Androgen receptor CAG repeat length modifies the effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin on receptor activity in human prostate cells

Androgen Receptor Genotype in Humans and Susceptibility to Endocrine Disruptors

Although animal studies have raised concern that the influence of endocrine-disrupting compounds would obstruct the development of the male reproductive system, in general, exposure levels far above those found in humans have been needed to induce reproductive toxicity in animal models. Human data are inconclusive and have evoked the question whether endocrine-disrupting compounds can have any impact on hormonal function and thus health consequences when natural hormones are present. Indeed, many contaminants with hormone-like activity are much less potent than endogenous hormones themselves: 17β-oestradiol was, for instance, estimated to be 17,000 times more potent than o,p'-DDT. However, humans are exposed to a multitude of agents, and when present in sufficient number and concentration, they might in principle act collected on the actions of endogenous hormones. Whether such effects will be physiologically relevant is still not known. Nevertheless, in the worst-case scenario, there are no threshold levels below which there are no effects at all, and one target molecule is the androgen receptor. This mini review focuses on the androgen receptor gene, its link with classical endocrine disruptors and smoking, and how common genetic variants in the androgen receptor gene may influence physiological outcomes.

Short androgen receptor poly-glutamine-promoted endometrial cancer is associated with benzo[a]pyrene-mediated aryl hydrocarbon receptor activation

The androgen receptor (AR) poly‐glutamine polymorphism (AR‐Q) was reported to play role in endometrial cancer (EMCA) development, yet controversial. Environmental factors interact with genetic variation have been reported in EMCA. Aerosol toxins, polycyclic aromatic hydrocarbon benzo[a]pyrene (BaP), are EMCA facilitators. This report examined the interplay between AR‐Qs and BaP in EMCA. During analysing patient AR‐Q polymorphism and Aryl hydrocarbon Receptor (AhR) expressions, we found overall survival (OS) benefit is ascending with AR‐Q lengths (5‐year OS of 61.3% in Q length <20 and 88% in Q length >23). And AhR is higher expressed in short AR‐Q tumour compared to that in long AR‐Q patient. In vitro study found androgen‐response element (ARE) activity descends with AR‐Qs length (Q13 > Q25 > Q35), whereas BaP suppresses ARE activities in EMCA cells. Furthermore, AR‐Q13 (but not AR‐Q25, or ‐35) enhances BaP‐induced dioxin‐responsive element (DRE) activity. Lastly, AR‐Q13 exerts higher colony‐forming capacity than other AR‐Qs, and knock‐down AhR abolished AR‐Q13‐mediated colony numbers. This study demonstrated a possible interaction of gene (AR‐Q polymorphism) and environmental toxins (e.g. BaP) to affect cancer progression. A large‐scale epidemiology and public health survey on the interaction of environmental toxin and AR poly‐Q in EMCA is suggested.

The AhR Ligand, TCDD, Regulates Androgen Receptor Activity Differently in Androgen-Sensitive versus Castration-Resistant Human Prostate Cancer Cells

The reported biological effects of TCDD include induction of drug metabolizing enzymes, wasting syndrome and tumor promotion. TCDD elicits most of its effects through binding the aryl hydrocarbon receptor (AhR). TCDD induced degradation of AhR has been widely reported and requires ubiquitination of the protein. The rapid depletion of AhR following TCDD activation serves as a mechanism to modulate AhR mediated gene induction. In addition to inducing AhR degradation, TCDD has been reported to induce degradation of hormone receptors. The studies reported here, evaluate the effect of TCDD exposure on androgen receptor (AR) expression and activity in androgen-sensitive LNCaP and castration-resistant C4-2 prostate cancer cells. Our results show that TCDD exposure does not induce AhR or AR degradation in C4-2 cells. However, both AhR and AR are degraded in LNCaP cells following TCDD exposure. In addition, TCDD enhances AR phosphorylation and induces expression of AR responsive genes in LNCaP cells. Our data reveals that TCDD effect on AR expression and activity differs in androgen-sensitive and castration-resistant prostate cancer cell models.

