title: Expression and localization of a novel Rab small G protein (Rab38) in the rat lung.
abstract: 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.
authors.affiliation: Department of Internal Medicine, Division of Respiratory Disease, Kanazawa Medical University, Ishikawa, Japan. k-osanai@kanazawa-med.ac.jp
authors.forename: K
authors.initials: K
authors.lastname: Osanai
authors.forename: M
authors.initials: M
authors.lastname: Iguchi
authors.forename: K
authors.initials: K
authors.lastname: Takahashi
authors.forename: Y
authors.initials: Y
authors.lastname: Nambu
authors.forename: T
authors.initials: T
authors.lastname: Sakuma
authors.forename: H
authors.initials: H
authors.lastname: Toga
authors.forename: N
authors.initials: N
authors.lastname: Ohya
authors.forename: H
authors.initials: H
authors.lastname: Shimizu
authors.forename: J H
authors.initials: JH
authors.lastname: Fisher
authors.forename: D R
authors.initials: DR
authors.lastname: Voelker
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D015870:Gene Expression; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D008168:Lung / Q000737:chemistry / Q000378:metabolism*; D016676:Macrophages, Alveolar / Q000166:cytology / Q000378:metabolism; D008297:Male; D008969:Molecular Sequence Data; D011650:Pulmonary Alveoli / Q000166:cytology / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D013047:Specific Pathogen-Free Organisms; D020691:rab GTP-Binding Proteins / Q000235:genetics* / Q000378:metabolism
chemical_list: D012333:RNA, Messenger; C498787:Rab38 protein, rat; D020691:rab GTP-Binding Proteins