Expression of recombinant androgen receptor in cultured mammalian cells

New advances of the androgen receptor in prostate cancer: report from the 1st International Androgen Receptor Symposium

The androgen receptor (AR) is a crucial player in various aspects of male reproduction and has been associated with the development and progression of prostate cancer (PCa). Therefore, the protein is the linchpin of current PCa therapies. Despite great research efforts, the AR signaling pathway has still not been deciphered, and the emergence of resistance is still the biggest problem in PCa treatment. To discuss the latest developments in AR research, the "1st International Androgen Receptor Symposium" offered a forum for the exchange of clinical and scientific innovations around the role of the AR in prostate cancer (PCa) and to stimulate new collaborative interactions among leading scientists from basic, translational, and clinical research. The symposium included three sessions covering preclinical studies, prognostic and diagnostic biomarkers, and ongoing prostate cancer clinical trials. In addition, a panel discussion about the future direction of androgen deprivation therapy and anti-AR therapy in PCa was conducted. Therefore, the newest insights and developments in therapeutic strategies and biomarkers are discussed in this report.

Up-Regulation of Follistatin-Like 1 By the Androgen Receptor and Melanoma Antigen-A11 in Prostate Cancer

BACKGROUND

High affinity androgen binding to the androgen receptor (AR) activates genes required for male sex differentiation and promotes the development and progression of prostate cancer. Human AR transcriptional activity involves interactions with coregulatory proteins that include primate-specific melanoma antigen-A11 (MAGE-A11), a coactivator that increases AR transcriptional activity during prostate cancer progression to castration-resistant/recurrent prostate cancer (CRPC).

METHODS

Microarray analysis and quantitative RT-PCR were performed to identify androgen-regulated MAGE-A11-dependent genes in LAPC-4 prostate cancer cells after lentivirus shRNA knockdown of MAGE-A11. Chromatin immunoprecipitation was used to assess androgen-dependent AR recruitment, and immunocytochemistry to localize an androgen-dependent protein in prostate cancer cells and tissue and in the CWR22 human prostate cancer xenograft.

RESULTS

Microarray analysis of androgen-treated LAPC-4 prostate cancer cells indicated follistatin-like 1 (FSTL1) is up-regulated by MAGE-A11. Androgen-dependent up-regulation of FSTL1 was inhibited in LAPC-4 cells by lentivirus shRNA knockdown of AR or MAGE-A11. Chromatin immunoprecipitation demonstrated AR recruitment to intron 10 of the FSTL1 gene that contains a classical consensus androgen response element. Increased levels of FSTL1 protein in LAPC-4 cells correlated with higher levels of MAGE-A11 relative to other prostate cancer cells. FSTL1 mRNA levels increased in CRPC and castration-recurrent CWR22 xenografts in association with predominantly nuclear FSTL1. Increased nuclear localization of FSTL1 in prostate cancer was suggested by predominantly cytoplasmic FSTL1 in benign prostate epithelial cells and predominantly nuclear FSTL1 in epithelial cells in CRPC tissue and the castration-recurrent CWR22 xenograft. AR expression studies showed nuclear colocalization of AR and endogenous FSTL1 in response to androgen.

CONCLUSION

AR and MAGE-A11 cooperate in the up-regulation of FSTL1 to promote growth and progression of CRPC. Prostate 77:505-516, 2017. © 2016 Wiley Periodicals, Inc.

Androgen receptor regulation by histone methyltransferase Suppressor of variegation 3-9 homolog 2 and Melanoma antigen-A11

Androgen receptor (AR) transcriptional activity depends on interactions between the AR NH₂-terminal region and transcriptional coregulators. A yeast two-hybrid screen of a human testis library using predicted α-helical NH₂-terminal fragment AR-(370-420) as bait identified suppressor of variegation 3-9 homolog 2 (SUV39H2) histone methyltransferase as an AR interacting protein. SUV39H2 interaction with AR and the AR coregulator, melanoma antigen-A11 (MAGE-A11), was verified in two-hybrid, in vitro glutathione S-transferase affinity matrix and coimmunoprecipitation assays. Fluorescent immunocytochemistry colocalized SUV39H2 and AR in the cytoplasm without androgen, in the nucleus with androgen, and with MAGE-A11 in the nucleus independent of androgen. Chromatin immunoprecipitation using antibodies raised against SUV39H2 demonstrated androgen-dependent recruitment of AR and SUV39H2 to the androgen-responsive upstream enhancer of the prostate-specific antigen gene. SUV39H2 functioned cooperatively with MAGE-A11 to increase androgen-dependent AR transcriptional activity. SUV39H2 histone methyltransferase is an AR coactivator that increases androgen-dependent transcriptional activity through interactions with AR and MAGE-A11.

Melanoma antigen-A11 regulates substrate-specificity of Skp2-mediated protein degradation

Melanoma antigen-A11 (MAGE-A11) is a proto-oncogene involved in androgen receptor signaling and androgen-dependent cell growth. In this report we provide evidence that MAGE-A11 interacts with Skp2 (S phase kinase-associated protein), the substrate recognition protein of the Skp1-Cullin1-F-box E3 ubiquitin ligase, and with Skp2 binding protein, cyclin A. A similar cyclin A binding motif in MAGE-A11 and Skp2 was consistent with a competitive relationship between MAGE-A11 and Skp2 in binding cyclin A. Skp2 inhibited MAGE-A11 interaction with cyclin A. Differential effects of MAGE-A11 on Skp2-mediated protein degradation were also revealed. MAGE-A11 increased Skp2-mediated degradation of cyclin A and retinoblastoma-related protein p130. In contrast, MAGE-A11 decreased Skp2-mediated degradation of E2F1 and Skp2 self-ubiquitination. Stabilization of E2F1 by MAGE-A11 was associated with sequestration and inactivation of Skp2 through the formation of an E2F1-MAGE-A11-Skp2 complex. We conclude that direct interactions of MAGE-A11 with Skp2 and cyclin A regulate the substrate-specificity of Skp2-mediated protein degradation.

