Department of Biochemistry, Stellenbosch University, Stellenbosch, South Africa.
Sci Rep. 2018 Sep 24;8(1):14266. doi: 10.1038/s41598-018-32440-z.
Glucocorticoids (GCs), acting via the glucocorticoid receptor (GRα), remain the mainstay therapeutic choice for the treatment of inflammation. However, chronic GC use, aside from generating undesirable side-effects, results in GRα down-regulation, often coupled to a decrease in GC-responsiveness, which may culminate in acquired GC resistance. The current study presents evidence for a novel role of the dimerization state of the GRα in mediating GC-mediated GRα turnover. Through comparing the effects of dimerization promoting GCs on down-regulation of a transfected human wild type GRα (hGRwt) or a dimerization deficient GRα mutant (hGRdim), we established that a loss of receptor dimerization restricts GRα turnover, which was supported by the use of the dimerization abrogating Compound A (CpdA), in cells containing endogenous GRα. Moreover, we showed that the dimerization state of the GRα influenced the post-translational processing of the receptor, specifically hyper-phosphorylation at Ser404, which influenced the interaction of GRα with the E3 ligase, FBXW7α, thus hampering receptor turnover via the proteasome. Lastly, the restorative effects of CpdA on the GRα pool, in the presence of Dex, were demonstrated in a combinatorial treatment protocol. These results expand our understanding of factors that contribute to GC-resistance and may be exploited clinically.
糖皮质激素（GCs）通过糖皮质激素受体（GRα）发挥作用，仍然是治疗炎症的主要治疗选择。然而，除了产生不良副作用外，慢性 GC 使用还会导致 GRα下调，通常伴随着 GC 反应性降低，这可能导致获得性 GC 抵抗。本研究提出了 GRα二聚化状态在介导 GC 介导的 GRα周转中的新作用的证据。通过比较促进二聚化的 GC 对转染的人野生型 GRα（hGRwt）或二聚化缺陷的 GRα突变体（hGRdim）的下调作用，我们确定了受体二聚化的丧失限制了 GRα周转，这得到了使用二聚化消除化合物 A（CpdA）在含有内源性 GRα的细胞中的支持。此外，我们表明 GRα的二聚化状态影响受体的翻译后处理，特别是 Ser404 的过度磷酸化，这影响了 GRα与 E3 连接酶 FBXW7α 的相互作用，从而通过蛋白酶体阻碍受体周转。最后，在 Dex 存在的情况下，CpdA 在组合治疗方案中对 GRα库的恢复作用得到了证明。这些结果扩展了我们对导致 GC 抵抗的因素的理解，并可能在临床上得到利用。
