Geuze H J, Slot J W, Strous G J, Hasilik A, von Figura K
J Cell Biol. 1985 Dec;101(6):2253-62. doi: 10.1083/jcb.101.6.2253.
Immunogold double-labeling and ultrathin cryosections were used to compare the subcellular distribution of albumin, mannose 6-phosphate receptor (MPR), galactosyltransferase, and the lysosomal enzymes cathepsin D, beta-hexosaminidase, and alpha-glucosidase in Hep G2 cells. MPR and lysosomal enzymes were found throughout the stack of Golgi cisternae and in a trans-Golgi reticulum (TGR) of smooth-surfaced tubules with coated buds and vesicles. The trans-Golgi orientation of TGR was ascertained by the co-localization with galactosyltransferase. MPR was particularly abundant in TGR and CURL, the compartment of uncoupling receptors and ligands. Both TGR and CURL also contained lysosomal enzymes, but endogenous albumin was detected in TGR only. The coated buds on TGR tubules contained MPR, lysosomal enzymes, as well as albumin. MPR and lysosomal enzymes were also found in coated pits of the plasma membrane. CURL tubules seemed to give rise to smooth vesicles, often of the multivesicular body type. In CURL, the enzymes were found in the lumina of the smooth vesicles while MPR prevailed in the tubules. These observations suggest a role of CURL in transport of lysosomal enzymes to lysosomes. When the cells were treated with the lysosomotropic amine primaquine, binding of anti-MPR to the cells in culture was reduced by half. Immunocytochemistry showed that MPR accumulated in TGR, especially in coated buds. Since these buds contain endogenous albumin and lysosomal enzymes also, these data suggest that coated vesicles originating from TGR provide for a secretory route in Hep G2 cells and that this pathway is followed by the MPR system as well.
采用免疫金双标记和超薄冷冻切片技术，比较白蛋白、甘露糖6 - 磷酸受体（MPR）、半乳糖基转移酶以及溶酶体酶组织蛋白酶D、β - 己糖胺酶和α - 葡萄糖苷酶在肝癌细胞系Hep G2中的亚细胞分布。在整个高尔基体潴泡堆栈以及具有被膜小芽和小泡的光滑表面小管的反式高尔基体网状结构（TGR）中发现了MPR和溶酶体酶。通过与半乳糖基转移酶的共定位确定了TGR的反式高尔基体取向。MPR在TGR和CURL（解偶联受体和配体的区室）中特别丰富。TGR和CURL也都含有溶酶体酶，但仅在TGR中检测到内源性白蛋白。TGR小管上的被膜小芽含有MPR、溶酶体酶以及白蛋白。在质膜的被膜小窝中也发现了MPR和溶酶体酶。CURL小管似乎产生光滑小泡，通常是多囊泡体类型。在CURL中，酶存在于光滑小泡的腔内，而MPR在小管中占优势。这些观察结果表明CURL在溶酶体酶向溶酶体的转运中起作用。当用溶酶体亲和胺伯氨喹处理细胞时，抗MPR与培养细胞的结合减少了一半。免疫细胞化学显示MPR在TGR中积累，特别是在被膜小芽中。由于这些小芽也含有内源性白蛋白和溶酶体酶，这些数据表明源自TGR的被膜小泡在Hep G2细胞中提供了一条分泌途径，并且MPR系统也遵循这条途径。
