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 C-terminal region of parathyroid hormone-related protein (PTHrP) containing the sequence (107-111) appears to be a potent inhibitor of osteoclastic bone resorption. In the present study, we have investigated the effect of human (h)PTHrP (107-139) and hPTHrP (107-111)NH2 on the proliferation of osteoblastic rat osteosarcoma UMR 106 cells. We found that both C-terminal PTHrP peptides, like hPTHrP (1-141), were antimitogenic for these cells, between 1 pM and 10 nM. [Tyr34]hPTHrP (1-34)NH2 was as potent as these peptides but less effective as growth inhibitor in these cells. UMR 106 cells were found to produce and secrete immunoreactive PTHrP. Addition of anti-PTHrP neutralizing antibodies to C- and N-terminal epitopes of PTHrP increased the growth of these cells. Our data suggest that the antiproliferative effect of these C-terminal PTHrP analogs may be independent of cyclic adenosine 3':5'-monophosphate (cAMP) and mediated by protein kinase C. These findings support an autocrine role of PTHrP in bone metabolism.
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PMID:Antiproliferative effect of the C-terminal fragments of parathyroid hormone-related protein, PTHrP-(107-111) and (107-139), on osteoblastic osteosarcoma cells. 900 50

In a previous study, we demonstrated that parathyroid hormone (PTH) inhibits mitogen-activated protein (MAP) kinase activation in osteosarcoma cells via a protein kinase A-dependent pathway. Here, we show that PTH can induce a transient activation of MAP kinase as well. This was observed in both Chinese hamster ovary R15 cells stably expressing high levels of rat PTH/PTH-related peptide receptor and parietal yolk sac carcinoma cells expressing the receptor endogenously. PTH was a strong activator of adenylate cyclase and phospholipase C in Chinese hamster ovary R15 cells. PTH-induced MAP kinase activation did not depend on activation of Gi, phorbol ester-sensitive protein kinase C, elevated intracellular calcium levels, or release of Gbetagamma subunits. It could, however, be mimicked by addition of forskolin or 8-bromo-cAMP to these cells. Prolonged treatment with forskolin caused sustained protein kinase A activity, whereas MAP kinase activity returned to basal levels. Subsequent treatment with PTH or 8-bromo-cAMP did not result in MAP kinase activation, whereas phorbol ester- or insulin-induced MAP kinase activation was unaffected. Finally, expression of a dominant negative form of Ras (RasAsn-17), which completely blocked insulin-induced MAP kinase activation, did not affect activation by PTH or cAMP. In conclusion, PTH regulates MAP kinase activity in a cell type-specific fashion. The activation of MAP kinase by PTH is mediated by cAMP and independent of Ras.
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PMID:Parathyroid hormone activates mitogen-activated protein kinase via a cAMP-mediated pathway independent of Ras. 901 86

The multidrug resistance (MDR) phenotype that is mediated by an overexpression of P-glycoprotein, has been suggested to be related also to an increased activity of protein kinase C (PKC) and to changes in phospholipid pattern. By electron microscope quantitative immunocytochemistry, we investigated whether PKC and other elements of the polyphosphoinositide signal transduction system are affected in an MDR variant of the human osteosarcoma cell line Saos-2. These cells, which are characterized by an increased expression of P-glycoprotein not only at the plasma membrane but also at the nuclear level, showed increased intranuclear amounts of phosphatidylinositol 4,5-bisphosphate and of phospholipase C beta 1, while both the amount and activity of both nuclear and cellular PKC were not modified with respect to sensitive cells. These results suggest that, in this model, the changes observed in the elements of nuclear signal transduction could be related to previously reported modifications of the MDR phenotype, but that P-glycoprotein phosphorylation is not dependent from increased PKC activity.
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PMID:Increase of nuclear phosphatidylinositol 4,5-bisphosphate and phospholipase C beta 1 is not associated to variations of protein kinase C in multidrug-resistant Saos-2 cells. 908 Apr 7

