Ligand-independent activation of the androgen receptor by insulin-like growth factor-i and the role of the MAPK pathway in skeletal muscle cells

In this study, the roles of the p38 MAPK, ERK1/2 and JNK signaling pathway in IGF-I-induced AR induction and activation were examined. C2C12 cells were treated with IGF-I in the absence or presence of various inhibitors of p38 MAPK (SB203580), ERK1/2 (PD98059), and JNK (SP600125). Inhibition of the MAPK pathway with SB203580, PD98059, or SP600125 significantly decreased IGF-I-induced AR phosphorylation and total AR protein expression. IGF-I-induced nuclear fraction of total AR and phosphorylated AR were significantly inhibited by SB203580, PD98059, or SP600125. Furthermore, IGF-I-induced AR mRNA and skeletal α-actin mRNA were blocked by those inhibitors in dose-dependent manner. Confocal images showed that IGF-I-induced AR nuclear translocation from cytosol was significantly blocked by SB203580, PD98059, or SP600125, suggesting that the MAPK pathway regulates IGF-I-induced AR nuclear localization in skeletal muscle cells. The present results suggest that the MAPK pathways are required for the ligand-independent activation of AR by IGF-I in C2C12 skeletal muscle cells.     

Positive regulation of the Egr-1/osteopontin positive feedback loop in rat vascular smooth muscle cells by TGF-β, ERK, JNK, and p38 MAPK signaling

Previous studies identified a positive feedback loop in rat vascular smooth muscle cells (VSMCs) in which early growth response factor-1 (Egr-1) binds to the osteopontin (OPN) promoter and upregulates OPN expression, and OPN upregulates Egr-1 expression via the extracellular signal-regulated protein kinase (ERK) signaling pathway. The current study examined whether transforming growth factor-β (TGF-β) activity contributes to Egr-1 binding to the OPN promoter, and whether other signaling pathways act downstream of OPN to regulate Egr-1 expression. ChIP assays using an anti-Egr-1 antibody showed that amplification of the OPN promoter sequence decreased in TGF-β DNA enzyme-transfected VSMCs relative to control VSMCs. Treatment of VSMCs with PD98059 (ERK inhibitor), SP600125 (JNK inhibitor), or SB203580 (p38 MAPK inhibitor) significantly inhibited OPN-induced Egr-1 expression, and PD98059 treatment was associated with the most significant decrease in Egr-1 expression. OPN-stimulated VSMC cell migration was inhibited by SP600125 or SB203580, but not by PD98059. Furthermore, MTT assays showed that OPN-mediated cell proliferation was inhibited by PD98059, but not by SP600125 or SB203580. Taken together, the results of the current study show that Egr-1 binding to the OPN promoter is positively regulated by TGF-β, and that the p38 MAPK, JNK, and ERK pathways are involved in OPN-mediated Egr-1 upregulation.     

