Regulation of miRNA-21 by reactive oxygen species-activated ERK/NF-κB in arsenite-induced cell transformation

After acute exposure of cells to arsenic, reactive oxygen species mediate changes in cell behavior, including activation of proliferative signaling. For chronic exposure to arsenic, however, the function of reactive oxygen species in cell transformation remains poorly understood. Although microRNA-21 (miR-21) has been implicated in various aspects of carcinogenesis, its functions and molecular mechanisms in carcinogen-induced tumorigenesis are unclear. The purpose of this study was to determine if miR-21 is involved in arsenite-induced malignant transformation and to characterize the associated signaling pathways. During arsenite-induced transformation of human embryo lung fibroblast (HELF) cells, miR-21 was upregulated, and the extracellular signal-regulated kinase (ERK)/nuclear factor-κB (NF-κB) signal pathway was activated. Moreover, superoxide radical dismutase (a scavenger of superoxide) and catalase (a scavenger of hydroperoxides) blocked the arsenite-induced effects in HELF cells and mouse embryonic fibroblasts. Blockage of ERK by the inhibitor U0126 or inhibition of NF-κB p65 by siRNA or Bay 11-7082 prevented the increases in miR-21 and the decreases in Spry1, Pten, and Pdcd4, the target proteins of miR-21, induced by arsenite. As determined by a ChIP-qPCR assay, NF-κB p65 regulated miR-21 expression by binding directly to the promoter of miR-21. Further, anti-miR-21 downregulated miR-21 expression and prevented the arsenite-induced activation of ERK via the increase in Spry1, indicating that miR-21 has a feedback effect in regulating ERK activation. Overexpression of miR-21 with an miR-21 mimic and feedback activation of ERK and NF-κB via the decrease in Spry1 promoted the malignancy of HELF cells exposed to arsenite, but knockdown of miR-21 with anti-miR-21 and feedback blockage of ERK and NF-κB activation through an increase in Spry1 decreased anchorage-independent growth of arsenite-transformed cells. Thus, the transformation of HELF cells induced by chronic exposure to arsenite is mediated by increased miR-21 expression, which, in turn, is mediated by reactive oxygen species activation of the ERK/NF-κB pathway.     

Hydrogen peroxide induces apoptosis in HeLa cells through mitochondrial pathway

Cervical cancer is the most common cancer amongst females in India and is associated with high risk HPVs, reactive oxygen species (ROS), and excessive inflammation in most cases. ROS in turn affects the expression of pro- and anti-apoptotic proteins. The objective of the present study was to elucidate the effect of hydrogen peroxide (H(2)O(2)) on apoptotic signaling molecules in vitro. HeLa cell line expresses the Human papilloma virus - 18, E6 oncoprotein which causes the ubiquitin mediated degradation of p53 protein and is thus p53 deficient. p53 is known to act as a cellular stress sensor and triggers apoptosis. p73, a member of the p53 family also induces apoptosis in response to DNA damaging agents but unlike p53, it is infrequently mutated in human tumors. We demonstrate here, that in HeLa cells, apoptosis is triggered by H(2)O(2) via the mitochondrial pathway involving upregulation of p73, and its downstream target Bax. This was accompanied by upregulation of ERK, JNK, c-Myc, Hsp-70 and down regulation of anti-apoptotic Bcl-XL, release of cytochrome c from mitochondria and activation of caspases-9 and -3.     

Role of ERK in Hydrogen Peroxide-Induced Cell Death of Human Glioma Cells

Oxidative stress is known to induce cell death in a wide variety of cell types, apparently by modulating intracellular signaling pathways. Activation of extracellular signal-regulated kinase (ERK) in oxidative stress remains controversial. In some cellular systems, the ERK activation is associated with protection against oxidative stress, while in other system, the ERK activation is involved in apoptotic cell death. The present study was undertaken to examine the role of ERK activation in H₂O₂-induced cell death of human glioma (A172) cells. H₂O₂ resulted in a time- and dose-dependent cell death, which was largely attributed to apoptosis. H₂O₂ treatment caused marked sustained activation of ERK. The ERK activation and cell death induced by H₂O₂ was prevented by catalase, the hydrogen peroxide scavenger, and U0126, an inhibitor of ERK upstream kinase MEK1/2. Transient transfection with constitutive active MEK1, an upstream activator of ERK1/2, increased H₂O₂-induced cell death, whereas transfection with dominant-negative mutants of MEK1 decreased the cell death. The ERK activation and cell death caused by H₂O₂ was inhibited by antioxidants (N-acetylcysteine and trolox), Ras inhibitor, and suramin. H₂O₂ produced depolarization of mitochondrial membrane potential and its effect was prevented by catalase and U0126. Taken together, these findings suggest that growth factor receptor/Ras/MEK/ERK signaling pathway plays an active role in mediating H₂O₂-induced apoptosis of human glioma cells and functions upstream of mitochondria-dependent pathway to initiate the apoptotic signal.     

