Protein kinase C activation blocks calcium receptor signaling in Xenopus laevis oocytes.
We examined whether calcium receptor (CaR) signaling is affected by protein kinase C (PKC) activation by assessing the effects of phorbol-12-myristate-13-acetate (PMA) on 45Ca2+ efflux from Xenopus laevis oocytes expressing wild-type (WT) and mutant bovine parathyroid CaRs. Raising extracellular [Ca2+] ([Ca2+]0) from 0.5 to 5.5 mM increased 45Ca efflux (26 +/- 3-fold) in oocytes expressing full-length and C-terminally truncated receptor (amino acid 1-895). These increases in 45Ca efflux were blocked by 88 +/- 3% after PMA treatment for 20 min. Three consensus PKC phosphorylation sites (Thr-647, Ser-795, and Thr-889) were mutated in the context of the full-length and truncated CaR. PMA treatment inhibited high [Ca2+]0-induced responses in oocytes expressing the Ser795Ala CaR (1-895), Thr889Ala CaR (1-895), and Ser795Ala/Thr889Ala CaR (1-895) by 30-40% compared with untreated controls (P < 0.05). A triple mutant of the full-length CaR demonstrated similarly reduced susceptibility to inhibition of 45Ca efflux by PMA. Thus, these sites are important in mediating the effects of PKC activation on CaRs, but other residues and effector molecules are likely to participate in the effects of PKC on CaR-induced signal transduction in target cells.
Chang
W
W
Endocrine Research Unit, Department of Veterans Affairs Medical Center, Department of Medicine, University of California, San Francisco 94121, USA.
Pratt
S
S
Chen
T H
TH
Shoback
D
D
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000502:physiology*; D002417:Cattle; D004789:Enzyme Activation; D005260:Female; D009865:Oocytes; D010766:Phosphorylation; D017354:Point Mutation; D011493:Protein Kinase C / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014982:Xenopus laevis
D002135:Calcium-Binding Proteins; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium