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)

Parathyroid hormone (PTH) is a promising anabolic agent for the treatment of osteoporosis. However, PTH is also potently catabolic. To help delineate the molecular mediators of PTH's opposing effects on skeletal metabolism, we have examined PTH-induced regulator of G-protein signaling-2 (RGS-2) expression and function in murine osteoblasts. RGS proteins are GTPase-activating proteins (GAPs) that regulate GTP-binding protein-coupled receptor (GPCR) signaling by enhancing the intrinsic GTPase activity of Galpha subunits. We found that 10 nmol/L PTH maximally induced RGS-2 mRNA in murine MC3T3-E1 cells, rat Py1a and ROS-17/2.8 cells, primary mouse osteoblasts (MOB cells), and mouse calvariae organ culture at 1-2 h posttreatment. PTH signaling through its receptor, PTHR1, is coupled to cAMP-protein kinase A (PKA), protein kinase C (PKC), and calcium signaling pathways. We examined the effect of selective signaling agonists and antagonists on RGS-2 expression in MOB cells to determine which pathway(s) mediates PTH-induced RGS-2 expression. Although selective activation of all three pathways led to RGS-2 expression, cAMP-PKA activation with 10 nmol/L PTH and 10 micromol/L forskolin elicited the strongest induction. Similarly, RGS-2 mRNA expression was most strongly inhibited by the PKA inhibitor, H89 (10-30 micromol/L). The phorbol ester, PMA (1 micromol/L), which activates the PKC pathway, and ionomycin (1 micromol/L), which activates the calcium pathway, produced small but detectable elevations in RGS-2 mRNA levels. Overnight treatment with 1 micromol/L PMA to deplete PKC did not affect subsequent RGS-2 induction by PTH, but significantly inhibited PMA-induced RGS-2 expression. Treatment with 1-100 nmol/L PTH(3-34), which does not activate cAMP-PKA signaling, did not induce RGS-2 expression. MOB cells pretreated with 3 microg/mL cycloheximide produced sustained RGS-2 mRNA levels 2 h after 10 nmol/L PTH treatment. Actinomycin D (5 microg/mL) completely blocked 10 nmol/L PTH-induced RGS-2 expression. Finally, we tested the effect of RGS-2 overexpression on PTH- and fluprostenol-induced interleukin (IL)-6 promoter activity in MOB cells. PTH induces IL-6 through PKA activation, whereas fluprostenol induces IL-6 through PKC activation. We found that RGS-2 overexpression significantly inhibited IL-6 promoter activity following fluprostenol treatment, but not following PTH treatment. We conclude that RGS-2 is a PTH-induced primary response gene in murine osteoblasts that is induced mainly through the cAMP-PKA pathway and specifically inhibits Galphaq-coupled receptors.
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PMID:Parathyroid hormone induces RGS-2 expression by a cyclic adenosine 3',5'-monophosphate-mediated pathway in primary neonatal murine osteoblasts. 1199 4

Parathyroid hormone (PTH)-related protein (PTHrP) seems to affect bone resorption by interaction with bone cytokines, among them interleukin-6 (IL-6). Recent studies suggest that nuclear factor (NF)-kappaB activation has an important role in bone resorption. We assessed whether the N-terminal fragment of PTHrP, and its C-terminal region, unrelated to PTH, can activate NF-kappaB, and its relationship with IL-6 gene induction in different rat and human osteoblastic cell preparations. Here we present molecular data demonstrating that both PTHrP (1-36) and PTHrP (107-139) activate NF-kappaB, leading to an increase in IL-6 mRNA, in these cells. Using anti-p65 and anti-p50 antibodies, we detected the presence of both proteins in the activated NF-kappaB complex. This effect induced by either the N- or C-terminal PTHrP domain in osteoblastic cells appears to occur by different intracellular mechanisms, involving protein kinase A or intracellular Ca(2+)/protein kinase C activation, respectively. However, the effect of each peptide alone did not increase further when added together. Our findings lend support to the hypothesis that the C-terminal domain of PTHrP, in a manner similar to its N-terminal fragment, might stimulate bone resorption. These studies also provide further insights into the putative role of PTHrP as a modulator of bone remodeling.
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PMID:Both N- and C-terminal domains of parathyroid hormone-related protein increase interleukin-6 by nuclear factor-kappa B activation in osteoblastic cells. 1200 Jul 45

Parathyroid hormone (PTH) stimulates receptor activator of nuclear factor-kappaB ligand (RANKL) mRNA and inhibits osteoprotegerin (OPG) mRNA expression in murine bone marrow cultures. To understand the mechanisms influencing these responses, we investigated the role of the protein kinase A (PKA) and protein kinase C (PKC) pathways in the regulation of RANKL and OPG mRNA expression in murine bone marrow cultures. Murine bone marrow cells were stimulated with bovine PTH(1-34) and (1-34) amide, which activate both pathways; PTH(3-34), which more selectively activates the PKC and calcium pathways; and human PTH (1-31), which stimulates adenylyl cyclase, but not protein kinase C. We also examined agents that more directly activate either the PKA pathway (forskolin [FSK] and 8-bromo cAMP [8-Br-cAMP]) or the PKC pathway (phorbol 12-myristate 13-acetate [PMA]) in murine bone marrow cultures. After 1 h, RANKL mRNA expression was stimulated to a similar degree by agents that activate either or both the PKA and PKC pathways. However, this effect was sustained for 24 h only with agents that stimulated PKA. OPG mRNA expression was inhibited by all agents that stimulated PKA at 6 h. In contrast, PKC-specific stimulators [PMA and bPTH(3-34)] had no effect on OPG regulation in this culture system. To determine the involvement of the PKC signaling pathway in responses of RANKL, bone marrow cells were pretreated with PMA for 24 h and then treated with PTH(1-34) or FSK for 2 h. PMA pretreatment did not alter the ability of PTH or FSK to stimulate RANKL or inhibit OPG mRNA expression. Treatment of cells with H-89, a PKA inhibitor, significantly reduced the ability of PTH and FSK to induce RANKL and inhibit OPG mRNA expression. Calphostin C, a PKC inhibitor, significantly reduced PMA-stimulated RANKL mRNA expression without altering PTH- or FSK-mediated effects on RANKL or OPG mRNA. Cycloheximide, an inhibitor for protein synthesis, inhibited PTH-stimulated RANKL mRNA expression by 60% without altering the effect of PTH on OPG mRNA expression. To examine the involvement of prostaglandin in PMA-mediated responses, cells were treated with indomethacin, a nonspecific prostaglandin G/H synthase (PGHS) inhibitor, or NS-398, a selective inhibitor of PGHS-2. Neither PGHS inhibitor altered PMA-induced effects on RANKL and OPG mRNA expression. These results demonstrate that the PKA pathway is predominantly involved in the effects of PTH on RANKL mRNA expression in murine bone marrow cultures, but there is also a PKC-mediated response, which is not sustained. Inhibition of OPG by PTH appears to be a selective PKA response.
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PMID:Regulation of receptor activator of nuclear factor-kappa B ligand and osteoprotegerin mRNA expression by parathyroid hormone is predominantly mediated by the protein kinase a pathway in murine bone marrow cultures. 1211 Apr 42

Parathyroid hormone (PTH) is a major regulator of osteoclast formation and activation, effects that are associated with reciprocal up- and down-regulation of RANKL and osteoprotegerin (OPG), respectively. The roles of specific downstream signals generated by the activated PTH/PTH-related protein (PTHrP) receptor (PTH1R), such as cyclic adenosine monophosphate/protein kinase A (cAMP/PKA) and phospholipase C/protein kinase C (PLC/PKC), in controlling RANKL and OPG expression and osteoclastogenesis remain uncertain. In MS1 conditionally transformed clonal murine marrow stromal cells, which support PTH-induced osteoclast formation from cocultured normal spleen cells, PTH(1-34) increased RANKL and macrophage colony-stimulating factor (M-CSF) mRNA expression and decreased that of OPG when present continuously for 7-20 days at 37 degrees C in the presence of dexamethasone (Dex). In cells precultured for 7 days and then treated with PTH(1-34), similar reciprocal regulation of RANKL and OPG occurred, maximally at 6-24 h, that was of greater amplitude than the changes induced by chronic (7-10 days) PTH exposure. These acute effects of PTH(1-34) were mimicked by PKA stimulators (8-bromoadenosine [8Br]-cAMP or forskolin [FSK]), blocked by the PKA inhibitor Rp-cAMPs but unaffected by the PKC inhibitor GF109203X. Amino-truncated PTH(1-34) analogs PTH(5-34) and PTH(7-34) neither increased cAMP production in MS1 cells nor regulated RANKL or OPG mRNA. Reciprocal RANKL/OPG mRNA regulation was induced in MS1 cells by PTH(3-34) but only at high concentrations that also increased cAMP. The highly PKA-selective PTH analog [Gly1,Arg19]human PTH(1-28) exerted effects similar to PTH(1-34) on RANKL and OPG mRNAs and on osteoclast formation, both in MS1/spleen cell cocultures and in normal murine bone marrow cultures. The direct PKC stimulator 12-O-tetradecanoylphorbol-13-acetate (PMA) did not induce RANKL mRNA in MS1 cells, but it did up-regulate OPG mRNA and also antagonized osteoclast formation induced by PTH(1-34) in both MS1/spleen cocultures and normal bone marrow cultures. Thus, cAMP/PKA signaling via the PTH1R is the primary mechanism for controlling RANKL-dependent osteoclastogenesis, although direct PKC activation may negatively regulate this effect of PTH by inducing expression of OPG.
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PMID:Cyclic adenosine monophosphate/protein kinase A mediates parathyroid hormone/parathyroid hormone-related protein receptor regulation of osteoclastogenesis and expression of RANKL and osteoprotegerin mRNAs by marrow stromal cells. 1221 38

