Ramadoss Preeti, Petrulis John R, Hollingshead Brett D, Kusnadi Ann, Perdew Gary H
Center for Molecular Toxicology and Carcinogenesis and the Department of Veterinary Science, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
Biochemistry. 2004 Jan 27;43(3):700-9. doi: 10.1021/bi035827v.
The aryl hydrocarbon receptor (AhR) mediates the toxicologic and carcinogenic properties of 2,3,7,8-tetrachlorodibenzo-p-dioxin. In the cytoplasm, the AhR is complexed with a dimer of hsp90, and the hepatitis B virus X-associated protein 2 (XAP2). Most studies that have examined the ability of XAP2 to modulate the AhR have characterized the mouse receptor (mAhR). However, the amino acid sequence of mAhR is significantly different from human AhR (hAhR) in the carboxy terminal half of the protein, and this could lead to differences in the behavior of the two receptors. mAhR-yellow fluorescent protein (YFP) and hAhR-YFP were used to compare nucleocytoplasmic shuttling properties and the ability of XAP2 to modulate their activity. As reported previously, mAhR localized predominantly in the nucleus and was redistributed to the cytoplasm by coexpression of XAP2 in COS-1 cells. Leptomycin B treatment revealed that XAP2 blocked mAhR-YFP translocation to the nucleus in the absence of ligand. In contrast, hAhR-YFP localized predominantly in the cytoplasm, and coexpression of XAP2 did not affect this localization, and did not block nuclear accumulation in the presence of leptomycin B. An XAP2 fusion protein with a nuclear localization signal fused to the carboxy terminus (XAP2-NLS) was utilized to test whether this protein could drag the AhR into the nucleus. Coexpression of mAhR-YFP and XAP2-NLS caused cytoplasmic localization of the mAhR, while hAhR-YFP was partially localized in the nucleus, suggesting that XAP2 remains bound to the hAhR during nucleocytoplasmic shuttling. The presence of XAP2 in the ligand-bound hAhR complex enhanced the rate of nuclear translocation but repressed transcriptional activity. Together, these results suggest that the hAhR differs biochemically from the mAhR.
芳烃受体（AhR）介导2,3,7,8-四氯二苯并对二恶英的毒理学和致癌特性。在细胞质中，AhR与热休克蛋白90（hsp90）的二聚体以及乙型肝炎病毒X相关蛋白2（XAP2）形成复合物。大多数研究XAP2调节AhR能力的实验都以小鼠受体（mAhR）为研究对象。然而，mAhR的氨基酸序列在蛋白质的羧基末端一半与人类AhR（hAhR）有显著差异，这可能导致两种受体行为的差异。使用mAhR-黄色荧光蛋白（YFP）和hAhR-YFP来比较核质穿梭特性以及XAP2调节它们活性的能力。如先前报道，mAhR主要定位于细胞核，并通过在COS-1细胞中共表达XAP2而重新分布到细胞质中。雷帕霉素B处理表明，在没有配体的情况下，XAP2阻止mAhR-YFP转运到细胞核。相反，hAhR-YFP主要定位于细胞质，XAP2的共表达不影响这种定位，并且在存在雷帕霉素B的情况下不阻止核积累。利用一种在羧基末端融合了核定位信号的XAP2融合蛋白（XAP2-NLS）来测试该蛋白是否能将AhR拖入细胞核。mAhR-YFP与XAP2-NLS的共表达导致mAhR定位于细胞质，而hAhR-YFP部分定位于细胞核，这表明在核质穿梭过程中XAP2仍然与hAhR结合。配体结合的hAhR复合物中XAP2的存在提高了核转运速率，但抑制了转录活性。总之，这些结果表明hAhR在生物化学性质上与mAhR不同。
