Requirement of the collagenous domain for carbohydrate processing and secretion of a surfactant protein, SP-A.
Two distinct intracellular forms of surfactant protein Mr = 35,000 (SP-A) were demonstrated in both purified type II epithelial cells and rat lung in vivo. High-mannose precursors of Mr = 30,000 and 34,000 comprised a significant fraction of intracellular SP-A in vivo and in vitro. A second intracellular pool was demonstrated in lamellar body enriched fractions, which contained endoglycosidase-H resistant, sialylated forms of SP-A. Intracellular transport and secretion of SP-A was not altered by inhibitors of carbohydrate processing. However, incubation of type II cells with alpha,alpha'-dipyridyl or cis-4-hydroxy-L-proline, agents which disrupt triple-helix formation within collagenous peptide domains, inhibited sialylation, intracellular transport to the lamellar body fraction and secretion. In the presence of either alpha,alpha'-dipyridyl or cis-4-hydroxy-L-proline, high mannose precursors accumulated intracellularly and were not secreted after 16-18 h. Thus, high-mannose precursors in proximal intracellular pool(s) and sialylated forms in lamellar body-enriched fractions represent two major intracellular storage forms of SP-A in vitro and in vivo. SP-A is routed by processes dependent upon the hydroxylation of the collagenous domain of the polypeptide. Transport and secretion of SP-A are not dependent upon the addition or processing of asparagine-linked carbohydrate.
O'Reilly
M A
MA
University of Cincinnati, College of Medicine, Department of Pediatrics, OH 45267-0541.
Nogee
L
L
Whitsett
J A
JA
D000135:Acid Phosphatase / Q000096:biosynthesis; D000818:Animals; D002458:Cell Fractionation / Q000379:methods; D002478:Cells, Cultured; D002499:Centrifugation, Density Gradient / Q000379:methods; D003094:Collagen; D006023:Glycoproteins / Q000235:genetics*; D008168:Lung / Q000166:cytology / Q000378:metabolism*; D008297:Male; D009940:Organoids / Q000378:metabolism / Q000648:ultrastructure; D011499:Protein Processing, Post-Translational; D011510:Proteolipids / Q000096:biosynthesis / Q000235:genetics*; D037662:Pulmonary Surfactant-Associated Protein A; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants / Q000096:biosynthesis / Q000235:genetics*; D051381:Rats; D011919:Rats, Inbred Strains; D013347:Subcellular Fractions / Q000378:metabolism
D006023:Glycoproteins; D011510:Proteolipids; D037662:Pulmonary Surfactant-Associated Protein A; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants; D003094:Collagen; D000135:Acid Phosphatase