Parathyroid hormone (PTH) functions in part by regulating osteoblast cytokine expression. We recently demonstrated that PTH induced a rapid and transient increase in interleukin-6 (IL-6) mRNA expression in rat bones in vivo. To determine the molecular basis of this effect, we analyzed the human IL-6 promoter fused (-1,179 to +9) with the chloramphenicol acetyltransferase (CAT) reporter gene in stable transfections into human osteoblast-like osteosarcoma SaOS-2 cells. We compared the effects of PTH on IL-6 expression with adenylate cyclase activator forskolin, PKC activator phorbol 12-myristate 13-acetate (PMA), calcium ionophore A23187, interleukin-1 alpha (IL-1 alpha), prostaglandin E-2 (PGE-2), RS-66271 (a parathyroid hormone-related peptide analog), and platelet-derived growth factor-BB (PDGF-BB). Analyses of cell clones showed that IL-6 promoter expression was extremely low in the unstimulated state. Exposure to PTH (0.001-100 nM) for 12 h stimulated CAT expression in a dose-dependent manner (200-500% of control). Treatment with IL-1 alpha was more potent than PTH in inducing transcription of the IL-6 promoter (900-1,000%). Activation of the cAMP-PKA pathway by treatment with forskolin induced a comparable level of induction with PTH. Together, the effects of PTH and forskolin were additive. RS-66271, previously shown to have PTH-like effects, induced a comparable level of IL-6 promoter expression. When examined together, PTH+RS-66271 effects were comparable to PTH effects alone. Exposure to PGE-2, PMA, PDGF-BB, or A23187 for 12 h did not significantly alter IL-6 promoter expression. These results demonstrate PTH, forskolin, the PTHrP analog RS-66271, and IL-1 alpha stimulate IL-6 expression by stimulating gene transcription. The response to forskolin suggests that the messenger system mediated by PKA is sufficient to induce IL-6 expression.
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PMID:Parathyroid hormone (1-34)-mediated interleukin-6 induction. 932 32

The enzymes and substrates involved in phosphoinositide signal transduction which have been detected in the nucleus of several cell types have been demonstrated to be responsive to agonists. The complexity of this aspect of inositide function has been previously analyzed in some cell models characterized by a mitogenic or differentiating response to specific factors. An interesting experimental model is represented by human derived osteosarcoma Saos-2 cells, characterized by the expression of high affinity receptors for interleukin 1 alpha (IL-1 alpha), which is one of the most potent stimulators of bone resorption. In particular, we investigated the earliest intracellular events following the binding of IL-1 alpha to its receptor, involving the inositide signal transduction pathway. Saos-2 cells present a partitioning of the phosphoinositidase (PLC) isoforms; in fact, the nucleus contains both PLC beta 1 and gamma 1, while the cytoplasm contains almost exclusively the gamma 1 isoform. IL-1 alpha evokes a rapid and transient increase of the PLC beta 1 activity in the nucleus, which causes the hydrolysis of phosphatidylinositol mono- and bis-phosphate. In response to IL-1 alpha, not only the canonical inositol lipid pathway appears to be involved; also the 3'-phosphorylated lipids generated by phosphatidylinositol 3-kinase (PI 3-K), which may act as second messengers, appear to be affected. In fact, Saos-2 cells present a nuclear PI 3-K activity which can be enhanced by the IL-1 alpha treatment. Among the possible targets of the second messengers released by the nuclear PLC beta 1 activation, we found that some protein kinase C isoforms, namely the epsilon and zeta, which are present within the nucleus, are activated after IL-1 alpha exposure. These activated PKC isoforms, in turn, could modulate the activity of the transcription factor NFkB, which, 5 min after IL-1 alpha treatment, has already translocated to the nucleus and bound to DNA to promote gene activation. The actual role of the inositide pathway in the Saos-2 cell function has also been investigated by utilizing cell clones transfected with the mouse sequence of the PLC beta 1.
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PMID:Nuclear lipid-dependent signal transduction in human osteosarcoma cells. 938 81

