Medical Research Council Laboratory of Molecular Biology, Cambridge CB2 0QH, UK.
Mol Biol Cell. 2010 Nov 15;21(22):3998-4008. doi: 10.1091/mbc.E10-05-0457. Epub 2010 Sep 22.
While many of the proteins required for autophagy have been identified, the source of the membrane of the autophagosome is still unresolved with the endoplasmic reticulum (ER), endosomes, and mitochondria all having been evoked. The integral membrane protein Atg9 is delivered to the autophagosome during starvation and in the related cytoplasm-to-vacuole (Cvt) pathway that occurs constitutively in yeast. We have examined the requirements for delivery of Atg9-containing membrane to the yeast autophagosome. Atg9 does not appear to originate from mitochondria, and Atg9 cannot reach the forming autophagosome directly from the ER or early Golgi. Components of traffic between Golgi and endosomes are known to be required for the Cvt pathway but do not appear required for autophagy in starved cells. However, we find that pairwise combinations of mutations in Golgi-endosomal traffic components apparently only required for the Cvt pathway can cause profound defects in Atg9 delivery and autophagy in starved cells. Thus it appears that membrane that contains Atg9 is delivered to the autophagosome from the Golgi-endosomal system rather than from the ER or mitochondria. This is underestimated by examination of single mutants, providing a possible explanation for discrepancies between yeast and mammalian studies on Atg9 localization and autophagosome formation.
虽然已经鉴定出许多自噬所需的蛋白质，但自噬体膜的来源仍未解决，内质网 (ER)、内体和线粒体都被提及过。完整的膜蛋白 Atg9 在饥饿时被递送到自噬体中，并且在酵母中持续发生的相关细胞质到液泡 (Cvt) 途径中也是如此。我们已经检查了将含有 Atg9 的膜递送到酵母自噬体的要求。Atg9 似乎不是来自线粒体，而且 Atg9 不能直接从 ER 或早期高尔基体到达正在形成的自噬体。众所周知，高尔基体和内体之间的运输成分是 Cvt 途径所必需的，但在饥饿细胞中似乎不需要自噬。然而，我们发现，Cvt 途径所必需的高尔基体-内体运输成分的两两组合突变显然会导致饥饿细胞中 Atg9 递送到自噬体和自噬的严重缺陷。因此，似乎含有 Atg9 的膜是从高尔基体-内体系统而不是 ER 或线粒体递送到自噬体的。这是通过检查单个突变体低估的，为酵母和哺乳动物研究中关于 Atg9 定位和自噬体形成的差异提供了可能的解释。
