Androgen receptor signalling in the prostate

Comprehensive biomarker profiles and chemometric filtering of urinary metabolomics for effective discrimination of prostate carcinoma from benign hyperplasia

Prostate cancer (PCa) is the most commonly diagnosed cancer in male individuals, principally affecting men over 50 years old, and is the leading cause of cancer-related deaths. Actually, the measurement of prostate-specific antigen level in blood is affected by limited sensitivity and specificity and cannot discriminate PCa from benign prostatic hyperplasia patients (BPH). In the present paper, 20 urine samples from BPH patients and 20 from PCa patients were investigated to develop a metabolomics strategy useful to distinguish malignancy from benign hyperplasia. A UHPLC-HRMS untargeted approach was carried out to generate two large sets of candidate biomarkers. After mass spectrometric analysis, an innovative chemometric data treatment was employed involving PLS-DA classification with repeated double cross-validation and permutation test to provide a rigorously validated PLS-DA model. Simultaneously, this chemometric approach filtered out the most effective biomarkers and optimized their relative weights to yield the highest classification efficiency. An unprecedented portfolio of prostate carcinoma biomarkers was tentatively identified including 22 and 47 alleged candidates from positive and negative ion electrospray (ESI+ and ESI-) datasets. The PLS-DA model based on the 22 ESI+ biomarkers provided a sensitivity of 95 ± 1% and a specificity of 83 ± 3%, while that from the 47 ESI- biomarkers yielded an 88 ± 3% sensitivity and a 91 ± 2% specificity. Many alleged biomarkers were annotated, belonging to the classes of carnitine and glutamine metabolites, C21 steroids, amino acids, acetylcholine, carboxyethyl-hydroxychroman, and dihydro(iso)ferulic acid.

Androgen receptor positively regulates gonadotropin-releasing hormone receptor in pituitary gonadotropes

Within pituitary gonadotropes, the gonadotropin-releasing hormone receptor (GnRHR) receives hypothalamic input from GnRH neurons that is critical for reproduction. Previous studies have suggested that androgens may regulate GnRHR, although the mechanisms remain unknown. In this study, we demonstrated that androgens positively regulate Gnrhr mRNA in mice. We then investigated the effects of androgens and androgen receptor (AR) on Gnrhr promoter activity in immortalized mouse LβT2 cells, which represent mature gonadotropes. We found that AR positively regulates the Gnrhr proximal promoter, and that this effect requires a hormone response element (HRE) half site at -159/-153 relative to the transcription start site. We also identified nonconsensus, full-length HREs at -499/-484 and -159/-144, which are both positively regulated by androgens on a heterologous promoter. Furthermore, AR associates with the Gnrhr promoter in ChIP. Altogether, we report that GnRHR is positively regulated by androgens through recruitment of AR to the Gnrhr proximal promoter.

Metabolic Roles of Androgen Receptor and Tip60 in Androgen-Dependent Prostate Cancer

Androgen receptor (AR)-mediated signaling is essential for the growth and differentiation of the normal prostate and is the primary target for androgen deprivation therapy in prostate cancer. Tat interactive protein 60 kDa (Tip60) is a histone acetyltransferase that is critical for AR activation. It is well known that cancer cells rewire their metabolic pathways in order to sustain aberrant proliferation. Growing evidence demonstrates that the AR and Tip60 modulate key metabolic processes to promote the survival of prostate cancer cells, in addition to their classical roles. AR activation enhances glucose metabolism, including glycolysis, tricarboxylic acid cycle and oxidative phosphorylation, as well as lipid metabolism in prostate cancer. The AR also interacts with other metabolic regulators, including calcium/calmodulin-dependent kinase kinase 2 and mammalian target of rapamycin. Several studies have revealed the roles of Tip60 in determining cell fate indirectly by modulating metabolic regulators, such as c-Myc, hypoxia inducible factor 1α (HIF-1α) and p53 in various cancer types. Furthermore, Tip60 has been shown to regulate the activity of key enzymes in gluconeogenesis and glycolysis directly through acetylation. Overall, both the AR and Tip60 are master metabolic regulators that mediate cellular energy metabolism in prostate cancer, providing a framework for the development of novel therapeutic targets in androgen-dependent prostate cancer.

Prospective evaluation of urinary steroids and prostate carcinoma-induced deviation: preliminary results

BACKGROUND

The serum prostate-specific antigen is the most widespread biomarker for prostate disease. Its low specificity for prostatic malignancies is a matter of concern and the reason why new biomarkers for screening purposes are needed. The correlation between altered production of the main steroids and prostate carcinoma (PCa) occurrence is historically known. The purpose of this study is to evaluate the modifications of a comprehensive urinary endogenous steroidal profile (USP) induced by PCa, by multivariate statistical methods.

METHODS

A total of 283 Italian subjects were included in the study, 139 controls and 144 PCa-affected patients. The USP, including 17 steroids and five urinary steroidal ratios, was quantitatively evaluated using gas chromatography coupled with single quadrupole mass spectrometry (GC-MS). The data were interpreted using a chemometric, multivariate approach (intrinsically more sensible to alterations with respect to traditional statistics) and a model for the discrimination of cancer-affected profiles was built.

RESULTS

Two multivariate classification models were calculated, the former including three steroids with the highest statistical significance (e.g. testosterone, etiocholanolone and 7β-OH-DHEA) and PSA values, the latter considering the three steroids' levels only. Both models yielded high sensitivity and specificity scores near to 70%, resulting significantly higher than PSA alone.

CONCLUSIONS

Three USP steroids resulted significantly altered in our PCa population. These preliminary results, combined with the simplicity and low-cost of the analysis, open to further investigation of the potential role of this restricted USP in PCa diagnosis.

Untargeted Metabolomic Profile for the Detection of Prostate Carcinoma-Preliminary Results from PARAFAC2 and PLS-DA Models

Prostate-specific antigen (PSA) is the main biomarker for the screening of prostate cancer (PCa), which has a high sensibility (higher than 80%) that is negatively offset by its poor specificity (only 30%, with the European cut-off of 4 ng/mL). This generates a large number of useless biopsies, involving both risks for the patients and costs for the national healthcare systems. Consequently, efforts were recently made to discover new biomarkers useful for PCa screening, including our proposal of interpreting a multi-parametric urinary steroidal profile with multivariate statistics. This approach has been expanded to investigate new alleged biomarkers by the application of untargeted urinary metabolomics. Urine samples from 91 patients (43 affected by PCa; 48 by benign hyperplasia) were deconjugated, extracted in both basic and acidic conditions, derivatized with different reagents, and analyzed with different gas chromatographic columns. Three-dimensional data were obtained from full-scan electron impact mass spectra. The PARADISe software, coupled with NIST libraries, was employed for the computation of PARAFAC2 models, the extraction of the significative components (alleged biomarkers), and the generation of a semiquantitative dataset. After variables selection, a partial least squares-discriminant analysis classification model was built, yielding promising performances. The selected biomarkers need further validation, possibly involving, yet again, a targeted approach.

