Dauner Kristin, Eid Walaa, Raghupathy Riya, Presley John F, Zha Xiaohui
From the Chronic Disease Program, Ottawa Hospital Research Institute and.
Department of Biochemistry, Microbiology, and Immunology, University of Ottawa, Ottawa, Ontario K1H 8L6, Canada and.
J Biol Chem. 2017 Apr 7;292(14):5737-5747. doi: 10.1074/jbc.M116.771451. Epub 2017 Feb 14.
The plasma membrane of mammalian cells undergoes constitutive endocytosis, endocytic sorting, and recycling, which delivers nutrients to the lysosomes. The receptors, along with membrane lipids, are normally returned to the plasma membrane to sustain this action. It is not known, however, whether this process is influenced by metabolic conditions. Here we report that endocytic recycling requires active mechanistic target of rapamycin (aka mammalian target of rapamycin) (mTORC1), a master metabolic sensor. Upon mTORC1 inactivation, either by starvation or by inhibitor, recycling receptors and plasma membrane lipids, such as transferrin receptors and sphingomyelin, are delivered to the lysosomes. This lysosomal targeting is independent of canonical autophagy: both WT and Atg5 mouse embryonic fibroblasts responded similarly. Furthermore, we identify hepatocyte growth factor-regulated tyrosine kinase substrate (Hrs), an endosomal sorting complexes required for transport (ESCORT-0) component, as a downstream target of mTORC1. Hrs requires mTORC1 activity to maintain its protein expression level. Silencing Hrs without decreasing mTORC1 activity is sufficient to target transferrin and sphingomyelin to the lysosomes. It is thus evident that the canonical recycling pathway is under the regulation of mTORC1 and likely most predominant in proliferating cells where mTORC1 is highly active.
哺乳动物细胞的质膜会经历组成型内吞作用、内吞分选和再循环，这些过程将营养物质输送到溶酶体。受体与膜脂通常会回到质膜以维持这一过程。然而，目前尚不清楚该过程是否受代谢条件的影响。在此，我们报告内吞再循环需要活性雷帕霉素机制靶点（又称哺乳动物雷帕霉素靶点）（mTORC1），这是一种主要的代谢传感器。在mTORC1失活时，无论是通过饥饿还是抑制剂处理，再循环受体和质膜脂类，如转铁蛋白受体和鞘磷脂，都会被输送到溶酶体。这种溶酶体靶向作用独立于经典自噬：野生型和Atg5基因敲除的小鼠胚胎成纤维细胞反应相似。此外，我们确定肝细胞生长因子调节的酪氨酸激酶底物（Hrs），一种转运所需的内体分选复合物（ESCORT-0）组分，是mTORC1的下游靶点。Hrs需要mTORC1的活性来维持其蛋白表达水平。在不降低mTORC1活性的情况下沉默Hrs足以将转铁蛋白和鞘磷脂靶向输送到溶酶体。因此很明显，经典的再循环途径受mTORC1的调控，并且可能在mTORC1高度活跃的增殖细胞中最为显著。