内皮素-1对大鼠血管平滑肌细胞产生MCP-1的影响及其机制

目的：观察内皮素-1（ET-1）对大鼠血管平滑肌细胞（VSMCs）产生单核细胞趋化蛋白-1（MCP-1）的影响及其机制。方法：培养大鼠血管平滑肌细胞（VSMCs）。细胞分为2组：ET-1刺激组：以不同浓度ET-1刺激VSMCs不同时间;阻断剂干预组：VSMCs分别与不同阻断剂[ET_AR、ET_BR阻断剂BQ123、BQ788,抗氧化剂N-乙酰半胱氨酸（NAC）,ERK、p38MAPK、JNK及NF-κB抑制剂PD98059、SB203580、SP600125及PDTC]预先孵育30 min,再加入ET-1刺激24 h。在预定时间,以酶联免疫吸附（ELISA）法、逆转录聚合酶链反应（RT-PCR）法分别测定不同因素下VSMCs MCP-1蛋白质及mRNA表达量。VSMCs分别与不同阻断剂（BQ123、BQ788、NAC、PD98059、SB203580及SP600125预先孵育20 min,再加入ET-1刺激5 min,免疫印迹（WB）法测定VSMCs胞浆中细胞外调节蛋白激酶（ERK）、p38丝裂原活化蛋白激酶（p38MAPK）、c-Jun氨基末端激酶（JNK）及其各自磷酸化蛋白质的水平。各项检测均重复3次。结果：ET-1能刺激VSMCs MCP-1蛋白质及mRNA表达,其表达量随ET-1浓度及刺激时间的增加呈升高趋势（P<0.05,P<0.01）;BQ123、NAC、PD98059、SB203580及PDTC能显著抑制ET-1诱导的大鼠VSMCs MCP-1蛋白质及mRNA表达（P<0.01）,而BQ788及SP600125对此作用无明显影响。BQ123、NAC与PD98059或SB203580能分别抑制ET-1刺激后VSMCs胞浆内ERK及p38MAPK的磷酸化（P<0.05,P<0.01）,而ET-1对JNK的磷酸化无明显激活作用。结论：ET-1通过ET_AR、ROS、ERK、p38MAPK及NF-κB诱导大鼠VSMCs产生MCP-1。     

Reduced Parasite Motility and Micronemal Protein Secretion by a p38 MAPK Inhibitor Leads to a Severe Impairment of Cell Invasion by the Apicomplexan Parasite Eimeria tenella

E. tenella infection is associated with a severe intestinal disease leading to high economic losses in poultry industry. Mitogen activated protein kinases (MAPKs) are implicated in early response to infection and are divided in three pathways: p38, extracellular signal-regulated protein kinase (ERK) and c-Jun N-terminal kinase (JNK). Our objective was to determine the importance of these kinases on cell invasion by E. tenella. We evaluated the effect of specific inhibitors (ERK: PD98059, JNKII: SP600125, p38 MAPK: SB203580) on the invasion of epithelial cells. Incubation of SP600125 and SB203580 with epithelial cells and parasites significantly inhibited cell invasion with the highest degree of inhibition (90%) for SB203580. Silencing of the host p38α MAPK expression by siRNA led to only 20% decrease in cell invasion. In addition, when mammalian epithelial cells were pre-treated with SB203580, and washed prior infection, a 30% decrease in cell invasion was observed. This decrease was overcome when a p38 MAPK activator, anisomycin was added during infection. This suggests an active but limited role of the host p38 MAPK in this process. We next determined whether SB203580 has a direct effect on the parasite. Indeed, parasite motility and secretion of micronemal proteins (EtMIC1, 2, 3 and 5) that are involved in cell invasion were both decreased in the presence of the inhibitor. After chasing the inhibitor, parasite motility and secretion of micronemal proteins were restored and subsequently cell invasion. SB203580 inhibits cell invasion by acting partly on the host cell and mainly on the parasite.     

Roles of mitogen-activated protein kinase pathways during <Emphasis Type="Italic">Escherichia coli-</Emphasis>induced apoptosis in U937 cells

Escherichia coli (E. coli) infections play an important and growing role in the clinic. In the present study, we investigated the involvement of members of the mitogen-activated protein kinase (MAPK) superfamily, including extracellular signal-regulated kinase (ERK), c-Jun NH₂-terminal kinase (JNK) and p38 MAPK, and caspase-3 and 9 activity in E. coli-induced apoptosis in human U937 cells. We found that E. coli induces apoptosis in U937 cell lines in a dose- and time-dependent manner, p38 MAPK and JNK were activated after 10 min of infection with E. coli. In contrast, ERK1/2 was down-regulated in a time-dependent manner. The levels of total (phosphorylation state-independent) p38 MAPK, JNK and ERK1/2 did not change in E. coli-infected U937 cells at all times examined. Moreover, exposure of U937 cells to E. coli led to caspase-3 and 9 activity. For the evaluation of the role of MAPKs, PD98059, SB203580 and SP600125 were used as MAPKs inhibitors for ERK1/2, p38 MAPK and JNK. Inhibition of ERK1/2 with PD98059 caused further enhancement in apoptosis and caspase-3 and 9 activity, while a selective p38 MAPK inhibitor, SB203580 and JNK inhibitor, SP600125 significantly inhibited E. coli-induced apoptosis and caspase-3 and 9 activity in U937 cells. The results were further confirmed by the observation that the caspase inhibitors Z-DEVD-FMK and Z-LEHD-FMK blocked E. coli-induced U937 apoptosis. Taken together, we have shown that E. coli increase p38 MAPK and JNK and decrease ERK1/2 phosphorylation and increase caspase-3 and 9 activity in U937 cells.     

