Functional characterization of human organic cation transporter OCTN1 single nucleotide polymorphisms in the Japanese population.
The organic cation transporter OCTN1 (SLC22A4) is expressed ubiquitously, with strong expression in kidney, trachea, bone marrow, and fetal liver, and it mediates transport of organic cations in a pH-dependent manner. Recent studies have identified single nucleotide polymorphisms (SNPs) of OCTN1 in the Japanese population. Two SNPs present in the exon regions, c1063t and g1531a, cause amino acid mutation, Thr306Ile (T306I) and Gly462Glu (G462E), respectively. We examined the influence of these SNPs on the intracellular localization, protein expression, and transport activity of OCTN1. Immunocytochemical analysis showed similar localizations of OCTN1 in cellular membranes of HEK293 cells transiently transfected with an expression plasmid DNA for OCTN1 or its SNP allelic variants. The Km and Vmax values for tetraethylammonium (TEA) uptake by T306I were similar to those of the wild-type even when the Vmax value was normalized for the expression level of OCTN1 protein. In contrast, G462E had almost negligible transport activity, although the protein expression level of G462E was equivalent to that of the wild-type. We conclude that the SNP that causes the single amino acid mutation T306I does not affect TEA transport activity, whereas the mutation G462E abrogates the TEA transport activity, presumably affecting the physiological function of OCTN1 and/or the pharmacological characteristics of its substrates.
Kawasaki
Yuki
Y
Division of Pharmaceutical Science, Graduate School of Natural Science and Technology, Kanazawa University, Kakuma-machi, Kanazawa, Ishikawa 920-1192, Japan.
Kato
Yukio
Y
Sai
Yoshimichi
Y
Tsuji
Akira
A
D044466:Asian People / Q000235:genetics; D002460:Cell Line; D005786:Gene Expression Regulation / Q000502:physiology; D006801:Humans; D026901:Membrane Transport Proteins / Q000096:biosynthesis / Q000235:genetics*; D027701:Organic Cation Transport Proteins; D020641:Polymorphism, Single Nucleotide / Q000235:genetics*; D013379:Substrate Specificity; D027981:Symporters
D026901:Membrane Transport Proteins; D027701:Organic Cation Transport Proteins; C109807:SLC22A4 protein, human; D027981:Symporters