McIntosh D, Timar J, Davies A J
Department of Pharmacy, University of Manchester, United Kingdom.
Eur J Cell Biol. 1990 Jun;52(1):77-86.
The binding, internalization and recycling of the plant toxin ricin, was studied using electron microscopy and biochemical techniques. For the electron microscope study, ricin was visualized using a gold-labeled second antibody, in the cells of the EJ human bladder carcinoma line growing in monolayer culture. The labeled antibody/toxin complex was found to enter the cell in coated pits and to accumulate in endosomes and to a lesser extent in vesicles associated with the Golgi system. The complex recycled to the cell surface partly in uncoated vesicles, but largely in multivesicular bodies which appeared to exocytose their contents to the extracellular space. Twenty hours after the initial contact with ricin as much as 50% of the cellular label was found on the cell surface mainly associated with shed vesicles. When cells were treated with unlabeled ricin holotoxin and then after 20 h stained post-fixation, ricin molecules, partly associated with vesicles, were present on the cell surface. Biochemical studies showed that ricin was internalized by cells and then released in an intact form to the extracellular space. It was found that less than 10% of the released material had been degraded during its passage through the cells, which is in accord with the low level of label found in the lysosomal system during the morphological study.
利用电子显微镜和生化技术研究了植物毒素蓖麻毒素的结合、内化和循环。在单层培养中生长的EJ人膀胱癌细胞系的细胞中，为进行电子显微镜研究，使用金标记的二抗对蓖麻毒素进行可视化。发现标记的抗体/毒素复合物通过有被小窝进入细胞，并在内体中积累，在较小程度上也在与高尔基体系统相关的囊泡中积累。该复合物部分通过无被囊泡循环至细胞表面，但主要通过多泡体循环，多泡体似乎将其内容物胞吐到细胞外空间。在与蓖麻毒素初次接触20小时后，发现多达50%的细胞标记物出现在细胞表面，主要与脱落的囊泡相关。当用未标记的蓖麻毒素全毒素处理细胞，然后在20小时后进行后固定染色时，部分与囊泡相关的蓖麻毒素分子出现在细胞表面。生化研究表明，蓖麻毒素被细胞内化，然后以完整形式释放到细胞外空间。研究发现，释放的物质在通过细胞的过程中降解的不到10%，这与形态学研究中在溶酶体系统中发现的低标记水平一致。
