Intracellular signal transduction by the extracellular calcium-sensing receptor of Xenopus melanotrope cells.
The extracellular calcium-sensing receptor (CaR) is expressed in various types of endocrine pituitary cell, but the intracellular mechanism this G protein-coupled receptor uses in these cells is not known. In the present study we investigated possible intracellular signal transduction pathway(s) utilized by the CaR of the endocrine melanotrope cells in the intermediate pituitary lobe of the South African-clawed toad Xenopus laevis. For this purpose, the effects of various pharmacological agents on CaR-evoked secretion of radiolabeled secretory peptides from cultured melanotrope cells were assessed. CaR-evoked secretion, induced by the potent CaR agonist L-phenylalanine (L-Phe), could not be inhibited by cholera toxin, nor by NPC-15437 and PMA, indicating that neither G(s)/PKA nor G(q)/PKC pathways are involved. However, pertussis toxin (G(i/o) protein inhibitor), genistein (inhibitor of PTKs), wortmannin/LY-294002 (PI3-K inhibitor) and U-0126 (inhibitor of extracellular signal-regulated kinase, ERK) all substantially inhibited CaR-evoked secretion, indicating that the Xenopus melanotrope cell possesses a PI3-K/MAPK system that plays some role in CaR-signaling. Since no direct effect of L-Phe on ERK phosphorylation could be shown it is concluded that CaR must act primarily through another, still unknown, signaling pathway in Xenopus melanotropes. Our results indicate that the PI3-K/MAPK system has a facilitating effect on CaR-induced secretion, possibly by sensitizing the CaR.
Department of Cellular Animal Physiology, Donders Centre for Neuroscience, EURON European Graduate School for Neuroscience, Radboud University Nijmegen, Toernooiveld 1, 6525 ED Nijmegen, The Netherlands.
Maarten J J
MJ
van den Hurk
Peter M J M
PM
Cruijsen
Joost P H
JP
Schoeber
Wim J J M
WJ
Scheenen
Eric W
EW
Roubos
Bruce G
BG
Jenks
D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D015153:Blotting, Western; D002070:Butadienes / Q000494:pharmacology; D002478:Cells, Cultured; D002772:Cholera Toxin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000032:analysis / Q000378:metabolism; D019205:GTP-Binding Protein alpha Subunits, Gs / Q000037:antagonists & inhibitors / Q000378:metabolism; D019833:Genistein / Q000494:pharmacology; D042541:Intracellular Space / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D009570:Nitriles / Q000494:pharmacology; D037342:Pertussis Toxin / Q000494:pharmacology; D010649:Phenylalanine / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010880:Piperidines / Q000494:pharmacology; D011863:Radioimmunoassay; D044169:Receptors, Calcium-Sensing / Q000037:antagonists & inhibitors / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D000077191:Wortmannin; D014982:Xenopus laevis / Q000378:metabolism*
D000730:Androstadienes; D002070:Butadienes; D002772:Cholera Toxin; D000242:Cyclic AMP; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D019205:GTP-Binding Protein alpha Subunits, Gs; D019833:Genistein; D020928:Mitogen-Activated Protein Kinases; D009570:Nitriles; D037342:Pertussis Toxin; D010649:Phenylalanine; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010880:Piperidines; D044169:Receptors, Calcium-Sensing; D000077191:Wortmannin; C113580:U 0126; C069701:NPC 15437