Aryl hydrocarbon receptor-mediated transcription: ligand-dependent recruitment of estrogen receptor alpha to 2,3,7,8-tetrachlorodibenzo-p-dioxin-responsive promoters.

Using chromatin immunoprecipitation assays, we studied the 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-mediated recruitment of the aryl hydrocarbon receptor (AhR) and several co-regulators to the CYP1A1 promoter. AhR displayed a time-dependent recruitment, reaching a peak at 75 min and maintaining promoter occupancy for the remainder of the time course. Recruitment of AhR was followed by TIF2/SRC2, which preceded CBP, histone H3 acetylation, and RNA polymerase II (RNAPII). Simultaneous recruitment to the enhancer and the TATA box region suggests the formation of a large multiprotein complex bridging the two promoter regions. Interestingly, estrogen receptor alpha (ERalpha) displayed a TCDD- and time-dependent recruitment to the CYP1A1 promoter, which was increased by co-treatment with estradiol. Transfection in HuH7 human liver cells confirmed previously reported ERalpha enhancement of AhR activity. In contrast, TCDD did not induce the recruitment of ERalpha to the estrogen-responsive pS2 promoter, and after 120 min of co-treatment with estradiol, ERalpha is still present on the CYP1A1 promoter but no longer at pS2. RNA interference studies with T47D cells support a role for ERalpha in TCDD-dependent CYP1A1 expression. Our data suggest that ERalpha acts as a coregulator of AhR-mediated transcriptional activation and that the recruitment of ERalpha by AhR represents a novel mechanism AhR-ERalpha cross talk.

Co-planar 3,3',4,4',5-pentachlorinated biphenyl and non-co-planar 2,2',4,6,6'-pentachlorinated biphenyl differentially induce recruitment of oestrogen receptor alpha to aryl hydrocarbon receptor target genes.

In the present study we examined the ability of 3,3',4,4',5-pentachlorinated biphenyl [PCB126 (polychlorinated biphenyl 126)], a prototypical AHR (aryl hydrocarbon receptor) agonist, and 2,2',4,6,6'-PCB (PCB104), which does not activate AHR, to induce the recruitment of ERalpha (oestrogen receptor alpha) to CYP1A1 (cytochrome P4501A1 gene) and CYP1B1 promoters in T-47D human breast cancer cells and other cell lines. PCB126 treatment strongly induced CYP1A1 and CYP1B1 mRNA expression that was unaffected by co-treatment with E2 (17beta-oestradiol). PCB104 failed to induce changes in either CYP1A1 or CYP1B1 expression levels. ChIP (chromatin immunoprecipitation) assays show that PCB126, but not PCB104, increased the promoter occupancy by ERalpha to CYP1A1 and CYP1B1 promoters. Co-treatment with PCB126+E2 significantly enhanced the promoter occupancy of ERalpha at CYP1A1, whereas co-treatment with PCB126+4-hydroxytamoxifen or ICI182,780 did not. Competitive binding studies revealed that neither PCB126 nor PCB104 bound to ERalpha. HEK-293 cells (human embryonic kidney-293 cells) stably transfected with ERalpha showed significantly higher PCB126-induced CYP1A1 expression compared with empty vector controls, whereas no increase was observed in cells stably transfected with ERalpha lacking its N-terminal AF1 (activation function-1) domain (ERalphaDeltaAF1). Despite no increase in AHR-mediated gene expression, ChIP assays revealed that ERalphaDeltaAF1 was present at CYP1A1 and CYP1B1 promoters. HC11 mouse mammary cells stably expressing shRNA (small-hairpin RNA) against ERalpha showed an 8-fold reduction in PCB126-dependent Cyp1a1 expression. Our results provide further evidence that AHR agonists induce ERalpha promoter occupancy at AHR target genes through indirect activation of ERalpha, and support a role for ERalpha in AHR transactivation.

Estrogen receptor (ER) beta modulates ERalpha-mediated transcriptional activation by altering the recruitment of c-Fos and c-Jun to estrogen-responsive promoters.

In this study, an estrogen receptor (ER) alpha-expressing T47D cell line containing an inducible tet-off FLAG-ERbeta was used to examine the influence of ERbeta on ERalpha activity. Real-time PCR analysis of mRNA levels of two well-studied estrogen-responsive genes, pS2 and progesterone receptor (PR), showed that the expression levels of both genes were reduced in the presence of ERbeta. Chromatin immunoprecipitation assays showed that the 17beta-estradiol (E2)-induced recruitment patterns to the pS2 and PR promoters were similar for both ERalpha and ERbeta. ERbeta expression did not significantly influence the kinetic recruitment profile of ERalpha to the pS2 promoter, but it was evident that ERalpha occupancy at the PR promoter was reduced. The E2-induced recruitment of c-Fos to a 12-O-tetradecanoylphorbol-13-acetate response element site in the PR promoter was significantly reduced in the presence of ERbeta, whereas only a slight reduction in the recruitment of c-Fos to the pS2 promoter was observed. ERbeta expression resulted in a significant reduction in the E2-induced expression of c-Fos mRNA. The recruitment pattern of c-Jun was also altered by ERbeta, although the expression levels of c-Jun were not. Expression of ERbeta caused a further 30-50% decrease of the E2-induced reduction in ERalpha protein after 3 h of E2 treatment, showing that ERbeta influences ERalpha protein levels. The altered recruitment of the activating protein-1 complex, combined with the reduction in ERalpha protein levels, may partly explain the antagonistic effect of ERbeta on ERalpha-mediated transcription.

