Androgen receptor gene CAG repeats, estrogen exposure status, and breast cancer susceptibility

Recent advances of therapeutic targets based on the molecular signature in breast cancer: genetic mutations and implications for current treatment paradigms

Breast cancer is the most common malignancy in women all over the world. Genetic background of women contributes to her risk of having breast cancer. Certain inherited DNA mutations can dramatically increase the risk of developing certain cancers and are responsible for many of the cancers that run in some families. Regarding the widespread multigene panels, whole exome sequencing is capable of providing the evaluation of genetic function mutations for development novel strategy in clinical trials. Targeting the mutant proteins involved in breast cancer can be an effective therapeutic approach for developing novel drugs. This systematic review discusses gene mutations linked to breast cancer, focusing on signaling pathways that are being targeted with investigational therapeutic strategies, where clinical trials could be potentially initiated in the future are being highlighted.

CAG repeat polymorphisms in the androgen receptor and breast cancer risk in women: a meta-analysis of 17 studies

The association between polymorphic CAG repeats in the androgen receptor gene in women and breast cancer susceptibility has been studied extensively. However, the conclusions regarding this relationship remain conflicting. The purpose of this meta-analysis was to identify whether androgen receptor CAG repeat lengths were related to breast cancer susceptibility. The MEDLINE, PubMed, and EMBASE databases were searched through to December 2014 to identify eligible studies. Data and study quality were rigorously assessed by two investigators according to the Newcastle-Ottawa Quality Assessment Scale. The publication bias was assessed by the Begg’s test. Seventeen eligible studies were included in this meta-analysis. The overall analysis suggested no association between CAG polymorphisms and breast cancer risk (odds ratio [OR] 1.031, 95% confidence interval [CI] 0.855–1.245). However, in the subgroup analysis, we observed that long CAG repeats significantly increased the risk of breast cancer in the Caucasian population (OR 1.447, 95% CI 1.089–1.992). Additionally, the risk was significantly increased in Caucasian women carrying two alleles with CAG repeats ≥22 units compared with those with two shorter alleles (OR 1.315, 95% CI 1.014–1.707). These findings suggest that long CAG repeats increase the risk of breast cancer in Caucasian women. However, larger scale case-control studies are needed to validate our results.

Trinucleotide repeat expansions in human breast cancer-susceptibility genes: relevant targets for aspirin chemoprevention?

PURPOSE

Defining novel molecular mechanisms pertinent to aspirin chemoprevention of breast cancer (BC) and to explain controversial epidemiological results in this regard.

METHODS

Literature search in relevant databases with the following key words; aspirin, nucleotide repeat expansions, breast cancer. Human genome contains nucleotide repeat expansions and exon-1 of the androgen receptor gene AR contains a CAG string with an average of 20 repeats. Longer AR CAG repeats associate with lower AR protein functioning leading relatively higher estrogen receptor signals and higher risk of hormone receptor-positive BC. Nucleotide repeat expansions also exist in E2F4 and POLG genes in BC. In cell culture models, aspirin reduces CAG.CTG expansions in kidney cells and restores myogenic differentiation in cells obtained from tissues with myotonic dystrophy, a disorder caused by large CTG expansions.

CONCLUSIONS

We hypothesize that aspirin reduction of trinucleotide repeat expansions in breast cancer-susceptibility genes may be one of the relevant mechanisms of its chemopreventive effects.

Increased expression of ACTH (MC2R) and androgen (AR) receptors in giant bilateral myelolipomas from patients with congenital adrenal hyperplasia

BACKGROUND

Although chronic adrenocorticotropic hormone (ACTH) and androgen hyperstimulation are assumed to be involved in the pathogenesis of adrenal myelolipomas associated with poor-compliance patients with congenital adrenal hyperplasia (CAH), the expression of their receptors has not yet been demonstrated in these tumors so far.

METHODS

We analyzed Melanocortin 2 receptor (MC2R), Androgen Receptor (AR), Leptin (LEP), and Steroidogenic factor 1 (SF1) expression using real-time qRT-PCR in two giant bilateral adrenal myelolipomas from two untreated simple virilizing CAH cases and in two sporadic adrenal myelolipomas. In addition, the X-chromosome inactivation pattern and CAG repeat numbers in AR exon 1 gene were evaluated in the 4 cases.

