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)

Loss of ovarian function following menopause results in a substantial increase in bone turnover and a critical imbalance between bone formation and resorption. This imbalance leads to a progressive loss of trabecular bone mass and eventually osteoporosis, in part the result of increased osteoclastogenesis. Enhanced formation of functional osteoclasts appears to be the result of increased elaboration by support cells of osteoclastogenic cytokines such as IL-1, tumor necrosis factor, and IL-6, all of which are negatively regulated by estrogens. We show here that estrogen can suppress receptor activator of NF-kappaB ligand (RANKL) and macrophage colony-stimulating factor (M-CSF)-induced differentiation of myelomonocytic precursors into multinucleated tartrate-resistant acid phosphatase-positive osteoclasts through an estrogen receptor-dependent mechanism that does not require mediation by stromal cells. This suppression is dose-dependent, isomer-specific, and reversed by ICI 182780. Furthermore, the bone-sparing analogues tamoxifen and raloxifene mimic estrogen's effects. Estrogen blocks RANKL/M-CSF-induced activator protein-1-dependent transcription, likely through direct regulation of c-Jun activity. This effect is the result of a classical nuclear activity by estrogen receptor to regulate both c-Jun expression and its phosphorylation by c-Jun N-terminal kinase. Our results suggest that estrogen modulates osteoclast formation both by down-regulating the expression of osteoclastogenic cytokines from supportive cells and by directly suppressing RANKL-induced osteoclast differentiation.
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PMID:Estrogens suppress RANK ligand-induced osteoclast differentiation via a stromal cell independent mechanism involving c-Jun repression. 1086 27

Recent studies have revealed that both transforming growth factor-beta (TGF-beta) and activin A play pivotal roles in osteoclastogenesis. In this report, we show that the effect of TGF-beta family members, TGF-beta1 and activin A, but not BMP-2, enhance multinucleated osteoclast-like cell (OCL) formation induced by receptor activator of NF-kappaB ligand (RANKL) in isolated bone marrow macrophages and monocytic cell line, RAW264.7. TGF-beta1 and activin A caused the growth suppression and concomitant expression of tartrate-resistant acid phosphatase (TRAP) and c-Src, without inducing syncytium formation or increasing the survival rate in RAW264.7 cells. Although TGF-beta1 and activin A had no effect on NF-kappaB and JNK activities, these factors enhanced the expression of JunB, a component of the AP-1 transcriptional complex. These results suggest that TGF-beta1 and activin A may function as commitment factors in osteoclastic differentiation, not as a crucial component for terminal differentiation to form multinucleated OCLs nor in OCL survival.
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PMID:Role of TGF-beta family in osteoclastogenesis induced by RANKL. 1174 86

Phosphatidylinositol 3-kinase (PI 3-kinase) and mitogen-activated protein kinases (MAPKs) have been implicated in diverse cellular functions, including proliferation, migration, and survival. In this study, we examined the involvement of these kinases in osteoclast differentiation by employing specific inhibitors of the kinases. The osteoclast differentiation was assessed in three different culture systems: a coculture of mouse bone marrow cells with mouse calvarial osteoblasts, a mouse bone marrow cell culture in the presence of receptor activator of NF-kappaB ligand (RANKL) and macrophage-colony stimulating factor (M-CSF), and a culture of bone-resident osteoclast precursor cells driven by RANKL and M-CSF. LY294002, a specific inhibitor of PI 3-kinase, potently inhibited osteoclast differentiation in all culture systems when assessed by both tartrate-resistant acid phosphatase (TRAP) staining and dentine resorption assays. Inhibition of p38 MAPK by SB202190 resulted in a strong suppression in the exogenous RANKL dependent mouse bone marrow and bone resident precursor cell cultures. Another MAPK pathway inhibitor (PD98059), which blocks the activation of extracellular signal-regulated kinase (ERK) by inhibiting the upstream kinase MAPK-ERK kinase (MEK) 1, exerted an inhibitory effect on osteoclast differentiation only at the highest concentration tested (30 micromol/L) in many cases. Whether the signaling pathways involving these kinases are activated by RANKL was also examined. The RANKL-stimulated phosphorylation of Akt, a downstream target of PI 3-kinase, and that of ERK were observed. RANKL also stimulated the activity of p38. These results suggest that PI 3 kinase, p38, and ERK play roles in osteoclast differentiation, at least in part, by participating in RANKL signaling.
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PMID:The phosphatidylinositol 3-kinase, p38, and extracellular signal-regulated kinase pathways are involved in osteoclast differentiation. 1179 67