Study of the insulin signaling pathways in the regulation of ACAT1 expression in cultured macrophages

Objective

To determine the signaling pathways and components involved in insulin-mediated regulation of Acyl-CoA: cholesterol acyltransferase1 (ACAT1).

Methods

THP-1 cells were cultured in RPMI 1640 medium and were induced into macrophages in the presence of 160 nM phorbol 12-myristate 13-acetate (PMA). Before insulin was added in, macrophages were preincubated with the inhibitors of the insulin signaling pathway, including wortmannin, phosphatidylinositol 3-kinase (PI3 K) inhibitor; PD98059, extracellular signal-regulated kinase (ERK) inhibitor; SB203580, p38 mitogen-activated protein kinase (p38MAPK) inhibitor; SP600125, c-Jun N-terminal kinase (JNK) inhibitor and U73122, phospholipase C-γ (PLC-γ) inhibitor. ACAT1 mRNA and protein expression level in macrophages were determined by real-time quantitative polymerase chain reaction and western blotting, respectively.

Results

Real-time quantitative polymerase chain reaction and western blotting demonstrated that PD98059, SB203580 or SP600125 down-regulated the expression of ACAT1 in a dose-dependent manner. However, no obvious alteration was found in wortmannin and U73122 groups.

Conclusion

These results suggest that the ERK, p38MAPK and JNK signaling pathways may be involved in insulin-mediated regulation of ACAT1, but no PI3K and PLC-γ signaling pathways were involved in the present study.     

Cinnamaldehyde-induced apoptosis in human PLC/PRF/5 cells through activation of the proapoptotic Bcl-2 family proteins and MAPK pathway

Cinnamaldehyde (Cin) has been shown to be effective in inducing apoptotic cell death in a number of human cancer cells. However, the intracellular death signaling mechanisms by which Cin inhibits tumor cell growth are poorly understood. In this study, we investigated the effect of mitogen-activated protein kinases (MAPKs) inhibitors [namely SP600125 (a specific JNK inhibitor), SB203580 (a specific p38 inhibitor) and PD98059 (a specific ERK inhibitor)] on the stress-responsive MAPK pathway induced by Cin in PLC/PRF/5 cells. Trypan blue staining assay indicated that Cin was cytotoxic to PLC/PRF/5 cells. Cin caused cell cycle perturbation (S-phase arrest) and triggered apoptosis as revealed by the externalization of annexin V-targeted phosphatidylserine and accumulation of sub-G1 peak. It down-regulated the Bcl-2 and Mcl-1 expression, and up-regulated Bax protein in a time-response manner. Treatment with 1 microM Cin resulted in an activation of caspase-8 and cleavage of Bid to its truncated form in a time-dependent pattern. JNK, ERK and p38 kinases in cells were activated and phosphorylated after Cin treatment. Pre-incubation with SP600125 and SB203580 markedly suppressed the effect of Cin-induced apoptosis, but not PD98059. Both SP600125 and SB203580 significantly prevented the phosphorylation of JNK and p38 proteins, but not ERK. These results conclude that Cin triggers apoptosis in PLC/PRF/5 cells could be through the activation of pro-apoptotic Bcl-2 family (Bax and Bid) proteins and MAPK signaling pathway.     

