Cloning and characterization of the human urea transporter UT-A1 and mapping of the human Slc14a2 gene

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Abstract
We have isolated and characterized the human homolog of the rat largest urea transporter of the UT-A family (hUT-A1). The 4.2-kb hUT-A1 cDNA encodes a 920-amino acid peptide, which is 89% identical to the rat UT-A1 protein. By Northern hybridization, hUT-A1 expression is detected in the human inner medulla as a ∼4.4-kb mRNA transcript. By Western analysis, hUT-A1 is identified as a ∼100-kDa protein in the human inner medulla. By immunohistochemistry, hUT-A1 expression is localized to the inner medullary collecting duct (IMCD). When transfected into HEK-293 cells hUT-A1 cDNA is translated into a ∼98-kDa protein. Expression of hUT-A1 in Xenopus oocytes results in phloretin-inhibitable uptake of14C-urea, which shows only modest stimulation by cAMP, suggesting that in the human IMCD vasopressin may have a limited role in the short-term regulation of hUT-A1-mediated urea transport. We determined the organization of the human Slc14a2 gene and identified 20 exons distributed over ∼67.5 kb on chromosome 18, from which hUT-A1 and the other human urea transporter, hUT-A2, are transcribed.