title: Transepithelial fluxes of adenosine and 2'-deoxyadenosine across human renal proximal tubule cells: roles of nucleoside transporters hENT1, hENT2, and hCNT3.
abstract: This study examined the roles of human nucleoside transporters (hNTs) in mediating transepithelial fluxes of adenosine, 2'-deoxyadenosine, and three purine nucleoside anti-cancer drugs across polarized monolayers of human renal proximal tubule cells (hRPTCs), which were shown in previous studies to have human equilibrative NT 1 (hENT1) and 2 (hENT2) and human concentrative NT 3 (hCNT3) activities (11). Early passage hRPTCs were cultured on transwell inserts under conditions that induced formation of polarized monolayers with experimentally accessible apical and basolateral domains. Polarized hRPTC cultures were monitored for inhibitor sensitivities and sodium-dependence of the following: 1) transepithelial fluxes of radiolabeled adenosine, 2'-deoxyadenosine, fludarabine (9-beta-d-arabinosyl-2-fluoroadenine), cladribine (2-chloro-2'-deoxyadenosine), and clofarabine (2-chloro-2'-fluoro-deoxy-9-beta-d-arabinofuranosyladenine); 2) mediated uptake of radiolabeled adenosine, 2'-deoxyadenosine, fludarabine, cladribine, and clofarabine from either apical or basolateral surfaces; and 3) relative apical cell surface hCNT3 protein levels. Transepithelial fluxes of adenosine were mediated from apical-to-basolateral sides by apical hCNT3 and basolateral hENT2, whereas transepithelial fluxes of 2'-deoxyadenosine were mediated from basolateral-to-apical sides by apical hENT1 and basolateral human organic anion transporters (hOATs). The transepithelial fluxes of adenosine, hCNT3-mediated cellular uptake of adenosine, and relative apical cell surface hCNT3 protein levels correlated positively in polarized hRPTCs. The purine nucleoside anti-cancer drugs fludarabine, cladribine, and clofarabine, like adenosine exhibited apical-to-basolateral fluxes. Collectively, this evidence suggested that apical hCNT3 and basolateral hENT2 are involved in proximal tubular reabsorption of adenosine and some nucleoside drugs and that apical hENT1 and basolateral hOATs are involved in proximal tubular secretion of 2'-deoxyadenosine.
authors.affiliation: Cross Cancer Institute, 11560 Univ. Ave. NW, Edmonton, Alberta T6G 1Z2 Canada.
authors.forename: Adam N
authors.initials: AN
authors.lastname: Elwi
authors.forename: Vijaya L
authors.initials: VL
authors.lastname: Damaraju
authors.forename: Michelle L
authors.initials: ML
authors.lastname: Kuzma
authors.forename: Delores A
authors.initials: DA
authors.lastname: Mowles
authors.forename: Stephen A
authors.initials: SA
authors.lastname: Baldwin
authors.forename: James D
authors.initials: JD
authors.lastname: Young
authors.forename: Michael B
authors.initials: MB
authors.lastname: Sawyer
authors.forename: Carol E
authors.initials: CE
authors.lastname: Cass
mesh_terms: D000241:Adenosine / Q000031:analogs & derivatives / Q000378:metabolism*; D000970:Antineoplastic Agents / Q000378:metabolism; D002478:Cells, Cultured; D003839:Deoxyadenosines / Q000378:metabolism*; D004847:Epithelial Cells / Q000378:metabolism; D033721:Equilibrative Nucleoside Transporter 1 / Q000235:genetics / Q000378:metabolism*; D033722:Equilibrative-Nucleoside Transporter 2 / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000502:physiology; D006801:Humans; D007687:Kidney Tubules, Proximal / Q000166:cytology*; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D027361:Organic Anion Transporters / Q000235:genetics / Q000378:metabolism
chemical_list: D000970:Antineoplastic Agents; D003839:Deoxyadenosines; D033721:Equilibrative Nucleoside Transporter 1; D033722:Equilibrative-Nucleoside Transporter 2; D026901:Membrane Transport Proteins; D027361:Organic Anion Transporters; C438649:SLC29A1 protein, human; C438654:SLC29A2 protein, human; C065171:cif nucleoside transporter; D000241:Adenosine; C058118:2'-deoxyadenosine