Extracellular-superoxide dismutase expression during monocytic differentiation of U937 cells

Free Radical-Mediated Protein Radical Formation in Differentiating Monocytes

Free radical-mediated activation of inflammatory macrophages remains ambiguous with its limitation to study within biological systems. U-937 and HL-60 cell lines serve as a well-defined model system known to differentiate into either macrophages or dendritic cells in response to various chemical stimuli linked with reactive oxygen species (ROS) production. Our present work utilizes phorbol 12-myristate-13-acetate (PMA) as a stimulant, and factors such as concentration and incubation time were considered to achieve optimized differentiation conditions. ROS formation likely hydroxyl radical (HO^●) was confirmed by electron paramagnetic resonance (EPR) spectroscopy combined with confocal laser scanning microscopy (CLSM). In particular, U-937 cells were utilized further to identify proteins undergoing oxidation by ROS using anti-DMPO (5,5-dimethyl-1-pyrroline N-oxide) antibodies. Additionally, the expression pattern of NADPH Oxidase 4 (NOX4) in relation to induction with PMA was monitored to correlate the pattern of ROS generated. Utilizing macrophages as a model system, findings from the present study provide a valuable source for expanding the knowledge of differentiation and protein expression dynamics.

Inhibitory effects of 4-hydroperoxy-2-decenoic acid ethyl ester on phorbol ester- and TGF-β1-induced MMPs expression

Matrix metalloproteinases (MMPs), zinc-containing proteinases, play a critical role in tumour progression by degrading extracellular matrix components. MMP2 and MMP9 are secreted from tumour-associated macrophages as well as tumour cells and have been implicated in the formation of the tumour microenvironment. Therefore, the inhibition of these MMPs may suppress tumour progression and metastasis. 4-Hydroperoxy-2-decenoic acid ethyl ester (HPO-DAEE) is known to cause apoptosis in the human lung cancer cell line A549 by inducing endoplasmic reticulum (ER) stress. However, the effects of HPO-DAEE on tumour progression remain unclear. HPO-DAEE pre-treatment significantly suppressed phorbol 12-myristate 13-acetate (TPA)-triggered MMP activation in human monocytic THP-1 cells. It also enhanced the expression of haem oxygenase-1, an antioxidant enzyme, and suppressed the TPA-triggered intracellular accumulation of reactive oxygen species (ROS). Furthermore, HPO-DAEE suppressed transforming growth factor-β1-triggered human prostate cancer PC3 cell migration and this was accompanied by the inhibition of MMP expression and activities. The present results indicate that HPO-DAEE may exert inhibitory effects on tumour progression by suppressing MMP expression and activities.

[Regulation of Extracellular Redox Homeostasis in Tumor Microenvironment]

Excessive generation of reactive oxygen species (ROS) has been implicated in the progression of tumors. Superoxide dismutase 3 (SOD3) is a copper-containing secretory antioxidative enzyme that plays a critical role in redox homeostasis, particularly in extracellular spaces. Considerable evidence suggests that SOD3 protein expression is significantly decreased or lost in several tumor tissues, and this loss results in tumor metastasis. On the other hand, epigenetic disturbances, including DNA hyper-/hypomethylation, histone de/acetylation, and histone de/methylation, may be involved in tumorigenesis and the progression of metastasis. However, regulation of SOD3 in the tumor microenvironment and the involvement of epigenetics in its expression remain unclear. To elucidate the molecular mechanisms underlying SOD3 expression, we investigated the involvement of epigenetics, including DNA methylation and histone modifications, in its regulation in tumor cells and macrophages. SOD3 expression in human monocytic THP-1 cells and human lung cancer A549 cells was silenced by DNA hypermethylation within the SOD3 promoter region. Furthermore, the DNA demethylase, ten-eleven translocation 1, was shown for the first time to play a key role in regulation of DNA methylation within that region. We also demonstrated that myocyte enhancer factor 2 functioned as one of the transcription factors of SOD3 expression in THP-1 cells. Collectively, these novel results will contribute to the elucidation of epigenetic redox regulation, and may provide important insights into tumorigenesis and tumor metastasis.

