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Human surfactant protein C (hSP-C1-197) is synthesized as a 197 amino acid p roprotein and cleaved to a mature 3.7 kD form. Although interstitial lung disea se in patients with mutations of the hSP-C gene is becoming increasingly recogn ized, the mechanisms linking molecular events with clinical pathogenesis are not fully defined. We describe a full-term infant with respiratory insufficiency a ssociated with a spontaneous heterozygous mutation resulting in a substitution o f lysine for glutamic acid at position 66 (= E66K) of the proximal hSP-C COOH f lanking propeptide. Lung histology and biochemical studies of the index patient (hSP-CE66K) revealed nonspecific interstitial pneumonia, increased alveolar tot al phospholipid lacking phosphatidylglycerol, and increased surfactant protein A . Localization of proSP-C from lung sections prepared from this patient using i mmunofluorescence 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 o f proSP-C, fusion proteins consisting of enhanced green fluorescent protein (EG FP) and hSP-C 1-197 (wild type)-or mutant hSP-CE66K were generated and trans fected into A549 cells. EGFP/hSP-C1-197 was expressed within CD-63-positive, EEA-1-negative vesicles, whereas EGFP/hSP-CE66K localized to EEA-1 positive vesicles. The E66K substitution is representative of a newclass of SP-Cmutatio n associated with interstitial lung disease that is diverted from the normal bio synthetic pathway. We propose that, similar to other storage disorders, lung inj ury results from induction of a toxic gain of function induced by the mutant pro duct that is subject to genetic modifiers and environmental influences.
Human surfactant protein C (hSP-C1-197) is synthesized as a 197 amino acid p roprotein and cleaved to a mature 3.7 kD form. Although interstitial lung disea se in patients with mutations of the hSP-C gene is becoming more recognized, the mechanisms linking molecular events with clinical pathogenesis are not fully defined. We describe a full-term infant with respiratory insufficiency a ssociated with a spontaneous heterozygous mutation resulting in a substitution of lysine for glutamic acid at position 66 (= E66K) of the proximal hSP -Ch COOH f lanking propeptide. Lung histology and biochemical studies of the index patient (hSP-CE66K) revealed nonspecific interstitial pneumonia, increased alveolar tot al phospholipid lacking phosphatidylglycerol, and increased surfactant protein A. Localization of proSP-C from lung sections prepared from this patient using i mmunofluorescence and immunogold electron microscopy revealed abnormal proSP-C staining in endosomal-like vesicles of typ e 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 (EG FP) and hSP-C 1-197 (wild type) -or EGFP / hSP-C1-197 was expressed within CD-63-positive, EEA-1-negative vesicles, EGFP / hSP-CE66K localized to EEA-1 positive vesicles. The proposed E66K substitution is representative of a new class of SP-Cmutatio n associated with interstitial lung disease that is diverted from the normal bio synthetic pathway. We propose that, similar to other storage disorders, lung inj ury results from induction of a toxic gain of function induced by the mutant pro duct that is subject to genetic modifiers and environmental influences.