The human androgen receptor: complementary deoxyribonucleic acid cloning, sequence analysis and gene expression in prostate

Gain in transcriptional activity by primate-specific coevolution of melanoma antigen-A11 and its interaction site in androgen receptor

Male sex development and growth occur in response to high affinity androgen binding to the androgen receptor (AR). In contrast to complete amino acid sequence conservation in the AR DNA and ligand binding domains among mammals, a primate-specific difference in the AR NH(2)-terminal region that regulates the NH(2)- and carboxyl-terminal (N/C) interaction enables direct binding to melanoma antigen-A11 (MAGE-11), an AR coregulator that is also primate-specific. Human, mouse, and rat AR share the same NH(2)-terminal (23)FQNLF(27) sequence that mediates the androgen-dependent N/C interaction. However, the mouse and rat AR FXXLF motif is flanked by Ala(33) that evolved to Val(33) in primates. Human AR Val(33) was required to interact directly with MAGE-11 and for the inhibitory effect of the AR N/C interaction on activation function 2 that was relieved by MAGE-11. The functional importance of MAGE-11 was indicated by decreased human AR regulation of an androgen-dependent endogenous gene using lentivirus short hairpin RNAs and by the greater transcriptional strength of human compared with mouse AR. MAGE-11 increased progesterone and glucocorticoid receptor activity independently of binding an FXXLF motif by interacting with p300 and p160 coactivators. We conclude that the coevolution of the AR NH(2)-terminal sequence and MAGE-11 expression among primates provides increased regulatory control over activation domain dominance. Primate-specific expression of MAGE-11 results in greater steroid receptor transcriptional activity through direct interactions with the human AR FXXLF motif region and indirectly through steroid receptor-associated p300 and p160 coactivators.

Systematic analysis of microRNAs targeting the androgen receptor in prostate cancer cells

Androgen receptor (AR) is expressed in all stages of prostate cancer progression, including in castration-resistant tumors. Eliminating AR function continues to represent a focus of therapeutic investigation, but AR regulatory mechanisms remain poorly understood. To systematically characterize mechanisms involving microRNAs (miRNAs), we conducted a gain-of function screen of 1129 miRNA molecules in a panel of human prostate cancer cell lines and quantified changes in AR protein content using protein lysate microarrays. In this way, we defined 71 unique miRNAs that influenced the level of AR in human prostate cancer cells. RNA sequencing data revealed that the 3'UTR of AR (and other genes) is much longer than currently used in miRNA target prediction programs. Our own analyses predicted that most of the miRNA regulation of AR would target an extended 6 kb 3'UTR. 3'UTR-binding assays validated 13 miRNAs that are able to regulate this long AR 3'UTR (miR-135b, miR-185, miR-297, miR-299-3p, miR-34a, miR-34c, miR-371-3p, miR-421, miR-449a, miR-449b, miR-634, miR-654-5p, and miR-9). Fifteen AR downregulating miRNAs decreased androgen-induced proliferation of prostate cancer cells. In particular, analysis of clinical prostate cancers confirmed a negative correlation of miR-34a and miR-34c expression with AR levels. Our findings establish that miRNAs interacting with the long 3'UTR of the AR gene are important regulators of AR protein levels, with implications for developing new therapeutic strategies to inhibit AR function and androgen-dependent cell growth.

Analysis of interdomain interactions of the androgen receptor

High-affinity binding of testosterone or dihydrotestosterone to the androgen receptor (AR) triggers the androgen-dependent AR NH2- and carboxyl-terminal (N/C) interaction between the AR NH2-terminal FXXLF motif and the activation function 2 (AF2) hydrophobic binding surface in the ligand-binding domain. The functional importance of the AR N/C interaction is supported by naturally occurring loss-of-function AR AF2 mutations where AR retains high-affinity androgen binding but is defective in AR FXXLF motif binding. Ligands with agonist activity in vivo such as testosterone, dihydrotestosterone, and the synthetic anabolic steroids induce the AR N/C interaction and increase AR transcriptional activity in part by slowing the dissociation rate of bound ligand and stabilizing AR against degradation. AR ligand-binding domain competitive antagonists inhibit the agonist-dependent AR N/C interaction. Although the human AR N/C interaction is important for transcriptional activity, it has an inhibitory effect on transcriptional activity from AF2 by competing for p160 coactivator LXXLL motif binding. The primate-specific AR coregulatory protein, melanoma antigen gene protein-A11 (MAGE-A11), modulates the AR N/C interaction through a direct interaction with the AR FXXLF motif. Inhibition of AF2 transcriptional activity by the AR N/C interaction is relieved by AR FXXLF motif binding to the F-box region of MAGE-11. Described here are methods to measure the androgen-dependent AR N/C interdomain interaction and the influence of transcriptional coregulators.

Transcriptional synergy between melanoma antigen gene protein-A11 (MAGE-11) and p300 in androgen receptor signaling

Androgen receptor (AR)-mediated gene regulation involves interactions with coregulatory proteins that include the melanoma antigen gene protein-A11 (MAGE-11). To understand the functional significance of sequence similarity between MAGE-11 and the adenovirus early protein E1A, we determined whether MAGE-11 contributes to AR transcriptional activity through an interaction with p300, a potent and ubiquitous transcriptional regulator. Here, we report that MAGE-11 interacts with the NH(2)-terminal region of p300 through the MAGE-11 MXXIF motif (185)MXXIF(189), with transcriptional activity depending on the MAGE-11 F-box and MAPK phosphorylation. The MAGE-11- and p300-dependent increase in AR transactivation required the NH(2)-terminal regions of AR and p300, p300 acetyltransferase activity, and the AR FXXLF motif (23)FQNLF(27) interaction with MAGE-11. MAGE-11 linked AR to p300 and the p160 coactivator, transcriptional intermediary protein 2 (TIF2). The p300 NH(2)-terminal FXXLF motif (33)FGSLF(37) was required for transcriptional activation by TIF2. Increased expression of p300 decreased the ubiquitinylation of MAGE-11 and transiently increased endogenous MAGE-11 levels. Autoacetylation of p300 and decreased acetylation of TIF2 were evident in the MAGE-11, p300, and TIF2 complex. The studies suggest that MAGE-11 links NH(2)-terminal domains of AR and p300 to promote transcriptional synergy through a cadre of FXXLF-related interacting motifs.

Expressions of androgen receptor and its co-regulators in carcinoma ex pleomorphic adenoma of salivary gland

AIMS

Androgen receptor (AR) signalling is involved in cancer progression. The expression of AR has been reported in carcinoma ex pleomorphic adenoma (CXPA) of salivary gland, however AR gene status and the expressions of cofactors for AR signalling have not been investigated. The aims of this study were to investigate the expressions of each of the molecules that contribute to AR activation with or without ligands in CXPA. In addition, AR gene amplification and single-nucleotide polymorphism were investigated.