17-β-estradiol enhances neutrophil extracellular trap formation by interaction with estrogen membrane receptor

Cell death-associated neutrophil extracellular trap formation (NETosis) occurs during various autoimmune diseases including systemic lupus erythematosus and rheumatoid arthritis, as well as during gestation. Although increasing estrogen concentrations associated with pregnancy might induce NETosis via nuclear estrogen receptor (ERα/ERβ), little is known about the mechanisms associated with estrogen-induced NETosis. Here, we investigated the effects of estrogen (17-β-estradiol; E2) on NETosis, focusing on mechanisms associated with estrogen membrane receptor (GPR30) in neutrophil-like HL-60 cells. Our results show that E2 and the GPR30 agonist G-1 increases level of NETosis and NET formation. Moreover, NETosis-associated intracellular and extracellular histone citrullination and peptidyl arginine deiminase 4 (PAD4) expression were also increased by E2 or G-1 treatment. Furthermore, GPR30 antagonist pre-treatment inhibited increases in NETosis and PAD4 expression mediated by G-1 and partially inhibited these effects mediated by E2. These results demonstrate that E2 treatment induces NETosis via not only ERα/ERβ but also GPR30 in neutrophil-like HL-60 cells.

Induction of Human-Lung-Cancer-A549-Cell Apoptosis by 4-Hydroperoxy-2-decenoic Acid Ethyl Ester through Intracellular ROS Accumulation and the Induction of Proapoptotic CHOP Expression

Royal jelly, a natural product secreted by honeybees, contains several fatty acids, such as 10-hydroxy-2-decenoic acid (DE), and shows anti- and pro-apoptotic properties. 4-Hydroperoxy-2-decenoic acid ethyl ester (HPO-DAEE), a DE derivative, exhibits potent antioxidative activity; however, it currently remains unclear whether HPO-DAEE induces cancer-cell death. In the present study, treatment with HPO-DAEE induced human-lung-cancer-A549-cell death (52.7 ± 10.2%) that was accompanied by DNA fragmentation. Moreover, the accumulation of intracellular reactive oxygen species (ROS, 2.38 ± 0.1-fold) and the induction of proapoptotic CCAAT-enhancer-binding-protein-homologous-protein (CHOP) expression (18.4 ± 4.0-fold) were observed in HPO-DAEE-treated cells. HPO-DAEE-elicited CHOP expression and cell death were markedly suppressed by pretreatment with N-acetylcysteine (NAC), an antioxidant, by 2.40 ± 1.57-fold and 5.7 ± 1.6%, respectively. Pretreatment with 4-phenylbutyric acid (PBA), an inhibitor of endoplasmic reticulum stress, also suppressed A549-cell death (38.4 ± 1.1%). Furthermore, we demonstrated the involvement of extracellular-signal-regulated protein kinase (ERK) and p38-related signaling in HPO-DAEE-elicited cell-death events. Overall, we concluded that HPO-DAEE induces A549-cell apoptosis through the ROS-ERK-p38 pathway and, at least in part, the CHOP pathway.

Copper chaperone antioxidant-1, Atox-1, is involved in the induction of SOD3 in THP-1 cells

Superoxide dismutase (SOD) 3, a copper (Cu)-containing anti-oxidative enzyme, plays a key role in extracellular redox homeostasis. Cu chaperone antioxidant-1 (Atox-1) not only delivers Cu ions to SOD3 at the trans-Golgi network, it also functions as a transcription factor of SOD3; however, the role of Atox-1 in the regulation of SOD3 during the monocytic differentiation of THP-1 cells has not yet been elucidated. A treatment with 12-O-tetradecanoylphorbol-13-acetate (TPA) induced the expression of the Cu transport protein ATP7A in THP-1 cells. On the other hand, the nuclear translocation of Atox-1 was detected in TPA-treated THP-1 cells, and was suppressed in the presence of the Cu chelator, bathocuproinedisulfonic acid. Furthermore, Atox-1 bound to the SOD3 promoter region in TPA-treated THP-1 cells. The overexpression of Atox-1 in THP-1 cells significantly enhanced TPA-elicited SOD3 expression, whereas its knockdown suppressed this induction. The present results demonstrate that Atox-1 functions as a key molecule in TPA-elicited SOD3 expression.