Sexual steroids in serum and prostatic tissue of human non-cancerous prostate (STERPROSER trial)

BACKGROUND

The specific involvement of the sex steroids in the growth of the prostatic tissue remains unclear. Sex steroid concentrations in plasma and in fresh surgical samples of benign central prostate were correlated to prostate volume.

METHODS

Monocentric prospective study performed between September 2014 and January 2017. Age, obesity parameters, and both serum and intraprostatic concentrations of sex steroids were collected complying with the latest Endocrine Society guidelines and the steroids assessed by GC/MS. Statistical calculations were adjusted for age and body mass index (BMI).

RESULTS

Thirty-two patients, equally divided between normal- and high-volume prostate groups, were included in the analysis. High-volume prostate patients were older, heavier and had higher BMI. Comparison adjusted for age and BMI showed higher DHT concentrations in high-volume prostate. Both normal- and high-volume prostate tissues concentrate sex steroids in a similar way. Comparison of enzymatic activity surrogate marker ratios within tissue highlighted similar TT/E1 and TT/E2 ratios, and higher DHT/E1 ratio and lower DHT/PSA ratio in the high-volume prostates.

CONCLUSIONS

STERPROSER trial provides evidence for higher DHT concentration in highvolume prostates, that could reflect either higher 5-alpha reductase expression or lower expression of downstream metabolizing enzymes such as 3a-hydoxysteroid dehydrogenase.

Estrogen receptor (α and β) but not androgen receptor expression is correlated with recurrence, progression and survival in post prostatectomy T3N0M0 locally advanced prostate cancer in an urban Greek population

The objective of this study was to evaluate the expression of estrogen receptors (ER(α) and ER(β)) and androgen receptors (ARs) as prognostic factors for biochemical recurrence, disease progression and survival in patients with pT3N0M0 prostate cancer (PCa) in an urban Greek population. A total of 100 consecutive patients with pT3N0M0 PCa treated with radical prostatectomy participated in the study. The mean age and follow-up were 64.2 and 6 years, respectively. The HSCORE was used for semi-quantitative analysis of the immunoreactivity of the receptors. The prognostic value of the ER(α) and ER(β) and AR was assessed in terms of recurrence, progression, and survival. AR expression was not associated with any of the above parameters; however, both ERs correlated with the prognosis. A univariate Cox regression analysis showed that ER(α) positive staining was significantly associated with a greater hazard for all outcomes. Increased ER(β) staining was significantly associated with a lower hazard for all outcomes in the univariate analysis. When both ER HSCORES were used for the analysis, it was found that patients with high ER(α) or low ER(β) HSCORES compared with patients with negatively stained ER(α) and >1.7 hSCORE ER(β) had 6.03, 10.93, and 10.53 times greater hazard for biochemical disease recurrence, progression of disease and death, respectively. Multiple Cox proportional hazard analyses showed that the age, preoperative prostate specific antigen, Gleason score and ERs were independent predictors of all outcomes. ER expression is an important prognosticator after radical prostatectomy in patients with pT3N0M0 PCa. By contrast, AR expression has limited prognostic value.

Loss of ATF3 promotes hormone-induced prostate carcinogenesis and the emergence of CK5(+)CK8(+) epithelial cells

Steroid sex hormones can induce prostate carcinogenesis, and are thought to contribute to the development of prostate cancer during aging. However, the mechanism for hormone-induced prostate carcinogenesis remains elusive. Here we report that activating transcription factor 3 (ATF3) – a broad stress sensor – suppressed hormone-induced prostate carcinogenesis in mice. While implantation of testosterone and estradiol (T+E₂) pellets for 2 months in wild-type mice rarely induced prostatic intraepithelial neoplasia (PIN) in dorsal prostates (1 out of 8 mice), loss of ATF3 led to the appearance of not only PIN but also invasive lesions in almost all examined animals. The enhanced carcinogenic effects of hormones on ATF3-deficient prostates did not appear to be caused by a change in estrogen signaling, but were more likely a consequence of elevated androgen signaling that stimulated differentiation of prostatic basal cells into transformation-preferable luminal cells. Indeed, we found that hormone-induced lesions in ATF3-knockout mice often contained cells with both basal and luminal characteristics, such as p63⁺ cells (a basal cell marker) showing luminal-like morphology, or cells double-stained with basal (CK5⁺) and luminal (CK8⁺) markers. Consistent with these findings, low ATF3 expression was found to be a poor prognostic marker for prostate cancer in a cohort of 245 patients. Our results thus support that ATF3 is a tumor suppressor in prostate cancer.

The natural compound Guttiferone F sensitizes prostate cancer to starvation induced apoptosis via calcium and JNK elevation

BACKGROUND

In a cytotoxicity screen in serum-free medium, Guttiferone F showed strong growth inhibitory effect against prostate cancer cells.

METHODS

Prostate cancer cells LNCaP and PC3 were treated with Guttiferone F in serum depleted medium. Sub-G1 phase distributions were estimated with flow cytometry. Mitochondrial disruption was observed under confocal microscope using Mitotracker Red staining. Gene and protein expression changes were detected by real-time PCR and Western blotting. Ca(2+) elevation was examined by Fluo-4 staining under fluorescence microscope. PC3 xenografts in mice were examined by immunohistochemical analysis.

RESULTS

Guttiferone F had strong growth inhibitory effect against prostate cancer cell lines under serum starvation. It induced a significant increase in sub-G1 fraction and DNA fragmentation. In serum-free medium, Guttiferone F triggered mitochondria dependent apoptosis by regulating Bcl-2 family proteins. In addition, Guttiferone F attenuated the androgen receptor expression and phosphorylation of ERK1/2, while activating the phosphorylation of JNK and Ca(2+) flux. Combination of caloric restriction with Guttiferone F in vivo could increase the antitumor effect without causing toxicity.

CONCLUSIONS

Guttiferone F induced prostate cancer cell apoptosis under serum starvation via Ca(2+) elevation and JNK activation. Combined with caloric restriction, Guttiferone F exerted significant growth inhibition of PC3 cells xenograft in vivo. Guttiferone F is therefore a potential anti-cancer compound.

Prolonged exposure to (R)-bicalutamide generates a LNCaP subclone with alteration of mitochondrial genome

Advanced prostate cancers, initially sensitive to androgen deprivation therapy, frequently progress to the castration-resistant prostate cancer phenotype (CRPC) through mechanisms not yet fully understood. In this study we investigated mitochondrial involvement in the establishment of refractoriness to hormone therapy. Two human prostate cancer cell lines were used, the parental LNCaP and the resistant LNCaP-Rbic, the latter generated after continuous exposure to 20 μM of (R)-bicalutamide, the active enantiomer of Casodex®. We observed a significant decrease in mtDNA content and a lower expression of 8 mitochondria-encoded gene transcripts involved in respiratory chain complexes in both cell lines. We also found that (R)-bicalutamide differentially modulated dynamin-related protein (Drp-1) expression in LNCaP and LNCaP-Rbic cells. These data seem to indicate that the androgen-independent phenotype in our experimental model was due, at least in part, to alterations in mitochondrial dynamics and to a breakdown in the Drp-1-mediated mitochondrial network.

