Rusten Tor Erik, Rodahl Lina M W, Pattni Krupa, Englund Camilla, Samakovlis Christos, Dove Stephen, Brech Andreas, Stenmark Harald
Department of Biochemistry, The Norwegian Radium Hospital and the University of Oslo, Montebello, N-0310 Oslo, Norway.
Mol Biol Cell. 2006 Sep;17(9):3989-4001. doi: 10.1091/mbc.e06-03-0239. Epub 2006 Jul 12.
The trafficking of endocytosed receptors through phosphatidylinositol 3-phosphate [PtdIns(3)P]-containing endosomes is thought to attenuate their signaling. Here, we show that the PtdIns(3)P 5-kinase Fab1/PIKfyve controls trafficking but not silencing of endocytosed receptors. Drosophila fab1 mutants contain undetectable phosphatidylinositol 3,5-bisphosphate levels, show profound increases in cell and organ size, and die at the pupal stage. Mutant larvae contain highly enlarged multivesicular bodies and late endosomes that are inefficiently acidified. Clones of fab1 mutant cells accumulate Wingless and Notch, similarly to cells lacking Hrs, Vps25, and Tsg101, components of the endosomal sorting machinery for ubiquitinated membrane proteins. However, whereas hrs, vps25, and tsg101 mutant cell clones accumulate ubiquitinated cargo, this is not the case with fab1 mutants. Even though endocytic receptor trafficking is impaired in fab1 mutants, Notch, Wingless, and Dpp signaling is unaffected. We conclude that Fab1, despite its importance for endosomal functions, is not required for receptor silencing. This is consistent with the possibility that Fab1 functions at a late stage in endocytic receptor trafficking, at a point when signal termination has occurred.
通过含磷脂酰肌醇3-磷酸[PtdIns(3)P]的内体对内吞受体进行运输，被认为会减弱其信号传导。在此，我们表明PtdIns(3)P 5-激酶Fab1/PIKfyve控制内吞受体的运输，但不影响其沉默。果蝇fab1突变体的磷脂酰肌醇3,5-二磷酸水平检测不到，细胞和器官大小显著增加，并在蛹期死亡。突变幼虫含有高度增大的多囊泡体和晚期内体，其酸化效率低下。fab1突变体细胞克隆积累无翅蛋白和Notch，类似于缺乏Hrs、Vps25和Tsg101的细胞，这些是泛素化膜蛋白内体分选机制的组成部分。然而，虽然hrs、vps25和tsg101突变体细胞克隆积累泛素化货物，但fab1突变体并非如此。尽管fab1突变体内吞受体运输受损，但Notch、无翅蛋白和Dpp信号传导不受影响。我们得出结论，尽管Fab1对内体功能很重要，但受体沉默并不需要它。这与Fab1在内吞受体运输后期、信号终止发生时发挥作用的可能性是一致的。
