Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P41181 (collecting duct)
 5,183 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The terminal part of the inner medullary collecting duct exhibits a high degree of water permeability that is independent of increased intracellular cAMP and not accounted for by the activity of the known renal epithelial water channels CHIP28 (28-kDa channel-forming integral protein) and WCH-CD (collecting duct water channel protein). Starting with rat kidney papilla mRNA, reverse transcription PCR was performed with degenerate primers assuming that the putative channel would be a member of the major intrinsic protein (MIP) family of proteins. A cDNA fragment was identified and used to screen a rat kidney cDNA library. A 1.9-kb cDNA clone was isolated. The open reading frame of 876 bp coded for a protein of 292 amino acids (M(r), 31,431). Aquaporin 3 (AQP3; 31.4-kDa water channel protein) is a newly discovered member of the MIP family. Northern blot analysis showed a single transcript for AQP3 of approximately 1.9 kb present in the renal medulla, predominantly in the inner medulla. With in situ hybridization, abundant message was found in the cells of the medullary collecting ducts. Injection of the complementary RNA of AQP3 into Xenopus oocytes markedly increased the osmotic water permeability. This permeability had an energy of activation of 3.0 kcal/mol (1 cal = 4.184 J), it was fully blocked by 1 mM p-chloromercuriphenylsulfonate, and this inhibition was reversed by 5 mM dithiothreitol. cAMP did not increase this water permeability. AQP3 did not permit passage of monovalent ions (Na, K, Cl); however, it is slightly permeable to urea. The present study demonstrates the existence of an additional water channel, AQP3, in epithelial cells of the medullary collecting duct.
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PMID:Cloning and expression of AQP3, a water channel from the medullary collecting duct of rat kidney. 752 88

A 1.8-kb cDNA clone (designed hKID, gene symbol AQP2L) with homology to the aquaporins was isolated from a human kidney cDNA library. The longest open reading frame of 846 bp encoded a 282-amino-acid hydrophobic protein that contained the conserved NPA motifs of MIP family members. Cell-free translation produced a nonglycosylated protein migrating at 29 kDa. Amino acid alignment showed the greatest homology of hKID to human MIP (48% identity) and AQP-2 (52%), with lesser homology to human MIWC (AQP-4, 34%), CHIP28 (AQP-1, 38%), and GLIP (AQP-3, 22%). Northern blot analysis revealed a 2.2-kb transcript expressed only in human kidney. PCR/Southern blot analysis of human kidney cDNA using primers flanking the hKID coding sequence revealed expression of a full-length mRNA and short transcripts with partial exon 1 and partial exon 4 deletions. Expression of hKID cRNA in Xenopus oocytes did not increase glycerol or urea permeability, but increased osmotic water permeability from (2.8 +/- 0.5) x 10(-4) to (7.4 +/- 0.7) x 10(-4) cm/s (10 degrees C) in a mercurial-sensitive manner. Sequence comparison of hKID cDNA with a cloned 21-kb genomic DNA indicated three introns (lengths 0.7, 0.25, and 0.4 kb) separating four exons with boundaries at amino acids 121, 174, and 201. The hKID promoter was identified and contained TATA, SP1, E-box, and AP1 and AP2 elements; primer extension revealed hKID transcription initiation 654 bp upstream from the translational initiation site. Genomic Southern blot indicated a single-copy hKID gene. PCR analysis of a human/rodent somatic hybrid panel localized the hKID gene to chromosome 12. Chromosomal fluorescence in situ hybridization mapped the hKID (AQP2L) gene to chromosome locus 12q13, the same location as the AQP. 2 and MIP genes. The high sequence homology, similar genomic structure, and identical chromosomal loci of hKID, MIP, and AQP-2 suggest a MIP family gene cluster at chromosome locus 12q13. Further work is needed to establish the physiological significance of hKID.
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PMID:cDNA cloning and gene structure of a novel water channel expressed exclusively in human kidney: evidence for a gene cluster of aquaporins at chromosome locus 12q13. 881 90

The rat renal urea transporter UT-A includes four isoforms. UT-A1, UT-A3, and UT-A4 are transcribed from a single initiation site at the 5'-end of the gene; a distinct internal initiation site is used for UT-A2 transcription. We cloned 1.3 kilobases (kb) of the 5'-flanking region upstream of the transcription start site of UT-A1, UT-A3, and UT-A4. This region contains three CCAAT sequences but lacks a TATA motif. A tonicity-responsive enhancer (TonE) was identified at -377bp. The 1.3-kb full fragment subcloned into pGL3 vector induced luciferase activity in Madin-Darby canine kidney cells and in mouse inner medullary collecting duct cells in isotonic medium. Luciferase activity was increased significantly in hypertonic medium, whereas deletion or mutation of the TonE sequence abolished this response. Electrophoretic mobility shift assay using the 5' UT-A TonE sequence as DNA probe showed formation of a specific DNA-protein complex with nuclear extracts from cells exposed to hypertonic medium and was weakly detectable in isotonic controls. A supershift in the mobility of the DNA-protein complex was observed with antiserum targeted to the TonE-binding protein (TonEBP). Co-transfection with dominant-negative TonEBP abolished the luciferase activity induced by the UT-A 1.3-kb construct under hypertonic and isotonic conditions. These data suggest that the TonE/TonEBP pathway mediates tonicity-responsive transcriptional regulation of UT-A1, UT-A3, and UT-A4 expression.
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PMID:The TonE/TonEBP pathway mediates tonicity-responsive regulation of UT-A urea transporter expression. 1099 47