Gupta D K, Schmidt A, von Figura K, Hasilik A
Hoppe Seylers Z Physiol Chem. 1984 Aug;365(8):867-76. doi: 10.1515/bchm2.1984.365.2.867.
Precursors of cathepsin D and beta-hexosaminidase synthesized in the U937 monocyte line are processed to mature forms with similar kinetics as in fibroblasts. In U937 cells the processing of the precursor of the beta-chain of beta-hexosaminidase, however, results in a larger fragment that resembles a processing intermediate in fibroblasts. This difference is explained by differences in the equipment of the cells with proteinases, since cross-feeding of the precursors to the cells results in a processing characteristic for the recipient cell type. In sucrose gradients the precursors are found partly in a low- and partly in a high-density region. Mature polypeptides and activity of lysosomal enzymes fractionate mainly in the higher density region. In U937 cells the transport and maturation of endogenous lysosomal enzymes are less sensitive to bases (NH4Cl, chloroquine, tilorone) and to antibody against the mannose 6-phosphate specific receptors than in fibroblasts. A small portion of enzymes released from U937 cells contains the markers recognized by the mannose-6-phosphate specific receptors. U937 cells express these receptors and utilize them for transport of endogenous and exogenous lysosomal enzymes. It appears, however, that a fraction of lysosomal enzymes is transported in U937 cells independent of the mannose-6-phosphate-specific receptors.
在U937单核细胞系中合成的组织蛋白酶D和β-己糖胺酶的前体被加工成成熟形式，其动力学与成纤维细胞中的相似。然而，在U937细胞中，β-己糖胺酶β链前体的加工产生了一个更大的片段，类似于成纤维细胞中的加工中间体。这种差异可以用细胞中蛋白酶装备的差异来解释，因为将前体交叉投喂给细胞会导致受体细胞类型的加工特征。在蔗糖梯度中，前体部分存在于低密度区域，部分存在于高密度区域。成熟多肽和溶酶体酶的活性主要在较高密度区域分级。与成纤维细胞相比，在U937细胞中，内源性溶酶体酶的运输和成熟对碱（氯化铵、氯喹、泰洛龙）和针对甘露糖6-磷酸特异性受体的抗体不太敏感。从U937细胞释放的一小部分酶含有被甘露糖-6-磷酸特异性受体识别的标记。U937细胞表达这些受体，并利用它们运输内源性和外源性溶酶体酶。然而，似乎U937细胞中的一部分溶酶体酶的运输独立于甘露糖-6-磷酸特异性受体。