Ten-eleven translocation 1 functions as a mediator of SOD3 expression in human lung cancer A549 cells

Superoxide dismutase (SOD) 3, one of the SOD isozymes, plays a pivotal role in extracellular redox homeostasis. The expression of SOD3 is regulated by epigenetics in human lung cancer A549 cells and human monocytic THP-1 cells; however, the molecular mechanisms governing SOD3 expression have not been elucidated in detail. Ten-eleven translocation (TET), a dioxygenase of 5-methylcytosine (5mC), plays a central role in DNA demethylation processes and induces target gene expression. In the present study, TET1 expression was abundant in U937 cells, but its expression was weakly expressed in A549 and THP-1 cells. These results are consistent with the expression pattern of SOD3 and its DNA methylation status in these cells. Moreover, above relationship was also observed in human breast cancer cells, human prostate cancer cells, and human skin fibroblasts. The overexpression of TET1-catalytic domain (TET1-CD) induced the expression of SOD3 in A549 cells, and this was accompanied by the direct binding of TET1-CD to the SOD3 promoter region. Furthermore, in TET1-CD-transfected A549 cells, the level of 5-hydroxymethylcytosine within that region was significantly increased, whereas the level of 5mC was decreased. The results of the present study demonstrate that TET1 might function as one of the key molecules in SOD3 expression through its 5mC hydroxylation in A549 cells.

CAPE increases the expression of SOD3 through epigenetics in human retinal endothelial cells

Extracellular-superoxide dismutase (EC-SOD or SOD3), which catalyzes the dismutation of superoxide anions into hydrogen peroxide, plays a key role in vascular protection against reactive oxygen species (ROS). The excess generation of ROS is closely involved in the pathogenesis of diabetic retinopathy (DR); therefore, the maintenance of SOD3 expression at high levels is important for the prevention of DR. In the present study, we showed that caffeic acid phenethyl ester (CAPE) increased the expression of SOD3 through the acetylation of histone within the SOD3 promoter region in human retinal endothelial cells (HRECs). Histone acetylation within its promoter was focused on the inhibition of histone deacetylase (HDAC), and we examined the involvement of myocyte enhancer factor 2 (MEF2) and HDAC1 in CAPE-elicited SOD3 expression. Our results demonstrate that SOD3 silencing in basal HRECs is regulated by HDAC1 composed with MEF2A/2D hetero dimers. Moreover, phosphorylation of threonine 312 in MEF2A and dissociation of HDAC1 from SOD3 promoter play pivotal roles in CAPE-elicited SOD3 expression. Overall, our findings provide that CAPE may be one of the seed compounds that maintain redox homeostasis.

TLR2 activation induces antioxidant defence in human monocyte-macrophage cell line models

When monocytes are recruited to inflammation/infection sites, extravasate and differentiate into macrophages, they encounter increasing levels of oxidative stress, both from exogenous and endogenous sources. In this study, we aimed to determine whether there are specific biochemical mechanisms responsible for an increase in oxidative stress resistance in differentiating macrophages. We performed experiments on in vitro cell line models of the monocyte-macrophage differentiation axis (less differentiated THP-1 cells and more differentiated Mono Mac 6 cells). At the same time, we verified the hypothesis that activating monocyte/macrophage innate immune response by pathogens (exemplified by stimulating the TLR2 pattern recognition receptor) would further strengthen cellular antioxidant defences. We found that resistance to exogenous oxidative stress increased substantially both during differentiation and upon activation of TLR2. This increase in antioxidant resistance was accompanied by decrease in free radical damage to cellular proteins. On the molecular level, this resistance was mediated especially by increased levels and activity of glutathione, glutathione-related antioxidant enzymes and Mn superoxide dismutase, as shown by gene expression assays, Western blotting and enzyme activity assays. Moreover, upon TLR2 activation additional molecular mechanisms came into play, conferring additional resistance levels even upon differentiated macrophage-like cells, mainly related to thioredoxin-linked antioxidant enzymes.

Protein Thiol Redox Signaling in Monocytes and Macrophages

SIGNIFICANCE

Monocyte and macrophage dysfunction plays a critical role in a wide range of inflammatory disease processes, including obesity, impaired wound healing diabetic complications, and atherosclerosis. Emerging evidence suggests that the earliest events in monocyte or macrophage dysregulation include elevated reactive oxygen species production, thiol modifications, and disruption of redox-sensitive signaling pathways. This review focuses on the current state of research in thiol redox signaling in monocytes and macrophages, including (i) the molecular mechanisms by which reversible protein-S-glutathionylation occurs, (ii) the identification of bona fide S-glutathionylated proteins that occur under physiological conditions, and (iii) how disruptions of thiol redox signaling affect monocyte and macrophage functions and contribute to atherosclerosis. Recent Advances: Recent advances in redox biochemistry and biology as well as redox proteomic techniques have led to the identification of many new thiol redox-regulated proteins and pathways. In addition, major advances have been made in expanding the list of S-glutathionylated proteins and assessing the role that protein-S-glutathionylation and S-glutathionylation-regulating enzymes play in monocyte and macrophage functions, including monocyte transmigration, macrophage polarization, foam cell formation, and macrophage cell death.