PCA3 noncoding RNA is involved in the control of prostate-cancer cell survival and modulates androgen receptor signaling

BACKGROUND

PCA3 is a non-coding RNA (ncRNA) that is highly expressed in prostate cancer (PCa) cells, but its functional role is unknown. To investigate its putative function in PCa biology, we used gene expression knockdown by small interference RNA, and also analyzed its involvement in androgen receptor (AR) signaling.

METHODS

LNCaP and PC3 cells were used as in vitro models for these functional assays, and three different siRNA sequences were specifically designed to target PCA3 exon 4. Transfected cells were analyzed by real-time qRT-PCR and cell growth, viability, and apoptosis assays. Associations between PCA3 and the androgen-receptor (AR) signaling pathway were investigated by treating LNCaP cells with 100 nM dihydrotestosterone (DHT) and with its antagonist (flutamide), and analyzing the expression of some AR-modulated genes (TMPRSS2, NDRG1, GREB1, PSA, AR, FGF8, CdK1, CdK2 and PMEPA1). PCA3 expression levels were investigated in different cell compartments by using differential centrifugation and qRT-PCR.

RESULTS

LNCaP siPCA3-transfected cells significantly inhibited cell growth and viability, and increased the proportion of cells in the sub G0/G1 phase of the cell cycle and the percentage of pyknotic nuclei, compared to those transfected with scramble siRNA (siSCr)-transfected cells. DHT-treated LNCaP cells induced a significant upregulation of PCA3 expression, which was reversed by flutamide. In siPCA3/LNCaP-transfected cells, the expression of AR target genes was downregulated compared to siSCr-transfected cells. The siPCA3 transfection also counteracted DHT stimulatory effects on the AR signaling cascade, significantly downregulating expression of the AR target gene. Analysis of PCA3 expression in different cell compartments provided evidence that the main functional roles of PCA3 occur in the nuclei and microsomal cell fractions.

CONCLUSIONS

Our findings suggest that the ncRNA PCA3 is involved in the control of PCa cell survival, in part through modulating AR signaling, which may raise new possibilities of using PCA3 knockdown as an additional therapeutic strategy for PCa control.

The AR dependent cell cycle: mechanisms and cancer relevance

Prostate cancer cells are exquisitely dependent on androgen receptor (AR) activity for proliferation and survival. As these functions are critical targets of therapeutic intervention for human disease, it is imperative to delineate the mechanisms by which AR engages the cell cycle engine. More than a decade of research has revealed that elegant intercommunication between AR and the cell cycle machinery governs receptor-dependent cellular proliferation, and that perturbations in this process occur frequently in human disease. Here, AR-cell cycle interplay and associated cancer relevance will be reviewed.

Recent developments in antiandrogens and selective androgen receptor modulators

The androgens testosterone and dihydrotestosterone play an essential role in the development and maintenance of primary and secondary male characteristics. Androgens bind to a specific androgen receptor (AR), a ligand-dependent transcription factor which controls the expression of a large number of downstream target genes. The AR is an essential player in early and late prostate cancer, and may also be involved in some forms of breast cancer. It also represents a drug target for the treatment of hypogonadism. Recent studies furthermore indicate that targeting the AR in pathologies such as frailty syndrome, cachexia or polycystic ovary syndrome may have clinical benefit. Numerous AR ligands with very different pharmacological properties have been identified in the last 40 years and helped to treat several of these diseases. However, progress still needs to be made in order to find compounds with an improved profile with regard to efficacy, differentiation and side-effects. This will only be achieved through a better understanding of the mechanisms involved in normal and aberrant AR signaling.

The Culinary-Medicinal Mushroom Coprinus comatus as a Natural Antiandrogenic Modulator

Prostate cancer is the most common cancer diagnosed in men. Chemotherapy, androgen ablation, and androgen antagonist treatments have proven to have significant effects in the early stages of prostate cancer, whereas advanced prostate cancer is resilient to such treatments. The androgen receptor (AR), a ligand-dependent transcription factor, is the major drug target of prostate cancer therapy. Transition to the androgen-independent stage involves the activation of signaling pathways, AR gene mutations, and other mechanisms. Higher basidiomycetes mushrooms have been used since ancient times in folk medicine to treat a diversity of diseases, including cancer. The present study evaluates the antiandrogenic activity of different Coprinus comatus strains in their ability to interfere with AR function. The authors found that the most active extract was C comatus strain 734 extracted with hexane (CC734-H). This extract was able to (1) inhibit AR-mediated reporter activity, (2) inhibit the proliferation and viability of the LNCaP cell line, and (3) inhibit the colony formation of the LNCaP cell line, in comparison to the DU-145, PC-3, and MDA-Kb2 cells. In addition, CC734-H was able to reduce AR levels and prostate-specific antigen gene expression in the LNCaP-treated cell line. This study illustrates the potential of the C comatus mushroom as a natural antiandrogenic modulator that could serve in the treatment of prostatic diseases.

Effect of combined hormonal and insulin therapy on the steroid hormone receptors and growth factors signalling in diabetic mice prostate

Diabetes causes harmful effects on prostatic morphology and function. However, there still are doubts about the occurrence of various diseases in the prostate, as well as abnormal angiogenesis in relation to diabetes. Thus, the aim of this study was to correlate and quantify the level of the steroid hormone receptors and the angiogenic and antiangiogenic factors in non-obese diabetic mice (Nod) after combined hormonal and insulin therapy. Sixty mice were divided into six groups after 20 days of diabetes: the control group received 0.9% NaCl, as did the diabetic group. The diabetic-insulin group received insulin, the diabetic-testosterone group received testosterone cypionate, the diabetic-oestrogen group received 17β-oestradiol, and the diabetic-insulin-testosterone-oestrogen group received insulin, testosterone and oestrogen simultaneously. After 20 days, the ventral lobe was processed for immunocytochemical and hormonal analyses. The results showed that the lowest serum testosterone and androgen receptor levels were found in the diabetic group and the highest testosterone and androgen receptor levels in the diabetic-insulin-testosterone-oestrogen group. The serum oestrogen level and its receptor showed changes opposite to those of testosterone and its receptor. The endostatin reactivity was mainly decreased in diabetic mice. The greatest IGFR-1 and VEGF reactivities occurred in diabetic mice. Thus, diabetes led to the prostatic hormonal imbalance, affecting molecular dynamics and angiogenesis in this organ. Combined insulin and steroid hormone therapy partially restored the hormonal and angiogenic imbalance caused by diabetes.

Androgen-related expression of G-proteins in ovarian cancer

BACKGROUND

Epidemiological and in vitro data implicate androgens in the aetiology of ovarian cancer, but the mechanisms by which this is mediated are unclear. In this study, we wished to examine the effects of androgens on gene expression in ovarian cancer.

METHODS

The expression of androgen receptor (AR) in OVCAR3 and OSEC2 cells was confirmed using immunoblotting and response to androgens was measured using flow cytometric assessment of S-phase fraction. The differential gene expression between androgen stimulated and unstimulated OVCAR3 ovarian cancer cells was examined with a cDNA microarray. The upregulation of a subset of these genes was then confirmed with reverse transcriptase PCR in both OVCAR3 and OSEC2, an ovarian epithelial cell line. Finally, the clinical significance of this upregulation was investigated by examining the expression of Rab25 and Rab35, two G-protein-related molecules in an ovarian cancer tissue microarray (TMA).