RESULTS

The MC2R gene was overexpressed in myelolipomas from 3 out of 4 patients. AR overexpression was detected in 2 tumors: a giant bilateral myelolipoma in a CAH patient and a sporadic case. Simultaneous overexpression of AR and MC2R genes was found in two of the cases. Interestingly, the bilateral giant myelolipoma associated with CAH that had high androgen and ACTH levels but lacked MC2R and AR overexpression presented a significantly shorter AR allele compared with other tumors. In addition, X-chromosome inactivation pattern analysis showed a polyclonal origin in all tumors, suggesting a stimulatory effect as the trigger for tumor development.

CONCLUSION

These findings are the first evidence for MC2R or AR overexpression in giant bilateral myelolipomas from poor-compliance CAH patients.

Microsatellites in the estrogen receptor (ESR1, ESR2) and androgen receptor (AR) genes and breast cancer risk in African American and Nigerian women

Genetic variants in hormone receptor genes may be crucial predisposing factors for breast cancer, and microsatellites in the estrogen receptor (ESR1, ESR2) and androgen receptor (AR) genes have been suggested to play a role. We studied 258 African-American (AA) women with breast cancer and 259 hospital-based controls, as well as 349 Nigerian (NG) female breast cancer patients and 296 community controls. Three microsatellites, ESR1_TA, ESR2_CA and AR_CAG, in the ESR1, ESR2 and AR genes, respectively, were genotyped. Their repeat lengths were then analyzed as continuous and dichotomous variables. Analyses of continuous variables showed no association with breast cancer risk in either AA or NG at ESR1_TA; AA cases had shorter repeats in the long allele of ESR2_CA than AA controls (Mann-Whitney P= 0.036; logistic regression P = 0.04, OR= 0.91, 95% CI 0.83-1.00), whereas NG patients had longer repeats in the short allele than NG controls (Mann-Whitney P= 0.0018; logistic regression P= 0.04, OR= 1.06, 95% CI 1.00-1.11); and AA cases carried longer repeats in the short allele of AR_CAG than AA controls (Mann-Whitney P= 0.038; logistic regression P = 0.03, OR= 1.08, 95% CI 1.01-1.15). When allele sizes were categorized as dichotomous variables, we discovered that women with two long alleles of ESR2_CA had increased risk of breast cancer (OR = 1.38, 95% CI 1.10-1.74; P = 0.006). This is the first study to investigate these three microsatellites in hormonal receptor genes in relation to breast cancer risk in an indigenous African population. After adjusting for multiple-testing, our findings suggest that ESR2_CA is associated with breast cancer risk in Nigerian women, whereas ESR1_TA and AR_CAG seem to have no association with the disease among African American or Nigerian women.

Implications of single nucleotide polymorphisms in CD44 exon 2 for risk of breast cancer

CD44 is a cell-surface glycoprotein involved in many cellular functions including lymphocyte activation, recirculation and homing, hematopoiesis and tumor metastasis, suggesting that CD44 may play an important role in breast cancer development. In this study, we examined whether CD44 exon 2 polymorphisms are associated with increased susceptibility to breast cancer. Direct nucleotide sequencing analysis showed that multiple single nucleotide polymorphisms were present in the CD44 exon 2 coding region in female patients with breast cancer. There was no significant difference in the frequency of any one single nucleotide polymorphism in the CD44 exon 2 coding region between patients with breast cancer and normal donors. However, CD44 polymorphisms in the CD44 exon 2 coding region were identified in approximately 40% of patients with breast cancer, which was significantly higher than in normal donors (odds ratio, 9.34; 95% confidence interval = 2.58-33.82; P < 0.0001). The Wilcoxon-Mann-Whitney test analysis showed that the patients with the CD44 polymorphisms in CD44 exon 2 coding sequence had breast cancer at earlier ages, 49 ± 3 versus 62 ± 2 years (P < 0.0005), and larger tumor burdens (4.9 ± 1.22 vs. 1.6 ± 0.15 mm, P < 0.01) at the time of diagnosis. Interestingly, African-American female patients having the CD44 polymorphisms in CD44 exon 2 coding sequence were diagnosed with breast cancer at very young age (41 ± 2 years). Our results show that CD44 exon 2 polymorphisms are associated with breast cancer development, and such analysis may be effectively used in the evaluation of risk, prediction of cancer, prevention, diagnosis, and epidemiological studies of breast cancer.

