A second distinct family of anion exchangers, SLC26, in addition to the classical SLC4 (or anion exchanger) family, has recently been delineated. Particular interest in this gene family is stimulated by the fact that the SLC26A2, SLC26A3, and SLC26A4 genes have been recognized as the disease genes mutated in diastrophic dysplasia, congenital chloride diarrhea, and Pendred syndrome, respectively. We report the expansion of the SLC26 gene family by characterizing three novel tissue-specific members, named SLC26A7, SLC26A8, and SLC26A9, on chromosomes 8, 6, and 1, respectively. The SLC26A7-A9 proteins are structurally very similar at the amino acid level to the previous family members and show tissue-specific expression in kidney, testis, and lung, respectively. More detailed characterization by immunohistochemistry and/or in situ hybridization localized SLC26A7 to distal segments of nephrons, SLC26A8 to developing spermatocytes, and SLC26A9 to the lumenal side of the bronchiolar and alveolar epithelium of lung. Expression of SLC26A7-A9 proteins in Xenopus oocytes demonstrated chloride, sulfate, and oxalate transport activity, suggesting that they encode functional anion exchangers. The functional characterization of the novel tissue-specific members may provide new insights to anion transport physiology in different parts of body.

A unique characteristic of endothelial cells from high endothelial venules (HEVEC) in lymphoid organs and chronically inflamed tissues is their capacity to incorporate large amounts of sulfate into sialomucin-type counter-receptors for the lymphocyte homing receptor L-selectin. We have previously shown that HEVEC express two functional classes of sulfate transporters: sodium/sulfate cotransporters and sulfate/anion exchangers. Here, we report the molecular cloning from human HEVEC of a 2.9-kb cDNA encoding SLC26A7, a novel member of the SLC26 (solute carrier 26) sulfate/anion exchanger family. SLC26A7 exhibits 30% identity with three known sulfate transporters from the SLC26 family: SLC26A2 (also known as DTDST), SLC26A1 (also known as SAT1), and SLC26A3 (also known as DRA). Northern blot analysis revealed specific expression of SLC26A7 mRNA in kidney. Alternative splicing and polyadenylation of SLC26A7 pre-mRNA in kidney suggest the existence of two protein isoforms, SLC26A7.1 and SLC26A7.2, differing in their carboxy termini.