RESULTS

OVCAR3 and OSEC2 cells were shown to express the AR and showed an increase in S-phase fraction in response to androgen treatment. Treatment of OVCAR3 cells with androgen resulted in a significant upregulation of 121 genes. These findings were confirmed for a subset of seven monomeric G-protein-related genes in both OVCAR3 and OSEC2 cells. After staining for Rab25 and Rab35, the majority of TMA sections examined showed expression for Rab25 (92%) and Rab35 (95%). The expression of Rab25 correlated with histological grade, and expression was higher in endometrioid (median histoscore 10.5) than serous (7.5) or mucinous (5.3) tumours. The expression of Rab25 correlated positively with AR expression supporting its role as an androgen responsive gene in ovarian cancer.

CONCLUSIONS

These results suggest that androgens can effect expression of the oncogenic GTPases in ovarian cancer. We propose that the androgen responsive Rab35 may have clinical importance as a biomarker of AR function.

Differential effects of diabetes induced by streptozotocin and that develops spontaneously on prostate growth in Bio Breeding (BB) rats

We investigated molecular changes in the response to insulin in prostates of spontaneously developed (Bio Breeding) and streptozotocin (STZ)-induced diabetic rats that received sufficient amounts (euglycemic group), or suboptimal doses (hyperglycemic group) of insulin for 32 weeks, using Affymetrix GeneChip analysis of gene expression. Alterations in gene expression levels identified by microarray analysis, having potential biological relevance to prostate growth, were verified by real-time reverse transcription polymerase chain reaction (RT-PCR). A significant decrease in the weight of ventral prostate was observed in the hyperglycemic STZ-induced but not spontaneously developed diabetic group. Microarray analysis revealed that gene expression profiles were distinctly different in each region of the prostate, and that hyperglycemic diabetes in spontaneously developed and STZ-diabetic rats was associated with differential changes in the prostatic expression levels of 856 genes, of which 35 were related to cell growth, proliferation and death. RT-PCR data verified significant differences in the mRNA expression levels of Igfbp6, Tieg, and Clu between euglycemic and hyperglycemic groups, whereas expression levels of these genes in control and euglycemic diabetic groups were not significantly different. In ventral prostate, the mRNA expression levels of Igfbp6 and Tieg were significantly higher in the hyperglycemic STZ-induced diabetic than in the hyperglycemic spontaneously diabetic BBDP/Wor rats. Our data demonstrate that the diabetes induced by STZ in the BBDR/Wor rats affects prostate growth and the molecular response to insulin differently than that observed in BBDP/Wor rats that develop diabetes spontaneously.

AR, the cell cycle, and prostate cancer

The androgen receptor (AR) is a critical effector of prostate cancer development and progression. The dependence of this tumor type on AR activity is exploited in treatment of disseminated prostate cancers, wherein ablation of AR function (achieved either through ligand depletion and/or the use of AR antagonists) is the first line of therapeutic intervention. These strategies are initially effective, and induce a mixed response of cell cycle arrest or apoptosis in prostate cancer cells. However, recurrent, incurable tumors ultimately arise as a result of inappropriately restored AR function. Based on these observations, it is imperative to define the mechanisms by which AR controls cancer cell proliferation. Mechanistic investigation has revealed that AR acts as a master regulator of G1-S phase progression, able to induce signals that promote G1 cyclin-dependent kinase (CDK) activity, induce phosphorylation/inactivation of the retinoblastoma tumor suppressor (RB), and thereby govern androgen-dependent proliferation. These functions appear to be independent of the recently identified TMPRSS2-ETS fusions. Once engaged, several components of the cell cycle machinery actively modulate AR activity throughout the cell cycle, thus indicating that crosstalk between the AR and cell cycle pathways likely modulate the mitogenic response to androgen. As will be discussed, discrete aberrations in this process can alter the proliferative response to androgen, and potentially subvert hormonal control of tumor progression.

Structural dynamics of the human androgen receptor: implications for prostate cancer and neurodegenerative disease

The AR (androgen receptor) is a ligand-activated transcription factor that mediates the action of the steroids testosterone and dihydrotestosterone. Alterations in the AR gene result in a number of clinical disorders, including: androgen-insensitivity, which leads to disruption of male development; prostate cancer; and a neuromuscular degenerative condition termed spinal bulbar muscular atrophy or Kennedy's disease. The AR gene is X-linked and the protein is coded for by eight exons, giving rise to a C-terminal LBD (ligand-binding domain; exons 4-8), linked by a hinge region (exon 4) to a Zn-finger DBD (DNA-binding domain; exons 2 and 3) and a large structurally distinct NTD (N-terminal domain; exon 1). Identification and characterization of mutations found in prostate cancer and Kennedy's disease patients have revealed the importance of structural dynamics in the mechanisms of action of receptors. Recent results from our laboratory studying genetic changes in the LBD and the structurally flexible NTD will be discussed.

Stimulation of Steroid Receptor Coactivator-3 (SRC-3) Gene Overexpression by a Positive Regulatory Loop of E2F1 and SRC-3

Steroid receptor coactivator 3 (SRC-3, amplified in breast cancer 1, or ACTR) is a transcriptional coactivator for nuclear receptors and certain other transcription factors such as E2F1. SRC-3 is overexpressed in breast cancers, and its overexpression is sufficient to cause mammary carcinomas in vivo. However, the mechanisms controlling endogenous SRC-3 overexpression are unknown. In this study, we identified the first exon and analyzed the 5′ regulatory sequence of the SRC-3 gene. We found three evolutionarily conserved regions (ECRs) in the 5′ SRC-3 regulatory sequence, and ECR2 makes a major contribution to the SRC-3 promoter activity. The ECR2 region (bp −250/+350) contains several specificity protein 1 (Sp1) binding sites and two E2F1 binding sites. We show that E2F1 can significantly activate the ECR2 promoter activity in a dose-dependent manner. Furthermore, overexpression of E2F1 significantly increases the promoter activity of the endogenous SRC-3 gene and boosts SRC-3 expression in vivo. Conversely, knockdown of E2F1 reduces SRC-3 expression. We demonstrate that the mechanism of E2F1 activity on SRC-3 promoter is independent of the E2F binding sites but relies on the Sp1 element located at bp +150/+160. Sp1, E2F1, and SRC-3 are specifically recruited to this Sp1 site and the interaction between E2F1 and Sp1 is essential to modulate SRC-3 expression. Moreover, SRC-3 coactivates E2F1 activity and thereby additively stimulates a further increase in SRC-3 expression in vivo. These results suggest that in cells with hyperactive E2F1, such as the case encountered in breast cancer cells, there is a positive feedback regulatory loop consisting of E2F1 and SRC-3 to maintain high levels of SRC-3 and E2F1 activity, which may partially interpret the oncogenic role of SRC-3 overexpression.

