Kino Tomoshige, Souvatzoglou Emanuel, Charmandari Evangelia, Ichijo Takamasa, Driggers Paul, Mayers Chantal, Alatsatianos Anton, Manoli Irini, Westphal Heiner, Chrousos George P, Segars James H
Pediatric Endocrinology Section, Reproductive Biology and Medicine Branch, NICHD, National Institutes of Health, Bethesda Maryland 20892, USA.
J Biol Chem. 2006 Apr 7;281(14):9118-26. doi: 10.1074/jbc.M509339200. Epub 2006 Feb 8.
Glucocorticoids regulate many crucial biologic functions through their cytoplasmic/nuclear glucocorticoid receptors (GR). Excess, deficiency, or alteration in tissue sensitivity to glucocorticoids has been associated with major causes of human morbidity and mortality. Brx, a cytoplasmic Rho family guanine nucleotide exchange factor, binds to and influences the activity of several nuclear hormone receptors. We examined the functional and molecular interactions between GR and Brx. The glucocorticoid sensitivity of lymphocytes obtained from mice haplo-insufficient for Brx was significantly decreased. Conversely, GR-mediated transcriptional activity of a glucocorticoid response element (GRE)-mediated glucocorticoid-responsive promoter was enhanced by Brx in a guanine nucleotide exchange factor domain-dependent fashion. Brx interacted with GR, forming a ternary complex with RhoA. In a chromatin immunoprecipitation assay, Brx and RhoA were co-precipitated with GREs only in the presence of ligand-activated GR. Extracellularly administered lysophosphatidic acid, which activates its signaling cascade through a specific membrane GTP-binding protein (G-protein)-coupled receptor in a G-protein alpha(13)-, Brx-, and RhoA-dependent fashion, enhanced GR transcriptional activity, whereas depletion of endogenous Brx attenuated this effect. These findings suggest that glucocorticoid signaling and, hence, the tissue sensitivity to glucocorticoids, may be coupled to extracellular signals via Brx and small G-proteins. Nuclear Brx might act as a local GRE-GR-transcriptosome activator by mediating the effect of small G-proteins on glucocorticoid-regulated genes.
糖皮质激素通过其细胞质/细胞核糖皮质激素受体（GR）调节许多关键的生物学功能。糖皮质激素过量、缺乏或组织对其敏感性改变与人类发病和死亡的主要原因相关。Brx是一种细胞质Rho家族鸟嘌呤核苷酸交换因子，可与几种核激素受体结合并影响其活性。我们研究了GR与Brx之间的功能和分子相互作用。从Brx单倍体不足的小鼠获得的淋巴细胞对糖皮质激素的敏感性显著降低。相反，Brx以鸟嘌呤核苷酸交换因子结构域依赖性方式增强了糖皮质激素反应元件（GRE）介导的糖皮质激素反应性启动子的GR介导的转录活性。Brx与GR相互作用，与RhoA形成三元复合物。在染色质免疫沉淀试验中，仅在配体激活的GR存在下，Brx和RhoA与GREs共沉淀。细胞外施用溶血磷脂酸，其通过特定的膜鸟苷三磷酸结合蛋白（G蛋白）偶联受体以G蛋白α(13)-、Brx-和RhoA依赖性方式激活其信号级联反应，增强了GR转录活性，而内源性Brx的缺失减弱了这种效应。这些发现表明，糖皮质激素信号传导以及因此组织对糖皮质激素的敏感性可能通过Brx和小G蛋白与细胞外信号偶联。核Brx可能通过介导小G蛋白对糖皮质激素调节基因的作用而作为局部GRE-GR转录体激活剂。
