Activation of steroid hormone–receptor complexes in intact target cells in physiological conditions
Activation of steroid hormone–receptor complexes in intact target cells in physiological conditions
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生理条件下完整靶细胞中类固醇激素受体复合物的激活
作者：
A. Munck;R. Foley
在生理温度下，糖皮质激素1 -5与其他类固醇激素6一样，最初与正常靶细胞（如大鼠胸腺细胞）相互作用，形成糖皮质激素-受体复合物，这些复合物似乎首先位于细胞质中，然后迅速与细胞核结合。在低温（0-4 °C）下，激素与靶细胞或来自这些细胞的胞质溶胶一起孵育时，形成不与细胞核结合的“非活化”复合物;随后细胞1 -5或胞质溶胶与细胞核一起加热2，7-11，导致形成核结合复合物。如最初用雌激素12和后来用糖皮质激素2，7- 10，13所示，如果在0-4 °C下形成的具有非活化复合物的细胞质在不存在核的情况下被加热到20-37 °C，则复合物变得“活化”，并且然后即使在低温下也将结合到核。活化也可以通过增加离子强度7 - 9，13、凝胶过滤、稀释和其他处理14来实现，已被广泛研究，并且已知除了对核的亲和力增强之外还伴随着几种变化。对于糖皮质激素-受体复合物，变化包括对DNA的亲和力增强7，10，13-15和在磷酸纤维素16，DEAE-Sephadex 17和DEAE-cellulose 18柱上的迁移率改变。这最后一个性质是我们在实验中使用的。尽管有许多关于活化的已发表研究，但仅在正常体温下暴露于类固醇的细胞或胞质溶胶中未活化复合物的形成和随后的活化显然从未得到证实。因此，不知道非活化复合物和活化在生理条件下是否具有任何显著作用，并且至少一种众所周知的类固醇激素作用方案19不包括活化步骤。因此，当类固醇激素在生理温度下与细胞质受体结合时，它们可能立即形成活化的复合物。这里描述的结果表明，对于糖皮质激素，可以排除这种替代方案：当这些类固醇在37 °C下与大鼠胸腺细胞中的受体相互作用时，它们最初形成非活化复合物，随后产生活化复合物。
AT physiological temperatures glucocorticoids1–5, in common with other steroid hormones6, initially interact with normal target cells such as the rat thymocyte by forming hormone–receptor complexes that seem first to be located in the cytoplasm and then rapidly become bound to the nucleus. At low temperatures (0–4 °C) the hormones, when incubated either with target cells or with cytosols from such cells, form ‘non-activated’ complexes that do not bind to nuclei; subsequent warming of the cells1–5, or of the cytosols together with nuclei2,7–11, leads to the formation of nuclear-bound complexes. As shown originally with oestrogens12 and later with glucocorticoids2,7–10,13, if cytosols with non-activated complexes formed at 0–4 °C are warmed to 20–37 °C in the absence of nuclei, the complexes become ‘activated’, and will then bind to nuclei even at low temperatures. Activation, which can also be brought about by increased ionic strength7–9,13, gel filtration, dilution and other treatments14, has been studied extensively and is known to be accompanied by several changes other than enhanced affinity for nuclei. For glucocorticoid–receptor complexes the changes include enhanced affinity for DNA7,10,13–15 and altered mobility on phosphocellulose16, DEAE-Sephadex17 and DEAE-cellulose18 columns. This last property is the one we have used in our experiments. Despite the many published studies on activation, formation of non-activated complexes and subsequent activation have apparently never been demonstrated in cells or cytosols exposed to steroids at normal body temperatures only. Consequently, it is not known whether non-activated complexes and activation have any significant role in physiological conditions, and at least one well known scheme of steroid hormone action19 does not include the activation step. It is therefore possible that when steroid hormones bind to cytoplasmic receptors at physiological temperatures they immediately form activated complexes. The results described here show that for glucocorticoids this alternative can be excluded: when these steroids interact with receptors in rat thymus cells at 37 °C they initially form non-activated complexes, and subsequently give rise to activated complexes.