Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.1.27.1 (RNase)
16,360 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The aquaporins transport water through membranes of numerous tissues, but the molecular mechanisms for sensing changes in extracellular osmolality and regulating water balance in brain are unknown. We have isolated a brain aquaporin by homology cloning. Like aquaporin 1 (AQP1, also known as CHIP, channel-forming integral membrane protein of 28 kDa), the deduced polypeptide has six putative transmembrane domains but lacks cysteines at the known mercury-sensitive sites. Two initiation sites were identified encoding polypeptides of 301 and 323 amino acids; expression of each in Xenopus oocytes conferred a 20-fold increase in osmotic water permeability not blocked by 1 mM HgCl2, even after substitution of cysteine at the predicted mercury-sensitive site. Northern analysis and RNase protection demonstrated the mRNA to be abundant in mature rat brain but only weakly detectable in eye, kidney, intestine, and lung. In situ hybridization of brain localized the mRNA to ependymal cells lining the aqueduct, glial cells forming the edge of the cerebral cortex and brainstem, vasopressin-secretory neurons in supraoptic and paraventricular nuclei of hypothalamus, and Purkinje cells of cerebellum. Its distinctive expression pattern implicates this fourth mammalian member of the aquaporin water channel family (designated gene symbol, AQP4) as the osmoreceptor which regulates body water balance and mediates water flow within the central nervous system.
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PMID:Molecular characterization of an aquaporin cDNA from brain: candidate osmoreceptor and regulator of water balance. 752 31

The RNase protection assay was applied to quantify mRNA expression of five principal mammalian water channels in 18 different rat tissues, and to determine the influence of dehydration on renal water channel expression. Probes consisted of labeled cRNAs transcribed from cDNA fragments of rat CHIP28 (AQP-1, bp 238-575 of coding sequence), AQP-CD (AQP2, bp 53-606), MIWC (AQP4, bp 235-572), GLIP (AQP3, bp 219-604), and AQP5 (bp 56-612). Results were normalized to expression of rat beta-actin by quantitative densitometry of autoradiograms. CHIP28 mRNA was expressed strongly in heart, kidney > placenta, skeletal muscle, and urinary bladder and detected weakly in eye, lung, trachea, spleen, liver, colon, prostate, and skin. AQP-CD was detected only in kidney. MIWC mRNA expression was highest in brain, followed by eye, trachea, lung, stomach, kidney, and skeletal muscle. GLIP was found in eye, trachea, kidney, urinary bladder, skin, prostate, placenta, and skeletal muscle. AQP5 was detected in salivary gland, eye, lung, and trachea. An alternatively spliced form of MIWC (sMIWC) was also identified in lung and kidney by RNase protection assay, corresponding to deletion of exon 2 of MIWC. In response to dehydration (3 days, -15 % body weight), renal expression of CHIP28 and MIWC were unchanged, whereas expression of AQP-CD and GLIP were increased significantly by 2.18 +/- 0.04 and 1.36 +/- 0.11 fold (SE, n = 5), respectively. These results establish quantitative values for aquaporin transcript expression in multiple mammalian tissues. The sensitive RNase protection assay revealed the expression of water channels in several tissues not studied previously or in which mRNA levels were too low to detect by Northern blot analysis. The observation of GLIP up-regulation in kidney by dehydration suggests a role in the urinary concentrating mechanism.
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PMID:Quantitative analysis of aquaporin mRNA expression in rat tissues by RNase protection assay. 867 43

The aquaporin family of membrane water transport proteins are expressed in diverse tissues, and in brain the predominant water channel protein is AQP4. Here we report the isolation and characterization of the human AQP4 cDNAs and genomic DNA. Two cDNAs were isolated corresponding to the two initiating methionines (M1 in a 323-aa polypeptide and M23 in a 301-aa polypeptide) previously identified in rat [Jung, J.S., Bhat, R.V., Preston, G.M., Guggino, W.B. & Agre, P. (1994) Proc. Natl. Acad. Sci. USA 91, 13052-13056]. Similar to other aquaporins, the AQP4 gene is composed of four exons encoding 127, 55, 27, and 92 amino acids separated by introns of 0.8, 0.3, and 5.2 kb. Unlike other aquaporins, an alternative coding initiation sequence (designated exon 0) was located 2.7 kb upstream of exon 1. When spliced together, M1 and the subsequent 10 amino acids are encoded by exon 0; the next 11 amino acids and M23 are encoded by exon 1. Transcription initiation sites have been mapped in the proximal promoters of exons 0 and 1. RNase protection revealed distinct transcripts corresponding to M1 and M23 mRNAs, and AQP4 immunoblots of cerebellum demonstrated reactive polypeptides of 31 and 34 kDa. Using a P1 and a lambda EMBL subclone, the chromosomal site of the human AQP4 gene was mapped to chromosome 18 at the junction of q11.2 and q12.1 by fluorescence in situ hybridization. These studies may now permit molecular characterization of AQP4 during human development and in clinical disorders.
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PMID:The human AQP4 gene: definition of the locus encoding two water channel polypeptides in brain. 885 81

