Carver L A, LaPres J J, Jain S, Dunham E E, Bradfield C A
McArdle Laboratory for Cancer Research, University of Wisconsin Medical School, Madison, Wisconsin 53706, USA.
J Biol Chem. 1998 Dec 11;273(50):33580-7. doi: 10.1074/jbc.273.50.33580.
The unliganded aryl hydrocarbon receptor (AHR) is found in a complex with other proteins including the 90-kDa heat shock protein (Hsp90) and a 37-kDa protein we refer to as ARA9. We found that the three tetratricopeptide repeats found in the COOH terminus of ARA9 are necessary and sufficient for interaction with the AHR complex. Conversely, the AHR's "repressor"/Hsp90 binding domain is required for interaction with ARA9. Because ARA9 closely resembles the 52-kDa FK506-binding protein (FKBP52), found in the unliganded glucocorticoid receptor (GR) complex, we compared the binding specificities of ARA9 and FKBP52 for AHR and GR. In co-immunoprecipitation experiments, ARA9 specifically associated with AHR-Hsp90 complex but not with GR-Hsp90 complexes. In addition, ARA9 showed a greater capacity than FKBP52 to associate with AHR-Hsp90 complexes. The biological importance of this interaction was suggested by the observation that in a yeast expression system ARA9 expression enhanced the response of AHR to the agonist beta-napthoflavone, decreasing the EC50 by greater than 5-fold and increasing the maximal response 2.5-fold. In contrast, co-expression of FKBP52 had no effect on AHR signaling. In addition, although ARA9 contains a domain similar to that found in other FK506-binding proteins, ARA9 binding to 3H-FK506 could not be detected. Finally, we have characterized the developmental and expression pattern of ARA9 in the developing mouse embryo and mapped the ARA9 locus to human chromosome 11q13.3.
未结合配体的芳烃受体（AHR）与包括90 kDa热休克蛋白（Hsp90）和一种我们称为ARA9的37 kDa蛋白在内的其他蛋白质形成复合物。我们发现，ARA9羧基末端的三个四肽重复序列对于与AHR复合物的相互作用是必需且充分的。相反，AHR的“阻遏物”/Hsp90结合结构域是与ARA9相互作用所必需的。由于ARA9与未结合配体的糖皮质激素受体（GR）复合物中发现的52 kDa FK506结合蛋白（FKBP52）非常相似，我们比较了ARA9和FKBP52对AHR和GR的结合特异性。在共免疫沉淀实验中，ARA9特异性地与AHR - Hsp90复合物结合，而不与GR - Hsp90复合物结合。此外，ARA9与AHR - Hsp90复合物结合的能力比FKBP52更强。在酵母表达系统中观察到ARA9表达增强了AHR对激动剂β - 萘黄酮的反应，使半数有效浓度（EC50）降低超过5倍，最大反应增加2.5倍，这表明了这种相互作用的生物学重要性。相比之下，FKBP52的共表达对AHR信号传导没有影响。此外，尽管ARA9含有一个与其他FK506结合蛋白中发现的结构域相似的结构域，但未检测到ARA9与3H - FK506的结合。最后，我们已经确定了ARA9在发育中的小鼠胚胎中的发育和表达模式，并将ARA9基因座定位到人类染色体11q13.3。
