Henmi Yuji, Morikawa Yoshiaki, Oe Natsuko, Ikeda Narumi, Fujita Akikazu, Takei Kohji, Minogue Shane, Tanabe Kenji
Medical Research Institute, Tokyo Women's Medical University, Tokyo 162-8666, Japan Department of Neuroscience, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama 700-8558, Japan.
Department of Neuroscience, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama 700-8558, Japan.
Mol Biol Cell. 2016 Mar 15;27(6):990-1001. doi: 10.1091/mbc.E15-08-0564. Epub 2016 Jan 28.
Phosphatidylinositol 4-kinase IIα (PtdIns4KIIα) localizes to the trans-Golgi network and endosomal compartments and has been implicated in the regulation of endosomal traffic, but the roles of both its enzymatic activity and the site of its action have not been elucidated. This study shows that PtdIns4KIIα is required for production of endosomal phosphatidylinositol 4-phosphate (PtdIns(4)P) on early endosomes and for the sorting of transferrin and epidermal growth factor receptor into recycling and degradative pathways. Depletion of PtdIns4KIIα with small interfering RNA significantly reduced the amount of vesicular PtdIns(4)P on early endosomes but not on Golgi membranes. Cells depleted of PtdIns4KIIα had an impaired ability to sort molecules destined for recycling from early endosomes. We further identify the Eps15 homology domain-containing protein 3 (EHD3) as a possible endosomal effector of PtdIns4KIIα. Tubular endosomes containing EHD3 were shortened and became more vesicular in PtdIns4KIIα-depleted cells. Endosomal PtdIns(4,5)P2 was also significantly reduced in PtdIns4KIIα-depleted cells. These results show that PtdIns4KIIα regulates receptor sorting at early endosomes through a PtdIns(4)P-dependent pathway and contributes substrate for the synthesis of endosomal PtdIns(4,5)P2.
磷脂酰肌醇4-激酶IIα（PtdIns4KIIα）定位于反式高尔基体网络和内体区室，并且与内体运输的调控有关，但其酶活性和作用位点的作用尚未阐明。本研究表明，早期内体上内体磷脂酰肌醇4-磷酸（PtdIns(4)P）的产生以及转铁蛋白和表皮生长因子受体分选到再循环和降解途径中都需要PtdIns4KIIα。用小干扰RNA耗尽PtdIns4KIIα可显著降低早期内体上囊泡状PtdIns(4)P的量，但不影响高尔基体膜上的量。耗尽PtdIns4KIIα的细胞从早期内体中分选注定要再循环的分子的能力受损。我们进一步确定含Eps15同源结构域蛋白3（EHD3）为PtdIns4KIIα可能的内体效应器。在耗尽PtdIns4KIIα的细胞中，含有EHD3的管状内体缩短并变得更具囊泡状。耗尽PtdIns4KIIα的细胞中内体PtdIns(4,5)P2也显著减少。这些结果表明，PtdIns4KIIα通过依赖PtdIns(4)P的途径调节早期内体上的受体分选，并为内体PtdIns(4,5)P2的合成提供底物。