Endocrine disrupters: the new players able to affect the epigenome

Epigenetics represents the way by which the environment is able to program the genome; there are three main levels of epigenetic control on genome: DNA methylation, post-translational histone modification and microRNA expression. The term Epigenetics has been widened by NIH to include “both heritable changes in gene activity and expression but also stable, long-term alterations in the transcriptional potential of a cell that are not necessarily heritable.” These changes might be produced mostly by the early life environment and might affect health influencing the susceptibility to develop diseases, from cancer to mental disorder, during the entire life span. The most studied environmental influences acting on epigenome are diet, infections, wasting, child care, smoking and environmental pollutants, in particular endocrine disrupters (EDs). These are environmental xenobiotics able to interfere with the normal development of the male and female reproductive systems of wildlife, of experimental animals and possibly of humans, disrupting the normal reproductive functions. Data from literature indicate that EDs can act at different levels of epigenetic control, in some cases transgenerationally, in particular when the exposure to these compounds occurs during the prenatal and earliest period of life. Some of the best characterized EDs will be considered in this review. Among the EDs, vinclozolin (VZ), and methoxychlor (MXC) promote epigenetic transgenerational effects. Polychlorinated biphenils (PCBs), the most widespread environmental EDs, affect histone post-translational modifications in a dimorphic way, possibly as the result of an alteration of gene expression of the enzymes involved in histone modification, as the demethylase Jarid1b, an enzyme also involved in regulating the interaction of androgens with their receptor.

Influence of Low-Level Prenatal Exposure to PCDD/Fs and PCBs on Empathizing, Systemizing and Autistic Traits: Results from the Duisburg Birth Cohort Study

BACKGROUND

Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and polychlorinated biphenyls (PCBs) are assumed to act as endocrine disruptor chemicals. Prenatal exposure to these pollutants might influence fetal steroid hormone levels, which are thought to be related to sex-typical development and autistic traits.

OBJECTIVES

We examined associations of prenatal levels of PCDD/Fs and PCBs with autism traits and sex-typical behaviour in childhood.

METHODS

We measured levels of PCDD/Fs and PCBs in maternal blood samples during pregnancy using gas chromatography/high-resolution mass spectrometry. Sex-typical behaviour was assessed at 9 years of age (n = 96) and autistic traits at 10 years of age using the Social Responsiveness Scale (SRS; n = 100). Multiple regression analyses were conducted to estimate the associations between prenatal exposure and outcome variables.

RESULTS

Blood concentrations (WHO2005-TEq) of ƩPCDD/Fs ranged from 2.93-46.45 pg/g lipid base (median = 12.91 pg/g lipid base) and concentrations of ƩPCBs were in the range of 1.24-25.47 pg/g lipid base (median = 6.85 pg/g lipid base) which is within the range of German background exposure. We found significant negative associations between PCDD/F levels in maternal blood and SRS scores in the whole group (β = -6.66, p < .05), in girls (β = -10.98, p < .05) and, in one SRS subscale, in boys (β = -6.86, p < .05). For PCB levels, associations with one SRS subscale were significant for the whole study group as were associations with two subscales in girls. We did not find significant associations between PCDD/F or PCB levels and sex-typical behaviour for either sex.

CONCLUSIONS

In an earlier part of this study, prenatal exposure to PCDD/Fs and PCBs was found to be associated with lower testosterone levels, therefore, our findings are consistent with the idea that autism spectrum conditions are related to fetal androgen levels. Several possible mechanisms, through which PCDD/Fs and PCBs might influence autistic behaviour, are discussed.

Correlation study between the polymorphism of repetitive sequence in gene CAG of androgen receptor and the occurrence and progression of prostate cancer

OBJECTIVE

To explore the relation between the polymorphism of repetitive sequence in gene CAG of androgen receptor (AR) and the susceptibility and clinical stages as well as pathological grading of prostate cancer among Han population.

METHOD

Sixty-eight cases with prostate cancer hospitalized in Urinary Surgery Department from Feb. 2010 to Feb. 2012 and 60 healthy cases were chosen as research subjects. Methods of PCR and direct sequencing were adopted to detect DNA sequence of AR gene and the length of repetitive sequence in CAG.

RESULTS

The lengths of repetitive sequence in CAG of patients with prostate cancer and healthy people were (22.3±4.6) and (23.0±4.9), respectively showing no statistical significance. Comparing length (repetitive sequence of CAG)>22, those with that < 22 suffer a remarkably higher risk of prostate cancer (P<0.05). The number of repetitive sequence in CAG of patients at clinical stage C-D was less than that of patients at stage B, and the number of repetitive sequence in CAG of patients with poorly differentiated prostate cancer was also less than that of patients with moderately and highly differentiated prostate cancer. But there was no statistical significance int the difference (P>0.05); the proportion of patients with length <22 at clinical stage C-D was much larger than that of patients at clinical stage B (P<0.05), and as the aggravation of pathological grading, the proportion of patients with the length <22 was also remarkably increased and there was significant difference between patients with highly differentiated prostate cancer and those with poorly differentiated prostate cancer (P<0.05).

