ChuHee Lee

Toll-like receptor 9 dependent activation of MAPK and NF-kB is required for the CpG ODN-induced matrix metalloproteinase-9 expression

Unmethylated CpG oligodeoxynucleotides (CpG ODNs) activate immune cells to produce immune mediators. This study demonstrates that in murine macrophage RAW 264.7 cells, CpG ODN-mediated matrix metalloproteinase-9 (MMP-9) expression is regulated at transcriptional level and requires de novo protein synthesis. Inhibition of ERK and p38 MAPK, but not JNK, results in significant decrease of CpG ODN-induced MMP-9 expression. We found that endosomal maturation inhibitors, chloroquine and bafilomycin A, block CpG ODN-induced ERK and p38 MAPK activation and the subsequent MMP-9 expression. We also observed that CpG ODN induces NF-κ B activation and NF-κ B is a downstream target of p38 MAPK. Taken together, our data demonstrate that CpG ODN triggers MMP-9 expression via TLR-9 dependent ERK and p38 MAPK activation followed by NF-κ B activation.

Glycogen synthase kinase 3β and β-catenin pathway is involved in toll-like receptor 4-mediated NADPH oxidase 1 expression in macrophages

Macrophage activation contributes to the pathogenesis of atherosclerosis. In the vascular system, the major source of reactive oxygen species is the NADPH oxidase (Nox) family. Nox1 is induced by lipopolysaccharide (LPS) in macrophages, but the expression mechanism is not fully understood. We found that LPS causes β‐catenin accumulation by glycogen synthase kinase 3β (GSK3β) inactivation, and that β‐catenin accumulation increases Nox1 expression. LPS induced Nox1 mRNA expression and reactive oxygen species generation in Raw264.7 cells. Using bone marrow‐derived macrophages from toll‐like receptor 4 mutant mice, we also tested whether LPS‐induced Nox1 expression is toll‐like receptor 4 dependent. LPS caused GSK3β phosphorylation, induced β‐catenin accumulation and increased nuclear translocation. The GSK3β inhibitor LiCl potentiated LPS‐induced Nox1 expression in accordance with β‐catenin accumulation and nuclear translocation. Conversely, ectopic expression of a constitutively active GSK3β mutant severely attenuated Nox1 expression. These findings identify a novel regulatory pathway controlling Nox1 expression by LPS‐stimulated macrophages.

Serum Amyloid A Induces Contrary Immune Responses via Formyl Peptide Receptor-Like 1 in Human Monocytes

Although the level of serum amyloid A has been reported to be up-regulated during inflammatory response, the role of serum amyloid A on the regulation of inflammation and immune response has not been elucidated. We found that serum amyloid A stimulated the production of tumor necrosis factor (TNF)-α and interleukin (IL)-10, which are proinflammatory and anti-inflammatory cytokines, respectively, in human monocytes. Low concentrations of serum amyloid A stimulated TNF-α production with maximal activity at 6 h after stimulation, whereas high concentrations of serum amyloid A stimulated IL-10 production with maximal activity at 12 h. The activations of the two cytokines by serum amyloid A occurred at both the transcription and translational levels. Signaling events induced by serum amyloid A included the activation of two mitogen-activated protein kinases (extracellular signal-regulated kinase and p38 kinase), which were found to be required for TNF-α and IL-10 production, respectively. The stimulation of formyl peptide receptor-like-1-expressing RBL-2H3 cells, but not of vector-expressing RBL-2H3 cells with serum amyloid A, induced mitogen-activated protein kinases activation and the accumulation of the RNAs of these two cytokines. Together, our findings suggest that serum amyloid A modulates contrary immune responses via formyl peptide receptor-like 1, by inducing TNF-α or IL-10, and demonstrate that extracellular signal-regulated kinase and p38 kinase play counteracting roles in this process.

Induction of Cellular Senescence by Secretory Phospholipase A2 in Human Dermal Fibroblasts through an ROS-Mediated p53 Pathway

Secretory phospholipase A(2) (sPLA(2)) is involved in various cellular physiological and pathological responses, especially in inflammatory responses. Accumulating evidence suggests that inflammation is an underlying basis for the molecular alterations that link aging and age-related pathological processes. However, the involvement of sPLA(2) in cellular senescence is not clear. In this study, we found that sPLA(2) treatment induces cellular senescence in human dermal fibroblasts (HDFs), as confirmed by increases in senescence-associated beta-galactosidase activity, changes in cell morphology, and upregulation of p53/p21 protein levels. sPLA(2)-induced senescence was observed in p16-knockdown HDFs and p16-null mouse fibroblasts, but not in p53-knockdown HDFs and p53-null mouse fibroblasts. Treatment with sPLA(2) increases reactive oxygen species (ROS) production, and an antioxidant, N-acetylcysteine, inhibits sPLA(2)-induced cellular senescence. These results suggest that sPLA(2) has a role in cellular senescence in HDFs during inflammatory response by promoting ROS-dependent p53 activation and might therefore contribute to inflammatory disorders associated with aging.