METHODS

Ten cases of CXPA and 23 cases of pleomorphic adenomas (PA) of the salivary glands were immunostained for the AR co-regulators (SRC1, p300, and NCoR1) and the signalling molecules involved in the ligand-independent pathway (i.e., HER-2/neu and STAT3). AR gene amplification and single-nucleotide polymorphism were investigated by dual-coloured fluorescent in situ hybridisation and polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP), respectively.

RESULTS

AR expression was observed in nine of 10 cases of CXPA and in 30.4% of PA cases, a statistically significant difference. The expression, with low or high intensity, of HER-2/neu and STAT3 was more frequent in CXPA (6/10 and 9/10, respectively) than in PA (0% and 46.7%). The expression of co-activators was also stronger, though only slightly, in CXPA than in PA. The gain of chromosome X and AR gene amplification were not observed in any CXPA or PA cases, and the G --> A allele in codon 211 was detected in only one case (a CXPA).

CONCLUSIONS

These results suggest that although AR may be activated in the pathway with or without ligands, the expression of co-regulators and AR gene aberrations are not involved in the carcinogenesis of CXPA.

Androgen regulation of the prostatic tumour suppressor NKX3.1 is mediated by its 3' untranslated region

The homeodomain transcription factor NKX3.1 is a prostate-specific tumour suppressor, expression of which is reduced or undetectable in the majority of metastatic prostate tumours. In the normal prostate and in prostate cancer cells, NKX3.1 expression is under tight androgenic control that we have shown to be mediated by its ~2.5 kb 3'UTR (3' untranslated region). Reporter deletion analysis of the NKX3.1 3'UTR identified three regions that were transactivated by DHT (5alpha-dihydrotestosterone) in the AR (androgen receptor)-expressing prostate cancer cell line LNCaP. Reversal of DHT effects by the anti-androgen bicalutamide supported an AR-mediated mechanism, and bioinformatic analysis of the NKX3.1 3'UTR identified canonical AREs (androgen-response elements) in each of the androgen-responsive regions. EMSAs (electrophoretic mobility-shift assays) indicated binding of the AR DNA-binding domain to two of the AREs, a proximal ARE at +2378-2392 from the transcription start site, and a more distal ARE at +3098-3112. ChIP (chromatin immunoprecipitation) analysis provided further evidence of ligand-dependent recruitment of endogenous AR to sequence encompassing each of the two elements, and site-directed mutagenesis and deletion analysis confirmed the contribution of each of the AREs in reporter assays. The present studies have therefore demonstrated that the NKX3.1 3'UTR functions as an androgen-responsive enhancer, with the proximal ARE contributing the majority and the distal ARE providing a smaller, but significant, proportion of the androgen responsiveness of the NKX3.1 3'UTR. Characterization of androgen-responsive regions of the NKX3.1 gene will assist in the identification of transcriptional regulatory mechanisms that lead to the deregulation of NKX3.1 expression in advanced prostate cancers.

Androgens and the male reproductive tract: an overview of classical roles and current perspectives

Androgens are steroid hormones that play key roles in the development and maintenance of male phenotype and reproductive function. These hormones also affect the function of several non-reproductive organs, such as bone and skeletal muscle. Endogenous androgens exert most of their effects by genomic mechanisms, which involve hormone binding to the androgen receptor (AR), a ligand-activated transcription factor, resulting in the modulation of gene expression. AR-induced non-genomic mechanisms have also been reported. A large number of steroidal and non-steroidal AR-ligands have been developed for therapeutic use, including the treatment of male hypogonadism (AR agonists) and prostate diseases (AR antagonists), among other pathological conditions. Here, the AR gene and protein structure, mechanism of action and AR gene homologous regulation were reviewed. The AR expression pattern, its in vivo regulation and physiological relevance in the developing and adult testis and epididymis, which are sites of sperm production and maturation, respectively, were also presented.

Melanoma antigen gene protein-A11 (MAGE-11) F-box links the androgen receptor NH2-terminal transactivation domain to p160 coactivators

Androgen-dependent transcriptional activity by the androgen receptor (AR) and its coregulators is required for male reproductive development and function. In humans and other primates, melanoma antigen gene protein-A11 (MAGE-11) is an AR selective coregulator that increases AR transcriptional activity. Here we show that the interaction between AR and MAGE-11 is mediated by AR NH(2)-terminal FXXLF motif binding to a highly conserved MAGE-11 F-box in the MAGE homology domain, and is modulated by serum stimulation of mitogen-activated protein kinase phosphorylation of MAGE-11 Ser-174. The MAGE-11-dependent increase in AR transcriptional activity is mediated by a direct interaction between MAGE-11 and transcriptional intermediary factor 2 (TIF2) through the NH(2)-terminal region of TIF2, and by a MAGE-11 FXXIF motif interaction with an F-box-like region in activation domain 1 of TIF2. The results suggest that MAGE-11 functions as a bridging factor to recruit AR coactivators through a novel FXX(L/I)F motif-F-box interaction paradigm.

Detailed analysis of X chromosome inactivation in a 49,XXXXX pentasomy

Background

Pentasomy X (49,XXXXX) has been associated with a severe clinical condition, presumably resulting from failure or disruption of X chromosome inactivation. Here we report that some human X chromosomes from a patient with 49,XXXXX pentasomy were functionally active following isolation in inter-specific (human-rodent) cell hybrids. A comparison with cytogenetic and molecular findings provided evidence that more than one active X chromosome was likely to be present in the cells of this patient, accounting for her abnormal phenotype.

Results

5-bromodeoxyuridine (BrdU)-pulsed cultures showed different patterns among late replicating X chromosomes suggesting that their replication was asynchronic and likely to result in irregular inactivation. Genotyping of the proband and her mother identified four maternal and one paternal X chromosomes in the proband. It also identified the paternal X chromosome haplotype (P), indicating that origin of this X pentasomy resulted from two maternal, meiotic non-disjunctions. Analysis of the HUMANDREC region of the androgen receptor (AR) gene in the patient's mother showed a skewed inactivation pattern, while a similar analysis in the proband showed an active paternal X chromosome and preferentially inactivated X chromosomes carrying the 173 AR allele. Analyses of 33 cell hybrid cell lines selected in medium containing hypoxanthine, aminopterin and thymidine (HAT) allowed for the identification of three maternal X haplotypes (M1, M2 and MR) and showed that X chromosomes with the M1, M2 and P haplotypes were functionally active. In 27 cell hybrids in which more than one X haplotype were detected, analysis of X inactivation patterns provided evidence of preferential inactivation.

