Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.11.13 (protein kinase C)
 49,245 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The discovery of a calcium receptor has stimulated interest in the signaling events underlying extracellular calcium ([Ca2+]o)-induced cell-specific responses. In osteoblasts, elevated levels of extracellular calcium mediate both mitogenesis and chemotaxis. Here we provide evidence that [Ca2+]o-stimulated chemotaxis of MC3T3-E1 osteoblast-like cells involves a G-protein-linked calcium-sensing receptor. [Ca2+]o promotes chemotaxis in a concentration-dependent manner. Pertussis toxin blocked almost all of [Ca2+]o-stimulated chemotaxis but had only a small effect on platelet-derived growth factor (PDGF)-stimulated chemotaxis. Consistent with the signaling model for PDGF-mediated chemotaxis, activation of phospholipase C played a critical role in [Ca2+]o-initiated chemotaxis: U-73122, an inhibitor of the activation of phospholipase C, blocked approximately 50% of PDGF-stimulated chemotaxis but blocked nearly all of the [Ca2+]o-stimulated chemotaxis. Down-regulation of protein kinase C also blocked about 50% of PDGF-stimulated chemotaxis but did not block [Ca2+]o-stimulated chemotaxis. Thus, unlike PDGF-mediated chemotaxis, chemotaxis stimulated by [Ca2+]o does not appear to require protein kinase C activation. This finding suggests events downstream of inositol 1,4,5-trisphosphate production rather than diacylglycerol production are critical to [Ca2+]o-promoted chemotaxis of MC3T3-E1 cells. The signal transduction mechanism underlying PDGF-induced chemotaxis involves the activation of phosphoinositide 3-kinase, as judged by the in vivo production of phosphatidylinositol 3,4-diphosphate and 3,4,5-trisphosphate and the partial sensitivity of chemotaxis to wortmannin, an inhibitor of phosphoinositide 3-kinase. In contrast, [Ca2+]o-stimulated chemotaxis was not blocked by wortmannin and elevations in [Ca2+]o did not increase the production of lipid products of phosphoinositide 3-kinase. Overall, [Ca2+]o-promoted chemotaxis of osteoblasts appears to utilize a unique signaling mechanism via a calcium-sensing receptor.
 ...
PMID:Extracellular calcium and platelet-derived growth factor promote receptor-mediated chemotaxis in osteoblasts through different signaling pathways. 911 Oct 36

1. Expression of receptors to extracellular calcium enables parafollicular cells of the thyroid gland (PF cells) to release calcitonin (CT) and serotonin (5-HT) in response to increased external Ca2+. Recently, a calcium-sensing receptor (CaR), similar to the G protein-coupled receptor for external Ca2+ cloned from parathyroid gland, was shown to be expressed in PF cells. Using a highly purified preparation of sheep PF cells, we have examined the electrical and biochemical processes coupling CaR activation to hormone release. 2. Whole-cell recordings in the permeabilized-patch configuration show that elevated extracellular Ca2+ concentration ([Ca2+]0) depolarizes these cells and induces oscillations in membrane potential. In voltage clamp, high [Ca2+]0 activates a cation conductance that underlies the depolarization. This conductance is cation selective, with a reversal potential near -25 mV indicating poor ion selectivity. 3. The CaR expressed in these cells is activated by other multivalent cations with a rank order potency of Gd3+ > Ba2+ > Ca2+ > > Mg2+. The insensitivity of these cells to high external Mg2+ contrasts with the reported sensitivity of the cloned CaR from parathyroid. 4. Elevation of [Ca2+]0 also stimulates increases in intracellular Ca2+ concentration ([Ca2+]i) and this effect is largely inhibited by the Ca2+ channel blocker nimodipine, indicating that L-type voltage-gated Ca2+ channels contribute to the response to elevated [Ca2+]0. 5. Elevated [Ca2+]0 induces an inward current under conditions where the only permeant external cation is Ca2+, indicating that influx via the cation conductance is another source of the increases in [Ca2+]i. 6. Extracellular Ca2+ stimulates 5-HT release with an EC50 of 1.5 mM. Nimodipine blocks 90% of the Ca2+0-induced 5-HT release, while other inhibitors of voltage-gated calcium channels had no effect. These data support an important role for L-type Ca2+ channels in CaR-induced hormone secretion. Although earlier studies indicate that high [Ca2+]0 induces release of Ca2+ from intracellular stores, thapsigargin-induced depletion of these stores did not affect secretion from these cells, indicating that Ca2+ influx is necessary and sufficient for the Ca2+0-induced 5-HT secretion. 7. Inhibition of protein kinase C (PKC) using chelerythrine, staurosporine, or calphostin C inhibited Ca2+0-induced 5-HT release by 50% while phorobol ester-induced 5-HT secretion was completely inhibited. Thus, PKC is an important component of the pathway linking CaR activation to hormone release. However, another as yet unknown second messenger also contributes to this pathway. 8. We tested the contribution of two different phospholipases to the CaR responses to determine the source of the PKC activator diacylglycerol (DAG). Selective inhibition of phosphatidylinositol-specific phospholipase C (PI-PLC) with U73122 had no effect on the response to elevated [Ca2+]0. However, pretreatment with D609, a selective inhibitor of phosphatidylcholine-specific phospholipase C (PC-PLC), inhibited Ca(2+)-induced 5-HT release to 50% of control indicating that phosphatidylcholine is a likely source of DAG in the response of PF cells to elevated [Ca2+]0.
 ...
PMID:Mechanism of extracellular Ca2+ receptor-stimulated hormone release from sheep thyroid parafollicular cells. 923 95

