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Functional genetic diversity in the high-affinity carnitine transporter OCTN2 (SLC22A5).
Mol Pharmacol. 2006 Nov; 70(5):1602-11.MP

Abstract

Systemic carnitine deficiency (SCD) is a rare autosomal recessive disease resulting from defects in the OCTN2 (SLC22A5) gene, which encodes the high-affinity plasma membrane carnitine transporter. Although OCTN2 is fairly well studied in its relationship with SCD, little is known about the carrier frequency of disease-causing alleles of OCTN2, or of more common functional polymorphisms in this gene. To address these issues, we screened for genetic variants in the OCTN2 coding region by direct sequencing of the exons and flanking intronic region of OCTN2 in a large sample (n = 276) of ethnically diverse subjects. In addition, we established lymphoblastoid cell lines from subjects homozygous for either allele of the previously identified promoter region variant, -207G>C. We found eight amino acid sequence variants of OCTN2, of which three (Phe17Leu, Leu144Phe, and Pro549Ser) were polymorphic in at least one ethnic group. When assayed for functional activity by expression in human embryonic kidney 293 cells, using as probes both the endogenous substrate (l-carnitine) and the organic cation tetraethylammonium, three variants showed functional differences from the reference OCTN2 (Phe17Leu, Tyr449Asp, Val481Phe; p < 0.05). Further studies of the Phe17Leu polymorphism showed a reduced V(max) for l-carnitine transport to approximately 50% of the reference OCTN2. Confocal microscopy studies using an OCTN2-GFP fusion protein showed that Phe17Leu had distinct subcellular localization from the reference OCTN2, with diffuse cytoplasmic retention of Phe17Leu, in contrast to reference OCTN2, which localized specifically to the plasma membrane. Lymphoblasts from subjects homozygous for the -207G allele showed increased l-carnitine transport compared with the -207C/C homozygotes (p < 0.05). This study suggests that although loss-of-function mutations in OCTN2 are likely to be rare, common variants of OCTN2 found in healthy populations may contribute to variation in the disposition of carnitine and some clinically used drugs.

Authors+Show Affiliations

Department of Biopharmaceutical Sciences, University of California, San Francisco, 94143-2911, USA.No affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info available

Pub Type(s)

Journal Article
Research Support, N.I.H., Extramural
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

16931768

Citation

Urban, Thomas J., et al. "Functional Genetic Diversity in the High-affinity Carnitine Transporter OCTN2 (SLC22A5)." Molecular Pharmacology, vol. 70, no. 5, 2006, pp. 1602-11.
Urban TJ, Gallagher RC, Brown C, et al. Functional genetic diversity in the high-affinity carnitine transporter OCTN2 (SLC22A5). Mol Pharmacol. 2006;70(5):1602-11.
Urban, T. J., Gallagher, R. C., Brown, C., Castro, R. A., Lagpacan, L. L., Brett, C. M., Taylor, T. R., Carlson, E. J., Ferrin, T. E., Burchard, E. G., Packman, S., & Giacomini, K. M. (2006). Functional genetic diversity in the high-affinity carnitine transporter OCTN2 (SLC22A5). Molecular Pharmacology, 70(5), 1602-11.
Urban TJ, et al. Functional Genetic Diversity in the High-affinity Carnitine Transporter OCTN2 (SLC22A5). Mol Pharmacol. 2006;70(5):1602-11. PubMed PMID: 16931768.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Functional genetic diversity in the high-affinity carnitine transporter OCTN2 (SLC22A5). AU - Urban,Thomas J, AU - Gallagher,Renata C, AU - Brown,Chaline, AU - Castro,Richard A, AU - Lagpacan,Leah L, AU - Brett,Claire M, AU - Taylor,Travis R, AU - Carlson,Elaine J, AU - Ferrin,Thomas E, AU - Burchard,Esteban G, AU - Packman,Seymour, AU - Giacomini,Kathleen M, Y1 - 2006/08/24/ PY - 2006/8/26/pubmed PY - 2006/12/9/medline PY - 2006/8/26/entrez SP - 1602 EP - 11 JF - Molecular pharmacology JO - Mol Pharmacol VL - 70 IS - 5 N2 - Systemic carnitine deficiency (SCD) is a rare autosomal recessive disease resulting from defects in the OCTN2 (SLC22A5) gene, which encodes the high-affinity plasma membrane carnitine transporter. Although OCTN2 is fairly well studied in its relationship with SCD, little is known about the carrier frequency of disease-causing alleles of OCTN2, or of more common functional polymorphisms in this gene. To address these issues, we screened for genetic variants in the OCTN2 coding region by direct sequencing of the exons and flanking intronic region of OCTN2 in a large sample (n = 276) of ethnically diverse subjects. In addition, we established lymphoblastoid cell lines from subjects homozygous for either allele of the previously identified promoter region variant, -207G>C. We found eight amino acid sequence variants of OCTN2, of which three (Phe17Leu, Leu144Phe, and Pro549Ser) were polymorphic in at least one ethnic group. When assayed for functional activity by expression in human embryonic kidney 293 cells, using as probes both the endogenous substrate (l-carnitine) and the organic cation tetraethylammonium, three variants showed functional differences from the reference OCTN2 (Phe17Leu, Tyr449Asp, Val481Phe; p < 0.05). Further studies of the Phe17Leu polymorphism showed a reduced V(max) for l-carnitine transport to approximately 50% of the reference OCTN2. Confocal microscopy studies using an OCTN2-GFP fusion protein showed that Phe17Leu had distinct subcellular localization from the reference OCTN2, with diffuse cytoplasmic retention of Phe17Leu, in contrast to reference OCTN2, which localized specifically to the plasma membrane. Lymphoblasts from subjects homozygous for the -207G allele showed increased l-carnitine transport compared with the -207C/C homozygotes (p < 0.05). This study suggests that although loss-of-function mutations in OCTN2 are likely to be rare, common variants of OCTN2 found in healthy populations may contribute to variation in the disposition of carnitine and some clinically used drugs. SN - 0026-895X UR - https://www.unboundmedicine.com/medline/citation/16931768/Functional_genetic_diversity_in_the_high_affinity_carnitine_transporter_OCTN2__SLC22A5__ L2 - http://molpharm.aspetjournals.org/cgi/pmidlookup?view=long&amp;pmid=16931768 DB - PRIME DP - Unbound Medicine ER -