Receptor activator of NF-kappaB ligand (RANKL) activates signaling pathways that regulate osteoclast differentiation, function, and survival. The microphthalmia transcription factor (MITF) is required for terminal differentiation of osteoclasts. To determine whether MITF could be a target of RANKL signaling, a phosphospecific MITF antibody directed against conserved residue Ser(307), a potential mitogen-activated protein kinase (MAPK) site, was produced. Using this antibody, we could demonstrate that MITF was rapidly and persistently phosphorylated upon stimulation of primary osteoclasts with RANKL and that phosphorylation of Ser(307) correlated with expression of the target gene tartrate-resistant acid phosphatase. MITF phosphorylation at Ser(307) also correlated with persistent activation of p38 MAPK, and p38 MAPK could utilize MITF Ser(307) as a substrate in vitro. The phosphorylation of MITF and activation of target gene expression in osteoclasts were blocked by p38 MAPK inhibitor SB203580. In transient transfections, a constitutively active Rac1 or MKK6 gene could collaborate with MITF to activate the tartrate-resistant acid phosphatase gene promoter dependent on Ser(307). Dominant negative p38 alpha and beta could inhibit the collaboration between upstream signaling components and MITF in the transient assays. These results indicate that MITF is a target for the RANKL signaling pathway in osteoclasts and that phosphorylation of MITF leads to an increase in osteoclast-specific gene expression.
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PMID:Microphthalmia transcription factor is a target of the p38 MAPK pathway in response to receptor activator of NF-kappa B ligand signaling. 1179 6

Calmodulin plays an important role in regulating the function of mature osteoclasts. However, its role in osteoclastogenesis has not been investigated. In the present study, we examined the role of calmodulin in osteoclastogenesis using in vivo and in vitro systems. Calmodulin antagonists, trifluoperazine (TFP), W7, and tamoxifen, dose-dependently inhibited osteoclast formation, which occurred only in the last 24 h of a 4-d osteoclastogenesis culture using mouse bone marrow macrophages. Inhibitory effects were quantitated by measuring tartrate-resistant acid phosphatase activity and counting osteoclast numbers. In contrast, bis indolylmaleimide, a protein kinase C inhibitor, showed no such inhibitory effect even when applied at a concentration that was 10-fold greater than its IC50. Overexpressing calmodulin by recombinant retrovirus reversed the inhibitory effect of TFP on osteoclast-like differentiation in RAW264.7 cells. Furthermore, administration of TFP to mice was as effective as estrogen in abolishing the ovariectomy-induced increment of osteoclastogenesis as determined by quantitative assessment of tartrate-resistant acid phosphatase activity in tibias, which led to the recovery of the ovariectomy-induced decrement in trabecular bone volume. To investigate potential cellular and molecular mechanisms by which calmodulin antagonists inhibit osteoclastogenesis, Z-VAD-FMK, a broad caspase inhibitor, failed to block the inhibitory effect of TFP on mouse osteoclast formation, indicating that apoptosis is not the underlying mechanism. Pretreatment of RAW264.7 cells with different concentrations of TFP dose-dependently inhibited receptor activator of nuclear factor kappaB ligand-stimulated phosphorylation of c-Jun N-terminal kinase and inhibitory kappaBalpha but not that of p38. Taken together, our data indicate that calmodulin mediates osteoclast differentiation, possibly via modulating specific receptor activator of NF-kappaB-signaling pathways.
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PMID:The role of calmodulin in the regulation of osteoclastogenesis. 1296 67