Post-translational Down-regulation of Melanoma Antigen-A11 (MAGE-A11) by Human p14-ARF Tumor Suppressor

X-linked primate-specific melanoma antigen-A11 (MAGE-A11) is a human androgen receptor (AR) coactivator and proto-oncogene expressed at low levels in normal human reproductive tract tissues and at higher levels in castration-resistant prostate cancer where it is required for androgen-dependent cell growth. In this report, we show that MAGE-A11 is targeted for degradation by human p14-ARF, a tumor suppressor expressed from an alternative reading frame of the p16 cyclin-dependent kinase inhibitor INK4a/ARF gene. MAGE-A11 degradation by the proteasome was mediated by an interaction with p14-ARF and was independent of lysine ubiquitination. A dose-dependent inverse relationship between MAGE-A11 and p14-ARF correlated with p14-ARF inhibition of the MAGE-A11-induced increase in androgen-dependent AR transcriptional activity and constitutive activity of a splice variant-like AR. Reciprocal stabilization between MAGE-A11 and AR did not protect against degradation promoted by p14-ARF. p14-ARF prevented MAGE-A11 interaction with the E2F1 oncoprotein and inhibited the MAGE-A11-induced increase in E2F1 transcriptional activity. Post-translational down-regulation of MAGE-A11 promoted by p14-ARF was independent of HDM2, the human homologue of mouse double minute 2, an E3 ubiquitin ligase inhibited by p14-ARF. However, MAGE-A11 had a stabilizing effect on HDM2 in the absence or presence of p14-ARF and cooperated with HDM2 to increase E2F1 transcriptional activity in the absence of p14-ARF. We conclude that degradation of MAGE-A11 promoted by the human p14-ARF tumor suppressor contributes to low levels of MAGE-A11 in nontransformed cells and that higher levels of MAGE-A11 associated with low p14-ARF increase AR and E2F1 transcriptional activity and promote the development of castration-resistant prostate cancer.

Mechanism of androgen receptor corepression by CKβBP2/CRIF1, a multifunctional transcription factor coregulator expressed in prostate cancer

The transcription factor coregulator Casein kinase IIβ-binding protein 2 or CR6-interacting factor 1 (CKβBP2/CRIF1) binds the androgen receptor (AR) in prostate cancer cells and in response to dihydrotestosterone localizes with AR on the prostate-specific antigen gene enhancer, but does not bind DNA suggesting CKβBP2/CRIF1 localization in chromatin is determined by AR. In this study we show also that CKβBP2/CRIF1 inhibits wild-type AR and AR N-terminal transcriptional activity, binds to the AR C-terminal region, inhibits interaction of the AR N- and C-terminal domains (N/C interaction) and competes with p160 coactivator binding to the AR C-terminal domain, suggesting CKβBP2/CRIF1 interferes with AR activation functions 1 and 2. CKβBP2/CRIF1 is expressed mainly in stromal cells of benign prostatic hyperplasia and in stroma and epithelium of prostate cancer. CKβBP2/CRIF1 protein is increased in epithelium of androgen-dependent prostate cancer compared to benign prostatic hyperplasia and decreased slightly in castration recurrent epithelium compared to androgen-dependent prostate cancer. The multifunctional CKβBP2/CRIF1 is a STAT3 interacting protein and reported to be a coactivator of STAT3. CKβBP2/CRIF1 is expressed with STAT3 in prostate cancer where STAT3 may help to offset the AR repressor effect of CKβBP2/CRIF1 and allow AR regulation of prostate cancer growth.

Proto-oncogene activity of melanoma antigen-A11 (MAGE-A11) regulates retinoblastoma-related p107 and E2F1 proteins

Melanoma antigen-A11 (MAGE-A11) is a low-abundance, primate-specific steroid receptor coregulator in normal tissues of the human reproductive tract that is expressed at higher levels in prostate cancer. Increased expression of MAGE-A11 enhances androgen receptor transcriptional activity and promotes prostate cancer cell growth. Further investigation into the mechanisms of MAGE-A11 function in prostate cancer demonstrated interactions with the retinoblastoma-related protein p107 and Rb tumor suppressor but no interaction with p130 of the Rb family. MAGE-A11 interaction with p107 was associated with transcriptional repression in cells with low MAGE-A11 and transcriptional activation in cells with higher MAGE-A11. Selective interaction of MAGE-A11 with retinoblastoma family members suggested the regulation of E2F transcription factors. MAGE-A11 stabilized p107 by inhibition of ubiquitination and linked p107 to hypophosphorylated E2F1 in association with the stabilization and activation of E2F1. The androgen receptor and MAGE-A11 modulated endogenous expression of the E2F1-regulated cyclin-dependent kinase inhibitor p27(Kip1). The ability of MAGE-A11 to increase E2F1 transcriptional activity was similar to the activity of adenovirus early oncoprotein E1A and depended on MAGE-A11 interactions with p107 and p300. The immunoreactivity of p107 and MAGE-A11 was greater in advanced prostate cancer than in benign prostate, and knockdown with small inhibitory RNA showed that p107 is a transcriptional activator in prostate cancer cells. These results suggest that MAGE-A11 is a proto-oncogene whose increased expression in prostate cancer reverses retinoblastoma-related protein p107 from a transcriptional repressor to a transcriptional activator of the androgen receptor and E2F1.

