Involvement of protein kinase C-alpha and -epsilon in extracellular Ca2+ signalling mediated by the calcium sensing receptor

The sensing of extracellular Ca2+ concentration ([Ca2+]) and modulation of cellular processes associated with acute or sustained changes in [Ca2+](o) are cell-type specific and mediated by the calcium sensing receptor (CaR). [Ca2+](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 [Ca2+]. activated PKC-alpha and PKC-epsilon 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 [Ca2+] 0 required influx of Ca(2+)through Ni2+-sensitive Ca2+ channels and phospliatidylinositol-dependent phospholipase C-beta activity. Inhibition of PKC by co-expression of dominant-negative (DN) mutants of PKC-alpha or -epsilon 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 [Ca2+](o). Activation of ERK1/2 by high [Ca2+]. was not necessary for the [Ca2+](o)-regulated secretion of parathyroid hormone (PTH) in dispersed bovine parathyroid cells. These data suggest that the CaR-mediated [Ca2+] signal leading to regulated PTH secretion that requires diacylglycerol-responsive PKC isoforms is not mediated via the ERK pathway. (C) 2004 Elsevier Inc. All rights reserved.