Involvement of protein kinase C-alpha and -epsilon in extracellular Ca(2+) signalling mediated by the calcium sensing receptor.
The sensing of extracellular Ca(2+) concentration ([Ca(2+)](o)) and modulation of cellular processes associated with acute or sustained changes in [Ca(2+)](o) are cell-type specific and mediated by the calcium sensing receptor (CaR). [Ca(2+)](o) signalling requires protein kinase C (PKC), but the identity and role of PKC isoforms in CaR-mediated responses remain unclear. Here we show that high [Ca(2+)](o) activated PKC-alpha and PKC- in parathyroid cells and in human embryonic kidney (HEK293) cells overexpressing the CaR (HEK-CaR) and that this response correlated with the CaR-dependent activation of mitogen-activated protein kinases ERK1/2. Activation of ERK1/2 by acute high [Ca(2+)](o) required influx of Ca(2+)through Ni(2+)-sensitive Ca(2+)channels and phosphatidylinositol-dependent phospholipase C-beta activity. Inhibition of PKC by co-expression of dominant-negative (DN) mutants of PKC-alpha or - with the CaR attenuated sustained ERK1/2 activation. Overexpression of a PKC phosphorylation site (T888A) mutant CaR in HEK293 cells showed that this site was important for ERK1/2 activation at high [Ca(2+)](o). Activation of ERK1/2 by high [Ca(2+)](o) was not necessary for the [Ca(2+)](o)-regulated secretion of parathyroid hormone (PTH) in dispersed bovine parathyroid cells. These data suggest that the CaR-mediated [Ca(2+)](o) signal leading to regulated PTH secretion that requires diacylglycerol-responsive PKC isoforms is not mediated via the ERK pathway.
Sakwe
Amos M
AM
Department of Medical Biochemistry and Microbiology, Uppsala University, SE-751 23 Uppsala, Sweden. Amos.Sakwe@imbim.uu.se
Larsson
Mårten
M
Rask
Lars
L
D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D015220:Calcium Channels / Q000378:metabolism; D002417:Cattle; D002460:Cell Line; D002470:Cell Survival; D002478:Cells, Cultured; D004789:Enzyme Activation; D006801:Humans; D007668:Kidney / Q000166:cytology; D020928:Mitogen-Activated Protein Kinases / Q000187:drug effects / Q000378:metabolism; D009154:Mutation; D010280:Parathyroid Glands / Q000166:cytology / Q000378:metabolism; D010281:Parathyroid Hormone / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation; D011493:Protein Kinase C / Q000235:genetics / Q000378:metabolism*; D051571:Protein Kinase C-alpha; D051744:Protein Kinase C-epsilon; D044169:Receptors, Calcium-Sensing / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction
D015220:Calcium Channels; D010281:Parathyroid Hormone; D044169:Receptors, Calcium-Sensing; D019869:Phosphatidylinositol 3-Kinases; C496628:PRKCA protein, human; C497255:PRKCE protein, human; D011493:Protein Kinase C; D051571:Protein Kinase C-alpha; D051744:Protein Kinase C-epsilon; D020928:Mitogen-Activated Protein Kinases; D002118:Calcium