Conclusion

Our findings indicated that 12% of X chromosomes with the M1 haplotype, 43.5% of X chromosomes with the M2 haplotype, and 100% of the paternal X chromosome (with the P haplotype) were likely to be functionally active in the proband's cells, a finding indicating that disruption of X inactivation was associated to her severe phenotype.

Molecular studies of a patient with complete androgen insensitivity and a 47,XXY karyotype

A phenotypic female with complete androgen insensitivity from a maternally inherited mutation in the androgen receptor had a 47,XXY karyotype. Partial maternal X isodisomy explained the expression of androgen insensitivity despite the presence of 2 X chromosomes.

Comparison of the molecular consequences of different mutations at residue 754 and 690 of the androgen receptor (AR) and androgen insensitivity syndrome (AIS) phenotype

OBJECTIVE

Androgen insensitivity syndrome (AIS) is associated with mutations throughout the androgen receptor (AR) gene. Different mutations at the same codon have been identified in individuals with various phenotypes suggesting the nature of the codon substituted may influence the degree of AIS. We investigated if phenotype could be predicted by comparing the functionality of AR mutations with those at the same codon of known phenotype.

PATIENTS

We identified patients from the Cambridge Disorders of Sex Development Database with the AR substitutions: Phe754Ser with microphallus without hypospadias and Asp690Val with complete AIS. Mutations Phe754Leu, Phe754Val and Asp690deletion (Asp690del) have previously been reported to be associated with different degrees of AIS.

DESIGN

We characterized the functional properties of Phe754Ser, Phe754Leu, Phe754Val, Asp690Val and Asp690del receptor mutants in vitro and used the crystal structure of the AR ligand binding domain to model the mutations.

RESULTS

The receptor mutants Phe754Ser, Phe754Leu and Phe754Val bound androgen with decreasing affinity, while Asp690Val showed reduced affinity compared to Asp690del. A similar pattern of reduced activation was seen on androgen responsive elements. We suggest how the mutations could affect AR structure, resulting in the observed phenotypes.

CONCLUSIONS

The relative functional properties of Phe754 and Asp690 mutant AR receptors correlate broadly with their specific phenotypes. Therefore, comparing the molecular consequences of novel mutations with others at the same codon may be a useful aid to AIS patient management, particularly for sex of rearing decisions when prediction of functionality is important.

Molecular biology of sperm maturation in the human epididymis

Male infertility is a frequent cause of childlessness, and, indeed, a comparison of the contributions to conception failure made by male and female factors shows them to be equally frequent. In practice, male infertility appears to be resistant to most treatments. However, the major reason for this may be that often attempts are carried out without knowing the cause of the problem. Unlike in women, obstructions and hormonal disorders are rare in male infertility. Rather, it would appear that sperm disorders are the most common cause, reflecting a variety of pathogenetic mechanisms. Defects in sperm morphology, defective sperm movement, deficient development or functional failure of the acrosome, and the excessive generation of reactive oxygen species are changes that are often seen in infertile semen, but little is known about their aetiology. In 5–10% of men being treated for infertilty, an autoimmune reaction against spermatozoa is observed. Although the correlation between the presence of systemic antisperm antibodies and fertility potential is poor, the appearance of sperm-bound antibodies of immunoglobulin class IgA in semen seems to be closely associated with infertility. Studies in laboratory animals and humans have shown that complementary adhesion molecules are located on the surface of oocytes and spermatozoa. These molecules interact and lead to gamete fusion. Abnormalities in these molecules on the sperm surface might be expected to contribute to male infertility. However, their clinical significance has not yet been documented, and the molecular basis of human gamete interaction is far from being understood. Therefore, the key to understanding male infertility may lie in basic research which directly targets the fundamental cellular and molecular biology of the human spermatozoon.

Increased expression of androgen receptor coregulator MAGE-11 in prostate cancer by DNA hypomethylation and cyclic AMP

Melanoma antigen gene protein-A11 (MAGE-11) of the MAGE family of cancer germ-line antigens increases androgen receptor (AR) transcriptional activity through its interaction with the AR NH(2)-terminal FXXLF motif. The present study investigated the regulatory mechanisms that control MAGE-11 expression during androgen deprivation therapy and prostate cancer progression. Studies include the CWR22 xenograft model of human prostate cancer, clinical specimens of benign and malignant prostate, and prostate cancer cell lines. MAGE-11 mRNA levels increased 100- to 1,500-fold during androgen deprivation therapy and prostate cancer progression, with highest levels in the castration-recurrent CWR22 xenograft and clinical specimens of castration-recurrent prostate cancer. Pyrosequencing of genomic DNA from prostate cancer specimens and cell lines indicated the increase in MAGE-11 resulted from DNA hypomethylation of a CpG island in the 5' promoter of the MAGE-11 gene. Sodium bisulfite sequencing of genomic DNA from benign and malignant prostate tumors and prostate cancer cell lines revealed DNA hypomethylation at individual CpG sites at the transcription start site were most critical for MAGE-11 expression. Cyclic AMP (cAMP) also increased MAGE-11 expression and AR transcriptional activity in prostate cancer cell lines. However, cAMP did not alter DNA methylation of the promoter and its effects were inhibited by extensive DNA methylation in the MAGE-11 promoter region. Increased expression of the AR coregulator MAGE-11 through promoter DNA hypomethylation and cAMP provides a novel mechanism for increased AR signaling in castration-recurrent prostate cancer.

A novel androgen receptor splice variant is up-regulated during prostate cancer progression and promotes androgen depletion-resistant growth

The androgen receptor (AR) plays a key role in progression to incurable androgen ablation-resistant prostate cancer (PCA). We have identified three novel AR splice variants lacking the ligand-binding domain (designated as AR3, AR4, and AR5) in hormone-insensitive PCA cells. AR3, one of the major splice variants expressed in human prostate tissues, is constitutively active, and its transcriptional activity is not regulated by androgens or antiandrogens. Immunohistochemistry analysis on tissue microarrays containing 429 human prostate tissue samples shows that AR3 is significantly up-regulated during PCA progression and AR3 expression level is correlated with the risk of tumor recurrence after radical prostatectomy. Overexpression of AR3 confers ablation-independent growth of PCA cells, whereas specific knockdown of AR3 expression (without altering AR level) in hormone-resistant PCA cells attenuates their growth under androgen-depleted conditions in both cell culture and xenograft models, suggesting an indispensable role of AR3 in ablation-independent growth of PCA cells. Furthermore, AR3 may play a distinct, yet essential, role in ablation-independent growth through the regulation of a unique set of genes, including AKT1, which are not regulated by the prototype AR. Our data suggest that aberrant expression of AR splice variants may be a novel mechanism underlying ablation independence during PCA progression, and AR3 may serve as a prognostic marker to predict patient outcome in response to hormonal therapy. Given that these novel AR splice variants are not inhibited by currently available antiandrogen drugs, development of new drugs targeting these AR isoforms may potentially be effective for treatment of ablation-resistant PCA.

