title: Glyoxalate reductase/hydroxypyruvate reductase interacts with the sodium-dependent vitamin C transporter-1 to regulate cellular vitamin C homeostasis.
abstract: The human sodium-dependent vitamin C transporter 1 (hSVCT1) contributes to cellular uptake of ascorbic acid (AA). Although different aspects of hSVCT1 cell biology have been extensively studied, nothing is currently known about the broader hSVCT1 interactome that modulates its role in cellular physiology. Here, we identify the enzyme human glyoxalate reductase/hydroxypyruvate reductase (hGR/HPR) as an hSVCT1 associated protein by yeast two-hybrid (Y2H) screening of a human liver cDNA library. The interaction between hSVCT1 and hGR/HPR was further confirmed by in vitro GST pull-down assay, in vivo coimmunoprecipitation and mammalian two-hybrid firefly luciferase assays. This interaction had functional significance as coexpression of hGR/HPR with hSVCT1 led to an increase in AA uptake. Reciprocally, siRNA-mediated knockdown of endogenous hGR/HPR led to an inhibition of AA uptake. Given that oxalate is a degradation product of vitamin C and hGR/HPR acts to limit cellular oxalate levels, this association physically couples two independent regulators of cellular oxalate production. Furthermore, confocal imaging of human liver HepG2 cells coexpressing GFP-hSVCT1 and hGR/HPR-mCherry demonstrated that these two proteins colocalize within a subpopulation of intracellular organelles. This provides a possible molecular basis for organellar AA transport and regulation of local glyoxylate/glycolate concentration in the vicinity of organelle membranes.
authors.affiliation: Department of of Medicine, University of California, Irvine, CA 92697, USA. vsubrama@uci.edu
authors.forename: Veedamali S
authors.initials: VS
authors.lastname: Subramanian
authors.forename: Svetlana M
authors.initials: SM
authors.lastname: Nabokina
authors.forename: Joseph R
authors.initials: JR
authors.lastname: Patton
authors.forename: Jonathan S
authors.initials: JS
authors.lastname: Marchant
authors.forename: Hamid
authors.initials: H
authors.lastname: Moradi
authors.forename: Hamid M
authors.initials: HM
authors.lastname: Said
mesh_terms: D000429:Alcohol Oxidoreductases / Q000235:genetics / Q000378:metabolism*; D001205:Ascorbic Acid / Q000378:metabolism*; D056945:Hep G2 Cells; D006706:Homeostasis; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism; D008099:Liver / Q000378:metabolism; D010070:Oxalates / Q000378:metabolism; D011485:Protein Binding; D021381:Protein Transport; D034741:RNA, Small Interfering; D060347:Sodium-Coupled Vitamin C Transporters / Q000378:metabolism*; D020798:Two-Hybrid System Techniques
chemical_list: D010070:Oxalates; D034741:RNA, Small Interfering; C555162:SLC23A1 protein, human; D060347:Sodium-Coupled Vitamin C Transporters; D000429:Alcohol Oxidoreductases; C020830:glyoxylate reductase; D001205:Ascorbic Acid
keywords: transport; uptake; vitamin C; yeast two-hybrid