Hydrogen peroxide mediates Rac1 activation of S6K1

We previously reported that hydrogen peroxide (H2O2) mediates mitogen activation of ribosomal protein S6 kinase 1 (S6K1) which plays an important role in cell proliferation and growth. In this study, we investigated a possible role of H2O2 as a molecular linker in Rac1 activation of S6K1. Overexpression of recombinant catalase in NIH-3T3 cells led to the drastic inhibition of H2O2 production by PDGF, which was accompanied by a decrease in S6K1 activity. Similarly, PDGF activation of S6K1 was significantly inhibited by transient transfection or stable transfection of the cells with a dominant-negative Rac1 (Rac1N17), while overexpression of constitutively active Rac1 (Rac1V12) in the cells led to an increase in basal activity of S6K1. In addition, stable transfection of Rat2 cells with Rac1N17 dramatically attenuated the H2O2 production by PDGF as compared with that in the control cells. In contrast, Rat2 cells stably transfected with Rac1V12 produced high level of H2O2 in the absence of PDGF, comparable to that in the control cells stimulated with PDGF. More importantly, elimination of H2O2 produced in Rat2 cells overexpressing Rac1V12 inhibited the Rac1V12 activation of S6K1, indicating the possible role of H2O2 as a mediator in the activation of S6K1 by Rac1. However, H2O2 could be also produced via other pathway, which is independent of Rac1 or PI3K, because in Rat2 cells stably transfected with Rac1N17, H2O2 could be produced by arsenite, which has been shown to be a stimulator of H2O2 production. Taken together, these results suggest that H2O2 plays a pivotal role as a mediator in Rac1 activation of S6K1.     

IL-10 synergistically enhances GM-CSF-induced CCR1 expression in myelomonocytic cells

CC chemokine receptor 1 (CCR1) has been implicated in inflammation. The present study examined the signaling mechanisms that mediate GM-CSF/IL-10-induced synergistic CCR1 protein expression in monocytic U937 cells. GM-CSF alone markedly increased both the mRNA and protein expression of CCR1. IL-10 augmented GM-CSF-induced CCR1 protein expression with no effect on mRNA expression. PD098059 and U0126 (two MEK inhibitors), and LY294002 (a PI3K inhibitor) inhibited GM-CSF/IL-10-induced CCR1 gene and protein expression. PD098059, U0126, and LY294002 also attenuated chemotaxis of GM-CSF/IL-10-primed U937 cells in response to MIP-1alpha. Immunoblotting studies show that GM-CSF alone induced ERK2 phosphorylation; whereas, IL-10 alone induced p70(S6k) phosphorylation in U937 cells. Neither cytokine when used alone induced PKB/Akt phosphorylation. Combined GM-CSF/IL-10 treatment of U937 cells induced phosphorylation of ERK2, p70(S6k), and PKB/Akt. PD098059 and U0126 completely abrogated ERK2 phosphorylation; whereas, LY294002 completely blocked PKB/Akt and p70(S6k) phosphorylation. Our findings indicate that IL-10 may potentiate GM-CSF-induced CCR1 protein expression in U937 cells via activation of PKB/Akt and p70(S6k).     

Arsenite induces cell transformation by reactive oxygen species, AKT, ERK1/2, and p70S6K1

Arsenic is naturally occurring element that exists in both organic and inorganic formulations. The inorganic form arsenite has a positive association with development of multiple cancer types. There are significant populations throughout the world with high exposure to arsenite via drinking water. Thus, human exposure to arsenic has become a significant public health problem. Recent evidence suggests that reactive oxygen species (ROS) mediate multiple changes to cell behavior after acute arsenic exposure, including activation of proliferative signaling and angiogenesis. However, the role of ROS in mediating cell transformation by chronic arsenic exposure is unknown. We found that cells chronically exposed to sodium arsenite increased proliferation and gained anchorage-independent growth. This cell transformation phenotype required constitutive activation of AKT, ERK1/2, mTOR, and p70S6K1. We also observed these cells constitutively produce ROS, which was required for the constitutive activation of AKT, ERK1/2, mTOR, and p70S6K1. Suppression of ROS levels by forced expression of catalase also reduced cell proliferation and anchorage-independent growth. These results indicate cell transformation induced by chronic arsenic exposure is mediated by increased cellular levels of ROS, which mediates activation of AKT, ERK1/2, and p70S6K1.     

