PDF(Pubmed)
Abstract：
Retromer prevents the destruction of numerous receptors by recycling them from endosomes to the trans-Golgi network or plasma membrane. This enables retromer to fine-tune the activity of many signaling pathways in parallel. However, the mechanism(s) by which retromer function adapts to environmental fluctuations such as nutrient withdrawal and how this affects the fate of its cargoes remains incompletely understood. Here, we reveal that macroautophagy/autophagy inhibition by MTORC1 controls the abundance of retromer+ endosomes under nutrient-replete conditions. Autophagy activation by chemical inhibition of MTOR or nutrient withdrawal does not affect retromer assembly or its interaction with the RAB7 GAP protein TBC1D5, but rather targets these endosomes for bulk destruction following their capture by phagophores. This process appears to be distinct from amphisome formation. TBC1D5 and its ability to bind to retromer, but not its C-terminal LC3-interacting region (LIR) or nutrient-regulated dephosphorylation, is critical for retromer to be captured by autophagosomes following MTOR inhibition. Consequently, endosomal recycling of its cargoes to the plasma membrane and trans-Golgi network is impaired, leading to their lysosomal turnover. These findings demonstrate a mechanistic link connecting nutrient abundance to receptor homeostasis.Abbreviations: AMPK, 5\'-AMP-activated protein kinase; APP, amyloid beta precursor protein; ATG, autophagy related; BafA, bafilomycin A1; CQ, chloroquine; DMEM, Dulbecco\'s minimum essential medium; DPBS, Dulbecco\'s phosphate-buffered saline; EBSS, Earle\'s balanced salt solution; FBS, fetal bovine serum; GAP, GTPase-activating protein; MAP1LC3/LC3, microtubule associated protein 1 light chain 3; LIR, LC3-interacting region; LANDO, LC3-associated endocytosis; LP, leupeptin and pepstatin; MTOR, mechanistic target of rapamycin kinase; MTORC1, MTOR complex 1; nutrient stress, withdrawal of amino acids and serum; PDZ, DLG4/PSD95, DLG1, and TJP1/zo-1; RPS6, ribosomal protein S6; RPS6KB1/S6K1, ribosomal protein S6 kinase B1; SLC2A1/GLUT1, solute carrier family 2 member 1; SORL1, sortillin related receptor 1; SORT1, sortillin 1; SNX, sorting nexin; TBC1D5, TBC1 domain family member 5; ULK1, unc-51 like autophagy activating kinase 1; WASH, WASH complex subunit.
摘要：
Retromer通过将许多受体从内体再循环到反式高尔基体网络或质膜来防止它们的破坏。这使得逆转录分子能够并行地微调许多信号传导途径的活性。然而,逆向功能适应环境波动的机制，如营养戒断，以及这如何影响其货物的命运，仍未完全了解。这里,我们发现，在营养充足的条件下，MTORC1对巨自噬/自噬的抑制作用控制着retromer+内体的丰度。通过化学抑制MTOR或营养撤除的自噬激活不会影响逆转录组装或其与RAB7GAP蛋白TBC1D5的相互作用，而是靶向这些内体，以在它们被吞噬细胞捕获后进行大量破坏。该过程似乎与两性体形成不同。TBC1D5及其结合逆转录的能力，但不是其C端LC3相互作用区（LIR）或营养调节的去磷酸化，对于MTOR抑制后自噬体捕获逆转录分子至关重要。因此,其货物向质膜和跨高尔基网络的内体再循环受损，导致它们的溶酶体周转。这些发现证明了将营养丰度与受体稳态联系起来的机制联系。
