Calnexin mediates the maturation of GPI-anchors through ER retention
Calnexin mediates the maturation of GPI-anchors through ER retention
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Calnexin 通过 ER 保留介导 GPI 锚的成熟
DOI：
10.1074/jbc.ra120.015577
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发表时间：
2020-11-27
影响因子：
4.8
通讯作者：
Fujita, Morihisa
中科院分区：
文献类型：
--
作者：
Guo, Xin-Yu;Liu, Yi-Shi;Fujita, Morihisa
在内质网(ER)中监测糖基磷脂酰肌醇锚定蛋白(GPI-APs)的蛋白质折叠和脂类状态，钙粘蛋白在GPI-APs的成熟过程中起双重作用。在本研究中，我们研究了Calnexin在内质网GPI-AP的质量控制和脂质重塑中的作用。通过直接将N-葡聚糖结合到蛋白质上，观察到Calnexin有效地将GPI-AP保留在内质网中，直到它们被正确折叠。此外，足够的内质网滞留时间对GPI-肌醇脱酰化至关重要，GPI-肌醇脱酰化是由GPI后附着蛋白1(PGAP1)介导的。一旦钙粘蛋白/钙网织蛋白循环被破坏，错误折叠和肌醇酰化的GPI-AP就不能保留在内质网中，而暴露在质膜上。在钙粘蛋白/钙网蛋白缺陷型细胞中，内源性GPI锚定的碱性磷酸酶在细胞表面表达，但其活性显著降低。内质网应激诱导错误折叠的GPI-AP的表面表达，但由于它们在内质网中保留的时间延长，GPI-肌醇发生了适当的脱酰化。我们的结果表明，钙粘蛋白介导的GPI-AP的内质网质量控制系统对于蛋白质折叠和GPI-肌醇去酰化都是必要的。
The protein folding and lipid moiety status of glycosylphosphatidylinositol-anchored proteins (GPI-APs) are monitored in the endoplasmic reticulum (ER), with calnexin playing dual roles in the maturation of GPI-APs. In the present study, we investigated the functions of calnexin in the quality control and lipid remodeling of GPI-APs in the ER. By directly binding the N-glycan on proteins, calnexin was observed to efficiently retain GPI-APs in the ER until they were correctly folded. In addition, sufficient ER retention time was crucial for GPI-inositol deacylation, which is mediated by post-GPI attachment protein 1 (PGAP1). Once the calnexin/calreticulin cycle was disrupted, misfolded and inositol-acylated GPI-APs could not be retained in the ER and were exposed on the plasma membrane. In calnexin/calreticulin-deficient cells, endogenous GPI-anchored alkaline phosphatase was expressed on the cell surface, but its activity was significantly decreased. ER stress induced surface expression of misfolded GPI-APs, but proper GPI-inositol deacylation occurred due to the extended time that they were retained in the ER. Our results indicate that calnexin-mediated ER quality control systems for GPI-APs are necessary for both protein folding and GPI-inositol deacylation.