We report three novel activating mutations in the calcium-sensing receptor (CASR) that are responsible for autosomal dominant hypocalcemia (ADH) in three unrelated families. Each mutation involves a missense substitution resulting in a nonconservative amino acid alteration, P221L, E228Q, and Q245R. These mutations were observed in affected family members, but not in unaffected family members or in unrelated control samples. All three mutations are clustered in the extracellular domain of the CASR in a region dominated by negatively charged amino acids. Each mutant and wild-type receptor was expressed in Cos-1 cells. A luciferase reporter gene assay was utilized to detect the level of receptor activity by utilizing a protein kinase C-activated promoter to drive the production of luciferin, the reporter gene product. All three mutant receptors exhibited an increased sensitivity to calcium at all concentrations tested when compared to the wild-type receptor, supporting the hypothesis that these are activating mutations and are responsible for the ADH phenotype in these families. The data presented in this study suggest the importance of this highly negatively charged region of the extracellular domain in normal CASR function.
 ...
PMID:Three novel activating mutations in the calcium-sensing receptor responsible for autosomal dominant hypocalcemia. 1113 51

Elevated extracellular calcium (Ca(e)) stimulates both chemotaxis and mitogenesis of MC3T3-E1 osteoblasts via a calcium-sensing receptor (CasR). Ca(e)-mediated chemotaxis of these bone-forming cells is dependent on phospholipase C (PLC) and blocked by the Gi-protein inhibitor pertussis toxin. In this study, we examine the signaling mechanisms by which the CasR stimulates PLC activity in MC3T3-E1 osteoblasts. We found that elevated Ca(e) stimulated PLC-gamma1 tyrosine phosphorylation in a time-dependent and Ca(e)-concentration-dependent manner. The maximal increase in PLC-gamma1 tyrosine phosphorylation was observed 3-5 min after increasing Ca(e) by 3.2 mmol/L from 1.8 mmol/L. Elevated Ca(e) also promoted a rapid increase in both inositol 1,4,5-trisphosphate [Ins(1,4,5)P3], a second messenger formed by PLC-mediated hydrolysis of phosphatidylinositol 4,5-bisphosphate, and cytosolic free calcium ([Ca+2]i). The kinetics of the CasR-mediated increases in Ins(1,4,5)P3 and [Ca+2]i and the sensitivity of the Ca(e)-stimulated elevation in [Ca+2]i to U73122 (a PLC inhibitor) together suggest that the osteoblast CasR is coupled via Gq to PLC-beta. U73122 blocked the Ca(e)-promoted, but not PDGF-promoted, PLC-gamma1 tyrosine phosphorylation, suggesting that the activation of PLC-beta is upstream of PLC-gamma1 activation. Inhibition of protein kinase C (PKC) disrupted Ca(e)-stimulated tyrosine phosphorylation of PLC-gamma1. In addition, exposure to pertussis toxin or exogenous activation of protein kinase A (PKA) inhibited PLC-gamma1 tyrosine phosphorylation in response to Ca(e). The results indicate that: (a) the osteoblast CasR activates PLC-gamma1 downstream of PLC-beta in a PKC-dependent manner; (b) PKA is a negative regulator of Ca(e)-promoted PLC-gamma1 phosphorylation; and (c) Gq and Gi are both involved in the CasR-mediated phosphorylation of PLC-gamma1.
 ...
PMID:Calcium-sensing receptor-mediated activation of phospholipase C-gamma1 is downstream of phospholipase C-beta and protein kinase C in MC3T3-E1 osteoblasts. 1193 46

