title: Quantitative metabolic flux analysis reveals an unconventional pathway of fatty acid synthesis in cancer cells deficient for the mitochondrial citrate transport protein.
abstract: The mitochondrial citrate transport protein (CTP), encoded by SLC25A1, accommodates bidirectional trafficking of citrate between the mitochondria and cytosol, supporting lipid biosynthesis and redox homeostasis. Genetic CTP deficiency causes a fatal neurodevelopmental syndrome associated with the accumulation of L- and D-2-hydroxyglutaric acid, and elevated CTP expression is associated with poor prognosis in several types of cancer, emphasizing the importance of this transporter in multiple human pathologies. Here we describe the metabolic consequences of CTP deficiency in cancer cells. As expected from the phenotype of CTP-deficient humans, somatic CTP loss in cancer cells induces broad dysregulation of mitochondrial metabolism, resulting in accumulation of lactate and of the L- and D- enantiomers of 2-hydroxyglutarate (2HG) and depletion of TCA cycle intermediates. It also eliminates mitochondrial import of citrate from the cytosol. To quantify the impact of CTP deficiency on metabolic flux, cells were cultured with a set of13C-glucose and13C-glutamine tracers with resulting data integrated by metabolic flux analysis (MFA). CTP-deficient cells displayed a major restructuring of central carbon metabolism, including suppression of pyruvate dehydrogenase (PDH) and induction of glucose-dependent anaplerosis through pyruvate carboxylase (PC). We also observed an unusual lipogenic pathway in which carbon from glucose supplies mitochondrial production of alpha-ketoglutarate (AKG), which is then trafficked to the cytosol and used to supply reductive carboxylation by isocitrate dehydrogenase 1 (IDH1). The resulting citrate is cleaved to produce lipogenic acetyl-CoA, thereby completing a novel pathway of glucose-dependent reductive carboxylation. In CTP deficient cells, IDH1 inhibition suppresses lipogenesis from either glucose or glutamine, implicating IDH1 as a required component of fatty acid synthesis in states of CTP deficiency.
authors.affiliation: Children's Medical Center Research Institute, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390, USA. Electronic address: lei3.jiang@utsouthwestern.edu.
authors.forename: Lei
authors.initials: L
authors.lastname: Jiang
authors.affiliation: Children's Medical Center Research Institute, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390, USA; Royal Stoke University Hospital, Newcastle Rd, Stoke-on-Trent, ST4 6QG, United Kingdom.
authors.forename: Adam
authors.initials: A
authors.lastname: Boufersaoui
authors.affiliation: Children's Medical Center Research Institute, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390, USA.
authors.forename: Chendong
authors.initials: C
authors.lastname: Yang
authors.affiliation: Children's Medical Center Research Institute, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390, USA.
authors.forename: Bookyung
authors.initials: B
authors.lastname: Ko
authors.affiliation: Departments of Pathology and Pediatrics, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390, USA; Department of Pathology and Laboratory Medicine, Children's Health, 1935 Medical District Drive, Dallas, TX 75235, USA.
authors.forename: Dinesh
authors.initials: D
authors.lastname: Rakheja
authors.affiliation: Children's Medical Center Research Institute, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390, USA; University of Texas at Dallas, 800 W Campbell Rd, Richardson, TX, USA.
authors.forename: Gerardo
authors.initials: G
authors.lastname: Guevara
authors.affiliation: Children's Medical Center Research Institute, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390, USA.
authors.forename: Zeping
authors.initials: Z
authors.lastname: Hu
authors.affiliation: Children's Medical Center Research Institute, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390, USA; Department of Pediatrics, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390, USA; McDermott Center for Human Growth and Development, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390, USA. Electronic address: Ralph.Deberardinis@UTSouthwestern.edu.
authors.forename: Ralph J
authors.initials: RJ
authors.lastname: DeBerardinis
mesh_terms: D027321:Anion Transport Proteins / Q000172:deficiency*; D045744:Cell Line, Tumor; D005227:Fatty Acids / Q000096:biosynthesis* / Q000235:genetics; D006801:Humans; D008928:Mitochondria / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D024101:Mitochondrial Proteins / Q000172:deficiency*; D009363:Neoplasm Proteins / Q000172:deficiency / Q000378:metabolism; D009369:Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D027361:Organic Anion Transporters
chemical_list: D027321:Anion Transport Proteins; D005227:Fatty Acids; D024101:Mitochondrial Proteins; D009363:Neoplasm Proteins; D027361:Organic Anion Transporters; C532592:Slc25a1 protein, human
keywords: 2HG; Cancer metabolism; Citrate transporter; IDH1; Lung cancer; SLC25A1