Chemoprevention of prostate cancer

Prostate cancer is a common malignancy with multiple potential opportunities for cancer prevention. As the genetic basis of this malignancy is further understood, prevention strategies will be developed for individual patients based on specific risk factors and pathways of carcinogenesis. The PCPT has conclusively proven that prostate cancer prevention is possible. The results of the SELECT should be available within several years. An enormous challenge for the medical community will be the development of an efficient strategy to evaluate the substantial number of dietary, behavioral, and pharmacologic prevention opportunities. Ultimately, the goal of prostate can-cer prevention is to (1) identify men who are destined to develop clinically significant prostate cancer, and (2) provide individualized agents to prevent disease development.

Effect of insulin treatment on tissue size of the genitourinary tract in BB rats with spontaneously developed and streptozotocin-induced diabetes

To examine the differences between spontaneous and streptozotocin (STZ)-induced diabetes, four parallel studies were performed; three studies of diabetes-prone BB (BBDP/Wor) rats maintained for 8, 16, and 32 weeks and one study of STZ-injected diabetes-resistant BB (BBDR/Wor) rats maintained for 32 weeks. Each diabetic study has three groups of rats: a control group; a euglycemic group, which received sufficient amounts of insulin; and a hyperglycemic group, which received a suboptimal dose of insulin. The extent of tissue weight changes was generally shown to be less dramatic in the euglycemic diabetic than in the hyperglycemic diabetic rats. STZ-induced diabetes increased the bladder weight more dramatically (up to 3-fold) than did spontaneous diabetes (up to 2-fold). Furthermore, a significant decrease in the size of the adrenal gland (20%) and testis (10%) is observed only with spontaneous diabetes, whereas a significant decrease in the size of the ventral prostate (30%) is observed only with STZ-induced diabetes, although the serum testosterone levels are similar in both groups. Our data demonstrate that there are differences in the effect of insulin treatment on the tissue size of the genitourinary tract between spontaneously developed and streptozotocin-induced diabetes in BB rats.

Effects of 2,4-D and DCP on the DHT-induced androgenic action in human prostate cancer cells

2,4-Dichlorophenoxyacetic acid (2,4-D) and its metabolite 2,4-dichlorophenol (DCP) are used extensively in agriculture as herbicides, and are suspected of potential endocrine disruptor activity. In a previous study, we showed that these compounds exhibited synergistic androgenic effects by co-treatment with testosterone in the Hershberger assay. To elucidate the mechanisms of the synergistic effects of these compounds on the androgenicity of testosterone, the androgenic action of 2,4-D and DCP was characterized using a mammalian detection system in prostate cancer cell lines. In in vitro assay systems, while 2,4-D or DCP alone did not show androgenic activity, 2,4-D or DCP with 5alpha-dihydroxytestosterone (DHT) exhibited synergistic androgenic activities. Co-treatment of 10 nM 2,4-D or DCP with 10 nM DHT was shown to stimulate the cell proliferation by 1.6-fold, compared to 10 nM DHT alone. In addition, in transient transfection assays, androgen-induced transactivation was also increased to a maximum of 32-fold or 1.28-fold by co-treatment of 2,4-D or DCP with DHT, respectively. However, 2,4-D and DCP exerted no effects on either mRNA or protein levels of AR. In a competitive AR binding assay, 2,4-D and DCP inhibited androgen binding to AR, up to 50% at concentrations of approximately 0.5 microM for both compounds. The nuclear translocation of green fluorescent protein-AR fusion protein in the presence of DHT was promoted as the result of the addition of 2,4-D and DCP. Collectively, these results that 2,4-D and DCP enhanced DHT-induced AR transcriptional activity might be attributable, at least in part, to the promotion of AR nuclear translocation.

Mutation of histidine 874 in the androgen receptor ligand-binding domain leads to promiscuous ligand activation and altered p160 coactivator interactions

The androgen receptor (AR) signaling pathway is a major therapeutic target in the treatment of prostate cancer. The AR functions as a ligand-activated transcription factor in the presence of the cognate hormone ligands testosterone and dihydrotestosterone (DHT). We have characterized a highly conserved sequence at the C-terminal end of helix 10/11 in the ligand-binding domain (LBD), which is prone to receptor point mutations in prostate cancer. This sequence includes threonine 877 that is involved in hydrogen bonding to the D ring of the steroid molecule and leads to promiscuous ligand activation of the AR when mutated to alanine or serine. A second mutation in this region, H874Y, also results in a receptor protein that has broadened ligand-binding specificity, but retains an affinity for DHT (K(d) = 0.77 nm) similar to that of the wild-type receptor. The structure of the mutant LBD, expressed in Escherichia coli, is not dramatically altered compared with the wild-type AR-LBD in the presence of DHT, but shows a modestly increased sensitivity to protease digestion in the absence of hormone. This mutant AR showed wild-type AR-LBD/N-terminal domain interactions, but significantly enhanced binding and transactivation activity with all three members of the p160 family of coactivator proteins. Together, these phenotypic changes are likely to confer a selective advantage for tumor cells in a low androgen environment resulting from hormone therapy.

Regulation of androgen receptor and histone deacetylase 1 by Mdm2-mediated ubiquitylation

The androgen receptor (AR) is a member of the nuclear hormone receptor family of transcription factors and plays a critical role in regulating the expression of genes involved in androgen-dependent and -independent tumour formation. Regulation of the AR is achieved by alternate binding of either histone acetyltransferase (HAT)-containing co-activator proteins, or histone deacetylase 1 (HDAC1). Factors that control AR stability may also constitute an important regulatory mechanism, a notion that has been confirmed with the finding that the AR is a direct target for Mdm2-mediated ubiquitylation and proteolysis. Using chromatin immunoprecipitation (ChIP) and re-ChIP analyses, we show that Mdm2 associates with AR and HDAC1 at the active androgen-responsive PSA promoter in LNCaP prostate cancer cells. Furthermore, we demonstrate that Mdm2-mediated modification of AR and HDAC1 catalyses protein destabilization and attenuates AR sactivity, suggesting that ubiquitylation of the AR and HDAC1 may constitute an additional mechanism for regulating AR function. We also show that HDAC1 and Mdm2 function co-operatively to reduce AR-mediated transcription that is attenuated by the HAT activity of the AR co-activator Tip60, suggesting interplay between acetylation status and receptor ubiquitylation in AR regulation. In all, our data indicates a novel role for Mdm2 in regulating components of the AR transcriptosome.