The calcium-sensing receptor (CaR) activation has recently been shown to modulate the ERK1 and ERK2 cascade in different cell lines. The present study investigated this pathway in human normal and tumoral parathyroid cells. In cells from normal parathyroids and almost all hyperplasia increasing extracellular calcium concentrations (Ca(o)(2+)) induced a significant activation of ERK1 and -2, the percent stimulation over basal activity (at 0.5 mM Ca(o)(2+)) being 545 +/- 140 and 800 +/- 205 in normal cells and 290 +/- 71 and 350 +/- 73 in hyperplasia at 1 and 2 mM Ca(o)(2+), respectively. This effect was mediated by CaR because it was mimicked by the receptor agonist gadolinium and neomycin. Basal and Ca(o)(2+)-stimulated ERK1 and -2 activity was nearly abolished by the PKC inhibitor calphostin C, and PKA changes did not affect ERK1 and -2 activity. PI3K blockade by wortmannin, known to prevent G protein betagamma subunit effect on ERK1 and -2, induced a 30% reduction of the Ca(o)(2+)-stimulated ERK1 and -2 activity. Adenomatous cells showed high PKC-dependent ERK1 and -2 activity in resting conditions that was unresponsive to high Ca(o)(2+). A role of MAPK on PTH secretion was suggested by the finding that PD98059, a specific MEK inhibitor, abolished the inhibitory effect of 1.5 mM Ca(o)(2+) on PTH release from normal parathyroid cells. In conclusion, these data first demonstrate that CaR activation, through the PKC pathway and, to a lesser extent, PI3K, increases ERK1 and -2 activity in normal parathyroid cells and this cascade seems to be involved in the modulation of PTH secretion by Ca(o)(2+). Interestingly, this signaling pathway is disrupted in parathyroid tumors.
 ...
PMID:Mitogen-activated protein kinase cascade in human normal and tumoral parathyroid cells. 1199 64

In this study, the human calcium-sensing receptor (CaR) stably expressed in HEK293 cells was investigated with regard to the phosphorylation-induced desensitization of its signaling pathway. The receptor is known to activate the phospholipase C/inositol-1,4,5-trisphosphate (IP 3 ) signaling cascade, thus stimulating protein kinase C (PKC). In contrast, the adenylylcyclase/cAMP signaling pathway that activates protein kinase A (PKA) is believed to be coupled to the receptor via an inhibitory G-protein. We elucidated the roles of PKC and PKA by measuring Ca 2+o -stimulated accumulation of total inositol phosphates and by individually and simultaneously inhibiting the two kinases pharmacologically in HEK293 cells, which stably expressed the human CaR. Pharmacological inhibition of PKC resulted in a 5-fold enhancement of IP 3 signaling, whereas blocking PKA had almost no effect. IP 3 signaling activity increased even more (10-fold) however, when the two kinases were inhibited simultaneously. Apart from validating the role of PKC as a potent down-regulator of signaling of the human CaR in this cell system, this study suggests that both kinases synergize in inhibiting Ca 2+o -stimulated IP 3 signaling in CaR-transfected HEK293 cells.
 ...
PMID:Signaling of the human calcium-sensing receptor expressed in HEK293-cells is modulated by protein kinases A and C. 1260 46

Elevated extracellular calcium ([Ca2+]o) and other agonists potentially acting via the calcium-sensing receptor (CaR) increase parathyroid hormone-related peptide (PTHrP) release from H-500 Leydig cells. Here, we provide strong evidence for the CaR's involvement by using a dominant negative CaR that attenuates high [Ca2+]o-induced PTHrP release. This effect is likely transcriptional, because high [Ca2+]o upregulates the PTHrP transcript, an effect that is abolished by actinomycin D. Regulation of PTHrP release by the CaR involves activation of PKC as well as ERK1/2, p38 MAPK, and JNK pathways. However, we show for the first time that high [Ca2+]o-induced activation of the stress-activated protein kinase SEK1 is PKC independent, because there is an additive effect of a PKC inhibitor in combination with the JNK inhibitor on [Ca2+]o-stimulated PTHrP release. Furthermore, high [Ca2+]o, in a PKC-independent fashion, induces phosphorylation of ERK1/2, SEK1, p38 MAPK, and its downstream transcription factor ATF-2. We conclude that CaR regulation of PTHrP release in H-500 cells involves activation of PKC as well as the ERK1/2, p38 MAPK, and JNK pathways.
 ...
PMID:Calcium-sensing receptor stimulates PTHrP release by pathways dependent on PKC, p38 MAPK, JNK, and ERK1/2 in H-500 cells. 1270 Jan 62

