Posttranslational processing of surfactant protein C in rat type II cells.
Pulmonary surfactant consists of phospholipids and proteins that form a stable monolayer at the surface of the alveoli to prevent lung collapse. Surfactant protein C (SP-C) is a hydrophobic 4-kDa palmitoylated protein derived from a 21-kDa precursor. We determined the membrane insertion, proteolytic processing, and subcellular location of 21-kDa proSP-C. In vitro, proSP-C associated with canine microsomes, and the NH2-terminal of proSP-C was protected from digestion with proteinase K, suggesting that proSP-C was inserted in a type III transmembrane configuration. Treatment of freshly isolated rat type II cells with cerulenin blocked acylation of the 21-kDa precursor. Pulse-chase labeling of type II cells demonstrated proSP-C processing intermediates of 19, 16, and 13 kDa that contained the NH2-terminal of proSP-C. Proteolytic processing of proSP-C was inhibited by incubation at 20 degrees C, suggesting that processing of proSP-C begins in a late Golgi or post-Golgi compartment. Immunogold labeling of rat lung with an antiserum to the NH2-terminal of proSP-C identified proSP-C in the trans-Golgi and multivesicular bodies but not in lamellar bodies. These findings suggest that proSP-C processing takes place in the trans-Golgi and multivesicular bodies before SP-C is incorporated into lamellar bodies.
Vorbroker
D K
DK
Children's Hospital Medical Center, Division of Pulmonary Biology, Cincinnati, Ohio 45229-3039, USA.
Voorhout
W F
WF
Weaver
T E
TE
Whitsett
J A
JA
D000818:Animals; D002569:Cerulenin / Q000494:pharmacology; D004285:Dogs; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D010447:Peptide Hydrolases / Q000378:metabolism; D014176:Protein Biosynthesis; D011499:Protein Processing, Post-Translational; D011510:Proteolipids / Q000378:metabolism*; D011650:Pulmonary Alveoli / Q000166:cytology / Q000378:metabolism*; D011663:Pulmonary Surfactants / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013696:Temperature; D013997:Time Factors
D011510:Proteolipids; D011663:Pulmonary Surfactants; D002569:Cerulenin; D010447:Peptide Hydrolases