Androgen receptor polymorphisms: association with prostate cancer risk, relapse and overall survival

Prostate cancer biology & genomics

Prostate Cancer is now the second biggest cause of cancer mortality in the UK. Media coverage has been rising, with some attributing to a rise in the cases diagnosed and treated in the NHS down to the “Fry and Turnbull effect”. Our understanding of prostate cancer has increased tremendously in the past decades, with advances in molecular biology and genomics driving the way to new treatments and diagnostics. This Special Edition of Translational Andrology and Urology 2019: Prostate Cancer Biology and Genomics aims to review the current state of prostate cancer genomics, proteomics, diagnostics and treatment.

Association between polymorphic CAG repeat lengths in the androgen receptor gene and susceptibility to prostate cancer: A systematic review and meta-analysis

BACKGROUND

Previous studies have been conducted to reveal the relationship between androgen receptor CAG polymorphism and risk of prostate cancer, yet the results were elusive and controversial. Thus, this meta-analysis was performed to clarify this association.

METHODS

To obtain the relevant available studies, online databases PubMed, Embase, and Web of science were searched until September 1st, 2016. The pooled odds ratios (ORs) with 95% confidence intervals (CIs) were used to assess the strength of such association. Subgroup analyses were conducted based on ethnicity and source of controls. Moreover, Begg's funnel plots and Egger's linear regression test were conducted to test the publication bias.

RESULTS

Overall, our results enrolled 51 studies indicated that significant increased risk of prostate cancer was associated with androgen receptor CAG polymorphism (OR  =  0.77, 95% CI: 0.67-0.89). In addition, compared with CAG repeat <20, 22, carriers of ≧20, 22 repeats had decreased risk of prostate cancer (cut-off point  =  20: OR  =  0.27, 95% CI: 0.13-0.52; cut-off point  =  22: OR  =  0.82, 95% CI: 0.70-0.97). However, when cut-off point  =  23, no significant result was detected in such association (pooled OR  =  0.88, 95% CI: 0.63-1.24). When cut-off point is 22, the results were positive only in Asian population (OR  =  0.53, 95% CI: 0.32-0.89) in the subgroup analysis by ethnicity. Besides, when the studies were stratified by source of controls, the results were not significant in both the subgroup of population-based controls and hospital-based controls.

CONCLUSIONS

This meta-analysis suggested the carriers of short polymorphic CAG repeats might increase susceptibility to prostate cancer, which held potential as a detecting marker of the risk of prostate cancer.

Androgen receptor gene polymorphisms and risk of prostate cancer: a meta-analysis

Although the association between CAG and GGN repeats in the androgen receptor gene and prostate cancer risk has been widely studied, it remains controversial from previous meta-analyses and narrative reviews. Therefore, we performed this meta-analysis to provide more precise estimates with sufficient power. A total of 51 publications with 61 studies for CAG repeats and 14 publications with 16 studies for GGN repeats were identified in the meta-analysis. The results showed that short CAG repeats (<22 repeats) carriers presented an elevated risk of prostate cancer than long CAG repeats (≥22) carriers (OR = 1.31, 95% CI 1.16 to 1.47). Prostate cancer cases presented an average fewer CAG repeats (MD = −0.85, 95% CI −1.28 to −0.42) than controls. Short GGN repeats (≤16) carriers presented an increased risk of prostate cancer than long GGN repeats (>16) carriers (OR = 1.38, 95% CI 1.05 to 1.82). In subgroup analyses, the abovementioned significant association was predominantly observed in Caucasian populations. The meta-analysis showed that short CAG and GGN repeats in androgen receptor gene were associated with increased risk of prostate cancer, especially in Caucasians.

Shorter GGN Repeats in Androgen Receptor Gene Would Not Increase the Risk of Prostate Cancer

The association between the polymorphic GGN repeat in androgen receptor gene and prostate cancer susceptibility has been studied extensively. But the results of these polymorphisms with prostate cancer risk remain inconclusive. Previous meta-analysis showed short GGN repeats (≤16 repeats) had high risks for prostate cancer compared with longer GGN repeats (>16 repeats). Many studies have been published since the release of the previous meta-analysis. Here, we conducted an updated meta-analysis to demonstrate whether short repeats have higher risks for prostate cancer compared to long repeats. Five databases (PubMed, EMBASE, Cochrane Library, The China National Knowledge Infrastructure, and Web of Science) were last searched until January 1, 2016. Random- or fixed-effects model was performed based on the heterogeneity among studies. The potential publication bias was assessed via Begg funnel plot and Egger regression test. Twelve out of 157 studies were extracted. The result indicated that there was no significant difference between short repeat group and long repeat group in the overall analysis ( I² = 80.6%, P = .000, odds ratio = 1.31, 95% confidence interval: 0.93-1.83). There was no association between the length of GGN repeats and the occurrence of prostate cancer in both Caucasian and African American ( I² = 6.7%, P = .359, odds ratio = 1.11, 95% confidence interval: 0.94-1.32; and I² = 74.1%, P = .050, odds ratio = 0.963, 95% confidence interval: 0.36-2.58). Our result demonstrated that a shorter GGN repeat polymorphism cannot increase the risk of prostate cancer compared to the longer GGN repeats. That's different with previous meta-analysis.

Positive association of the androgen receptor CAG repeat length polymorphism with the risk of prostate cancer

Prostate cancer (PC) is the most frequently diagnosed cancer in Ecuador (15.6%). The androgen receptor gene codes for a protein that has an androgen‑binding domain, DNA‑binding domain and N‑terminal domain, which contains two polymorphic trinucleotide repeats (CAG and GGC). The aim of the present study was to determine whether variations in the number of repetitions of CAG and GGC are associated with the pathological features and the risk of developing PC. The polymorphic CAG and GGC repeat lengths in 108 mestizo patients with PC, 148 healthy mestizo individuals, and 78 healthy indigenous individuals were examined via a retrospective case‑control study. Genotypes were determined by genomic sequencing. The results demonstrated that patients with ≤21 CAG repeats have an increased risk of developing PC [odds ratio (OR)=2.99, 95% confidence interval (CI) =1.79‑5.01; P<0.001]. The presence of ≤21 CAG repeats was also associated with a tumor stage ≥T2c (OR=4.75; 95% CI=1.77‑12.72; P<0.005) and a Gleason score ≥7 (OR=2.9; 95% CI=1.1‑7.66; P=0.03). In addition, the combination of ≤21 CAG and ≥17 GGC repeats was associated with the risk of developing PC (OR=2.42; 95% CI=1.38‑4.25; P=0.002) and with tumor stage ≥T2c (OR=2.77; 95% CI=1.13‑6.79; P=0.02). In conclusion, the histopathological characteristics and PC risk in Ecuadorian indigenous and mestizo populations differs in association with the CAG repeats, and the combination of CAG and GGC repeats.

Androgen receptor-related diseases: what do we know?

The androgen receptor (AR) and the androgen-AR signaling pathway play a significant role in male sexual differentiation and the development and function of male reproductive and non-reproductive organs. Because of AR's widely varied and important roles, its abnormalities have been identified in various diseases such as androgen insensitivity syndrome, spinal bulbar muscular atrophy, benign prostatic hyperplasia, and prostate cancer. This review provides an overview of the function of androgens and androgen-AR mediated diseases. In addition, the diseases delineated above are discussed with respect to their association with mutations and other post-transcriptional modifications in the AR. Finally, we present an introduction to the potential therapeutic application of most recent pharmaceuticals including miRNAs in prostate cancer that specifically target the transactivation function of the AR at post-transcriptional stages.