Calcium-Independent Phospholipase A2β-Akt Signaling Is Involved in Lipopolysaccharide-Induced NADPH Oxidase 1 Expression and Foam Cell Formation

Foam cell formation is the most important process in atherosclerosis, and low density lipoprotein oxidation by reactive oxygen species (ROS) is the key step in the conversion of macrophages to foam cells. This study reveals the control mechanism of the gene for NADPH oxidase 1 (Nox1), which produces ROS in the formation of foam cells by stimulating TLR4. Treatment of macrophages by the TLR4 agonist LPS stimulated ROS production and ROS-mediated macrophage to foam cell conversion. This LPS-induced ROS production and foam cell formation could be abrogated by pretreatment of macrophages with N-acetyl cysteine or apocynin. LPS increased Nox1 promoter activity, and resultant expression of mRNA and protein. Small interfering RNA mediated inhibition of Nox1 expression decreased LPS-induced ROS production and foam cell formation. LPS-mediated Nox1 expression and the responses occurred in a calcium-independent phospholipase A2 (iPLA2)-dependent manner. The iPLA2β-specific inhibitor S-BEL or iPLA2β small interfering RNA attenuated LPS-induced Nox1 expression, ROS production, and foam cell formation. In addition, activation of iPLA2β by LPS caused Akt phosphorylation and was followed by increased Nox1 expression. These results suggest that the binding of LPS and TLR4 increases Nox1 expression through the iPLA2β-Akt signaling pathway, and control ROS production and foam cell formation.

Activation of toll-like receptor-9 induces matrix metalloproteinase-9 expression through Akt and tumor necrosis factor-α signaling

CpG oligodeoxunucleotide (ODN) plays an important role in immune cell function. The present study examined whether temporal control of toll‐like receptor (TLR)‐9 by CpG ODN can regulate the expression of matrix metalloproteinase‐9 (MMP‐9). CpG ODN induced the release of tumor necrosis factor (TNF)‐α and the expression of TNF receptor (TNFR)‐II, but not of TNFR‐I, in a time‐dependent manner and stimulated significant, though delayed, MMP‐9 expression. The endosomal acidification inhibitors, chloroquine or bafilomycin A, inhibited CpG ODN‐induced TNF‐α, TNFR‐II, and MMP‐9 expression. CpG ODN induced the phosphorylation of Akt, and the inhibition of Akt by LY294002 suppressed CpG ODN‐induced TNF‐α, TNFR‐II, and MMP‐9 expressions. Moreover, neutralizing TNF‐α antibody significantly suppressed CpG ODN‐induced MMP‐9 expression, suggesting the involvement of TNF‐α. These observations suggest that CpG ODN may play important roles in macrophage activation by regulating the expression of MMP‐9 via a TLR‐9/Akt/TNF‐α‐dependent signaling pathway.

RGS2 Suppresses Breast Cancer Cell Growth via a MCPIP1‐Dependent Pathway

Regulator of G protein signaling 2 (RGS2) is a member of a family of proteins that functions as a GTPase‐activating protein (GAP) for Gα subunits. RGS2 mRNA expression is lower in breast cancerous tissues than in normal tissues. In addition, expression of RGS2 is also lower in MCF7 (cancerous breast cells) than in MCF10A (normal breast cells). Here we investigated whether RGS2 inhibits growth of breast cancer cells. RGS2 overexpression in MCF7 cells inhibited epidermal growth factor‐ or serum‐induced proliferation. In HEK293T cells expressing RGS2, cell growth was also significantly suppressed (In addition, exogenous expression of RGS2 in HEK293T cells resulted in the significant suppression of cell growth). These results suggest that RGS2 may have a tumor suppressor function. MG‐132 treatment of MCF7 cells increased endogenous or exogenous RGS2 levels, suggesting a post‐transcriptional regulatory mechanism that controls RGS2 protein levels. RGS2 protein was degraded polyubiquitinated the K71 residue, but stabilized by deubiquitinase monocyte chemotactic protein‐induced protein 1 (MCPIP1), and not affected by dominant negative mutant (C157A) of MCPIP1. Gene expression profiling study showed that overexpression of RGS2 decreased levels of testis specific Y encoded like protein 5 (TSPYL5), which plays a causal role in breast oncogenesis. TSPYL5 protein expression was low in MCF10A and high in MCF7 cells, showing the opposite aspect to RGS2 expression. Additionally, RGS2 or MCPIP1 overexpression in MCF7 cells decreased TSPYL5 protein level, indicating that RGS2 stabilized by MCPIP1 have diminished TSPYL5 protein levels, thereby exerting an inhibitory effect of breast cancer cell growth. J. Cell. Biochem. 116: 260–267, 2015.

