Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, OH, USA.
Genomic Medicine Institute, Lerner Research Institute of Cleveland Clinic, Cleveland, OH, USA.
Biochem Biophys Res Commun. 2019 Apr 2;511(2):356-362. doi: 10.1016/j.bbrc.2019.02.053. Epub 2019 Feb 18.
The endoplasmic reticulum-Golgi intermediate compartment protein-53 (ERGIC-53, aka LMAN1), which cycles between the endoplasmic reticulum (ER) and Golgi, is a known cargo receptor for a number of soluble proteins. However, whether LMAN1 plays a role as a trafficking factor in the central nervous system is largely unknown. Here, we determined the role of LMAN1 on endogenous protein levels of the Cys-loop superfamily of neuroreceptors, including gamma-aminobutyric acid type A receptors (GABARs), 5-hydroxytryptamine (serotonin) type 3 (5-HT) receptors, and nicotinic acetylcholine receptors (nAChRs). Knockdown of LMAN1 reduces the surface trafficking of endogenous β3 subunits of GABARs in mouse hypothalamic GT1-7 neurons. Furthermore, Western blot analysis of brain homogenates from LMAN1 knockout mice demonstrated that loss of LMAN1 decreases the total protein levels of 5HTA receptors and γ2 subunits of GABARs. LMAN1 knockout regulates the ER proteostasis network by upregulating ERP44 without changing calnexin levels. Interestingly, despite the critical role of the glycan-binding function of LMAN1 in its other known cargo clients, LMAN1 interacts with GABARs in a glycan-independent manner. In summary, LMAN1 is a trafficking factor for certain neuroreceptors in the central nervous system. This is the first report of LMAN1 function in membrane protein trafficking.
内质网-高尔基体中间区蛋白-53（ERGIC-53，又名 LMAN1）在内质网（ER）和高尔基体之间循环，是许多可溶性蛋白的已知货物受体。然而，LMAN1 是否在中枢神经系统中作为一种运输因子发挥作用，在很大程度上尚不清楚。在这里，我们确定了 LMAN1 在 Cys 环超家族神经受体（包括γ-氨基丁酸 A 型受体（GABARs）、5-羟色胺（血清素）3 型（5-HT）受体和烟碱型乙酰胆碱受体（nAChRs））内源性蛋白水平中的作用。LMAN1 的敲低减少了小鼠下丘脑 GT1-7 神经元中内源性 GABARsβ3 亚基的表面转运。此外，对 LMAN1 敲除小鼠脑匀浆的 Western blot 分析表明，LMAN1 的缺失降低了 5HTA 受体和 GABARsγ2 亚基的总蛋白水平。LMAN1 敲除通过上调 ERP44 而不改变 calnexin 水平来调节 ER 蛋白稳态网络。有趣的是，尽管 LMAN1 的聚糖结合功能在其其他已知货物客户中起着关键作用，但 LMAN1 以不依赖聚糖的方式与 GABARs 相互作用。总之，LMAN1 是中枢神经系统中某些神经受体的运输因子。这是 LMAN1 在膜蛋白运输中功能的首次报道。
