Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.11.1 (protein kinase)
 81,284 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The bile salt export pump (Bsep), a member of the ATP-binding cassette superfamily of transporters, mediates the ATP-dependent canalicular secretion of bile salts. We have cloned and expressed the mouse Bsep (mBsep) protein in Sf9 insect cells, and characterized its transport and ATPase properties. Because its deduced amino acid sequence predicts multiple phosphorylation sites for protein kinase A, protein kinase C (PKC) and Ca(2+)-calmodulin dependent kinase II, we have also tested whether mBsep undergoes phosphorylation. MBsep transports both glycine and taurine conjugated bile salts. Sf9 cell membranes that express mBsep exhibit higher basal ATPase activity than control membranes, and this is further stimulated by bile salts and inhibited by vanadate. Taurochenodeoxycholate is transported with the highest affinity and is the most potent inducer of ATPase activity. Cyclosporin A, glibenclamide and rifamycin SV, all competitive inhibitors of Bsep transport, also reduced the bile salt-stimulated ATPase activity. MBsep exists as a phospho-protein when expressed in Sf9 cells and the immunoprecipitated mBsep complex is a substrate for the catalytic subunit of PKC. When mBsep and the alpha-isoform of mouse PKC are co-expressed in Sf9 cells, a ninefold stimulation of phosphorylation occurs. This is further increased to 18-fold after activation by phorbol ester. Given that bile salts activate selected PKC isoforms in hepatocytes, including the alpha isoform, the phosphorylation of mBsep by PKCalpha may represent a point of regulation for this transporter that is mediated by its own substrate.
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PMID:Characterization of the mouse bile salt export pump overexpressed in the baculovirus system. 1134 52

Hydrophobic bile acids impair gallbladder emptying in vivo and inhibit gallbladder muscle contraction in response to CCK-8 in vitro. This study was aimed at determining the mechanisms of muscle cell dysfunction caused by bile acids in guinea pig gallbladders. Muscle cells were obtained by enzymatic digestion. Taurochenodeoxycholic acid (TCDC), a hydrophobic bile acid, caused a contraction of up to 15% and blocked CCK-induced contraction. Indomethacin abolished the TCDC-induced contraction. Hydrophilic bile acid tauroursodeoxycholic acid (TUDC) had no effect on muscle contraction but prevented the TCDC-induced contraction and its inhibition on CCK-induced contraction. Pretreatment with NADPH oxidase inhibitor PH2I, xanthine oxidase inhibitor allopurinol, and free-radical scavenger catalase also prevented TCDC-induced contraction and its inhibition of the CCK-induced contraction. TCDC caused H2O2 production, lipid peroxidation, and increased PGE2 synthesis and activities of catalase and SOD. These changes were significantly inhibited by pretreatment of PH2I or allopurinol. Inhibitors of cytosolic phospholipase A2 (cPLA2), protein kinase C (PKC), and mitogen-activating protein kinase (MAPK) also blocked the TCDC-induced contraction. It is concluded that hydrophobic bile acids cause muscle cell dysfunction by stimulating the formation of H2O2 via activation of NADPH and xanthine oxidase. H2O2 causes lipid peroxidation and activates cPLA2 to increase PGE2 production, which, in turn, stimulates the synthesis of free-radical scavengers through the PKC-MAPK pathway.
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PMID:Effects of bile acids on the muscle functions of guinea pig gallbladder. 1206 95

Hydrophobic bile salts induce either necrosis or apoptosis depending on the severity of the injury caused by them. Since bile salt-induced apoptosis is influenced by Ca2+- and protein kinase-signaling pathways, and both necrosis and apoptosis share common initiating mechanisms, we analyzed whether these signaling cascades also influence bile salt-induced necrosis in isolated rat hepatocytes. Taurochenodeoxycholate (TCDC, 0.25-1.50 mM, 2 h) reduced, in a dose-dependent manner, the percentage of viable hepatocytes, and increased the release of the cytosolic enzyme, lactate dehydrogenase (LDH) and alanine aminotransferase (ALAT), and that of the plasma membrane enzyme, alkaline phosphatase (AP). The PKC inhibitors, H7 (100 microM) and chelerythrine (2.5 microM), both prevented significantly TCDC-induced necrosis. On the contrary, the PKA activator, dibutyryl-cAMP, exacerbated TCDC-induced cell damage in a dose-dependent manner; this effect was more likely due to cAMP-mediated PKA activation, as the PKA inhibitor, KT5720 (1 microM), counteracted this effect. Instead, the intracellular Ca2+ chelator, BAPTA/AM (20 microM), was without effect. TCDC (1 mM) increased lipid peroxidation from 0.7 +/- 0.2 to 7.5 +/- 0.9 nmol of malondialdehyde per mg of protein, p < 0.001; the addition of the free radical scavenger, diphenyl-p-phenylendiamine, completely blocked this increase and prevented significantly TCDC-induced necrosis. PKC inhibition induced only a slight attenuation of TCDC-induced lipid peroxidation. Possible mechanisms accounting for the modulatory effect of signal transduction pathways on TCDC-induced necrosis, including signaling influence on TCDC transport events and TCDC-induced oxidative stress, are discussed.
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PMID:Signaling modulation of bile salt-induced necrosis in isolated rat hepatocytes. 1549 97