Ethnic variation in allele distribution of the androgen receptor (AR) (CAG)n repeat

The androgen receptor (AR) is important in reproductive organ development, as well as tissue homeostasis of the pancreas, liver, and skeletal muscle in adulthood. The trinucleotide (CAG)(n) repeat polymorphism in exon 1 of the AR gene is thought to regulate AR activity, with longer alleles conferring reduced receptor activity. Therefore, the evaluation of the allelic distribution of the AR (CAG)(n) repeat in various ethnic groups is crucial in understanding the interindividual variability in AR activity. We evaluated ethnic variation of this AR polymorphism by genotyping individuals from the multiethnic Hyperglycemia and Adverse Pregnancy Outcome study cohort. We genotyped 4421 Caucasian mothers and 3365 offspring of European ancestry; 1494 Thai mothers and 1742 offspring; 1119 Afro-Caribbean mothers and 1142 offspring; and 780 Hispanic mothers and 770 offspring of Mexican ancestry from Bellflower, California. The distributions of (CAG)(n) alleles among all 4 ethnic groups are significantly different (P < .0001). Pairwise tests confirmed significant differences between each pair of ethnicities tested (P < 10(-28)). The relative AR (CAG)(n) repeat length in the different groups was as follows: Afro-Caribbean (shortest repeat lengths and greatest predicted AR activity) < Caucasian < Hispanic < Thai (longest repeat length and lowest predicted AR activity). Significant interethnic differences in the allele frequencies of the AR exon 1 (CAG)(n) polymorphism exist. Our results suggest that there may be potential ethnic differences in androgenic pathway activity and androgen sensitivity.

Polymorphisms in the AR and PSA genes as markers of susceptibility and aggressiveness in prostate cancer

The study of genes involved in androgen pathway can contribute to a better knowledge of prostate cancer. Our aim was to examine if polymorphisms in prostate-specific antigen (PSA) and androgen receptor (AR) genes were involved in prostate cancer risk and aggressiveness. Genotypes were determined by PCR-RFLP (PSA) or using a 377 ABI DNA Sequencer (AR). PSA(G/G) genotype (OR = 1.78, 95% CI = 1.06–2.99) and AR short CAG repeats (OR = 1.89, 95% CI = 1.21–2.96) increased risk for prostate cancer and were related with tumor aggressiveness. About 38.3% of tumors showed microsatellite instability. In conclusion, polymorphisms in these genes may be indicated as potential biomarkers for prostate cancer.

Selected estrogen receptor 1 and androgen receptor gene polymorphisms in relation to risk of breast cancer and fibrocystic breast conditions among Chinese women

BACKGROUND

Polymorphisms in sex hormone receptor-encoding genes may alter the activity of sex hormone receptors and thereby affect susceptibility to breast cancer and related outcomes.

METHODS

In a case-control study of women from Shanghai, China, we examined the risk of breast cancer and fibrocystic breast conditions associated with the ESR1 PvuII (rs2234693) and XbaI (rs9340799) and AR CAG repeat ((CAG)(n)) and GGC repeat ((GGC)(n)) polymorphisms among 614 women with breast cancer, 467 women with fibrocystic conditions, and 879 women without breast disease. We also evaluated whether risk differed by the presence/absence of proliferative changes (in the extratumoral epithelium or fibrocystic lesion), menopausal status, or body mass index (BMI). Age-adjusted odds ratios (ORs) and 95% confidence intervals (95% CI) were calculated using logistic regression.

RESULTS

Only associations with AR (CAG)(n) and (GGC)(n) genotypes were detected. Allocating AR (CAG)(n) genotypes into six categories, with the (CAG)(22-24)/(CAG)(22-24) genotype category designated as the reference group, the (CAG)(>24)/(CAG)(>24) genotype category was associated with an increased risk of fibrocystic breast conditions (OR, 1.8; 95% CI, 1.1-3.0). Relative to the AR (GGC)(17)/(GGC)(17) genotype, the (GGC)(17)/(GGC)(14) genotype was associated with elevated risks of incident breast cancer (OR, 2.6; 95% CI, 1.3-5.4) and fibrocystic conditions (OR, 2.3; 95% CI, 1.1-4.5). Results did not differ according to proliferation status, menopausal status, or BMI.

CONCLUSION

Although these data lend support for a link between AR variation and breast disease development, given the low frequency of the putative risk-conferring genotypes and other constraints, further confirmation of our results is needed.