The chocolate mutation, which is associated with oculocutaneous albinism in mice, has been attributed to a G146T transversion in the conserved GTP/GDP-interacting domain of Rab38, a small GTPase that regulates intracellular vesicular trafficking. Rab38 displays a unique tissue-specific expression pattern with highest levels present in the lung. The purpose of this study was to characterize the effects of Rab38-G146T on lung phenotype and to investigate the molecular basis of the mutant gene product (Rab38 cht protein). Chocolate lungs exhibited a uniform enlargement of the distal airspaces with mild alveolar destruction as well as a slight increase in lung compliance. Alveolar type II cells were engorged with lamellar bodies of increased size and number. Hydrophobic surfactant constituents (ie, phosphatidylcholine and surfactant protein B) were increased in lung tissues but decreased in alveolar spaces, consistent with a malfunction in lamellar body secretion and the subsequent cellular accumulation of these organelles. In contrast to wild-type Rab38, native Rab38 cht proteins were found to be hydrophilic and not bound to intracellular membranes. Unexpectedly, recombinant Rab38 cht proteins retained GTP-binding activity but failed to undergo prenyl modification that is required for membranebinding activity. These results suggest that the genetic abnormality of Rab38 affects multiple lysosome-related organelles , resulting in lung disease in addition to oculocutaneous albinism. (Am J

Several Long-Evans rat substrains carrying the phenotype of oculocutaneous albinism and bleeding diathesis are a rat model of Hermansky-Pudlak syndrome (HPS). The mutation responsible for the phenotype (Ruby) was identified as a point mutation in the initiation codon of Rab38 small GTPase that regulates intracellular vesicle transport. As patients with HPS often develop life-limiting interstitial pneumonia accompanied by abnormal morphology of alveolar type II cells, we investigated lung surfactant system in Long-Evans Cinnamon rats, one strain of the Ruby rats. The lungs showed conspicuous morphology of type II cells containing markedly enlarged lamellar bodies. Surfactant phosphatidylcholine and surfactant protein B were increased in lung tissues and lamellar bodies but not in alveolar lumen. Expression levels of mRNA for surfactant proteins A, B, C, and D were not altered. Isolated type II cells showed aberrant secretory pattern of newly synthesized [ 3 H]phosphatidylcholine, i.e., decreased basal secretion and remarkably amplified agonist-induced secretion.[ 3 H]phosphatidylcholine synthesis and uptake by type II cells were not altered. Thus Rab38-deficient type II cells appear to carry abnormality in lung surfactant secretion but not in synthesis or uptake. These results suggest that aberrant lung surfactant secretion may be involved in the pathogenesis of interstitial pneumonia in HPS.Ruby; Long-Evans Cinnamon rat; alveolar type II cells; lamellar body HERMANSKY-PUDLAK SYNDROME (HPS) is a rare autosomal recessive disorder resulting from abnormal trafficking relating to lysosome-related organelles such as melanosomes, platelet dense granules, and lamellar bodies in alveolar type II cells (10,29). HPS is clinically characterized by oculocutaneous albinism, bleeding diathesis, and, based on its genetic background, additional abnormalities such as progressive interstitial pneumonia. Interstitial pneumonia is the most serious complication arising in patients with HPS and has no effective therapy and is generally fatal by middle age. The lung histology show interstitial pneumonia characterized by enlarged alveolar type II cells that are fulfilled with giant lamellar bodies containing prominently increased surfactant phospholipids (16). It is possible that lung surfactant abnormalities may be closely related to lung pathology in HPS lungs.Several Long-Evans (LE) substrains including Fawn-hooded (FH) and Tester-Moriyama (TM) rats show oculocutaneous albinism and bleeding diathesis and hence are considered to be rat models of human HPS. The responsible gene Ruby was recently identified as Rab38 (18), a member of the Rab small GTPase family that regulates intracellular vesicle transport. A point mutation found in the initiation codon of Rab38 has been assumed to cause null translation of the protein. LE Cinnamon (LEC) rats, which carry ATP7B gene mutation and have been used as a rat model of Wilson disease (31), have also been identified as Ruby rats that harbor the Rab38 mutation (18). Thus Rab38 has been nominated...

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. Small GTP-binding proteins are a group of monomeric intracellular proteins that have GTP/GDP binding and GTPase activities, and mediate essential cell functions, including cell growth/differentiation, cytoskeletal configuration (cell movement, change of shape, and contraction and relaxation), and intracellular vesicle transport, including exocytosis and endocytosis. 1,2 The ras p21 was found first and was soon followed by several other proteins. Now, more than 50 members form a ras superfamily. They have highly conserved domains, contributing to interaction with guanine nucleotides, in organisms from yeast through mammals. Most of these proteins are prenylated at their carboxy termini and specific subsets are also modified by palmitoylation. The ras-related superfamily is now recognized as consisting of three major gene families (ras, rho, and rab) and other minor families.The rab family has more than 30 members, the largest number among small G proteins. The Rab proteins are known to localize to specific cell organelles, and are found in both membrane-bound and cytosolic forms. 2,3 Thus, they are believed to mediate intracellular vesicle transport among restricted intracellular compartments. Although current information in the sequence database indicates more than 30 members, there are few Rab proteins for which intracellular localization and function have been clarified.A novel cDNA has been cloned from the rat lung cDNA library encoding a rab-related small G protei...

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BackgroundCigarette smoke induced oxidative stress has been shown to reduce silent information regulator 1 (Sirt1) levels in lung tissue from smokers and patients with COPD patients. Sirt1 is known to inhibit endothelial senescence and may play a protective role in vascular cells. Endothelial progenitor cells (EPCs) are mobilized into circulation under various pathophysiological conditions, and are thought to play an important role in tissue repair in chronic obstructive lung disease (COPD). Therefore, Sirt1 and EPC-associated mRNAs were measured in blood samples from patients with COPD and from cultured CD34+ progenitor cells to examine whether these genes are associated with COPD development.MethodsThis study included 358 patients with a smoking history of more than 10 pack-years. RNA was extracted from blood samples and from CD34+ progenitor cells treated with cigarette smoke extract (CSE), followed by assessment of CD31, CD34, Sirt1 mRNA, miR-34a, and miR-126-3p expression by real-time RT-PCR.ResultsThe expression of CD31, CD34, Sirt1 mRNAs, and miR-126-3p decreased and that of miR-34a increased in moderate COPD compared with that in control smokers. However, no significant differences in these genes were observed in blood cells from patients with severe COPD compared with those in control smokers. CSE significantly decreased Sirt1 and increased miR-34a expression in cultured progenitor cells.ConclusionSirt1 expression in blood cells from patients with COPD could be a biomarker for disease stability in patients with moderate COPD. MiR-34a may participate in apoptosis and/or senescence of EPCs in smokers. Decreased expression of CD31, CD34, and miR-126-3p potentially represents decreased numbers of EPCs in blood cell from patients with COPD.