MAPKs抑制剂对大鼠肝细胞GSH代谢相关酶的影响

目的：观察丝裂原活化的蛋白激酶（MAPKs）抑制剂对大鼠肝细胞谷胱甘肽（GSH）代谢的影响,确定哪条途径与GSH代谢相关。方法：体外培养BRL大鼠肝细胞,以c-Jun NH2-末端激酶（JNK）途径抑制剂SP600125、p38途径抑制剂SB203580、细胞外信号调节激酶1/2（ERK1/2）途径抑制剂PD98659处理24 h,采用MTT法测定细胞活力,高效液相色谱法测定细胞内GSH含量,Luminex法测定JNK和磷酸化JNK （p-JNK）的蛋白表达,采用试剂盒测定GSH代谢酶活性。结果：SP600125浓度>5 μmol/L,SB203580浓度>20 μmol/L,PD98659浓度>40 μmol/L时,细胞活力受抑制;SP600125能显著减少大鼠肝细胞内还原型GSH的含量,SB203580和PD98659作用不明显;SP600125显著减少磷酸化JNK （p-JNK）蛋白表达,显著增强谷胱甘肽过氧化物酶（GSH-Px）的活力。结论：JNK MAPK途径参与了大鼠肝细胞GSH的代谢。     

SAPK/JNK plays a role in transforming growth factor-beta-induced VEGF synthesis in osteoblasts.

We previously reported that transforming growth factor-beta (TGF-beta) activates p44/p42 mitogen-activated protein (MAP) kinase and p38 MAP kinase, resulting in the stimulation of vascular endothelial growth factor (VEGF) synthesis in osteoblast-like MC3T3-E1 cells. In the present study, we investigated the involvement of stress-activated protein kinase/c- Jun N-terminal kinase (SAPK/JNK), another member of the MAP kinase superfamily, in TGF-beta-induced VEGF synthesis in these cells. TGF-beta markedly induced SAPK/JNK phosphorylation. SP600125, a specific inhibitor of SAPK/JNK, markedly reduced TGF-beta-induced VEGF synthesis. SP600125 suppressed TGF-beta-induced SAPK/JNK phosphorylation. PD98059, an inhibitor of upstream kinase of p44/p42 MAP kinase and SB203580, an inhibitor of p38 MAP kinase, each failed to reduce TGF-beta-induced SAPK/JNK phosphorylation. A combination of SP600125 and PD98059 or SP600125 and SB203580 suppressed TGF-beta-stimulated VEGF synthesis in an additive manner. These results strongly suggest that TGF-beta activates SAPK/JNK in osteoblasts, and that SAPK/JNK plays a role in addition to p42/p44 MAP kinase and p38 MAP kinase in TGF-beta-induced VEGF synthesis.     

Involvement of MAPK signaling pathway in the osteogenic gene expressions of Cervi Pantotrichum Cornu in MG-63 human osteoblast-like cells

Aims

The purposes of this study were to determine whether Cervi Pantotrichum Cornu (CPC) has osteogenic activities in human osteoblastic MG-63 cells and to investigate the underlying molecular mechanism.

Main methods

The effects of CPC on alkaline phosphatase activity, collagen synthesis, and calcium deposits were measured. The COL1A1, ALPL, BGLAP, and SPP1 expressions were measured by real-time PCR. Phosphorylated MAP kinases (ERK1/2, JNK1/2, p38, ELK1, and cJUN) were studied by western blot analysis. The involvement of MAPK pathway in osteogenic gene expressions was determined by using each selective MAPK inhibitor (PD98059, SP600125, and SB203580).

Key findings

CPC increased alkaline phosphatase activity, collagen synthesis, and calcium deposits. CPC activated ERK1/2, JNK1/2, p38, and ELK1 phosphorylation except cJUN. CPC increased the COL1A1, ALPL, BGLAP, and SPP1 gene expressions. The elevated COL1A1 and BGLAP expressions were inhibited by PD98059, SP600125 or SB203580. The elevated ALPL expression was blocked by SB203580. The elevated SPP1 expression was inhibited by SP600125 or SB203580. CPC increased COL1A1 and BGLAP expressions via ERK1/2, JNK1/2, and p38 MAPKs pathways and SPP1 expression via JNK1/2 and p38 pathways. p38 pathway is needed for ALPL expression.

