Characterization of cysteamine induction of the 22K prolactin variant in the rat pituitary.
Characterization of cysteamine induction of the 22K prolactin variant in the rat pituitary.
复制标题
大鼠垂体中 22K 催乳素变体半胱胺诱导的表征。
DOI：
10.1159/000126357
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发表时间：
1993
影响因子：
4.1
通讯作者：
Powers,CA
中科院分区：
文献类型：
--
作者：
Anthony,PK;Powers,CA
腺激肽释放酶(GK)是一种雌激素诱导和多巴胺抑制的催乳素蛋白水解酶，被认为在催乳素(PRL)向新的激素形式的转化过程中发挥作用。最近的研究表明，在硫醇的存在下，GK在体外可以将PRL从25K形式转化为22K形式--硫醇似乎可以将PRL转化为GK底物的构象(折叠状态)。我们和其他人已经报道了大鼠脑垂体中22K催乳素的变异，半胱胺(CSH)的注射可以增加这种变异，半胱胺是一种生物硫醇，已知在体外和体内都能改变催乳素的构象。本研究进一步表征了22K PRL变异的CSH诱导。用雌激素刺激的大鼠进行CSH的剂量-反应和时间-过程研究。通过蛋白质印迹分析研究CSH对22K催乳素水平的影响。对未还原的样品(硫醇和二硫化物用碘乙酰胺捕获)进行Western印迹分析，研究PRL构象的变化。CSH以剂量依赖的方式增加22K PRL，与PRL构象变化的剂量-反应曲线呈良好的相关性。300 mg/kg的CSH可使22K PRL的垂体水平增加10到15倍。在时程研究中，22K催乳素水平在服用CSH后2小时内达到峰值，2~16小时趋于平稳，24小时接近对照组水平。CSH诱导的PRL构象变化在给药后1h达到高峰，2~8h基本持平，16h内达到对照水平。因此，PRL构象的变化先于22K PRL水平的变化。溴隐亭不能模仿CSH的作用，溴隐亭是一种阻止催乳素释放的多巴胺激动剂。CSH对22K PRL的诱导依赖于雌激素的预处理，但CSH对PRL构象的影响不受雌激素处理的影响。结果支持CSH通过将PRL转化为GK底物来增加22K PRL变异的假说。
Glandular kallikrein (GK) is an estrogen-induced and dopamine-repressed lactotroph protease postulated to play a role in the processing of prolactin (PRL) to novel hormonal forms. Recent studies have shown that GK can process PRL in vitro from a 25K form to a 22K form in the presence of thiols -which appear to transform PRL into conformations (folding states) that are GK substrates. We and others have reported 22K PRL variants in the rat pituitary which can be increased by the administration of cysteamine (CSH), a biological thiol known to alter PRL conformation in vitro and in vivo. The present study further characterized CSH induction of the 22K PRL variant. Estrogen-primed rats were used in dose-response and time-course studies with CSH. CSH effects on 22K PRL levels were studied by Western blot analysis of reduced pituitary extracts (disulfides reduced with dithiothreitol before electrophoresis). Changes in PRL conformation were studied by Western blot analysis of nonreduced samples (thiols and disulfides trapped with iodoacetamide). CSH increased 22K PRL in a dose-dependent manner that was well correlated with the dose-response curve for changes in PRL conformation. CSH at 300 mg/kg produced 10- to 15-fold increases in pituitary levels of 22K PRL. In the time course study, 22K PRL levels peaked within 2 h, plateaued between 2 and 16 h, and approached control levels by 24 h after CSH dosing. CSH-elicited changes in PRL conformation peaked within 1 h, plateaued between 2 and 8 h, and reached control levels within 16 h of CSH dosing. Thus, changes in PRL conformation preceded the changes in 22K PRL levels. CSH actions were not mimicked by bromocriptine, a dopamine agonist that blocks PRL release. CSH-induction of 22K PRL was dependent upon estrogen pretreatment; however, CSH effects on PRL conformation were independent of estrogen treatment. The results support the hypothesis that CSH increases the 22K PRL variant by converting PRL into conformations which are GK substrates.