Melanoma antigen-A11 (MAGE-A11) enhances transcriptional activity by linking androgen receptor dimers

Prostate cancer growth and progression depend on androgen receptor (AR) signaling through transcriptional mechanisms that require interactions with coregulatory proteins, one of which is the primate-specific steroid receptor coregulator melanoma antigen-A11 (MAGE-A11). In this report, we provide evidence how increased expression of MAGE-A11 during prostate cancer progression enhances AR signaling and prostate cancer growth. MAGE-A11 protein levels were highest in castration-recurrent prostate cancer. The cyclic AMP-induced increase in androgen-dependent and androgen-independent AR transcriptional activity correlated with an increase in MAGE-A11 and was inhibited by silencing MAGE-A11 expression. MAGE-A11 mediated synergistic AR transcriptional activity in LAPC-4 prostate cancer cells. The ability of MAGE-A11 to rescue transcriptional activity of complementary inactive AR mutants and promote coimmunoprecipitation between unlike forms of AR suggests that MAGE-A11 links transcriptionally active AR dimers. A model for the AR·MAGE-A11 multidimeric complex is proposed in which one AR FXXLF motif of the AR dimer engages in the androgen-dependent AR NH(2)- and carboxyl-terminal interaction, whereas the second FXXLF motif region of the AR dimer interacts with dimeric MAGE-A11. The AR·MAGE-A11 multidimeric complex accounts for the dual functions of the AR FXXLF motif in the androgen-dependent AR NH(2)- and carboxyl-terminal interaction and binding MAGE-A11 and for synergy between reported AR splice variants and full-length AR. We conclude that the increased expression of MAGE-A11 in castration-recurrent prostate cancer, which is enhanced by cyclic AMP signaling, increases AR-dependent growth of prostate cancer by MAGE-A11 forming a molecular bridge between transcriptionally active AR dimers.

Androgen receptor exon 1 mutation causes androgen insensitivity by creating phosphorylation site and inhibiting melanoma antigen-A11 activation of NH2- and carboxyl-terminal interaction-dependent transactivation

Naturally occurring germ line mutations in the X-linked human androgen receptor (AR) gene cause incomplete masculinization of the external genitalia by disrupting AR function in males with androgen insensitivity syndrome. Almost all AR missense mutations that cause androgen insensitivity syndrome are located in the highly structured DNA and ligand binding domains. In this report we investigate the functional defect associated with an AR exon 1 missense mutation, R405S, that caused partial androgen insensitivity. The 46,XX heterozygous maternal carrier had a wild-type Arg-405 CGC allele but transmitted an AGC mutant allele coding for Ser-405. At birth, the 46,XY proband had a bifid scrotum, hypospadias, and micropenis consistent with clinical stage 3 partial androgen insensitivity. Androgen-dependent transcriptional activity of AR-R405S expressed in CV1 cells was less than wild-type AR and refractory in androgen-dependent AR NH(2)- and carboxyl interaction transcription assays that depend on the coregulator effects of melanoma antigen-A11. This mutation created a Ser-405 phosphorylation site evident by the gel migration of an AR-R405S NH(2)-terminal fragment as a double band that converted to the wild-type single band after treatment with λ-phosphatase. Detrimental effects of the R405S mutation were related to the proximity of the AR WXXLF motif (433)WHTLF(437) required for melanoma antigen-A11 and p300 to stimulate transcriptional activity associated with the AR NH(2)- and carboxyl-terminal interaction. We conclude that the coregulator effects of melanoma antigen-A11 on the AR NH(2)- and carboxyl-terminal interaction amplify the androgen-dependent transcriptional response to p300 required for normal human male sex development in utero.

Structural features discriminate androgen receptor N/C terminal and coactivator interactions

Human androgen receptor (AR) transcriptional activity involves interdomain and coactivator interactions with the agonist-bound AR ligand binding domain (LBD). Structural determinants of the AR NH(2)- and carboxyl-terminal interaction between the AR NH(2)-terminal FXXLF motif and activation function 2 (AF2) in the LBD were shown previously by crystallography. In this report, we provide evidence for a region in AR LBD helix 12 outside the AF2 binding cleft that facilitates interactions with the FXXLF and LXXLL motifs. Mutagenesis of glutamine 902 to alanine in AR LBD helix 12 (Q902A) disrupted AR FXXLF motif binding to AF2, but enhanced coactivator LXXLL motif binding. Functional compensation for defective FXXLF motif binding by AR-Q902A was suggested by the slower dissociation rate of bound androgen. Functional importance of glutamine 902 was indicated by the charged residue germline mutation Q902R that caused partial androgen insensitivity, and a similar somatic mutation Q902K reported in prostate cancer, both of which increased the androgen dissociation rate and decreased AR transcriptional activity. High affinity equilibrium androgen binding was retained by alanine substitution mutations at Tyr-739 in AR LBD helix 5 or Lys-905 in helix 12 structurally adjacent to AF2, whereas transcriptional activity decreased and the androgen dissociation increased. Deleterious effects of these loss of function mutations were rescued by the helix stabilizing AR prostate cancer somatic mutation H874Y. Sequence NH(2)-terminal to the AR FXXLF motif contributed to the AR NH(2)- and carboxyl-terminal interaction based on greater AR-2-30 FXXLF motif peptide binding to the agonist-bound AR LBD than a shorter AR-20-30 FXXLF motif peptide. We conclude that helix 12 residues outside the AF2 binding cleft modulate AR transcriptional activity by providing flexibility to accommodate FXXLF or LXXLL motif binding.

Ligand competition binding assay for the androgen receptor

Evaluating endocrine activities of environmental chemicals or screening for new small molecule modulators of the androgen receptor (AR) transcription activity requires standardized and reliable assay procedures. Scintillation proximity assays (SPA) are sensitive and reliable techniques that are suitable for ligand competition binding assays. We have utilized a radiolabeled ligand competition binding assay for the androgen receptor (AR) that can be carried out in a 384-well format. This standardized, highly reproducible and low-cost assay has been automated for high-throughput screening (HTS) purposes.

