Clift-O'Grady L, Linstedt A D, Lowe A W, Grote E, Kelly R B
Department of Biochemistry and Biophysics, University of California, San Francisco 94143-0448.
J Cell Biol. 1990 May;110(5):1693-703. doi: 10.1083/jcb.110.5.1693.
The presence of unique proteins in synaptic vesicles of neurons suggests selective targeting during vesicle formation. Endocrine, but not other cells, also express synaptic vesicle membrane proteins and target them selectively to small intracellular vesicles. We show that the rat pheochromocytoma cell line, PC12, has a population of small vesicles with sedimentation and density properties very similar to those of rat brain synaptic vesicles. When synaptophysin is expressed in nonneuronal cells, it is found in intracellular organelles that are not the size of synaptic vesicles. The major protein in the small vesicles isolated from PC12 cells is found to be synaptophysin, which is also the major protein in rat brain vesicles. At least two of the minor proteins in the small vesicles are also known synaptic vesicle membrane proteins. Synaptic vesicle-like structures in PC12 cells can be shown to take up an exogenous bulk phase marker, HRP. Their proteins, including synaptophysin, are labeled if the cells are surface labeled and subsequently warmed. Although the PC12 vesicles can arise by endocytosis, they seem to exclude the receptor-mediated endocytosis marker, transferrin. We conclude that PC12 cells contain synaptic vesicle-like structures that resemble authentic synaptic vesicles in physical properties, protein composition and endocytotic origin.
神经元突触小泡中独特蛋白质的存在表明在小泡形成过程中存在选择性靶向。内分泌细胞而非其他细胞也表达突触小泡膜蛋白，并将它们选择性地靶向到小的细胞内小泡。我们发现大鼠嗜铬细胞瘤细胞系PC12有一群小泡，其沉降和密度特性与大鼠脑突触小泡非常相似。当突触素在非神经元细胞中表达时，它存在于大小并非突触小泡的细胞内细胞器中。从PC12细胞中分离出的小泡中的主要蛋白质被发现是突触素，它也是大鼠脑小泡中的主要蛋白质。小泡中至少两种次要蛋白质也是已知的突触小泡膜蛋白。PC12细胞中的突触小泡样结构可摄取外源性总体积标记物辣根过氧化物酶（HRP）。如果对细胞进行表面标记并随后升温，其蛋白质（包括突触素）会被标记。尽管PC12小泡可通过内吞作用产生，但它们似乎排除了受体介导的内吞标记物转铁蛋白。我们得出结论，PC12细胞含有突触小泡样结构，这些结构在物理性质、蛋白质组成和内吞起源方面类似于真正的突触小泡。