In this study, we examined the effect of activation of protein kinase C (PKC) pathways on the regulation of 1,25-dihydroxyvitamin D receptors (VDR) in rat osteosarcoma (ROS) 17/2.8 cells. Activation of PKC with phorbol 12-myristate 13-acetate (PMA) resulted in a time- and dose-dependent increase in VDR expression in ROS cells. Treatment of ROS cells with 4alpha-phorbol 12,13-dedeconate, a PKC-inactive phorbol ester, had no effect on VDR expression. Oleoyl acetyl glycerol (OAG), a synthetic diacylglycerol, stimulated VDR up-regulation in ROS cells. The PKC inhibitors (H-7, staurosporin, and sphingosine) all blocked PMA-mediated up-regulation of VDR in a dose-dependent manner. We next examined the interaction of 1,25(OH)2D3 and PKC activation by PMA on the regulation of VDR in ROS cells. We found that PMA or 1,25(OH)2D3 treatment alone resulted in a 50 and 200% increase in VDR, respectively. PMA treatment alone resulted in a 50% increase in VDR protein and a marginal 20% increase in VDR mRNA. 1,25(OH)2D3 up-regulation of VDR was associated with a 2-fold increase in VDR mRNA. In contrast, co-treatment of ROS cells with PMA and 1,25(OH)2D3 resulted in a synergistic 10-fold induction of VDR mRNA and the appearance of a 7.2 kb VDR transcript. VDR protein was also synergistically up-regulated by combined PMA and 1,25(OH)2D3 treatment of ROS cells. Scatchard analysis demonstrated that the synergistic effect of PMA and 1,25(OH)2D3 on VDR protein expression was not associated with any change in the affinity of VDR for 1,25(OH)2D3. The synergistic effect of 1,25(OH)2D3 and PMA on VDR expression supports a link between PKC signal pathways and the function of VDR.
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PMID:Phorbol 12-myristate 13-acetate and 1,25-dihydroxyvitamin D3 regulate 1,25-dihydroxyvitamin D3 receptors synergistically in rat osteosarcoma cells. 939 48

Interleukin-1 (IL-1) is an important factor in bone metabolism, and its actions may be mediated in part via prostaglandins. Prostaglandin G/H synthase (PGHS), a critical enzyme in the synthesis of prostaglandins, has two isoforms, PGHS-1, which is generally constitutively expressed, and PGHS-2, which is inducible. This study examines the effects of IL-1 on PGHS-2 mRNA expression in human osteosarcoma MG-63 cells, the human osteoblast-like initial transfectant (HOBIT) cell line, and primary human osteoblastic (HOB) cells. IL-1 induced PGHS-2 mRNA expression in MG-63 cells within 1 h, and expression was maintained for 24 h. There was a dose-related increase in PGHS-2 mRNA levels with 1-100 ng/ml of IL-1. Induction of PGHS-2 protein and media prostaglandin E2 (PGE2) paralleled induction of PGHS-2 mRNA levels. IL-1 similarly induced PGHS-2 mRNA expression and PGE2 production in HOBIT and HOB cells. Among other potential agonists, phorbol myristate acetate (PMA) was a potent inducer of PGHS-2 expression, while forskolin (FSK), serum, and prostaglandins had little effect. Cycloheximide enhanced effects of both IL-1 and PMA, suggesting that de novo protein synthesis is not required for induction of PGHS-2. Twenty-four hours of PMA pretreatment blocked the induction of PGHS-2 by PMA but not by IL-1, suggesting that IL-1 induction of PGHS-2 mRNA is not dependent on the protein kinase C pathway. Although FSK alone had little effect, it enhanced induction of PGHS-2 mRNA by IL-1. PGHS-1 was constitutively expressed and showed little change with treatment. In summary, we show that IL-1 is a potent inducer of PGHS-2 expression and PGE2 production in human osteosarcoma cells as well as in osteoblastic cells derived from normal human bone.
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PMID:Regulation of prostaglandin G/H synthase-2 expression by interleukin-1 in human osteoblast-like cells. 966 Oct 70

Integrin alpha2beta1 is a heterodimeric transmembrane receptor for collagens. In osteogenic cells the expression of alpha2beta1 integrin is induced by both Kirsten sarcoma virus and chemical transformation. The association of alpha2 integrin with transformed cell phenotype was studied further by testing the effects of two tumor promoters, 12-O-tetradecanoylphorbol 13-acetate (TPA) and okadaic acid (OA), on human MG-63 osteosarcoma cells. TPA, an activator of protein kinase C, increased the cell surface expression of alpha2 integrin and the corresponding mRNA levels. Nuclear run-on assays indicated that TPA activated the transcription of alpha2 integrin gene. TPA also slightly increased the expression of alpha3 integrin but had no effect on the transcription of alpha5, alphav, or beta1 integrin subunits. OA, an inhibitor of serine/threonine phosphatases, increased alpha2 integrin gene transcription and mRNA levels, but in contrast to TPA, OA decreased alpha3 integrin expression. The increased expression of alpha2 integrin on TPA-treated MG-63 cells led to faster cell spreading on type I collagen. Our results link the enhanced transcription of alpha2 integrin gene to tumor progression and show the independent regulation of alpha2 integrin compared to other integrin genes.
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PMID:Transcription of alpha2 integrin gene in osteosarcoma cells is enhanced by tumor promoters. 971 43

