Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.1.26.9 (ribonuclease)
 6,589 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We previously cloned, sequenced, and expressed two distinct mammalian Na+/H+ exchanger isoforms (NHE-1 and NHE-2). We report here the cloning of a composite cDNA which encodes a third mammalian isoform (NHE-3), which is expressed specifically in intestine and kidney. The protein deduced from the longest open reading frame of this composite sequence has 832 amino acids with a calculated Mr of 92,747. The hydrophobicity plot of NHE-3 is very similar to that of NHE-1 and NHE-2. NHE-3 is also predicted to have 10-12 membrane-spanning domains and a long cytoplasmic domain which contains putative protein kinase phosphorylation motifs. NHE-3 exhibits overall 41% amino acid identity with NHE-1. NHE-3 is likely a glycoprotein as it has one potential N-linked glycosylation site, which is conserved in all NHEs identified. Northern blot analysis of poly(A+) RNA isolated from rabbit ileum using NHE-3 cDNA as a probe hybridized to a single 5.4-kilobase transcript. More detailed tissue distribution of message was performed by ribonuclease protection assay. It was found that NHE-3 message is only expressed in intestine and kidney, with the kidney cortex having the most abundant message, followed by intestine and kidney medulla. In intestine, ileum and ascending colon have the same amount of message, with much lesser amounts in jejunum. The message is absent from duodenum and descending colon, which lack the neutral NaCl absorptive process. Thus, NHE-3 might be involved in Na+ absorption in intestinal and renal epithelial cells.
 ...
PMID:Cloning and sequencing of a rabbit cDNA encoding an intestinal and kidney-specific Na+/H+ exchanger isoform (NHE-3). 137 92

A unique Na+/H+ exchanger isoform, NHE-2, was cloned and characterized. NHE-2 is a protein of 809 amino acids with a calculated size of 90,787. It exhibits overall amino acid identity of 50, 44, and 60% with other cloned mammalian Na+/H+ exchangers NHE-1, NHE-3, and NHE-4, respectively. Northern blot analysis of poly(A+) RNA isolated from rabbit ileum, kidney cortex, and kidney medulla using NHE-2 cDNA as a probe revealed messages of 5.2, 4.2, and 3.2 kilobases with relative abundance (in descending order) kidney medulla > kidney cortex > ileum. More detailed tissue distribution of message was performed by ribonuclease protection assay. NHE-2 was predominantly expressed in kidney, intestine, and adrenal gland with a small amount in skeletal muscle and trachea. Stable expression of NHE-2 in PS120 fibroblasts confirmed that NHE-2 is a functional Na+/H+ exchanger which is defined by amiloride-sensitive Na+-dependent alkalinization of acid-loaded cells. NHE-2 has the same Ki for amiloride inhibition as NHE-1 (1 microM) but is 25-fold more resistant to ethylisopropylamiloride inhibition than is NHE-1 (500 versus 20 nM). Like NHE-1, NHE-2 can be activated by serum. Expression of NHE-2 in a polarized human intestinal epithelial cell line, Caco-2 cells, results in functional expression of NHE-2 in the apical membrane. Thus, we conclude that NHE-2 is a candidate to be an apical membrane Na+/H+ exchanger in intestinal and renal epithelial cells.
 ...
PMID:Cloning and expression of a rabbit cDNA encoding a serum-activated ethylisopropylamiloride-resistant epithelial Na+/H+ exchanger isoform (NHE-2). 768 25

