Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.7.6 (RNA polymerase)
 34,946 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Glucagon stimulates the vesicle trafficking of aquaporin-8 (AQP8) water channels to the rat hepatocyte canalicular membranes, a process thought to be relevant to glucagon-induced bile secretion. In this study, we investigated whether glucagon is able to modulate the gene expression of hepatocyte AQP8. Glucagon was administered to rats at 0.2 mg/100 g body wt ip in 2, 3, or 6 equally spaced doses for 8, 16, and 36 h, respectively. Immunoblotting analysis showed that hepatic 34-kDa AQP8 was significantly increased by 79 and 107% at 16 and 36 h, respectively. Hepatic AQP9 protein expression remained unaltered. AQP8 mRNA expression, assessed by real-time PCR, was not modified over time, suggesting a posttranscriptional mechanism of AQP8 protein increase. Glucagon effects on AQP8 were directly studied in primary cultured rat hepatocytes. Immunoblotting and confocal immunofluorescence microscopy confirmed the specific glucagon-induced AQP8 upregulation. The RNA polymerase II inhibitor actinomycin D was unable to prevent glucagon effect, providing additional support to the nontranscriptional upregulation of AQP8. Cycloheximide also showed no effect, suggesting that glucagon-induced AQP8 expression does not depend on protein synthesis but rather on protein degradation. Inhibitory experiments suggest that a reduced calpain-mediated AQP8 proteolysis could be involved. The action of glucagon on hepatocyte AQP8 was mimicked by dibutyryl cAMP and suppressed by PKA or phosphatidylinositol-3-kinase (PI3K) inhibitors. In conclusion, our data suggest that glucagon induces the gene expression of rat hepatocyte AQP8 by reducing its degradation, a process that involves cAMP-PKA and PI3K signal pathways.
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PMID:Glucagon induces the gene expression of aquaporin-8 but not that of aquaporin-9 water channels in the rat hepatocyte. 1919 45

Polycystic kidney disease (PKD) is the most common life-threatening genetic disorder with bilateral cysts caused by increased level of cyclic adenosine 3',5'-monophosphate (cAMP). Since adenylyl cyclases (ACs) catalyze cAMP formation, pharmacological characterization of renal AC isoforms is essential. Therefore, we analyzed differences in activation, inhibition, and regulation of AC isoforms in rabbit cortex and medulla membranes. Glucagon, [8-arginine]vasopressin (AVP) and catecholamines significantly activated cortical AC. However, in medulla only glucagon and AVP activated AC. Under Mg(2+) conditions the profile of cortical membrane AC enzyme kinetics and the inhibitory profile of 2'(3')-O-(N-methylanthraniloyl) (MANT) nucleotides resembled recombinant AC5. In contrast, the K (i) values of MANT nucleotides for medullary membrane AC and its kinetic properties were similar to those of recombinant AC1. Reverse-transcriptase PCR confirmed the presence of AC1 and AC5 in medulla and cortex, respectively. Cortical AC was sensitive to inhibition by Ca(2+), corroborating the importance of AC5. However, Ca(2+)/CaM dependency specific for AC1 was not found in medulla. In conclusion, according to expression, kinetics and inhibition by MANT nucleotides both parts of the kidney differ in their AC isoforms. Whereas Ca(2+)-inhibitable AC5 was confirmed in renal cortex, the initially assumed AC1 activation in medulla could not be confirmed, pointing to the involvement of another AC isoform with some similarity to AC1. Since PKD is characterized by predominant involvement of the collecting duct and the distal nephrons located in renal cortex, AC5 may be the major AC isoform in this part of the kidney where cAMP increases cyst growth. Thus, potent and selective AC5 inhibitors could constitute a novel approach to treat PKD.
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PMID:Pharmacological characterization of adenylyl cyclase isoforms in rabbit kidney membranes. 2127 30