Cloning and characterization of a novel human pH-dependent organic cation transporter, OCTN1.
cDNA for a novel proton/organic cation transporter, OCTN1, was cloned from human fetal liver and its transport activity was investigated. OCTN1 encodes a 551-amino acid protein with 11 transmembrane domains and one nucleotide binding site motif. It is strongly expressed in kidney, trachea, bone marrow and fetal liver and in several human cancer cell lines, but not in adult liver. When expressed in HEK293 cells, OCTN1 exhibited saturable and pH-dependent [3H]tetraethyl ammonium uptake with higher activity at neutral and alkaline pH than at acidic pH. Furthermore, treatment with metabolic inhibitors reduced the uptake, which is consistent with the presence of the nucleotide binding site sequence motif. Although its subcellular localization and detailed functional characteristics are not clear at present, OCTN1 appears to be a novel proton antiporter that functions for active secretion of cationic compounds across the renal epithelial brush-border membrane. It may play a role in the renal excretion of xenobiotics and their metabolites.
Tamai
I
I
Faculty of Pharmaceutical Sciences, Kanazawa University, Japan.
Yabuuchi
H
H
Nezu
J
J
Sai
Y
Y
Oku
A
A
Shimane
M
M
Tsuji
A
A
D000255:Adenosine Triphosphate / Q000502:physiology; D000328:Adult; D000595:Amino Acid Sequence; D002352:Carrier Proteins / Q000235:genetics* / Q000502:physiology; D002412:Cations; D002460:Cell Line; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D005333:Fetus; D018507:Gene Expression Regulation, Developmental / Q000502:physiology*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D017136:Ion Transport / Q000235:genetics; D007668:Kidney; D007700:Kinetics; D008099:Liver; D008565:Membrane Proteins / Q000235:genetics* / Q000502:physiology; D026901:Membrane Transport Proteins; D008969:Molecular Sequence Data; D009928:Organ Specificity; D027701:Organic Cation Transport Proteins; D012333:RNA, Messenger / Q000032:analysis; D027981:Symporters; D019789:Tetraethylammonium / Q000378:metabolism*
D002352:Carrier Proteins; D002412:Cations; D018076:DNA, Complementary; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D027701:Organic Cation Transport Proteins; D012333:RNA, Messenger; C109807:SLC22A4 protein, human; D027981:Symporters; D019789:Tetraethylammonium; D000255:Adenosine Triphosphate