Disease relevance of ARNT

• The t(1;12)(q21;p13) translocation of human acute myeloblastic leukemia results in a TEL-ARNT fusion [1].
• BRCA1 modulates xenobiotic stress-inducible gene expression by interacting with ARNT in human breast cancer cells [2].
• In an effort to better understand the mechanism of toxicity of 2,3,7, 8-tetrachlorodibenzo-p-dioxin, we employed an iterative search of human expressed sequence tags to identify novel basic-helix-loop-helix-PAS (bHLH-PAS) proteins that interact with either the Ah receptor (AHR) or the Ah receptor nuclear translocator (ARNT) [3].
• In mice bearing Hep3B hepatoma, curcumin retarded tumor growth and suppressed ARNT, erythropoietin, and vascular endothelial growth factor in tumors [4].
• In conclusion, the female reproductive tract expresses mRNA for the transcription factors AHR and ARNT, and changes in their expression at select target sites in specific pathological conditions such as endometriosis and uterine leiomyomas suggest a potential role for these factors in the pathogenesis of these conditions [5].

Psychiatry related information on ARNT

• Individual difference in expression levels of Ahr and Arnt mRNA was observed in liver, lung and blood [6].
• Shared decision-making in the medical encounter: what does it mean? (or it takes at least two to tango) [7].
• It takes two to tango but one to infect (on the underestimation of the calculated risk for infection with HIV in sexual encounters, arising from nondisclosure of previous risk behavior or seropositivity) [8].

High impact information on ARNT

• "It takes two to tango": understanding how centrosome duplication is regulated throughout the cell cycle [9].
• Two regulatory proteins, the aromatic (aryl) hydrocarbon receptor (AhR) and the AhR nuclear translocator (Arnt), mediate induction [10].
• A single Drosophila gene encoding a bHLH/PAS protein homologous to the vertebrate ARNT protein was isolated and may serve as a partner for both Trh and Sim [11].
• Meiotic chromosomes: it takes two to tango [12].

Chemical compound and disease context of ARNT

• Finally, we have found that xenobiotic (TCDD) treatments of breast cancer cells containing reduced levels of BRCA1 cause the transcription factor ARNT to become unstable [2].
• We have previously shown that the C-terminal PAS domains of an HIF-alpha isoform (HIF-2alpha) and ARNT interact in vitro, and that mutations in the solvent-exposed beta-sheet surface of the HIF-2alpha domain not only disrupt this interaction, but also greatly attenuate the hypoxia response in living cells [13].
• Human AhR and Arnt with a C-terminal histidine tag have been expressed functionally using a baculovirus expression system [14].
• We have also shown that arsenite specifically induces HIF-1alpha, but not HIF-1beta, protein levels in prostate cancer cells in a mTOR-dependent manner [15].
• We examine one particular model of shared decision making [Charles, C., Gafni, A., Whelan, T, 1997. Shared decision-making in the medical encounter: what does it mean? (or it takes at least two to tango). Social Science & Medicine 44, 681-692.]. The model has four main characteristics [16].

Biological context of ARNT

• We demonstrate by yeast two-hybrid, glutathione S-transferase pulldown, and mammalian reporter gene assays that ARNT requires its helix 2 domain but not its transactivation domain to interact with SRC-1 [17].
• The sequence of events following the binding of the AhR/AhR nuclear translocator protein (ARNT) heterodimer to dioxin response elements has yet to be completely understood [18].
• Coimmunoprecipitation studies, yeast two-hybrid analysis, and transient transfection experiments demonstrated that MOP1 and MOP2 dimerize with ARNT and that these complexes are transcriptionally active at defined DNA enhancer sequences in vivo [3].
• Specific transcriptional activation mediated by AHR/ARNT heterodimer, which is a functional indicator of receptor expression, was assessed by beta-galactosidase activity produced from a reporter plasmid [19].
• Like the well characterized NLS of the SV40 T-antigen, this variant bipartite type of ARNT NLS was also mediated by the two components of nuclear pore targeting complex, PTAC58 and PTAC97, to target to the nuclear rim in an in vitro nuclear transport assay [20].

Anatomical context of ARNT

• These results suggest that HIF-1alphaZ functions as a dominant-negative isoform of HIF-1 by sequestering ARNT in the cytosol [21].
• This study shows the biological importance of ARNT splice variants in the behavior of human breast cancer and suggests that the breast cell lines in which the splice variant was discovered may be useful models for further investigation [22].
• Metabolic [(32)P]orthophosphate labeling of human ARNT-transfected COS-1 cells, in conjunction with phosphoamino acid analysis, Edman degradation, and phosphopeptide mapping, demonstrated that ARNT is predominantly phosphorylated on serine residues and that serine 348 (S348) in the PAS domain is phosphorylated [23].
• Constitutive expression of AhR (primarily cytoplasmic) and ARNT (nuclear and cytoplasmic) by the majority of adult basal and secretory EC, CaP, and smooth muscle cells was confirmed in situ [24].
• HIF-2alpha and ARNT proteins localized to the developing epithelium as well as mesenchymal, most likely vascular, structures in the parenchyma [25].

