Caenorhabditis elegansorthologs of the aryl hydrocarbon receptor and its heterodimerization partner the aryl hydrocarbon receptor nuclear translocator

Abstract

The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor, until now described only in vertebrates, that mediates many of the carcinogenic and teratogenic effects of certain environmental pollutants. Here, we describe orthologs of AHR and its dimerization partner AHR nuclear translocator (ARNT) in the nematode Caenorhabditis elegans, encoded by the genes ahr-1 and aha-1, respectively. The corresponding proteins, AHR-1 and AHA-1, share biochemical properties with their mammalian cognates. Specifically, AHR-1 forms a tight association with HSP90, and AHR-1 and AHA-1 interact to bind DNA fragments containing the mammalian xenobiotic response element with sequence specificity. Yeast expression studies indicate that C. elegans AHR-1, like vertebrate AHR, requires some form of posttranslational activation. Moreover, this requirement depends on the presence of the domains predicted to mediate binding of HSP90 and ligand. Preliminary experiments suggest that if AHR-1 is ligand-activated, its spectrum of ligands is different from that of the mammalian receptor: C. elegans AHR-1 is not photoaffinity labeled by a dioxin analog, and it is not activated by ␤-naphthof lavone in the yeast system. The discovery of these genes in a simple, genetically tractable invertebrate should allow elucidation of AHR-1 function and identification of its endogenous regulators.

The Caenorhabditis elegans hif-1 gene encodes a bHLH-PAS protein that is required for adaptation to hypoxia

“…This hypothesis predicted that (i) hif-1 mutants would be deficient in hypoxia response; (ii) the hif-1 gene product would interact with aha-1, the C. elegans ortholog of mammalian ARNT (19); (iii) HIF-1 protein would be more highly expressed in hypoxic conditions; and (iv) both aha-1 and hif-1 would be expressed in most, if not all, cells.…”

“…The mammalian hypoxia-inducible factors consist of two protein subunits: HIF-1␣ (or the related HIF-2␣ or HIF-3␣) and ARNT (or ARNT2 or ARNT3) (2). To determine whether C. elegans HIF-1 forms a similar complex, we assayed its ability to bind AHA-1, the ortholog of mammalian ARNT (19). We expressed both gene products in rabbit reticulocyte lysates and immunoprecipitated the proteins with an antibody that specifically recognizes AHA-1.…”

“…HIF-1 and AHA-1 were expressed in rabbit reticulocyte lysates (Promega TNT system) by using expression constructs pR33 and pJ343 (19). Radiolabeled methionine was included in the translation reaction, and the products were assayed by SDS͞PAGE.…”

When evolution is the solution to pollution: Key principles, and lessons from rapid repeated adaptation of killifish (Fundulus heteroclitus) populations

“…Differences in AHR properties, including affinity for ligand binding, explain differences in sensitivity to DLCs in several vertebrate systems, including strains of rodents (Moffat, Roblin, Harper, Okey, & Pohjanvirta, 2007; Poland, Palen, & Glover, 1994), species of birds (Farmahin et al., 2013; Karchner, Franks, Kennedy, & Hahn, 2006), and populations of some fish (Atlantic tomcod) (Wirgin et al., 2011). (At the extreme end of this spectrum are invertebrates, which have AHR proteins that lack the ability to bind DLCs [Powell‐Coffman, Bradfield, & Wood, 1998; Butler, Kelley, Powell, Hahn, & Van Beneden, 2001] and also are largely insensitive to DLC toxicity [Hahn, 1998a]. ) Ligand affinity is not the only factor that controls sensitivity, however.…”

Hypoxia-induced Synthesis of Hemoglobin in the Crustacean Daphnia magna Is Hypoxia-inducible Factor-dependent

“…HIF proteins are members of the family of basic helix-loop-helix/PAS (Per/ARNT/Sim) transcription factors (31)(32)(33). The functional complex consists of a heterodimer of ␣-and ␤-subunits in mammals (34,35), Caenorhabditis elegans (36,37), and Drosophila (38 -41). This heterodimer is present only at low pO 2 when it activates expression of target genes through specific binding to short cis-regulatory E-box motifs called hypoxia response elements (HREs) in the promoter and/or enhancer regions of these genes.…”