CRITICAL ISSUES

Protein-S-glutathionylation/deglutathionylation in monocytes and macrophages has emerged as a new and important signaling paradigm, which provides a molecular basis for the well-established relationship between metabolic disorders, oxidative stress, and cardiovascular diseases.

FUTURE DIRECTIONS

The identification of specific S-glutathionylated proteins as well as the mechanisms that control this post-translational protein modification in monocytes and macrophages will facilitate the development of new preventive and therapeutic strategies to combat atherosclerosis and other metabolic diseases. Antioxid. Redox Signal. 25, 816-835.

Royal Jelly Constituents Increase the Expression of Extracellular Superoxide Dismutase through Histone Acetylation in Monocytic THP-1 Cells

Extracellular superoxide dismutase (EC-SOD) is one of the main SOD isozymes and plays an important role in the prevention of cardiovascular diseases by accelerating the dismutation reaction of superoxide. Royal jelly includes 10-hydroxy-2-decenoic acid (10H2DA, 2), which regulates the expression of various types of genes in epigenetics through the effects of histone deacetylase (HDAC) antagonism. The expression of EC-SOD was previously reported to be regulated epigenetically through histone acetylation in THP-1 cells. Therefore, we herein evaluated the effects of the royal jelly constituents 10-hydroxydecanoic acid (10HDA, 1), sebacic acid (SA, 3), and 4-hydroperoxy-2-decenoic acid ethyl ester (4-HPO-DAEE, 4), which is a derivative of 2, on the expression of EC-SOD in THP-1 cells. The treatment with 1 mM 1, 2, or 3 or 100 μM 4 increased EC-SOD expression and histone H3 and H4 acetylation levels. Moreover, the enrichment of acetylated histone H4 was observed in the proximal promoter region of EC-SOD and was caused by the partial promotion of ERK phosphorylation (only 4) and inhibition of HDAC activities, but not by the expression of HDACs. Overall, 4 exerted stronger effects than 1, 2, or 3 and has potential as a candidate or lead compound against atherosclerosis.

Caffeic acid phenethyl ester suppresses monocyte adhesion to the endothelium by inhibiting NF-κB/NOX2-derived ROS signaling

Caffeic acid phenethyl ester (CAPE), one of the major polyphenols, exhibits anti-oxidative, anti-bacterial, and anti-cancer properties. Atherosclerosis is a chronic inflammatory disease, the progression of which is closely related to the accumulated adhesion of inflammatory monocytes/macrophages to the endothelium. We herein determined whether CAPE and its derivatives suppressed THP-1 cell adhesion to human umbilical vein endothelial cells (HUVEC). Of the four polyphenols tested, CAPE significantly suppressed the 12-O-tetradecanoylphorbol 13-acetate (TPA)-elicited expression of cluster for differentiation (CD) 11b, 14, and 36, and this was accompanied by the inhibition of THP-1 cell adhesion to HUVEC. CAPE also suppressed the activation of TPA-elicited nuclear factor-κB (NF-κB) and accumulation of NADPH oxidase 2 (NOX2)-derived reactive oxygen species (ROS), but did not affect extracellular signal-regulated kinase (ERK) phosphorylation. Taken together, these results demonstrated that CAPE suppressed THP-1 cell adhesion to HUVEC through, at least in part, the NF-κB, NOX2, and ROS-derived signaling axis.

Suppression of EC-SOD by oxLDL During Vascular Smooth Muscle Cell Proliferation

Reactive oxygen species (ROS) produced by endothelial cells and macrophages play important roles in atherogenesis because they promote the formation of oxidized low-density lipoproteins (oxLDL). Extracellular-superoxide dismutase (EC-SOD) is mainly produced by vascular smooth muscle cells (VSMCs), is secreted into the extracellular space, and protects cells from the damaging effects of the superoxide anion. Thus, the expression of EC-SOD in VSMCs is crucial for protecting cells against atherogenesis; however, oxLDL-induced changes in the expression of EC-SOD in VSMCs have not yet been examined. We herein showed that oxLDL decreased EC-SOD mRNA and protein levels by binding to lectin-like oxidized LDL receptor-1 (LOX-1). Moreover, we demonstrated the significant role of mitogen-activated protein kinase (MEK)/extracellular-regulated protein kinase (ERK) signaling in oxLDL-elicited reductions in the expression of EC-SOD and proliferation of VSMCs. The results obtained with the FCS treatment indicate that oxLDL-elicited reductions in the expression of EC-SOD are related to the proliferation of VSMCs. We herein showed for the first time that luteolin, a natural product, restored oxLDL-induced decreases in the expression of EC-SOD and proliferation of VSMCs. Collectively, the results of the present study suggest that oxLDL accelerates the development of atherosclerosis by suppressing the expression of EC-SOD and also that luteolin has potential as a treatment for atherosclerosis. J. Cell. Biochem. 117: 2496-2505, 2016. © 2016 Wiley Periodicals, Inc.

