Section on Molecular Signal Transduction, Program for Developmental Neuroscience, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA.
EMBO J. 2019 Apr 15;38(8):e100312. doi: 10.15252/embj.2018100312. Epub 2019 Mar 13.
The small GTPase Rab7 is a key organizer of receptor sorting and lysosomal degradation by recruiting of a variety of effectors depending on its GDP/GTP-bound state. However, molecular mechanisms that trigger Rab7 inactivation remain elusive. Here we find that, among the endosomal pools, Rab7-positive compartments possess the highest level of PI4P, which is primarily produced by PI4K2A kinase. Acute conversion of this endosomal PI4P to PI(4,5)P causes Rab7 dissociation from late endosomes and releases a regulator of autophagosome-lysosome fusion, PLEKHM1, from the membrane. Rab7 effectors Vps35 and RILP are not affected by acute PI(4,5)P production. Deletion of PI4K2A greatly reduces PIP5Kγ-mediated PI(4,5)P production in Rab7-positive endosomes leading to impaired Rab7 inactivation and increased number of LC3-positive structures with defective autophagosome-lysosome fusion. These results reveal a late endosomal PI4P-PI(4,5)P -dependent regulatory loop that impacts autophagosome flux by affecting Rab7 cycling and PLEKHM1 association.
小分子 GTP 酶 Rab7 是一种关键的受体分拣和溶酶体降解的组织者，它通过招募各种效应因子来实现，这取决于其 GDP/GTP 结合状态。然而，触发 Rab7 失活的分子机制仍然难以捉摸。在这里，我们发现，在内涵体池中，Rab7 阳性隔室具有最高水平的 PI4P，PI4P 主要由 PI4K2A 激酶产生。这种内涵体 PI4P 急性转化为 PI(4,5)P 会导致 Rab7 从晚期内涵体解离，并将自噬体-溶酶体融合的调节剂 PLEKHM1 从膜上释放出来。Rab7 效应物 Vps35 和 RILP 不受急性 PI(4,5)P 产生的影响。PI4K2A 的缺失大大减少了 Rab7 阳性内涵体中 PIP5Kγ 介导的 PI(4,5)P 的产生，导致 Rab7 失活受损，LC3 阳性结构数量增加，自噬体-溶酶体融合缺陷。这些结果揭示了一个晚期内涵体 PI4P-PI(4,5)P 依赖性调节环，通过影响 Rab7 循环和 PLEKHM1 结合来影响自噬体流。
