Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.1.27.1 (RNase)
 16,360 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

The sodium-hydrogen exchanger (NHE) has been implicated in bone resorption by osteoclasts. We have studied expression of NHE-1, an isoform of the NHE, in chicken bone marrow mononuclear phagocyte precursors during differentiation into the osteoclast phenotype in culture. A monoclonal anti-body raised against the carboxy-terminus of NHE-1 detected the presence of a 100 kDa protein (similar to the mammalian form of NHE-1) in the osteoclasts. Laser scanning confocal microscopy revealed association with the alpha(v)beta(3) integrin and focal adhesion kinase (pp(125)FAK) at the basolateral membrane (BLM) of the osteoclast in addition to a more generalized cellular distribution. A fragment of avian NHE-1 cDNA was obtained by polymerase chain reaction cloning, and it was used to characterize expression of NHE-1 transcripts in cultured chicken osteoclast precursors. The avian NHE-1 message was a 3.9 kB band on Northern analysis, which differed from the mammalian message. Retinoic acid (RA) elicited an increase in the steady-state intracellular pH (pH(1)) from 6.87 to 7.10 in the absence of bicarbonate and was inhibited by ethylisopropylamiloride, an inhibitor of Na-H exchange. Using ribonuclease protection assays, we found that NHE-1 transcripts are induced as cells differentiate in vitro and in response to 13-cis-RA. Western blot analysis indicated that protein levels also increased in response to 13-cis-RA. Our results demonstrate expression of NHE-1 in avian osteoclasts with a complex cellular distribution in culture, and NHE-1 expression is induced as cells differentiate into mature osteoclasts in response to 13-cis-RA.
 ...
PMID:Cellular distribution and regulation of NHE-1 isoform of the NA-H exchanger in the avian osteoclast. 883 1

Recent studies have indicated the presence of Na+/H+ and Cl-/HCO-3 exchange activities in lung alveolar and tracheal tissues of various species. To date, the identity of the Na+/H+ (NHE) and Cl-/HCO-3 (AE) exchanger isoforms and their regional distribution in human airways are not known. Molecular species of the NHE and AE gene families and their relative abundance in the human airway regions were assessed utilizing RT-PCR and the RNase protection assay, respectively. Organ donor lung epithelia from various bronchial regions (small, medium, and large bronchi and trachea) were harvested for RNA extraction. Gene-specific primers for the human NHE and AE isoforms were utilized for RT-PCR. Our results demonstrated that NHE1, AE2, and brain AE3 isoforms were expressed in all regions of the human airways, whereas NHE2, NHE3, AE1, and cardiac AE3 were not detected. RNase protection studies for NHE1 and AE2, utilizing glyceraldehyde-3-phosphate dehydrogenase as an internal standard, demonstrated that there were regional differences in the NHE1 mRNA levels in human airways. In contrast, the levels of AE2 mRNA remained unchanged. Differential expression of these isoforms in the human airways may have functional significance related to the airway absorption and secretion of electrolytes.
 ...
PMID:Expression of the Na+/H+ and Cl-/HCO-3 exchanger isoforms in proximal and distal human airways. 1036 22

Molecular species of the Na(+)-H(+) exchanger (NHE) and anion exchanger (AE) gene families and their relative abundance in the human airway regions were assessed utilizing RT-PCR and the RNase protection assay, respectively. Organ donor lung epithelia from various bronchial regions (small, medium, and large bronchi and trachea) were harvested for RNA extraction. Gene-specific primers for the human NHE and AE isoforms were utilized for RT-PCR. Our results demonstrated that NHE1, AE2, and brain AE3 isoforms were expressed in all regions of the human airway, whereas NHE2, NHE3, AE1, and cardiac AE3 were not detected. RNase protection studies for NHE1 and AE2, utilizing glyceraldehyde-3-phosphate dehydrogenase as an internal standard, demonstrated that there were regional differences in the NHE1 mRNA levels in human airways. In contrast, the levels of AE2 mRNA remained unchanged. Differential regional expression of NHE1 isoform may be related to a higher acid load in the tracheal epithelial cells than in epithelia of distal airways. Fluctuations in PCO(2) during inspiration and expiration are probably larger in the tracheal lumen than in the lumen of distal airways with associated larger swings in intracellular pH with each respiratory cycle. Immunohistochemical staining for AE2 protein demonstrated localization to the epithelial cells of human bronchial mucosa.
 ...
PMID:Detection of Cl--HCO3- and Na+-H+ exchangers in human airways epithelium. 1187 73

Although cardiac NHE1 is activated during myocardial ischemia and reperfusion injury, little is known about changes in expression in non-infarcted myocardium after acute myocardial infarction (AMI). The purpose of this study was to examine left ventricular function and region dependent NHE1 expression after myocardial infarction. Therefore, we produced two AMI models in rats, a small infarction model which was continuously ligated at the branches of the left coronary artery, and an extensive infarction model continuously ligated at the root of the artery. We examined NHE1 mRNA expression using RNase protection assay and protein levels using Western blot analysis in non-infarcted myocardium during the 24 hour period after AMI. The level of NHE1 mRNA and protein expression in the whole heart including the infarcted myocardium did not change after a small infarction. On the other hand, in the case of an extensive infarction, the levels of NHE1 mRNA and protein expression decreased significantly by 21.5% (P<0.05) and by 22.0% (P<0.05), respectively, in non-infarcted myocardium. Left ventricular systolic pressure (LVSP) decreased significantly by 13% and 38% with the branch and root ligation, respectively. However, left ventricular end-diastolic pressure (LVEDP) only increased with the root ligation. These results indicate that NHE1 expression decreased in response to extensive myocardial infarction only in non-infarcted myocardium. The present study may be important in furthering the understanding of NHE1 in myocardial infarction and suggests that decreased expression of NHE1 in non-infarcted myocardium may decrease the extent of cardiac cell injury.
 ...
PMID:Decreased expression of Na+/H+ exchanger isoform 1 (NHE1) in non-infarcted myocardium after acute myocardial infarction. 1222 2