Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0043167 (pertussis)
 19,595 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

G protein-coupled receptors initiate signaling cascades after associating with heterotrimeric G proteins. This is typically initiated by agonist binding, but can also occur spontaneously, particularly in receptors bearing distinct missense mutations. Two such mutations in the parathyroid hormone receptor are associated with constitutive activity, manifesting clinically as Jansen's metaphyseal chondroplasia. We introduce analogous mutations separately and together into the secretin receptor to explore their impact on another family member. Constructs were expressed transiently in COS cells, and had binding and signaling (cAMP generation) studied. Each construct was processed appropriately to lead to cell surface expression and signaling. Secretin bound to the wild-type receptor with two affinity states recognized, 1% of sites in the high affinity state (Ki = 0.5 +/- 0.1 nM) and 99% in the low affinity state (Ki = 23 +/- 3 nM). Mutant receptor binding best fit a single affinity state, having values for Ki of 5 +/- 1 nM (H156R), 8 +/- 1 nM (T322P) and 6 +/- 1 nM (H156R/T322P), with each of these demonstrating a shift to higher affinity than the predominent low affinity state of the wild-type receptor. Each mutant receptor expressed small to moderate constitutive activity, with basal levels of cAMP activity greater than control (P < .01): H156R, 1.4-fold; T322P, 4.5-fold and H156R/T322P, 6.8-fold. The level of basal activity of even the most active construct was only 15% of the maximal response of wild-type receptor. Although each of the single site mutants responded to secretin by increasing their cAMP levels in a concentration-dependent manner, the dual mutant decreased its cAMP in response to hormone (EC50 = 13 nM). Thus, a natural agonist had become an inverse agonist at this unique construct. Because this could reflect reduced normal coupling with Gs or increased aberrant coupling with Gi, the mechanism was further explored using pertussis toxin and a stable analogue of GTP. Although ligand-binding determinants were retained in the dual receptor mutant, the conformation of this receptor upon secretin binding effected a reduction in its basal coupling with Gs, thereby resulting in inverse agonism.
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PMID:Protean effects of a natural peptide agonist of the G protein-coupled secretin receptor demonstrated by receptor mutagenesis. 969 8

Secretin plays a key role in the regulation of normal cholangiocyte physiology via secretin receptor (SCTR). SCTR expression is upregulated during extrahepatic cholestasis induced by bile duct ligation and closely associated with cholangiocyte proliferative responses. Although well studied in normal cholangiocytes, the role of secretin and the expression of SCTR in the regulation of cholangiocarcinoma proliferation are unknown. In vitro, secretin (10(-7) M) displayed differential effects on normal cholangiocyte [H-69 and human intrahepatic biliary epithelial cell line (HIBEpiC)] and cholangiocarcinoma (Mz-ChA-1, HuH-28, TFK-1, SG231, CCLP1 and HuCC-T1) cell lines as such secretin is mitogenic for normal cholangiocytes and antiproliferative for cholangiocarcinoma. As expected in normal cholangiocytes (HIBEpiC), secretin increased intracellular cyclic adenosine monophosphate (cAMP) levels. However, the effect of secretin on intracellular cAMP levels was suppressed in Mz-ChA-1 cells. Secretin-stimulated intracellular cAMP levels in Mz-ChA-1 were restored by pretreatment with pertussis toxin, suggesting that the receptor coupled to Galpha(i) rather than Galpha(s). SCTR expression was found to be downregulated in 4 of the 6 cholangiocarcinoma cell lines evaluated and in human cholangiocarcinoma biopsy samples. In vivo, secretin significantly inhibited the tumor size and more than doubled tumor latency, which was associated with a decrease in proliferating cell nuclear antigen and an increase in cleaved-caspase 3 expression levels. Our results demonstrate that secretin and/or the modulation of SCTR expression might have potential as a therapeutic tool in the treatment of cholangiocarcinoma.
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PMID:Secretin inhibits cholangiocarcinoma growth via dysregulation of the cAMP-dependent signaling mechanisms of secretin receptor. 1990 46