Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.11.24 (mitogen-activated protein kinase)
 95,810 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The calcium-sensing receptor (CaR) recently has been shown to activate MAP kinase (ERK1/2) in various cell types as well as in heterologous expression systems. In this study we show that the CaR agonist NPS R-467 (1 microm), which does not activate the CaR by itself, robustly activates ERK1/2 in the presence of a low concentration of Ca(2+) (0.5 mm CaCl(2)) in human embryonic kidney (HEK) cells permanently expressing the human CaR (HEK-hCaR). Ca(2+) (4 mm) also activates ERK1/2 but with differing kinetics. CaR-dependent ERK1/2 activation begins to desensitize to 4 mm Ca(2+) after 10 min, whereas there is no desensitization to NPS R-467/CaCl(2) as late as 4 h. Moreover, recovery from desensitization occurs as rapidly as 30 min with 4 mm CaCl(2). Pretreatment of HEK-hCaR cells with concanavalin A (250 microg/ml) to block CaR internalization completely eliminated the NPS R-467/CaCl(2)-mediated ERK1/2 activation but did not block the 2-min time point of 4 mm Ca(2+)-mediated ERK1/2 activation. Neither dominant-negative dynamin (K44A) nor dominant-negative beta-arrestin inhibited ERK1/2 activation by either CaR agonist treatment, suggesting that CaR-elicited ERK1/2 signaling occurs via a dynamin-independent pathway. Pertussis toxin pretreatment partially attenuated the 4 mm Ca(2+)-ERK1/2 activation; this attenuated activity was completely restored by co-expression of the Galpha(i2) (C351I) but not Galpha(i1) (C351I) or Galpha(i3) (C351I) G proteins, PTX-insensitive G protein mutants. Taken together, these data suggest that both 4 mm Ca(2+) and NPS R-467/CaCl(2) activate ERK1/2 via distinguishable pathways in HEK-hCaR cells and may represent a nexus to differentially regulate differentiation versus proliferation via CaR activation.
 ...
PMID:Calcium-sensing receptor-mediated ERK1/2 activation requires Galphai2 coupling and dynamin-independent receptor internalization. 1470 66

We have previously reported that high extracellular Ca2+ stimulates parathyroid hormone-related protein (PTHrP) release from human prostate and breast cancer cell lines as well as from H-500 rat Leydig cancer cells, an action mediated by the calcium-sensing receptor (CaR). Activating the CaR leads to phosphorylation of mitogen-activated protein kinases (MAPKs) that participate in PTHrP synthesis and secretion. Because the CaR is a G protein-coupled receptor (GPCR), it is likely to transactivate the epidermal growth factor receptor (EGFR) or the platelet-derived growth factor receptor (PDGFR). In this study, we hypothesized that activation of the CaR transactivates the EGFR or PDGFR, and examined whether transactivation affects PTHrP secretion in PC-3 human prostate cancer cells. Using Western analysis, we observed that an increase in extracellular Ca2+ resulted in delayed activation of extracellular signal-regulated kinase (ERK) in PC-3 cells. Pre-incubation with AG1478 (an EGFR kinase inhibitor) or an EGFR neutralizing antibody inhibited the high Ca2+ -induced phosphorylation of ERK1/2. GM6001, a pan matrix metalloproteinase (MMP) inhibitor, also partially suppressed the ERK activation, but AG1296 (a PDGFR kinase inhibitor) did not. High extracellular Ca2+ stimulates PTHrP release during a 6-h incubation (1.5- to 2.5- and 3- to 4-fold increases in 3.0 and 7.5 mM Ca2+, respectively). When cells were preincubated with AG1478, GM6001, or an antihuman heparin-binding EGF (HB-EGF) antibody, PTHrP secretion was significantly inhibited under basal as well as high Ca2+ conditions, while AG1296 had no effect on PTHrP secretion. Taken together, these findings indicate that activation of the CaR transactivates the EGFR, but not the PDGFR, leading to phosphorylation of ERK1/2 and resultant PTHrP secretion, although CaR-EGFR-ERK might not be the only signaling pathway for PTHrP secretion. This transactivation is most likely mediated by activation of MMP and cleavage of proheparin-binding EGF (proHB-EGF) to HB-EGF.
 ...
PMID:Calcium-sensing receptor activation stimulates parathyroid hormone-related protein secretion in prostate cancer cells: role of epidermal growth factor receptor transactivation. 1533 2

