Glycosylation and secretion of surfactant-associated glycoprotein A.
Glycosylation and secretion of surfactant-associated glycoprotein A.
复制标题
DOI：
10.1016/s0021-9258(18)95731-5
复制
发表时间：
1985-12
期刊：
影响因子：
--
通讯作者：
J. Whitsett;G. Ross;T. Weaver;W. Rice;C. Dion;W. Hull
中科院分区：
文献类型：
--
作者：
J. Whitsett;G. Ross;T. Weaver;W. Rice;C. Dion;W. Hull
在分离的大鼠肺II型上皮细胞中发现了主要的表面活性物质相关蛋白糖蛋白A的合成。主要的分泌形式与天冬酰胺连接的复合型低聚糖以糖蛋白的形式迁移(32,000-36,000道尔顿，等电点4.2-4.8)。糖蛋白的初级体外翻译产物以约26,000道尔顿的五种不同蛋白的形式迁移到30,000-34,000道尔顿，内糖苷酶F敏感的形式。这些体外处理过的糖蛋白A与从[35S]蛋氨酸标记的II型细胞中免疫沉淀的细胞内形式共同迁移。用[35S]蛋氨酸标记的细胞进行的脉冲追逐实验表明，可以快速合成34,000道尔顿的内切糖苷酶敏感前体，等电点为4.7-4.8，这些前体既不是从II型细胞分泌的，也不是从肺泡灌洗液的表面活性物质中检测到的。这些高甘露糖形式被缓慢地加工成更酸性的、耐内糖苷酶H的、神经氨酸酶敏感的形式。在10~180min之间，完全唾液酸化或其他糖苷酶H抗性的形式是细胞内糖蛋白A的一小部分，16h后，细胞内糖蛋白A主要以内糖苷酶H抗性形式存在。成熟的唾液酸化糖蛋白A的分泌在标记后1h首次检测到，在16-24 h追踪期后也很容易检测到。衣霉素阻断N-连接蛋白的糖基化，导致三个主要的26,000道尔顿蛋白的合成，这些蛋白与肺泡灌洗液表面活性物质中存在的非糖化的表面活性相关蛋白A1以及大鼠肺多聚(A+)mRNA的主要体外翻译产物共同迁移。衣霉素抑制糖蛋白A.swainsonine的分泌，从而抑制高尔基体α-甘露糖苷酶II，完全抑制完全唾液酸化分子的合成。苦马豆素产生的糖蛋白A对神经氨酸酶和内切糖苷酶H都敏感，并且很容易分泌。莫能菌素是一种改变蛋白质运输的离子载体，它显著抑制细胞内唾液酸化和分泌。这些研究表明，肺II型细胞迅速合成和处理表面活性物质相关的糖蛋白A前体，形成内糖苷酶H敏感形式，这些形式在分泌之前被缓慢地唾液分析。
Synthesis of glycoprotein A, the major surfactant-associated protein, was demonstrated in Type II epithelial cells isolated from rat lung. Predominant, secreted forms migrated as glycoproteins with asparagine-linked, complex-type oligosaccharides (32,000-36,000 daltons, pI 4.2-4.8). Primary in vitro translation products of the glycoprotein migrated as five distinct proteins of approximately 26,000 daltons which were processed by pancreatic microsomal membranes in vitro to 30,000-34,000-dalton, endoglycosidase F-sensitive forms. These in vitro processed forms of glycoprotein A co-migrated with intracellular forms immunoprecipitated from [35S]methionine-labeled, Type II cells. Pulse-chase experiments with [35S]methionine-labeled cells demonstrated rapid synthesis of endoglycosidase H-sensitive precursors of 34,000 daltons, pI 4.7-4.8, which were neither secreted from Type II cells nor detected in surfactant from alveolar lavage. These high-mannose forms were slowly processed to more acidic, endoglycosidase H-resistant, neuraminidase-sensitive forms. At between 10 and 180 min, fully sialylated or other endoglycosidase H-resistant forms were a minor fraction of intracellular glycoprotein A. After 16 h, intracellular glycoproteins A were primarily present as endoglycosidase H-resistant forms. Secretion of mature, sialylated, glycoprotein A was first detected 1 h after labeling, and was also readily detected after 16-24 h chase period. Tunicamycin, which blocks N-linked protein glycosylation, resulted in synthesis of three major 26,000-dalton proteins which co-migrated with the nonglycosylated, surfactant-associated proteins A1 present in surfactant from alveolar lavage and with the major in vitro translation products of rat lung poly(A+) mRNA. Tunicamycin inhibited secretion of glycoprotein A. Swainsonine, which inhibits Golgi alpha-mannosidase II, completely inhibited synthesis of the fully sialylated molecule. Swainsonine produced forms of glycoprotein A which were both neuraminidase- and endoglycosidase H-sensitive and were readily secreted. Monensin, an ionophore that alters protein transport, markedly inhibited intracellular sialylation and secretion. These studies demonstrate that pulmonary Type II cells rapidly synthesize and process surfactant-associated glycoprotein A precursors to endoglycosidase H-sensitive forms, which are slowly sialylated prior to secretion.