Sorting of two polytopic proteins, the gamma-aminobutyric acid and betaine transporters, in polarized epithelial cells.
The gamma-aminobutyric acid transporter (GAT-1) isoform of the gamma-aminobutyric acid and the betaine (BGT) transporters exhibit distinct apical and basolateral distributions when introduced into Madin-Darby canine kidney cells (Pietrini, G., Suh, Y. J., Edelman, L., Rudnick, G., and Caplan, M. J. (1994) J. Biol. Chem. 269, 4668-4674). We have investigated the presence of sorting signals in their COOH-terminal cytosolic domains by expression in Madin-Darby canine kidney cells of mutated and chimeric transporters. Whereas truncated GAT-1 (DeltaC-GAT) maintained the original functional activity and apical localization, either the removal (DeltaC-myc BGT) or the substitution (BGS chimera) of the cytosolic tail of BGT generated proteins that accumulated in the endoplasmic reticulum. Moreover, we have found that the cytosolic tail of BGT redirected apical proteins, the polytopic GAT-1 (GBS chimera) and the monotopic human nerve growth factor receptor, to the basolateral surface. These results suggest the presence of basolateral sorting information in the cytosolic tail of BGT. We have further shown that information necessary for the exit of BGT from the endoplasmic reticulum and for the basolateral localization of the GBS chimera is contained in a short segment, rich in basic residues, within the cytosolic tail of BGT.
Perego
C
C
Consiglio Nazionale delle Ricerche Cellular and Molecular Pharmacology Center, Department of Pharmacology, University of Milan, Milan 20129, Italy.
Bulbarelli
A
A
Longhi
R
R
Caimi
M
M
Villa
A
A
Caplan
M J
MJ
Pietrini
G
G
D000595:Amino Acid Sequence; D000818:Animals; D001692:Biological Transport; D002352:Carrier Proteins / Q000378:metabolism* / Q000648:ultrastructure; D002451:Cell Compartmentation; D002460:Cell Line; D002462:Cell Membrane / Q000648:ultrastructure*; D016764:Cell Polarity; D003600:Cytosol / Q000648:ultrastructure; D004285:Dogs; D004721:Endoplasmic Reticulum / Q000378:metabolism; D019084:Fluorescent Antibody Technique, Indirect; D050485:GABA Plasma Membrane Transport Proteins; D006801:Humans; D008565:Membrane Proteins / Q000378:metabolism* / Q000648:ultrastructure; D026901:Membrane Transport Proteins; D008969:Molecular Sequence Data; D027361:Organic Anion Transporters; D017475:Receptors, Nerve Growth Factor / Q000737:chemistry / Q000378:metabolism; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins; D013329:Structure-Activity Relationship; D014162:Transfection
D002352:Carrier Proteins; D050485:GABA Plasma Membrane Transport Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D027361:Organic Anion Transporters; D017475:Receptors, Nerve Growth Factor; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins; C493413:SLC6A1 protein, human; C072207:betaine plasma membrane transport proteins