Vesicle Transport in Endosomal and Lysosomal Systems

真核细胞已经形成了一系列的内膜系统，这些系统已经分化成执行各种功能。它们参与内吞和胞吐的途径。V-ATPase是一种多亚单位酶，负责内膜系统的酸化。我们发现了小鼠Vo亚基a(a1、a2、a3和a4)的多种亚型，而c和c“亚基是由单基因编码的。A1主要定位于分泌小泡，A2与高尔基体有关，而A3是晚期内切/溶酶体驻留。这些结果表明，多种异构体在一定程度上导致了酸性器官的不同定位和功能，溶酶体的功能是由准确的膜保证的。我们发现，小鼠合成素7定位于晚期内吞体内，其显性负性突变体阻止了内吞体内从早期到晚期的转运。因此，Synaxin 7介导了从早期的内小体到晚期的内小体和溶酶体的内吞运输。我们也对细胞如何获得其特定功能的分子机制感兴趣。破骨细胞通过质膜上的V-ATPase产生胞外酸性物质。在破骨细胞前体中，具有A3亚型的V-ATPase定位于溶酶体。在刺激下，A3异构体被转运到质膜，表明V-ATPase和A3异构体在分化过程中被运输到细胞外围，最终组装到成熟破骨细胞的质膜中。我们的研究表明，内酶体/溶酶体和质膜上的膜动力学参与了骨吸收等细胞特异性功能的调节和表达。

Eukaryotic cells have developed an array of endomembrane systems that have differentiated to carry out various functions. They are involved in the pathways of endocytosis and exocytosis. V-ATPase is a multi-subunit enzyme responsible for acidification of the endomembrane systems. We found multiple isoforms of mouse Vo subunit a (a1, a2, a3 and a4), whereas c and c" subunits are encoded by single genes. a1 is predominantly localized to secretory vesicles, and a2 is associated with Golgi, whereas a3 is a late endosomal/lysosomal resident. These results demonstrated that the multiple isoforms are, in part, responsible for the deiverse localization and function of the acidic organelles.The lysosome functions are ensured by accurate membrane. We found that mouse syntaxin 7 is localized to late endosomes and that its dominant negative mutant blocked endocytic transport from early to late endosomes. Thus, syntaxin 7 mediates the endocytic trafficking from early endosomes to late endosomes and lysosomes.We were also interested in the molecular mechanisms how the cells acquire their specific functions. Osteoclasts generate an extracellular acidic milleu by V-ATPase localized to the plasma membrane. In the osteoclast precursor, the V-ATPase with the a3 isoforms was localized to lysosomes. Upon stimulation, the a3 isoform was transported to the plasma membrane, indicating that V-ATPases with the a3 isoform localized in late-endosomes/lysosomes were transported to the cell periphery during differentiation, and finally assembled into the plasma membrane of mature osteoclasts.Our studies demonstrated that the membrane dynamics along the endosome/lysosome and plasma membranes are involved in the regulation and expression of cell-specific functions like bone-resorption.