Receptor activator of NF-kappaB ligand (RANKL) is essential for differentiation and function of osteoclasts. The negative signaling pathways downstream of RANKL are not well characterized. By retroviral transduction of RAW264.7 cells with a dominant negative Src homology 2 domain-containing phosphatase-1 (SHP-1)(C453S), we studied the role of tyrosine phosphatase SHP-1 in RANKL-induced osteoclastogenesis. Over-expression of SHP-1(C453S) significantly enhanced the number of tartrate-resistant acid phosphatase-positive multinuclear osteoclast-like cells in response to RANKL in a dose-dependent manner. RANKL induced the recruitment of SHP-1 to a complex containing TNFR-associated factor (TRAF)6. GST pull down experiments indicated that the association of SHP-1 with TRAF6 is mediated by SHP-1 lacking the two Src homology 2 domains. RANKL-stimulated IkappaB-alpha phosphorylation, IkappaB-alpha degradation and DNA binding ability of NF-kappaB were increased after over-expression of SHP-1(C453S). However, RANKL-induced phosphorylation of mitogen-activated protein kinases, extracellular signal-regulated kinase, c-Jun N-terminal kinase, and p38 mitogen-activated protein kinase, was unchanged. In addition, SHP-1 regulated RANKL-stimulated tyrosine phosphorylation of p85 subunit of phosphatidylinositol 3 kinase and the phosphorylation of Akt. Increased numbers of osteoclasts contribute to severe osteopenia in Me(v)/Me(v) mice due to mutation of SHP-1. Like RAW264.7 cells expressing SHP-1(C453S), the bone marrow macrophages of Me(v)/Me(v) mice generated much more osteoclast-like cells than that of littermate controls in response to RANKL. Furthermore compared with controls, RANKL induces enhanced association of TRAF6 and RANK in both RAW264.7 cells expressing SHP-1(C453S) and bone marrow macrophages from Me(v)/Me(v) mice. Therefore, SHP-1 plays a role in signals downstream of RANKL by recruitment to the complex containing TRAF6 and these observations may help to understand the mechanism of osteoporosis in Me(v)/Me(v) mice.
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PMID:Receptor activator of NF-kappa B ligand stimulates recruitment of SHP-1 to the complex containing TNFR-associated factor 6 that regulates osteoclastogenesis. 1450 Jun 59

The role of the tumor necrosis factor (TNF) superfamily member receptor activator of nuclear factor kappa B ligand (RANKL) in promoting the differentiation of osteoclasts has been extensively characterized. In this study, we have investigated the effect of TNF-related apoptosis-inducing ligand (TRAIL), a member of the TNF superfamily of cytokines, in osteoclastogenesis, by using human peripheral blood mononuclear cells and the RAW264.7 murine monocytic cell line. Both cell models differentiate into osteoclast-like cells in presence of RANKL plus macrophage-colony-stimulating factor (M-CSF), as evaluated in terms of tartrate-resistant acid phosphatase (TRAP)-positive multinucleated cells and bone resorption activity. Unexpectedly, when added in culture in combination with RANKL plus M-CSF, TRAIL inhibited osteoclastic differentiation in both cell models. To investigate the molecular mechanism underlining such inhibitory activity, we analyzed the effect of TRAIL on the mitogen-activated protein kinases (MAPKs) pathways, which play a key role in osteoclastogenesis. Treatment with RANKL plus M-CSF activated both the ERK1/2 and p38/MAPK pathways, which are essential for proliferation and differentiation of preosteoclasts, respectively. Of note, the addition of TRAIL to RANKL plus M-CSF did not affect ERK1/2 but it profoundly inhibited p38/MAPK phosphorylation. Thus, our data demonstrate that TRAIL blocks osteoclastic differentiation and suggest that inhibition of the p38/MAPK pathway by TRAIL likely plays an important role in this process.
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PMID:TNF-related apoptosis-inducing ligand (TRAIL) blocks osteoclastic differentiation induced by RANKL plus M-CSF. 1850 44