The carboxyl(C)-truncated human (h) PTH (hPTH) analog hPTH(1-31), which activates adenylyl cyclase (AC), but not protein kinase C, in rat osteosarcoma cells, exerts an anabolic effect on rat bone in vivo similar to that of hPTH(1-34). It has been proposed, therefore, that this action of PTH(1-34) is mediated exclusively by stimulation of AC via the rat type-1 PTH/PTH-related peptide (PTHrP) receptor (PTH1R). To determine whether this selective signaling pattern also might be a property of the hPTH1R, we studied signal transduction via heterologously expressed hPTH1Rs in response to activation by hPTH(1-34), hPTH(1-31), and a C-truncated analog that does not increase rat bone mass in vivo, hPTH(1-30). In porcine LLC-PK1 cells that stably expressed recombinant hPTH1Rs, these three peptides activated AC identically (EC50 = 1-2 nM). In cells with comparable expression of rat PTH1Rs, AC activation by hPTH(1-34) and hPTH(1-31) again was identical, whereas full activation by hPTH(1-30) required higher concentrations (EC50 = 10 nM vs. 1 nM). Surprisingly, hPTH(1-31) fully stimulated phospholipase C (PLC), via both species of PTH1Rs, with potency that was similar (hPTH1Rs) or slightly reduced (rat PTH1Rs), relative to that of hPTH(1-34). hPTH(1-30), however, was 5-fold less potent than hPTH(1-34) in activating PLC via hPTH1Rs and showed weak and only partial activity via the rat PTH1R. Comparable results were obtained when human and rat PTH1Rs were transiently expressed heterologously in COS-7 cells or homologously in HEK 293 and UMR 106-01 cells, respectively. Binding affinities of these C-truncated peptides to human and rat PTH1Rs were concordant with their relative potencies in activating PLC. We conclude that hPTH(1-31) and, to a lesser extent, hPTH(1-30) can activate PLC, as well as AC, via both rat and human PTH1Rs. Accordingly, a role for PLC activation in the anabolic action of PTH in vivo cannot be excluded.
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PMID:Type-1 parathyroid hormone (PTH)/PTH-related peptide (PTHrP) receptors activate phospholipase C in response to carboxyl-truncated analogs of PTH(1-34). 975 12

The effects of natural lipid-soluble antioxidant, alpha-tocopherol (alpha-TP), and the synthetic water-soluble antioxidant, phenosan potassium salt (Ph-K), in a broad range of concentrations down to ultralow doses (10(-4)-10(-20) M) on the activity of protein kinase C (PKC) have been studied. It was shown that alpha-TP is a potent inhibitor of the rabbit heart enzyme: the maximum extent of inhibition is 80%. The effects of alpha-TP on the main kinetic parameters of the PKC activity differ at the alpha-TP physiological (10(-4) M) and ultralow (10(-14) M) concentrations: at 10(-14) M, alpha-TP acts as an allosteric inhibitor with Hill's coefficient about 2 and doubles the PKC affinity to the substrate (histone H-1). It was concluded that alpha-TP is more efficient inhibitor at ultralow concentration. Ph-K added to normal (A7r5 rat vascular smooth muscle cells, VSMC) and tumor cells (Saos-2 human osteosarcoma) growing in a culture has been found to be a PKC superactivator. The maximum activation is 400-500%, which is more than two times as high as the effect of the best activator of this enzyme, phorbol ester (TPA). It was demonstrated that irrespective of the effector action (activation or inhibition), the dose-effect curves are of the bimodal type with two maxima at the high (or physiological) (10(-4)-10(-7) M) and ultralow (10(-14)-10(-19) M) concentrations of the antioxidants and the so-called "silence zones" between them, in which the effect of antioxidants is significantly reduced or absent (tumor cells). For the first time, these bimodal curves were observed at the enzyme level. The results obtained are discussed considering various hypotheses of the effect of ultralow doses of biologically active compounds and the PKC activity regulation in normal and tumor cells by the antioxidants.
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PMID:Natural (alpha-tocopherol) and synthetic (phenosan potassium salt) antioxidants regulate the protein kinase C activity in a broad concentration range (10(-4)-10(-20) M). 987 48


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