Hess P, Payvar F
E. A. Doisy Department of Biochemistry and Molecular Biology, Saint Louis University School of Medicine, Missouri 63104.
J Biol Chem. 1992 Feb 15;267(5):3490-7.
Glucocorticoid regulatory elements, denoted GREs and delayed secondary GREs (sGREs), bind the purified glucocorticoid receptors via distinctive sequence motifs and confer a primary and delayed secondary hormone inducibility, respectively, upon a linked reporter construct in stably transfected mammalian cells. The delayed secondary responses, but not the primary responses, are preceded by a time lag of several hours and blocked by protein synthesis inhibitors. In this report, we further characterized and distinguished these hormonal inductions. A 206-base pair DNA fragment from the hepatic rat alpha 2u-globulin (RUG) gene, containing at least two delayed sGREs, was specifically activated by glucocorticoids in a dose-dependent manner via a process which is sensitive to receptor antagonist RU486. Delayed sGRE-stimulated production of correctly initiated transcripts was preceded by a time lag of 2 h, a time when the GRE-mediated induction had reached maximal levels. A pulse of glucocorticoids sustained maximal activation of the delayed secondary response but not the primary response. In fact, hormone withdrawal triggered a premature induction of this delayed secondary response, suggesting that delayed sGREs are under both negative and positive control of the hormone receptor. Two separable elements of the 206-base pair fragment, including the 29-base pair sequence of a single receptor binding site, activated the reporter expression as effectively with transient, pulsatile exposure to hormone as with continuous exposure. Our results suggest that the information content of a hormonal pulse is retained, or "memorized," more persistently by a receptor binding site of delayed sGREs than those of the prototypical GREs.
糖皮质激素调节元件，即糖皮质激素反应元件（GREs）和延迟性二级糖皮质激素反应元件（sGREs），通过独特的序列基序与纯化的糖皮质激素受体结合，并分别赋予稳定转染的哺乳动物细胞中连接的报告基因构建体初级和延迟性二级激素诱导性。延迟性二级反应而非初级反应之前有几个小时的时间延迟，并被蛋白质合成抑制剂阻断。在本报告中，我们进一步对这些激素诱导进行了表征和区分。来自大鼠肝脏α2u-球蛋白（RUG）基因的一个206个碱基对的DNA片段，包含至少两个延迟性sGREs，通过对受体拮抗剂RU486敏感的过程，被糖皮质激素以剂量依赖性方式特异性激活。延迟性sGRE刺激产生正确起始的转录本之前有2小时的时间延迟，此时GRE介导的诱导已达到最大水平。一次糖皮质激素脉冲维持了延迟性二级反应的最大激活，但没有维持初级反应的最大激活。事实上，激素撤离引发了这种延迟性二级反应的过早诱导，这表明延迟性sGREs受激素受体的正负调控。206个碱基对片段的两个可分离元件，包括单个受体结合位点的29个碱基对序列，在短暂、脉冲式暴露于激素时与持续暴露时一样有效地激活了报告基因的表达。我们的结果表明，与典型的GREs相比，延迟性sGREs的受体结合位点更持久地保留或“记忆”了激素脉冲的信息内容。