Myogenic tone of small arteries is dependent on the presence of extracellular calcium (Ca(o)(2+)), and, recently, a receptor that senses changes in Ca(2+), the calcium-sensing receptor (CaR), has been detected in vascular tissue. We investigated whether the CaR is involved in the regulation of myogenic tone in rat subcutaneous small arteries. Immunoblot analysis using a monoclonal antibody against the CaR demonstrated its presence in rat subcutaneous arteries. To determine whether the CaR was functionally active, segments of artery (< 250 microm internal diameter) mounted in a pressure myograph with an intraluminal pressure of 70 mmHg were studied after the development of myogenic tone. Increasing Ca(o)(2+) concentration ([Ca(2+)](o)) cumulatively from 0.5 to 10 mM induced an initial constriction (0.5-2 mM) followed by dilation (42 +/- 5% loss of tone). The dose-dependent dilation was mimicked by other known CaR agonists including magnesium (1-10 mM) and the aminoglycosides neomycin (0.003-10 mM) and kanamycin (0.003-3 mM). PKC activation with the phorbol ester phorbol-12,13-dibutyrate (20nM) inhibited the dilation induced by high [Ca(2+)](o) or neomycin, whereas inhibition of PKC with GF109203X (10 microM) increased the responses to Ca(o)(2+) or neomycin, consistent with the role of PKC as a negative regulator of the CaR. We conclude that rat subcutaneous arteries express a functionally active CaR that may be involved in the modulation of myogenic tone and hence the regulation of peripheral vascular resistance.
 ...
PMID:Evidence for a functional calcium-sensing receptor that modulates myogenic tone in rat subcutaneous small arteries. 1557 43

The calcium-sensing receptor (CaR) is an allosteric protein that responds to extracellular Ca(2+) ([Ca(2+)](o)) and aromatic amino acids with the production of different patterns of oscillations in intracellular Ca(2+) concentration ([Ca(2+)](i)). An increase in [Ca(2+)](o) stimulates phospholipase C-mediated production of inositol 1,4,5-trisphosphate and causes sinusoidal oscillations in [Ca(2+)](i). Conversely, aromatic amino acid-induced CaR activation does not stimulate phospholipase C but engages an unidentified signaling mechanism that promotes transient oscillations in [Ca(2+)](i). We show here that the [Ca(2+)](i) oscillations stimulated by aromatic amino acids were selectively abolished by TRPC1 down-regulation using either a pool of small inhibitory RNAs (siRNAs) or two different individual siRNAs that targeted different coding regions of TRPC1. Furthermore, [Ca(2+)](i) oscillations stimulated by aromatic amino acids were also abolished by inhibition of TRPC1 function with an antibody that binds the pore region of the channel. We also show that aromatic amino acid-stimulated [Ca(2+)](i) oscillations can be prevented by protein kinase C (PKC) inhibitors or siRNA-mediated PKCalpha down-regulation and impaired by either calmodulin antagonists or by the expression of a dominant-negative calmodulin mutant. We propose a model for the generation of CaR-mediated transient [Ca(2+)](i) oscillations that integrates its stimulation by aromatic amino acids with TRPC1 regulation by PKC and calmodulin.
 ...
PMID:Requirement of the TRPC1 cation channel in the generation of transient Ca2+ oscillations by the calcium-sensing receptor. 1704 20

Fibroblasts isolated from jaw cysts expressed calcium-sensing receptor (CasR). In the fibroblasts elevated extracellular Ca(2+) ([Ca(2+)](o)) increased fluo-3 fluorescence intensity, and the production of inositol(1,4,5)trisphosphate and active protein kinase C. Phospholipase C inhibitor U-73122 attenuated the Ca(2+)-induced increase in fluo-3 fluorescence intensity. Elevated [Ca(2+)](o) enhanced the expression of cyclooxygenase-2 (COX-2) mRNA and protein, and the secretion of prostaglandin E(2) in the fibroblasts. CasR activator neomycin also increased the expression of COX-2 mRNA, and U-73122 attenuated the Ca(2+)-induced expression of COX-2 mRNA. Elevated [Ca(2+)](o)-induced phosphorylation of extracellular signal-regulated protein kinase-1/2 (ERK1/2), p38 mitogen-activated protein kinase (MAPK), and c-Jun N-terminal kinase (JNK), and U-73122 inhibited the Ca(2+)-induced phosphorylation. The inhibitors for each kinase, PD98059, SB203580, and SP600125, attenuated the Ca(2+)-induced expression of COX-2 mRNA. These results suggest that in jaw cyst fibroblasts elevated extracellular Ca(2+) may enhance COX-2 expression via the activation of ERK1/2, p38 MAPK, and JNK through CasR.
 ...
PMID:Ca2+ stimulates COX-2 expression through calcium-sensing receptor in fibroblasts. 1709 11


1 2 3 4 Next >>