H2O2 is required for UVB-induced EGF receptor and downstream signaling pathway activation

Ultraviolet radiation (UVR)-induced receptor phosphorylation is increasingly recognized as a widely occurring phenomenon. However, the mechanisms, mediators, and sequence of events involved in this process remain ill-defined. We have recently shown that exposure of human keratinocytes to physiologic doses of ultraviolet B radiation (UVB) activates epidermal growth factor receptor (EGFR)/extracellular-regulated kinase 1 and 2 (ERK1/2), and p38 signaling pathways via reactive oxygen species. Here we demonstrate that UVB exposure increased intra- and extracellular H2O2 production rapidly in a time-dependent manner. An EGFR-specific monoclonal antibody abrogated EGFR autophosphorylation and markedly decreased the phosphorylation of ERK1/2 whereas p38 activation was unaffected. Overexpression of catalase strongly inhibited UVB-induced EGFR/ERK1/2 pathway activation. These findings establish the sequence of events after UVB irradiation: (i) H2O2 generation, (ii) EGFR phosphorylation, and (iii) ERK activation. Our results identify UVB-induced H2O2 as a second messenger that is required for EGFR and dependent downstream signaling pathways activation.     

Leptin enhances alpha1(I) collagen gene expression in LX-2 human hepatic stellate cells through JAK-mediated H2O2-dependent MAPK pathways

Leptin, a liver profibrogenic cytokine, induces oxidative stress in hepatic stellate cells (HSCs), with increased formation of the oxidant H2O2, which signals through p38 and extracellular signal-regulated kinase 1/2 (ERK1/2) pathways, stimulating tissue inhibitor of metalloproteinase-1 production. Since oxidative stress is a pathogenic mechanism of liver fibrosis and activation of collagen gene is a marker of fibrogenesis, we evaluated the effects of leptin on collagen I expression. We report here that, in LX-2 human HSCs, leptin enhances the levels of alpha1(I) collagen mRNA, promoter activity and protein. Janus kinase (JAK)1 and JAK2 were activated. H2O2 formation was increased; this was prevented by the JAK inhibitor AG490, suggesting a JAK-mediated process. ERK1/2 and p38 were activated, and the activation was blocked by catalase, consistent with an H2O2-dependent mechanism. AG490 and catalase also prevented leptin-stimulated alpha1(I) collagen mRNA expression. PD098059, an ERK1/2 inhibitor, abrogated ERK1/2 activation and suppressed alpha1(I) collagen promoter activity, resulting in mRNA down-regulation. The p38 inhibitor SB203580 and overexpression of dominant negative p38 mutants abrogated p38 activation and down-regulated the mRNA. While SB203580 had no effect on the promoter activity, it reduced the mRNA half-life from 24 to 4 h, contributing to the decreased mRNA level. We conclude that leptin stimulates collagen production through the H2O2-dependent and ERK1/2 and p38 pathways via activated JAK1 and JAK2. ERK1/2 stimulates alpha1(I) collagen promoter activity, whereas p38 stabilizes its mRNA. Accordingly, interference with leptin-induced oxidative stress by antioxidants provides an opportunity for the prevention of liver fibrosis.     

Differential role of hydrogen peroxide in UV-induced signal transduction

The present study investigated the differential requirement of ROS in UV-induced activation of these pathways. Exposure of the mouse epidermal C141 cells to UV radiation led to generation of ROS as measured by electron spin resonance (ESR) and by H2O2 and O2. fluorescence staining assay. Treatment of cells with UV radiation or H2O2 also markedly activated Erks, JNKs, p38 kinase and led to increases in phosphorylation of Akt and p70(S6k) in mouse epidermal JB6 cells. The scavenging of UV-generated H2O2 by N-acety-L-cyteine (NAC, a general antioxidant) or catalase (a specific H2O2 inhibitor) inhibited UV-induced activation of JNKs, p38 kinase, Akt and p70(S6k), while it did not show any inhibitory effects on Erks activation. Further, pretreatment of cells with sodium formate (an .OH radical scavenger) or superoxide dismutase (O2-. radical scavenger) did not inhibit any of these pathways. These results demonstrate that H2O2 generation is required for UV-induced phosphorylation of Akt and p70(S6k), and involved in activation of JNKs and p38 kinase, but not Erks.     