Cross Talk Mechanism among EMT, ROS, and Histone Acetylation in Phorbol Ester-Treated Human Breast Cancer MCF-7 Cells

Epithelial-mesenchymal transition (EMT) plays a pivotal role in the progression of cancer, and some transcription factors including Slug and Snail are known to be involved in EMT processes. It has been well established that the excess production of reactive oxygen species (ROS) and epigenetics such as DNA methylation and histone modifications participate in carcinogenesis; however, the cross talk mechanism among EMT, ROS, and epigenetics remains unclear. In the present study, we demonstrated that the treatment of human breast cancer MCF-7 cells with phorbol ester (TPA), a protein kinase C activator, significantly induced cell proliferation and migration, and these were accompanied by the significant induction of Slug expression. Moreover, the TPA-elicited induction of Slug expression was regulated by histone H3 acetylation and NADPH oxidase (NOX) 2-derived ROS signaling, indicating that ROS and histone acetylation are involved in TPA-elicited EMT processes. We herein determined the cross talk mechanism among EMT, ROS, and histone acetylation, and our results provide an insight into the progression of cancer metastasis.

Down-regulation of superoxide dismutase 1 by PMA is involved in cell fate determination and mediated via protein kinase D2 in myeloid leukemia cells

Myeloid leukemia cells maintain a high intracellular ROS level and use redox signals for survival. The metabolism of ROS also affects cell fate, including cell death and differentiation. Superoxide dismutases (SODs) are major antioxidant enzymes that have high levels of expression in myeloid leukemia cells. However, the role of SODs in the regulation of myeloid leukemia cells' biological function is still unclear. To investigate the function of SODs in myeloid leukemia cell death and differentiation, we used myeloid leukemia cell lines K562, MEG-01, TF-1, and HEL cells for this study. We found that PMA-induced megakaryocytic differentiation in myeloid leukemia cells is accompanied by cell death and SOD1 down-regulation, while SOD2 expression is not affected. The role of SOD1 is verified when ATN-224, a SOD1 specific inhibitor, inhibits cell proliferation and promotes cell death in myeloid leukemia cells without PMA treatment. Moreover, inhibition or silencing of SODs further increases cell death and decreases polyploidization induced by PMA while they were partially reversed by SOD1 overexpression. Thus, SOD1 expression is required for myeloid leukemia cell fate determination. In addition, the knockdown of PKD2 reduces cell death and promotes polyploidization induced by PMA. PMA/PKD2-mediated necrosis via PARP cleavage involves both SOD1-dependent and -independent pathways. Finally, ATN-224 enhanced the inhibition of cell proliferation by Ara-C. Taken together, the results demonstrate that SOD1 regulates cell death and differentiation in myeloid leukemia cells. ATN-224 may be beneficial for myeloid leukemia therapy.

Oxidized low-density lipoprotein accelerates the destabilization of extracellular-superoxide dismutase mRNA during foam cell formation

Extracellular-superoxide dismutase (EC-SOD) is one of the main anti-oxidative enzymes that protect cells against the damaging effects of superoxide. In the present study, we investigated the regulation of EC-SOD expression during the oxidized low density lipoprotein (oxLDL)-induced foam cell formation of THP-1-derived macrophages. The uptake of oxLDL into THP-1-derived macrophages was increased and EC-SOD expression was decreased in a time-dependent manner by oxLDL. Furthermore, EC-SOD suppression by oxLDL was mediated by the binding to scavenger receptors, especially CD36, from the results with siRNA experience. EC-SOD expression is known to be regulated by histone acetylation and binding of the transcription factor Sp1/3 to the EC-SOD promoter region in human cell lines. However, oxLDL did not affect these processes. On the other hand, the stability of EC-SOD mRNA was decreased by oxLDL. Moreover, oxLDL promoted destabilization of ectopically expressed mRNA from EC-SOD or chimeric Cu,Zn-SOD gene with the sequence corresponding to 3'UTR of EC-SOD mRNA, whereas oxLDL had no effect on ectopic mRNA produced from EC-SOD gene lacking the sequence. These results suggested that oxLDL decreased the expression of EC-SOD, which, in turn, accelerated the destabilization of EC-SOD mRNA, leading to weaker protection against oxidative stress and atherosclerosis.

