Sheppard K E
Baker Medical Research Institute, Prahan, Victoria, Australia.
J Neuroendocrinol. 1995 Nov;7(11):833-40. doi: 10.1111/j.1365-2826.1995.tb00723.x.
Unliganded glucocorticoid receptors (GR) are localized in the cytoplasm and are associated with heat shock protein (hsp)90, hsp70, and a member of the immunophilin family, FK506 binding protein 59 (FKBP59). Several members of the cyclophilin and FKBP families have now been shown to associate with unactivated steroid receptors, however the physiological role these immunophilins play in steroid receptor function is questionable. In the present study we have measured GR binding and nuclear translocation of activated receptor in corticotrope cells following treatment with the immunophilin ligands FK506 and cyclospcrin A (CsA). Extensive GR binding studies in AtT20 cells, a mouse corticotrope tumor cell line failed to demonstrate an effect of FK506 or CsA on either the ability of GR to bind ligand, or on nuclear translocation of the liganded receptor at either a saturating or subsaturating dose of dexamethasone (DEX). Consistent with the binding data, functionally, neither CsA nor FK506 altered the glucocorticoid induced decrease in either proopiomelanocortin (POMC) derived peptide secretion or POMC heteronuclear (hn) RNA expression. Despite the fact these drugs did not modulate the actions of glucocorticoids on corticotrope cells, both FK506 and CsA were potent stimulators of basal beta-endorphin secretion (4-6 fold) from rat anterior pituitary cultures and AtT20 cells. In addition, FK506 and CsA potentiated beta-endorphin secretion induced by corticotropin releasing factor (CRF) and phorbol ester, but had no apparent acute (60 min) effect on POMC hnRNA levels. Unlike the acute actions of these immunosuppressant drugs, chronic (24 h) treatment lead to a decrease in cytoplasmic POMC mRNA with no apparent change in the amount of secreted beta-endorphin. Taken together these data suggest that FK506 and CsA do not alter GR activation or function in corticotrope cells, however, they are potent but short lived stimulators of POMC-derived peptide secretion. The observation that CsA and FK506 stimulate POMC-derived peptide secretion, and potentiate both phorbol ester and CRF induced secretion, suggests that these immunosuppressant drugs are acting upon a common point within these intracellular pathways.
未结合配体的糖皮质激素受体（GR）定位于细胞质中，并与热休克蛋白（hsp）90、hsp70以及免疫亲和素家族的一个成员FK506结合蛋白59（FKBP59）相关联。亲环蛋白和FKBP家族的几个成员现已被证明与未活化的类固醇受体相关联，然而这些免疫亲和素在类固醇受体功能中所起的生理作用值得怀疑。在本研究中，我们在用免疫亲和素配体FK506和环孢菌素A（CsA）处理后，测量了促肾上腺皮质激素细胞中GR的结合以及活化受体的核转位。在小鼠促肾上腺皮质激素肿瘤细胞系AtT20细胞中进行的广泛GR结合研究未能证明FK506或CsA对GR结合配体的能力或在饱和或亚饱和剂量的地塞米松（DEX）下配体化受体的核转位有影响。与结合数据一致，在功能上，CsA和FK506均未改变糖皮质激素诱导的源自阿片促黑激素皮质素原（POMC）的肽分泌或POMC异核（hn）RNA表达的降低。尽管这些药物并未调节糖皮质激素对促肾上腺皮质激素细胞的作用，但FK506和CsA都是大鼠垂体前叶培养物和AtT20细胞基础β-内啡肽分泌的有效刺激剂（4 - 6倍）。此外，FK506和CsA增强了促肾上腺皮质激素释放因子（CRF）和佛波酯诱导的β-内啡肽分泌，但对POMC hnRNA水平没有明显的急性（60分钟）影响。与这些免疫抑制药物的急性作用不同，慢性（24小时）处理导致细胞质POMC mRNA减少，而分泌的β-内啡肽量没有明显变化。综上所述，这些数据表明FK506和CsA不会改变促肾上腺皮质激素细胞中GR的激活或功能，然而，它们是POMC衍生肽分泌的有效但短暂的刺激剂。CsA和FK506刺激POMC衍生肽分泌，并增强佛波酯和CRF诱导的分泌这一观察结果表明，这些免疫抑制药物作用于这些细胞内途径中的一个共同点。