Familial benign hypocalciuric hypercalcemia (FBHH), in which calcium homeostasis is disordered, can be distinguished from mild primary hyperparathyroidism by the finding of a heterozygous loss-of-function mutation in the calcium-sensing receptor (CaSR). Here, we report a Polish kindred with FBHH, the proband of which had undergone an unsuccessful parathyroidectomy. Direct sequence analysis of exon 4 of her CASR gene identified a heterozygous R227Q mutation in the extracellular domain of the receptor. This mutation segregated with other affected family members. A de novo heterozygous R227L mutation had previously been identified in a case of neonatal hyperparathyroidism. We performed a functional analysis by transiently transfecting wild-type and mutant (R227Q, R227L) CaSRs in human embryonic kidney (HEK293) cells. Both mutant receptors were expressed at a similar level to that of the wild-type, demonstrated a 160-kDa molecular species consistent with having undergone full maturation, and were visualized on the cell surface. Although both mutants were impaired in their MAPK responses to increasing extracellular calcium concentrations relative to wild type, this was more marked for R227L (EC(50) = 9.7 mM) than R227Q (EC(50) = 7.9 mM) relative to wild type (EC(50) = 3.7 mM). When cotransfected with wild-type CaSR to mimic the heterozygous state, the curves for both R227Q and R227L were right shifted intermediate to the curves for wild type and the respective mutant. This differential responsiveness may account, in part, for the markedly different clinical presentation of the R227Q mutation, classic FBHH, vs. the neonatal hyperparathyroidism of the R227L mutation.
 ...
PMID:Functional characterization of calcium-sensing receptor codon 227 mutations presenting as either familial (benign) hypocalciuric hypercalcemia or neonatal hyperparathyroidism. 1557 18

Epidermal growth factor (EGF) plays an important role in the physiology and pathophysiology of the Leydig cell. In H-500 rat Leydig cancer cells, a model for humoral hypercalcemia of malignancy (HHM), we previously showed that the calcium-sensing receptor (CaR) stimulates PTHrP release and proliferation, both involving multiple mitogen-activated protein kinases. An emerging concept of signaling by G-protein coupled receptors (GPCR) is that it occurs via transactivation of receptor tyrosine kinases. Therefore, we investigated whether stimulation with calcium activates the EGFR in H-500 Leydig cancer cells. We show that treatment of H-500 cells with Ca(2+) results in EGFR phosphorylation. The CaR-induced activation of ERK1/2, induction of PTHrP release and stimulation of cellular proliferation in H-500 cells are likewise mediated, in large part, through the EGFR. In conclusion, the calcium activates the EGFR, possibly through the CaR, to regulate downstream signaling events and important biological functions in a model of HHM.
 ...
PMID:High calcium activates the EGF receptor potentially through the calcium-sensing receptor in Leydig cancer cells. 1601 33

