Microautophagy of the nucleus coincides with a vacuolar diffusion barrier at nuclear-vacuolar junctions.
Microautophagy of the nucleus coincides with a vacuolar diffusion barrier at nuclear-vacuolar junctions.
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DOI：
10.1091/mbc.e09-09-0782
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发表时间：
2010-12
影响因子：
3.3
通讯作者：
Mayer A
中科院分区：
文献类型：
--
作者：
Dawaliby R;Mayer A
核-空泡（NV）连接是酵母细胞器的接触部位。它们将细胞器界面的核孔排除在外。在液泡侧，脂质依赖性过程将特定的膜蛋白（如V-ATP酶）从接触部位排除。这表明NV结建立了选择性扩散势垒。核通过核-液泡（NV）连接与酵母液泡结合。在营养限制下，NV连接内陷并将充满核物质的囊泡释放到空泡中，导致核（PMN）的零碎微自噬。我们发现，跨液泡膜的电化学梯度促进NV连接处的内陷。现有的内陷持续独立的梯度，但最终释放的PMN囊泡需要再次V-ATP酶活性。我们发现，NV路口形成的液泡膜上的扩散屏障，排除V-ATP酶，但丰富的VTC复合物和其他膜整合蛋白。V-ATP酶排斥依赖于NV连接蛋白Nvj 1 p、Vac 8 p和电化学梯度。它还取决于脂质代谢的因素，如氧固醇结合蛋白Osh 1 p和烯酰辅酶A还原酶Tsc 13 p，它们在NV连接处富集，并依赖于Lag 1 p和Fen 1 p。我们的观察结果表明，NV连接形成在两个可分离的步骤：NVj 1 p和Vac 8 p足以建立两个膜之间的接触。需要电化学电位和脂质修饰酶来建立空泡扩散屏障，使NV连接内陷，并形成PMN囊泡。
Nuclear-vacuolar (NV) junctions are organelle contact sites in yeast. They exclude nuclear pores from the organelle interface. On the vacuolar side, a lipid-dependent process excludes specific membrane proteins, such as V-ATPase, from the contact site. This suggests that NV junctions establish selective diffusion barriers. Nuclei bind yeast vacuoles via nucleus-vacuole (NV) junctions. Under nutrient restriction, NV junctions invaginate and release vesicles filled with nuclear material into vacuoles, resulting in piecemeal microautophagy of the nucleus (PMN). We show that the electrochemical gradient across the vacuolar membrane promotes invagination of NV junctions. Existing invaginations persist independently of the gradient, but final release of PMN vesicles requires again V-ATPase activity. We find that NV junctions form a diffusion barrier on the vacuolar membrane that excludes V-ATPase but is enriched in the VTC complex and accessible to other membrane-integral proteins. V-ATPase exclusion depends on the NV junction proteins Nvj1p,Vac8p, and the electrochemical gradient. It also depends on factors of lipid metabolism, such as the oxysterol binding protein Osh1p and the enoyl-CoA reductase Tsc13p, which are enriched in NV junctions, and on Lag1p and Fen1p. Our observations suggest that NV junctions form in two separable steps: Nvj1p and Vac8p suffice to establish contact between the two membranes. The electrochemical potential and lipid-modifying enzymes are needed to establish the vacuolar diffusion barrier, invaginate NV junctions, and form PMN vesicles.