Phytoestrogens, which have structural similarity to 17beta-estradiol, have been reported to act as agonists/antagonists of estrogen in animals and humans. Estrogen is known to have an important role in maintaining bone mass, because the concentration of serum estrogen decreases after menopause and the estrogen deficiency causes bone loss. In this study, we investigated the effects of coumestrol and other phytoestrogens on osteoclast differentiation using estrogen receptor alpha-transfected RAW264.7 (RAW264.7-ERalpha) cells. When the cells were cultured with the receptor activator of nuclear factor kappa B-ligand (RANKL), both formation of tartrate-resistant acid phosphatase (TRAP) positive multinucleated cells and TRAP activity were increased compared with control cells that were cultured in the absence of RANKL. Coumestrol decreased RANKL-induced formation of TRAP-positive multinucleated cells and TRAP activity dose-dependently. RANKL-stimulated RAW264.7-ERalpha cells formed resorption pits on calcium phosphate films and the pit formation was inhibited by coumestrol in a dose-dependent manner. RT-PCR analyses revealed that coumestrol (10 microM) decreased mRNA levels of calcitonin receptor (CTR) and matrix metalloproteinase-9 (MMP9) in RANKL-treated cells. In addition, pretreatment of coumestrol decreased RANKL-induced phosphorylation of extracellular signal-regulated kinases/p44/42 (ERK1/2). These results suggest that coumestrol has an inhibitory effect on the differentiation of osteoclasts, at least partially via ERK1/2 pathway.
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PMID:Effects of the phytoestrogen coumestrol on RANK-ligand-induced differentiation of osteoclasts. 1536 96

This study examined the role of osteopontin (OPN), a phosphorylated secreted glycoprotein, in the promotion of trophoblastic cell migration, an early event in the embryo implantation process. Three human choriocarcinoma cell lines, namely JAR, BeWo, and JEG-3, were treated with variants of OPN differing in the extent of phosphorylation following sequential dephosphorylation with tartrate-resistant acid phosphatase (TRAP), and their migratory response was measured. The highly phosphorylated human milk form of OPN (OPN-1) strongly triggered migration in all three cell lines, whereas the less phosphorylated variants, OPN-2a and OPN-2b, failed to stimulate migration. JAR cell migration in response to OPN-1 was accompanied by a rapid rearrangement of actin filaments to the cellular membrane. Using broad spectrum protein kinase profiling, we identified p70 S6 kinase as a major signal transduction pathway activated by OPN-1 during the migratory response in JAR cells. Activation was blocked completely by rapamycin and LY294002, thus demonstrating that OPN-1-stimulated migration occurs through mTOR and PI3K pathways, respectively. Conversely, PD98059 did not affect the activation of p70 S6 kinase by OPN-1, therefore, this response does not involve the Ras/ MAPK signaling cascade. Together, these data show that the highly phosphorylated human OPN-1 can stimulate trophoblastic cell migration and provides evidence for the involvement of the PI3K/mTOR/p70 S6 kinase pathway in the JAR cells response. Because both OPN and TRAP are expressed in the uterus during early pregnancy, it is conceivable that extracellular phosphatases such as TRAP may modify OPN charge state and thus modulate cell migration.
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PMID:Phosphorylated osteopontin promotes migration of human choriocarcinoma cells via a p70 S6 kinase-dependent pathway. 1569 79

Hyaluronic acid (HA) is a component of the extracellular matrix that has been shown to play an important role in bone formation, resorption, and mineralization both in vivo and in vitro. We examined the effects of HA at several molecular weights on osteoclast formation and function induced by RANKL (receptor activator of NF-kappa B ligand) in a mouse monocyte cell line (RAW 264.7). HA at M(r) < 8,000 (low molecular weight HA (LMW-HA)) enhanced tartrate-resistant acid phosphatase-positive multinucleated cell formation and tartrate-resistant acid phosphatase activity induced by RANKL in a dose-dependent manner, whereas HA at M(r) > 900,000 (high molecular weight HA (HMW-HA)) showed no effect on osteoclast differentiation. LMW-HA enhanced pit formation induced by RAW 264.7 cells, whereas HMW-HA did not, and LMW-HA stimulated the expression of RANK (receptor activator of NF-kappa B) protein in RAW 264.7 cells. In addition, we found that LMW-HA enhanced the levels of c-Src protein and phosphorylation of ERKs and p38 MAPK in RAW 264.7 cells stimulated with RANKL, whereas the p38 MAPK inhibitor SB203580 inhibited RANKL-induced osteoclast differentiation. This enhancement of c-Src and RANK proteins induced by LMW-HA was inhibited by CD44 function-blocking monoclonal antibody. These results indicate that LMW-HA plays an important role in osteoclast differentiation and function through the interaction of RANKL and RANK.
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PMID:Mechanisms involved in enhancement of osteoclast formation and function by low molecular weight hyaluronic acid. 1575 5


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