title: IDO induces expression of a novel tryptophan transporter in mouse and human tumor cells.
abstract: IDO is the rate-limiting enzyme in the kynurenine pathway, catabolizing tryptophan to kynurenine. Tryptophan depletion by IDO-expressing tumors is a common mechanism of immune evasion inducing regulatory T cells and inhibiting effector T cells. Because mammalian cells cannot synthesize tryptophan, it remains unclear how IDO(+) tumor cells overcome the detrimental effects of local tryptophan depletion. We demonstrate that IDO(+) tumor cells express a novel amino acid transporter, which accounts for ∼50% of the tryptophan uptake. The induced transporter is biochemically distinguished from the constitutively expressed tryptophan transporter System L by increased resistance to inhibitors of System L, resistance to inhibition by high concentrations of most amino acids tested, and high substrate specificity for tryptophan. Under conditions of low extracellular tryptophan, expression of this novel transporter significantly increases tryptophan entry into IDO(+) tumors relative to tryptophan uptake through the low-affinity System L alone, and further decreases tryptophan levels in the microenvironment. Targeting this additional tryptophan transporter could be a way of pharmacological inhibition of IDO-mediated tumor escape. These findings highlight the ability of IDO-expressing tumor cells to thrive in a tryptophan-depleted microenvironment by expressing a novel, highly tryptophan-specific transporter, which is resistant to inhibition by most other amino acids. The additional transporter allows tumor cells to strike the ideal balance between supply of tryptophan essential for their own proliferation and survival, and depleting the extracellular milieu of tryptophan to inhibit T cell proliferation.
authors: Medical Research Council Human Immunology Unit, Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, Headington OX3 9DS, United Kingdom.
authors: Jonathan D
authors: JD
authors: Silk
authors: Samira
authors: S
authors: Lakhal
authors: Robert
authors: R
authors: Laynes
authors: Laura
authors: L
authors: Vallius
authors: Ioannis
authors: I
authors: Karydis
authors: Cornelius
authors: C
authors: Marcea
authors: C A Richard
authors: CA
authors: Boyd
authors: Vincenzo
authors: V
authors: Cerundolo
mesh_terms: D027062:Amino Acid Transport System L / Q000276:immunology* / Q000378:metabolism; D000818:Animals; D001692:Biological Transport / Q000276:immunology; D049109:Cell Proliferation; D002470:Cell Survival / Q000276:immunology; D006367:HeLa Cells; D006801:Humans; D050503:Indoleamine-Pyrrole 2,3,-Dioxygenase / Q000276:immunology* / Q000378:metabolism; D051379:Mice; D009369:Neoplasms / Q000201:enzymology / Q000276:immunology*; D013601:T-Lymphocytes / Q000276:immunology / Q000378:metabolism; D014364:Tryptophan / Q000276:immunology* / Q000378:metabolism
chemical_list: D027062:Amino Acid Transport System L; D050503:Indoleamine-Pyrrole 2,3,-Dioxygenase; D014364:Tryptophan