Wubbolts R, Fernandez-Borja M, Jordens I, Reits E, Dusseljee S, Echeverri C, Vallee R B, Neefjes J
Netherlands Cancer Institute, Department of Tumor Biology, Plesmanlaan 121, The Netherlands.
J Cell Sci. 1999 Mar;112 ( Pt 6):785-95. doi: 10.1242/jcs.112.6.785.
MHC class II molecules exert their function at the cell surface by presenting to T cells antigenic fragments that are generated in the endosomal pathway. The class II molecules are targetted to early lysosomal structures, termed MIIC, where they interact with antigenic fragments and are subsequently transported to the cell surface. We previously visualised vesicular transport of MHC class II-containing early lysosomes from the microtubule organising centre (MTOC) region towards the cell surface in living cells. Here we show that the MIIC move bidirectionally in a 'stop-and-go' fashion. Overexpression of a motor head-deleted kinesin inhibited MIIC motility, showing that kinesin is the motor that drives its plus end transport towards the cell periphery. Cytoplasmic dynein mediates the return of vesicles to the MTOC area and effectively retains the vesicles at this location, as assessed by inactivation of dynein by overexpression of dynamitin. Our data suggest a retention mechanism that determines the perinuclear accumulation of MIIC, which is the result of dynein activity being superior over kinesin activity. The bidirectional nature of MIIC movement is the result of both kinesin and dynein acting reciprocally on the MIIC during its transport. The motors may be the ultimate targets of regulatory kinases since the protein kinase inhibitor staurosporine induces a massive release of lysosomal vesicles from the MTOC region that is morphologically similar to that observed after inactivation of the dynein motor.
MHC II类分子通过将在内体途径中产生的抗原片段呈递给T细胞，从而在细胞表面发挥其功能。II类分子靶向早期溶酶体结构，即MIIC，在那里它们与抗原片段相互作用，随后被转运到细胞表面。我们之前在活细胞中观察到含MHC II类的早期溶酶体从微管组织中心（MTOC）区域向细胞表面的囊泡运输。在这里我们表明，MIIC以“走走停停”的方式双向移动。一种缺失马达头部的驱动蛋白的过表达抑制了MIIC的运动性，表明驱动蛋白是驱动其向细胞周边进行正向运输的马达。细胞质动力蛋白介导囊泡返回MTOC区域，并通过过表达动力蛋白抑制因子使动力蛋白失活来评估，它有效地将囊泡保留在这个位置。我们的数据表明存在一种决定MIIC核周积累的保留机制，这是动力蛋白活性优于驱动蛋白活性的结果。MIIC运动的双向性质是驱动蛋白和动力蛋白在其运输过程中对MIIC相互作用的结果。这些马达可能是调节激酶的最终靶点，因为蛋白激酶抑制剂星形孢菌素会诱导溶酶体囊泡从MTOC区域大量释放，其形态与动力蛋白马达失活后观察到的相似。
