Banting G, Maile R, Roquemore E P
Department of Biochemistry, University of Bristol, Bristol BS8 1TD, UK.
J Cell Sci. 1998 Dec;111 ( Pt 23):3451-8. doi: 10.1242/jcs.111.23.3451.
It has been shown previously that whilst the rat type I integral membrane protein TGN38 (ratTGN38) is predominantly localised to the trans-Golgi network this protein does reach the cell surface from where it is internalised and delivered back to the trans-Golgi network. This protein thus provides a suitable tool for the investigation of trafficking pathways between the trans-Golgi network and the cell surface and back again. The human orthologue of ratTGN38, humTGN46, behaves in a similar fashion. These proteins are internalised from the cell surface via clathrin mediated endocytosis, a process which is dependent upon the GTPase activity of dynamin. We thus reasoned that humTGN46 would accumulate at the surface of cells rendered defective in clathrin mediated endocytosis by virtue of the fact that they express a GTPase defective mutant of dynamin I. It did not. In fact, expression of a dominant negative GTPase defective mutant of dynamin I had no detectable effect on the steady state distribution of humTGN46. One explanation for this observation is that humTGN46 does not travel directly to the cell surface from the trans-Golgi network. Further studies on cells expressing the dominant negative GTPase defective mutant of dynamin I indicate that the major recycling pathway for humTGN46 is in fact between the trans-Golgi network and the early endosome.
先前的研究表明，大鼠I型整合膜蛋白TGN38（ratTGN38）主要定位于反式高尔基体网络，但该蛋白确实能到达细胞表面，并从那里内化后再运回反式高尔基体网络。因此，这种蛋白为研究反式高尔基体网络与细胞表面之间以及再返回的运输途径提供了一个合适的工具。大鼠TGN38的人类同源物humTGN46也有类似的行为。这些蛋白通过网格蛋白介导的内吞作用从细胞表面内化，这一过程依赖于发动蛋白的GTP酶活性。因此我们推断，humTGN46会在因表达发动蛋白I的GTP酶缺陷型突变体而导致网格蛋白介导的内吞作用有缺陷的细胞表面积累。但事实并非如此。实际上，发动蛋白I的显性负性GTP酶缺陷型突变体的表达对humTGN46的稳态分布没有可检测到的影响。对此观察结果的一种解释是，humTGN46并非直接从反式高尔基体网络运输到细胞表面。对表达发动蛋白I的显性负性GTP酶缺陷型突变体的细胞的进一步研究表明，humTGN46的主要再循环途径实际上是在反式高尔基体网络和早期内体之间。
