Transport systems of this type catalyze facilitated diffusion of water (by an energy-independent process) by passage through a transmembrane aqueous pore or channel without evidence for a carrier-mediated mechanism.
The cDNA and the gene of human aquaporin8 (AQP8) were cloned from human testis cDNA and a genomic library, respectively. The AQP8 cDNA encodes 261 amino acids. The identity of the amino acid sequence to other aquaporins is highest with a plant water channel, gamma-TIP (40.4%), while AQP2 and AQP3 are 28.9 and 29.5% identical to human AQP8, respectively. The human AQP8 is only 74.9% identical to rat AQP8 and 76.0% identical to mouse AQP8. In Northern blot analysis, approximately 1.35-kb human AQP8 mRNA was expressed in pancreas and colon, but not in other tissues. Absence of human AQP8 in testis is noteworthy as rat AQP8 was abundantly expressed in testis. The expression of human AQP8 cRNA in Xenopus oocytes increased osmotic water permeability by 10-fold. AQP8 was not permeable to urea nor to glycerol. The AQP8 gene has five introns, and the locations of exon-intron boundaries were different from those of the other mammalian aquaporins, suggesting its separate phylogenetic origin.
Catalysis of the transfer of bile acid from one side of a hepatocyte plasma membrane into a bile canaliculus. Bile canaliculi are the thin tubes formed by hepatocyte membranes. Bile acids are any of a group of steroid carboxylic acids occurring in bile, where they are present as the sodium salts of their amides with glycine or taurine.
Any process that results in a change in state or activity of a cell (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of a cAMP (cyclic AMP, adenosine 3',5'-cyclophosphate) stimulus.
Evidence
1:
Inferred from Expression PatternUniProtKB
Cell membrane aquaporins (AQPs) may con t r i b u t e importantly to the regulation of intramembranous absorption of amniotic fluid. Recently, the authors demonstrated that human amnion AQP3 expression is upregulated by second-messenger cyclic adenosine monophosphate (cAMP). The present study was undertaken to determine the cAMP regulation of other AQP types, specifically AQP1, 8, and 9, in human amnion epithelia in vitro. Human amnion epithelial cell cultures were prepared from amnion of normal-term pregnancy. To investigate the effect of cAMP on AQP expression, primary human amnion cell cultures were incubated for 2, 10, and 20 hours with culture medium containing either 50 microM forskolin, an adenylate cyclase activator that stimulates cellular production of cAMP, or 100 microM SP-cAMP, a cAMP agonist that stimulates protein kinase A. Total RNA was isolated from the cultured cells, and semiquantitative real-time reverse transcription polymerase chain reaction was carried out to determine the relative level of AQPs mRNA expression. In primary amnion epithelial cell culture, AQP1 mRNA expression increased significantly at 10 hours (0.219 +/- 0.006 to 0.314 +/- 0.008, P < .05) and remained elevated for 20 hours (0.223 +/- 0.004 to 0.323 +/- 0.012, P < .05) following forskolin treatment. AQP8 mRNA expression increased significantly at 2 hours (0.069 +/- 0.003 to 0.086 +/- 0.012, P < .05) and remained upregulated for 20 hours following forskolin treatment. Forskolin stimulation of AQP9 mRNA expression was evidenced by 10 hours (0.098 +/- 0.005 to 0.115 +/- 0.006, P < .05) and maintained for 20 hours. In contrast to forskolin, SP-cAMP incubation resulted in no change in AQP1, 8, or 9 mRNA expression. Human amnion epithelial cell AQP1, 8, and 9 mRNA expression is upregulated by cAMP as their expression is simulated by forskolin. Lack of effect of SP-cAMP, the protein kinase A activator, on AQP1, 8, and 9 mRNA expression suggests that cAMP upregulates human amnion AQP1, 8, and 9 mRNA expression via the protein kinase A independent pathway.
The directed movement of substances (such as macromolecules, small molecules, ions) into, out of or within a cell, or between cells, or within a multicellular organism by means of some agent such as a transporter or pore.
The cDNA and the gene of human aquaporin8 (AQP8) were cloned from human testis cDNA and a genomic library, respectively. The AQP8 cDNA encodes 261 amino acids. The identity of the amino acid sequence to other aquaporins is highest with a plant water channel, gamma-TIP (40.4%), while AQP2 and AQP3 are 28.9 and 29.5% identical to human AQP8, respectively. The human AQP8 is only 74.9% identical to rat AQP8 and 76.0% identical to mouse AQP8. In Northern blot analysis, approximately 1.35-kb human AQP8 mRNA was expressed in pancreas and colon, but not in other tissues. Absence of human AQP8 in testis is noteworthy as rat AQP8 was abundantly expressed in testis. The expression of human AQP8 cRNA in Xenopus oocytes increased osmotic water permeability by 10-fold. AQP8 was not permeable to urea nor to glycerol. The AQP8 gene has five introns, and the locations of exon-intron boundaries were different from those of the other mammalian aquaporins, suggesting its separate phylogenetic origin.
Protein involved in the transport of a molecule (metabolite, protein, etc), a ion or an electron across cell membranes, inside the cell or in a tissue fluid.
A reference proteome is a set of protein sequences derived from a complete proteome which constitutes a defined standard for a particular user community. Reference proteomes are manually defined according to a number of criteria. They cover the proteomes of well- studied model organisms and other proteomes of interest for biomedical and biotechnological research. Reference proteomes have been selected to provide broad coverage of the tree of life, and constitute a representative cross-section of the taxonomic diversity to be found within UniProtKB.
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