Influence of CAG Repeat Polymorphism on the Targets of Testosterone Action

In the last decade, ample evidence has demonstrated the growing importance of androgen receptor (AR) CAG repeat polymorphism in andrology. This genetic parameter is able to condition the peripheral effects of testosterone and therefore to influence male sexual function and fertility, cardiovascular risk, body composition, bone metabolism, the risk of prostate and testicular cancer, the psychiatric status, and the onset of neurodegenerative disorders. In this review, we extensively discuss the literature data and identify a role for AR CAG repeat polymorphism in conditioning the systemic testosterone effects. In particular, our main purpose was to provide an updated text able to shed light on the many and often contradictory findings reporting an influence of CAG repeat polymorphism on the targets of testosterone action.

Hormonal profile and androgen receptor study in prepubertal girls with hypertrichosis

Background

Prepubertal hypertrichosis is a reportedly benign condition characterized by an excessive growth of vellous hair in non-androgen dependent areas of the body compared to the amount usually present in normal subjects of the same age, race and sex. Although this condition is usually considered idiopathic and regarded as benign, it may be very disturbing cosmetically, causing significant patient and parental anxiety.

Method

We performed a hormonal and androgen receptor study in 42 prepubertal girls with hypertrichosis and 29 control girls from 2 to 8 years of age. Both groups underwent a determination of basal LH, FSH, 17OH progesterone, androstenedione, testosterone, estradiol and SHBG, abdominal ultrasound to assess ovarian morphology, and the number of androgen receptor CAG/GGC repeats in DNA obtained from peripheral leukocytes.

Results

The hypertrichosis score was higher in the cases compared to controls. Serum gonadotropins and sex steroids were similar in both groups, but SHBG was significantly lower in the girls with hypertrichosis (71.1 ± 2.9 vs 81.9 ± 3.0 nmol/L, p < 0.02). The distribution of shorter, larger and total alleles was not statistically different between cases and controls. The combined analysis of CAG/GGC, however, showed a significantly higher prevalence of the most androgen-sensitive haplotypes (1–2: <22CAG + 17/17GGC- < 14CAG + 17/18GGC) in girls with hypertrichosis compared to controls.

Conclusions

We conclude that girls with hypertrychosis exhibit AR(s) with enhanced sensitivity, which may facilitate the growth of their body hair.

Influence of music on steroid hormones and the relationship between receptor polymorphisms and musical ability: a pilot study

Studies have shown that music confers plasticity to the brain. In a preliminary pilot study, we examined the effect of music listening on steroid hormones and the relationship between steroid hormone receptor polymorphisms and musical ability. Twenty-one subjects (10 males and 11 females) were recruited and divided into musically talented and control groups. The subjects selected (1) music they preferred (chill-inducing music) and (2) music they did not like. Before and after the experiments, saliva was collected to measure the levels of steroid hormones such as testosterone, estradiol, and cortisol. DNA was also isolated from the saliva samples to determine the androgen receptor (AR) and arginine vasopressin receptor 1A genotypes. Advanced Measures of Music Audiation (AMMA) was used to determine the musical ability of the subjects. With both types of music, the cortisol levels decreased significantly in both sexes. The testosterone (T) levels declined in males when they listened to both types of music. In females, the T levels increased in those listening to chill-inducing music but declined when they listened to music they disliked. However, these differences were not significant. The 17-beta estradiol levels increased in males with both types of music, whereas the levels increased with chill-inducing music but declined with disliked music in females. The AMMA scores were higher for the short repeat length-type AR than for the long repeat length-type. Comparisons of AR polymorphisms and T levels before the experiments showed that the T levels were within the low range in the short repeat length-type group and there was a positive relationship with the repeat length, although it was not significant. This is the first study conducted in humans to analyze the relationships between the AR gene, T levels, and musical ability.

Molecular markers in sex hormone pathway genes associated with the efficacy of androgen-deprivation therapy for prostate cancer

Although most advanced prostate cancer patients respond to androgen-deprivation therapy (ADT), the efficacy is widely variable. We investigated whether the host genetic variations in sex hormone pathway genes are associated with the efficacy of ADT. A cohort of 645 patients with advanced prostate cancer treated with ADT was genotyped for 18 polymorphisms across 12 key genes involved in androgen and estrogen metabolism. We found that after adjusting for known risk factors in multivariate Cox regression models, AKR1C3 rs12529 and AR-CAG repeat length remained significantly associated with prostate cancer-specific mortality (PCSM) after ADT (P ≤ 0.041). Furthermore, individuals carrying two unfavorable genotypes at these loci presented a 13.7-fold increased risk of PCSM compared with individuals carrying zero (P<0.001). Our results identify two candidate molecular markers in key genes of androgen and estrogen pathways associated with PCSM after ADT, establishing the role of pharmacogenomics in this therapy.

Androgen receptor GGC polymorphism and testosterone levels associated with high risk of prostate cancer and benign prostatic hyperplasia

Polymorphic GGC repeats in the androgen receptor (AR) gene can alter transactivation of androgen-responsive genes and increase the risk of benign prostatic hyperplasia (BPH) and prostate cancer (PCa). We investigated the association between GGC repeat length, testosterone levels and the risk of developing PCa and BPH in a population from southern Brazil. A sample comprising 130 PCa, 126 BPH and 88 control patients was evaluated. DNA was extracted from leukocytes and the AR gene was analyzed by fragment analysis. The hazard ratio (HR) was estimated. GGC mean length was not different between the three study groups. The risk of developing PCa in individuals with GGC > 19 was 3.300 (95 %CI 1.385-7.874) higher when compared to the GGC ≤ 19 group (p = 0.007). The risk of developing PCa and BPH in individuals with total testosterone levels <4 ng/mL was 2.799 (95 % CI 1.362-5.754). (p = 0.005) and 2.786 (95 % CI 1.470-5.280) (p = 0.002), respectively. Total testosterone levels in patients with GGC > 19 were significantly lower when compared to patients in the GGC ≤ 19 group. Our data suggest that the presence of a high number of polymorphic GGC repeats in the AR gene is associated with an increased risk of developing PCa and BPH, and that lower testosterone levels also increase the risk of developing these diseases.

Polymorphisms in androgen signaling pathway predisposing to prostate cancer

Prostate cancer is the most frequent male malignancy diagnosed in western countries and androgens are known to mediate key physiological processes in prostate tissue. Since endogenous androgens have long been considered to be risk factors for prostate cancer, genes involved in androgen biosynthesis and metabolism have been extensively studied. In this review, association of androgen pathway genes, their polymorphic sites and risk of prostate cancer in different ethnic backgrounds is addressed together with their use to predict susceptibility and clinical outcomes of prostate cancer patients. The effect of the polymorphisms seems vary in different patients, populations and ethnic backgrounds. To date it is evident that the association between androgen pathway gene polymorphisms and prostate cancer risk is complex and many of the results are characterized by irreproducibility, which can be attributed to a variety of biological, statistical and technical reasons. In the future, with increasing knowledge, developing technologies and new genomic biomarkers it likely becomes possible to better estimate the risk of prostate cancer, and distinguish indolent disease from aggressive based on molecular profiling, and the analysis of gene-gene and gene-environment interactions.

