Hyperosmotic Stress Induces Unconventional Autophagy Independent of the Ulk1 Complex
Hyperosmotic Stress Induces Unconventional Autophagy Independent of the Ulk1 Complex
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DOI：
10.1128/mcb.00024-19
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发表时间：
2019-06
影响因子：
5.3
通讯作者：
Naoki Tamura;S. Kageyama;M. Komatsu;S. Waguri
中科院分区：
文献类型：
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作者：
Naoki Tamura;S. Kageyama;M. Komatsu;S. Waguri
自噬被认为是一种抵抗高渗胁迫的适应机制。尽管据报道该过程是由mTORC1的抑制触发的，但精确的下游机制仍然难以捉摸。在这里，我们证明了高血压应激诱导的自噬不同于常规的小鼠胚胎成纤维细胞（MEFs）和人T24细胞中的大自噬。摘要自噬被认为是机体对高渗胁迫的一种适应机制。尽管据报道该过程是由mTORC1的抑制触发的，但精确的下游机制仍然难以捉摸。在这里，我们证明了高血压应激诱导的自噬不同于常规的小鼠胚胎成纤维细胞（MEFs）和人T24细胞中的大自噬。结果表明，高渗胁迫后，分离膜标记WIPI2和Atg16L的细胞质斑点增加。它们被发现与选择性自噬底物SQSTM 1/p62的斑点部分共定位，并且被磷脂酰肌醇3-激酶（PI3K）的抑制剂或人Vps34（hVps34）（PI3K的一种组分）的敲低所减少。此外，通量测定显示SQSTM 1/p62和NcoA4通过溶酶体途径降解。令人惊讶的是，Ulk1，这是饥饿诱导的大自噬必不可少的，保持失活的高渗应激下，这是部分由mTOR活性。因此，Ulk 1复合物在高渗胁迫下不成核。最后，自噬甚至在RB1CC1/FIP200或Atg13缺陷的MEFs中进行，其编码Ulk1复合物的组分。这些数据表明，高血压应激诱导的自噬代表了一种绕过Ulk1信号传导的非常规自噬类型。
Autophagy is considered an adaptive mechanism against hyperosmotic stress. Although the process has been reported to be triggered by the inhibition of mTORC1, the precise downstream mechanisms remain elusive. Here, we demonstrate that hyperosmotic-stress-induced autophagy is different from conventional macroautophagy in mouse embryonic fibroblasts (MEFs) and human T24 cells. ABSTRACT Autophagy is considered an adaptive mechanism against hyperosmotic stress. Although the process has been reported to be triggered by the inhibition of mTORC1, the precise downstream mechanisms remain elusive. Here, we demonstrate that hyperosmotic-stress-induced autophagy is different from conventional macroautophagy in mouse embryonic fibroblasts (MEFs) and human T24 cells. Our results indicated that cytoplasmic puncta for the isolation membrane markers WIPI2 and Atg16L increased after hyperosmotic stress. They were found to partially colocalize with puncta for a selective autophagy substrate, SQSTM1/p62, and were shown to be diminished by inhibitors of phosphatidylinositol 3-kinase (PI3K) or by knockdown of human Vps34 (hVps34), a component of PI3K. In addition, flux assays showed that SQSTM1/p62 and NcoA4 were degraded by the lysosomal pathway. Surprisingly, Ulk1, which is essential for starvation-induced macroautophagy, remained inactivated under hyperosmotic stress, which was partially caused by mTOR activity. Accordingly, the Ulk1 complex was not nucleated under hyperosmotic stress. Finally, autophagy proceeded even in MEFs deficient in RB1CC1/FIP200 or Atg13, which encode components of the Ulk1 complex. These data suggest that hyperosmotic-stress-induced autophagy represents an unconventional type of autophagy that bypasses Ulk1 signaling.