Androgen insensitivity syndrome

Over the past four years, major advances in the understanding of the aetiology and pathogenesis of the androgen insensitivity syndrome (AIS) have occurred. This review aims to summarize current information on clinical, diagnostic, therapeutic and molecular aspects of AIS.

Hormonal abnormalities leading to disorders of sexual development

Normal human sexual development occurs in a highly regulated process that comprises three distinct phases: establishment of chromosomal sex, development of the sex-specific gonads and phenotypic differentiation of the internal ductal anatomy and external genitalia. The latter two phases are mediated by specific hormonal effector molecules, including anti-Müllerian hormone and testosterone, and their dysregulation often leads to the development of a phenotypic disorder of sexual differentiation. This review describes the hormonal mediators that are involved in sexual development and the disorders of sexual differentiation that arise from their dysfunction.

Methods for measuring ligand dissociation and nuclear receptor turnover in whole cells

Understanding the molecular mechanisms of steroid hormone action requires assays that measure rates of ligand dissociation and receptor degradation. Ligand dissociation is a pseudo-first order reaction of a high affinity [3H]-labeled ligand. Receptor turnover as described here is the rate of degradation of a radiolabeled receptor. The methods make use of transient expression of a nuclear receptor in cultured cells and are applicable to all nuclear receptors. Rates of ligand dissociation and receptor degradation provided the first insight into the interdomain interactions of the androgen receptor and the molecular basis for the phenotypic effects of naturally occurring androgen receptor loss-of-function germline mutations and gain-of-function somatic mutations, and for the potency differences between the biologically active androgens, testosterone, and dihydrotestosterone.

Androgen receptor gene polymorphism and sex hormones in elderly men: the Tromsø study

The aim of this study was to examine whether CAG/GGN repeats are significant modulators of serum concentrations of total and free testosterone (T) as well as of luteinizing hormone (LH) in elderly men. Sixty-nine 60- to 80-year-old men with subnormal T levels (< or = 11.0 nmol L(-1)) and 104 men with normal T levels taking part in a nested case-control study were used for these analyses. Sex hormones were measured and free T was calculated. The CAG and GGN polymorphisms in the androgen receptor gene were determined by polymerase chain reaction and subsequent direct sequencing. There were no differences in the CAG and GGN repeat lengths between the groups. In cross-sectional analyses of the whole cohort, total and free T were positively associated with CAG length (all P < 0.05) before, but not after, waist circumference or body mass index was added to the model. CAG repeat lengths were weakly, but not independently, associated with total and free T. These findings indicate that when clinically evaluating T and LH levels in elderly men, the CAG and GGN repeat lengths do not need to be taken into consideration.

Hereditary retinoblastoma transmitted by maternal germline mosaicism

BACKGROUND

Investigating transmission of a constitutive, g78238C > T (R552X), RB1 mutation in four affected children descended from three different unaffected fathers and an unaffected mother.

PROCEDURES

Sequence data analyses and allele-specific PCR assays were used to investigate the presence of the mutation in four affected children, five unaffected sibs (or half-sibs), and the unaffected mother. Haplotyping was carried out for confirming that the children descended from different fathers.

RESULTS

Haplotyping excluded the possibility of paternal transmission of a de novo mutation and provided evidence of maternal germline mosaicism. The mutation was apparently absent in blood- and buccal cell-DNA of the mother who also showed a normal fundoscopy.

CONCLUSIONS

Our findings indicated that mosaicism was restricted to the maternal germline. The mutational event must have occurred at least 4 weeks post-conception, unlike the early mutational events of most mosaics, occurring between fertilization and the 8th day of conception. The implications of these findings are discussed in view that genetic counselling should discriminate between germline mosaicism and de novo events in pseudo-low-penetrant hereditary retinoblastoma.

A novel mutation F826L in the human androgen receptor in partial androgen insensitivity syndrome; increased NH2-/COOH-terminal domain interaction and TIF2 co-activation

A novel mutation F826L located within the ligand binding domain (LBD) of the human androgen receptor (AR) was investigated. This mutation was found in a boy with severe penoscrotal hypospadias (classified as 46,XY DSD). The AR mutant F826L appeared to be indistinguishable from the wild-type AR, with respect to ligand binding affinity, transcriptional activation of MMTV-luciferase and ARE2-TATA-luciferase reporter genes, protein level in genital skin fibroblasts (GSFs), and sub-cellular distribution in transfected cells. However, an at least two-fold higher NH2-/COOH-terminal domain interaction was found in luciferase and GST pull-down assays. A two-fold increase was also observed for TIF2 (transcription intermediary factor 2) co-activation of the AR F826L COOH-terminal domain. This increase could not be explained by a higher stability of the mutant protein, which was within wild-type range. Repression of transactivation by the nuclear receptor co-repressor (N-CoR) was not affected by the AR F826L mutation. The observed properties of AR F826L would be in agreement with an increased activity rather than with a partial defective AR transcriptional activation. It is concluded that the penoscrotal hypospadias in the present case is caused by an as yet unknown mechanism, which still may involve the mutant AR.

Site-specific androgen receptor serine phosphorylation linked to epidermal growth factor-dependent growth of castration-recurrent prostate cancer

The androgen receptor (AR) is required for prostate cancer development and contributes to tumor progression after remission in response to androgen deprivation therapy. Epidermal growth factor (EGF) increases AR transcriptional activity at low levels of androgen in the CWR-R1 prostate cancer cell line derived from the castration-recurrent CWR22 prostate cancer xenograft. Here we report that knockdown of AR decreases EGF stimulation of prostate cancer cell growth and demonstrate a mechanistic link between EGF and AR signaling. The EGF-induced increase in AR transcriptional activity is dependent on phosphorylation at mitogen-activated protein kinase consensus site Ser-515 in the AR NH(2)-terminal region and at protein kinase C consensus site Ser-578 in the AR DNA binding domain. Phosphorylation at these sites alters the nuclear-cytoplasmic shuttling of AR and AR interaction with the Ku-70/80 regulatory subunits of DNA-dependent protein kinase. Abolishing AR Ser-578 phosphorylation by introducing an S578A mutation eliminates the AR transcriptional response to EGF and increases both AR binding of Ku-70/80 and nuclear retention of AR in association with hyperphosphorylation of AR Ser-515. The results support a model in which AR transcriptional activity increases castration-recurrent prostate cancer cell growth in response to EGF by site-specific serine phosphorylation that regulates nuclear-cytoplasmic shuttling through interactions with the Ku-70/80 regulatory complex.

