Nonspecific interstitial pneumonia, alveolar proteinosis, and abnormal proprotein trafficking resulting from a spontaneous mutation in the surfactant protein C gene.
Human surfactant protein C (hSP-C(1-197)) is synthesized as a 197 amino acid proprotein and cleaved to a mature 3.7 kD form. Although interstitial lung disease in patients with mutations of the hSP-C gene is becoming increasingly recognized, the mechanisms linking molecular events with clinical pathogenesis are not fully defined. We describe a full-term infant with respiratory insufficiency associated with a spontaneous heterozygous mutation resulting in a substitution of lysine for glutamic acid at position 66 (= E66K) of the proximal hSP-C COOH flanking propeptide. Lung histology and biochemical studies of the index patient (hSP-C(E66K)) revealed nonspecific interstitial pneumonia, increased alveolar total phospholipid lacking phosphatidylglycerol, and increased surfactant protein A. Localization of proSP-C from lung sections prepared from this patient using immunofluorescence and immunogold electron microscopy revealed abnormal proSP-C staining in endosomal-like vesicles of type II cells distinct from SP-B. To evaluate the effect of the E66K substitution on intracellular trafficking of proSP-C, fusion proteins consisting of enhanced green fluorescent protein (EGFP) and hSP-C(1-197) (wild type) or mutant hSP-C(E66K) were generated and transfected into A549 cells. EGFP/hSP-C(1-197) was expressed within CD-63-positive, EEA-1-negative vesicles, whereas EGFP/hSP-C(E66K) localized to EEA-1 positive vesicles. The E66K substitution is representative of a new class of SP-C mutation associated with interstitial lung disease that is diverted from the normal biosynthetic pathway. We propose that, similar to other storage disorders, lung injury results from induction of a toxic gain of function induced by the mutant product that is subject to genetic modifiers and environmental influences.
Stevens
Paul A
PA
Pulmonary and Critical Care Division, University of Pennsylvania School of Medicine, 421 Curie Blvd., Philadelphia, PA 19104-6160, USA.
Pettenazzo
Andrea
A
Brasch
Frank
F
Mulugeta
Surafel
S
Baritussio
Aldo
A
Ochs
Matthias
M
Morrison
Lake
L
Russo
Scott J
SJ
Beers
Michael F
MF
D015153:Blotting, Western; D018893:Bronchoalveolar Lavage; D045744:Cell Line, Tumor; D004247:DNA / Q000378:metabolism; D017931:DNA Primers / Q000737:chemistry; D018076:DNA, Complementary / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D018698:Glutamic Acid / Q000737:chemistry; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006801:Humans; D015151:Immunoblotting; D007150:Immunohistochemistry; D007223:Infant; D008168:Lung / Q000473:pathology; D017563:Lung Diseases, Interstitial / Q000235:genetics* / Q000473:pathology*; D008239:Lysine / Q000737:chemistry; D008297:Male; D008856:Microscopy, Fluorescence; D016253:Microscopy, Immunoelectron; D008858:Microscopy, Phase-Contrast; D008954:Models, Biological; D009154:Mutation; D010743:Phospholipids / Q000378:metabolism; D021381:Protein Transport; D011649:Pulmonary Alveolar Proteinosis / Q000235:genetics* / Q000473:pathology*; D037721:Pulmonary Surfactant-Associated Protein C / Q000235:genetics*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D013501:Surface-Active Agents / Q000378:metabolism; D013997:Time Factors; D014057:Tomography, X-Ray Computed; D014162:Transfection
D017931:DNA Primers; D018076:DNA, Complementary; D010743:Phospholipids; D037721:Pulmonary Surfactant-Associated Protein C; D011993:Recombinant Fusion Proteins; D013501:Surface-Active Agents; D049452:Green Fluorescent Proteins; D018698:Glutamic Acid; D004247:DNA; D008239:Lysine