title: Role of organic cation transporter 3 (SLC22A3) and its missense variants in the pharmacologic action of metformin.
abstract: OBJECTIVE
  The goals of this study were to determine the role of organic cation transporter 3 (OCT3) in the pharmacological action of metformin and to identify and functionally characterize genetic variants of OCT3 with respect to the uptake of metformin and monoamines.
  
  
  METHODS
  For pharmacological studies, we evaluated metformin-induced activation of AMP-activated protein kinase, a molecular target of metformin. We used quantitative PCR and immunostaining to localize the transporter and isotopic uptake studies in cells transfected with OCT3 and its nonsynonymous genetic variants for functional analyses.
  
  
  RESULTS
  Quantitative PCR and immunostaining showed that OCT3 was expressed high on the plasma membrane of skeletal muscle and liver, target tissues for metformin action. Both the OCT inhibitor, cimetidine, and OCT3-specific short hairpin RNA significantly reduced the activating effect of metformin on AMP-activated protein kinase. To identify genetic variants in OCT3, we used recent data from the 1000 Genomes and the Pharmacogenomics of Membrane Transporters projects. Six novel missense variants were identified. In functional assays, using various monoamines and metformin, three variants, T44M (c.131C>T), T400I (c.1199C>T) and V423F (c.1267G>T) showed altered substrate specificity. Notably, in cells expressing T400I and V423F, the uptakes of metformin and catecholamines were significantly reduced, but the uptakes of metformin, 1-methyl-4-phenylpyridinium and histamine by T44M were significantly increased more than 50%. Structural modeling suggested that these two variants may be located in the pore lining (T400) or proximal (V423) membrane-spanning helixes.
  
  
  CONCLUSIONS
  Our study suggests that OCT3 plays a role in the therapeutic action of metformin and that genetic variants of OCT3 may modulate metformin and catecholamine action.
authors.affiliation: Department of Bioengineering and Therapeutic Sciences, University of California at San Francisco, San Francisco, California 94158, USA.
authors.forename: Ligong
authors.initials: L
authors.lastname: Chen
authors.forename: Bradley
authors.initials: B
authors.lastname: Pawlikowski
authors.forename: Avner
authors.initials: A
authors.lastname: Schlessinger
authors.forename: Swati S
authors.initials: SS
authors.lastname: More
authors.forename: Doug
authors.initials: D
authors.lastname: Stryke
authors.forename: Susan J
authors.initials: SJ
authors.lastname: Johns
authors.forename: Michael A
authors.initials: MA
authors.lastname: Portman
authors.forename: Eugene
authors.initials: E
authors.lastname: Chen
authors.forename: Thomas E
authors.initials: TE
authors.lastname: Ferrin
authors.forename: Andrej
authors.initials: A
authors.lastname: Sali
authors.forename: Kathleen M
authors.initials: KM
authors.lastname: Giacomini
mesh_terms: D000595:Amino Acid Sequence; D002460:Cell Line; D014644:Genetic Variation; D007004:Hypoglycemic Agents / Q000378:metabolism / Q000494:pharmacology*; D008687:Metformin / Q000378:metabolism / Q000494:pharmacology*; D008969:Molecular Sequence Data; D020125:Mutation, Missense; D027701:Organic Cation Transport Proteins / Q000235:genetics* / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D014162:Transfection; D000099254:Organic Cation Transporter 3
chemical_list: D007004:Hypoglycemic Agents; D008687:Metformin; D027701:Organic Cation Transport Proteins; D012333:RNA, Messenger; D000099254:Organic Cation Transporter 3