Molecular profiling of human prostate tissues: insights into gene expression patterns of prostate development during puberty

Testosterone production surges during puberty and orchestrates massive growth and reorganization of the prostate gland, and this glandular architecture is maintained thereafter throughout adulthood. Benign prostatic hyperplasia (BPH) and prostate adenocarcinoma (PCA) are common diseases in adulthood that do not develop in the absence of androgens. Our objective was to gain insight into gene expression changes of the prostate gland at puberty, a crucial juncture in prostate development that is androgen dependent. Understanding the role played by androgens in normal prostate development may provide greater insight into androgen involvement in prostatic diseases. Benign prostate tissues obtained from pubertal and adult age group cadaveric organ donors were harvested and profiled using 20,000 element cDNA microarrays. Statistical analysis of the microarray data identified 375 genes that were differentially expressed in pubertal prostates relative to adult prostates including genes such as Nkx3.1, TMEPAI, TGFBR3, FASN, ANKH, TGFBR2, FAAH, S100P, HoxB13, fibronectin, and TSC2 among others. Comparisons of pubertal and BPH expression profiles revealed a subset of genes that shared the expression pattern between the two groups. In addition, we observed that several genes from this list were previously demonstrated to be regulated by androgen and hence could also be potential in vivo targets of androgen action in the pubertal human prostate. Promoter searches revealed the presence of androgen response elements in a cohort of genes including tumor necrosis factor-alpha induced adipose related protein, which was found to be induced by androgen. In summary, this is the first report that provides a comprehensive view of the molecular events that occur during puberty in the human prostate and provides a cohort of genes that could be potential in vivo targets of androgenic action during puberty.

The scaffolding protein RACK1 interacts with androgen receptor and promotes cross-talk through a protein kinase C signaling pathway

The androgen receptor (AR), a member of the nuclear hormone receptor superfamily, functions as a ligand-dependent transcription factor that regulates genes involved in cell proliferation and differentiation. Using a C-terminal region of the human AR in a yeast two-hybrid screen, we have identified RACK1 (receptor for activated C kinase-1) as an AR-interacting protein. In this report we found that RACK1, which was previously shown to be a protein kinase C (PKC)-anchoring protein that determines the localization of activated PKCbetaII isoform, facilitates ligand-independent AR nuclear translocation upon PKC activation by indolactam V. We also observed RACK1 to suppress ligand-dependent and -independent AR transactivation through PKC activation. In chromatin immunoprecipitation assays, we demonstrate a decrease in AR recruitment to the AR-responsive prostate-specific antigen (PSA) promoter following stimulation of PKC. Furthermore, prolonged exposure to indolactam V, a PKC activator, caused a reduction in PSA mRNA expression in prostate cancer LNCaP cells. Finally, we found PKC activation to have a repressive effect on AR and PSA protein expression in androgen-treated LNCaP cells. Our data suggest that RACK1 may function as a scaffold for the association and modification of AR by PKC enabling translocation of AR to the nucleus but rendering AR unable to activate transcription of its target genes.

Stat3 enhances transactivation of steroid hormone receptors

BACKGROUND: Steroid hormone receptors (SHRs) are members of the superfamily of ligand-activated transcription factors that regulate many biological processes. Co-regulators act as bridging molecules between the SHR and general transcription factors to enhance transactivation of target genes. Previous studies demonstrated that Stat3 is constitutively activated in prostate cancer and can enhance prostate specific antigen (PSA) expression and promote androgen independent growth. In this study, we investigate whether Stat3 can enhance steroid hormone receptors activation. METHODS: CV-1 cells in which plasmids expressing androgen receptor (AR), glucocorticoid receptor (GR), progesterone receptor (PR) or estrogen receptor (ER) were cotransfected with a constitutively active STAT3 mutant. RESULTS: Stat3 stimulates the transcriptional activity of all four SHR tested, AR, GR, PR and ER, in a hormone-dependent manner. Stat3 acts in a synergistic fashion with other coactivators such as SRC-1, pCAF, CBP, and TIF-2 on the transcriptional activity of these SHR. In addition, Stat3 significantly enhanced the sensitivity of androgen receptor in response to androgen. STAT3 did not affect the specificity of AR for other steroid hormones other than androgen or binding of AR to other hormone responsive elements. CONCLUSIONS: These findings suggest that Stat3 can enhance the transactivation of AR, GR, PR and ER, and activated Stat3 could have a role in the development or progression of a hypersensitive AR.

The role of dihydrotestosterone in benign prostatic hyperplasia

This article examines the role of the androgen dihydrotestosterone (DHT) in the healthy and diseased prostate and considers the implications of the data on DHT for therapeutic approaches to benign prostatic hyperplasia (BPH). Development and maintenance of the normal prostate, as well as development of BPH, depend on a functional androgen-signaling axis, components of which include: (1) testosterone synthesis in the testes and adrenal glands; (2) conversion of testosterone to DHT; (3) transport of DHT to target tissues; and (4) binding of DHT to the androgen receptor with consequent modulation of genes. DHT plays a beneficial role in the developing prostate but it can be detrimental in the adult prostate in that it causes pathologic prostate growth. The role of DHT in other adult tissues is uncertain. DHT has not been shown to perform beneficial functions unique from testosterone in the adult male, and it is believed that its fundamental effect is to amplify testosterone's weaker hormonal signal. Increased understanding of the cellular mechanisms by which the androgen-signaling axis functions has led to advances in treatment for prostate disease. In BPH, the 5alpha-reductase inhibitors--the only class of therapy to act at the pathophysiologic substrate of the disease--arrest the disease process, reduce prostate volume, improve symptoms, and reduce the risk of acute urinary retention and BPH-related surgery. The availability of dutasteride, the first dual (Type 1/Type 2) 5alpha-reductase inhibitor, offers the opportunity for rapid and consistent inhibition of DHT.

NF-kappaB and TNF-alpha stimulate androgen receptor expression in Sertoli cells

Germ cell development within the mammalian testis requires testosterone stimulation of somatic Sertoli cells via interaction with intracellular androgen receptors (AR). AR expression levels undergo marked changes during spermatogenesis suggesting that the modulation of AR expression is an important mechanism to regulate Sertoli cell responsiveness to testosterone. An analysis of the AR gene promoter revealed three kappaB enhancer elements that interacted with Sertoli cell p50 and RelA NF-kappaB proteins, and the overexpression of these NF-kappaB subunits in Sertoli cells stimulated AR promoter activity. Moreover, TNF-alpha, a secretory product of round spermatids, stimulated NF-kappaB binding to the AR promoter, induced AR promoter activity, and increased endogenous AR expression in primary cultures of Sertoli cells. Given the requirement of testosterone for spermatogenesis and the importance of AR in mediating Sertoli cell responsiveness to testosterone, the stimulation of AR expression by NF-kappaB and TNF-alpha may represent an important regulatory mechanism required to maintain efficient spermatogenesis.

Androgen-independent prostate cancer: potential role of androgen and ErbB receptor signal transduction crosstalk

In prostate cancer (PC), increasing evidence suggests that androgen receptor (AR) signalling is functional under conditions of maximal androgen blockade. PC cells survive and proliferate in the altered hormonal environment possibly by interactions between growth factor-activated pathways and AR signalling. The present review article summarizes the current evidence of this crosstalk and focuses on the interactions among the ErbB receptor network, its downstream pathways, and the AR. The potential role of this crosstalk in the development of androgen independence and in relation to antiandrogen therapy is discussed. Such interactions provide insight into possible complementary or additional strategies in the management of PC.

