title: Glyoxylate is a substrate of the sulfate-oxalate exchanger, sat-1, and increases its expression in HepG2 cells.
abstract: OBJECTIVE
  Hyperoxaluria is a major problem causing nephrolithiasis. Little is known about the regulation of oxalate transport from the liver, the main organ for oxalate synthesis, into the circulation. Since the sulfate anion transporter-1(sat-1) is present in the sinusoidal membrane of hepatocytes and translocates oxalate, its impact on increased oxalate synthesis was studied.
  
  
  METHODS
  Sat-1 expressing oocytes were used for cis-inhibition, trans-stimulation, and efflux experiments with labelled sulfate and oxalate to demonstrate the interactions of oxalate, glyoxylate, and glycolate with sat-1. HepG2 cells were incubated with oxalate and its precursors (glycine, hydroxyproline, glyoxylate, and glycolate). Changes in endogenous sat-1 mRNA-expression were examined using real-time PCR. After incubation of HepG2 cells in glyoxylate, sat-1 protein-expression was analysed by Western blotting, and sulfate uptake into HepG2 cells was measured. RT-PCR was used to screen for mRNA of other transporters.
  
  
  RESULTS
  While oxalate and glyoxylate inhibited sulfate uptake, glycolate did not. Sulfate and oxalate uptake were trans-stimulated by glyoxylate but not by glycolate. Glyoxylate enhanced sulfate efflux. Glyoxylate was the only oxalate precursor stimulating sat-1 mRNA-expression. After incubation of HepG2 cells in glyoxylate, both sat-1 protein-expression and sulfate uptake into the cells increased. mRNA-expression of other transporters in HepG2 cells was not affected by glyoxylate treatment.
  
  
  CONCLUSIONS
  The oxalate precursor glyoxylate was identified as a substrate of sat-1. Upregulated expression of sat-1 mRNA and of a functional sat-1 protein indicates that glyoxylate may be responsible for the elevated oxalate release from hepatocytes observed in hyperoxaluria.
authors.affiliation: Vegetative Physiologie und Pathophysiologie, Universitätsmedizin Göttingen, Georg-August Universität Göttingen, Germany. Schnedler@physiol.med.uni-goettingen.de
authors.forename: Nina
authors.initials: N
authors.lastname: Schnedler
authors.forename: Gerhard
authors.initials: G
authors.lastname: Burckhardt
authors.forename: Birgitta C
authors.initials: BC
authors.lastname: Burckhardt
mesh_terms: D000818:Animals; D027321:Anion Transport Proteins / Q000235:genetics* / Q000378:metabolism*; D001483:Base Sequence; D017931:DNA Primers / Q000235:genetics; D005260:Female; D006016:Glycolates / Q000378:metabolism / Q000494:pharmacology; D006038:Glyoxylates / Q000378:metabolism* / Q000494:pharmacology; D056945:Hep G2 Cells; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D006959:Hyperoxaluria / Q000150:complications / Q000378:metabolism; D066298:In Vitro Techniques; D008954:Models, Biological; D053040:Nephrolithiasis / Q000209:etiology / Q000378:metabolism; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism; D010070:Oxalates / Q000378:metabolism / Q000494:pharmacology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D000076988:Sulfate Transporters; D013431:Sulfates / Q000378:metabolism; D015854:Up-Regulation / Q000187:drug effects; D014982:Xenopus laevis
chemical_list: D027321:Anion Transport Proteins; D017931:DNA Primers; D006016:Glycolates; D006038:Glyoxylates; D010070:Oxalates; D012333:RNA, Messenger; D011994:Recombinant Proteins; C473560:SLC26A1 protein, human; D000076988:Sulfate Transporters; D013431:Sulfates; C031149:glycolic acid; C031150:glyoxylic acid