Vitamin D receptor (VDR) mediates the biological function of the steroid hormone calcitriol, which is the metabolically active version of vitamin D. Calcitriol is important for a wide array of physiological functions, including calcium and phosphate homeostasis. In contrast to mammals, which harbor one VDR encoding gene, teleosts possess two orthologous vdr genes encoding Vdr alpha (Vdra) and Vdr beta (Vdrb). Genome mining identified the vdra and vdrb paralogs in the Atlantic cod (Gadus morhua) genome, which were further characterized regarding their phylogeny, tissue-specific expression, and transactivational properties induced by calcitriol. In addition, a selected set of polycyclic aromatic hydrocarbons (PAHs), including naphthalene, phenanthrene, fluorene, pyrene, chrysene, benzo[a]pyrene (BaP), and 7-methylbenzo[a]pyrene, were assessed for their ability to modulate the transcriptional activity of gmVdra and gmVdrb in vitro. Both gmVdra and gmVdrb were activated by calcitriol with similar potencies, but gmVdra produced significantly higher maximal fold activation. Notably, none of the tested PAHs showed agonistic properties towards the Atlantic cod Vdrs. However, binary exposures of calcitriol together with phenanthrene, fluorene, or pyrene, antagonized the activation of gmVdra, while chrysene and BaP significantly potentiated the calcitriol-mediated activity of both receptors. Homology modeling, solvent mapping, and docking analyses complemented the experimental data, and revealed a putative secondary binding site in addition to the canonical ligand-binding pocket (LBP). Calcitriol was predicted to interact with both binding sites, whereas PAHs docked primarily to the LBP. Importantly, our in vitro data suggest that PAHs can interact with the paralogous gmVdrs and interfere with their transcriptional activities, and thus potentially modulate the vitamin D signaling pathway and contribute to adverse effects of crude oil and PAH exposures on cardiac development and bone deformities in fish.

维生素 D 受体 (VDR) 介导类固醇激素骨化三醇的生物功能，骨化三醇是维生素 D 的代谢活性版本。骨化三醇对于多种生理功能都很重要，包括钙和磷酸盐稳态。与含有一个 VDR 编码基因的哺乳动物相反，硬骨鱼拥有两个编码 Vdr α (Vdra) 和 Vdr β (Vdrb) 的直系同源vdr基因。基因组挖掘鉴定了大西洋鳕鱼 ( Gadus morhua ) 基因组中的vdra和vdrb旁系同源物，并进一步对其系统发育、组织特异性表达和骨化三醇诱导的反式激活特性进行了表征。此外，还评估了一组选定的多环芳烃 (PAH) 的调节能力，包括萘、菲、芴、芘、屈、苯并[a]芘 (BaP) 和 7-甲基苯并[a]芘gmVdra和gmVdrb的体外转录活性。 gmVdra 和 gmVdrb 均被骨化三醇激活，具有相似的效力，但 gmVdra 产生显着更高的最大激活倍数。值得注意的是，所测试的多环芳烃均未表现出对大西洋鳕鱼 Vdrs 的拮抗特性。然而，骨化三醇与菲、芴或芘的二元暴露会拮抗 gmVdra 的激活，而 chrysene 和 BaP 显着增强骨化三醇介导的两种受体的活性。同源建模、溶剂图谱和对接分析补充了实验数据，并揭示了除了典型的配体结合口袋（LBP）之外的假定的第二结合位点。预计骨化三醇会与两个结合位点相互作用，而 PAH 主要与 LBP 对接。 重要的是，我们的体外数据表明，PAH 可以与旁系同源 gmVdrs 相互作用并干扰其转录活性，从而可能调节维生素 D 信号通路，并导致原油和 PAH 暴露对鱼类心脏发育和骨骼畸形的不利影响。