Shorter CAG repeats in androgen receptor and non-GG genotypes in prostate-specific antigen loci are associated with decreased risk of benign prostatic hyperplasia and prostate cancer

The age-adjusted risk of prostate cancer (PC) has increased in Singapore since 1968. We investigated the relationship between polymorphisms in four genes, androgen receptor (AR), prostate-specific antigen (PSA), 5alpha-reductase type II (SRD5A2) and cytochrome P450c17alpha (CYP17) and PC and benign prostatic hyperplasia (BPH). Men with shorter CAG repeats in AR and above 69 years at diagnosis showed a trend of decreased PC risk (OR=0.28, 95% CI=0.08-1.03; p=0.05). Shorter CAG repeats and non-GG genotypes in the AR and PSA loci, respectively, showed a trend of decreased PC risk (OR=0.25, 95% CI=0.06-1.03; p=0.06) and a significantly decreased BPH risk (OR=0.38, 95% CI=0.15-0.94; p=0.04). The results indicate that allelic variation in PSA promoter activity may be androgen dependent and interaction of genes in androgen pathway may influence the risk of BPH and PC in Singapore males.

Longitudinal analysis of androgen deprivation of prostate cancer cells identifies pathways to androgen independence

BACKGROUND

Following androgen ablation therapy, the majority of prostate cancer patients develop treatment resistance with a median time of 18-24 months to disease progression.

METHODS

To identify molecular targets that promote prostate cancer cell survival and contribute to androgen independence, we evaluated changes in LNCaP cell gene expression during 12 months of androgen deprivation. At time points reflecting critical growth and phenotypic changes, we performed Affymetrix expression array analysis to examine the effects of androgen deprivation during the acute response, during the period of apparent quiescence, and following the emergence of a highly proliferative, androgen-independent prostate cancer cell phenotype (LNCaP-AI).

RESULTS

We discovered alterations in gene expression for molecules associated with promoting prostate cancer cell growth and survival, and regulating cell cycle progression and apoptosis. Additionally, expression of AR co-regulators, adrenal androgen metabolizing enzymes, and markers of neuroendocrine disease were significantly altered.

CONCLUSIONS

These findings contribute greatly to our understanding of androgen-independent prostate cancer. The value of this longitudinal approach lies in the ability to examine gene expression changes throughout the adaptive response to androgen deprivation; it provides a more dynamic illustration of genes which contribute to disease progression in addition to specific genes which constitute an androgen-independent phenotype.

A role for the androgen-receptor in clinically localized and advanced prostate cancer

Earlier studies of androgen-receptor (AR) expression using frozen prostate tissue, and later studies using archived specimens, produced the consensus that ligand-stabilized AR is nuclear, AR expression is similar in benign epithelia and stroma, AR expression is greater in secretory epithelia than basal cells, and AR expression is more variable in prostate cancer (CaP) than in benign prostatic hyperplasia (BPH). Accurate measurement of AR expression remains technically challenging but necessary to evaluate the relevance of AR to clinical CaP. Recent studies demonstrated that AR expression in epithelia and stroma may be prognostic in clinically localized CaP, and AR expression may play a role in racial differences in CaP mortality and predict response to androgen deprivation therapy. High levels of AR and AR-regulated gene expression indicate a central role for AR in growth regulation of castration-recurrent CaP. New treatments for the lethal phenotype of CaP require better understanding of AR transactivation during androgen deprivation therapy.

Hormone control and expression of androgen receptor coregulator MAGE-11 in human endometrium during the window of receptivity to embryo implantation

The androgen receptor (AR) is a ligand-activated transcription factor of the male and female reproductive tracts whose activity is modulated by coregulator binding. We recently identified melanoma antigen gene protein-11 (MAGE-11) of the MAGEA gene family that functions as an AR coregulator by binding the AR N-terminal FXXLF motif. Here we report that MAGE-11 is expressed in a temporal fashion in endometrium of normally cycling women. Highest levels of MAGE-11 mRNA and protein occur in the mid-secretory stage, coincident with the window of uterine receptivity to embryo implantation. Studies in human endometrial cell lines together with the hormone profile of the menstrual cycle and pattern of estrogen receptor-alpha expression in cycling endometrium suggest the rise in MAGE-11 mRNA results from down-regulation by estradiol during the proliferative phase and up-regulation by cyclic AMP signaling in the early and mid-secretory stage. In agreement with its coregulatory function, MAGE-11 localizes with AR in glandular epithelial cell nuclei in the mid-secretory stage. The increase in AR protein in the mid-secretory endometrium without an increase in AR mRNA suggests MAGE-11 stabilizes AR in glandular epithelial cell nuclei. This was supported by expression studies at low androgen levels indicating AR stabilization by MAGE-11 dependent on the AR N-terminal transactivation domain. The results suggest that MAGE-11 functions as a coregulator that increases AR transcriptional activity during the establishment of uterine receptivity in the human female.

Epidermal-growth-factor-dependent phosphorylation and ubiquitinylation of MAGE-11 regulates its interaction with the androgen receptor

The androgen receptor (AR) is a ligand-activated transcription factor that interacts with coregulatory proteins during androgen-dependent gene regulation. Melanoma antigen gene protein 11 (MAGE-11) is an AR coregulator that specifically binds the AR NH(2)-terminal FXXLF motif and modulates the AR NH(2)- and carboxyl-terminal N/C interaction to increase AR transcriptional activity. Here we demonstrate that epidermal growth factor (EGF) signaling increases androgen-dependent AR transcriptional activity through the posttranslational modification of MAGE-11. EGF in the presence of dihydrotestosterone stabilizes the AR-MAGE complex through the site-specific phosphorylation of MAGE-11 at Thr-360 and ubiquitinylation at Lys-240 and Lys-245. The time-dependent EGF-induced increase in AR transcriptional activity by MAGE-11 is mediated through AR activation functions 1 and 2 in association with the increased turnover of AR and MAGE-11. The results reveal a dynamic mechanism whereby growth factor signaling increases AR transcriptional activity through the covalent modification of an AR-specific coregulatory protein. Sequence conservation of the MAGE-11 phosphorylation and ubiquitinylation sites throughout the MAGE gene family suggests common regulatory mechanisms for this group of cancer-testis antigens.