Corepressor effect on androgen receptor activity varies with the length of the CAG encoded polyglutamine repeat and is dependent on receptor/corepressor ratio in prostate cancer cells

The response of prostate cells to androgens reflects a combination of androgen receptor (AR) transactivation and transrepression, but how these two processes differ mechanistically and influence prostate cancer risk and disease outcome remain elusive. Given recent interest in targeting AR transrepressive processes, a better understanding of AR/corepressor interaction and responses is warranted. Here, we used transactivation and interaction assays with wild-type and mutant ARs, and deletion AR fragments, to dissect the relationship between AR and the corepressor, silencing mediator for retinoic acid and thyroid hormone receptors (SMRT). We additionally tested how these processes are influenced by AR agonist and antagonist ligands, as well as by variation in the polyglutamine tract in the AR amino terminal domain (NTD), which is encoded by a polymorphic CAG repeat in the gene. SMRT was recruited to the AR ligand binding domain by agonist ligand, and as determined by the effect of strategic mutations in activation function 2 (AF-2), requires a precise conformation of that domain. A distinct region of SMRT also mediated interaction with the AR-NTD via the transactivation unit 5 (TAU5; residues 315-538) region. The degree to which SMRT was able to repress AR increased from 17% to 56% as the AR polyglutamine repeat length was increased from 9 to 42 residues, but critically this effect could be abolished by increasing the SMRT:AR molar ratio. These data suggest that the extent to which the CAG encoded polyglutamine repeat influences AR activity represents a balance between corepressor and coactivator occupancy of the same ligand-dependent and independent AR interaction surfaces. Changes in the homeostatic relationship of AR to these molecules, including SMRT, may explain the variable penetrance of the CAG repeat and the loss of AR signaling flexibility in prostate cancer progression.

Association of rs6983561 polymorphism at 8q24 with prostate cancer mortality in a Japanese population

We conducted present study to address whether the rs6983561 polymorphism, an established genetic marker for prostate cancer susceptibility, was a prognostic indicator. We genotyped 518 Japanese patients with prostate cancer and analysed their survival retrospectively. As a result, patients with the CA/CC genotype of rs6983561 survived significantly longer than those with the AA genotype (P = .033).

BACKGROUND

Genome-wide association studies have revealed several genetic variants at 8q24 that are associated with prostate cancer susceptibility. Rs6983561 (A/C) is a single-nucleotide polymorphism located at 8q24 that has been established as a genetic risk marker for prostate cancer susceptibility. The present study investigated the association between the rs6983561 polymorphism and prostate cancer mortality in a Japanese population.

PATIENTS AND METHODS

The study examined 518 native Japanese male patients with sporadic prostate cancer. Germline DNA samples were obtained from all participants and genotyping of rs6983561 was performed using a TaqMan assay. Observation periods were from the date of diagnosis of prostate cancer to May 21, 2010. The Cox proportional hazards model was used to estimate the cause-specific survival (CSS) and the overall survival (OS).

RESULTS

Patients with the CA/CC genotype of rs6983561 survived significantly longer than those with the AA genotype. In a multivariate model, the hazard ratios (HRs) and 95% confidence intervals (CIs) of the CSS and the OS for the rs6983561 polymorphism were 2.438 (1.262 - 5.046, P = .007) and 1.957 (1.142 - 3.485, P = .014), respectively. When the analysis was restricted to subjects with metastatic disease, the HRs of the CSS and the OS were 3.353 (95% CI, 1.689 - 7.446; P = 3.76 x 10(-4)) and 3.361 (95% CI, 1.741 - 7.136; P = 1.70 x 10(-4)), respectively.

CONCLUSION

In the Japanese population examined in this study, the rs6983561 polymorphism at 8q24 was significantly associated with prostate cancer mortality, especially among patients with metastatic disease.

The CAG repeat polymorphism of androgen receptor gene and prostate cancer: a meta-analysis

The association between the polymorphic CAG repeat in androgen receptor gene (AR) and prostate cancer susceptibility has been studied extensively. However, the results are contradictory. The purpose of our meta-analysis was to investigate whether CAG repeat related to prostate cancer risk and had genetic heterogeneity across different geographic regions and study designs. Random-effects model was performed irrespective of between-study heterogeneity. Data and study quality were assessed in duplicate. Publication bias was assessed by the fail-safe number and Egger's test. There were 16 (patients/controls: 2972/3792), 19 (3835/4908) and 12 (3372/2631) study groups for comparisons of ≥ 20, 22 and 23 repeats of CAG sequence, respectively. Compared with CAG repeat <20, 22 or 23, carriers of ≥ 20, 22 or 23 repeats had 21% (95% CI: 0.61-1.02; P = 0.076), 5% (95% CI: 0.81-1.11; P = 0.508) and 5% (95% CI: 0.76-1.20; P = 0.681) decreased risk of prostate cancer. After classifying studies by geographic areas, carriers of ≥ 20 repeats had 11% decreased risk in populations from USA, 53% from Europe, and 20% from Asia (P > 0.05), whereas comparison of ≥ 23 repeats with others generated a significant prediction in European populations (OR = 1.17; P = 0.039). Stratification by study designs revealed no material changes in risk estimation. Meta-regression analysis found no significant sources of between-study heterogeneity for age, study design and geographic region for all comparisons. There was no identified publication bias. Taken together, our results demonstrated that AR CAG repeat polymorphism with ≥ 20 repeats might confer a protective effect among the prostate cancer patients with 45 years older but not all the prostate cancer patients.

Steroid hormone receptors in cancer development: a target for cancer therapeutics

The steroid hormone receptors (SHRs) are ligand-dependent intracellular transcription factors that are known to influence the development and growth of many human cancers. SHRs pass signals from a steroid/hormone to the target genes by interacting with specific response element DNA sequences and various coregulatory proteins that consists of activators and/or corepressors. Disruptions in physiological functions of SHRs leads to several types of malignancies such as breast cancer, leukemia and lymphoma, prostate cancer, ovarian cancer, and lung cancer among others. Steroids/hormones/SHRs and their coregulators have opened up a unique window for novel steroid-based targeted therapies for cancer. Thus, dysregulation of SHR signaling in cancers compared with normal tissues can be exploited to target drugs that prevent and treat human cancers. In recent years, hormonal therapy has made a major contribution to the treatment of several cancers including reduced recurrence rates and longer survival rates. Development of various steroid receptor modulators and their potential therapeutic efficacies has provided us a great opportunity to effectively manage diseases like cancer in future. In this review article, we have summarized up-to-date knowledge of the role of SHRs in the development and progression of cancers, and potential endocrine-based therapeutic approaches to tackle these diseases.

Possible association between the androgen receptor gene and autism spectrum disorder

Autism is a highly heritable disorder but the specific genes involved remain largely unknown. The higher prevalence of autism in men than in women, in conjunction with a number of other observations, has led to the suggestion that prenatal brain exposure to androgens may be of importance for the development of this condition. Prompted by this hypothesis, we investigated the potential influence of variation in the androgen receptor (AR) gene on the susceptibility for autism. To this end, 267 subjects with autism spectrum disorder and 617 controls were genotyped for three polymorphisms in exon 1 of the AR gene: the CAG repeat, the GGN repeat and the rs6152 SNP. In addition, parents and affected siblings were genotyped for 118 and 32 of the cases, respectively. Case-control comparisons revealed higher prevalence of short CAG alleles as well as of the A allele of the rs6152 SNP in female cases than in controls, but revealed no significant differences with respect to the GGN repeat. Analysis of the 118 families using transmission disequilibrium test, on the other hand, suggested an association with the GGN polymorphism, the rare 20-repeat allele being undertransmitted to male cases and the 23-repeat allele being overtransmitted to female cases. Sequencing of the AR gene in 46 patients revealed no mutations or rare variants. The results lend some support for an influence of the studied polymorphisms on the susceptibility for autism, but argue against the possibility that mutations in the AR gene are common in subjects with this condition.