α-Tomatine inhibits growth and induces apoptosis in HL-60 human myeloid leukemia cells

α-tomatine is a glycoalkaloid that occurs naturally in tomatoes (Lycopersicon esculentum). In the present study, the effects of α-tomatine on human myeloid leukemia HL-60 cells were investigated. Treatment of HL-60 cells with α-tomatine resulted in growth inhibition and apoptosis in a concentration-dependent manner. Tomatidine, the aglycone of tomatine had little effect on the growth and apoptosis of HL-60 cells. Growth inhibition and apoptosis induced by α-tomatine in HL-60 cells was partially abrogated by addition of cholesterol indicating that interactions between α-tomatine and cell membrane-associated cholesterol may be important in mediating the effect of α-tomatine. Activation of nuclear factor-κB by the phorbol ester, 12-O-tetradecanoylphorbol-13-acetate failed to prevent apoptosis in HL-60 cells treated with α-tomatine. In animal experiments, it was found that treatment of mice with α-tomatine inhibited the growth of HL-60 xenografts in vivo. Results from the present study indicated that α-tomatine may have useful anti-leukemia activities.

MCP-1-induced protein promotes endothelial-like and angiogenic properties in human bone marrow monocytic cells

Monocytic cells enhance neovascularization by releasing proangiogenic mediators and/or by transdifferentiating into endothelial-like cells. However, the mechanisms that govern this transdifferentiation process are largely unknown. Recently, monocyte chemotactic protein-1 (MCP-1)-induced protein (MCPIP) has been identified as a novel CCCH-type zinc-finger protein expressed primarily in monocytic cells. Here, we analyzed whether MCPIP might exert angiogenic effects by promoting differentiation of monocytic cells into endothelial cell (EC)-like phenotype. The expression of MCPIP increased during MCP-1-induced transdifferentiation in human bone marrow mononuclear cells (BMNCs). Knockdown of MCPIP with small interfering RNA (siRNA) abolished MCP-1-induced expression of EC markers Flk-1 and Tie-2 in human BMNCs. BMNCs transfected with MCPIP expression vector displayed EC-like morphology accompanied by downregulation of monocytic markers CD14 and CD11b, upregulation of EC markers Flk-1 and Tie-2, induction of cadherin (cdh)-12 and -19, activation of endoplasmic reticulum (ER) stress, and autophagy. Knockdown of cdh-12 or cdh-19 markedly inhibited MCPIP-induced enhancement of cell attachment and EC-marker expression. Inhibition of ER stress by tauroursodeoxycholate abolished MCPIP-induced expression of EC markers. Inhibition of autophagy by knockdown of Beclin-1 with siRNA or by an autophagy inhibitor 3'-methyladenine inhibited MCPIP-induced expression of EC markers. Expression of MCPIP in BMNCs enhanced uptake of acetylated low-density lipoprotein (acLDL), formation of EC-colony, incorporation of cells into capillary-like structure on Matrigel, and exhibited increased neovascularization in the ischemic hindlimb in mice. These results demonstrate that MCPIP may be an important regulator of inflammatory angiogenesis and provide novel mechanistic insights into the link between MCP-1 and cardiovascular diseases.

Epigenetic regulation of extracellular-superoxide dismutase in human monocytes

Extracellular-superoxide dismutase (EC-SOD) is a major SOD isozyme mainly present in the vascular wall and plays an important role in normal redox homeostasis. We previously showed the significant reduction or induction of EC-SOD during human monocytic U937 or THP-1 cell differentiation induced by 12-O-tetradecanoylphorbol-13-acetate (TPA), respectively; however, its cell-specific expression and regulation have not been fully elucidated. It has been reported that epigenetic factors, such as DNA methylation and histone modification, are involved in several kinds of gene regulation. In this study, we investigated the involvement of epigenetic factors in EC-SOD expression and determined high levels of DNA methylation within promoter and coding regions of EC-SOD in THP-1 cells compared to those in U937 cells. Moreover, treatment with a DNA methyltransferase inhibitor, 5-azacytidine, significantly induced the expression of EC-SOD in THP-1 cells, indicating the importance of DNA methylation in the suppression of EC-SOD expression; however, the DNA methylation status did not change during THP-1 cell differentiation induced by TPA. On the other hand, we detected histone H3 and H4 acetylation during differentiation. Further, pretreatment with histone acetyltransferase inhibitors, CPTH2 or garcinol, significantly suppressed the TPA-inducible EC-SOD expression. We also determined the epigenetic suppression of EC-SOD in peripheral blood mononuclear cells. Treatment with granulocyte macrophage colony-stimulating factor (GM-CSF)/granulocyte-CSF induced that expression. Overall, these findings provide novel evidence that cell-specific and TPA-inducible EC-SOD expression are regulated by DNA methylation and histone H3 and H4 acetylation in human monocytic cells.

