Department of Cellular and Molecular Medicine, University of California San Diego, La Jolla, CA 92093-0668.
Department of Biomedical Sciences of Cells and Systems, University of Groningen, University Medical Center Groningen, 9713 AV Groningen, The Netherlands.
Proc Natl Acad Sci U S A. 2022 Feb 8;119(6). doi: 10.1073/pnas.2117554119.
Fragments of the endoplasmic reticulum (ER) are selectively delivered to the lysosome (mammals) or vacuole (yeast) in response to starvation or the accumulation of misfolded proteins through an autophagic process known as ER-phagy. A screen of the deletion library identified as a candidate knockout strain that is defective in ER-phagy during starvation conditions, but not bulk autophagy. We find that loss of End3 and its stable binding partner Pan1, or inhibition of the Arp2/3 complex that is coupled by the End3-Pan1 complex to endocytic pits, blocks the association of the cortical ER autophagy receptor, Atg40, with the autophagosomal assembly scaffold protein Atg11. The membrane contact site module linking the rim of cortical ER sheets and endocytic pits, consisting of Scs2 or Scs22, Osh2 or Osh3, and Myo3 or Myo5, is also needed for ER-phagy. Both Atg40 and Scs2 are concentrated at the edges of ER sheets and can be cross-linked to each other. Our results are consistent with a model in which actin assembly at sites of contact between the cortical ER and endocytic pits contributes to ER sequestration into autophagosomes.
内质网（ER）的碎片在饥饿或错误折叠蛋白积累时通过自噬过程被选择性地递送至溶酶体（哺乳动物）或液泡（酵母），这种自噬过程称为 ER 自噬。通过对 缺失文库的筛选，我们鉴定出 是一种候选敲除菌株，它在饥饿条件下的 ER 自噬中存在缺陷，但不是大量自噬。我们发现 End3 及其稳定结合伴侣 Pan1 的缺失，或抑制与 End3-Pan1 复合物偶联的 Arp2/3 复合物，会阻止皮质 ER 自噬受体 Atg40 与自噬体组装支架蛋白 Atg11 的结合。连接皮质 ER 片层和胞饮陷窝边缘的膜接触位点模块，由 Scs2 或 Scs22、Osh2 或 Osh3 和 Myo3 或 Myo5 组成，也需要 ER 自噬。Atg40 和 Scs2 都集中在 ER 片层的边缘，可以相互交联。我们的结果与这样一种模型一致，即皮质 ER 与胞饮陷窝之间接触部位的肌动蛋白组装有助于将 ER 隔离到自噬体中。
