Department of Cellular and Molecular Medicine, University of California San Diego, La Jolla, CA 92093-0668.
Proc Natl Acad Sci U S A. 2024 Jun 11;121(24):e2321991121. doi: 10.1073/pnas.2321991121. Epub 2024 Jun 5.
The endoplasmic reticulum (ER) undergoes degradation by selective macroautophagy (ER-phagy) in response to starvation or the accumulation of misfolded proteins within its lumen. In yeast, actin assembly at sites of contact between the cortical ER (cER) and endocytic pits acts to displace elements of the ER from their association with the plasma membrane (PM) so they can interact with the autophagosome assembly machinery near the vacuole. A collection of proteins tether the cER to the PM. Of these, Scs2/22 and Ist2 are required for cER-phagy, most likely through their roles in lipid transport, while deletion of the tricalbins, //3, bypasses those requirements. An artificial ER-PM tether blocks cER-phagy in both the wild type (WT) and a strain lacking endogenous tethers, supporting the importance of cER displacement from the PM. Scs2 and Ist2 can be cross-linked to the selective cER-phagy receptor, Atg40. The COPII cargo adaptor subunit, Lst1, associates with Atg40 and is required for cER-phagy. This requirement is also bypassed by deletion of the ER-PM tethers, suggesting a role for Lst1 prior to the displacement of the cER from the PM during cER-phagy. Although pexophagy and mitophagy also require actin assembly, deletion of ER-PM tethers does not bypass those requirements. We propose that within the context of rapamycin-induced cER-phagy, Scs2/22, Ist2, and Lst1 promote the local displacement of an element of the cER from the cortex, while Tcb1/2/3 act in opposition, anchoring the cER to the plasma membrane.
内质网（ER）在受到饥饿或腔内错误折叠蛋白积累的刺激下，通过选择性的巨自噬（ER-phagy）进行降解。在酵母中，肌动蛋白在皮质内质网（cER）和内吞陷窝之间接触部位的组装作用是将 ER 的元件从与质膜（PM）的关联中移位，以便它们可以与靠近液泡的自噬体组装机制相互作用。一组蛋白质将 cER 固定在 PM 上。在这些蛋白质中，Scs2/22 和 Ist2 对于 cER-phagy 是必需的，最可能是通过它们在脂质运输中的作用，而三钙结合蛋白 //3 的缺失则绕过了这些要求。人工 ER-PM 连接物会阻止野生型（WT）和缺乏内源性连接物的菌株中的 cER-phagy，这支持了 cER 从 PM 移位的重要性。Scs2 和 Ist2 可以与选择性 cER-phagy 受体 Atg40 交联。COPII 货物衔接子亚基 Lst1 与 Atg40 结合，并且是 cER-phagy 所必需的。这种要求也被 ER-PM 连接物的缺失所绕过，这表明在 cER-phagy 过程中 cER 从 PM 移位之前，Lst1 发挥作用。尽管 pexophagy 和 mitophagy 也需要肌动蛋白组装，但 ER-PM 连接物的缺失并没有绕过这些要求。我们提出，在 rapamycin 诱导的 cER-phagy 中，Scs2/22、Ist2 和 Lst1 促进 cER 的一个元件从皮质局部移位，而 Tcb1/2/3 则起拮抗作用，将 cER 锚定在质膜上。
