Intracellular processing of pulmonary surfactant protein B in an endosomal/lysosomal compartment.
Intracellular processing of pulmonary surfactant protein B in an endosomal/lysosomal compartment.
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DOI：
10.1152/ajplung.1992.263.4.l479
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发表时间：
1992-10
期刊：
影响因子：
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通讯作者：
W. Voorhout;T. Veenendaal;H. Haagsman;T. Weaver;J. Whitsett;L.M.G. Van Golde;H. Geuze
中科院分区：
文献类型：
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作者：
W. Voorhout;T. Veenendaal;H. Haagsman;T. Weaver;J. Whitsett;L.M.G. Van Golde;H. Geuze
疏水性表面活性剂蛋白 B (SP-B) 在 II 型肺泡细胞中合成为 40 kDa 前体蛋白，通过 39 kDa 和 23 kDa 中间体加工成成熟的 8 kDa 大小。为了确定 SP-B 加工的位点，使用两种可区分 SP-B 前体形式和成熟形式的多克隆抗体，在人肺超薄冷冻切片上研究了 SP-B 前体形式和成熟形式的亚细胞分布。使用抗人溶酶体膜糖蛋白 CD63 的抗体来识别内体/溶酶体途径中的细胞器。前体 SP-B 存在于内质网、高尔基复合体和多泡体中，但不存在于层状体和质膜中。成熟的SP-B存在于多泡体和板层体中，但在内质网和高尔基复合体中几乎完全不存在。通过计数不同区室中代表前体或成熟 SP-B 的金颗粒对免疫金标记进行半定量评估，结果表明，成熟与前体的比率在内质网和高尔基复合体中较低（分别为 0.13 和 0.11），在多泡体中增加至 3.4，在板层体中很高（65）。多泡体和层状体含有溶酶体膜标记 CD63，因此是溶酶体途径的一部分。这些数据强烈表明，前体 SP-B 在细胞内在内体/溶酶体区室中（最有可能在多泡体中）被蛋白水解加工成其成熟的 8-kDa 形式。
The hydrophobic surfactant protein B (SP-B) is synthesized in alveolar type II cells as a 40-kDa precursor protein that is processed via 39- and 23-kDa intermediates to the mature 8-kDa size. To determine the site of SP-B processing, the subcellular distribution of the precursor and mature forms of SP-B was investigated on ultrathin cryosections of human lung using two polyclonal antibodies that discriminate between precursor forms and the mature form of SP-B. An antibody against the human lysosomal membrane glycoprotein CD63 was used to identify organelles in the endosomal/lysosomal pathway. Precursor SP-B was present in the endoplasmic reticulum, the Golgi complex, and multivesicular bodies but was absent from lamellar bodies and plasma membrane. Mature SP-B was present in multivesicular bodies and lamellar bodies but almost completely absent in the endoplasmic reticulum and the Golgi complex. Semiquantitative evaluation of the immunogold labeling by counting the gold particles representing precursor or mature SP-B in the different compartments showed that the mature-to-precursor ratio was low in the endoplasmic reticulum and the Golgi complex (0.13 and 0.11, respectively), increased in the multivesicular bodies to 3.4, and was very high (65) in lamellar bodies. Multivesicular bodies and lamellar bodies contain the lysosomal membrane marker CD63 and are therefore part of the lysosomal pathway. These data strongly suggest that precursor SP-B is proteolytically processed to its mature 8-kDa form intracellularly in an endosomal/lysosomal compartment, most probably in multivesicular bodies.