Significance

These results imply that MAPK signaling pathway is an indispensable factor for bone matrix genes expression of CPC in MG-63 human osteoblast-like cells.     

Specific inhibitor of MEK-mediated cross-talk between ERK and p38 MAPK during differentiation of human osteosarcoma cells

Osteosarcoma is the most common primary malignant bone tumor, accounting for approximately 20% of all primary sarcomas in bone. Although treatment modalities have been improved over the past decades, it is still a tumor with a high mortality rate in children and young adults. Based on histological considerations, osteosarcoma arises from impaired differentiation of these immature cells into more mature types and that correction of this impairment may reduce malignancy and increase the efficiency of chemotherapy. The purpose of this study was to determine the effect of specific inhibitors of MAPK extracellular signaling-regulated kinase (ERK) kinase (MEK) and p38 on the differentiation of human osteosarcoma cell line SaOS-2 cells. We found that PD98059, a specific inhibitor of MEK, inhibited the serum-stimulated proliferation of SaOS-2 cells; whereas SB203580, a specific inhibitor of p38 MAPK, had little effect on it. SB203580 suppressed ALPase activity, gene expression of type I collagen, and expression of ALP and BMP-2 mRNAs; whereas PD98059 upregulated them dose dependently. In addition, immunoblot and immunostaining analysis revealed that phosphorylation of ERK was increased by treatment with SB203580; whereas PD98059 increased the phosphorylation of p38, which implies a seesaw-like balance between ERK and p38 phosphorylation. We suggest that osteosarcoma cell differentiation is regulated by the balance between the activities of the ERK and p38 pathways and that the MEK/ERK pathway negatively regulates osteosarcoma cell differentiation, whereas the p38 pathway does so positively. MEK inhibitor may thus be a good candidate for altering the expression of the osteosarcoma malignant phenotype.     

EGF Enhances ADSCs Secretion via ERK and JNK Pathways

The objective of this work was to study the effect of epidermal growth factor (EGF) induced secretions of angiogenesis factors in adipose-derived stem cells (ADSCs) and the involvement of mitogen-activated protein kinases (MAPK). ADSCs were cultured and ELISA assays were performed to quantify the vascular endothelial growth factor, the hepatocyte growth factor, and the stromal derived factor-1 in ADSC-conditioned medium before and after EGF treatments and after pharmacological inhibition of MAPKs with PD98059, SB203580, and SP600125. The tube formation assay was used to test the effects of EGF treated and inhibitor treated ADSCs on the human umbilical vein endothelial cells (HUVECs) tube formation. Liposuction was applied and ADSCs were cultured successfully. The ADSCs released a variety of angiogenic factors, with the EGF treatments enhancing secretions and promoting the HUVEC tube formation. The MAPK inhibitors PD98059 and SP600125 increased the paracrine to promote tubular formation, while the SB203580 played an opposite role. In conclusion, (1) the in vitro cultured ADSCs secrete various angiogenic factors and the EGF amplifies the secretion and can enhance the ADSCs on the HUVEC tube formation. (2) ERK1/2 and JNK pathway may be involved in the enhanced secretion capacity of ADSCs while the p38 pathway may exert an opposite effect.     

Involvement of p38 MAPK and ERK/MAPK pathways in staurosporine-induced production of macrophage inflammatory protein-2 in rat peritoneal neutrophils.

