Kyoung-jin Min

Astrocytes Induce Hemeoxygenase-1 Expression in Microglia: A Feasible Mechanism for Preventing Excessive Brain Inflammation

Microglia are the major inflammatory cells in the brain, in which microglial inflammatory responses are modulated by interactions with other brain cells. Here, we show that astrocytes, the most abundant cells in the brain, can secrete one or more factors capable of modulating microglial activation by regulating the microglial levels of reactive oxygen species (ROS). Treatment of microglia with astrocyte culture-conditioned media (ACM) increased the expression level and activity of hemeoxygenase-1 (HO-1). ACM also induced nuclear translocation of the nuclear factor E2-related factor 2 transcription factor, increased the binding activity of the antioxidant response element (ARE), and enhanced HO-1 promoter activity in an ARE-dependent manner. Furthermore, treatment with ACM suppressed interferon-γ (IFN-γ)-induced ROS production, leading to reduced inducible nitric oxide synthase (iNOS) expression and nitric oxide (NO) release. In agreement with these results, mimickers of HO-1 products, such as bilirubin, ferrous iron, and a carbon monoxide-releasing molecule, reduced IFN-γ-induced iNOS expression and/or NO release. Finally, we found that the active component(s) in ACM was heat labile and smaller than 3 kDa. Together, these results suggest that astrocytes could cooperate with microglia to prevent excessive inflammatory responses in the brain by regulating microglial expression of HO-1 and production of ROS.

Barrier protective effects of withaferin A in HMGB1-induced inflammatory responses in both cellular and animal models.

Withaferin A (WFA), an active compound from Withania somnifera, is widely researched for its anti-inflammatory, cardioactive and central nervous system effects. In this study, we first investigated the possible barrier protective effects of WFA against pro-inflammatory responses in human umbilical vein endothelial cells (HUVECs) and in mice induced by high mobility group box 1 protein (HMGB1) and the associated signaling pathways. The barrier protective activities of WFA were determined by measuring permeability, leukocytes adhesion and migration, and activation of pro-inflammatory proteins in HMGB1-activated HUVECs. We found that WFA inhibited lipopolysaccharide (LPS)-induced HMGB1 release and HMGB1-mediated barrier disruption, expression of cell adhesion molecules (CAMs) and adhesion/transendothelial migration of leukocytes to human endothelial cells. WFA also suppressed acetic acid-induced hyperpermeability and carboxymethylcellulose-induced leukocytes migration in vivo. Further studies revealed that WFA suppressed the production of interleukin 6, tumor necrosis factor-α (TNF-α) and activation of nuclear factor-κB (NF-κB) by HMGB1. Collectively, these results suggest that WFA protects vascular barrier integrity by inhibiting hyperpermeability, expression of CAMs, adhesion and migration of leukocytes, thereby endorsing its usefulness as a therapy for vascular inflammatory diseases.

Withaferin A inhibits JAK/STAT3 signaling and induces apoptosis of human renal carcinoma Caki cells.

Withaferin A, the active component of Withania somnifera, causes cytotoxicity in a variety of tumor cell lines. In this study, we show that withaferin A inhibits constitutive and IL-6-induced phosphorylation of STAT3 (on Tyr705), but not IFN-γ-induced STAT1 phosphorylation. Withaferin A-induced down-regulation of STAT3 activation is associated with a reduction in Janus-activated kinase 2 (JAK2) activity. Withaferin A also down-regulates the expression of STAT3 regulated genes such as Bcl-xL, Bcl-2, cyclin D1 and survivin. The apoptotic effect of withaferin A in Caki human renal cancer cells was investigated. Withaferin A induced dose-dependent apoptotic cell death in Caki cells, as measured by FACS analysis and PARP cleavage. Furthermore, overexpression of STAT3 attenuated withaferin A-induced apoptosis. Taken together, the present study provides strong evidence that down-regulation of the STAT3 signaling pathway mediates withaferin A-induced apoptosis.

β-Lapachone induces programmed necrosis through the RIP1-PARP-AIF-dependent pathway in human hepatocellular carcinoma SK-Hep1 cells.

β-Lapachone activates multiple cell death mechanisms including apoptosis, autophagy and necrotic cell death in cancer cells. In this study, we investigated β-lapachone-induced cell death and the underlying mechanisms in human hepatocellular carcinoma SK-Hep1 cells. β-Lapachone markedly induced cell death without caspase activation. β-Lapachone increased PI uptake and HMGB-1 release to extracellular space, which are markers of necrotic cell death. Necrostatin-1 (a RIP1 kinase inhibitor) markedly inhibited β-lapachone-induced cell death and HMGB-1 release. In addition, β-lapachone activated poly (ADP-ribosyl) polymerase-1(PARP-1) and promoted AIF release, and DPQ (a PARP-1 specific inhibitor) or AIF siRNA blocked β-lapachone-induced cell death. Furthermore, necrostatin-1 blocked PARP-1 activation and cytosolic AIF translocation. We also found that β-lapachone-induced reactive oxygen species (ROS) production has an important role in the activation of the RIP1-PARP1-AIF pathway. Finally, β-lapachone-induced cell death was inhibited by dicoumarol (a NQO-1 inhibitor), and NQO1 expression was correlated with sensitivity to β-lapachone. Taken together, our results demonstrate that β-lapachone induces programmed necrosis through the NQO1-dependent ROS-mediated RIP1-PARP1-AIF pathway.

