Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, 5 center drive, Bethesda, MD 20892, USA.
Cell Biosci. 2013 May 23;3(1):24. doi: 10.1186/2045-3701-3-24.
Early endosomal autoantigen 1 (EEA1) is a membrane tethering factor required for the fusion and maturation of early endosomes in endocytosis. How the activity of EEA1 is regulated in cells is unclear.
Here we show that endogenous EEA1 is prone to monoubiquitination at multiple sites, owing to an intrinsic affinity to ubiquitin conjugating enzymes (E2). The E2 interactions enable a ubiquitin ligase (E3) independent mechanism that decorate EEA1 with multiple mono-ubiquitin moieties. Expression of an ubiquitin-EEA1 chimera that mimics native mono-ubiquitinated EEA1 generates giant endosomes abutting the nucleus. Several lines of evidence suggest that this phenotype is due to increased endosome fusion and a simultaneous blockade on an endosome recycling pathway. The latter is likely caused by diminished endosome fission in cells expressing ubiquitin-EEA1.
Our results demonstrate that ubiquitination may dramatically affect the activity of an endosome fusion factor to alter endosome morphology and trafficking pattern, and thereby implicating an unexpected role of ubiquitin signaling in endocytosis.
早期内体自身抗原 1（EEA1）是内吞作用中早期内体融合和成熟所必需的膜连接因子。EEA1 的活性在细胞中是如何被调节的还不清楚。
在这里，我们表明内源性 EEA1 由于其对泛素连接酶（E2）的固有亲和力，容易在多个位点发生单泛素化。E2 相互作用使 EEA1 能够通过一种 E3 独立的机制被多个单泛素基团修饰。表达一种模拟天然单泛素化 EEA1 的泛素-EEA1 嵌合体可导致与核相邻的巨大内体。有几条证据表明，这种表型是由于内体融合增加，同时阻断内体再循环途径所致。在后一种情况下，可能是由于表达泛素-EEA1 的细胞中的内体裂变减少所致。
我们的结果表明，泛素化可能会显著影响内体融合因子的活性，从而改变内体的形态和运输模式，这表明泛素信号在胞吞作用中具有意想不到的作用。