Increased risk of prostate cancer associated with AA genotype of cyclin D1 gene A870G polymorphism

CCND1 mRNA is alternatively spliced to produce 2 transcripts, and the splicing pattern may be modulated by a frequent A870G single-nucleotide polymorphism within the conserved splice donor site of exon 4. Several studies have suggested a significant association between the CCND1 genotype and onset or progression of various cancers. To investigate the correlation of the polymorphism with genetic susceptibility to PCa and its disease status, we examined the polymorphism in 214 cases of PCa, 234 cases of BPH and 254 male controls. The CCND1 A allele was more frequently observed in the PCa group (p = 0.015) and the BPH group (p = 0.018) than the control group. Men with the AA genotype had an increased risk of PCa (aOR = 1.93, 95% CI 1.13-3.30, p = 0.016) and BPH (aOR = 1.84, 95% CI 1.09-3.09, p = 0.023) compared to those with the GG genotype. No significant association was observed when men with the AG genotype were compared to those with the GG genotype (PCa: aOR = 1.00, 95% CI 0.65-1.54, BPH: aOR = 0.91, 95% CI 0.60-1.39). The risk of PCa associated with the AA genotype appeared to be stronger in men aged 73 years or younger (aOR = 2.89, 95% CI 1.38-6.01, p = 0.005), whereas no association was found in men older than 73 years (aOR = 1.02, 95% CI 0.44-2.34). No significant difference in genotype frequency was found among patients with low-, intermediate- and high-grade tumors (p = 0.730) or between patients with localized and metastatic PCa (p = 0.679). However, in patients with high-grade or metastatic PCa, a significantly increased risk associated with the AA genotype compared to controls was observed, while no significant results were found in those with low/intermediate or localized PCa. The A allele of the CCND1 A870G polymorphism was recessively associated with susceptibility to PCa and BPH in a Japanese population, giving a 2-fold increased risk of PCa and BPH in men with the AA genotype compared to those with the GG genotype. Although the risk of PCa associated with the AA genotype appeared to contribute especially to men aged 73 years or younger and the A allele may be associated with disease status of PCa, these conjectures require validation in future studies on a larger number of subjects.

Androgen receptor length polymorphism associated with prostate cancer risk in Hispanic men

PURPOSE

The transcriptional activation domain of the androgen receptor gene includes a CAG repeat length polymorphism. A smaller number of repeats is reported to increase the risk of prostate cancer. We investigated the association of CAG repeat length and the risk of prostate cancer in a case-control study of Hispanic men.

MATERIALS AND METHODS

To estimate the magnitude of the association of repeat length with prostate cancer risk, samples from 82 white patients of Hispanic origin (Hispanic) with prostate cancer and 145 Hispanic controls were genotyped. To determine the allelic distribution of repeats by race/ethnicity we genotyped 132 black men, 163 white men of nonHispanic origin (white) and 175 Hispanic men with no family history of prostate cancer, and performed pairwise comparison.

RESULTS

In the case-control study of Hispanic men with a repeat length of 18 or less versus greater than 18 we found an approximately 3-fold increased risk of prostate cancer (OR 2.7, 95% CI 1.21 to 6.01, t test p = 0.013, age adjusted OR 3.03, 95% CI 1.27 to 7.26). The distribution of alleles differed significantly by race/ethnicity. The mean prevalence of short CAG repeat alleles plus or minus SD was higher in black than in white men (19.8 +/- 3.2 versus 21.8 +/- 2.7, t test p <0.0001) and lower in Hispanic men than in other white men (22.7 +/- 3.3, t test p = 0.014).

CONCLUSIONS

To our knowledge, our study represents the first case-control study of the androgen receptor gene in a Hispanic population and provides evidence of the increased prostate cancer risk associated with short CAG repeats. Our results suggest that short CAG repeats are associated with an increased prostate cancer risk in Hispanic men.

Identification of human male germ cell-associated kinase, a kinase transcriptionally activated by androgen in prostate cancer cells

Androgen is involved in both normal development and malignant transformation of prostate cells. The signal transduction pathways associated with these processes are not well understood. Using a novel kinase display approach, we have identified a protein kinase, human male germ cell-associated kinase (hMAK), which is transcriptionally induced by the androgenic hormone 5alpha-dihydrotestosterone (DHT). The kinetics of induction is rapid and dose-dependent, and the induction is not blocked by cycloheximide treatment. Real time reverse transcription-PCR studies demonstrated a 9-fold induction of hMAK by 10 nm DHT at 24 h post-stimulation. The expression levels of hMAK in prostate cancer cell lines are in general higher than those of normal prostate epithelial cells. A reverse transcription-PCR product encompassing the entire hMAK open reading frame was isolated. The results from sequencing analysis showed that the hMAK protein is 623 amino acids in length and contains a kinase catalytic domain at its N terminus, followed by a proline/glutamine-rich domain. The catalytic domain of this kinase contains sequence motifs related to both the cyclin-dependent kinase and the mitogen-activated protein kinase families. When expressed in COS1 cells, hMAK is kinase-active as demonstrated by autophosphorylation and phosphorylation of exogenous substrate and is localized in the nucleus. A 3.7-kilobase pair promoter of the hMAK locus was isolated from a human genomic DNA bacterial artificial chromosome clone and was shown to be activated by DHT. This activation can be blocked by an anti-androgen drug bicalutamide (Casodex), implicating the involvement of androgen receptor in this process. Taken together, these data suggest that hMAK is a protein kinase targeted by androgen that may participate in androgen-mediated signaling in prostate cancer cells.

Expression of somatostatin receptor subtypes 2 and 4 in human benign prostatic hyperplasia and prostatic cancer

BACKGROUND

The presence of receptor subtypes for the inhibitory peptide somatostatin in prostatic tissue has been a controversial issue with conflicting reports. To elucidate whether prostatic epithelial cells express mRNA for somatostatin receptor (SSTR) subtype 2 and 4, we have investigated the localization of SSTR2 and SSTR4 transcripts in prostatic tissues by in situ hybridization.

METHODS

Nonradioactive in situ hybridization was performed with specific fluorescein-labeled SSTR2 and SSTR4 riboprobes on consecutive sections of benign prostatic hyperplasia (BPH) and prostate cancer tissues.

RESULTS

We report, for the first time, tissue localization of SSTR2 and SSTR4 mRNA in BPH and malignant cells of human prostate. Hybridization signals for SSTR4 mRNA transcripts were confined to the prostatic epithelium (12 of 16 BPH cases, and in 12 of 13 carcinoma cases), whereas SSTR2 transcripts were predominantly localized in the stromal compartment but also were detectable in epithelial cells in a significant number of specimens (11 of 17 BPH cases, and in 12 of 14 carcinoma cases). Furthermore, the staining intensity for SSTR2 and SSTR4 transcripts is stronger in malignant cells compared with adjacent BPH epithelium.

CONCLUSION

The data presented suggest that the expression of SSTR2 and SSTR4 transcripts is up-regulated in malignant cells and that not only SSTR2 agonists, but also compounds targeting the SSTR4 subtype may have a potential role in the treatment of prostate cancer.

