Dexras1/AGS-1, a steroid hormone-induced guanosine triphosphate-binding protein, inhibits 3′,5′-cyclic adenosine monophosphate-stimulated secretion in AtT-20 corticotroph cells
Dexras1/AGS-1, a steroid hormone-induced guanosine triphosphate-binding protein, inhibits 3′,5′-cyclic adenosine monophosphate-stimulated secretion in AtT-20 corticotroph cells
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DOI：
10.1210/en.142.6.2631
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发表时间：
2001-06-01
期刊：
影响因子：
4.8
通讯作者：
Dorin, RI
中科院分区：
文献类型：
--
作者：
Graham, TE;Key, TA;Dorin, RI
Dexras1 是一种新型 GTP 结合蛋白，与小分子量 GTP 酶 Ras 家族具有结构相似性，并且在地塞米松治疗过程中被强烈而快速地诱导。 Dexras1 的功能及其对促肾上腺皮质激素细胞中糖皮质激素依赖性信号传导的贡献尚不清楚。本研究旨在检验 Dexras1 在 AtT-20 促肾上腺皮质激素细胞系中肽激素分泌调节中的潜在作用。为了确定独立于糖皮质激素治疗而表达的 Dexras1 的影响，将野生型和组成型活性突变体 Dexras1 蛋白的表达质粒与人 GH (hGH) 共转染，这为刺激耦合分泌途径提供了异位标记。在瞬时转染的 AtT-20 和 COS-7 细胞中检查了野生型和突变型 Dexras1 蛋白的 GTP 结合特性以及 GTP 与 GDP 的比率。与 5 mM 8-Br-cAMP 或对照孵育 2 小时后，评估分泌的刺激成分和组成成分。相对于对照，cAMP 处理导致 hGH 分泌增加一倍。野生型 Dexras1 的共转染对 cAMP 刺激的 hGH 分泌没有影响，但组成型活性突变体 Dexras[A178V] 将刺激的分泌减弱 86%（P < 0.01）。含有羧基末端异戊二烯化位点缺失的双突变体 Dexras [A178V/C277term] 不会抑制 cAMP 刺激的 hGH 分泌，表明该效应是异戊二烯化依赖性的。这些发现表明，Dexras1 的激活具有重要的功能后果，导致抑制促肾上腺皮质细胞中的刺激-分泌耦合。由于Dexrasl信使RNA在糖皮质激素治疗期间被强烈且快速地诱导，因此这些结果提出了Dexrasl可能参与控制糖皮质激素对促肾上腺皮质激素细胞中肽激素分泌的快速调节作用的信号转导途径的可能性。
Dexras1 is a novel GTP-binding protein that shares structural similarity with the Ras family of small molecular weight GTPases and is strongly and rapidly induced during treatment with dexamethasone. The function of Dexras1 and its contribution to glucocorticoid-dependent signaling in the corticotroph cell are unknown. The present study was undertaken to examine the potential role of Dexras1 in the regulation of peptide hormone secretion in the AtT-20 corticotroph cell line. To determine the effects of Dexras1 expressed independently of glucocorticoid treatment, expression plasmids for wild-type and constitutively active mutant Dexrasl proteins were cotransfected with human GH (hGH), which provides an ectopic marker for the stimulus-coupled secretory pathway. GTP binding properties and the GTP to GDP ratio of wild-type and mutant Dexrasl proteins were examined in transiently transfected AtT-20 and COS-7 cells. Stimulated and constitutive components of secretion were assessed after 2-h incubations with 5 mM 8-Br-cAMP or control. cAMP treatment led to a a-fold increase in hGH secretion relative to control. Cotransfection of wild-type Dexrasl had no effect on cAMP-stimulated hGH secretion, but a constitutively active mutant, Dexras[A178V], attenuated stimulated secretion by 86% (P < 0.01). A double-mutant containing a deletion of the carboxyl terminus isoprenylation site, Dexras [A178V/C277term], did not inhibit cAMP-stimulated hGH secretion, indicating that the effect is prenylation dependent. These findings suggest that activation of Dexras1 has important functional consequences leading to inhibition of stimulus-secretion coupling in corticotroph cells. Because Dexrasl messenger RNA is strongly and rapidly induced during glucocorticoid treatment, these results raise the possibility that Dexrasl may participate in the signal transduction pathways that govern the rapid regulatory effects of glucocorticoids on peptide hormone secretion in corticotroph cells.