Androgen receptor signaling and mutations in prostate cancer

Normal and neoplastic growth of the prostate gland are dependent on androgen receptor (AR) expression and function. Androgenic activation of the AR, in association with its coregulatory factors, is the classical pathway that leads to transcriptional activity of AR target genes. Alternatively, cytoplasmic signaling crosstalk of AR by growth factors, neurotrophic peptides, cytokines or nonandrogenic hormones may have important roles in prostate carcinogenesis and in metastatic or androgen-independent (AI) progression of the disease. In addition, cross-modulation by various nuclear transcription factors acting through basal transcriptional machinery could positively or negatively affect the AR or AR target genes expression and activity. Androgen ablation leads to an initial favorable response in a significant number of patients; however, almost invariably patients relapse with an aggressive form of the disease known as castration-resistant or hormone-refractory prostate cancer (PCa). Understanding critical molecular events that lead PCa cells to resist androgen-deprivation therapy is essential in developing successful treatments for hormone-refractory disease. In a significant number of hormone-refractory patients, the AR is overexpressed, mutated or genomically amplified. These genetic alterations maintain an active presence for a highly sensitive AR, which is responsive to androgens, antiandrogens or nonandrogenic hormones and collectively confer a selective growth advantage to PCa cells. This review provides a brief synopsis of the AR structure, AR coregulators, posttranslational modifications of AR, duality of AR function in prostate epithelial and stromal cells, AR-dependent signaling, genetic changes in the form of somatic and germline mutations and their known functional significance in PCa cells and tissues.

Gestational and neonatal-onset hypothyroidism alters androgen receptor status in rat prostate glands at adulthood

BACKGROUND

Infertility associated with congenital and early childhood hypothyroidism is an important reproductive health problem in men. Nevertheless, the exact mechanism underlying hypothyroidism-induced changes in the prostate gland, an androgen-dependent organ that contributes a significant portion of the seminal plasma remains obscure. The present study tested the hypothesis "transient gestational- or neonatal-onset hypothyroidism may have duration dependent and lobe specific effect on androgen receptor (AR) status in the prostate glands of adult rats."

METHODS

Hypothyroidism was induced in pregnant and lactating rats by feeding 0.05% methimazole (MMI) through drinking water during fetal and neonatal milestones of testicular and prostatic development. Pregnant dams had MMI exposure from 9th day post-coitum (dpc) to 14 dpc (group II) or 21 dpc (group III). Lactating mothers had MMI exposure from day 1 post-partum (dpp) to 14 dpp (group IV) or up to 29 dpp (group V). AR status in the dorsolateral and ventral prostate lobes (DLP and VP) of the pups was assessed by RT-PCR, western blot and radio receptor assay.

RESULTS

AR mRNA expression consistently decreased in the DLP of all groups, whereas it increased in VP of group III and V rats. AR protein consistently decreased in both DLP and VP of all experimental rats. AR nuclear ligand-binding activity diminished in groups II and IV, whereas it increased in groups III and V.

CONCLUSION

The results obtained support the proposed hypothesis and indicate that an optimum thyroid activity during pre- and neonatal period determines AR status in the prostate glands at adulthood.

Identification of SRC3/AIB1 as a preferred coactivator for hormone-activated androgen receptor

Transcription activation by androgen receptor (AR), which depends on recruitment of coactivators, is required for the initiation and progression of prostate cancer, yet the mechanisms of how hormone-activated AR interacts with coactivators remain unclear. This is because AR, unlike any other nuclear receptor, prefers its own N-terminal FXXLF motif to the canonical LXXLL motifs of coactivators. Through biochemical and crystallographic studies, we identify that steroid receptor coactivator-3 (SRC3) (also named as amplified in breast cancer-1 or AIB1) interacts strongly with AR via synergistic binding of its first and third LXXLL motifs. Mutagenesis and functional studies confirm that SRC3 is a preferred coactivator for hormone-activated AR. Importantly, AR mutations found in prostate cancer patients correlate with their binding potency to SRC3, corroborating with the emerging role of SRC3 as a prostate cancer oncogene. These results provide a molecular mechanism for the selective utilization of SRC3 by hormone-activated AR, and they link the functional relationship between AR and SRC3 to the development and growth of prostate cancer.

Characterization of a novel rat epididymal cell line to study epididymal function

The epididymis is an androgen-dependent organ that allows spermatozoa to become fully functional as they pass through this tissue. The specialized functions of the epididymis are mediated by interactions between epididymal epithelial cells and between epididymal cells and spermatozoa. Although the critical role of the epididymis in sperm maturation is well established, the mechanisms regulating cell-cell interactions remain poorly understood because of the lack of appropriate cell line models. We now report the characterization of a novel rat caput epididymal cell line (RCE) that was immortalized by transfecting primary cultures of rat epididymal cells with the simian virus 40 large T antigen. At the electron microscope level, the cell line was composed of epithelial principal cells with characteristics of in vivo cells; principal cells had well-developed Golgi apparatus, abundant endoplasmic reticulum cisternae, and few endosomes. RCE cells expressed the mRNAs coding for the androgen receptor, estrogen receptor alpha, and 4-ene-steroid-5-alpha-reductase types 1 and 2 as well as epididymal-specific markers Crisp-1 and epididymal retinoic acid binding protein. Epididymal retinoic acid binding protein expression was significantly induced with dihydrotestosterone, although this effect was not blocked by flutamide, suggesting that RCE cells are not androgen responsive. Neighboring cells formed tight and gap junctions characteristic of epididymal cells in vivo and expressed tight (occludin and claudin-1, -3, and -4) and gap junctional proteins (connexin-26, -30.3, -32, and -43). The RCE cell line displays many characteristics of epithelial principal cells, thus providing a model for studying epididymal cell functions.

Single-step purification of full-length human androgen receptor

The full-length human androgen receptor with an N-terminal biotin acceptor peptide tag was overexpressed in Spodoptera frugiperda cells in the presence of 1 µM dihydrotestosterone. Site-specific biotinylation of BAP was achieved in vivo by co-expression of E. coli biotin holoenzyme synthetase. The androgen receptor was purified by single-step affinity chromatography using Streptavidin Mutein Matrix under native conditions. The resultant protein was active, stable, 95% homogeneous, and we obtained sufficient yield for use in functional and structural studies.