Luteolin suppresses the differentiation of THP-1 cells through the Inhibition of NOX2 mRNA expression and the membrane translocation of p47phox

Luteolin (1), a natural product occurring in many vegetables and fruits, is known to have several biological activities. Cluster for differentiation (CD) families, such as CD11b, -14, and -36, are expressed during pathological processes of atherosclerosis and are used broadly as markers of monocytic differentiation into macrophages. Herein, it was investigated whether 1 and three other flavonoids [chrysin (2), apigenin (3), and tricetin (4)] blocked 12-O-tetradecanoylphorbol 13-acetate (TPA)-triggered induction of CD families, which were induced through the activation of protein kinase C (PKC), mitogen-activated protein kinase (MEK)/extracellular signal-regulated kinase (ERK), and NADPH oxidase (NOX)-derived reactive oxygen species (ROS). When compared to flavonoids 2-4, 1 blocked TPA-triggered induction of CD families and cell adherence of monocytic THP-1 cells. Luteolin completely blocked intracellular ROS generation, whereas it did not inhibit MEK/ERK phosphorylation. Moreover, pretreatment with 1 suppressed TPA-triggered induction of NOX2 and membrane translocation of p47(phox). Overall, it is revealed that 1 suppresses TPA-triggered induction of CD families by the prevention of NOX2 activation.

Arachidonic acid enhances TPA-induced differentiation in human leukemia HL-60 cells via reactive oxygen species-dependent ERK activation

The phorbol ester, 12-O-tetradecanoylphorbol-13-acetate (TPA), is a potent stimulator of differentiation in human leukemia cells; however, the effects of arachidonic acid (AA) on TPA-induced differentiation are still unclear. In the present study, we investigated the contribution of AA to TPA-induced differentiation of human leukemia HL-60 cells. We found that treatment of HL-60 cells with TPA resulted in increases in cell attachment and nitroblue tetrazolium (NBT)-positive cells, which were significantly enhanced by the addition of AA. Stimulation of TPA-induced intracellular reactive oxygen species (ROS) production by AA was detected in HL-60 cells via a DCHF-DA analysis, and the addition of the antioxidant, N-acetyl-cysteine (NAC), was able to reduce TPA+AA-induced differentiation in accordance with suppression of intracellular peroxide elevation by TPA+AA. Furthermore, activation of extracellular-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) by TPA+AA was identified in HL-60 cells, and the ERK inhibitor, PD98059, but not the JNK inhibitor, SP600125, inhibited TPA+AA-induced NBT-positive cells. Suppression of TPA+AA-induced ERK protein phosphorylation by PD98059 and NAC was detected, and AA enhanced ERK protein phosphorylation by TPA was in HL-60 cells. AA clearly increased TPA-induced HL-60 cell differentiation, as evidenced by a marked increase in CD11b expression, which was inhibited by NAC and PD98059 addition. Eicosapentaenoic acid (EPA) as well as AA showed increased intracellular peroxide production and differentiation of HL-60 cells elicited by TPA. Evidence of AA potentiation of differentiation by TPA in human leukemia cells HL-60 via activation of ROS-dependent ERK protein phosphorylation was first demonstrated herein.

Induction of IFNα or IL-12 depends on differentiation of THP-1 cells in dengue infections without and with antibody enhancement

Background

Appropriate induction of the early Th1 cytokine IL-12 is a critical defense directed against viral infection. We have previously shown that different viruses elicited either IL-12 or IFNα dependent Th1 reactions. Using dengue-2 virus, we sought to explore how dengue-2 induced IL-12 or IFNα expression by monocytic and its derived dendritic cells.

Methods

We employed human monocytic cell line, THP-1, to investigate whether differentiation of monocytic cells is involved in the switch between IFNα and IL-12 induction. Flow cytometry, RT-PCR and ELISA were respectively used to determine cell differentiation, IL-12 and IFNα mRNA expression and protein production.