Both intra- and extracellular calcium play multiple roles in the physiology and pathophysiology of cardiomyocytes, especially in stimulus-contraction coupling. The intracellular calcium level is closely controlled through the concerted actions of calcium channels, exchangers, and pumps; however, the expression and function(s) of the so-called calcium-sensing receptor (CaR) in the heart remain less well characterized. The CaR is a seven-transmembrane receptor, which, in response to noncovalent binding of extracellular calcium, activates intracellular effectors, including G proteins and extracellular signal-regulated kinases (ERK1/2). We have shown that cultured neonatal cardiomyocytes express the CaR messenger RNA and the CaR protein. Furthermore, increasing concentrations of extracellular calcium and a type II CaR activator "calcimimetic" caused inositol phosphate (IP) accumulation, downregulated tritiated thymidine incorporation, and supported ERK1/2 phosphorylation, suggesting that the CaR protein is functionally active. Interestingly, the calcimimetic induced a more rapid ERK1/2 phosphorylation than calcium and left-shifted the IP concentration-response curve for extracellular calcium, supporting the hypothesis that CaR is functionally expressed in cardiac myocytes. This notion was underscored by studies using a virus containing a dominant-negative CaR construct, because this protein blunted the calcium-induced IP response. In conclusion, we have shown that the CaR is functionally expressed in neonatal ventricular cardiomyocytes and that the receptor activates second messenger pathways, including IP and ERK, and decreases DNA synthesis. A specific calcium-sensing receptor on cardiac myocytes could play a role in regulating cardiac development, function, and homeostasis.
 ...
PMID:Calcium receptor is functionally expressed in rat neonatal ventricular cardiomyocytes. 1624 11

In the present study, we demonstrate that Ca2+-induced growth inhibition and induction of differentiation in a line of human colon carcinoma cells (CBS) is dependent on mitogen-activated protein (MAP) kinase signaling and is associated with upregulation of extracellular calcium-sensing receptor (CaSR) expression. When CBS cells were grown in Ca2+-free medium and then switched to medium supplemented with 1.4 mM Ca2+, proliferation was reduced and morphologic features of differentiation were expressed. E-cadherin, which was minimally expressed in nonsupplemented medium, was rapidly induced in response to Ca2+ stimulation. Sustained activation of the extracellular signal-regulated kinase (ERK) occurred in Ca2+-supplemented medium. When an inhibitor of ERK activation (10 microM U0126) was included in the Ca2+-supplemented culture medium, ERK-activation did not occur. Concomitantly, E-cadherin was not induced, cell proliferation remained high and differentiation was not observed. The same level of Ca2+ supplementation that induced MAP kinase activation also stimulated CaSR upregulation in CBS cells. A clonal isolate of the CBS line that did not upregulate CaSR expression in response to extracellular Ca2+ was isolated from the parent cells. This isolate failed to produce E-cadherin or undergo growth inhibition/induction of differentiation when exposed to Ca2+ in the culture medium. However, ERK-activation occurred as efficiently in this isolate as in parent CBS cells or in a cloned isolate that underwent growth reduction and differentiation in response to Ca2+ stimulation. Together, these data indicate that CaSR upregulation and MAP kinase signalling are both intermediates in the control of colon carcinoma cell growth and differentiation. They appear to function, at least in part, independently of one another.
 ...
PMID:Upregulation of calcium-sensing receptor and mitogen-activated protein kinase signalling in the regulation of growth and differentiation in colon carcinoma. 1627 66

Extracellular calcium (Ca(2+)(o)) can act as a first messenger in many cell types through a G protein-coupled receptor, calcium-sensing receptor (CaR). It is still debated whether the CaR is expressed in vascular smooth muscle cells (VSMCs). Here, we report the expression of CaR mRNA and protein in rat aortic VSMCs and show that Ca(2+)(o) stimulates proliferation of the cells. The effects of Ca(2+)(o) were attenuated by pre-treatment with MAPK kinase 1 (MEK1) inhibitor, as well as an allosteric modulator, NPS 2390. Furthermore, stimulation of the VSMCs with Ca(2+)(o)-induced phosphorylation of ERK1/2, but surprisingly did not cause inositol phosphate accumulation. We were not able to conclusively state that the CaR mediates Ca(2+)(o)-induced cell proliferation. Rather, an additional calcium-sensing mechanism may exist. Our findings may be of importance with regard to atherosclerosis, an inflammatory disease characterized by abnormal proliferation of VSMCs and high local levels of calcium.
 ...
PMID:Extracellular calcium sensing in rat aortic vascular smooth muscle cells. 1691 96