The GGN and CAG repeat polymorphisms in the exon-1 of the androgen receptor gene are, respectively, associated with insulin resistance in men and with dyslipidemia in women

The human androgen receptor (AR) gene possesses two trinucleotide repeats of CAG and GGN in exon-1. The GGN repeat affects the amount of AR protein translated, while the CAG repeat affects the efficiency of AR transcriptionaly. In this study, we have genotyped these polymorphic tracts in a representative sample of 557 Caucasian adult individuals (314 women and 243 men) from the Canary Islands, Spain (the ENCA Study), and investigated their association with fasting serum levels of lipids, glucose and insulin. The number of CAG repeats in women (expressed as the average length of the two alleles) was inversely correlated with serum levels of LDL-cholesterol (Spearman rho=-0.179; P<0.01). Women with an average number of CAG repeats in the upper tertile showed significantly lower levels of LDL-cholesterol than those grouped in the lower and middle tertile, after adjusting for age, body mass index, waist-to-hip ratio, smoking and alcohol drinking. The number of GGN repeats in men was correlated with fasting insulin levels (Spearman rho=-0.206; P<0.01), the homeostasis model assessment of insulin resistance (HOMA-IR; Spearman rho=-0.230; P<0.01) and the McAuley index of insulin sensitivity (Spearman rho=0.194; P<0.01). Men with a number of GGN repeats in the upper tertile showed lower levels of insulin and HOMA and a higher level of the McAuley index than those grouped in the lower and middle tertile, after adjusting for the variables listed above. These results support the hypothesis that the longer alleles of the CAG and GGN polymorphisms in the exon-1 of the AR gene, indicative of lower androgenic signaling, respectively protect women from developing dyslipemia and men from developing insulin resistance.

Short alleles of both GGN and CAG repeats at the exon-1 of the androgen receptor gene are associated to increased PSA staining and a higher Gleason score in human prostatic cancer

The exon 1 of the human androgen receptor (AR) gene contains two length polymorphisms of CAG (polyglutamine) and GGN (polyglycine). "In vitro" experiments suggest that the larger GGN repeats provide a lower AR-protein yield, whereas the larger CAG repeats decrease the AR transcriptional activity, both decreasing the AR signalling intensity. Here we have tested such possibilities in human prostatic cancer (CaP) specimens. We used 72 archival samples of radical prostatectomy. Parallel slides were used for AR protein or PSA immunohistochemistry, and for genotyping studies. Polymorphisms were genotyped by PCR, fragment length analysis and sequencing selected samples. The AR staining was positively correlated with the Gleason score (r=0.320; P=0.005), but it was not correlated to CAG or GGN repeat length or PSA staining. The number of GGN repeats was negatively correlated to the intensity of PSA staining (r=-0.243; P=0.04). Combination of short alleles of both tracts was significantly higher in: the heavier stained tertiles for PSA (P=0.03) and AR (P=0.06); and in the subgroup of samples having a Gleason score of 7 or higher (P=0.021). The results support the hypothesis that the shorter alleles of CAG and GGN repeats in the AR gene are associated to an increased AR signalling intensity in human prostate cancer, and with more aggressive forms of the disease.

Androgen receptor CAG repeat polymorphisms in canine prostate cancer

BACKGROUND

Relatively shorter lengths of the polymorphic polyglutamine repeat-1 of the androgen receptor (AR) have been associated with an increased risk of prostate cancer (PC) in humans. In the dog, there are 2 polymorphic CAG repeat (CAGr) regions.

OBJECTIVE

To investigate the relationship of CAGr length of the canine AR-gene and the development of PC.

ANIMALS

Thirty-two dogs with PC and 172 control dogs were used.

METHODS

DNA was extracted from blood. Both CAG repeats were amplified by polymerase chain reaction (PCR) and PCR products were sequenced.

RESULTS

In dogs with PC, CAG-1 repeat length was shorter (P = .001) by an increased proportion of 10 repeats (P = .011) and no 12 repeats (P = .0017) than in the control dogs. No significant changes were found in CAG-3 length distribution. CAG-1 and CAG-3 polymorphisms proved not to be in linkage disequilibrium. Breed difference in allelic distribution was found in the control group. Of the prostate-disease sensitive breeds, a high percentage (64.5%) of the shortest haplotype 10/11 was found in the Doberman, whereas Beagles and German Pointers had higher haplotype 12/11 (47.1 and 50%). Bernese Mountain dogs and Bouvier dogs both shared a high percentage of 11 CAG-1 repeats and 13 CAG-3 repeats. Differences in (combined) allelic distributions among breeds were not significant.

CONCLUSIONS AND CLINICAL IMPORTANCE

In this preliminary study, short CAG-1 repeats in the AR-gene were associated with an increased risk of developing canine PC. Although breed-specific differences in allelic distribution of CAG-1 and CAG-3 repeats were found, these could not be related to PC risk.

Inherited variation in hormone-regulating genes and prostate cancer survival

PURPOSE

Hormonal manipulation is the mainstay treatment of prostate cancer, notably in advanced stages. Despite initial favorably response, the cancer eventually develops hormone resistance resulting in disease progression and death. However, little is known about genetic determinants of disease progression and prostate cancer-specific death.

EXPERIMENTAL DESIGN

We analyzed a population-based cohort comprising 2,761 men diagnosed with prostate cancer from March 2001 to October 2003 and with complete follow-up through July 2006. During a median follow-up time of 3.8 years, a total of 300 men had died from prostate cancer. We genotyped 23 haplotype tagging single nucleotide polymorphisms in the genes AR, CYP17, and SRD5A2 and used Cox proportional hazards analyses to quantify associations between genotype and risk of dying from prostate cancer.

RESULTS

The variant 'A' allele of an AR promoter single nucleotide polymorphism, rs17302090, was borderline associated with a 50% increased risk of dying from prostate cancer (95% confidence interval, 1.0-2.3; P = 0.07). This finding was more pronounced in patients who received hormonal therapy as primary treatment at diagnosis (hazard ratio, 1.9; 95% confidence interval, 1.3-2.9; P = 0.007). We did not identify any associations between CYP17 or SRD5A2 variation and prostate cancer-specific death.

CONCLUSIONS

Our results suggest that inherited genetic variation in the androgen receptor gene affects hormonal treatment response and ultimately prostate cancer death.

Flanking polyproline sequences inhibit beta-sheet structure in polyglutamine segments by inducing PPII-like helix structure

Polyglutamine (poly(Q)) expansion is associated with protein aggregation into beta-sheet amyloid fibrils and neuronal cytotoxicity. In the mutant poly(Q) protein huntingtin, associated with Huntington's disease, both aggregation and cytotoxicity may be abrogated by a polyproline (poly(P)) domain flanking the C terminus of the poly(Q) region. To understand structural changes that may occur with the addition of the poly(P) sequence, we synthesized poly(Q) peptides with 3-15 glutamine residues and a corresponding set of poly(Q) peptides flanked on the C terminus by 11 proline residues (poly(Q)-poly(P)), as occurs in the huntingtin sequence. The shorter soluble poly(Q) peptides (three or six glutamine residues) showed polyproline type II-like (PPII)-like helix conformation when examined by circular dichroism spectroscopy and were monomers as judged by size-exclusion chromatography (SEC), while the longer poly(Q) peptides (nine or 15 glutamine residues) showed a beta-sheet conformation by CD and defined oligomers by SEC. Soluble poly(Q)-poly(P) peptides showed PPII-like content but SEC showed poorly defined, overlapping oligomeric peaks, and as judged by CD these peptides retained significant PPII-like structure with increasing poly(Q) length. More importantly, addition of the poly(P) domain increased the threshold for fibril formation to approximately 15 glutamine residues. X-ray diffraction, electron microscopy, and film CD showed that, while poly(Q) peptides with >or=6 glutamine residues formed beta-sheet-rich fibrils, only the longest poly(Q)-poly(P) peptide (15 glutamine residues) did so. From these and other observations, we propose that poly(Q) domains exist in a "tug-of-war" between two conformations, a PPII-like helix and a beta-sheet, while the poly(P) domain is conformationally constrained into a proline type II helix (PPII). Addition of poly(P) to the C terminus of a poly(Q) domain induces a PPII-like structure, which opposes the aggregation-prone beta-sheet. These structural observations may shed light on the threshold phenomenon of poly(Q) aggregation, and support the hypothesized evolution of "protective" poly(P) tracts adjacent to poly(Q) aggregation domains.