Stimulation of rat peritoneal neutrophils with staurosporine (64 nM) induced production of macrophage inflammatory protein-2 (MIP-2) and phosphorylation of p38 mitogen-activated protein kinase (MAPK) and extracellular signal-regulated kinase/MAP kinase (ERK/MAPK). The staurosporine-induced MIP-2 production at 4 h was inhibited by the highly specific p38 MAPK inhibitor SB 203580 and the MAPK/ERK kinase (MEK-1) inhibitor PD 98059 in a concentration-dependent manner. By treatment with SB 203580 (1 microM) or PD 98059 (50 microM), the staurosporine-induced increase in the levels of mRNA for MIP-2 was only partially lowered, although the staurosporine-induced MIP-2 production was completely inhibited. Consistent with the inhibition by the protein synthesis inhibitor cycloheximide, SB 203580 and PD 98059 inhibited MIP-2 production at 4 h either when added simultaneously with staurosporine or 2 h after stimulation with staurosporine. In contrast, the DNA-dependent RNA polymerase inhibitor actinomycin D did not inhibit MIP-2 production at 4 h when it was added 2 h after staurosporine stimulation. Dot blot analysis demonstrated that treatment with SB 203580 or PD 98059 down-regulates the stability of MIP-2 mRNA. These results suggested that p38 MAPK and ERK/MAPK pathways are involved in translation of MIP-2 mRNA to protein and stabilization of MIP-2 mRNA.     

Differential requirement of members of the MAPK family for CCL2 expression by hepatic stellate cells

Hepatic stellate cells (HSC) coordinate the liver wound-healing response through secretion of several cytokines and chemokines, including CCL2 (formerly known as monocyte chemoattractant protein-1). In this study, we evaluated the role of different proteins of the MAPK family (ERK, p38(MAPK), and JNK) in the regulation of CCL2 expression by HSC, as an index of their proinflammatory activity. Several mediators activated all three MAPK, including TNF, IL-1, and PDGF. To assess the relative role of the different MAPKs, specific pharmacological inhibitors were used; namely, SB203580 (p38(MAPK)), SP600125 (JNK), and PD98059 (MEK/ERK). The efficacy and specificity of the different inhibitors in our cellular system were verified analyzing the enzymatic activity of the different MAPKs using in vitro kinase assays and/or testing the inhibition of phosphorylation of downstream substrates. SB203580 and SP600125 dose-dependently inhibited CCL2 secretion and gene expression induced by IL-1 or TNF. In contrast, inhibition of ERK did not affect the upregulation of CCL2 induced by the two cytokines. Finally, activin A was also found to stimulate CCL2 expression and to activate ERK, JNK, p38, and their downstream targets. Unlike in cells exposed to proinflammatory cytokines, all three MAPKs were required to induce CCL2 secretion in response to activin. We conclude that members of the MAPK family differentially regulate cytokine-induced chemokine expression in human HSC.     

Activation of p90RSK and cAMP response element binding protein in stimulated neutrophils: novel effects of the pyridinyl imidazole SB 203580 on activation of the extracellular signal-regulated kinase cascade.

Neutrophils stimulated with the chemoattractant FMLP or the phorbol ester PMA are known to exhibit activation of a 90-kDa renaturable protein kinase. Activation of this kinase was maximal at approximately 1-3 min after cell stimulation and the time course for activation was similar to that of the extracellular-regulated kinases (ERKs) and p38-mitogen activated protein kinase (p38MAPK). Compounds that block activation of ERK-1/2 (PD 98059) or that inhibit the activity of p38MAPK (SB 203580) blocked activation of this 90-kDa kinase. SB 203580 is a highly selective inhibitor of p38MAPK in vitro and is under intense study as a lead compound for developing novel anti-inflammatory agents. However, we demonstrate that SB 203580 at concentrations >/=10 microM can also inhibit activation of ERK-1/2 in neutrophils. An Ab to the protein kinase p90RSK2 (also referred to as MAPKAP-K1b, or p90rsk) immunoprecipitated the active 90-kDa kinase from lysates of stimulated neutrophils. No activity was observed for this enzyme in immunoprecipitates obtained from unstimulated cells, and the amounts of activity were markedly reduced if the cells were treated with PD 98059 or SB 203580 before stimulation. Neutrophils stimulated with FMLP exhibited phosphorylation of the cAMP response element binding protein (CREB), and this reaction was inhibited by SB 203580 and PD 98059. These data establish that the renaturable 90-kDa protein kinase is p90RSK2 and that CREB may be a substrate for this enzyme in these cells. Novel effects of compound SB 203580 on stimulated neutrophils are also described.