Primary amenorrhea in a young Polish woman with complete androgen insensitivity syndrome and Sertoli-Leydig cell tumor: identification of a new androgen receptor gene mutation and evidence of aromatase hyperactivity and apoptosis dysregulation within the tumor

Primary amenorrhea in 46,XY females can be due to complete androgen insensitivity syndrome (CAIS), pure gonadal dysgenesis, 17-hydroxysteroid dehydrogenase deficiency, or mixed gonadal dysgenesis. The present paper describes a new de novo non-sense mutation in exon 1 (K141Z) of the androgen receptor gene (AR) and the expression in CAIS testis of aromatase, estrogen receptors, as well as proliferation- and apoptosis-associated proteins. CAIS is a rare disease characterized by absent virilization in 46,XY individuals and the development of a female phenotype despite normal or even elevated androgen levels. CAIS is usually caused by a mutation in AR, which leads to organ resistance to androgens. Testicular tumors such as Sertoli-Leydig cell tumor often develop in patients with CAIS. The immunohistochemical findings in the testes of our CAIS patient suggest that the high expression of aromatase and other molecular changes in the testis may be responsible for pubertal breast development and the increased risk of testicular tumor.

Modulation of androgen receptor activation function 2 by testosterone and dihydrotestosterone

The androgen receptor (AR) is transcriptionally activated by high affinity binding of testosterone (T) or its 5alpha-reduced metabolite, dihydrotestosterone (DHT), a more potent androgen required for male reproductive tract development. The molecular basis for the weaker activity of T was investigated by determining T-bound ligand binding domain crystal structures of wild-type AR and a prostate cancer somatic mutant complexed with the AR FXXLF or coactivator LXXLL peptide. Nearly identical interactions of T and DHT in the AR ligand binding pocket correlate with similar rates of dissociation from an AR fragment containing the ligand binding domain. However, T induces weaker AR FXXLF and coactivator LXXLL motif interactions at activation function 2 (AF2). Less effective FXXLF motif binding to AF2 accounts for faster T dissociation from full-length AR. T can nevertheless acquire DHT-like activity through an AR helix-10 H874Y prostate cancer mutation. The Tyr-874 mutant side chain mediates a new hydrogen bonding scheme from exterior helix-10 to backbone protein core helix-4 residue Tyr-739 to rescue T-induced AR activity by improving AF2 binding of FXXLF and LXXLL motifs. Greater AR AF2 activity by improved core helix interactions is supported by the effects of melanoma antigen gene protein-11, an AR coregulator that binds the AR FXXLF motif and targets AF2 for activation. We conclude that T is a weaker androgen than DHT because of less favorable T-dependent AR FXXLF and coactivator LXXLL motif interactions at AF2.

Complete androgen insensitivity without Wolffian duct development: the AR-A form of the androgen receptor is not sufficient for male genital development

BACKGROUND

The androgen receptor (AR) is essential for the differentiation of male external and internal genitalia. It is normally present in two forms, a full-length form B and an N-terminal truncated form A with still unknown function. Mutations in the AR gene cause androgen insensitivity syndrome (AIS), which is divided into subgroups according to the degree of undermasculinization. Patients with completely female external genitalia are classified as complete AIS (CAIS). However, a recent study has shown that some CAIS patients have signs of internal male genital differentiation due to missense mutations that show some degree of residual function.

OBJECTIVE

We aimed to study the expression of the different forms of the AR in two CAIS patients in relation to the development of male internal genital structures. One patient had a mutation (L7fsX33) that affects only the full-length AR-B form of the AR, whereas the other had a nonsense mutation (Q733X) affecting both isoforms.

MEASUREMENTS AND RESULTS

We thoroughly analysed internal genitalia at surgery and by histological examination. No signs of Wolffian duct (WD) development were present in any of the patients. Western blotting of proteins from gonadal and genital skin fibroblasts was performed with AR antibodies directed against different AR epitopes. The N-terminally truncated A form was expressed in normal amounts in the patient with the L7fsX33 mutation while no AR was detected in the other patient.

CONCLUSION

The presence of the AR-A form does not seem to be sufficient for WD maintenance and differentiation.

Immunocytochemical detection of the androgen receptor in fine needle aspirates from benign and malignant human prostate

A monoclonal antibody to the androgen receptor was applied to fine needle aspirates from patients with benign and malignant prostatic disease. The series includes six patients with benign hyperplasia and 24 patients with prostatic carcinomas. The androgen receptor was detected in most nuclei of both benign and malignant epithelial cells. The intensity of immunostaining varied. No obvious relation was observed between the intensity of the staining in benign versus malignant cells. In addition no clear differences were found in the proportion of androgen receptor positive cells in benign aspirates as compared with aspirates from well differentiated or moderately well differentiated prostatic carcinomas. The relative number of androgen receptor positive cells was highest in smears from poorly differentiated prostatic carcinomas.

Androgen receptor coregulators and their involvement in the development and progression of prostate cancer

The androgen receptor signaling axis plays an essential role in the development, function and homeostasis of male urogenital structures including the prostate gland although the mechanism by which the AR axis contributes to the initiation, progression and metastatic spread of prostate cancer remains somewhat enigmatic. A number of molecular events have been proposed to act at the level of the AR and associated coregulators to influence the natural history of prostate cancer including deregulated expression, somatic mutation, and post-translational modification. The purpose of this article is to review the evidence for deregulated expression and function of the AR and associated coactivators and corepressors and how such events might contribute to the progression of prostate cancer by controlling the selection and expression of AR targets.

Steroid hormone receptor gene polymorphisms and osteoporosis: a pharmacogenomic review

Osteoporosis is a common skeletal disorder with a strong genetic component. In recent years, significant progress has been made in understanding the genetic basis of osteoporosis. Given the biological significance of signalling through steroid hormone receptors, bone biology and calcium homeostasis, alleles of steroid hormone receptor genes have been postulated to contribute to the well-documented genetic predisposition to osteoporosis; and in different studies, these alleles have been associated with variation in bone mass and fracture risk. Even though results are still conflicting and the molecular mechanisms by which these polymorphisms influence receptor activity remain, in part, to be investigated, an additional important issue is represented by potential pharmacogenomic (the investigation of variations of DNA or RNA characteristics as related to drug response) or pharmacogenetic (the influence of variations of DNA sequence on drug response) implications. In fact, steroid hormone receptors actually mediate the action of several compounds known to positively or negatively affect bone homeostasis, such as vitamin D, estrogen and glucocorticoids. This review analyses major pharmacogenetic studies of polymorphisms in steroid hormone receptor genes.

Complete androgen insensitivity syndrome in a black South African family: a clinical and molecular investigation

OBJECTIVE

To present the first report of a clinical and molecular investigation of a black South African family with complete androgen insensitivity syndrome (CAIS).

METHODS

Biochemical and chromosomal analyses were performed. In addition, the molecular study included microsatellite analysis and DNA sequencing.