An IκBα phosphorylation inhibitor induces heme oxygenase-1(HO-1) expression through the activation of reactive oxygen species (ROS)–Nrf2–ARE signaling and ROS–PI3K/Akt signaling in an NF-κB-independent mechanism

Reactive oxygen species (ROS) are important signaling molecules in cells. Excessive ROS induce expression of inflammatory mediators, such as iNOS and COX2. Antioxidant enzymes, such as, heme oxygenase-1 (HO-1), tightly regulate ROS levels within cells. Here, we show that Bay 11-7082 (Bay) increased HO-1 mRNA and protein expression in human colon cancer HT29 cells. Bay induced translocation of NF-E2-related factor 2 (Nrf2) into nuclei and increased the binding activity of the antioxidant response element (ARE). In addition, PI3K/Akt inhibitor (LY294002) blocked Bay-induced HO-1 expression. Pretreatment with anti-oxidants (N-acetylcysteine (NAC) or glutathione) significantly reduced Bay-induced HO-1 mRNA/protein expression, nuclear translocation of Nrf2 and phosphorylation of Akt. However, PI3K/Akt signaling was independent of Bay-induced Nrf2 translocation and ARE binding activity. Furthermore, other NF-κB inhibitors, such as pyrrolidine dithiocarbamate (PDTC) and MG132, also increased HO-1 mRNA and protein expression. However, although overexpression of dominant negative inhibitory κB (IκB) reduced NF-κB-driven transcriptional activity, IκB overexpression did not increase HO-1 expression. Taken together, our results suggest that in human colon cancer HT29 cells, Bay induces HO-1 expression by increasing ROS production in an Nrf2-ARE and PI3K dependent manner, but Bay acts independently of NF-κB.

Withaferin A down-regulates lipopolysaccharide-induced cyclooxygenase-2 expression and PGE2 production through the inhibition of STAT1/3 activation in microglial cells.

Microglia are the major immune effector cells in the brain, and microglia activated by injury and infection can produce inflammatory mediators. A number of studies have reported that withaferin A has anti-inflammatory functions. However, the effects of withaferin A on the microglial inflammatory response have not been investigated. Our results show that withaferin A inhibited lipopolysaccharide (LPS)-induced cyclooxygenase (COX)-2 mRNA and protein expression and prostaglandin E2 (PGE(2)) production in BV2 murine microglial cells. Withaferin A had no effect on LPS-induced Akt and ERK phosphorylation, but phosphorylation of p38 and JNK was slightly decreased by withaferin A. Withaferin A significantly inhibited LPS-induced STAT1 and STAT3 phosphorylation in a dose-dependent manner. Furthermore, withaferin A inhibited nuclear translocation of STAT1 and interferon-gamma activated sequence (GAS)-promoter activity. Taken together, these results suggest that withaferin A inhibits LPS-induced PGE(2) production and COX-2 expression, at least in part, by blocking STAT1 and STAT3 activation.

Curcumin Significantly Enhances Dual PI3K/Akt and mTOR Inhibitor NVP-BEZ235-Induced Apoptosis in Human Renal Carcinoma Caki Cells through Down-Regulation of p53-Dependent Bcl-2 Expression and Inhibition of Mcl-1 Protein Stability

The PI3K/Akt and mTOR signaling pathways are important for cell survival and growth, and they are highly activated in cancer cells compared with normal cells. Therefore, these signaling pathways are targets for inducing cancer cell death. The dual PI3K/Akt and mTOR inhibitor NVP-BEZ235 completely inhibited both signaling pathways. However, NVP-BEZ235 had no effect on cell death in human renal carcinoma Caki cells. We tested whether combined treatment with natural compounds and NVP-BEZ235 could induce cell death. Among several chemopreventive agents, curcumin, a natural biologically active compound that is extracted from the rhizomes of Curcuma species, markedly induced apoptosis in NVP-BEZ235-treated cells. Co-treatment with curcumin and NVP-BEZ235 led to the down-regulation of Mcl-1 protein expression but not mRNA expression. Ectopic expression of Mcl-1 completely inhibited curcumin plus NVP-NEZ235-induced apoptosis. Furthermore, the down-regulation of Bcl-2 was involved in curcumin plus NVP-BEZ235-induced apoptosis. Curcumin or NVP-BEZ235 alone did not change Bcl-2 mRNA or protein expression, but co-treatment reduced Bcl-2 mRNA and protein expression. Combined treatment with NVP-BEZ235 and curcumin reduced Bcl-2 expression in wild-type p53 HCT116 human colon carcinoma cells but not p53-null HCT116 cells. Moreover, Bcl-2 expression was completely reversed by treatment with pifithrin-α, a p53-specific inhibitor. Ectopic expression of Bcl-2 also inhibited apoptosis in NVP-BE235 plus curcumin-treated cells. In contrast, NVP-BEZ235 combined with curcumin did not have a synergistic effect on normal human skin fibroblasts and normal human mesangial cells. Taken together, combined treatment with NVP-BEZ235 and curcumin induces apoptosis through p53-dependent Bcl-2 mRNA down-regulation at the transcriptional level and Mcl-1 protein down-regulation at the post-transcriptional level.

