Prima V, Depoix C, Masselot B, Formstecher P, Lefebvre P
INSERM U 459, Faculté de Médecine Henri Warembourg, IFR 22, Biologie et Pathologies des Régulations Cellulaires 1, place de Verdun, 59045, Lille, France.
J Steroid Biochem Mol Biol. 2000 Jan-Feb;72(1-2):1-12. doi: 10.1016/s0960-0760(99)00146-6.
The glucocorticoid receptor (GR) engages transient or stable interactions with chaperones (hsp90, hsp70), co-chaperones (p60/hop, hsp40) and several other polypeptides such as immunophilins (Cyp40, FKBP59) and p23 to achieve a high affinity ligand binding state. This complex dissociates in response to hormonal stimuli and holo-GR translocates into the nucleus, where it regulates the activity of glucocorticoid-sensitive genes. GR activity is controlled through its ligand binding domain by steroids displaying either agonistic or antagonistic activity. An alternative approach to modulate GR activity is to target receptor-associated proteins (RAPs), and several non steroidal compounds binding to RAPs affect GR transcriptional activity. We have studied the effect of such drugs on the intracellular localization of a EGFP-GR fusion protein, which has wild type GR pharmacological properties. Agonist and antagonist binding induced nuclear translocation of GR, whereas rifampicin was found to be inactive in our system. Immunosuppressants FK506 and cyclosporin A were able to induce partial nuclear translocation of GR, suggesting that potentiation of glucocorticoid action by these compounds may also proceed through enhanced GR nuclear transfer. Short treatment of cells with the hsp90 inhibitor geldanamycin (GA) did not prevent nuclear translocation of GR. However, longer treatments, in parrallel to the inhibition of GR transcriptional activity, strongly perturbed GR subcellular localization concomitantly to the disruption of the actin network, and caused GR aggregation and down-regulation. The GA-induced transcriptional shutdown was also observed for other nuclear receptors which do not interact stably with hsp90. Thus RAP-binding compounds may exert their effects at least in part through perturbation of the GR cytosol to nucleus partitioning, and identify these proteins as valuable therapeutic targets to control nuclear receptor activity.
糖皮质激素受体（GR）与伴侣蛋白（热休克蛋白90、热休克蛋白70）、共伴侣蛋白（p60/hop、热休克蛋白40）以及其他几种多肽如亲免素（环孢菌素40、FKBP59）和p23发生短暂或稳定的相互作用，以达到高亲和力配体结合状态。这种复合物会因激素刺激而解离，全激素GR易位进入细胞核，在细胞核中调节糖皮质激素敏感基因的活性。GR的活性通过其配体结合结构域由具有激动或拮抗活性的类固醇控制。调节GR活性的另一种方法是靶向受体相关蛋白（RAP），几种与RAP结合的值非甾体化合物会影响GR的转录活性。我们研究了此类药物对具有野生型GR药理学特性的EGFP-GR融合蛋白细胞内定位的影响。激动剂和拮抗剂结合诱导GR的核转位，而利福平在我们的系统中无活性。免疫抑制剂FK-506和环孢素A能够诱导GR的部分核转位，表明这些化合物对糖皮质激素作用的增强也可能通过增强GR的核转运来实现。用热休克蛋白90抑制剂格尔德霉素（GA）对细胞进行短时间处理并不能阻止GR核转位。然而，较长时间的处理，在抑制GR转录活性的同时，会强烈扰乱GR的亚细胞定位，同时破坏肌动蛋白网络，并导致GR聚集和下调。对于其他不与热休克蛋白90稳定相互作用的核受体，也观察到了GA诱导的转录关闭。因此，与RAP结合的化合物可能至少部分通过扰乱GR在细胞质与细胞核之间的分配发挥作用，并将这些蛋白确定为控制核受体活性的有价值的治疗靶点。