Epidermal growth factor increases coactivation of the androgen receptor in recurrent prostate cancer

Growth of normal and neoplastic prostate is mediated by the androgen receptor (AR), a ligand-dependent transcription factor activated by high affinity androgen binding. The AR is highly expressed in recurrent prostate cancer cells that proliferate despite reduced circulating androgen. In this report, we show that epidermal growth factor (EGF) increases androgen-dependent AR transactivation in the recurrent prostate cancer cell line CWR-R1 through a mechanism that involves a post-transcriptional increase in the p160 coactivator transcriptional intermediary factor 2/glucocorticoid receptor interacting protein 1 (TIF2/GRIP1). Site-specific mutagenesis and selective MAPK inhibitors linked the EGF-induced increase in AR transactivation to phosphorylation of TIF2/GRIP1. EGF signaling increased the coimmunoprecipitation of TIF2 and AR. AR transactivation and its stimulation by EGF were reduced by small interfering RNA inhibition of TIF2/GRIP1 expression. The data indicate that EGF signaling through MAPK increases TIF2/GRIP1 coactivation of AR transactivation in recurrent prostate cancer.

Coactivation of an endogenous progesterone receptor by TIF2 in COS-7 cells

Transfection experiments, a powerful tool to study the function of steroid hormone receptors and their coregulators, are often performed in COS-7 cells, because of high transfection efficiencies and expression levels. Here we report on the presence in COS-7 cells of an endogenous steroid hormone receptor, which is highly responsive to progesterone and the synthetic steroids R1881 and ORG2058, but not to 5 alpha-DHT. A 10-fold excess of the progesterone antagonist RU486 abolishes the stimulation by progesterone, while cotransfection with the coactivator TIF2 increases its activity 6- to 7-fold. A comparison of the ligand specificity with transfected androgen or progesterone receptors indicates that the endogenous receptor is a progesterone receptor. Its presence is confirmed by steroid-binding experiments, RT-PCR and Northern blot analysis. Consequently, progesterone receptor function may be studied conveniently in COS-7 cells without cotransfection of receptor, but the endogenous receptor may interfere in studies of ligand specificity and coactivation of cotransfected receptors.

Domain interactions between coregulator ARA(70) and the androgen receptor (AR)

The coregulator function of AR-associated protein 70 (ARA(70)) was investigated to further characterize its interaction with the AR. Using a yeast two-hybrid assay, androgen-dependent binding of ARA(70) deletion mutants to the AR ligand-binding domain (LBD) was strongest with ARA(70) amino acids 321-441 of the 614 amino acid ARA(70) protein. Mutations adjacent to or within an FxxLF motif in this 120-amino acid region abolished androgen-dependent binding to the AR-LBD both in yeast and in glutathione-S-transferase affinity matrix assays. Yeast one-hybrid assays revealed an intrinsic ARA(70) transcriptional activation domain within amino acids 296-441. In yeast assays the ARA(70) domains for transcriptional activation and for binding to the AR-LBD were inhibited by the C-terminal region of ARA(70). Full-length ARA(70) increased androgen-dependent AR transactivation in transient cotransfection assays using a mouse mammary tumor virus-luciferase reporter in CV1 cells. ARA(70) also increased constitutive transcriptional activity of an AR NH(2)-terminal-DNA binding domain fragment and bound this region in glutathione-S-transferase affinity matrix assays. Binding was independent of the ARA(70) FxxLF motif. The results identify an ARA(70) motif required for androgen-dependent interaction with the AR-LBD and demonstrate that ARA(70) can interact with the NH(2)-terminal and carboxyl-terminal regions of AR.

A novel method for the analysis of the androgen receptor

The role of the androgen receptor in the regulation of prostate cancer development and progression has been a focus of intense research. Until recent years, the level of expression of the androgen receptor protein was described qualitatively. Immunohistochemical parameters have been established that show a linear relationship between androgen receptor expression and immunostaining. Intensity of immunostaining can be accurately measured using computer-assisted color video image analysis. Studies of progression and treatment of prostate cancer will benefit from the ability to quantitatively measure androgen receptor expression.

Cloning of the hamster androgen receptor gene

Flank organs of male Golden Syrian hamsters contain sebaceous glands and hair follicles whose morphology and function are highly dependent on androgen, which makes these organs a useful model to study androgen action. In order to investigate molecular mechanisms of androgen action, we cloned a cDNA encoding the hamster androgen receptor (hamAR) by polymerase chain reaction (PCR) amplification of hamster testis cDNA. Nucleotide sequence analysis revealed that the cDNA has the capacity to encode a polypeptide of 900 amino acid. The deduced amino acid sequence was highly homologous to those of androgen receptors (AR) from other species. Western blot analysis of COS1 cells transfected with a vector expressing hamAR revealed that the recombinant ham AR was identical in size to that of endogeneous ham AR expressed in liver, sebaceous glands and testis. We further demonstrated that transfection of the hamAR expression vector into COS1 cells resulted in activation of a luciferase reporter gene containing multiple androgen responsive elements (ARE) in a testosterone-dependent manner. Availability of the recombinant hamAR clone along with the flank organ system should provide a more powerful tool than currently available to investigate androgen action at the molecular level.

Identification of a novel phosphorylation site in human androgen receptor by mass spectrometry

An N-terminal hexahistidine-tagged full-length human androgen receptor protein (His(6)-hAR) was overexpressed and purified to apparent homogeneity in the presence of dihydrotestosterone (DHT) in our previous studies. In-gel trypsin digestion of the purified DHT-bound His(6)-hAR, and tryptic peptide mapping using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI/TOF-MS), detected a total of 17 peptides (21% coverage of hAR) with 9 peptides originating from the ligand-binding domain (LBD, 31% coverage of LBD). Amino acid sequencing analysis of the tryptic peptides from a separate in-gel digestion of the His(6)-hAR, using HPLC-coupled electrospray ionization ion trap mass spectrometry (LC/ESI-ITMS and MS/MS), unambiguously confirmed 21 peptides with 19% coverage of the hAR, of which 11 peptides originated from the LBD (35% coverage of LBD). These 21 peptides included 11 out of the 17 peptides detected by MALDI/TOF-MS. In addition, a novel serine phosphorylation site (Ser(308)) within the N-terminal transactivation domain of hAR was identified.

