Voorhout W F, Weaver T E, Haagsman H P, Geuze H J, Van Golde L M
Laboratory of Veterinary Biochemistry, University of Utrecht, The Netherlands.
Microsc Res Tech. 1993 Dec 1;26(5):366-73. doi: 10.1002/jemt.1070260504.
Surfactant proteins A, B, and C (SP-A, SP-B, and SP-C) are synthesized in alveolar type II cells. SP-B and SP-C are both synthesized as large precursor molecules that are proteolytically processed to their mature sizes. In a previous immunoelectron microscopic study, we showed that precursor SP-B is processed to its mature size in multivesicular bodies. In the present study, using a specific antibody against precursor SP-C, we demonstrate that precursor SP-C is present in the same intracellular compartments of the biosynthetic pathway, i.e., endoplasmic reticulum, Golgi complex, and multivesicular bodies, as precursor SP-B. Since mature SP-C is known to be present in multilamellar bodies, this suggests a biosynthetic routing and site of processing of this protein similar to those of SP-B. Double-labeling experiments using antibodies against SP-A, precursor SP-B, precursor SP-C, and an antibody against HA I, an adaptor protein involved in the budding of transport vesicles from the Golgi complex, showed that the different surfactant proteins traverse and exit the Golgi complex via the same route. The surfactant proteins do not exit the Golgi complex via HA I-positive coated buds or vesicles. These data are in accordance with the concept that SP-A, SP-B, and SP-C are transported together through the same biosynthetic pathway via multivesicular bodies to multilamellar bodies.
表面活性蛋白A、B和C（SP-A、SP-B和SP-C）在肺泡II型细胞中合成。SP-B和SP-C均作为大的前体分子合成，经蛋白水解加工成成熟大小。在先前的免疫电子显微镜研究中，我们发现前体SP-B在多囊泡体中加工成成熟大小。在本研究中，使用针对前体SP-C的特异性抗体，我们证明前体SP-C与前体SP-B一样，存在于生物合成途径的相同细胞内区室，即内质网、高尔基体和多囊泡体中。由于已知成熟的SP-C存在于多层小体中，这表明该蛋白的生物合成途径和加工位点与SP-B相似。使用针对SP-A、前体SP-B、前体SP-C的抗体以及针对HA I（一种参与从高尔基体出芽转运小泡的衔接蛋白）的抗体进行的双标记实验表明，不同的表面活性蛋白通过相同途径穿过并离开高尔基体。表面活性蛋白不会通过HA I阳性被膜小芽或小泡离开高尔基体。这些数据与以下概念一致，即SP-A、SP-B和SP-C通过多囊泡体一起通过相同的生物合成途径转运到多层小体。