Inhibition of IL-6/STAT3 axis and targeting Axl and Tyro3 receptor tyrosine kinases by apigenin circumvent taxol resistance in ovarian cancer cells

Ovarian cancer is the number one cause of death from gynaecological malignancy. Platinum-based and taxol-based chemotherapy has been used as a standard therapy, but intrinsic and acquired resistance to chemotherapy is a major obstacle to treat the disease. In the present study, we found that in the chemoresistant ovarian cancer SKOV3/TR cells, interleukin-6 (IL-6), IL-6 receptor and signal transducers and activators of transcription 3 (STAT3) expression as well as STAT3 phosphorylation were upregulated compared to those in parental cells. Silencing of IL-6 using IL-6 siRNA was found to suppress IL-6 production, STAT3 and phosphoSTAT3 levels, which eventually reduced proliferation and clonogenicity of taxol-resistant SKOV3/TR cells. In addition, stattic, a STAT3 inhibitor, was found to result in decrease of cell viability and clonogenicity of these cells, indicating that the elevated IL-6 and STAT3, phosphoSTAT3 levels are associated with the development of taxol resistance. Next, we found anti-proliferative effect of apigenin on both SKOV3 and SKOV3/TR cells. RT-PCR and western blot results showed that apigenin significantly reduced the expression of Axl and Tyro3 receptor tyrosine kinases (RTKs) at mRNA and protein level, which account for its cytotoxic activity. We further found that apigenin decreased Akt phosphorylation and the level of B-cell lymphoma-extra large (Bcl-xl or BCL2-like 1 isoform 1), an inhibitor of apoptosis. On the contrary to these results, apigenin had no effect on IL-6 production, STAT3 and phosphoSTAT3 protein levels, suggesting that apigenin exerts its anti-proliferative activity via downregulation of Axl and Tyro3 expression, Akt phosphorylation and Bcl-xl expression, but not modulation of IL-6/STAT3 axis. Taken together, our data suggest that inhibition of IL-6/STAT3 signaling pathway and downregulation of Axl and Tyro3 RTKs expression might be a therapeutic strategy to overcome taxol resistance in ovarian cancer cells.

Identification of replicative senescence-associated genes in human umbilical vein endothelial cells by an annealing control primer system

Cellular senescence is regulated by specific genes in many organisms. The identification and functional analysis of senescence-associated genes could provide valuable insights into the senescence process. Here, we employed a new and improved differential display reverse transcription-polymerase chain reaction (DDRT-PCR) method that involves annealing control primers (ACPs) to identify genes that are differentially expressed in human umbilical endothelial cells during replicative senescence. Using 120 ACPs, we identified 31 differentially expressed genes (DEGs). Basic local alignment search tool (BLAST) search revealed 29 known genes and two unknown genes. Expression levels of the 29 known genes were confirmed by real-time quantitative RT-RCR and by Western blotting for eight of these genes. CD9 antigen, MHC class I chain-related sequence A (MICA) and cell division cycle 37 homolog (CDC37) were up-regulated, and bone morphogenetic protein 4 (BMP4), dickkopf-1 (DKK1), and transcription factor 7-like 1 (TCF7L1) were down-regulated in old cells. Treatment with recombinant human MICA caused a decrease in cell proliferation and an increase in senescence-associated beta-galactosidase staining. Further analysis of differentially expressed genes may provide insights into the molecular basis of replicative senescence and vascular diseases associated with cellular senescence.

Protein kinase C-η and phospholipase D2 pathway regulates foam cell formation via regulator of G protein signaling 2

Regulator of G protein signaling 2 (RGS2) is a GTPase-activating protein for Gαq, which is involved in regulating various vascular functions. To understand how RGS2 regulates foam cell formation, the present study identified signaling pathways controlled by lipopolysaccharide (LPS) and discovered new mechanisms whereby protein kinase C (PKC)-η and phospholipase D (PLD) 2 regulate RGS2 expression. The toll-like receptor (TLR) 4 agonist LPS caused foam cell formation of Raw264.7 macrophages and dramatically decreased RGS2 mRNA expression. RGS2 down-regulation by LPS was partially recovered by TLR4 small interfering RNA (siRNA). Peritoneal macrophages were separated from wild-type and TLR4 mutant mice, and treatment with LPS showed RGS2 expression decrease in wild-type macrophages but no change in TLR4 mutant macrophages. RGS2 overexpression was suppressed, whereas RGS2 down-regulation accelerated foam cell formation by LPS. Treatment of PKC-η pseudosubstrate weakened foam cell formation and recovered RGS2 down-regulation by LPS. In addition, LPS or phorbol 12-myristate 13-acetate stimulated PLD activity, and the pretreatment of PLD inhibitor weakened foam cell formation and recovered RGS2 down-regulation. Inhibition of PLD2 expression by siRNA also weakened foam cell formation and partially recovered LPS-mediated RGS2 down-regulation. On the other hand, PLD2 overexpression intensified RGS2 down-regulation and foam cell formation by LPS. These results suggest that LPS causes foam cell formation by increasing PKC-η and PLD2 activity by down-regulating RGS2 expression via TLR4 dependently.