National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Beijing 100101, China.
National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Beijing 100101, China; College of Life Sciences, University of Chinese Academy of Sciences, 19 Yuquan Road, Beijing 100049, China.
Curr Biol. 2018 Apr 23;28(8):1234-1245.e4. doi: 10.1016/j.cub.2018.03.002. Epub 2018 Apr 5.
The endoplasmic reticulum (ER) is the site of biogenesis of the isolation membrane (IM, autophagosome precursor) and forms extensive contacts with IMs during their expansion into double-membrane autophagosomes. Little is known about the molecular mechanism underlying the formation and/or maintenance of the ER/IM contact. The integral ER proteins VAPA and VAPB (VAPs) participate in establishing ER contacts with multiple membranes by interacting with different tethers. Here, we demonstrate that VAPs also modulate ER/IM contact formation. Depletion of VAPs impairs progression of IMs into autophagosomes. Upon autophagy induction, VAPs are recruited to autophagosome formation sites on the ER, a process mediated by their interactions with FIP200 and PI(3)P. VAPs directly interact with FIP200 and ULK1 through their conserved FFAT motifs and stabilize the ULK1/FIP200 complex at the autophagosome formation sites on the ER. The formation of ULK1 puncta is significantly reduced by VAPA/B depletion. VAPs also interact with WIPI2 and enhance the formation of the WIPI2/FIP200 ER/IM tethering complex. Depletion of VMP1, which increases the ER/IM contact, greatly elevates the interaction of VAPs with these autophagy proteins. The VAPB P56S mutation, which is associated with amyotrophic lateral sclerosis, reduces the ULK1/FIP200 interaction and impairs autophagy at an early step, similar to the effect seen in VAPA/B-depleted cells. Our study reveals that VAPs directly interact with multiple ATG proteins, thereby contributing to ER/IM contact formation for autophagosome biogenesis.
内质网（ER）是隔离膜（IM，自噬体前体）生物发生的部位，并且在其扩展为双层膜自噬体期间与 IM 形成广泛的接触。对于形成和/或维持 ER/IM 接触的分子机制知之甚少。完整的 ER 蛋白 VAPA 和 VAPB（VAPs）通过与不同的系绳相互作用参与与多个膜建立 ER 接触。在这里，我们证明 VAPs 还调节 ER/IM 接触形成。VAPs 的耗竭会损害 IM 向自噬体的进展。在自噬诱导时，VAPs 被募集到 ER 上的自噬体形成部位，这一过程由它们与 FIP200 和 PI(3)P 的相互作用介导。VAPs 通过其保守的 FFAT 基序直接与 FIP200 和 ULK1 相互作用，并在 ER 上的自噬体形成部位稳定 ULK1/FIP200 复合物。VAPA/B 耗竭显著减少 ULK1 斑点的形成。VAPs 还与 WIPI2 相互作用，并增强 WIPI2/FIP200 ER/IM 系绳复合物的形成。VMP1 的耗竭增加了 ER/IM 接触，大大增加了 VAPs 与这些自噬蛋白的相互作用。与肌萎缩侧索硬化症相关的 VAPB P56S 突变降低了 ULK1/FIP200 相互作用，并在早期阶段损害自噬，类似于 VAPA/B 耗竭细胞中观察到的效果。我们的研究表明，VAPs 直接与多种 ATG 蛋白相互作用，从而有助于自噬体生物发生的 ER/IM 接触形成。
