James H. Fisher

Isolation and sequence of a cDNA clone for the rat pulmonary surfactant-associated protein (PSP-A)

Pulmonary surfactant is composed mainly of phospholipid and two groups of apoproteins. One of these apoproteins is a family of glycoproteins (pulmonary surfactant-associated protein A, PSP-A). We have isolated and sequenced a cDNA clone encoding for rat PSP-A and the full amino acid sequence has been deduced from the nucleotide sequence. The sequence of 56 amino acids at the N-terminus of PSP-A isolated from rats treated with silica was determined independently, and there is complete agreement with the sequence deduced from the cDNA. Isolated rat alveolar type II cells contain two species of mRNA for this protein.

Expression and Localization of a Novel Rab Small G Protein (Rab38) in the Rat Lung

The Rab small G protein family participates in intracellular vesicle transport, including exocytosis and endocytosis. The cDNA encoding a novel Rab-related small G protein (Rab38) has been cloned from rat lung cDNA library and recorded in GenBank (accession no. M94043). However, the expression and localization of the protein in the lung remains primarily unknown. We produced polyhistidine-tagged recombinant Rab38 and a polyclonal antibody with a synthetic peptide. Immunohistochemistry demonstrated that the protein is specifically localized in alveolar type II cells and in bronchial epithelial cells. In situ hybridization using a digoxygenin-labeled RNA riboprobe clearly showed that the mRNA of the protein is localized in alveolar type II cells and bronchial epithelial cells, especially terminal airway epithelial cells. Western blot and reverse transcriptase-polymerase chain reaction showed distinct expression of the protein and mRNA in isolated alveolar type II cells, but not in alveolar macrophages. The native protein was predominantly hydrophobic and was enriched in a high-density vesicle fraction but was barely detectable in nuclear and lamellar body fractions in alveolar type II cells. Immunofluorescence cytochemistry performed on cultured alveolar type II cells showed that Rab38 distributed extensively in the cytoplasm with a distribution pattern similar to endoplasmic reticulum rather than other subcellular organelles. These results suggest that this novel rab small G protein (Rab38) mediates vesicular transport in terminal airway epithelium.