Androgen receptor genotyping in a large Australasian cohort with androgen insensitivity syndrome; identification of four novel mutations

We genotyped the androgen receptor (AR) gene in 31 Australasian patients with androgen insensitivity syndrome (AIS). The entire coding region of AR was examined including analysis of polymorphic CAG and GGN repeats in all patients. AR defects were found in 66.7% (6/9) of patients with complete AIS (CAIS) and 13.6% (3/22) of patients with partial AIS (PAIS). A novel deletion (N858delG) leading to a premature stop codon was found in CAIS patient P1. CAIS patient P2 has a novel deletion (N2676delGAGT) resulting in a stop at codon 787. These mutations would result in inactivation of AR protein. A novel insertion of a cysteine residue in the first zinc finger of the AR DNA-binding domain (N2045_2047dupCTG) was found in CAIS patient P3. PAIS patient P4 has a novel amino acid substitution (Arg760Ser) in the AR ligand binding domain, which may impair ligand binding. Five patients were found to have previously reported AR mutations and no mutations were identified in the remaining patients.

Somatic mutations at the trinucleotide repeats of androgen receptor gene in male hepatocellular carcinoma

Androgen and androgen receptor (AR) have long been implicated in liver carcinogenesis, especially for the male dominance feature. However, whether AR gene could occur in somatic mutations that might contribute to this process has not yet been studied. DNA sequencing and genotyping were conducted for detecting the genetic aberrations of AR gene in 257 primary hepatocellular carcinomas (HCCs) and also the dysplastic nodules (DN) from another 11 patients. Twenty-one AR somatic mutations causing amino acid changes were identified in HCC and even in the precancerous DN. The missense somatic mutations of AR were rare in HCC (2 cases) but the trinucleotide repeat (TNR) changes, both at (CAG)n and (GGC)n, was a more common one (19 cases). Notably, all these mutations occurred in male patients and most TNR changes belonged to the contraction type (15 out of 19 cases, 78.9%), which has been reported to associate with increased AR transcriptional activity. Most samples with TNR changes did not show microsatellite instability, suggesting a different cause for these TNR mutations. Although no significant correlation was identified between AR mutations and the clinicopathologic parameters, we found the (CAG)n length significantly shorter in hepatitis B virus (HBV)(+) HCCs than in HBV(-) HCCs and the (GGC)n length significantly correlates with the overall survival. In conclusion, the mis-sense somatic mutations of AR were rare in HCC but the TNR change was a more common one, which exclusively occurred in males. Moreover, the length of TNR carried clinical significance in special HCC group.

Androgen receptor and vitamin D receptor gene polymorphisms and prostate cancer risk

We study the CAG repeat region in exon 1 of the androgen receptor (AR) and the TaqI polymorphism in exon 9 of the vitamin D receptor (VDR) and the association with prostate cancer. 137 incidentally discovered, histologically verified prostate cancers were analysed for CAG repeat length in AR and genotype at the TaqI site of the VDR. 124 control subjects were analysed to determine the CAG repeat length and TaqI genotype determined for 176 control subjects. An unpaired t-test shows that the mean CAG repeat length was significantly (p<0.001) shorter among cases (20.1 repeats) compared with controls (22.5 repeats). Dividing the prostate cohort and controls into tertiles (< or = 19, 20-22, > or = 23 repeats) shows that short repeats are significantly more common among cases (odds ratio (OR) 4.45, p=0.00003). Genotype frequencies for the TaqI polymorphism reveals no significant differences between cases and controls. We conclude that men with a short CAG repeat in the androgen receptor gene have an increased risk of developing prostate cancer.

GGN repeat length and GGN/CAG haplotype variations in the androgen receptor gene and prostate cancer risk in south Indian men

The ethnic variation in the GGN and CAG microsatellites of the androgen receptor (AR) gene suggests their role in the substantial racial difference in prostate cancer risk. Hence, we performed a case-control study to assess whether GGN repeats independently or in combination with CAG repeats were associated with prostate cancer risk in South Indian men. The repeat lengths of the AR gene determined by Gene scan analysis, revealed that men with GGN repeats <or=21 had no significant risk compared to those with >21 repeats (OR 0.91 at 95% CI-0.52-1.58). However, when CAG repeats of our earlier study was combined with the GGN repeat data, the cases exhibited significantly higher frequency of the haplotypes CAG <or=19/GGN <or=21 (OR-5.2 at 95% CI-2.17-12.48, P < 0.001) and CAG <or=19/GGN > 21(OR-6.9 at 95%CI-2.85-17.01, P < 0.001) compared to the controls. No significant association was observed between GGN repeats and prostate-specific antigen levels and the age at diagnosis. Although a trend of short GGN repeats length in high-grade was observed, it was not significant (P = 0.09). Overall, our data reveals that specific GGN/CAG haplotypes (CAG <or=19/GGN <or=21 and CAG <or=19/GGN > 21) of AR gene increase the risk of prostate cancer and thus could serve as susceptibility marker for prostate cancer in South Indian men.

Testosterone levels in relation to oral contraceptive use and the androgen receptor CAG and GGC length polymorphisms in healthy young women

BACKGROUND

The combined effect from the androgen receptor (AR) CAG and GGC length polymorphisms on testosterone levels has not been studied in young women.

METHODS

Testosterone levels were measured in blood drawn on both menstrual cycle days 5-10 and 18-23 in 258 healthy women, aged < or =40 years, from high-risk breast cancer families. CAG and GGC length polymorphisms were analysed by PCR and fragment analyses. All women completed a questionnaire including information on oral contraceptive (OC) use and reproductive factors.

RESULTS

OC users had lower median testosterone levels than non-users during cycle days 5-10 and 18-23 (P < or = 0.005 for both). The BRCA mutation status was associated neither with testosterone levels nor with CAG or GGC length polymorphism. The CAG length polymorphism was not associated with testosterone levels. The cumulative number of long GGC alleles (> or =17 repeats) was significantly associated with lower testosterone levels in OC users during cycle days 5-10 (P(trend) =0.014), but not during cycle days 18-23 or in non-users. The interaction between the GGC length polymorphism and OC status was highly significant during cycle days 5-10 (P = 0.002) and near-significant during days 18-23 (P = 0.07). Incident breast cancer was more common in women with two short GGC alleles (log-rank P = 0.003).

CONCLUSION

The GGC repeat length was the only significant genetic factor modifying the testosterone levels in current OC users from high-risk families. Homozygosity for the short GGC allele may be linked to the increased risk of early-onset breast cancer after OC exposure in high-risk women.

Common genetic polymorphisms and prognosis of sporadic cancers: prostate cancer as a model

To date, most molecular epidemiological studies on gene polymorphisms in cancer have focused on the risk of development and susceptibility to cancer. However, interindividual genetic variation may contribute greatly to the treatment outcome and prognosis of cancer by affecting the interaction between cancer cells and hormones, growth factors and factors influencing the tumor microenvironment. In prostate cancer, several recent molecular epidemiological studies suggested the possibility of predicting treatment outcome and prognosis using genetic polymorphisms. Candidate genes are hormone-related, oncogenes, tumor-suppressor and cell cycle-growth control-related genes, as well as genes related to immune response, inflammatory change, neovasculization, and the extracellular matrix, genes involved in drug and xenobiotic metabolism and genes involved in DNA repair and genome stability. There remain a huge number of candidate genes whose polymorphisms may affect the progression and treatment outcome of various kinds of cancer, including that of prostate cancer.

