title: Discovering thiamine transporters as targets of chloroquine using a novel functional genomics strategy.
abstract: Chloroquine (CQ) and other quinoline-containing antimalarials are important drugs with many therapeutic benefits as well as adverse effects. However, the molecular targets underlying most such effects are largely unknown. By taking a novel functional genomics strategy, which employs a unique combination of genome-wide drug-gene synthetic lethality (DGSL), gene-gene synthetic lethality (GGSL), and dosage suppression (DS) screens in the model organism Saccharomyces cerevisiae and is thus termed SL/DS for simplicity, we found that CQ inhibits the thiamine transporters Thi7, Nrt1, and Thi72 in yeast. We first discovered a thi3Δ mutant as hypersensitive to CQ using a genome-wide DGSL analysis. Using genome-wide GGSL and DS screens, we then found that a thi7Δ mutation confers severe growth defect in the thi3Δ mutant and that THI7 overexpression suppresses CQ-hypersensitivity of this mutant. We subsequently showed that CQ inhibits the functions of Thi7 and its homologues Nrt1 and Thi72. In particular, the transporter activity of wild-type Thi7 but not a CQ-resistant mutant (Thi7(T287N)) was completely inhibited by the drug. Similar effects were also observed with other quinoline-containing antimalarials. In addition, CQ completely inhibited a human thiamine transporter (SLC19A3) expressed in yeast and significantly inhibited thiamine uptake in cultured human cell lines. Therefore, inhibition of thiamine uptake is a conserved mechanism of action of CQ. This study also demonstrated SL/DS as a uniquely effective methodology for discovering drug targets.
authors.affiliation: Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas, United States of America.
authors.forename: Zhiwei
authors.initials: Z
authors.lastname: Huang
authors.forename: Sankaranarayanan
authors.initials: S
authors.lastname: Srinivasan
authors.forename: Jianhuai
authors.initials: J
authors.lastname: Zhang
authors.forename: Kaifu
authors.initials: K
authors.lastname: Chen
authors.forename: Yongxiang
authors.initials: Y
authors.lastname: Li
authors.forename: Wei
authors.initials: W
authors.lastname: Li
authors.forename: Florante A
authors.initials: FA
authors.lastname: Quiocho
authors.forename: Xuewen
authors.initials: X
authors.lastname: Pan
mesh_terms: D000962:Antimalarials / Q000494:pharmacology*; D001692:Biological Transport / Q000187:drug effects / Q000235:genetics; D002738:Chloroquine / Q000494:pharmacology*; D015870:Gene Expression; D023281:Genomics; D006801:Humans; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D033703:Nucleoside Transport Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000502:physiology; D029701:Saccharomyces cerevisiae Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D013831:Thiamine / Q000378:metabolism*
chemical_list: D000962:Antimalarials; D026901:Membrane Transport Proteins; C528866:Nrt1 protein, S cerevisiae; D033703:Nucleoside Transport Proteins; C492291:SLC19A3 protein, human; D029701:Saccharomyces cerevisiae Proteins; C000592467:Thi72 protein, S cerevisiae; D002738:Chloroquine; D013831:Thiamine