Functional effects of protein sequence polymorphisms in the organic cation/ergothioneine transporter OCTN1 (SLC22A4)
Departments of aBiopharmaceutical Sciences, University of California San Francisco, San Francisco, California, USA. Pharmacogenetics and Genomics
(Impact Factor: 3.48).
10/2007; 17(9):773-82. DOI: 10.1097/FPC.0b013e3281c6d08e.
OCTN1 is a multispecific transporter of organic cations and zwitterions, including several clinically important drugs as well as the antioxidant ergothioneine. OCTN1 is highly expressed in the kidney, where it is thought to aid in active secretion of organic cations, and may facilitate the active reabsorption of ergothioneine. Genetic variation in OCTN1 may help to explain interindividual variability in the pharmacokinetics of many cationic or zwitterionic drugs.
We screened for human genetic variants in the OCTN1 coding region by direct sequencing in a large sample (n=270) of ethnically diverse healthy volunteers.
Six protein sequence-altering variants were identified, including five-amino-acid substitutions and one nonsense mutation. Two of the variants, T306I and L503F, were polymorphic, occurring at frequencies of 37 and 19%, respectively, in the total sample. Allele frequencies are varied by ethnicity. In biochemical assays, two of the variants (D165G and R282X) resulted in complete loss of transport function, and one variant (M205I) caused a reduction in activity to approximately 50% of the reference sequence protein. One variant, L503F, showed altered substrate specificity; this variant occurred at particularly high allele frequency (42%) in the European-American participants in our sample. Subcellular localization and ergothioneine inhibition kinetics were similar among the common amino-acid sequence variants of OCTN1.
The common OCTN1-L503F variant may explain a significant amount of population variation in the pharmacokinetics of OCTN1 substrate drugs. The rare loss-of-function variants provide a rational tool for studying the importance of ergothioneine in humans in vivo.
Available from: Michiko Kawamoto
- "Many genes that influence drug disposition are known to have polymorphisms that may play a critical role in determining interindividual variability in pharmacokinetics (Eichelbaum et al., 2006; Giacomini et al., 2007; Cropp et al., 2008). For example, recent studies have demonstrated that nonsynonymous SNPs in genes encoding membrane transporters such as organic anion/cation transporters contribute to interindividual variation in pharmacokinetics and drug response (Ieiri et al., 2006; Urban et al., 2007; Shu et al., 2008; Sissung et al., 2008). SNPs in noncoding regulatory regions have also been found to contribute to interindividual variation in the pharmacokinetics of various drugs (de Jong et al., 2006; Poonkuzhali et al., 2008; Wang et al., 2008). "
[Show abstract] [Hide abstract]
ABSTRACT: The organic cation/ergothioneine transporter OCTN1 (SLC22A4) and the high-affinity carnitine transporter OCTN2 (SLC22A5), play an important role in the disposition of xenobiotics and endogenous compounds. Here, we analyzed the sequence of the proximal promoter regions of OCTN1 and OCTN2 in four ethnic groups and determined the effects of the identified genetic variants on transcriptional activities and mRNA expression. Six variants were found in the proximal promoter of OCTN1, one of which showed high allele frequency ranging from 13 to 34% in samples from individuals with ancestries in Africa, Europe, China, and Mexico. OCTN1 haplotypes had similar activities as the reference in luciferase reporter assays. For OCTN2, three of the seven variants identified in the proximal promoter showed allele frequencies greater than 29.5% in all populations, with the exception of -207C>G (rs2631367) that was monomorphic in Asian Americans. OCTN2 haplotypes containing -207G, present in all populations, were associated with a gain of function in luciferase reporter assays. Consistent with reporter assays, OCTN2 mRNA expression levels in lymphoblastoid cell lines (LCLs) from gene expression analysis were greater in samples carrying a marker for -207G. This SNP seems to contribute to racial differences in OCTN2 mRNA expression levels in LCLs. Our study with healthy subjects (n = 16) homozygous for either -207C or -207G, showed no appreciable effect of this SNP on carnitine disposition. However, there were significant effects of gender on carnitine plasma levels (p < 0.01). Further in vivo studies of OCTN2 promoter variants on carnitine disposition and variation in drug response are warranted.
Journal of Pharmacology and Experimental Therapeutics 03/2009; 329(1):262-71. DOI:10.1124/jpet.108.146449 · 3.97 Impact Factor
[Show abstract] [Hide abstract]
ABSTRACT: The cellular defense system against harmful levels of reactive oxygen species consists of antioxidant enzymatic activities and small nonenzymatic molecules. L-ergothioneine has long been recognized as a potent and stable low-molecular-weight antioxidant that humans consume with diet and that accumulates in cells normally subjected to high levels of oxidative stress. As L-ergothioneine is plasma membrane-impermeative, its protective function is restricted to cells that express the L-ergothioneine-specific receptor/transporter OCTN1. Here we report for the first time that both as resident skin cells and in culture, epidermal keratinocytes synthesize OCTN1, which enables them to internalize and accumulate L-ergothioneine. This accumulation confers upon the cells an increased antioxidant potential. Consequently, it reduces the levels of reactive oxygen species and DNA, protein, and lipid damage in keratinocytes subjected to solar-simulating UV oxidative stress. Our results suggest that L-ergothioneine not only prevents oxidative damage but also may enable DNA repair in the UV-irradiated cells. The diminished oxidative damage to cellular constituents limits the apoptotic response and results in increased cell viability. The cells' ability to take up, accumulate, and utilize the potent antioxidant L-ergothioneine positions this naturally occurring amino acid and its receptor/transporter as an integral part of the antioxidative defense system of the skin.
Free Radical Biology and Medicine 05/2009; 46(8):1168-76. DOI:10.1016/j.freeradbiomed.2009.01.021 · 5.74 Impact Factor
Available from: Sook Wah Yee
[Show abstract] [Hide abstract]
ABSTRACT: Since the cloning of the first membrane transporter, our understanding of the role of transporters in clinical drug disposition and response has grown enormously. In parallel, large-scale genome-wide variation studies and the emerging field of pharmacogenomics have ushered in a new understanding of variations in drug response. At the crossroads of pharmacogenomics and transporter biology is the National Institutes of Health-funded Pharmacogenomics of Membrane Transporters (PMT) project, centered at the University of California, San Francisco.
Clinical Pharmacology & Therapeutics 11/2009; 87(1):109-16. DOI:10.1038/clpt.2009.226 · 7.90 Impact Factor
Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. The impact factor represents a rough estimation of the journal's impact factor and does not reflect the actual current impact factor. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.