Genetic Susceptibility to Prostate Cancer: Prostate-specific Antigen and its Interaction with the Androgen Receptor (United States)

OBJECTIVE

To determine whether directly observed prostate-specific antigen (PSA) promoter diploid haplotype, either alone or in conjunction with androgen receptor (AR) genotype, is associated with prostate cancer risk.

METHODS

We conducted a case-control study nested within the US population-based Cardiovascular Health Study cohort. Incident prostate cancers were identified by linkage to cancer registry records for the years 1989-2000. We genotyped 193 cases and 391 controls for the PSA -252 G/A and -158 G/A SNPs and the AR CAG microsatellite, and developed methods to directly determine proximal PSA promoter haplotypes. Exact logistic regression was used to estimate odds ratios and significance levels.

RESULTS

No significant associations were observed between PSA diplotype and prostate cancer overall. Short (< 20) AR CAG repeat lengths were associated with modest increases in the risk of prostate cancer (OR, 1.46; 95% CI, 0.97-2.19; p = 0.071) that were significant for advanced disease (OR, 1.82; 95% CI, 1.02-3.26; p = 0.044). Men who possessed two copies of the PSA*2 (-252G/-158G) haplotype and short AR CAG repeat lengths had a 4-fold (95% CI, 1.05-20.75; exact p = 0.040) increased risk of prostate cancer, and a 7-fold (95% CI, 1.25-39.78; exact p = 0.026) increased risk of advanced disease.

CONCLUSIONS

We found evidence that the PSA*2*2 diplotype in combination with short AR CAG alleles increases a man's risk of developing prostate cancer. These findings support an etiologic role in prostate cancer of genetic interactions between polymorphisms that increase AR transactivation strength and those that alter the regulatory regions of target genes such as PSA that are responsive to androgen stimulation.

Influence of Number of CAG Repeats on Local Control in the RTOG 86-10 Protocol

OBJECTIVES

The number of CAG repeats on the androgen receptor (AR) gene is inversely proportional to transcriptional activity. The purpose of this study was to determine if short-term androgen deprivation therapy (RT + HT) can improve outcome in patients with tumors with short CAG repeats (<19).

MATERIALS AND METHODS

Prostate cancer patients were randomized to receive either radiotherapy (RT) alone or (RT + HT) in the RTOG 86-10 study. CAG repeats were measured in 94 tumor specimens (21%; test cohort) of the 456 (parent cohort) analyzable cases. AR flow cytometry measurements were done on 13 patients. The effect on local failure (LF), distant metastases (DM), prostate cancer survival (PSS), and overall survival (OS) was studied.

RESULTS

Pretreatment characteristics and assigned treatment arm were not significantly different between the parent and test groups except for a significantly higher risk of death (P = 0.049) in the test group. The median CAG repeat was 19. There were no significant differences in stage, or Gleason score between high (19 or greater) and low CAG (<19) patients within each treatment group. Number of CAG repeats alone did not significantly influence LF, DM, PSS, and OS. However, when the CAG repeat outcome was studied in conjunction with androgen deprivation therapy, patients with CAG <19 who received H + RT had improved local control as compared with patients who received RT alone (P = 0.026, 5-year rates 4.6% versus 36.4%) and improved local control over patients with CAG > or =19 that received H + RT (P = 0.028).

CONCLUSIONS

Patients with short CAG repeats show a local control benefit with short-term androgen deprivation therapy, but no improvement in survival.

South Indian men with reduced CAG repeat length in the androgen receptor gene have an increased risk of prostate cancer

The androgen receptor (AR) gene possesses polymorphic CAG tandem repeats and the repeat length has been inversely related to the risk of prostate cancer (PCa). The distinct ethnic variation in the CAG repeat length may be correlated to differences in PCa risk in different populations. To evaluate the CAG repeat length in the AR gene and the implications for PCa, we screened 87 PCa patients and 120 control subjects from South India. The mean CAG repeat length in PCa patients was significantly smaller than that of controls (17.0 vs 20.7; P < 0.001). Men with < or = 19 CAG repeats had a significantly increased risk of cancer compared to those with >19 CAG repeats (age-adjusted OR = 7.01; 95% CI = 3.52-13.94; P < 0.001). However, no significant association was observed between CAG repeats and age of onset or prostate-specific antigen levels. Although there was a trend towards shorter CAG repeat length in high grades of cancer, it was not significant (P = 0.085). Thus, our results suggest an association between short CAG repeats in the AR gene and PCa risk in South Indian men. Further, we propose that CAG repeats could be used as a prognostic marker for PCa diagnosis.

Sex steroid hormones and the androgen receptor gene CAG repeat and subsequent risk of prostate cancer in the prostate-specific antigen era

OBJECTIVE

Sex steroid hormones are thought to contribute to the growth, differentiation, and progression of prostate cancer. We investigated plasma levels of sex steroid hormones and length of the androgen receptor gene CAG repeat in relation to incident prostate cancer diagnosed in the prostate-specific antigen (PSA) era.

METHODS

Using a nested case-control design, we included 460 prostate cancer cases diagnosed after providing a blood specimen in 1993 but before February 1998 among men in the Health Professionals Follow-up Study. Controls were 460 age-matched men without prostate cancer who had a screening PSA test after the date of providing a blood specimen. We measured plasma concentrations of total testosterone, free testosterone, dihydrotestosterone, androstanediol glucuronide, estradiol, and sex hormone binding globulin (SHBG) and determined the length of the androgen receptor gene CAG repeat. Conditional logistic regression was used to estimate odds ratios (OR) and 95% confidence intervals (CI) of prostate cancer.

RESULTS

Mean concentrations of the sex steroids adjusted for SHBG, and mean CAG repeat length did not differ significantly between the prostate cancer cases and controls. No significant associations with total prostate cancer were detected for plasma total testosterone concentration (comparing highest versus lowest quartiles: OR, 0.78; 95% CI, 0.48-1.28; P(trend) = 0.73) or the other sex hormones after adjusting for SHBG. However, plasma total testosterone concentration was positively associated with low-grade disease (Gleason sum < 7: OR, 1.91; 95% CI, 0.89-4.07; P(trend) = 0.02) and inversely associated with high-grade disease (Gleason sum > or = 7: OR, 0.26; 95% CI, 0.10-0.66; P(trend) = 0.01). Similar patterns for grade were observed for free testosterone. Short CAG repeat length was not associated with total prostate cancer (< or = 19 versus > or = 24: OR, 0.84; 95% CI, 0.57-1.23; P(trend) = 0.22) or grade of disease. No clear associations with regionally invasive or metastatic (> or = T3b, N1, or M1) were found for any of the hormones or the CAG repeat, although the number of these cases was small.

CONCLUSIONS

The overall lack of association of prostate cancer diagnosed in the PSA era with sex steroid hormones and the androgen receptor gene CAG repeat length is consistent with the hypothesis that these factors do not substantially contribute to the development of early prostate cancer in the PSA era. The influence of plasma total and free testosterone concentrations on prostate cancer grade merits further evaluation.

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.

