Characterization of a human colonic cDNA encoding a structurally novel urea transporter, hUT-A6.
Two closely related genes, UT-A (Slc14a2) and UT-B (Slc14a1), encode specialized transporter proteins that modulate the movement of urea across cell membranes. In this article, we report the characterization of a cDNA isolated from human colonic mucosa encoding a novel UT-A urea transporter, hUT-A6. The encoded protein is 235 amino acids (aa) in length, making it the smallest UT-A member characterized. On the basis of previous structural predictions, hUT-A6 is structurally unique in that it consists of a single hydrophobic core flanked by hydrophilic NH(2)- and COOH-terminal domains. The transcript encoding hUT-A6 contains a novel 129-bp exon, exon 5a, which, as a result of alternative splicing, introduces a unique 19-aa segment and a stop codon. Functionally, the protein transports urea, and this activity is inhibited by phloretin. Interestingly, despite the lack of a protein kinase A (PKA) consensus site [RK](2)-X-[ST], transport of urea by hUT-A6 is stimulated by PKA agonists. Deletion of the two PKA consensus sites from murine UT-A3 (mUT-A3) did not affect the stimulatory response of PKA agonists, which, together with the lack of PKA consensus sites in hUT-A6, indicates that regulation of hUT-A6 and mUT-A3 is not mediated through a classic PKA phosphorylation consensus.
Smith
Craig P
CP
School of Biological Sciences, University of Manchester, G.38, Stopford Bldg., Oxford Road, Manchester M13 9PT, United Kingdom. cpsmith@man.ac.uk
Potter
Elizabeth A
EA
Fenton
Robert A
RA
Stewart
Gavin S
GS
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015152:Blotting, Northern; D003106:Colon / Q000502:physiology; D000242:Cyclic AMP / Q000378:metabolism; D018076:DNA, Complementary / Q000502:physiology*; D006801:Humans; D007413:Intestinal Mucosa / Q000502:physiology*; D007668:Kidney / Q000502:physiology; D008297:Male; D026901:Membrane Transport Proteins / Q000235:genetics* / Q000378:metabolism*; D008969:Molecular Sequence Data; D010693:Phloretin / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013737:Testis / Q000502:physiology; D014981:Xenopus; D000096982:Urea Transporters
D000242:Cyclic AMP; D018076:DNA, Complementary; D026901:Membrane Transport Proteins; D010693:Phloretin; D000096982:Urea Transporters