The aryl hydrocarbon receptor (AHR) is a ligand-inducible transcription factor that is best known because it mediates the actions of polycyclic and halogenated aromatic hydrocarbon environmental toxicants such as 3-methylcholanthrene and 2,3,7,8-tetrachlorodibenzo-p-dioxin. We report here the successful identification of an endogenous ligand for this receptor; Ϸ20 g was isolated in pure form from 35 kg of porcine lung. Its structure was deduced as 2-(1H-indole-3-carbonyl)-thiazole-4-carboxylic acid methyl ester from extensive physical measurements and quantum mechanical calculations. In a reporter gene assay, this ligand activates the AHR with a potency five times greater than that of ␤-naphthoflavone, a prototypical synthetic AHR ligand. 2-(1H-indole-3-carbonyl)-thiazole-4-carboxylic acid methyl ester competes with 2,3,7,8-[ 3 H]tetrachlorodibenzo-p-dioxin for binding to human, murine, and fish AHRs, thus showing that AHR activation is caused by direct receptor binding, and that recognition of this endogenous ligand is conserved from early vertebrates (fish) to humans.

The aryl hydrocarbon receptor (AhR), a ligand-activated transcription factor mediates many biological processes. Herein, we investigated if 2-(1′H-indole-3′-carbonyl)-thiazole-4-carboxylic acid methyl ester (ITE, an endogenous AhR ligand) regulated proliferation and migration of human ovarian cancer cells via AhR. We found that AhR was widely present in many histotypes of ovarian cancer tissues. ITE suppressed OVCAR-3 cell proliferation and SKOV-3 cell migration in vitro, which were blocked by AhR knockdown. ITE also suppressed OVCAR-3 cell growth in mice. These data suggest that the ITE might potentially be used for therapeutic intervention for at least a subset of human ovarian cancer.

The dihydrolipoyl acetyltransferase (E2) component of mammalian pyruvate dehydrogenase complex (PDC) consists of 60 COOH-terminal domains as an inner assemblage and sequentially via linker regions an exterior pyruvate dehydrogenase (E1) binding domain and two lipoyl domains. Mature human E2, expressed in a protease-deficient Escherichia coli strain at 27°, was prepared in a highly purified form. Purified E2 had a high acetyltransferase activity, was well lipoylated based on its acetylation, and bound a large complement of bovine E1. Electron micrographs demonstrated that the inner core was assembled in the expected pentagonal dodecahedron shape with E1 binding around the inner core periphery.With saturating E1 and excess dihydrolipoyl dehydrogenase (E3) but no E3-binding protein (E3BP), the recombinant E2 supported the overall PDC reaction at 4% of the rate of bovine E2⅐E3BP subcomplex. The lipoates of assembled human E2 or its free bilipoyl domain region were reduced by E3 at rates proportional to the lipoyl domain concentration, but those of the E2⅐E3BP were rapidly used in a concentration-independent manner consistent with bound E3 rapidly using a set of lipoyl domains localized nearby. Given this restriction and the need for E3BP for high PDC activity, directed channeling of reducing equivalents to bound E3 must be very efficient in the complex.The recombinant E2 oligomer increased E1 kinase activity by up to 4-fold and, in a Ca 2؉ -dependent process, increased phospho-E1 phosphatase activity more than 15-fold. Thus the E2 assemblage fully provides the molecular intervention whereby a single E2-bound kinase or phosphatase molecule rapidly phosphorylate or dephosphorylate, respectively, many E2-bound E1. Thus, we prepared properly assembled, fully functional human E2 that mediated enhanced regulatory enzyme activities but, lacking E3BP, supported low PDC activity.Pyruvate dehydrogenase complexes from various sources are among the largest enzyme systems that serve strategic roles in metabolism (1, 2). The mammalian complex has a highly organized structure in which the dihydrolipoyl transacetylase (E2) 1 component has a central role in the organization and integrated chemical reactions of the complex, and supports enhanced functioning of dedicated kinase and phosphatase components (3-8). The other components of the mammalian complex required for the overall reaction are: the pyruvate dehydrogenase (E1) component, an ␣ 2 ␤ 2 tetramer present at 20 -30 copies (1); the dihydrolipoyl dehydrogenase (E3), a homodimer present in about 6 copies (9); and the E3-binding protein (E3BP) estimated at 6 -12 copies (10, 11). Dedicated and highly regulated kinase and phosphatase components control the conversion of E1 between an active (nonphosphorylated) form, E1a, and an inactive (phosphorylated) form, E1b.Mammalian PDC-E2 subunits have four flexibly connected domains and form the core of the complex in which 60 of its COOH-terminal inner (I) domains assemble into a dodecahedron-shaped structure with its other three domains ...

Mitochondria derived from Triticum timopheevi have a chimeric gene, orf256, immediately upstream from coxI. Antibodies to a peptide corresponding to a part of the encoded amino acid sequence of orf256 detect a 7 kDa protein on western blots of mitochondrial proteins from cytoplasmic male-sterile (cms) wheat (T. aestivum nucleus, T. timopheevi mitochondria) but not in mitochondrial proteins from T. aestivum, T. timopheevi, or cms plants restored to fertility by introduction of nuclear genes for fertility restoration. The 7 kDa protein appears to serve as a marker for cms wheat. Its occurrence as an integral protein of the inner membrane may indicate a cms effect through an influence on mitochondrial membrane function.