1. The calcitonin receptor stimulates Shc tyrosine phosphorylation and Erk1/2 activation. Involvement of Gi, protein kinase C, and calcium.
- Author
-
Chen Y, Shyu JF, Santhanagopal A, Inoue D, David JP, Dixon SJ, Horne WC, and Baron R
- Subjects
- Adenylate Cyclase Toxin, Animals, Calcitonin pharmacology, Calcium metabolism, Cell Line, Colforsin pharmacology, Enzyme Activation, Enzyme Inhibitors pharmacology, GRB2 Adaptor Protein, GTP-Binding Proteins metabolism, Ionomycin pharmacology, Pertussis Toxin, Phosphorylation, Phosphotyrosine metabolism, Protein Kinase C antagonists & inhibitors, Rabbits, Shc Signaling Adaptor Proteins, Tyrosine metabolism, Virulence Factors, Bordetella pharmacology, Adaptor Proteins, Signal Transducing, Adaptor Proteins, Vesicular Transport, Calcium-Calmodulin-Dependent Protein Kinases metabolism, Proteins metabolism, Receptors, Calcitonin physiology
- Abstract
While it is well established that adenylyl cyclase and phospholipase C-beta are two proximal signal effectors for the calcitonin receptor, the more distal signaling pathways are less well characterized. G protein-coupled receptors can activate Erk1/2 by Gs-, Gi-, or Gq-dependent signaling pathways, depending on the specific receptor and cell type examined. Since the calcitonin receptor can couple to all three of these G proteins, the ability of calcitonin to activate Erk1/2 was investigated. Calcitonin induced time- and concentration-dependent increases in Shc tyrosine phosphorylation, Shc-Grb2 association and Erk1/2 phosphorylation and activation in a HEK 293 cell line that stably expresses the rabbit calcitonin receptor C1a isoform. Pertussis toxin, which inactivates Gi, and calphostin C, a protein kinase C inhibitor, each partially inhibited calcitonin-induced Shc tyrosine phosphorylation, Shc-Grb2 association, and Erk1/2 phosphorylation. In contrast, neither forskolin nor H89, a protein kinase A inhibitor, had a significant effect on basal or calcitonin-stimulated Erk1/2 phosphorylation. Our results suggest that the calcitonin receptor induces Shc phosphorylation and Erk1/2 activation in HEK293 cells by parallel Gi- and PKC-dependent mechanisms. The calcitonin-induced elevation of cytosolic free Ca2+ was required for Erk1/2 phosphorylation, since preventing any change in cytosolic free Ca2+ by chelating both cytosolic and extracellular Ca2+ abolished the response. However, the change in Ca2+ that is induced by calcitonin is not sufficient to account for the calcitonin-induced Erk1/2 phosphorylation, since treatment with 100 nM ionomycin or 10 microM thapsigargin, each of which induced elevations of Ca2+ comparable to those induced by calcitonin, induced significantly less Erk1/2 phosphorylation than that induced by calcitonin. Erk1/2 may have important roles as downstream effectors mediating cellular responses to calcitonin stimulation.
- Published
- 1998
- Full Text
- View/download PDF