Serum and Urinary Prostate-specific Antigen and Urinary Human Glandular Kallikrein Concentrations Are Significantly Increased after Testosterone Administration in Female-to-Male Transsexuals

Background: The genes that encode prostate-specific antigen (PSA) and human glandular kallikrein (hK2) are up-regulated by androgens and progestins in cultured cells, but no published studies have described the effect of androgen administration in women on serum and urinary PSA or hK2.

Methods: We measured serum and urinary PSA and hK2 before, and 4 and 12 months post testosterone treatment by immunofluorometric methods in 32 female-to-male transsexuals.

Results: Mean serum PSA increased from 1.1 ng/L to 11.1 ng/L and then to 22 ng/L by 4 and 12 months post treatment, respectively; the corresponding mean values in urine were 17, 1420, and 18 130 ng/L, respectively. Serum hK2, another kallikrein closely related to PSA, remained undetectable at the three time points. However, urinary hK2 concentration rose from below the detection limit (<6 ng/L) before treatment to 18 and 179 ng/L by the 4th and the 12th month of treatment, respectively. All changes were statistically significant (P <0.001) at 4 months.

Conclusions: Testosterone administration increases serum and urinary PSA and urinary hK2 in women. These measurements may be useful as indicators of androgenic stimulation in women.

Transcriptional repression of the alpha-subunit gene by androgen receptor occurs independently of DNA binding but requires the DNA-binding and ligand-binding domains of the receptor

The pituitary glycoprotein hormones LH and FSH regulate the reproductive cycle and are sensitive to feedback by gonadal steroids. The common alpha-subunit shared by these hormones is transcriptionally repressed by androgen receptor (AR) in the presence of its ligand dihydrotestosterone. This identifies at least one mechanism that contributes to AR-dependent suppression of gonadotropin synthesis. Repression of alpha-subunit transcription by AR requires only the sequences within the first 480 bp of the promoter. While this region contains a high-affinity binding site for AR, this element does not mediate the suppressive effects of androgens. Instead, two other elements within the promoter-regulatory region (alpha-basal element and cAMP-regulatory element), which are important for expression of the alpha-subunit gene in gonadotropes, mediate the effects of AR. This suggests that AR inhibits activity of the alpha-subunit promoter by interfering with the transcriptional properties of the proteins that bind to alpha-basal element and the cAMP-regulatory elements. Furthermore, transfection analysis of various mutant ARs identified both the DNA-binding and ligand-binding domains of the receptor as critical for repression. Comparisons with the MMTV promoter revealed distinct structural requirements that underlie the transactivation and transrepression properties of AR.

Evidence for an anti-parallel orientation of the ligand-activated human androgen receptor dimer

Domain interactions of the human androgen receptor (AR) dimer were investigated using a protein-protein interaction assay in which the NH2- and carboxyl-terminal regions of human AR were fused to the Saccharomyces cerevisiae GAL4 DNA-binding domain and herpes simplex virus VP16 transactivation domain to produce chimeric proteins. Transcriptional activation of a GAL4 luciferase reporter vector up to 100-fold was greater than Fos/Jun leucine zipper binding, indicating stable AR interaction between AR NH2-terminal residues 1-503 and steroid-binding domain residues 624-919 that was specific for and dependent on androgen binding to the steroid-binding domain and was inhibited by anti-androgen binding. Deletion mutagenesis within the NH2-terminal region indicated transactivation domain residues 142-337 were not required for dimerization, whereas deletions near the NH2 terminus (delta 14-150) or NH2-terminal to the DNA-binding domain (delta 339-499) reduced or eliminated the AR interaction, respectively. An NH2-/NH2-terminal interaction was also observed, but no interaction was detected between ligand-free or bound steroid-binding domains. The results indicate that high affinity androgen binding promotes interactions between the NH2-terminal and steroid-binding domains of human AR, raising the possibility of an androgen-induced anti-parallel AR dimer.

Specificity of simple hormone response elements in androgen regulated genes

Androgen (AR) and glucocorticoid (GR) receptors recognize a family of 15 base pair partial palindromic hormone response elements (HRE). We have studied receptor interactions with several HREs from androgen regulated genes to determine their potential to mediate a selective androgen response. Synthetic oligonucleotides corresponding to the elements were analysed for receptor binding and steroid dependent transcriptional enhancer activities. Each HRE contained the 3' half-site sequence (5'-TGTNCT-3') of the glucocorticoid response element (GRE) consensus sequence. HREs that countained the 5' half-site GRE consensus sequence (5'-A/GGNACA/G-3') had the strongest and-rogen response element (ARE) and GRE activities. In methylation interference assays, AR and GR interacted with identical base contact sites in the response elements. Two elements that deviated from the GRE consensus sequence by a single optimal base in the 5' half, had reduced ARE activity with no significant change in GRE activity and displayed lower binding of AR than GR in mobility shift assays using purified DNA binding domain peptides. Transfections with AR/GR and GR/AR chimeras containing the N-terminal domain of one receptor linked to the DNA-binding and C-terminal domains of the other suggested that N-terminal domain functions of GR also contributed to the greater GRE than ARE activities of the response elements.

Androgen receptor antagonist versus agonist activities of the fungicide vinclozolin relative to hydroxyflutamide

The mechanism of antiandrogenic activity of vinclozolin (3-(3,5-dichlorophenyl)-5-methyl-5-vinyloxazolidine-2,4-dione), a dicarboximide fungicide under investigation for its potential adverse effects on human male reproduction, was investigated using recombinant human androgen receptor (AR). The two primary metabolites of vinclozolin in plants and mammals are M1 (2-[[3,5-dichlorophenyl)-carbamoyl]oxy]-2-methyl-3-butenoic acid) and M2 (3',5'-dichloro-2-hydroxy-2-methylbut-3-enanilide). Both metabolites, in a dose-dependent manner, target AR to the nucleus and inhibit androgen-induced transactivation mediated by the mouse mammary tumor virus promoter. M2 is a 50-fold more potent inhibitor than M1 and only 2-fold less than hydroxyflutamide. In the presence of dihydrotestosterone (50 nM), M2 (0.2-10 microM) inhibits androgen-induced AR binding to androgen response element DNA. In the absence of dihydrotestosterone, concentrations of 10 microM M2 or hydroxyflutamide promote AR binding to androgen response element DNA and activation of transcription. Agonist activities of M2 and hydroxyflutamide occur at 10-fold lower concentrations with the mutant AR (Thr877 to Ala) endogenous to LNCaP human prostate cancer cells. The results indicate that androgen antagonists can act as agonists, depending on ligand binding affinity, concentration, and the presence of competing natural ligands.

