title: Extracellular nucleotides inhibit oxalate transport by human intestinal Caco-2-BBe cells through PKC-δ activation.
abstract: Nephrolithiasis remains a major health problem in Western countries. Seventy to 80% of kidney stones are composed of calcium oxalate, and small changes in urinary oxalate affect risk of kidney stone formation. Intestinal oxalate secretion mediated by the anion exchanger SLC26A6 plays an essential role in preventing hyperoxaluria and calcium oxalate nephrolithiasis, indicating that understanding the mechanisms regulating intestinal oxalate transport is critical for management of hyperoxaluria. Purinergic signaling modulates several intestinal processes through pathways including PKC activation, which we previously found to inhibit Slc26a6 activity in mouse duodenal tissue. We therefore examined whether purinergic stimulation with ATP and UTP affects oxalate transport by human intestinal Caco-2-BBe (C2) cells. We measured [¹⁴C]oxalate uptake in the presence of an outward Cl⁻ gradient as an assay of Cl⁻/oxalate exchange activity, ≥50% of which is mediated by SLC26A6. We found that ATP and UTP significantly inhibited oxalate transport by C2 cells, an effect blocked by the PKC inhibitor Gö-6983. Utilizing pharmacological agonists and antagonists, as well as PKC-δ knockdown studies, we observed that ATP inhibits oxalate transport through the P2Y₂ receptor, PLC, and PKC-δ. Biotinylation studies showed that ATP inhibits oxalate transport by lowering SLC26A6 surface expression. These findings are of potential relevance to pathophysiology of inflammatory bowel disease-associated hyperoxaluria, where supraphysiological levels of ATP/UTP are expected and overexpression of the P2Y₂ receptor has been reported. We conclude that ATP and UTP inhibit oxalate transport by lowering SLC26A6 surface expression in C2 cells through signaling pathways including the P2Y₂ purinergic receptor, PLC, and PKC-δ.
authors.affiliation: Department of Medicine, University of Chicago, Chicago, IL 60637, USA.
authors.forename: Ruhul
authors.initials: R
authors.lastname: Amin
authors.forename: Sapna
authors.initials: S
authors.lastname: Sharma
authors.forename: Sireesha
authors.initials: S
authors.lastname: Ratakonda
authors.forename: Hatim A
authors.initials: HA
authors.lastname: Hassan
mesh_terms: D000255:Adenosine Triphosphate / Q000235:genetics / Q000378:metabolism; D000818:Animals; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D018938:Caco-2 Cells; D004789:Enzyme Activation; D055785:Gene Knockdown Techniques; D006801:Humans; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D010070:Oxalates / Q000378:metabolism*; D051745:Protein Kinase C-delta / Q000235:genetics / Q000378:metabolism*; D058473:Receptors, Purinergic P2Y2 / Q000235:genetics / Q000378:metabolism; D000076988:Sulfate Transporters; D014544:Uridine Triphosphate / Q000235:genetics / Q000378:metabolism
chemical_list: D026901:Membrane Transport Proteins; D010070:Oxalates; D058473:Receptors, Purinergic P2Y2; C439529:SLC26A6 protein, human; D000076988:Sulfate Transporters; D000255:Adenosine Triphosphate; D051745:Protein Kinase C-delta; D014544:Uridine Triphosphate
keywords: P2Y2 purinergic receptor; PKC-δ; SLC26A6; phospholipase C