CONCLUSIONS

There is correlation between the occurrence and development of prostate cancer in Han population and the polymorphism of repetitive sequence in gene CAG of androgen receptor. The less the number of repetitive sequence in CAG is, the higher the risk of prostate cancer will be and the more severe the clinical stage and pathological grading will be.

Gene-environment interactions in male reproductive health: special reference to the aryl hydrocarbon receptor signaling pathway

Over the last few decades, there have been numerous reports of adverse effects on the reproductive health of wildlife and laboratory animals caused by exposure to endocrine disrupting chemicals (EDCs). The increasing trends in human male reproductive disorders and the mounting evidence for causative environmental factors have therefore sparked growing interest in the health threat posed to humans by EDCs, which are substances in our food, environment and consumer items that interfere with hormone action, biosynthesis or metabolism, resulting in disrupted tissue homeostasis or reproductive function. The mechanisms of EDCs involve a wide array of actions and pathways. Examples include the estrogenic, androgenic, thyroid and retinoid pathways, in which the EDCs may act directly as agonists or antagonists, or indirectly via other nuclear receptors. Dioxins and dioxin-like EDCs exert their biological and toxicological actions through activation of the aryl hydrocarbon-receptor, which besides inducing transcription of detoxifying enzymes also regulates transcriptional activity of other nuclear receptors. There is increasing evidence that genetic predispositions may modify the susceptibility to adverse effects of toxic chemicals. In this review, potential consequences of hereditary predisposition and EDCs are discussed, with a special focus on the currently available publications on interactions between dioxin and androgen signaling.

Prostate-specific antigen levels in relation to background factors: are there links to endocrine disrupting chemicals and AhR expression?

BACKGROUND

Prostate-specific antigen (PSA) is a potential biomarker for early detection of prostate cancer (PCa) but its level is known to be affected by many background factors and roles of ubiquitous toxicants have not been determined. Endocrine disrupting chemicals (EDCs) are ubiquitous reproductive toxicants used in consumer products, which promote tumor formation in some reproductive model systems by binding to AhR, but human data on its expression in prostate cancer as well as its association with PSA levels are not clear. This study aimed to evaluate the expression levels of AhR and its association with serological levels of PSA and to detect possible effects of background factors and EDC exposure history on PSA levels in PCa cases.

MATERIALS AND METHODS

A cross-sectional study was conducted on the tissue levels of AhR and serum levels of PSA in 53 PCa cases from 2008-2011 and associations between each and background and lifestyle related factors were determined.

RESULTS

Although the AhR was overexpressed in PCa and correlated with the age of patients, it did not correlate with PSA levels.Of nutritional factors, increased intake of polysaturated fats and fish in the routine regimen of PCa cases increased the PSA levels significantly.

CONCLUSIONS

AhR overexpression in PCa pontws to roles of EDCs in PCa but without any direct association with PSA levels. However, PSA levels are affected by exposure to possible toxicants in foods whichneed to be assessed as possible risk factors of PCa in future studies.

Androgen receptor activation by polychlorinated biphenyls: epigenetic effects mediated by the histone demethylase Jarid1b

The exposure to environmental endocrine disrupting compounds (EDC), as polychlorinated biphenyls (PCBs), widely diffused in the environment may produce epigenetic changes that affect the endocrine system. We found that PCBs activate AR transcriptional activity and that this effect is potentiated by the demethylase Jarid1b, a histone demethylase that catalyzes the removal of trimethylation of lysine 4 on histone H3 (H3K4me3), induced by PCB. The aim of the present study was to investigate the effect of the treatment of cultured cells (HEK293) with a mixture of the most diffused environmental PCBs and, also with dihydrotestosterone (DHT), on the functional interaction between AR and Jarid1b. Although the effect induced by DHT on the AR transactivation was considerably higher, the PCB mixture produced an AR-mediated transactivation in a dose-dependent manner. Cotransfection with plasmids expressing Jarid1b and various AR isoforms containing polyglutamine tracts (polyQ tracts) of different lengths showed that Jarid1b potentiates the AR transcriptional activity induced by PCBs but only with the shortest AR isoform. The potentiating effect of Jarid1b on the AR is mediated by a direct interaction of the enzyme with the AR promoter. In fact, utilizing constructs containing AR promoters with a different length and a luciferase reporter gene, we showed that the effect of PCBs, but not of DHT, needs the presence of Jarid1b and of at least two DNA binding sites for Jarid1b.