Molecular cloning and functional analysis of SUT-1, a sulfate transporter from human high endothelial venules

High endothelial venules (HEV) are specialized postcapillary venules found in lymphoid organs and chronically inflamed tissues that support high level s of lymphocyte extravasation from the blood. One of the major characterist ics of HEV endothelial cells (HEVEC) is their capacity to incorporate large amounts of sulfate into sialomucin-type counter-receptors for the lymphocy te homing receptor L-selectin. Here, we show that HEVEC express two functio nal classes of sulfate transporters defined by their differential sensitivi ty to the anion-exchanger inhibitor 4,4'-diisothiocyanostilbene-2,2'-disulf onic acid (DIDS), and we report the molecular characterization of a DIDS-re sistant sulfate transporter from human HEVEC, designated SUT-1. SUT-1 belon gs to the family of Na+-coupled anion transporters and exhibits 40-50% amin o acid identity with the rat renal Na+/sulfate cotransporter, NaSi-1, as we ll as with the human and rat Na+/dicarboxylate cotransporters, NaDC-1/SDCT1 and NaDC-3/SDCT2. Functional expression studies in cRNA-injected Xenopus l aevis oocytes showed that SUT-1 mediates high levels of Naf-dependent sulfa te transport, which is resistant to DIDS inhibition, The SUT-1 gene mapped to human chromosome 7q33. Northern blotting analysis revealed that SUT-1 ex hibits a highly restricted tissue distribution, with abundant expression in placenta. Reverse transcription-PCR analysis indicated that SUT-1 and the diastrophic dysplasia sulfate transporter (DTD), one of the two known human DIDS-sensitive sulfate transporters, are coexpressed in HEVEC, SUT-1 and D TD could correspond, respectively, to the DIDS-resistant and DIDS-sensitive components of sulfate uptake in HEVEC Together these results demonstrate t hat SUT-1 is a distinct human Na+-coupled sulfate transporter, likely to pl ay a major role in sulfate incorporation in HEV.