Polymorphic GGC repeats in the androgen receptor gene are associated with hereditary and sporadic prostate cancer risk

Androgen receptor (AR) has long been hypothesized to play an important role in prostate cancer etiology. Two trinucleotide repeat polymorphisms (CAG and GGC repeats in exon 1 of the AR gene) have been investigated as risk factors for prostate cancer in several studies. However, the results are inconclusive, probably because of the variations of study designs, characteristics of study samples, and choices of analytical methods. In this study, we evaluated evidence for linkage and association between the two AR repeats and prostate cancer by using the following comprehensive approaches: (1) a combination of linkage and association studies, (2) a test for linkage by parametric analysis and the male-limited X-linked transmission/disequilibrium test (XLRC-TDT), (3) a test for association by using both population-based and family-based tests, and (4) a study of both hereditary and sporadic cases. A positive but weak linkage score (HLOD=0.49, P=0.12) was identified in the AR region by parametric analysis; however, stronger evidence for linkage in the region, especially at the GGC locus, was observed in the subset of families whose proband had < or = 16 GGC repeats (HLOD=0.70, P=0.07) or by using XLRC-TDT ( z'=2.65, P=0.008). Significantly increased frequencies of the < or = 16 GGC repeat alleles in 159 independent hereditary cases (71%) and 245 sporadic cases (68%) cases compared with 211 controls (59%) suggested that GGC repeats were associated with prostate cancer ( P=0.02). Evidence for the association between the < or = 16 GGC repeats and prostate cancer risk was stronger with XLRC-TDT ( z'=2.66, P=0.007). No evidence for association between the CAG repeats and prostate cancer risk was observed. The consistent results from both linkage and association studies strongly implicate the GGC repeats in the AR as a prostate cancer susceptibility gene. Further studies on this polymorphism in other independent data sets and functional analysis of the GGC repeat length on AR activity are warranted.     

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.     

Polymorphism of CAG repeats in androgen receptor of carnivores

Androgen effect is mediated by the androgen receptor (AR). The polymorphism of CAG triplet repeat (polyCAG), in the N-terminal transactivation domain of the AR protein, has been involved either in endocrine or neurological disorders in human. We obtained partial sequence of AR exon 1 in 10 carnivore species. In most carnivore species, polyglutamine length polymorphism presented in all three CAG repeat regions of AR, in contrast, only CAG-I site polymorphism presented in primate species, and CAG-I and CAG-III sites polymorphism presented in Canidae. Therefore, studies focusing on disease-associated polymorphism of poly(CAG) in carnivore species AR should investigate all three CAG repeats sites, and should not only consider CAG-I sites as the human disease studies. The trinucleotide repeat length in carnivore AR exon 1 had undergone from expansions to contractions during carnivores evolution, unlike a linear increase in primate species. Furthermore, the polymorphisms of the triplet-repeats in the same tissue (somatic mosaicism) were demonstrated in Moutain weasel, Eurasian lynx, Clouded leopard, Chinese tiger, Black leopard and Leopard AR. And, the abnormal stop codon was found in the exon 1 of three carnivore species AR (Moutain weasel, Eurasian lynx and Black leopard). It seemed to have a high frequency presence of tissue-specific somatic in carnivores AR genes. Thus the in vivo mechanism leading to such highly variable phenotypes of the described mutations, and their impact on these animals, are worthwhile to be further elucidated.     

GGC and StuI polymorphism on the androgen receptor gene in endometrial cancer patients

Androgens have an anti-proliferative effect on endometrial cells. Human androgen receptor (AR) gene contains two polymorphic short tandem repeats of GGC and CAG, and a single-nucleotide polymorphism on exon 1 that is recognized by the restriction enzyme, StuI. Prior studies have shown that the lengths of the CAG repeat are inversely and linearly related to AR activity and associated with endometrial cancer. However, little is known about the GGC repeat and the StuI polymorphism of the AR gene. Thus, we investigated whether these AR polymorphisms are risk factors for endometrial cancer. To test this hypothesis, the genetic distributions of these polymorphisms were investigated in blood samples from endometrial cancer patients and healthy controls. The allelic and genotyping profiles were analyzed by polymerase chain reaction (PCR), PCR-restriction fragment length polymorphism (PCR-RFLP), and direct DNA sequencing, and analyzed statistically. The GGC repeat was significantly longer in endometrial cancer patients as compared to normal healthy controls. In general, an increased risk of endometrial cancer was found with increasing GGC repeat. The relative risk for the 17 GGC repeat was greater than 4, as compared to controls. However, the StuI polymorphism was not significantly different between patients and controls. The findings suggest that increased numbers of GGC repeat on the AR gene may be a risk factor for endometrial cancer.     

