Identification of LBM180, a lamellar body limiting membrane protein of alveolar type II cells, as the ABC transporter protein ABCA3.
Lamellar bodies are the specialized secretory organelles of alveolar type II (ATII) epithelial cells through which the cell packages pulmonary surfactant and regulates its secretion. Surfactant within lamellar bodies is densely packed as circular arrays of lipid membranes and appears to be the product of several trafficking and biosynthetic processes. To elucidate these processes, we reported previously on the generation of a monoclonal antibody (3C9) that recognizes a unique protein of the lamellar body membrane of 180 kDa, which we named LBM180. We report that mass spectrometry of the protein precipitated by this antibody generated a partial sequence that is identical to the ATP-binding cassette protein, ABCA3. Homology analysis of partial sequences suggests that this protein is highly conserved among species. The ABCA3 gene transcript was found in cell lines of human lung origin, in ATII cells of human, rat, and mouse, as well as different tissues of rat, but the highest expression of ABCA3 was observed in ATII cells. Expression of this transcript was at its maximum prior to birth, and hormonal induction of ABCA3 transcript was observed in human fetal lung at the same time as other surfactant protein transcripts were induced, suggesting that ABCA3 is developmentally regulated. Molecular and biochemical studies show that ABCA3 is targeted to vesicle membranes and is found in the limiting membrane of lamellar bodies. Because ABCA3 is a member of a subfamily of ABC transporters that are predominantly known to be involved in the regulation of lipid transport and membrane trafficking, we speculate that this protein may play a key role in lipid organization during the formation of lamellar bodies.
Mulugeta
Surafel
S
Institute for Environmental Medicine, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA.
Gray
Joseph M
JM
Notarfrancesco
Kathleen L
KL
Gonzales
Linda W
LW
Koval
Michael
M
Feinstein
Sheldon I
SI
Ballard
Philip L
PL
Fisher
Aron B
AB
Shuman
Henry
H
D018528:ATP-Binding Cassette Transporters / Q000502:physiology*; D000595:Amino Acid Sequence; D000818:Animals; D001692:Biological Transport; D015152:Blotting, Northern; D002454:Cell Differentiation; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D017124:Conserved Sequence; D046508:Culture Techniques; D004847:Epithelial Cells / Q000378:metabolism*; D006801:Humans; D015151:Immunoblotting; D050356:Lipid Metabolism; D008168:Lung / Q000196:embryology / Q000378:metabolism; D013058:Mass Spectrometry; D051379:Mice; D008854:Microscopy, Electron; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D020411:Oligonucleotide Array Sequence Analysis; D010196:Pancreatic Elastase / Q000378:metabolism; D011233:Precipitin Tests; D011485:Protein Binding; D011650:Pulmonary Alveoli / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D014018:Tissue Distribution; D014162:Transfection
C441524:ABCA3 protein, human; D018528:ATP-Binding Cassette Transporters; D012333:RNA, Messenger; D010196:Pancreatic Elastase