Alleles with short CAG and GGN repeats in the androgen receptor gene are associated with benign endometrial cancer

The human androgen receptor (AR) gene possesses 2 trinucleotide repeats of CAG and GGN in exon 1. The CAG repeat corresponds to a polyglutamine tract in the N-terminal region of the receptor, that affects its transcriptional efficiency. The GGN repeat codifies for a polyglycine tract, and affects the amount of the AR protein transcribed. The endometrium contains ARs and the androgens have antiproliferative properties in cultured endometrial cancer (EC) cells. Larger CAG repeats of the AR gene give rise to a weaker transcriptional activity and have been found to be associated with endometrial carcinogenesis. The possible involvement of CAG and GGN tracts in the progression of EC is unknown. To study that possibility, we have genotyped both CAG and GGN polymorphisms of the AR gene in tumor tissue genomic DNA from a series of 204 consecutive patients with EC, and analyzed the results with regard to the pathological features and clinical outcome of patients. We classified the alleles as S (short <or= median; S-CAG <or=21 repeats; S-GGN <or=22 repeats) or L (long > median). The genotype with both S-CAG repeat alleles (SS-CAG) was more common in patients diagnosed at an early stage (41.6% SS-CAG vs 22.6% SL- and LL-CAG together, p = 0.048) and in tumors that did not invade the vascular space (43.0% SS-CAG vs 26.4% SL- and LL-CAG together, p = 0.034). The genotype with SS-GGN alleles was more common in well-differentiated tumors (41.2% SS-GGN vs 25.2% LS- and LL-GGN together, p = 0.017) and in endometrioid histological subtype tumors (35.3% SS-GGN vs 13.0% SL- and LL-GGN together, p = 0.034). When the genotypes of both repeats coexisting in each tumor specimen were taken into consideration, the relationship between the SS-CAG genotype and early stage remained only in the presence of the SS-GGN genotype (43.9% vs 0%, p = 0.01). No other associations were observed. In univariate survival analysis, patients with short alleles of both repeats (SS-CAG and SS-GGN genotypes simultaneously) had a lower risk of cancer-specific death (p = 0.032, mean follow-up: 63 months). Our data suggests that short CAG or GGN repeats of the AR gene are associated with a more benign condition of traditional prognostic variables in EC.

Polymorphisms in the androgen receptor and the prostate-specific antigen genes and prostate cancer risk

BACKGROUND

Prostate cancer (PCa) is an androgen-dependent disease. Polymorphic CAG and GGC microsatellites in the androgen receptor (AR) can alter transactivation of androgen-responsive genes in in vitro studies. Potentially, this may influence PCa risk.

METHODS

Germline DNA samples and survey data were collected from 591 newly diagnosed PCa cases and 538 population-based controls of similar age (40-64 years), from King County, WA. Odds ratios (ORs) and 95% confidence limits were estimated using logistic regression models.

RESULTS

No association was detected between PCa and having <22 versus > or =22 CAG repeats (OR = 1.1; 95% CI 0.9, 1.4) or < or =16 GGC versus >16 GGC repeats (OR = 1.0; 95% CI 0.9, 1.4). These findings were unchanged after controlling for body mass index or family history of PCa. No clear relation was detected between APS -158 G/A genotype and risk of PCa or serum prostate-specific antigen (PSA) levels. These findings did not differ by stage or grade of PCa.

CONCLUSIONS

We found no evidence that risk of PCa is associated with the AR CAG, GGC, or PSA-158 AREI genetic polymorphisms in middle-aged Caucasian men.

Polymorphic forms of prostate specific antigen and their interaction with androgen receptor trinucleotide repeats in prostate cancer

BACKGROUND

Recent data has suggested that polymorphisms in the prostate specific antigen (PSA) may increase prostate cancer (PC) risk. The PSA gene contains a G/A substitution in the androgen response element (ARE) 1 region. The androgen receptor (AR) gene has polymorphic regions containing variable length glutamine and glycine repeats and these are believed to be associated with PC risk. The effect on PC risks from PSA polymorphisms alone and synergistically with the AR gene was examined in this report.

METHODS

One hundred PC patients and an age matched cohort of 79 benign prostate hyperplasia and 67 population controls were entered in this study. DNA was extracted from blood and PSA/ARE promoter region amplified by PCR. PCR products were cut with Nhe 1 restriction enzyme to distinguish G/A alleles. AR/CAG and GGC repeat length was detected by automated fluorescence from PCR products.

RESULTS

We found a significantly higher PSA/GG distribution in PC (30%) than either benign prostatic hyperplasia (BPH) (18%) or population controls (16%) (P = 0.025). Furthermore the GG distribution within cases was even greater in younger men (< 65 years; 42%; P = 0.012). Additionally, when PSA genotype was cross classified with CAG repeat, significantly more cases than both BPH and population controls were observed to have a short (< 22) CAG/GG genotype (P = 0.006).

CONCLUSIONS

Our results indicate that the PSA/ARE GG genotype confers an increased risk of PC especially among younger men. Moreover, we confirm previous results that a short glutamine repeat in conjunction with GG genotype significantly increases the risk of malignant disease.

The relationship between the androgen receptor CAG repeat polymorphism length and the response to intermittent androgen suppression therapy for advanced prostate cancer

OBJECTIVE

To determine whether the duration of the off-treatment interval in patients being treated with intermittent androgen deprivation therapy can be predicted by the length of the CAG trinucleotide repeat polymorphism in the androgen receptor.

METHODS

This is a companion study to a prospective randomized trial, NCIC CTG PR-7, comparing intermittent to continuous androgen deprivation therapy in men with PSA progression after radiation therapy. The duration of the first off-treatment interval was established for 76 participants randomized to the intermittent therapy arm of the trial. Androgen receptor CAG repeat polymorphism lengths were determined for these 76 participants. Statistical analysis was completed to determine a relationship between CAG repeat length and the duration of the off-treatment interval.

RESULTS

A significant correlation was not established (P = 0.424) between androgen receptor CAG repeat length and the duration of the first off-treatment interval. Categorical analysis of CAG repeat lengths using 18 and 22 as cutoff points did not find any significant difference in the mean duration of the off-treatment interval between categories (P = 0.672 and 0.774, respectively).

CONCLUSION

No relationship was established between the duration of the first off-treatment interval and the CAG repeat length.

Association between hormonal genetic polymorphisms and early-onset prostate cancer

We investigated the association between seven polymorphisms in four candidate genes involved in vitamin D and androgen metabolism with early-onset prostate cancer (CaP) risk. The polymorphisms were genotyped in 288 UK males who were diagnosed with CaP at the age of 55 y or younger and up to 700 population-based controls. An additional 50 cases (not selected for age) and 76 controls were also genotyped. Short (< or =22 repeats) AR (CAG)(n) repeats were associated with a significantly reduced risk of early onset CaP (OR 0.68, 95% CI 0.50-0.91) compared with men with long (> 22) repeats. Men homozygous for the leucine variant of SRD5A2 p.89V > L were also found to be at a significantly increased risk of CaP compared with men who were homozygous for the valine allele (OR 1.84, 95% CI 1.15-2.98). No associations were found with the AR (GGC)(n), CYP17 Msp A1 I, VDR Taq I, SRD5A2 (TA)(n) and p.49A >T polymorphisms and CaP risk. These findings suggest that common polymorphisms in the AR and SRD5A2 genes may be associated with early-onset CaP in British men.

Effect of GGC (glycine) repeat length polymorphism in the human androgen receptor on androgen action

BACKGROUND

The human androgen receptor (AR) contains glutamine (CAG) and glycine (GGC) repeat length polymorphisms. Normal glutamine repeat length affects androgen action, but an effect of normal glycine repeat length has not been studied.