The calcium-sensing receptor (CaSR) exists in many tissues, and its expression has been identified in rat cardiac tissue. However, the physiological importance and pathophysiological involvement of CaSR in homeostatic regulation of cardiac function are unclear. To investigate the relation of CaSR and apoptosis in cardiomyocytes, we examined the role of the CaSR activator gadolinium chloride (GdCl(3)) in rat neonatal ventricular cardiomyocytes. Expression of the CaSR protein was observed by Western blot. The apoptotic ratio of rat neonatal ventricular cardiomyocytes was measured with flow cytometry and immunofluorescence techniques. A laser scan confocal microscope was used to detect the intracellular concentration of calcium ([Ca(2+)](i)) in rat neonatal ventricular cardiomyocytes using the acetoxymethyl ester of fluo-3 (fluo-3/(AM)) as a fluorescent dye. The results showed that GdCl(3) increased the phosphorylation of extracellular signal-regulated protein kinase (ERK), c-Jun NH(2)-terminal protein kinases (JNK), and p38. GdCl(3) also activated caspase 9 and increased apoptosis in myocyte by increasing [Ca(2+)](i). In conclusion, these results suggest that CaSR promotes cardiomyocyte apoptosis in rat neonatal ventricular cardiomyocytes through activation of mitogen-activated protein kinases and caspase 9 signaling pathways.
 ...
PMID:Calcium-sensing receptor induces rat neonatal ventricular cardiomyocyte apoptosis. 1704 14

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

The calcium-sensing receptor (CaR) mediates feedback control of Ca2+o (extracellular Ca2+) concentration. Although the mechanisms are not fully understood, the CaR couples to several important intracellular signalling enzymes, including PI-PLC (phosphoinositide-specific phospholipase C), leading to Ca2+i (intracellular Ca2+) mobilization, and ERK1/2 (extracellular-signal-regulated kinase 1/2). In addition to Ca2+o, the CaR is activated allosterically by several subclasses of L-amino acids, including the aromatics L-phenylalanine and L-tryptophan. These amino acids enhance the Ca2+o-sensitivity of Ca2+i mobilization in CaR-expressing HEK-293 (human embryonic kidney) cells and normal human parathyroid cells. Furthermore, on a background of a physiological fasting serum L-amino acid mixture, they induce a small, but physiologically significant, enhancement of Ca2+o-dependent suppression of PTH (parathyroid hormone) secretion. The impact of amino acids on CaR-stimulated ERK1/2, however, has not been determined. In the present study, we examined the effects of L-amino acids on Ca2+o-stimulated ERK1/2 phosphorylation as determined by Western blotting and a newly developed quantitative assay (SureFire). L-Amino acids induced a small, but significant, enhancement of Ca2+o-stimulated ERK1/2. In CaR-expressing HEK-293 cells, 10 mM L-phenylalanine lowered the EC50 for Ca2+o from approx. 2.3 to 2.0 mM in the Western blot assay and from 3.4 to 2.9 mM in the SureFire assay. The effect was stereoselective (L>D), and another aromatic amino acid, L-tryptophan, was also effective. The effects of amino acids were investigated further in HEK-293 cells that expressed the CaR mutant S169T. L-Phenylalanine normalized the EC50 for Ca2+o-stimulated Ca2+i mobilization from approx. 12 mM to 5.0 mM and ERK1/2 phosphorylation from approx. 4.6 mM to 2.6 mM. Taken together, the data indicate that L-phenylalanine and other amino acids enhance the Ca2+o-sensitivity of CaR-stimulated ERK1/2 phosphorylation; however, the effect is comparatively small and operates in the form of a fine-tuning mechanism.
 ...
PMID:Allosteric activation of the extracellular Ca2+-sensing receptor by L-amino acids enhances ERK1/2 phosphorylation. 1721 89


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>