| The intracellular routing, post-translational modification, and proteolytic processing of surfactant protein C (SP-C) were determined in Chinese hamster ovary cells expressing the human SP-C gene (CHO/SPC cells), murine fetal lung explant cultures, and primary cultures of rat Type II cells. ProSP-C was palmitoylated in CHO/SPC cells, murine fetal lung, and rat Type II cells and was associated with subcellular vesicles, consistent with the hypothesis that proSP-C traversed the endoplasmic reticulum (ER) and Golgi apparatus despite the lack of an amino terminal signal sequence. The amino terminus of proSP-C was protected from protease digestion after in vitro translation in the presence of canine microsomes, suggesting that proSP-C is inserted into the ER as a Type III transmembrane protein. Proteolytic processing intermediates containing the amino terminus of proSP-C were immunoprecipitated from radiolabeled rat Type II cells, demonstrating that the initial processing steps occur at the carboxy-terminus of proSP-C. The processing of 21 kDa proSP-C was blocked by incubation at 20... |