The article summarizes some of the recent developments in the understanding of the mechanisms of regulation of the proximal tubule apical membrane Na+/H+ antiporter NHE3. NHE3 antiporter has a major role in HCO3- and NaCl reabsorption in the proximal tubule. NHE3 protein is associated with the regulatory factor NHERF which interacts with ezrin, an actin-binding protein. This multi-protein complex constitutes a link between a membrane protein, NHE3, and actin cytoskeleton. Cytoskeleton organization has a key role to control NHE3 activity under normal conditions. Pharmacological perturbations of actin polymerization interfere with NHE3 activity. Parathyroid hormone-induced NHE3 activity inhibition results first, from a protein kinase A-mediated phosphorylation without protein trafficking, and then from endocytosis involving dynamin. The stimulatory effect of systemic angiotensin II concentrations on NHE3 activity is protein kinase C-dependent and results, at least in part, from exocytic insertion of the protein in luminal membranes. It requires cytoskeleton integrity.
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PMID:[Regulation of the luminal Na+/H+ exchanger NHE3 by intracellular protein trafficking]. 1222 55

Parathyroid hormone-related peptide (PTHrP) receptors, coupled to trimeric G proteins, operate in most target cells through at least three different transduction routes: Galpha s-mediated stimulation of adenylylcyclase (AC), Galpha q-mediated activation of phospholipase Cbeta (PLC) and mitogen-activated protein kinase (MAPK) activation. In this study we investigated the relative role of different pathways in human skin fibroblast proliferation. Using chemical inhibitors and activators of signal transduction, we demonstrated that: (i) AC/cAMP and PLC/1,4,5 inositol triphosphate/diacylglycerol second-messenger systems are simultaneously activated following PTHrP binding to its receptors; (ii) the mitogenic response to PTHrP derives from a balance between two counteracting pathways--an activating route mediated by protein kinase C (PKC) and an inhibitory route mediated by protein kinase A (PKA); (iii) PTHrP mitogenic effects are largely dependent on MAPKs, whose activity can be modulated by both PKA and PKC. Our results indicate that MAPKs are common targets of both transduction routes and, at the same time, their point of divergence in mediating PTHrP dual and opposite mitogenic effects.
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PMID:ERKs are the point of divergence of PKA and PKC activation by PTHrP in human skin fibroblasts. 1256 42

Growth factors, hormones, and matrix proteins regulate osteoblast proliferation and differentiation, acting through cognate receptors. Since each of the receptors are coupled to a variety of distinct signal transduction pathways, in this report we evaluated whether there is a common convergent intermediate step that allows cross-talk among the various pathways. Since extracellular signal-regulated kinases 1 and 2 (Erk1/2) play a role in mitogenesis and differentiation processes, we evaluated the effects of various osteotrophic factors on Erk1/2 phosphorylation in osteoblasts. Osteoblasts isolated from the metaphyseal marrow (MM) and diaphyseal marrow (DM) of 4-6 week old male rat longitudinal bones were grown to confluency and Erk1/2-phosphorylation was evaluated using antibodies that recognized either the total or the phosphorylated form of the kinase. There was very little Erk1/2 phosphorylation in cells kept in suspension. Both MM and DM cells attached to fibronectin (FN), demonstrated Erk1/2 phosphorylation that persisted for at least up to 8h. Platelet-derived growth factor AB (PDGF-AB) induced a transient and robust Erk1/2 phosphorylation that was attenuated by 2h. Studies with specific inhibitors indicated that the effects of these factors were mediated by protein kinase C, by receptor tyrosine kinase, as well as by protein phosphatases. Parathyroid hormone (PTH 1-34), a bone anabolic agent however, caused a down-regulation of FN stimulated Erk1/2 phosphorylation in MM derived cells. The inhibitory effect of PTH was mediated through cAMP-dependent protein kinase A (PKA) activation. The data collectively suggest that a combination of diverse extracellular stimuli regulates Erk1/2 phosphorylation that may ultimately influence osteoblast proliferation and/or differentiation.
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PMID:Distinct pathways of extracellular signal-regulated kinase activation by growth factors, fibronectin and parathyroid hormone 1-34. 1276 32

