MOLECULAR MECHANISM OF IMMUNE REGULATION BY BILE ACIDS

UDCA作为一种治疗胆固醇性胆结石的药物被广泛使用，目前用于多种肝脏疾病，包括原发性胆汁性肝硬化、原发性硬化性胆管炎、病毒性肝炎。尽管这些UDGA作用的潜在分子机制在很大程度上是未知的，但这些不同的免疫调节特性至少在一定程度上是由免疫抑制类固醇糖皮质激素共享的。我们发现UDCA在没有激动性配体的情况下激活潜伏的GR物种，并促进受体的核易位。在体外，易位的GR被证明能够结合GRE，然而，UDCA处理细胞后，糖皮质激素应答启动子的反激活非常弱。瞬时转染研究还表明，UDCA的转激活作用是由受体的配体结合域介导的。我们已经证明，在CHOpMTGR细胞中，UDCA既不会特异性结合GR，也不会干扰地塞米松与GR的特异性相互作用。因此，我们可以推测UDCA与细胞膜相互作用产生二次信号，促进hsp90和gr的解离。因此，UDCA处理可能会产生一个假定的二次信号，改变适合hsp90解离并随后转运到细胞核的配体结合域的构象。因此，识别UDCA处理后的这种假定的二次信号，不仅有助于理解UDCA作用的分子机制，也有助于理解完整细胞中GR的翻译后修饰。

UDCA, which has widely been used as a therapeutic drug for patients with cholesterol gall stones, is currently indicated for various liver diseases including primary biliary cirrhosis, primary sclerosing cholangitis, and viral hepatitis. Although underlying molecular mechanism for these UDGA action are largely unknown, these diverse immunomodulating properties are, at least in part, shared by immunosuppressive steroid glucocorticoids. We showed that UDCA activates the latent GR species in the absence of agonistic ligands, and promotes nuclear translocation of the receptor. The translocated GR is shown to be able to bind GRE in vitro, however, transactivation of the glucocorticoid-responsive promoter was very weakly induced after treatment of the cells with UDCA.Transient transfection studies also revealed that transactivational effect of UDCA was mediated by the ligand binding domain of the receptor We have shown that UDCA does not either specifically bind to GR or interfere with specific interaction between dexamethasone and GR in CHOpMTGR cells. Thus, we may speculate that UDCA interact with the cell membrane to generate secondary signal, which promotes dissociation of hsp9O and GR.Therefore, treatment with UDCA may generate a putative secondary signal, which alters the conformation of the ligand binding domain suitable for dissociation of hsp90 and subsequent translocation to the nucleus. To identify such putative secondary signal after treatment with UDCA, therefore, will facilitate understanding not only molecular mechanism(s) of UDCA action, but that for posttranslational modification of GR in intact cells as well.