Results

THP-1, expressing CD123, which is a plasmacytoid dendritic cell marker, but not CD14, CD11b or CD11c revealed IFNα mRNA expression while stimulated by dengue-2. In contrast, PMA-induced THP-1 differentiation toward monocytic cells expressed CD11b⁺, and CD14⁺, but not CD123, and revealed exclusively IL-12 expression while stimulated by dengue-2. Further studies showed that CD123⁺ expressing THP-1 cells elicited higher IFNα expression in dose and time dependent induction after infection, and PMA-induced monocytic differentiation of THP-1 cells revealed IL-12 expression. Antibody-dependent enhancement of DEN-2 infection significantly suppressed the DEN-2 induced IL-12 p40 expression in monocytic differentiated THP-1 cells.

Conclusions

Clarification and modulation of the early Th1 reaction in different monocytic cells may change or prevent complication from dengue infection.

Ethanol extract of Brazilian red propolis induces apoptosis in human breast cancer MCF-7 cells through endoplasmic reticulum stress

Propolis, a natural product collected from plants by honey bees, is commonly used in folk medicines. Endoplasmic reticulum (ER) stress is known to induce apoptosis through the induction of CCAAT/enhancer-binding protein homologous protein (CHOP). Here, we investigated whether ethanol extracts of propolis and caffeic acid phenethyl ester (CAPE) induce apoptosis, mitochondrial dysfunction, and ER stress in human breast cancer MCF-7 cells and human fibroblasts. Among several ethanol extracts of propolis and CAPE, Brazilian red propolis (BRP) significantly reduced MCF-7 cell viability through the induction of mitochondrial dysfunction, caspase-3 activity, and DNA fragmentation but did not affect those of fibroblasts. Moreover, treatment with BRP significantly induced CHOP expression in MCF-7 cells compared to fibroblasts. Further, pretreatment with a chemical chaperone, 4-phenylbutyric acid, suppressed BRP-triggered MCF-7 cell death. Overall, we revealed that an ethanol extract of BRP induces MCF-7 cell apoptosis through, at least in part, ER stress-related signaling.

Cell signaling through protein kinase C oxidation and activation

Due to the growing importance of cellular signaling mediated by reactive oxygen species (ROS), proteins that are reversibly modulated by these reactant molecules are of high interest. In this context, protein kinases and phosphatases, which act coordinately in the regulation of signal transduction through the phosphorylation and dephosphorylation of target proteins, have been described to be key elements in ROS-mediated signaling events. The major mechanism by which these proteins may be modified by oxidation involves the presence of key redox-sensitive cysteine residues. Protein kinase C (PKC) is involved in a variety of cellular signaling pathways. These proteins have been shown to contain a unique structural feature that is susceptible to oxidative modification. A large number of scientific studies have highlighted the importance of ROS as a second messenger in numerous cellular processes, including cell proliferation, gene expression, adhesion, differentiation, senescence, and apoptosis. In this context, the goal of this review is to discuss the mechanisms by which PKCs are modulated by ROS and how these processes are involved in the cellular response.

Extracellular-superoxide dismutase expression in COS7 cells exposed to cadmium chloride

Cadmium (Cd), an industrial and environmental pollutant, preferentially accumulates in the kidney, a major target for Cd-related toxicity. It has been reported that Cd exposure produces reactive oxygen species (ROS) and induces cytotoxicity. Extracellular-superoxide dismutase (EC-SOD) is an antioxidant enzyme that protects the cells from damaging effects of ROS; however, the effect of Cd on the expression of EC-SOD in COS7 cells remains unclear. In this study, exposure to cadmium chloride (CdCl₂) enhanced intracellular ROS generation and induced COS7 cell death. Moreover, exposure to Cd decreased the expression of EC-SOD at mRNA and protein levels, but not of other SOD isozymes, copper-and zinc-containing SOD and manganese-containing SOD. The reduction of EC-SOD and cell viability was partially attenuated by pretreatment with an antioxidant, N-acetylcysteine. Further, we determined the involvement of p38-mitogen-activated protein kinase (p38-MAPK) in the reduction of EC-SOD. From these observations, p38-MAPK signaling cascades activated by ROS play a pivotal role in the reduction of EC-SOD, and it is concluded that the reduction of EC-SOD leads to a decrease in the resistance to oxidative stress of Cd-exposed COS7 cells.