A novel surfactant protein C L55F mutation associated with interstitial lung disease alters subcellular localization of proSP-C in A549 cells

Background: Heterozygous mutations of SFTPC , the gene-encoding surfactant protein C (SP-C), result in interstitial lung disease (ILD). However, characterization of mutations located in the mature domain of precursor SP-C (proSP-C) is limited. This study examined the molecular pathogenesis of such a mutation of ILD. Methods: We employed sequencing of SFTPC and established A549 cells stably expressing several proSP-C mutants. Histopathology and transmission electron microscopy (TEM) of lung tissue from a pediatric patient with ILD were assessed. Effects of mutant proSP-C were evaluated by western blotting, immunofluorescence, and TEM. Results: Sequencing of SFTPC revealed a novel heterozygous mutation, c.163C>T (L55F). In lung tissue, abnormal localization of proSP-C was observed by immunohistochemistry, and small and dense lamellar bodies (LBs) in type II alveolar epithelial cells (AECs) were detected by TEM. TEM of A549 cells stably expressing proSP-C L55F displayed abnormal cytoplasmic organelles. ProSP-C L55F exhibited a band pattern similar to that of proSP-C WT for processed intermediates. Immunofluorescence studies demonstrated that proSP-C L55F partially colocalized in CD63-positive cytoplasmic vesicles of A549 cells, which was in contrast to proSP-C WT . Conclusion: We detected a novel c.163C>T mutation located in the mature domain of SFTPC associated with ILD that altered the subcellular localization of proSP-C in A549 cells.