Androgen receptor CAG polymorphism and prostate cancer risk

Recent studies have suggested that polymorphisms of the androgen receptor gene ( AR) may influence the risk of prostate cancer (PC) development and progression. Here, we analyzed the length of the CAG repeat of the AR gene in 1363 individuals, including patients with PC, benign prostate hyperplasia (BPH), and population controls. There was a tendency for short CAG repeats to be associated with PC. The Odds Ratio (OR) for PC was 1.47 ( P=0.05) when individuals with short CAG repeats (18). CAG repeat length was not significantly associated with family history, disease stage, grade, age at diagnosis, prostate-specific antigen (PSA) level at diagnosis, or prognosis of the patients. Unexpectedly, short CAG repeats were significantly less common in patients with BPH compared with controls (OR=0.47, P=0.03). Our results suggest that the CAG polymorphism of the AR gene is unlikely to have a major role in the development or progression of PC in the Finnish population. The association of CAG repeats with the risk of BPH warrants further study.     

DU-145 and PC-3 human prostate cancer cell lines express androgen receptor: implications for the androgen receptor functions and regulation

The majority of human prostate cancer cell lines, including the two "classical" cell lines DU-145 and PC-3, are reported to be androgen receptor (AR)-negative. However, other studies have provided evidence that the DU-145 and PC-3 cell lines express AR mRNA. These contradictory observations prompted us to investigate whether DU-145 and PC-3 cell lines express the androgen receptor. Using antipeptide antibodies directed against three distinct regions of the human AR protein and an improved method to detect AR protein in immunoblotting, we report that DU-145 and PC-3 cell lines express AR protein. We found that the relative levels of the AR mRNA and protein that were detected in DU-145 and PC-3 cell lines were lower than the LNCaP, an AR-positive cell line. Moreover, the antibody directed against the non-variant region (amino acids 299-315), but not the variant N- or C-terminal region (amino acids 1-20 and 900-919, respectively) of the human AR protein, detected the expression of AR in all prostate cancer cell lines. Notably, treatment of these cell lines with dihydrotestosterone (DHT) resulted in measurable increases in the AR protein levels and considerable nuclear accumulation. Although, treatment of DU-145 and PC-3 cells with DHT did not result in stimulation of the activity of an AR-responsive reporter, knockdown of AR expression in PC-3 cells resulted in decreases in p21(CIP1) protein levels, and a measurable decrease in the activity of the p21-luc-reporter. Our observations demonstrate the expression of AR protein in DU-145 and PC-3 prostate cancer cell lines.     

Evaluation of the effects of androgen receptor gene trinucleotide repeats and prostate-specific antigen gene polymorphisms on prostate cancer

The number of trinucleotide repeats [CAG (coding for polyglutamine), GGC (coding for polyglycine)] in the first exon of the androgen receptor (AR) gene and prostate-specific antigen (PSA) gene androgen response element I A/G polymorphism are both related to prostate cancer prognosis. We investigated whether these genomic changes occur in the AR and PSA genes, which are usually found in individuals with prostate cancer, of Turkish patients and to find out their distribution in the population. We used PCR and PCR-RFLP assays for AR and PSA genes, respectively, to detect molecular changes in 44 prostate cancer patients. Our findings indicate that individuals with prostate cancer tend to have around 18 CAG trinucleotide repeats. We observed significant differences between 22 controls, 33 benign prostate hyperplasia (BPH) patients and 44 adenocarcinoma patients for long CAG repeats. However, we did not find any significant differences in GGC repeats between controls, BPH and adenocarcinoma patients (P = 0.408). We also did not observe significant differences in the PSA A/G polymorphism frequency between controls, BPH and adenocarcinoma patients (P = 0.483). In conclusion, CAG and GGC repeats in the AR and PSA gene polymorphisms may be associated with prostate cancer risk and BPH in the Turkish population.     

The CAG repeat polymorphism of the androgen receptor gene and breast cancer

Background

Genetic variants in hormone receptor genes may be crucial predisposing factors for breast cancer, and microsatellites in the androgen receptor gene (AR) have been suggested to play a role. The aim of the study was to determine the association between the length of the CAG repeats in the AR gene and the development of breast cancer. Methodology: In total, 75 breast cancer cases and 50 healthy controls were analyzed for CAG repeats in the AR gene by polymerase chain reaction and the GeneScan/Genotyping technique.

Results

CAG repeat genotypes and alleles distribution were found to be significantly different between breast cancer patients and controls (P < 0.05). While the presence of CAG repeats shorter than 22 (classified as short, S) increases the risk of breast cancer, the risk is reduced by the presence of CAG repeats longer than 22. In the group of patients with breast cancer, a high tumor stage was found to have a significant association with genotype S/S of CAG repeats in the AR gene.

Conclusion

Our results suggest that the length of CAG repeats in the androgen receptor gene is associated with the risk of developing breast cancer.     