Quantification of androgen receptor and follicle-stimulating hormone receptor mRNA levels in human and monkey testes by a ribonuclease-protection assay

A sensitive, solution-hybridization ribonuclease-protection assay (RPA) was established to quantify the expression of mRNA for the androgen receptor (AR) and follicle-stimulating hormone receptor (FSHR) in total RNA samples isolated from tissues of the cynomolgous monkey, human testes obtained from elderly patients undergoing orchidectomy because of prostatic carcinoma or from transsexual men undergoing gender reassignment as well as human cell lines DU 145, REP and RVP. Sensitivity experiments revealed that, in the human and monkey, 1-2 micrograms of total RNA were sufficient to achieve quantifiable signals of the different receptor mRNA species. Quantification of AR and FSHR mRNA levels showed a 1.7-fold higher expression of AR mRNA and a 2.4-fold higher expression of FSHR mRNA in the monkey testes compared to human testes from patients with prostatic carcinoma. Normal spermatogenesis in both human and monkey testes indicated no relationship between spermatogenic status and receptor expression. The significantly lower expression of AR and FSHR mRNA in humans than in monkeys might therefore be either age- or species-related. Quantification of mRNA for AR and FSHR in the testis of the transsexual patients undergoing oestrogen and antiandrogen treatment displayed a drastic increase (4.5-fold) in mRNA for the AR, whereas mRNA for the FSHR was barely detectable. Due to its high sensitivity, reproducibility and its ability to quantify mRNA transcripts, the RPA is a useful tool for investigating expression of low abundant receptor genes and their regulation when only very small amounts of tissue are available. Furthermore, it is suitable for use in clinical and experimental studies in which accurate quantification of transcripts is necessary.

Selective effects of 8-Br-cAMP on agonists and antagonists of the glucocorticoid receptor

RU486 has been reported to be a glucocorticoid receptor (GR) and a progesterone receptor (PR) antagonist. We have analysed RU486 activity on the GR in WCL-2 (CHO) cells and in COS-7 cells transiently transfected with the mouse GR and with the reporter MMTVCAT (MCAT). These cell lines do not contain any active progesterone or androgen receptors. In both cell lines RU486 is a partial agonist of the GR with 10-15% of the activity of dexamethasone. As expected, RU486 is also a partial antagonist of the GR. Treatment of COS-7 cells with 8-Br-cAMP increases the agonist activity of both dexamethasone and RU486. This cAMP induced superactivation is seen with all steroids that have full or partial agonist activity. In contrast, the activities of ZK98.299 and R5020, which are complete antagonists of the GR without any agonist activity, are not affected by 8-Br-cAMP treatment. This effect of 8-Br-cAMP is not seen in WCL2 cells. 8-Br-cAMP, therefore, is not a switch which changes antagonists to agonists but is, rather, a cell specific activator of all agonists whether they have full or only partial agonist activity.

The receptor, metabolism and effects of androgen in osteoblastic MC3T3-E1 cells

We investigated the androgen receptor (AR), metabolism and effects of androgens in osteoblastic MC3T3-E1 cells. AR was proved as a transcript of a 10-kb mRNA and as a 110-kDa protein. An immunocytochemical study showed that AR was located mainly in the nuclei. Specific binding of [3H]DHT was observed in both the nuclear and cytosol fractions. MC3T3-E1 cells possessed approximately 1190 binding sites per cell and most of the sites (1150 sites) situated in the nucleus. The apparent Kd value in the nuclear fraction was 1.35 nM for [3H]DHT binding, and it was similar to that for [3H]testosterone. In the competition analysis, there was not much difference in the displacement of the [3H]DHT binding from AR between the addition of radioinert DHT and testosterone. In studies of 5 alpha-reductase activity and aromatase activity of the cells, both activities were lower than the respective values in classical androgen target tissues. Androgens stimulated the incorporation of [3H]thymidine into the cell, and DHT and testosterone had a similar potency on the cell proliferation. Thus, these results suggest testosterone itself acts mainly on the osteoblasts without conversion to DHT.

Human androgen receptor expressed in HeLa cells activates transcription in vitro

The androgen receptor (AR) is a ligand-responsive transcription factor, belonging to the class of steroid receptors. AR mutations have been associated with various X-linked diseases, characterized by complete or partial resistance to androgens. To further analyse the molecular mechanism of action of the AR, we have produced the human AR in HeLa cells with a Vaccinia virus expression system. Binding studies on infected HeLa cells demonstrate that the recombinant AR interacts specifically and with high affinity with natural and synthetic androgens. In a gel retardation assay the partially purified AR specifically recognizes an androgen response element of the rat prostatic binding protein gene. Moreover, the recombinant AR activates transcription in vitro from a synthetic promoter construct containing glucocorticoid response elements (GRE).

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.