METHODS

To determine whether glycine/GGC repeat length affects AR function, we constructed AR cDNA expression vectors with different GGC repeat lengths in the physiological range (13-17 GGCs). AR constructs were transfected into AR-negative DU145 human prostate cancer cells along with an androgen-responsive reporter plasmid (PSA-firefly luciferase) and a transfection efficiency control plasmid (Renilla luciferase).

RESULTS

Glycine repeat length had no significant effect on androgen-dependent AR transactivation activity expressed as firefly luciferase per unit amount of AR protein. However, AR protein levels (normalized for transfection efficiency) were inversely affected by glycine repeat length (P < 0.001; r = -0.9; e.g., GGC13 yielded 2.7 times more AR protein than did GGC17). Therefore, the net amount of AR activity per cell would be higher in cells expressing AR with a short glycine repeat. Based on programs that predict structure from RNA sequence, the GGC repeat can form a hairpin structure, the free energy of which decreases (i.e., hairpin stability increases) as a function of increasing repeat length. This suggests that hairpin stability may interfere with translation, accounting for the inverse effect of GGC repeat length on AR protein yields.

CONCLUSIONS

The ability of a short GGC repeat to enhance androgen action provides a biologically plausible mechanism to account for reports that a short GGC repeat in the AR gene is a risk factor for prostate cancer.

The Androgen Receptor: Unlocking the Secrets of Its Unique Transactivation Domain

Whereas the androgen receptor (AR) protein shares similarities in the structure of its DNA- and hormone-binding domains with other members of the steroid nuclear receptor family, the molecule in its unliganded form has a seemingly unordered amino-terminal transactivation domain unique to the AR. A comprehensive understanding of the specific sub-structures and protein-protein interactions inherent to this domain in both its inactive and activated states remains un-achieved. Therefore, the malleability of this peptide region in accommodating the diverse repertoire of transcription-modulating AR cofactors creates a great challenge for those intent on generating relevant three-dimensional molecular models. The AR transactivation domain achieves this flexibility through a series of conformational steps dependent on the presence of cofactors that induce allosteric changes, and thus has evolved several conserved peptide motifs representing key protein-protein interaction surfaces. Elucidation of these signaling regions, including their involvement in inducing AR transactivation domain structural changes, is of foremost interest in understanding how the AR achieves its pivotal role in regulating the androgen signaling axis particularly during the progression of prostate cancer.

Functional analysis of natural mutations in two TWIST protein motifs

The basic helix-loop-helix protein Twist, a transcriptional repressor, is essential for embryogenesis in both invertebrates and vertebrates. Haploinsufficiency of the human TWIST1 gene, which causes the craniosynostosis disorder Saethre-Chotzen syndrome (SCS), is related to failure to repress transcription of CDKN1A (which encodes p21/WAF1/CIP1), promoting osteoblast differentiation. We have examined the functional significance of natural TWIST1 variants present in craniosynostosis patients and in their healthy relatives. Both deletion and duplication variants of the glycine-rich tract Gly5AlaGly5 inhibited E2A (E12/E47)-dependent transcription of CDKN1A to a similar degree as wild-type protein, indicating that the length of this glycine tract is not critical for efficient transcriptional repression. We also evaluated a newly identified heterozygous TWIST1 variant (c.115C>G, encoding p.Arg39Gly), located within a putative nuclear localization signal (NLS), that was present in a child with mild SCS and her clinically unaffected father and grandmother. Unlike wild-type protein, this mutant required cotransfected E12 to localize to the nucleus, indicating that the NLS, including amino acid 39, is essential for nuclear localization; inhibition of E2A-dependent transcription of CDKN1A occurred normally. This analysis further dissects the structure-function relationships of TWIST and corroborates with phenotypic observations of disease expressivity.

Systematic evaluation of genetic variation at the androgen receptor locus and risk of prostate cancer in a multiethnic cohort study

Repeat length of the CAG microsatellite polymorphism in exon 1 of the androgen receptor (AR) gene has been associated with risk of prostate cancer in humans. This association has been the focus of >20 primary epidemiological publications and multiple review articles, but a consistent and reproducible association has yet to be confirmed. We systematically addressed possible causes of false-negative and false-positive association in >4,000 individuals from a multiethnic, prospective cohort study of prostate cancer, comprehensively studying genetic variation by microsatellite genotyping, direct resequencing of exons in advanced cancer cases, and haplotype analysis across the 180-kb AR genomic locus. These data failed to confirm that common genetic variation in the AR gene locus influences risk of prostate cancer. A systematic approach that assesses both coding and noncoding genetic variation in large and diverse patient samples can help clarify hypotheses about association between genetic variants and disease.

The impact of CAG repeats in exon 1 of the androgen receptor on disease progression after prostatectomy

BACKGROUND

The authors examined the impact of the number of CAG repeats in exon 1 of the androgen receptor on disease progression among men with prostate carcinoma after prostatectomy. This polymorphism has been associated with alterations in activity of the androgen receptor in in vitro systems and with the risk of clinically diagnosed prostate carcinoma in some epidemiologic studies. An earlier series found that, among men at low risk of progressive disease, a small number of CAG repeats predicted a high risk of recurrence, and the impact of CAG repeats varied among men with different risks of progressive disease.

METHODS

The authors analyzed specimens from a large clinical series of fixed tissue specimens from men who underwent prostatectomy at a single institution, including 413 American white men (WM) and 298 African-American men (AAM), with 5-10 years of available clinical follow-up.

RESULTS

There was little association between the number of CAG repeats and extent of disease, Gleason score, and preoperative PSA level at diagnosis. Overall, patients who had > 18 CAG repeats had a greater risk of recurrence compared with patients who had </= 18 CAG repeats (hazard ratio [HR] = 1.52; P = 0.03). Excess risk was not found among men who were at low risk of recurrence (HR = 0.93; P = 0.96); however, among men who were at high risk of recurrence, the risk elevated for WM (HR = 1.75; P = 0.28), AAM (HR = 1.49; P = 0.06), and both races combined (HR = 1.53; P = 0.03).

CONCLUSIONS

Overall, men with prostate carcinoma who had > 18 CAG repeats had an estimated 52% increased risk of disease recurrence. The increased risk could be attributed to men who were at high risk of recurrence.

Absence of a correlation of androgen receptor gene CAG repeat length and prostate cancer risk in an African-American population

Shorter androgen receptor gene CAG repeat length has been associated with an increased risk of prostate cancer, an earlier age of onset, and more advanced stage of disease. Studies comparing the distribution of CAG repeat lengths within different populations have reported that racial groups with higher prostate cancer incidence also have shorter CAG repeat lengths. We evaluated CAG repeat length in 685 black men in Louisiana, South Carolina, and the District of Columbia who were participating in prostate cancer screening, comparing the 118 who were diagnosed with prostate cancer with 567 who had normal serum prostate-specific antigen levels and no evidence of cancer on digital rectal examination. The median CAG repeat length was 21 among cases and 19 among controls (P = 0.11). Cases were significantly older than controls, with a median age of 68 years compared with 54 years (P < 0.0001). After adjusting for age, we found no association between prostate cancer risk and CAG repeat length (odds ratio, 1.05; 95% CI, 0.98-1.13; P = 0.16). Dividing CAG repeat lengths into septiles and calculating the odds ratio for each revealed no specific repeat-length range with a significantly elevated or depressed risk of prostate cancer, but a trend test showed a significant association between longer CAG repeat lengths and an elevated risk of prostate cancer (P = 0.02). Neither grade nor stage was associated with CAG repeat length. This study confirms earlier reports that black men have shorter CAG repeat lengths than reported white and Asian populations. We did not find an increased risk of prostate cancer among black men with fewer CAG repeats.