Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.2.1.23 (beta-galactosidase)
 14,648 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Aryl hydrocarbon receptor nuclear translocator (ARNT) is a component of the transcription factors, aryl hydrocarbon receptor (AhR) and hypoxia-inducible factor 1, which transactivate their target genes, such as CYP1A1 and erythropoietin, in response to xenobiotic aromatic hydrocarbons and to low O2 concentration, respectively. Since ARNT was isolated as a factor required for the nuclear translocation of AhR from the cytoplasm in response to xenobiotics, the subcellular localization of ARNT has been of great interest. 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. We found a clear nuclear localization of ARNT in the absence of exogenous ligands to AhR, and identified the nuclear localization signal (NLS) of amino acid residues 39-61. The characterized NLS consists of 23 amino acids, and can be classified as a novel variant of the bipartite type on the basis of having two separate regions responsible for efficient nuclear translocation activity, but considerable deviation of the sequence from the consensus of the classical bipartite type NLSs. 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.
 ...
PMID:A nuclear localization signal of human aryl hydrocarbon receptor nuclear translocator/hypoxia-inducible factor 1beta is a novel bipartite type recognized by the two components of nuclear pore-targeting complex. 921 13

The human aryl hydrocarbon receptor (AHR) and aryl hydrocarbon receptor nuclear translocator protein (ARNT) were coexpressed in the yeast Saccharomyces cerevisiae to create a system for the study of this heterodimeric transcription factor. 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. Yeast expressing AHR and ARNT displayed constitutive transcriptional activity that was not augmented by addition of AHR agonists in strains that required exogenous tryptophan for viability. In contrast, strains with an intact pathway for tryptophan biosynthesis responded to AHR agonists and had lower levels of background beta-galactosidase activity. Hexachlorobenzene, benzo(a)pyrene, and beta-naphthoflavone were effective AHR agonists in the yeast system, and had EC50 values of 200, 40, and 20 nM, respectively, for beta-galactosidase activity induction. Tryptophan, indole, indole acetic acid, and tryptamine activated transcription in yeast coexpressing AHR and ARNT (EC50 values approximately 300 microM). Indole-3-carbinol was an exceptionally potent AHR agonist (EC50 approximately 10 microM) in yeast. 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.
 ...
PMID:Expression of the human aryl hydrocarbon receptor complex in yeast. Activation of transcription by indole compounds. 940 59

Aryl hydrocarbons such as dioxins, polychlorinated biphenyls and polyaromatic hydrocarbons bind to the cellular aryl hydrocarbon receptor (AhR) in the initial step of their metabolism. The activation of intracellular signaling subsequent to the AhR binding is highly correlated with the toxicity and carcinogenicity of these chemicals. We produced Saccharomyces cerevisiae coexpressing mouse AhR and aryl hydrocarbon receptor nuclear translocator (Arnt) protein in accordance with Miller III's method for constructing yeasts with human Ahr and Arnt [Toxicol. Appl. Pharmacol. 160 (1998) 297]. Ligand treatment induced a dose-dependent increase in beta-galactosidase activity from a reporter plasmid in the yeast. Then, we compared activities of several ligands in yeast having the mouse Ahr/Arnt genes with those in yeast having the human genes, both of which have the same genetic background. There was no significant difference in the EC50 values of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), benzo[a]pyrene, 3-methylcholanthrene and beta-naphthoflavone between the mouse and human genes. However, indirubin, which was recently found in human urine as a potent AhR ligand [J. Biol. Chem. 276 (2001) 31475], had a 35-140 times higher EC50 value in the yeast with human genes than mouse genes. This difference might reflect species-specificity between mouse and human AhR/Arnt.
 ...
PMID:Construction of reporter yeasts for mouse aryl hydrocarbon receptor ligand activity. 1297 62

Endocrine systems of humans and animals are disturbed by dioxin-like compounds, which are ligands of the aryl hydrocarbon receptor (AhR). It is important to determine the accumulation of dioxin-like compounds in the environment for maintenance of human health. In this study, we developed a new method for screening ligands of the AhR using a yeast hybrid system. Reporter genes constructed by the insertion of dioxin response elements were integrated into HIS and lacZ yeast genomes. Then yeast was transformed with GAL4-activated domain-fused AhR and aryl hydrocarbon receptor nuclear translocator expression constructs. At 10(-4) M of beta-naphthoflavone, which is an AhR ligand, the absorbance of optical density at 600 nm (OD 600) and beta-galactosidase activity was significantly increased. beta-galactosidase activity was increased when the concentration of 3-methylcholanthrene (MC) was increased. ATP concentration increased as concentration of MC increased up to 10(-10) M but decreased at higher concentrations. The concentration of ATP in the cell suspensions increased linearly with OD 600, used as an index of cell density (r(2) = 0.8366, F = 209.9, p < 0.0001, n = 44). The established yeast assay could possibly be used in the future to detect dioxin-like compounds in environmental samples.
 ...
PMID:Development of a recombinant yeast assay to detect ah-receptor ligands. 2002 Oct 27