Inhibitory effects of melatonin on the lipopolysaccharide-induced CC chemokine expression in BV2 murine microglial cells are mediated by suppression of Akt-induced NF-κB and STAT/GAS activity

Abstract:  Melatonin influences sleep and circadian rhythm, and it has anti‐inflammatory functions. However, the mechanism of its anti‐inflammatory roles is not well understood. In our studies, we show that melatonin blocked lipopolysaccharide (LPS)‐induced CCL2 (monocyte chemotactic protein‐1; MCP‐1), CCL5 (Regulated upon Activation, Normal T‐cell Expressed, and Secreted), and CCL9 (macrophage inflammatory protein‐1γ) chemokine mRNA expression in BV2 murine microglial cells. Melatonin markedly inhibited LPS‐induced Akt phosphorylation and NF‐κB activation. Furthermore, melatonin inhibited LPS‐induced STAT1/3 phosphorylation and interferon‐gamma activated sequence (GAS)‐driven transcriptional activity. Interestingly, these effects were not associated with reactive oxygen species scavenging effects of melatonin or melatonin receptor signal pathways. Taken together, our results suggested that melatonin has anti‐inflammatory functions through down‐regulation of chemokine expression by inhibition of NF‐κB and STAT/GAS activation in LPS‐stimulated BV2 murine microglial cell line.

Antipsychotic agent thioridazine sensitizes renal carcinoma Caki cells to TRAIL-induced apoptosis through reactive oxygen species-mediated inhibition of Akt signaling and downregulation of Mcl-1 and c-FLIP(L)

Thioridazine has been known as an antipsychotic agent, but it also has anticancer activity. However, the effect of thioridazine on tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) sensitization has not yet been studied. Here, we investigated the ability of thioridazine to sensitize TRAIL-mediated apoptosis. Combined treatment with thioridazine and TRAIL markedly induced apoptosis in various human carcinoma cells, including renal carcinoma (Caki, ACHN, and A498), breast carcinoma (MDA-MB231), and glioma (U251MG) cells, but not in normal mouse kidney cells (TMCK-1) and human normal mesangial cells. We found that thioridazine downregulated c-FLIP(L) and Mcl-1 expression at the post-translational level via an increase in proteasome activity. The overexpression of c-FLIP(L) and Mcl-1 overcame thioridazine plus TRAIL-induced apoptosis. We further observed that thioridazine inhibited the Akt signaling pathway. In contrast, although other phosphatidylinositol-3-kinase/Akt inhibitors (LY294002 and wortmannin) sensitized TRAIL-mediated apoptosis, c-FLIP(L) and Mcl-1 expressions were not altered. Furthermore, thioridazine increased the production of reactive oxygen species (ROS) in Caki cells, and ROS scavengers (N-acetylcysteine, glutathione ethyl ester, and trolox) inhibited thioridazine plus TRAIL-induced apoptosis, as well as Akt inhibition and the downregulation of c-FLIP(L) and Mcl-1. Collectively, our study demonstrates that thioridazine enhances TRAIL-mediated apoptosis via the ROS-mediated inhibition of Akt signaling and the downregulation of c-FLIP(L) and Mcl-1 at the post-translational level.

Prothrombin Kringle-2 Activates Cultured Rat Brain Microglia

Microglia, the major immune effector cells in the CNS, become activated when the brain suffers injury. In this study, we observed that prothrombin, a zymogen of thrombin, induced NO release and mRNA expression of inducible NO synthase, IL-1β, and TNF-α in rat brain microglia. The effect of prothrombin was independent of the protease activity of thrombin since hirudin, a specific inhibitor of thrombin, did not inhibit prothrombin-induced NO release. Furthermore, factor Xa enhanced the effect of prothrombin on microglial NO release. Kringle-2, a domain of prothrombin distinct from thrombin, mimicked the effect of prothrombin in inducing NO release and mRNA expression of inducible NO synthase, IL-1β, and TNF-α. Prothrombin and kringle-2 both triggered the same intracellular signaling pathways. They both activated mitogen-activated protein kinases and NF-κB in a similar pattern. NO release stimulated by either was similarly reduced by inhibitors of the extracellular signal-regulated kinase pathway (PD98059), p38 (SB203580), NF-κB (N-acetylcysteine), protein kinase C (Go6976, bisindolylmaleimide, and Ro31-8220), and phospholipase C (D609 and U73122). These results suggest that prothrombin can activate microglia, and that, in addition to thrombin, kringle-2 is a domain of prothrombin independently capable of activating microglia.