Associations of ARNT with chemical compounds

• The coactivating effect of ARNT depends on physical interaction with the ERs and involves the C-terminal domain of ARNT and not the structurally conserved basic helix-loop-helix and PAS (Per-ARNT-Sim) motifs [26].
• Substitution of the target lysine with alanine enhanced the transcriptional potential of ARNT per se [27].
• We establish that the ability of ARNT to up-regulate HIF and diminish HIF sensitivity to GA is due to its ability to compete for the Hsp90 binding site on HIF [28].
• E2 responsiveness of the CD/L sequence was also dependent on an adjacent overlapping GCGTG motif corresponding to the dioxin-responsive element (DRE) core binding sequence, which is the cognate response element for the heterodimeric aryl hydrocarbon receptor (AhR)/AhR nuclear translocator (ARNT) transcription factor complex [29].
• We also found that curcumin stimulated the proteasomal degradation of ARNT via oxidation and ubiquitination processes [4].

Physical interactions of ARNT

• This yeast system is useful for the study of AHR/ARNT protein complexes, and may be generally applicable to the investigation of other multiprotein complexes [19].
• Both AHR and ARNT were capable of interacting directly with ER alpha, as ascertained by glutathione S-transferase pull-down [30].
• The phosphorylated HIF-1alpha was the major form that bound to ARNT [31].
• Furthermore, in vitro the receptor bound selectively to the basal transcription factors, the TATA-binding protein and TFIIF, whereas ARNT bound preferentially to TFIIF [32].
• Thus formed AhR/Arnt heterodimer binds a specific DNA sequence designated XRE in the promoter region of the target genes including CYP1A1, UDP-glucuronosyl transferase and others to enhance their expression [33].

Regulatory relationships of ARNT

• The aryl hydrocarbon (or dioxin) receptor (AhR) is a ligand-activated basic helix-loop-helix (bHLH) protein that heterodimerizes with the bHLH protein AhR nuclear translocator (ARNT) to form a complex that binds to xenobiotic regulatory elements in the enhancers of target genes [32].
• The aryl hydrocarbon receptor (AhR)/AhR nuclear translocator (ARNT) heterodimer complex activates gene transcription by binding to the DREs of CYP1B1 [34].
• Ectopically expressed ARNT was consistently able to enhance HIF-1alpha phosphorylation in a binding-dependent manner [31].
• We previously showed that estrogen receptor (ER)-negative breast cancer cell lines expressed a splice variant of ARNT that was associated with Ah nonresponsiveness [22].
• Aryl hydrocarbon nuclear translocator (ARNT) promotes oxygen-independent stabilization of hypoxia-inducible factor-1alpha by modulating an Hsp90-dependent regulatory pathway [28].

Other interactions of ARNT

• We confirm the interactions of ARNT and AHR with SRC-1 with immunocytochemical techniques [17].
• VEGF mRNA was not induced by hypoxia in mutant cells that do not express the HIF-1beta (ARNT) subunit [35].
• ER alpha-AHR-ARNT protein-protein interactions mediate estradiol-dependent transrepression of dioxin-inducible gene transcription [30].
• Arnt levels also correlated with CYP1B1 levels in induced lymphocytes (p < 0.01) [36].
• We did not detect previously published polymorphisms of ARNT (D511N) or the CYP1A1 promoter (G-469A and C-459T) in our subjects, suggesting that these polymorphisms are rare in the Japanese population [37].

Analytical, diagnostic and therapeutic context of ARNT

• Using immunoprecipitation, Western blotting, and glutathione S-transferase capture assays, a xenobiotic-independent interaction between BRCA1 and ARNT has been identified, although it is not yet known whether this is a direct or indirect interaction [2].
• Co-immunoprecipitation and co-localization assays revealed that RIP140 interacted with AhR, but not with ARNT, both in vitro and in cells [18].
• In this investigation, we analyzed the subcellular distribution of ARNT using transient expression of a fusion gene with beta-galactosidase and microinjection of recombinant proteins containing various fragments of ARNT in the linker region of glutathione S-transferase/green fluorescent protein [20].
• RT-PCR analyses did not indicate any changes in mRNA level of AHR and ARNT in the co-transfection studies [38].
• However, post-menopausal women on continuous hormone replacement therapy had greater expression of AHR but not of ARNT in the endometrium and myometrium when compared with women not taking hormones [5].

References