Export-deficient monoubiquitinated PEX5 triggers peroxisome removal in SV40 large T antigen-transformed mouse embryonic fibroblasts
Export-deficient monoubiquitinated PEX5 triggers peroxisome removal in SV40 large T antigen-transformed mouse embryonic fibroblasts
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DOI：
10.1080/15548627.2015.1061846
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发表时间：
2015-08-01
期刊：
影响因子：
13.3
通讯作者：
Fransen, Marc
中科院分区：
文献类型：
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作者：
Nordgren, Marcus;Francisco, Tania;Fransen, Marc
过氧化物酶体是一种普遍存在的细胞器，对人类健康至关重要。为了维持一个健康的细胞环境，功能失调和多余的过氧化物体需要有选择地去除。虽然新出现的证据表明，过氧化物体主要是通过吞噬来降解的，但对哺乳动物细胞中这一过程的触发因素和分子机制知之甚少。在这项研究中，我们证明了PEX5蛋白与一个庞大的C末端标签融合在一起，在SV40大T抗原转化的小鼠胚胎成纤维细胞中引发了过氧化物酶的降解。此外，我们提供的证据表明，这一过程是自噬依赖的，需要标记PEX5的N末端半胱氨酸残基的单素化以供循环使用。由于我们的发现还表明，在PEX5的C末端增加一个大的标签不会干扰PEX5的单泛素化，但强烈地抑制其从过氧化体膜上的输出，我们假设这样的标签模仿了一个不能从PEX5释放的货运蛋白，从而使单泛素化的PEX5在膜上保持足够长的时间，以便被自噬机制识别。这进而表明，过氧化物酶体相关PEX5的N-末端半胱氨酸的单泛素化不仅具有将过氧化物素循环回到胞浆的功能，而且还作为一种质量控制机制，通过有缺陷的蛋白质输入机制来消除过氧化物体。
Peroxisomes are ubiquitous cell organelles essential for human health. To maintain a healthy cellular environment, dysfunctional and superfluous peroxisomes need to be selectively removed. Although emerging evidence suggests that peroxisomes are mainly degraded by pexophagy, little is known about the triggers and molecular mechanisms underlying this process in mammalian cells. In this study, we show that PEX5 proteins fused to a bulky C-terminal tag trigger peroxisome degradation in SV40 large T antigen-transformed mouse embryonic fibroblasts. In addition, we provide evidence that this process is autophagy-dependent and requires monoubiquitination of the N-terminal cysteine residue that marks PEX5 for recycling. As our findings also demonstrate that the addition of a bulky tag to the C terminus of PEX5 does not interfere with PEX5 monoubiquitination but strongly inhibits its export from the peroxisomal membrane, we hypothesize that such a tag mimics a cargo protein that cannot be released from PEX5, thus keeping monoubiquitinated PEX5 at the membrane for a sufficiently long time to be recognized by the autophagic machinery. This in turn suggests that monoubiquitination of the N-terminal cysteine of peroxisome-associated PEX5 not only functions to recycle the peroxin back to the cytosol, but also serves as a quality control mechanism to eliminate peroxisomes with a defective protein import machinery.