The mRNA expression and localization of the aquaporin (AQP) family in rat kidney were examined by ribonuclease protection assay and immunohistochemistry. AQP1, AQP2, AQP3, and AQP4 mRNA were hardly detectable in 16-day gestation fetuses. AQP1 mRNA was explosively expressed at 1 wk, keeping the level throughout life. AQP2 mRNA expression was apparently noticed in 18-day fetuses and was enhanced gradually with age to reach a plateau at 4 wk. AQP3 and AQP4 mRNA expression was significantly found at birth but was not changed remarkably thereafter. AQP2 protein appeared first at the apical side of collecting duct cells in 18-day fetuses. The staining intensity at the site increased with age, and basolateral staining was added in adult rats. AQP3 was distinctly demonstrated at the basolateral side of collecting duct cells after birth, and the staining intensity was almost stable throughout life. The progressive induction of AQP2 expression in the first 4 wk after birth is presumed to contribute to the maturation of urinary concentrating capacity during the kidney development.
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PMID:Expression of AQP family in rat kidneys during development and maturation. 912 96

Lung fluid is reabsorbed rapidly at birth to permit alveolar respiration. We reported previously that expression of aquaporins (AQP) 1, 4, and 5 in rat lung increased just after birth. The hypothesis was tested that the increased AQP expression is associated with increased osmotic water permeability (Pf) between the airspace and capillary compartments. Pf was measured in isolated perfused fetal and newborn rabbit lungs using a pleural surface fluorescence method (Carter, E.P., M.A. Matthay, J. Farinas, and A.S. Verkman. 1996. J. Gen. Physiol. 108:133-142). In response to perfusate osmolality increase from 300 to 600 mosM, initial rates of osmotic equilibration were 1.13+/-0.13 mosM/s at 0-12 h after birth, increasing to 1.52+/-0.19 mosM/s at 12-24 h, and 1.83+/-0.10 mosM/s at 24-84 h. Corresponding Pf values (in cm/s x 10(-2)), computed from d[mosM]/dt and alveolar surface-to-volume ratios, were 1.03+/-0.11 (0-12 h), 1.51+/-0.16 (12-24 h), and 1.88+/-0.09 (24-84 h). Pf was relatively low in prenatal (1.22-1.27, fetal days 29 and 31) and adolescent (1.25+/-0.08, 21-d) rabbit lungs. To test for involvement of molecular water channels, measurements were made of Arrhenius activation energy (Ea), mercurial inhibition, diffusional water permeability (Pd), and AQP expression. Temperature-dependence measurements showed a 25% decrease in Ea for Pf in lungs < 1 d vs. 4 d. Pf was decreased 30% by 0.5 mM HgCl2 in < 1-d lungs and 44% in 4-d lungs. Pd was 1.0 x 10(-)5 cm/s and did not change when Pf was increased by 75%. RNase protection assay showed increased transcript expression in the first 24 h after birth for rabbit isoforms of AQP1 and AQP4. These results provide the first functional data on water permeability in perinatal lung. The increased water permeability after birth may facilitate the maintenance of dry alveoli.
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PMID:Developmental changes in water permeability across the alveolar barrier in perinatal rabbit lung. 927 23

A family of water-selective channels, aquaporins (AQP), has been demonstrated in various organs and tissues. However, the localization and expression of the AQP family members in the gastrointestinal tract have not been entirely elucidated. This study aimed to demonstrate the expression and distribution of several types of the AQP family and to speculate on their role in water transport in the rat gastrointestinal tract. By RNase protection assay, expression of AQP1-5 and AQP8 was examined in various portions through the gastrointestinal tract. AQP1 and AQP3 mRNAs were diffusely expressed from esophagus to colon, and their expression was relatively intense in the small intestine and colon. In contrast, AQP4 mRNA was selectively expressed in the stomach and small intestine and AQP8 mRNA in the jejunum and colon. Immunohistochemistry and in situ hybridization demonstrated cellular localization of these AQP in these portions. AQP1 was localized on endothelial cells of lymphatic vessels in the submucosa and lamina propria throughout the gastrointestinal tract. AQP3 was detected on the circumferential plasma membranes of stratified squamous epithelial cells in the esophagus and basolateral membranes of cardiac gland epithelia in the lower stomach and of surface columnar epithelia in the colon. However, AQP3 was not apparently detected in the small intestine. AQP4 was present on the basolateral membrane of the parietal cells in the lower stomach and selectively in the basolateral membranes of deep intestinal gland cells in the small intestine. AQP8 mRNA expression was demonstrated in the absorptive columnar epithelial cells of the jejunum and colon by in situ hybridization. These findings may indicate that water crosses the epithelial layer through these water channels, suggesting a possible role of the transcellular route for water intake or outlet in the gastrointestinal tract.
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PMID:Expression and localization of aquaporins in rat gastrointestinal tract. 1006 89

