Post-translational processing of surfactant protein c in rat type ii cells. Vorbroker, Diane K., Wim F. Voorhout, Timothy E. Weaver, Jeffrey A. Whitsett. Children's Hospital Medical Center, Division of Pulmonary Biology, Cincinnati, OH, 45229-3039; and *Department of Functional Morphology and Laboratory of Veterinary Biochemistry, University of Utrecht, Utrecht, Netherlands
APStracts 2:0121L, 1995.
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 amino terminus 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 amino terminus of proSP-C. Proteolytic processing of proSP-C was inhibited by incubation at 20 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 amino-terminus 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 multi- vesicular bodies before SP-C is incorporated into lamellar bodies. 

Received 16 February 1995; accepted in final form 11 July 1995.
APS Manuscript Number L50-5.
Article publication pending Am. J. Physiol. (Lung Cell. Mol.
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 30 July 1995.