Elevated serum progastrin-releasing peptide (31-98) in metastatic and androgen-independent prostate cancer patients

BACKGROUND

Increases in neuroendocrine phenotype and secretory products are closely correlated with tumor progression and androgen independence in prostate cancer. In this study, we explored this correlation using serum progastrin-releasing peptide (ProGRP), a carboxy-terminal region common to three subtypes of precursors for gastrin-releasing peptide (GRP), which is released from the neuroendocrine phenotype to act as a growth factor.

METHODS

In 60 patients with benign prostatic hyperplasia (BPH) and 200 with prostate cancer, serum ProGRP levels were determined with an enzyme-linked immunosorbent assay (ELISA) kit and evaluated in relation to clinical stage, hormonal treatment, and prostate-specific antigen (PSA) values. Fourteen randomly selected patients were entered in the follow-up study. Additionally, expression of ProGRP as determined by immunohistochemical analysis was compared to that of chromogranin-A (CgA) in tissue samples from several subjects.

RESULTS

We found a positive correlation between PSA and ProGRP in patients with untreated prostate cancer; no correlation was found in the treated groups. The increases in the ProGRP value and in the percentage of patients with higher than normal values were significant (P < 0.0001), especially in the androgen-independent group (P < 0.0001). A longitudinal study showed that, in a subset of patients, the ProGRP values tended to increase transiently when the cancer became androgen independent, but remained unchanged or decreased at the androgen-dependent stage. Positive staining for ProGRP occurred in a different distribution in neuroendocrine tissues than that of staining for CgA.

CONCLUSIONS

The clinical results demonstrated the existence of a regulatory mechanism for GRP, which to date had only been observed in cell lines. These findings suggest that GRP is a growth factor potentially upregulated by androgen but that does not rely principally on androgen modulation. The large overlap in levels of ProGRP among the groups limits the use of this value as a monitoring tool. Measurement of ProGRP, however, does have potential as an independent parameter to evaluate androgen-independent progression and to facilitate a new therapeutic strategy that may compensate for current limitations of diagnosis based on PSA alone.

Tip60 is a co-activator specific for class I nuclear hormone receptors

The nuclear hormone receptor superfamily is composed of a group of hormone-dependent transcription factors that play prominent roles in homeostatic events in vertebrates. A prerequisite for steroid hormone receptor activity is the binding of co-activator molecules to the activation function-2 domain of the receptor. The LXXLL motif/nuclear receptor box, contained within a number of co-activator molecules, mediates the interaction with nuclear hormone receptors. Tip60 (Tat-interactive protein 60 kDa), previously shown to bind to and enhance androgen receptor (AR)-mediated transactivation, contains a single nuclear receptor box at its extreme C terminus. We demonstrate that unlike members of the p160 co-activator family that interact predominantly with the N terminus of the AR in an LXXLL motif-independent manner, the LXXLL motif of Tip60 is required and is sufficient for AR interaction. Furthermore, by using the mammalian two-hybrid system and transient transfection experiments, we show that Tip60 preferentially interacts with and up-regulates class I nuclear receptors, suggesting that Tip60 is a steroid hormone receptor-specific co-activator. We conclude that Tip60 may specifically regulate a subset of nuclear hormone receptors, giving an indication to how regulated nuclear receptor activation can be achieved.

Hormonal treatment of patients with benign prostatic hyperplasia: pros and cons

The recognition that dihydrotestosterone is a "major player" in the development of benign prostatic hyperplasia (BPH) provided an impetus for the development of a 5a-reductase inhibitor, finasteride. During the past 5 years, a number of publications have noted that alpha blockers appear more efficacious than finasteride. This article reviews the role of hormones (particularly finasteride) in the treatment of lower urinary tract symptoms caused by BPH. These observations indicate that finasteride has a role in the management of larger prostates. Long-term use reduces the development of urinary retention and need for invasive procedures such as transurethral prostatectomy. The major adverse impact of finasteride is its effect on the patient's libido and sexual function. This is a less morbid problem for the elderly than the potential syncope associated with the use of alpha blockers. A greater understanding of the interaction of hormones on prostate receptors will provide newer tools for the treatment of BPH.

Loss of androgen receptor associated protein 70 (ARA70) expression in a subset of HER2-positive breast cancers

Co-transfection studies indicate that HER2 (erbB-2) overexpression results in the phosphorylation and enhanced transcriptional activity of the androgen receptor (AR). This amplification of AR action is further enhanced by the expression of ARA70, a putative co-activator with a predilection for the AR. Because androgens inhibit the growth of breast cancer cells whereas HER2 overexpression stimulates the growth of these cells, it seems possible that loss of expression of AR or ARA70 in some HER2 overexpressing tumors might confer a growth advantage to these cells. We examined ARA70 and AR expression in 20 HER2-positive (overexpressing) and 21 HER2-negative cases of breast invasive ductal carcinoma (IDC) to determine the relationship between loss of ARA70 and/or AR with HER2 overexpression. Strong ARA70 immunostaining was observed in all normal and breast epithelial cells in fibrocystic change and in in situ carcinoma present in the patient samples. Of the 41 cases of IDC, focal or complete loss of ARA70 protein expression was observed in 46% of the cases, with 60% of HER2-positive versus 33% of HER2-negative cases showing loss. Loss of AR expression was observed in 60% of HER2-positive versus 43% of HER2-negative cases. Remarkably, only 20% of HER2-positive tumors expressed both AR and ARA70, while 43% of HER2-negative tumors expressed both of these elements of the AR signaling pathway. This trend is consistent with a possible clinical relevance of the potential crosstalk between the HER2 and AR signaling pathways. Western blot analysis for ARA70 expression performed on frozen breast biopsies of normal or malignant breast tissue from four patients revealed a 70 kDa immunoreactive band in all four normal tissue samples, with an additional 35 kDa band in two of the breast cancer samples and in human breast cancer MCF-7 cells. This may reflect aberrant splicing in some breast cancers, leading to the emergence of the 35 kDa isoform.

E2F activity is biphasically regulated by androgens in LNCaP cells

Androgens exert a peculiar biphasic dose-dependent influence on the proliferation of LNCaP cells, a widely used model to study androgen effects on prostate cancer cells. Low concentrations of androgen stimulate proliferation, but high concentrations inhibit proliferation and induce strong expression of differentiation markers. In order to gain more insight into the molecular mechanisms that underlie these changes we studied the influence of a wide concentration range of the synthetic androgen R1881 on several cell cycle- and differentiation-related parameters. Low concentrations (0.1 nM), known to promote LNCaP cell proliferation, induce an increase of Retinoblastoma protein phosphorylation, accompanied by an increase of E2F-1 protein levels and E2F activity and by increased expression of the E2F-target gene products E2F-1 and cyclin A. High concentrations of R1881 (10 nM) induce strong expression of the differentiation marker prostate-specific antigen. Retinoblastoma protein is largely hypophosphorylated, resulting in low E2F activity and low concentrations of E2F-1 and cyclin A mRNA. Finally, there is a strong increase of p27(KIP1) protein, but not of p27(KIP1) mRNA. These results indicate that the biphasic dose response of LNCaP proliferation to androgen is closely reflected in Rb phosphorylation, E2F activity and p27(KIP1) protein expression.