Methylprednisolone stimulates rabbit ileal neutral NaCl absorption; and aminoglutethimide, which decreases glucocorticoid levels, decreases NaCl absorption. Studies were carried out to determine the mechanism of these effects and to determine which members of the gene family of mammalian Na+/H+ exchangers were involved. Rabbits were treated subcutaneously with methylprednisolone (40 mg daily for 24 or 72 h), aminoglutethimide (100 mg twice daily for 72 h), or saline as a control. Ileal brush border membranes were prepared by magnesium precipitation, and brush border Na+/H+ exchange was determined by 22Na+ uptake over 3-8 s. The 22Na+ uptake experiments were performed in the presence of a voltage clamp using either valinomycin/potassium or tetramethylammonium/nitrate to eliminate potential contributions by other electrogenic transport processes. Methylprednisolone treatment approximately doubled ileal brush border Na+/H+ exchange, whereas aminoglutethimide led to a 50% decrease in Na+/H+ exchange. These effects were specifically on Na+ uptake with an acid inside pH gradient, whereas diffusive Na+ uptake (no pH gradient), glucose-dependent Na+ uptake, and glucose and Na+ equilibrium volumes were not affected. To determine if the increase in Na+/H+ exchange was associated with an increase in message expression, mRNA levels were measured by ribonuclease protection assay. Methylprednisolone stimulated the NHE-3 mRNA level by 4-6-fold at 24 h, which remained increased at 72 h. In contrast, messages for NHE-1 and NHE-2 were not affected by methylprednisolone. In summary, 1) methylprednisolone stimulation of rabbit ileal Na+ absorption is due to stimulation of ileal villus cell brush border Na+/H+ exchange; 2) basal ileal brush border Na+/H+ exchange is dependent on glucocorticoid levels; and 3) an increase in NHE-3 message, but not in NHE-1 or NHE-2 message, correlates with the stimulation of ileal brush border Na+/H+ exchange. It is likely that NHE-3 is an Na+/H+ exchanger that is involved in ileal Na+ absorption.
 ...
PMID:Glucocorticoid stimulation of ileal Na+ absorptive cell brush border Na+/H+ exchange and association with an increase in message for NHE-3, an epithelial Na+/H+ exchanger isoform. 838 Jan 55

Data suggest that mineralocorticoid selectivity is differentially regulated in epithelial target tissues. We investigated whether the level of dietary NaCl intake influenced the expression and tissue distribution of 11-beta-hydroxysteroid dehydrogenase type 2 (11betaHSD-2), aldosterone receptor (MR), and glucocorticoid receptor (GR) in rat colon, kidney, and cardiovascular tissue. Rats were fed a diet with 0.01 or 3% NaCl for 10 days. Messenger RNAs were analyzed with ribonuclease protection assay, 11betaHSD-2 protein by Western blot analysis, and localization of GR and 11betaHSD-2 by immunohistochemistry. NaCl restriction elevated plasma renin and aldosterone concentration, whereas corticosterone was unaltered. In distal colon, 11betaHSD-2 mRNA and protein were augmented significantly by low-NaCl intake and immunolabeling was widely distributed in crypt and surface epithelium. The MR mRNA level was decreased, whereas GR mRNA was unaltered in distal colon. MR, GR, and 11betaHSD-2 mRNAs were not changed in kidney cortex and medulla, left cardiac ventricle, and aorta. Immunofluorescence labeling showed that GR and 11betaHSD-2 localization was mutually exclusive in kidney. In colon epithelium, nuclear staining for GR subsided as perinuclear 11betaHSD-2 immunoreactivity increased with NaCl restriction. As a functional correlate of increased 11betaHSD-2 expression in colon, the GR-stimulated sodium-hydrogen exchanger NHE-3 was lowered by NaCl restriction. Inhibition of 11betaHSD-2 activity by carbenoxolone during NaCl restriction stimulated NHE-3 expression in colon. Dexamethasone stimulated NHE-3 both in colon and kidney. These data indicate that mineralocorticoid selectivity is physiologically regulated by NaCl intake at the level of 11betaHSD-2 expression and tissue distribution in the distal colon, but not in the kidney.
 ...
PMID:Stimulation of 11-beta-hydroxysteroid dehydrogenase type 2 in rat colon but not in kidney by low dietary NaCl intake. 1284 61