Insulysin cleaves the APP cytoplasmic fragment at multiple sites.
Insulysin cleaves the APP cytoplasmic fragment at multiple sites.
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胰岛素在多个位点切割 APP 细胞质片段。
DOI：
10.1007/s11064-007-9449-z
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发表时间：
2007
影响因子：
4.4
通讯作者：
Sambamurti,Kumar
中科院分区：
文献类型：
--
作者：
Venugopal,Chitra;Pappolla,MiguelA;Sambamurti,Kumar
阿尔茨海默病（AD）中沉积的淀粉样肽（a β）是由β-和γ-分泌酶加工较大的整体膜蛋白前体（APP）产生的。γ-分泌酶对APP的膜内加工也产生细胞内片段CTFγ（又名AICD），该片段高度保守，被认为调节包括KAI-1和GSK3β在内的几种基因的转录。APP的胞内结构域也被caspase加工成31aa片段，有几组研究表明该片段可诱导细胞凋亡。尽管神经元持续产生大量CTFγ，但在细胞裂解物中通常检测到的CTFγ很少，这表明它在体内的转化非常迅速。先前的研究表明，胰岛素（IDE）是一种a β降解酶，在体外负责细胞溶胶介导的CTFγ降解。与这一发现一致，缺乏IDE的敲除小鼠在大脑中积累CTFγ至可检测水平，尽管其水平仍低于其前体，这表明它在大脑中继续被翻转。此外，当我们用IDE抑制剂处理培养细胞时，我们没有观察到细胞裂解物中CTFγ的增加，这表明IDE以外的途径也参与了CTFγ的转换。为了进一步了解CTFγ的转换，我们绘制了IDE切割位点的图谱，并打算对它们进行突变，以便在未来的研究中检查替代途径。Edman降解显示IDE在多个位点将CTFγ切割成5 - 14aa的小肽。裂解位点不显示IDE裂解存在任何序列特异性。了解CTFγ的转换机制对于理解该片段介导的APP的信号功能至关重要。目前的研究提出了IDE对CTFγ转换的有趣特异性，IDE先前已被确定为Aβ和CTFγ的主要降解酶。此外，该研究为细胞中存在其他ctf - γ降解途径提供了证据。
The amyloid peptide (Aβ) deposited in Alzheimer’s disease (AD) is generated by β- and γ-secretase processing of a larger integral membrane protein precursor (APP). Intramembrane processing of APP by γ-secretase also yields an intracellular fragment, CTFγ (a.k.a. AICD), which is highly conserved and is believed to regulate the transcription of several genes including KAI-1 and GSK3β. The intracellular domain of APP is also processed by caspase to a 31 aa fragment that was shown to induce apoptosis by several groups. Although large quantities of CTFγ are generated continuously by neurons, little if any is normally detected in cell lysates, which suggests that it is very rapidly turned over in vivo. Previous studies demonstrated that insulysin (IDE), an Aβ-degrading enzyme, is responsible for cytosol-mediated CTFγ degradation in vitro. Consistent with this finding, knockout mice lacking IDE accumulate CTFγ to detectable levels in the brain, although its levels remain lower than its precursor, suggesting that it continues to be turned over in the brain. Moreover, when we treated cultured cells with IDE inhibitors, we did not observe an increase in CTFγ in cell lysates, suggesting that pathways other than IDE are also involved in CTFγ turnover. To understand CTFγ turnover further, we have mapped the IDE cleavage sites with the intention of mutating them to examine alternative pathways in future studies. Edman degradation revealed that IDE cleaves CTFγ at multiple sites to small peptides ranging from 5 to 14 aa. The cleavage sites do not reveal the existence of any sequence specificity for IDE cleavage. Understanding the turnover mechanisms of CTFγ is critical to the understanding of the signaling function of APP mediated by this fragment. The current study presents the interesting specificity of CTFγ turnover by IDE, which has been previously identified as the major degrading enzyme for Aβ as well as CTFγ. In addition, the study provides evidence for the presence of alternative CTFγ-degrading pathways in the cell.