Catalase potentiates interleukin-1beta-induced expression of nitric oxide synthase in rat vascular smooth muscle cells

The role of reactive oxygen species (ROS) in regulating the expression of the inducible nitric oxide synthase (iNOS) was studied in rat aortic vascular smooth muscle cells (VSMC). We hypothesized that ROS regulate iNOS expression through the mitogen-activated protein kinases ERK and p38(MAPK). We found that interleukin-1beta (IL-1beta) stimulated the production of hydrogen peroxide (H2O2) which could be inhibited by loading the cells with the H2O2-scavenging enzyme catalase. Inhibition of the upstream ERK1,2 activator MEK1,2 with U0126 prevented IL-1beta-stimulated iNOS expression, while the p38MAPK inhibitor SB03580 potentiated iNOS expression. Loading the cells with catalase enhanced ERK activation and iNOS expression but had no effect on p38MAPK activation or PDGF-induced ERK activation. These data indicated that H2O2 negatively regulates iNOS expression through ERK inhibition independently of p38MAPK. The present results outline a novel role for H2O2 in suppressing signaling pathways leading to gene expression such as iNOS in VSMC in response to cytokines.     

白藜芦醇通过下调MEK/ERK/c-Jun信号通路抑制H2O2诱导的肺癌细胞增殖

目的:探讨白藜芦醇(Res)是否通过下调ERK激酶/胞外信号调节激酶/原癌基因(MEK/ERK/c-Jun)信号通路抑制小剂量过氧化氢(H2O2)诱导肺癌细胞增殖。方法:采用MTS实验检测小剂量20μM H2O2以及分别加入MEK阻断剂U0126和Res后H2O2对肺癌细胞NCI-H1395增殖的影响,采用Western Blot检测H2O2对ERK1/2和Akt蛋白磷酸化水平以及加入Res后H2O2对MEK、ERK1/2和c-Jun蛋白磷酸化水平的影响。结果:小剂量H2O2对肺癌细胞NCI-H1395具有促增殖作用,H2O2通过活化ERK1/2和Akt蛋白的磷酸化水平促进肺癌细胞NCI-H1395增殖,加入MEK阻断剂U0126后H2O2对肺癌细胞NCI-H1395增殖作用降低(P<0.05)。Res可抑制H2O2诱导的肺癌细胞NCI-H1395增殖,加入Res后,H2O2引起的MEK、ERK1/2和c-Jun蛋白磷酸化水平均降低(P<0.05)。结论:小剂量H2O2对肺癌细胞NCI-H1395具有促增殖作用,Res通过抑制MEK/ERK/c-Jun信号通路来抑制H2O2对肺癌细胞NCI-H1395的促增殖作用,其具体机制还需进一步研究。     

Oxidative signaling in renal epithelium: Critical role of cytosolic phospholipase A2 and p38(SAPK)

Previous studies from this laboratory have demonstrated a critical role of cytosolic phospholipase A2 (cPLA2) and arachidonic acid in angiotensin II (Ang II) AT2 receptor-mediated signal transduction in renal epithelium. In primary proximal tubular epithelial cells exposed to hydrogen peroxide (H2O2), both the selective cPLA2 inhibitors and the cPLA2 antisense oligonucleotides significantly attenuated H2O2-induced arachidonic acid liberation and activation of p38(SAPK), ERK1/2, and Akt1. This H2O2-induced kinase activation was significantly attenuated by a Src kinase inhibitor PP2, or by transient transfection of carboxyl-terminal Src kinase (CSK) that maintained Src in the dormant form. Under basal conditions, Src coimmunoprecipitated with epidermal growth factor receptor (EGFR), while H2O2 increased EGFR phosphorylation in the complex. We observed that inhibition of EGFR kinase activity with AG1478 significantly attenuated H2O2-induced p38(SAPK) and ERK1/2 activation, but did not inhibit Akt1 activation. Furthermore, it seems that p38(SAPK) is upstream of ERK1/2 and Akt1, since a p38(SAPK) inhibitor SB203580 significantly blocked H2O2-induced activation of ERK1/2 and Akt1. Interestingly, overexpression of the dominant-negative p38(SAPK) isoform alpha inhibited ERK1/2 but not Akt1 activation. Our observations demonstrate that in these nontransformed cells, activation of cPLA2 is a converging point for oxidative stress and Ang II, which share common downstream signaling mechanisms including Src and EGFR. In addition, p38(SAPK) provides a positive input to both growth and antiapoptotic signaling pathways induced by acute oxidative stress.     

