Mayr S, Welte T, Windegger M, Lechner J, May P, Heinrich P C, Horn F, Doppler W
Institut für Medizinische Chemie und Biochemie, Universität Innsbruck, Austria.
Eur J Biochem. 1998 Dec 1;258(2):784-93. doi: 10.1046/j.1432-1327.1998.2580784.x.
Prolactin has been reported to induce distinct sets of signal transducers and activators of transcription (STAT) in a cell-type-specific fashion. In the mammary epithelium, although STAT1, STAT3, STAT5A, STAT5B and STAT6 are present in a latent form, only STAT5A and STAT5B are activated. This selective activation of STAT5 by prolactin was also observed in COS-7 cells cotransfected with the long form of the mouse prolactin receptor (PRL-R) and expression vectors for STAT1, STAT3, STAT5 and STAT6. Mutated PRL-Rs and chimeric erythropoietin/gp130 (EPO/gp130) receptors with a tyrosine-containing motif attached at the carboxy terminus were employed to determine the sites in the PRL-R required for the specific activation of STAT5. The experiments revealed the importance of two motifs containing Y477 and Y578 in the PRL-R. When linked to the EPO/gp130 receptor, these sequences were sufficient to specifically induce DNA binding of STAT5 and to activate transcription from the beta-casein gene promoter. By contrast, only weakly they induced DNA binding of STAT6 and STAT3 and did not induce STAT1. A synthetic nonapeptide with phosphorylated Y477 was able to disrupt STAT5 DNA binding in vitro. Our results define structural domains within the carboxy terminus of the PRL-R which recruit STAT5 for signalling and which are capable of distinguishing STAT5 from other STAT proteins. The activity of STAT5 forms with deletions of the carboxy terminus was induced more strongly than that of their full-length counterparts 2 min after activation of the PRL-R. This effect was not dependent on the presence of Y477 and Y578 in the PRL-R, indicating that facilitated activation of short STAT5 isoforms relies on mechanisms other than increased coupling to specific regions of the PRL-R.
据报道，催乳素以细胞类型特异性方式诱导不同的信号转导和转录激活因子（STAT）。在乳腺上皮细胞中，虽然STAT1、STAT3、STAT5A、STAT5B和STAT6以潜伏形式存在，但只有STAT5A和STAT5B被激活。在用小鼠催乳素受体（PRL-R）长形式与STAT1、STAT3、STAT5和STAT6表达载体共转染的COS-7细胞中也观察到催乳素对STAT5的这种选择性激活。使用突变的PRL-R和在羧基末端连接有含酪氨酸基序的嵌合促红细胞生成素/gp130（EPO/gp130）受体来确定PRL-R中STAT5特异性激活所需的位点。实验揭示了PRL-R中两个包含Y477和Y578的基序的重要性。当与EPO/gp130受体相连时，这些序列足以特异性诱导STAT5的DNA结合并激活β-酪蛋白基因启动子的转录。相比之下，它们仅微弱地诱导STAT6和STAT3的DNA结合，且不诱导STAT1。一种磷酸化Y477的合成九肽能够在体外破坏STAT5的DNA结合。我们的结果确定了PRL-R羧基末端内的结构域，这些结构域招募STAT5进行信号传导，并且能够将STAT5与其他STAT蛋白区分开来。在激活PRL-R 2分钟后，羧基末端缺失的STAT5形式的活性比其全长对应物的活性诱导更强。这种效应不依赖于PRL-R中Y477和Y578的存在，表明短STAT5异构体的促进激活依赖于除与PRL-R特定区域增加偶联之外的机制。
