INSERM, INRAE, C2VN, Aix Marseille University, Marseille, France; Endocrinology, Metabolic Diseases and Nutrition Department, APHM, Marseille, France.
INSERM, INRAE, C2VN, Aix Marseille University, Marseille, France.
J Biol Chem. 2021 Jul;297(1):100818. doi: 10.1016/j.jbc.2021.100818. Epub 2021 May 23.
The cleavage of the insulin receptor by β-secretase 1 (BACE1) in the liver increases during diabetes, which contributes to reduce insulin receptor levels and impair insulin signaling. However, the precise signaling events that lead to this increased cleavage are unclear. We showed that BACE1 cleaves the insulin receptor in the early secretory pathway. Indeed, coimmunoprecipitation experiments reveal the interaction of the proforms of the two proteins. Moreover, fragments of insulin receptor are detected in the early secretory pathway and a mutated form of BACE1 that retains its prodomain cleaves an early secretory pathway-resident form of the insulin receptor. We showed that BACE1 proform levels are regulated by proteasome and/or lysosome-dependent degradation systems whose efficiencies are dependent on the O-GlcNacylation process. Our results showed that enhanced O-GlcNacylation reduces the efficiency of intracellular protein degradation systems, leading to the accumulation of the proform of BACE1 in the early secretory pathway where it cleaves the precursor of the insulin receptor. All these dysregulations are found in the livers of diabetic mice. In addition, we performed a screen of molecules according to their ability to increase levels of the insulin receptor at the surface of BACE1-overexpressing cells. This approach identified the aminosterol Claramine, which accelerated intracellular trafficking of the proform of BACE1 and increased autophagy. Both of these effects likely contribute to the reduced amount of the proform of BACE1 in the early secretory pathway, thereby reducing insulin receptor cleavage. These newly described properties of Claramine are consistent with its insulin sensitizing effect.
β 分泌酶 1（BACE1）在肝脏中对胰岛素受体的裂解在糖尿病期间增加，这有助于降低胰岛素受体水平并损害胰岛素信号。然而，导致这种增加裂解的确切信号事件尚不清楚。我们表明 BACE1 在早期分泌途径中裂解胰岛素受体。事实上，共免疫沉淀实验揭示了这两种蛋白质的前体形式的相互作用。此外，在早期分泌途径中检测到胰岛素受体的片段，并且保留其前结构域的突变形式的 BACE1 裂解胰岛素受体的早期分泌途径驻留形式。我们表明 BACE1 前体形式的水平受蛋白酶体和/或溶酶体依赖性降解系统的调节，其效率取决于 O-GlcNAcylation 过程。我们的结果表明，增强的 O-GlcNAcylation 降低了细胞内蛋白质降解系统的效率，导致 BACE1 的前体形式在早期分泌途径中积累，在那里它裂解胰岛素受体的前体。所有这些失调都在糖尿病小鼠的肝脏中发现。此外，我们根据它们增加 BACE1 过表达细胞表面胰岛素受体水平的能力对分子进行了筛选。这种方法鉴定了氨基甾醇 Claramine，它加速了 BACE1 前体的细胞内转运并增加了自噬。这两种效应都可能导致早期分泌途径中 BACE1 前体的量减少，从而减少胰岛素受体的裂解。Claramine 的这些新描述的特性与其胰岛素增敏作用一致。