Two cDNA isoforms of bovine aquaporin-4 (bAQP4-A and bAQP4-B) were newly isolated. Sequence analysis of both cDNAs revealed open reading frames of 972 (bAQP4-A) and 906 nucleotides (bAQP4-B) with deduced proteins of 323 (bAQP4-A) and 301 amino acid residues (bAQP4-B). Partial 5'-genomic sequence analysis showed that the 5'-noncoding sequences specific to bAQP4-A and -B transcripts were contained in distinct exons, exon 0 for bAQP4-A and new exon X for bAQP4-B. RNase protection assay demonstrated the definite expression of both isoforms in bovine brain. The deduced amino acid sequence of bAQP4-A was highly homologous to the human (97%), rat (95%), and mouse (93%) AQP4. Reverse transcription-PCR detected the expression of AQP4 mRNAs in bovine brain endothelial cells as well as in a variety of bovine organs such as brain, lung, spleen, and kidney. Northern blot analysis indicated that a 6.0 kb message is predominantly expressed in bovine brain and lung.
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PMID:Molecular cloning of two bovine aquaporin-4 cDNA isoforms and their expression in brain endothelial cells. 1067 41

We recently reported that secretin induces the exocytic insertion of functional aquaporin-1 water channels (AQP1) into the apical membrane of cholangiocytes and proposed that this was a key process in ductal bile secretion. Because AQP1 is present on the basolateral cholangiocyte membrane in low amounts, we hypothesized that another AQP must be expressed at this domain to facilitate transbasolateral water movement. Thus, we investigated the expression, subcellular localization, possible regulation by secretin, and functional activity of AQP4, a mercury-insensitive water channel expressed in other fluid transporting epithelia. Using reverse transcription-polymerase chain reaction (RT-PCR) on RNA prepared from purified rat cholangiocytes, we amplified a product of 311 bp that was 100% homologous to the reported AQP4 sequence. RNase protection assay confirmed the presence of an appropriate size transcript for AQP4 in cholangiocytes. Immunoblotting detected a band of approximately 31 kd corresponding to AQP4 in basolateral but not apical membranes of cholangiocytes. Secretin did not alter the amount of plasma membrane AQP4 but, as expected, induced AQP1 redistribution from intracellular to apical plasma membranes. Functional studies showed that AQP4 accounts for about 15% of total cholangiocyte membrane water permeability. Our results indicate that: (1) cholangiocytes express AQP4 messenger RNA (mRNA) and protein and (2) in contrast to AQP1, which is targeted to the apical cholangiocyte membrane by secretin, AQP4 is constitutively expressed on the basolateral cholangiocyte membrane and is secretin unresponsive. The data suggest that AQP4 facilitates the basolateral transport of water in cholangiocytes, a process that could be relevant to ductal bile formation.
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PMID:Expression of aquaporin-4 water channels in rat cholangiocytes. 1082 57

Aquaporins (AQPs) are a family of water-selective transporting proteins with homology to the major intrinsic protein (MIP) of lens [Cell 39 (1984) 49], that increase plasma membrane water permeability in secretory and absorptive cells. In the central nervous system (CNS), we detected the transcripts of AQP3, 5 and 8 in addition to the previously reported transcripts of AQP4 and 9 in astrocytes, of AQP3, 5 and 8 in neurons, of AQP8 in oligodendrocytes, and none of them in microglia using RNase protection assay and the reverse transcription-polymerase chain reaction (RT-PCR). Hypoxia evoked a marked decrease in the expression levels of AQP4, 5 and 9, but not of AQP3 and 8 mRNAs, and in astrocytes in vitro subsequent reoxygenation elicited the restoration of the expression of AQP4 and 9 to their basal levels. Interestingly, AQP5 showed a transient up-regulation (about 3-fold) and subsequent down-regulation of its expression within 20 h of reoxygenation after hypoxia. The changes in the profiles of AQP expression during hypoxia and reoxygenation were also observed by Western blot analysis. These results suggest that AQP5 may be one of the candidates for inducing the intracranial edema in the CNS after ischemia injury.
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PMID:Alterations in the expression of the AQP family in cultured rat astrocytes during hypoxia and reoxygenation. 1137 53

Of ten members of the aquaporin family (AQP), the mRNA expression and regulation of AQP1, AQP3, AQP4 and AQP9 in cultured human keratinocytes were examined by an RNase protection assay. AQP3 mRNA was expressed in growing and differentiating cells, while AQP9 mRNA was only detected in differentiating cells. The epidermis in skin-equivalent cultures expressed both AQP3 and AQP9 mRNA. However, neither AQP1 nor AQP4 mRNA was detectable in either monolayer or skin-equivalent cultures. Incubation of keratinocytes in sorbitol-added hypertonic medium increased AQP3 mRNA expression. This was confirmed using other solutes such as NaCl, mannitol, glucose and sucrose. The effect of sorbitol was reversible, dose-dependent and maximal at 24 h after addition. However, AQP1, AQP4 and AQP9 mRNA expression were unchanged under any of the hypertonic conditions examined. These findings indicated that osmotic stress up-regulates AQP3 gene expression in cultured keratinocytes.
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PMID:Osmotic stress up-regulates aquaporin-3 gene expression in cultured human keratinocytes. 1175 58


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