Protein phosphatase 2A-mediated cross-talk between p38 MAPK and ERK in apoptosis of cardiac myocytes

Mitogen-activated protein kinases (MAPKs) play different regulatory roles in signaling oxidative stress-induced apoptosis in cardiac ventricular myocytes. The regulation and functional role of cross-talk between p38 MAPK and extracellular signal-regulated kinase (ERK) pathways were investigated in cardiac ventricular myocytes in the present study. We demonstrated that inhibition of p38 MAPK with SB-203580 and SB-239063 enhanced H(2)O(2)-stimulated ERK phosphorylation, whereas preactivation of p38 MAPK with sodium arsenite reduced H(2)O(2)-stimulated ERK phosphorylation. In addition, pretreatment of cells with the protein phosphatase 2A (PP2A) inhibitors okadaic acid and fostriecin increased basal and H(2)O(2)-stimulated ERK phosphorylation. We also found that PP2A coimmunoprecipitated with ERK and MAPK/ERK (MEK) in cardiac ventricular myocytes, and H(2)O(2) increased the ERK-associated PP2A activity that was blocked by inhibition of p38 MAPK. Finally, H(2)O(2)-induced apoptosis was attenuated by p38 MAPK or PP2A inhibition, whereas it was enhanced by MEK inhibition. Thus the present study demonstrated that p38 MAPK activation decreases H(2)O(2)-induced ERK activation through a PP2A-dependent mechanism in cardiac ventricular myocytes. This represents a novel cellular mechanism that allows for interaction of two opposing MAPK pathways and fine modulation of apoptosis during oxidative stress.     

EphB1 recruits c-Src and p52Shc to activate MAPK/ERK and promote chemotaxis

Eph receptors and their ligands (ephrins) play an important role in axonal guidance, topographic mapping, and angiogenesis. The signaling pathways mediating these activities are starting to emerge and are highly cell- and receptor-type specific. Here we demonstrate that activated EphB1 recruits the adaptor proteins Grb2 and p52Shc and promotes p52Shc and c-Src tyrosine phosphorylation as well as MAPK/extracellular signal-regulated kinase (ERK) activation. EphB1-mediated increase of cell migration was abrogated by the MEK inhibitor PD98059 and Src inhibitor PP2. In contrast, cell adhesion, which we previously showed to be c-jun NH2-terminal kinase (JNK) dependent, was unaffected by ERK1/2 and Src inhibition. Expression of dominant-negative c-Src significantly reduced EphB1-dependent ERK1/2 activation and chemotaxis. Site-directed mutagenesis experiments demonstrate that tyrosines 600 and 778 of EphB1 are required for its interaction with c-Src and p52Shc. Furthermore, phosphorylation of p52Shc by c-Src is essential for its recruitment to EphB1 signaling complexes through its phosphotyrosine binding domain. Together these findings highlight a new aspect of EphB1 signaling, whereby the concerted action of c-Src and p52Shc activates MAPK/ERK and regulates events involved in cell motility.     

Involvement of MAPK activation in chemokine or COX-2 productions by Toxoplasma gondii

This experiment focused on MAPK activation in host cell invasion and replication of T. gondii, as well as the expression of CC chemokines, MCP-1 and MIP-1 alpha , and enzyme, COX-2/prostaglandin E2 (PGE2) in infected cells via western blot, [3H]-uracil incorporation assay, ELISA and RT-PCR. The phosphorylation of ERK1/2 and p38 in infected HeLa cells was detected at 1 hr and/or 6 hr postinfection (PI). Tachyzoite proliferation was reduced by p38 or JNK MAPK inhibitors. MCP-1 secretion was enhanced in infected peritoneal macrophages at 6 hr PI. MIP-1 alpha mRNA was increased in macrophages at 18 hr PI. MCP-1 and MIP-1 alpha were reduced after treatment with inhibitors of ERK1/2 and JNK MAPKs. COX-2 mRNA gradually increased in infected RAW 264.7 cells and the secretion of COX-2 peaked at 6 hr PI. The inhibitor of JNK suppressed COX-2 expression. PGE2 from infected RAW 264.7 cells was increased and synthesis was suppressed by PD98059, SB203580, and SP600125. In this study, the activation of p38, JNK and/or ERK1/2 MAPKs occurred during the invasion and proliferation of T. gondii tachyzoites in HeLa cells. Also, increased secretion and expression of MCP-1, MIP-1 alpha , COX-2 and PGE2 were detected in infected macrophages, and appeared to occur via MAPK signaling pathways.