The polyglycine and polyglutamine repeats in the androgen receptor gene in Japanese and Caucasian populations

Human androgen receptor (AR) gene contains two polymorphic trinucleotide repeats of CAG and GGC, which code for polyglutamine and polyglycine tracts in the N-terminal domain in which the receptor activity resides. Longer repeats induce decrease of transactivation function in the AR receptor, weaken an anti-proliferative effect on various steroid-related tissues, and may promote the carcinogenesis of these cancers, such as breast, endometrial, and ovarian cancers. However, the incidences of these steroid-related cancers are remarkably lower in Japanese than in Caucasians. We hypothesize that the GGC and CAG repeats in AR gene correspond to lower incidence of steroid-related cancers in the Japanese population. To test this hypothesis, these two polymorphic trinucleotide repeats in AR gene were genotyped in 221 Japanese and 177 Caucasians. The results of genotyping in these loci clearly show that the distribution of GGC repeat is significantly different between these populations (P<0.001). Japanese (73.7%) had 16 GGC repeats compared to 53.3% for Caucasians. Japanese (3.8%) also had 17 GGC repeats compared to 36.2% for Caucasians. No Japanese had more than 18 GGC repeats compared to 3.4% for Caucasians. The length of CAG repeats in the Japanese population was not significantly different than that of the Caucasian population, although the CAG repeats varied from 14 to 31 and 15 to 29 repeats in Japanese and German populations, respectively. This study demonstrates that the Japanese population has shorter GGC compared to the Caucasian population, which may explain the incidences of estrogen-related cancers in these populations.     

DNA haplotype analysis suggests linkage disequilibrium in the human insulin receptor gene

Summary Haplotypes of the insulin receptor gene were resolved in parents from Scandinavian nuclear families by studying the segregation of seven restriction fragment length polymorphisms (RFLPs). Of 97 unrelated parents, 41 had non-insulin-dependent diabetes mellitus (NIDDM). Considerable linkage disequilibrium in the region of the insulin receptor gene was found. Pairwise non-random associations were found between proximate RFLP sites, indicating the absence of recombinational hot spots between these sites. Thus, association studies between DNA polymorphisms at this locus and disease susceptibility genes could well be feasible in this population. Differences in the distribution of insulin receptor haplotypes were examined between NIDDM patients and healthy subjects. However, the differences observed were not statistically significant.     

Extent and consistency across generations of linkage disequilibrium in commercial layer chicken breeding populations

Recent studies report a surprisingly high degree of marker-to-marker linkage disequilibrium (LD) in ruminant livestock populations. This has important implications for QTL mapping and marker-assisted selection. This study evaluated LD between microsatellite markers in a number of breeding populations of layer chickens using the standardized chi-square (chi(2')) measure. The results show appreciable LD among markers separated by up to 5 cM, decreasing rapidly with increased separation between markers. The LD within 5 cM was strongly conserved across generations and differed among chromosomal regions. Using marker-to-marker LD as an indication for marker-QTL LD, a genome scan of markers spaced 2 cM apart at moderate power would have good chances of uncovering most QTL segregating in these populations. However, of markers showing significant trait associations, only 57% are expected to be within 5 cM of the responsible QTL, and the remainder will be up to 20 cM away. Thus, high-resolution LD mapping of QTL will require dense marker genotyping across the region of interest to allow for interval mapping of the QTL.     

Variability of CAG tandem repeats in exon 1 of the androgen receptor gene is not related with dog intersexuality

Numerous mutations of the human androgen receptor (AR) gene cause an intersexual phenotype, called the androgen insensitivity syndrome. The intersexual phenotype is also quite often diagnosed in dogs. The aim of this study was to conduct a comparative analysis of the entire coding sequence (eight exons) of the AR gene in healthy and four intersex dogs, as well as in three other canids (the red fox, arctic fox and Chinese raccoon dog). The coding sequence of the studied species appeared to be conserved (similarity above 97%) and polymorphism was found in exon 1 only. Altogether, 2 SNPs were identified in healthy dogs, 14 in red foxes, 16 in arctic foxes and 6 were found in Chinese raccoon dogs, respectively. Moreover, a variable number of tandem repeats (CAG and CAA), encoding an array of glutamines, was also observed in this exon. The CAA codon numbers were invariable within species, but the CAG repeats were polymorphic. The highest number of the CAG and CAA repeats was found in dogs (from 40 to 42) and the observed variability was similar in intersex and healthy dogs. In the other canids the variability fell within the following ranges: 29–37 (red fox), 37–39 (arctic fox) and 29–32 (Chinese raccoon dog). In addition, a polymorphic microsatellite marker in intron 2 was found in the dog, red fox and Chinese raccoon dog. It was concluded that the polymorphism level of the AR gene in the dog was lower than in the other canids and none of the detected polymorphisms, including variability of the CAG tandem repeats, could be related with the intersexual phenotype of the studied dogs.     

雄激素受体基因（CAG）重复序列长度多态性与前列腺疾病

雄激素受体基因中的CAG重复序列长度的多态性，与前列腺疾病的发病率密切相关，有可能成为有效的危险判定因子。本文试图对这方面的进展作一简要介绍。