The myotubularin phosphatase MTMR4 regulates sorting from early endosomes
The myotubularin phosphatase MTMR4 regulates sorting from early endosomes
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DOI：
10.1242/jcs.060103
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发表时间：
2010-09-15
影响因子：
4
通讯作者：
Mitchell, Christina A.
中科院分区：
文献类型：
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作者：
Naughtin, Monica J.;Sheffield, David A.;Mitchell, Christina A.
磷脂酰肌醇3-磷酸[PtdIns(3)P]通过早期核内体调节内噬运输和受体的分选，包括转铁蛋白（Tfn）的快速循环。然而，选择性地反对这一功能的磷酸肌醇磷酸酶是未知的。肌管蛋白是一个由8个催化活性酶和6个无活性酶组成的家族，它们水解PtdIns(3)P形成PtdIns。然而，每个肌管蛋白家族成员在调节内体PtdIns(3)P从而调节内吞运输中所起的作用尚未得到很好的确定。在这里，我们确定了肌管蛋白家族成员MTMR4，它定位于早期核内体，也定位于Rab11-和sec15阳性循环核内体。在MTMR4敲低或表达催化活性MTMR4， MTMR4（C407A）的细胞中，PtdIns(3) p修饰的内体数量显著增加。MTMR4过表达延迟了Tfn从早期核内体的退出和向质膜的再循环。相比之下，MTMR4（C407A）作为显性负构建体的表达显著加速了Tfn的循环。然而，在MTMR4敲除细胞中，Tfn的再循环没有变化，这表明其他mtm也可能有助于再循环。MTMR4调节Rab11的亚细胞分布，并且在rnai介导的MTMR4敲低的细胞中，Rab11被引导远离中心周围循环室。VAMP3是一种v-SNARE蛋白，存在于回收核内体和核内体衍生的运输囊泡中，其亚细胞分布也受到MTMR4的调节。因此，MTMR4定位于早期和再循环核内体的界面，通过这一途径调节运输。
Phosphatidylinositol 3-phosphate [PtdIns(3)P] regulates endocytic trafficking and the sorting of receptors through early endosomes, including the rapid recycling of transferrin (Tfn). However, the phosphoinositide phosphatase that selectively opposes this function is unknown. The myotubularins are a family of eight catalytically active and six inactive enzymes that hydrolyse PtdIns(3)P to form PtdIns. However, the role each myotubularin family member plays in regulating endosomal PtdIns(3)P and thereby endocytic trafficking is not well established. Here, we identify the myotubularin family member MTMR4, which localizes to early endosomes and also to Rab11- and Sec15-positive recycling endosomes. In cells with MTMR4 knockdown, or following expression of the catalytically inactive MTMR4, MTMR4(C407A), the number of PtdIns(3)P-decorated endosomes significantly increased. MTMR4 overexpression delayed the exit of Tfn from early endosomes and its recycling to the plasma membrane. By contrast, expression of MTMR4(C407A), which acts as a dominant-negative construct, significantly accelerated Tfn recycling. However, in MTMR4 knockdown cells Tfn recycling was unchanged, suggesting that other MTMs might also contribute to recycling. MTMR4 regulated the subcellular distribution of Rab11 and, in cells with RNAi-mediated knockdown of MTMR4, Rab11 was directed away from the pericentriolar recycling compartment. The subcellular distribution of VAMP3, a v-SNARE protein that resides in recycling endosomes and endosome-derived transport vesicles, was also regulated by MTMR4. Therefore, MTMR4 localizes at the interface of early and recycling endosomes to regulate trafficking through this pathway.