Expression of the amino acid transporter ATB 0+ in lung: possible role in luminal protein removal.
Normal lung function requires transepithelial clearance of luminal proteins; however, little is known about the molecular mechanisms of protein transport. Protein degradation followed by transport of peptides and amino acids may play an important role in this process. We previously cloned and functionally characterized the neutral and cationic amino acid transporter ATB(0+) and showed expression in the lung by mRNA analysis. In this study, the tissue distribution, subcellular localization, and function of the transporter in native tissue were investigated. Western blots showed expression of the ATB(0+) protein in mouse lung, stomach, colon, testis, blastocysts, and human lung. Immunohistochemistry revealed that ATB(0+) is predominantly expressed on the apical membrane of ciliated epithelial cells throughout mouse airways from trachea to bronchioles and in alveolar type I cells. Electrical measurements from mouse trachea preparations showed Na(+)- and Cl(-)-dependent, amino acid-induced short-circuit current consistent with the properties of ATB(0+). We hypothesize that, by removing amino acids from the airway lumen, the transporter contributes to protein clearance and, by maintaining a low nutrient environment, plays a role in lung defense.
Sloan
Jennifer L
JL
Department of Cell and Molecular Physiology and the Cystic Fibrosis/Pulmonary Research and Treatment Center, University of North Carolina, Chapel Hill, NC 27599, USA.
Grubb
Barbara R
BR
Mager
Sela
S
D026962:Amino Acid Transport System ASC / Q000502:physiology*; D000818:Animals; D015153:Blotting, Western; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D004563:Electrochemistry; D004847:Epithelial Cells / Q000378:metabolism; D006801:Humans; D007150:Immunohistochemistry; D008168:Lung / Q000378:metabolism*; D051379:Mice; D015778:Minor Histocompatibility Antigens; D012333:RNA, Messenger / Q000378:metabolism; D012137:Respiratory System / Q000166:cytology / Q000378:metabolism; D013347:Subcellular Fractions / Q000378:metabolism; D014018:Tissue Distribution
D026962:Amino Acid Transport System ASC; D015778:Minor Histocompatibility Antigens; D012333:RNA, Messenger; C420506:SLC1A5 protein, human; C498850:Slc1a5 protein, mouse