RESULTS

The index case, an unmarried 21-year-old black phenotypic female patient with primary amenorrhea, was identified in the Division of Endocrinology at a tertiary hospital affiliated with the University of the Witwatersrand. A detailed family history identified further potentially affected members (on the basis of primary amenorrhea), who were also included in the study. A total of 13 family members, including 6 affected subjects, were involved in the molecular study. All affected persons had a 46,XY karyotype, female phenotype, and hormonal profiles commensurate with their clinical diagnosis. The androgen receptor gene in an affected patient was examined for mutations by DNA sequencing. Mutation screening was extended to other family members. The genetic basis for CAIS in this large family is the missense mutation, D732Y, in exon 5 of the androgen receptor ligand-binding domain.

CONCLUSION

To our knowledge, this is the first case report of CAIS in South Africa in which molecular genetic techniques were used to substantiate the clinical diagnosis. The findings in this study have implications for genetic counseling in this family.

A naturally occurring mutation in the human androgen receptor of a subject with complete androgen insensitivity confers binding and transactivation by estradiol

The clinical phenotype of complete androgen insensitivity (CAIS) was associated with a mutation in the human androgen receptor (hAR) gene encoding the amino acid substitution, M745I, in the hAR protein. Transcriptional activation of hAR(M745I) by the synthetic androgen, methyltrienolone (R1881), was reduced compared to wild-type (wt) hAR. The transcriptional co-activator, androgen receptor associated protein 70 (ARA70), failed to enhance transactivation of hAR(M745I) at lower concentrations of R1881 (0.01-0.1 nM), whereas the p160 co-activators, SRC-1 and TIF2, stimulated activity. Transcriptional activity of hAR(M745I) was stimulated by 1 or 10 nM R1881 and activity was further enhanced by co-expression of ARA70 similar to that of the hAR(wt). Transcriptional activity of hAR(wt) was minimally stimulated by estradiol (E2) without or with co-expression of ARA70, whereas 10 or 100 nM E2 increased transactivation by hAR(M745I) of the androgen-responsive MMTV-luciferase reporter gene by 10-fold and activity was further enhanced by ARA70. Increasing concentrations of E2 competed more effectively for binding of R1881 to hAR(M745I) than to hAR(wt), indicative of the preferential binding of E2 to the mutant hAR. Partial tryptic digestion of hAR wt and M745I revealed that activation of the mutant protein was reduced in the presence of R1881. By contrast, tryptic digestion showed that the mutant hAR was activated by the binding of E2. In conclusion, the clinical phenotype of CAIS resulted from a hAR gene mutation encoding hAR(M745I) with reduced binding and transactivation by androgens, but the novel properties of enhanced affinity for and increased transactivation by estradiol.

Control of prostate cell growth: BMP antagonizes androgen mitogenic activity with incorporation of MAPK signals in Smad1

Alterations in the signaling pathways of bone morphogenetic proteins (BMPs) and activation of the ERK/MAP kinase (MAPK) pathway by growth factors have been implicated in the development and progression of prostate cancer. Smad1 acts as a substrate for MAPKs and also performs a central role in transmitting signals from BMPs. We found that BMPs/Smad1 signaling inhibits the growth of androgen-sensitive prostate cancer cells. Upon the incorporation of ERK/MAPK signals at its linker region, Smad1 physically interacts with androgen-activated androgen receptor (AR) and suppresses its functions. BMPs induce the function of Smad1 as an AR transcriptional corepressor. We demonstrated in vivo that Smad1 signaling is low in androgen-regulated growth of prostate cancer, is activated after castration, and also is decreased in hormone-independent tumors. The activation status of ERK/MAPK parallels Smad1 in the progression of prostate cancer; thus, our findings indicate a molecular basis for the integration of signals of MAPK and Smad1 in the progression and androgen regulation of prostate cancer.

Therapeutic potential of the SARMs: revisiting the androgen receptor for drug discovery

Selective androgen receptor modulators (SARMS) bind to the androgen receptor and demonstrate anabolic activity in a variety of tissues; however, unlike testosterone and other anabolic steroids, these nonsteroidal agents are able to induce bone and muscle growth, as well as shrinking the prostate. The potential of SARMS is to maximise the positive attributes of steroidal androgens as well as minimising negative effects, thus providing therapeutic opportunities in a variety of diseases, including muscle wasting associated with burns, cancer, end-stage renal disease, osteoporosis, frailty and hypogonadism. This review summarises androgen physiology, the current status of the R&D of SARMS and potential therapeutic indications for this emerging class of drugs.

Comparison of androgen receptor CAG and GGN repeat length polymorphism in humans and apes

Two polymorphic trinucleotide repeats of human androgen receptor gene (hAR), CAG and GGN which encode glutamine and glycine, have been shown to be associated with human diseases. The number of repeats ranges from 8 to 35 for the CAG and from 10 to 30 for the GGN in human populations. Longer CAG repeats are associated with reduced hAR transcriptional activity, spinal bulbar muscular atrophy and lower cognitive function in older men, whereas shorter CAG repeats are associated with increased risk of prostate cancer and infertility in men. The functional roles of the CAG and GGN repeats have not been clarified. In order to compare the sequence of the CAG and GGN regions in apes, we analyzed 57 chimpanzees, 18 gorillas, 20 orangutans, 16 agile gibbons, and 17 siamangs by PCR and electrophoresis. Two bonobos and one long-tailed macaque were also sequenced and the sequences of all species were aligned, respectively, with one human registered sequence. Seventeen different alleles (4, 7, 8, 9, 12, 14, 15, and 17-26 repeats) and 11 alleles (11-14 and 16-22 repeats) were detected at the CAG and the GGN loci, respectively. Although the repeat tract was conserved among apes, chimpanzees had alleles with a wide range of repeat lengths: (CAG)(14-26) and (GGN)(14-22). Gorillas were less polymorphic with the (CAG)(8) and (GGN)(19) alleles being most common, and orangutans exhibited monomorphic (CAG)(11) and (GGN)(22) alleles. On the other hand, agile gibbons and siamangs had the shortest (CAG)(4) allele, but showed variable length of GGN repeats (11-13 in agile gibbons and 16-21 in siamangs). In chimpanzees, frequent haplotypes consisting of short CAG repeats and long GGN repeats or vice versa was observed as in humans.

Effect of increasing ratio of estrogen: androgen on proliferation of normal human prostate stromal and epithelial cells, and the malignant cell line LNCaP

BACKGROUND

Changes in steroid ratios seen in the aging male are thought to promote prostate disease. The aims of this study were to compare the effects of varied ratios of steroids on growth of normal stromal and epithelial cell isolates, and the prostate cancer cell line, LNCaP.