Parathyroid hormone (PTH) significantly affects osteoblast function by altering gene expression. We have identified neuron-derived orphan receptor-1 (NOR-1) as a PTH-induced primary gene in osteoblastic cells. NOR-1, Nurr1, and Nur77 comprise the NGFI-B nuclear orphan receptor family and Nurr1 and Nur77 are PTH-induced primary osteoblastic genes. Ten nM PTH maximally induced NOR-1 mRNA at 2h in primary mouse osteoblasts and at 1h in mouse calvariae. Cycloheximide pretreatment did not inhibit PTH-induced NOR-1 mRNA. PTH activates cAMP-protein kinase A (PKA), protein kinase C (PKC), and calcium signaling. Forskolin (PKA activator) and PMA (PKC activator) mimicked PTH-induced NOR-1 mRNA. Ionomycin (calcium ionophore) and PTH(3-34), which do not activate PKA, failed to induce NOR-1 mRNA. PKA inhibition with H89 blocked PTH- and FSK-induced NOR-1 mRNA. PMA pretreatment to deplete PKC inhibited PMA-induced, but not PTH-induced, NOR-1 mRNA. We conclude that NOR-1 is a PTH-regulated primary osteoblastic gene that is induced mainly through cAMP-PKA signaling.
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PMID:Parathyroid hormone induces the nuclear orphan receptor NOR-1 in osteoblasts. 1278 80

Parathyroid hormone (PTH) stimulates both bone formation and resorption by activating diverse osteoblast signalling pathways. Upstream signalling for PTH stimulation of protein kinase C-alpha (PKCalpha) membrane translocation and subsequent expression of the pro-resorptive cytokine interleukin-6 (IL-6) was investigated in UMR-106 osteoblastic cells. PTH 1-34, PTH 3-34, PTHrP and PTH 1-31 stimulated PKCalpha translocation and IL-6 promoter activity. Pharmacologic intervention at the adenylyl cyclase (AC) pathway (forskolin, IBMX, PKI) failed to alter PTH 1-34- or PTH 3-34-stimulated PKCalpha translocation. The phosphoinositol-phospholipase C (PI-PLC) antagonist U73122 slightly decreased PTH 1-34-stimulated PKCalpha translocation; however, the control analogue U73343 acted similarly. Propranolol, an inhibitor of phosphatidic acid (PA) phosphohydrolase, decreased diacylglycerol (DAG) formation and attenuated PTH 1-34- and PTH 3-34-stimulated PKCalpha translocation and IL-6 promoter activity, suggesting a phospholipase D (PLD)-dependent mechanism. This is the first demonstration that PLD-mediated signalling leads to both PKC-alpha translocation and IL-6 promoter activation in osteoblastic cells.
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PMID:Role of protein kinase A, phospholipase C and phospholipase D in parathyroid hormone receptor regulation of protein kinase Calpha and interleukin-6 in UMR-106 osteoblastic cells. 1460 81

Parathyroid hormone (PTH) is an important peptide hormone regulator of bone formation and osteoblast activity. However, its mechanism of action in bone cells is largely unknown. This study examined the effect of PTH on mouse osteocalcin gene expression in MC3T3-E1 preosteoblastic cells and primary cultures of bone marrow stromal cells. PTH increased the levels of osteocalcin mRNA 4-5-fold in both cell types. PTH also stimulated transcriptional activity of a 1.3-kb fragment of the mouse osteocalcin gene 2 (mOG2) promoter. Inhibitor studies revealed a requirement for protein kinase A, protein kinase C, and mitogen-activated protein kinase pathways in the PTH response. Deletion of the mOG2 promoter sequence from -1316 to -116 caused no loss in PTH responsiveness whereas deletion from -116 to -34 completely prevented PTH stimulation. Interestingly, this promoter region does not contain the RUNX2 binding site shown to be necessary for PTH responsiveness in other systems. Nuclear extracts from PTH-treated MC3T3-E1 cells exhibited increased binding to OSE1, a previously described osteoblast-specific enhancer in the mOG2 promoter. Furthermore, mutation of OSE1 in DNA transfection assays established the requirement for this element in the PTH response. Collectively, these studies establish that actions of PTH on the osteocalcin gene are mediated by multiple signaling pathways and require OSE1 and associated nuclear proteins.
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PMID:Parathyroid hormone induction of the osteocalcin gene. Requirement for an osteoblast-specific element 1 sequence in the promoter and involvement of multiple-signaling pathways. 1463 12


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