Pathways and itinerary of clathrin-independent endocytosis

这个项目的重点是了解网格蛋白独立形式的内吞作用。 在没有网格蛋白外壳的情况下发生的内吞作用发生在所有细胞中，但了解甚少。 我们有兴趣研究通过这种机制进入细胞的货物蛋白，一旦它们被内化，它们的细胞内行程以及它们是否含有允许细胞内专门分选的氨基酸序列。 最近，我们发现了通过这种机制进入细胞的新货物蛋白，并发现这些新蛋白的一个子集一旦进入细胞就采取替代的交通路线。 主要组织相容性复合物I类蛋白（MHCI）是一种原型网格蛋白依赖性货物蛋白，内化后，它到达含有货物蛋白（如转铁蛋白受体）的内体，这些货物蛋白通过网格蛋白依赖性内吞作用进入。 从那里，MHCI要么行进到晚期内体和溶酶体，在那里它被降解，要么行进到再循环小管，将MHCI返回到细胞表面。 我们已经鉴定的新货物蛋白（CD 44，CD 98和CD 147）在许多细胞中显示出改变的行程，它们直接进入再循环小管，避免运输到晚期内体区室。 与这种改变的行程一致，我们发现CD 44，CD 98和CD 147是长寿命的蛋白质，并且不像MHCI那样降解，其被路由到晚期内体。 我们最近发现，当在细胞中表达时，E-3连接酶MARCH家族的特定成员靶向CD 44和CD 98进行降解。

This project is focused on understanding clathrin-independent forms of endocytosis. Endocytosis that occurs without clathrin coats occurs in all cells but is poorly understood. We are interested in studying the cargo proteins that enter cells by this mechanism, their intracellular itinerary once they have been internalized and whether they contain amino acid sequences that allow for specialized sorting within cells. Recently we identified new cargo proteins that enter cells by this mechanism and have found that a subset of these new proteins take alternative traffic routes once they have entered cells. The major histocompatibility complex Class I protein (MHCI), is a prototypical clathrin-indepenent cargo protein and after internalization it reaches endosomes that contain cargo proteins such as the transferrin receptor that enter via clathrin-depenent endocytosis. From there, MHCI travels either to late endosomes and lysosomes where it is degraded or on to recycling tubules that return MHCI back to the cell surface. The new cargo proteins that we have identified (CD44, CD98, and CD147) show an altered itinerary in many cells where they traffic directly into the recycling tubules and avoid trafficking to late endosomal compartments. Consistent with this altered itinerary, we find that CD44, CD98 and CD147 are long-lived proteins and are not degraded like MHCI, which is routed to late endosomes. We recently showed that specific members of the MARCH family of E-3 ligases when expressed in cells target CD44 and CD98 for degradation.