METHODS

The effect of altered steroid ratios on cell proliferation of normal stromal (PrSC) and epithelial (PrEC) prostate cells, and the malignant cell line, LNCaP, were assessed.

RESULTS

Increasing the ratios of both estrogen:dihydrotestosterone (DHT) and DHT:estrogen, stimulated PrSC proliferation, with increasing estrogen:DHT having the greatest effect. LNCaP proliferation was increased significantly by both steroids, but altered ratios had no additional effect. PrEC proliferation was unaffected when cells were grown alone, despite presence of androgen receptors (AR) and estrogen receptors (ER). When grown in co-culture PrEC cell proliferation was significantly increased by treatments.

CONCLUSIONS

PrSC proliferation is stimulated by an increasing ratio of estrogen:androgen. Proliferation of normal epithelial cells is stimulated as a result of an indirect action of steroids mediated by stromal cells. Malignant prostate cancer cells have an altered response in comparison.

Differential expression of p160 steroid receptor coactivators in the rat testis and epididymis

OBJECTIVE

Androgens are critical for the development and maintenance of male sexual characteristics. Their action is mediated through the androgen receptor (AR). Ligand-bound AR interacts with coactivator proteins that mediate transcriptional activation. Such coactivators include three members of the 160 kDa proteins (p160s): SRC-1, TIF2/GRIP1, and p/CIP/RAC3/ACTR/AIB1/TRAM-1. The aim of this study was to investigate the expression of the three p160 coactivators and their association with AR in testis and epididymis.

METHODS

We determined the localization of these three p160 coactivators in immature and mature rat testis, and epididymis by immunohistochemistry using the specific monoclonal antibodies. We also performed double immunofluorescence staining to examine whether p160s are colocalized with AR in these tissues.

RESULTS

In seminiferous tubules of mature rat testis, SRC-1 and TRAM-1 immunoreactivity was found predominantly in spermatogonia and spermatocytes. In contrast, TIF2 was expressed predominantly in Sertoli cells. AR was coexpressed with TIF2 in this cell type. In immature rat testis, however, all three coactivators were expressed in both germ cells and Sertoli cells. In the epididymis, SRC-1 and TIF2 immunoreactivities were localized in nuclei of epithelial cells. However, TRAM-1 immunostaining was observed in the luminal portion of the cytoplasm with greater intensity than in the nucleus, especially in the caput epididymidis.

CONCLUSIONS

The cell-type-specific expression of p160 coactivators suggests specific roles in male reproductive organs. Further, the strong cytoplasmic localization of TRAM-1 protein in epithelial cells of epididymis suggests that TRAM-1 may have additional role(s) in transcriptional regulation.

The 5α-Reductase Type II A49T and V89L High-Activity Allelic Variants are More Common in Men with Prostate Cancer Compared with the General Population

OBJECTIVES

To compare men with prostate disease with those from the general population regarding polymorphisms in the androgen receptor gene and in the 5alpha-reductase II (SRD5A2) gene.

MATERIALS AND METHODS

The SRD5A2 polymorphisms A49T, V89L and R227Q, the androgen receptor CAG and GGN repeats and sex hormone status was investigated in men with prostate cancer (CaP) (n=89), benign prostate hyperplasia (n=45) and healthy military conscripts (n=223).

RESULTS

The SRD5A2 high-activity allele variants A49T AT and V89L LL were more frequent in CaP-patients compared to general population, p=0.026 and p=0.05, respectively. CaP progression was, however, independent of SRD5A2 variants. In contrary, men with GGN<23 had a higher risk of dying from the disease than their counterparts with longer repeats.

CONCLUSIONS

Men with CaP were more often genetically predisposed to a higher enzymatic activity in the turn over from T to DHT compared to the general population. In our population, androgen receptor genotype affected CaP outcome.

Estrogen receptor alpha binds to peroxisome proliferator-activated receptor response element and negatively interferes with peroxisome proliferator-activated receptor gamma signaling in breast cancer cells

PURPOSE

The molecular mechanisms involved in the repressive effects exerted by estrogen receptors (ER) on peroxisome proliferator-activated receptor (PPAR) gamma-mediated transcriptional activity remain to be elucidated. The aim of the present study was to provide new insight into the crosstalk between ERalpha and PPARgamma pathways in breast cancer cells.

EXPERIMENTAL DESIGN

Using MCF7 and HeLa cells as model systems, we did transient transfections and electrophoretic mobility shift assay and chromatin immunoprecipitation studies to evaluate the ability of ERalpha to influence PPAR response element-mediated transcription. A possible direct interaction between ERalpha and PPARgamma was ascertained by co-immunoprecipitation assay, whereas their modulatory role in the phosphatidylinositol 3-kinase (PI3K)/AKT pathway was evaluated by determining PI3K activity and AKT phosphorylation. As a biological counterpart, we investigated the growth response to the cognate ligands of both receptors in hormone-dependent MCF7 breast cancer cells.

RESULTS

Our data show for the first time that ERalpha binds to PPAR response element and represses its transactivation. Moreover, we have documented the physical and functional interactions of ERalpha and PPARgamma, which also involve the p85 regulatory subunit of PI3K. Interestingly, ERalpha and PPARgamma pathways have an opposite effect on the regulation of the PI3K/AKT transduction cascade, explaining, at least in part, the divergent response exerted by the cognate ligands 17beta-estradiol and BRL49653 on MCF7 cell proliferation.

CONCLUSION

ERalpha physically associates with PPARgamma and functionally interferes with PPARgamma signaling. This crosstalk could be taken into account in setting new pharmacologic strategies for breast cancer disease.

Roles and regulation of Wnt signaling and beta-catenin in prostate cancer

The Wnt signaling pathway and its key component beta-catenin play critical roles in embryonic development as well as in human diseases, including various malignancies. Accumulated evidence has demonstrated a significant role for the Wnt pathway in the development and progression of human prostate cancer. The recent discovery of an interaction between beta-catenin and the androgen receptor (AR) suggests a possible mechanism of cross talk between Wnt and androgen signaling pathways. In this review, we summarize the recent progresses in this interesting and growing field. Particularly, we focus on the observation that the activation of the Wnt-mediated signal occurs in a different manner in prostate cancer than in colorectal cancer or other human malignancies. Since mutations in Adenomatous polyposis coli (APC), beta-catenin, and other components of the beta-catenin destruction complex are rare in prostate cancer cells, other regulatory mechanisms appear to play dominant roles in the activation of beta-catenin, such as loss or reduction of E-cadherin, a component of cell adhesion complex, and abnormal expression of Wnt ligands, receptors, inhibitors, and other co-regulators. Understanding the role and regulation of the Wnt signaling pathway in prostate cancer cells may help identify new targets for the prostate cancer therapy.