Immunocytochemical localization of androgen receptors in the male songbird and quail brain

The distribution of androgen receptors was studied in the brain of the Japanese quail (Coturnix japonica), the zebra finch (Taeniopygia guttata), and the canary (Serinus canaria) by immunocytochemistry with a polyclonal antibody (AR32) raised in rabbit against a synthetic peptide corresponding to a sequence located at the N-terminus of the androgen receptor molecule. In quail, androgen receptor-immunoreactive cells were observed in the nucleus intercollicularis and in various nuclei of the preoptic-hypothalamic complex, namely, the nucleus preopticus medialis, the ventral part of the nucleus anterior medialis hypothalami, the nucleus paraventricularis magnocellularis, the nucleus ventromedialis hypothalami, and the tuberal hypothalamus. In the two songbird species, labeled cells were also observed in various nuclei in the preoptic-hypothalamic region, in the nucleus taeniae, and in the nucleus intercollicularis. Additional androgen receptor-immunoreactive cells were present in the androgen-sensitive telencephalic nuclei that are part of the song control system. These immunoreactive cells filled and outlined the boundaries of the hyperstriatum ventrale, pars caudalis, nucleus magnocellularis neostriatalis anterioris (both in the lateral and medial subdivisions), and nucleus robustus archistriatalis. The immunoreactive material was primarily present in cell nuclei but a low level of immunoreactivity was also clearly detected in cytoplasm in some brain areas. These studies demonstrate, for the first time, that androgen receptors can be detected by immunocytochemistry in the avian brain and the results are in general agreement with the binding data obtained by autoradiography with tritiated dihydrotestosterone. Immunocytochemical methods offer several advantages over autoradiography and their use for the study of the androgen receptor will greatly facilitate the analysis of steroid-sensitive systems in the avian brain.

Androgen receptor heterogeneity in LNCaP cells is caused by a hormone independent phosphorylation step

Androgen receptor synthesis and modification were studied in the human LNCaP cell line. Immunoblotting showed that the androgen receptor migrated as a closely spaced 110-112 kDa doublet on SDS-PAGE gels. Most of the receptor protein is present in the higher molecular mass form. Labelling experiments with [35S]methionine showed that the androgen receptor is synthesized as a single 110 kDa protein which is rapidly converted to a 112 kDa protein. Upon alkaline phosphatase treatment a gradual elimination of the 112 kDa isoform with a concomitant increase of the 110 kDa isoform was seen, indicating that the observed 110 to 112 kDa upshift reflects androgen receptor phosphorylation. Furthermore, it is shown that both isoforms can bind hormone and undergo a hormone dependent transformation to a tight nuclear binding form, indicating that the 110 to 112 kDa conversion is not an obligatory step for hormone binding or receptor transformation.

Synthesis and post-translational modification of the androgen receptor in LNCaP cells

Androgen receptor synthesis and modification were studied in the human LNCaP cell line. Immunoblotting with a specific polyclonal antibody showed that the androgen receptor migrated as a closely spaced 110-112 kDa doublet on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) gels. Most of the receptor protein is present in the higher molecular mass form. Pulse labelling experiments with [35S]methionine showed that the androgen receptor is synthesized as a single 110 kDa protein which is rapidly converted to a 112 kDa protein. Alkaline phosphatase treatment of cytosols from [35S]methionine pulse labelled cells caused a gradual elimination of the 112 kDa isoform with a concomitant increase of the 110 kDa isoform. This indicates that the observed 110 to 112 kDa upshift of the newly synthesized androgen receptor reflects receptor phosphorylation. Both isoforms can bind hormone and can undergo a hormone dependent transformation to a tight nuclear binding form, indicating that the 110 to 112 kDa conversion is not an obligatory step for hormone binding or receptor transformation.

The mouse androgen receptor. Functional analysis of the protein and characterization of the gene

Screening a mouse genomic DNA library with human androgen-receptor (hAR) cDNA probes resulted in the isolation and characterization of eight genomic fragments that contain the eight exons of the mouse androgen-receptor (mAR) gene. On the basis of similarity to the hAR gene, the nucleotide sequences of the protein-coding parts of the exons as well as the sequences of the intron/exon boundaries were determined. An open reading frame (ORF) of 2697 nucleotides, which can encode an 899-amino-acid protein, could be predicted. The structure of the mAR ORF was confirmed by sequence analysis of mAR cDNA fragments, which were obtained by PCR amplification of mouse testis cDNA, using mAR specific primers. A eukaryotic mAR expression vector was constructed and mAR was transiently expressed in COS-1 cells. The expressed protein was shown by Western blotting to be identical in size with the native mAR. Co-transfection of HeLa cells with the mAR expression plasmid and an androgen-responsive chloramphenicol acetyltransferase (CAT) reporter-gene construct showed mAR to be able to trans-activate the androgen-responsive promoter in a ligand-dependent manner. Transcription-initiation sites of the mAR gene were identified by S1-nuclease protection experiments, and the functional activity of the promoter region was determined by transient expression of mAR promoter-CAT-reporter-gene constructs in HeLa cells. Structural analysis revealed the promoter of the mAR gene to be devoid of TATA/CCAAT elements. In addition, the promoter region is not remarkably (G + C)-rich. Potential promoter elements consist of a consensus Sp1 binding sequence and a homopurine stretch. The polyadenylation sites of mAR mRNA were identified by sequence similarity to the corresponding sites in the hAR mRNA.

Immunohistochemical study of androgen receptors in metastatic prostate cancer. Comparison of receptor content and response to hormonal therapy

A longstanding goal has been to determine whether androgen receptor (AR) levels could be used to predict the clinical response of metastatic prostate cancer to androgen withdrawal therapy. A major limitation of previous studies was the use of homogenized tissue, which yields an average AR content for all cells. By AR immunohistochemical study using an antibody specific for AR the authors assessed nuclear AR content specifically in the malignant epithelial cells of prostate needle biopsy specimens of 17 patients with Stage D prostate cancer. The authors found that prostate cancer contains AR-positive and AR-negative malignant cells before androgen withdrawal therapy, but the percentage of AR-positive cells did not predict the time to tumor progression after therapy. There was no significant correlation between the percentage of AR-positive malignant cells and the time to tumor progression. When patients were divided into two groups based on the median time to progression, the percentage of AR-positive nuclei was not significantly different in poor responders versus good responders. When patients were divided into two groups based on the median percentage of receptor-positive nuclei, Kaplan-Meier estimates of the progression-free interval revealed no significant difference between the group of patients with AR-poor tumors and patients with AR-rich tumors. Potential explanations for these results are discussed. The authors conclude that the percentage of AR-positive nuclei is not a sufficient criterion to predict tumor behavior.