumors in nude athymic BALB/c mice were sampled at various times after androgen withdrawal and after the development of androgen independence. Changes in the expression of cell cycle regulators were categorized into early and mid-to-late events. RESULTS AND CONCLUSIONS: Early events included a decrease in androgen receptor expression, followed by a short-term increase in expression of the p53 and p21/WAF1 proteins and a marked decrease in the Ki67 proliferative index. Mid-to-late events included progressive and sustained increases in p27 and p16 protein expression, a decrease in retinoblastoma protein expression, and an increase in the transcription factor E2F1. Changes in apoptosis (programmed cell death) were not observed at any time after androgen withdrawal. These data suggest that androgen withdrawal results in a cell stress response, in which increased p53 protein produces a cell cycle arrest, without activation of p53-mediated apoptosis. The proliferative index is further decreased through the action of the cyclin-dependent kinase inhibitors p27 and p16. Androgen-independent sublines emerged 80-400 days after androgen withdrawal, and these sublines had variable growth phenotypes but were associated with mdm2 protein overexpression and increased expression of cyclin D1. These results indicate that tumor regression in this human prostate cancer model is due to cell cycle arrest rather than to apoptosis and that the emergence of androgen independence is associated with a release from cell cycle arrest.

Androgens↗
PubMed2001

Androgen receptor signaling in androgen-refractory prostate cancer.

Prostate cancer is the second most prevalent cancer in males in the United States. Standard therapy relies on removing, or blocking the actions of, androgens. In most cases, this therapy results in a regression of the cancer because the prostate and most primary prostate tumors depend on androgens for growth and the avoidance of apoptosis. However, a portion of the cancers eventually relapse, at which point they are termed "androgen refractory" and can no longer be cured by conventional therapy of any type. The precise molecular events that lead from androgen-sensitive prostate cancer to androgen-refractory prostate cancer are, therefore, of great interest. This review seeks to identify specific molecular events that may be linked directly to the progression to androgen-refractory cancer. Some of the mechanisms appear to involve the androgen receptor (AR) directly and include mutations in, or amplification of, the AR gene in a manner that allows the AR to respond to low doses of androgens, other steroids, or antiandrogens. In a less direct manner, coactivators may increase the sensitivity of the AR to androgens and even other nonandrogenic substances through a number of mechanisms. Additional indirect mechanisms that do not result from mutation of the AR may involve activation of the AR by peptide growth factors or cytokines or may involve bypassing the AR entirely via other cellular pathways. Identification of the role of these mechanisms in the progression to androgen-refractory prostate cancer is critical for developing therapies capable of curing this disease.

Androgens↗