Quantitative codon optimisation of DNA libraries encoding sub-random peptides: design and characterisation of a novel library encoding transmembrane domain peptides.

Codons for amino acids sharing similar chemical properties seem to cluster on the genetic codon table. Such a geographical distribution of the codons was exploited to create chemically synthesised DNA that encodes peptide libraries containing only a subset of the 20 natural amino acids. The frequency of each amino acid in the subset was further optimised by quantitatively manipulating the ratio of the four phosphoamidites during chemical synthesis of the libraries. Peptides encoded by such libraries show a reduced complexity and could be enriched in peptides of a desired property, which are thus more suitable when screening for functional peptides. Proof of concept for the codon-biased design of peptide libraries was shown by design, synthesis, and characterisation of a transmembrane peptide library that contains >80% transmembrane peptides, representing a 160-fold enrichment compared with a fully randomised library.

Regional variation in use of exogenous and endogenous glomerular filtration rate (GFR) markers in Sweden.

BACKGROUND: Markers of renal function (glomerular filtration rate (GFR)) are frequently used in the Swedish health care. GFR is usually estimated based on plasma creatinine concentration, but plasma cystatin C concentration, creatinine clearance, iohexol clearance, and (51)Cr-EDTA clearance are also used. These markers are all part of the daily patient care, but there is little specific information on the clinical use of these markers. The aim of this study was to compare the use of these various GFR markers in different parts of Sweden and potential changes over time. METHODS: Retrospective study using questionnaires to collect information for the years 2006-2009 divided per county on the specific use of GFR markers with type of test reports. RESULTS: Plasma/serum creatinine concentration (96%) is by far the dominating GFR marker in Sweden, while cystatin C concentration (3.5%), creatinine clearance (0.1%), iohexol clearance (0.1%), and 51Cr-EDTA clearance (0.1%) are less frequently used. The use of GFR markers, including creatinine, continues to increase on a national level with the exception of creatinine clearance and 51Cr-EDTA clearance. There were considerable variations between different counties in the use of GFR markers and the type of test reports that the laboratories provided. CONCLUSIONS: The inter-county variations of GFR markers used in Sweden are large and indicate that savings associated with optimized test utilization in this regard could be substantial. Regional habits and traditions are likely to influence the variations in GFR marker use.

Estrogen receptor subtype- and promoter-specific modulation of aryl hydrocarbon receptor-dependent transcription.

In this study, we examined the role of estrogen receptors (ER) in aryl hydrocarbon receptor (AHR)-dependent transactivation. Chromatin immunoprecipitation assays showed that AHR agonists differentially induced recruitment of ERalpha to the AHR target genes CYP1A1 and CYP1B1. Cotreatment with 17beta-estradiol significantly increased beta-naphthoflavone (BNF)- and 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced recruitment of ERalpha to CYP1A1, whereas 3,3'-diindolylmethane induced promoter occupancy of ERalpha at CYP1A1 that was unaffected by cotreatment with 17beta-estradiol. Cyclical recruitment of AHR and ERalpha to CYP1A1 was only observed in cells treated with BNF. Stable and subtype-specific knockdown of ERalpha or ERbeta using shRNA showed that suppression of ERalpha significantly reduced, whereas knockdown of ERbeta significantly enhanced, AHR agonist-induced Cyp1a1 expression in HC11 mouse mammary epithelial cells. AHR agonist-induced Cyp1b1 expression was reduced by ERbeta knockdown but unaffected by ERalpha knockdown. The siRNA-mediated knockdown of ERalpha in MCF-7 human breast cancer cells did not affect 2,3,7,8-tetrachlorodibenzo-p-dioxin-dependent regulation of CYP1A1 and CYP1B1 mRNA expression. In agreement with our in vitro findings in the HC11 cells, ERalpha knockout mice exhibit reduced BNF-dependent induction of Cyp1a1 mRNA. These results establish ligand- and promoter-specific influences on the cyclical recruitment patterns for AHR and show ER species-, subtype-, and promoter-specific modulation of AHR-dependent transcription.