Daeho Cho

NDRG2 expression decreases with tumor stages and regulates TCF/β-catenin signaling in human colon carcinoma

NDRG (N-Myc downstream-regulated gene)-2 is a member of the NDRG family. Although it has been suggested that NDRG2 is involved in cellular differentiation and tumor suppression, its intracellular signal and regulatory mechanism are not well known. Here, we show the differential expression of NDRG2 in human colon carcinoma cell lines and tissues by reverse transcription–polymerase chain reaction and immunohistochemical analyses with monoclonal antibody against NDRG2. NDRG2 was strongly expressed in normal colonic mucosa and colonic adenomatous tissues (25 of 25) but not in all invasive cancer tissues [44 of 99 (44%)]. Most distinctive results indicated that the high expression level of NDRG2 has a positive correlation with tumor differentiation and inverse correlation with tumor invasion depth and Dukes’ stage of colon adenocarcinoma. To investigate the roles of NDRG2 in tumorigenesis, we used in vitro cell culture system. SW620 colon cancer cell line with a low level of intrinsic NDRG2 protein was transfected with NDRG2-expressing plasmid. TOPflash luciferase reporter assay showed that the transcriptional activity of T-cell factor (TCF)/lymphoid enhancer factor (LEF) was reduced by NDRG2 introduction, but not by the introduction of mutant NDRG2 generated by deletion or site-directed mutagenesis. Intracellular β-catenin levels were slightly reduced in the NDRG2-transfected SW620 cells and this regulation of β-catenin stability and TCF/LEF activity were mediated through the modulation of glycogen synthase kinase-3beta activity by NDRG2 function. Our results suggest that NDRG2 might play a pivotal role as a potent tumor suppressor by the attenuation of TCF/β-catenin signaling for the maintenance of healthy colon tissues.

Interleukin-18 is a critical factor for vascular endothelial growth factor-enhanced migration in human gastric cancer cell lines

Cell migration and angiogenesis are key steps in tumor metastasis. However, the mechanism of migration regulated by vascular endothelial growth factor (VEGF), a potent regulator of angiogenesis, is not completely understood. This study examined the relationship between VEGF and migration, along with the mechanism involved in the VEGF-regulated migration of human gastric cancer cells. The level of cell migration was increased by recombinant human (rh)VEGF-165 in the VEGF receptor-2-expressing SNU-601 cells. Interleukin (IL)-18 is associated with the malignant progression of tumors. Accordingly, this study examined the effect of IL-18 on the migration of cancer cells in order to identify the factors involved in VEGF-enhanced migration. Inhibiting IL-18 markedly reduced the level of VEGF-enhanced migration, and IL-18 increased cell migration directly through filamentous-actin polymerization and tensin downregulation. It was confirmed that rhVEGF-165 increased IL-18 production significantly. An antioxidant and an extracellular signal-regulated kinase (ERK)1/2-specific inhibitor blocked rhVEGF-165-enhanced IL-18 production. Accordingly, rhVEGF-165 increased the generation of region of interest (ROI) and activated the ERK1/2 pathway. These results suggest that rhVEGF-165 enhances IL-18 production via the generation of ROI and ERK1/2 phosphorylation, which results in the increased migration of gastric cancer cells.

Sodium Ascorbate (Vitamin C) Induces Apoptosis in Melanoma Cells via the Down-Regulation of Transferrin Receptor Dependent Iron Uptake

Sodium ascorbate (vitamin C) has a reputation for inconsistent effects upon malignant tumor cells, which vary from growth stimulation to apoptosis induction. Melanoma cells were found to be more susceptible to vitamin C toxicity than any other tumor cells. The present study has shown that sodium ascorbate decreases cellular iron uptake by melanoma cells in a dose‐ and time‐dependent fashion, indicating that intracellular iron levels may be a critical factor in sodium ascorbate‐induced apoptosis. Indeed, sodium ascorbate‐induced apoptosis is enhanced by the iron chelator, desferrioxamine (DFO) while it is inhibited by the iron donor, ferric ammonium citrate (FAC). Moreover, the inhibitory effects of sodium ascorbate on intracellular iron levels are blocked by addition of transferrin, suggesting that transferrin receptor (TfR) dependent pathway of iron uptake may be regulated by sodium ascorbate. Cells exposed to sodium ascorbate demonstrated down‐regulation of TfR expression and this precedes sodium ascorbate‐induced apoptosis. Taken together, sodium ascorbate‐mediated apoptosis appears to be initiated by a reduction of TfR expression, resulting in a down‐regulation of iron uptake followed by an induction of apoptosis. This study demonstrates the specific mechanism of sodium ascorbate‐induced apoptosis and these findings support future clinical trial of sodium ascorbate in the prevention of human melanoma relapse.

Induction of human promyelocytic leukemia HL-60 cell differentiation into monocytes by silibinin: involvement of protein kinase C.

The effect of silibinin, an active component of Silybum marianum, on cellular differentiation was investigated in the human promyelocytic leukemia HL-60 cell culture system. Treatment of HL-60 cells with silibinin inhibited cellular proliferation and induced cellular differentiation in a dose-dependent manner. Cytofluorometric analysis and morphologic studies indicated that silibinin induced differentiation of HL-60 cells predominantly into monocytes. Importantly, strongly synergistic induction of differentiation into monocytes was observed when silibinin was combined with 5 nM 1alpha,25-dihydroxyvitamin D(3) [1,25-(OH)(2)D(3)], a well-known differentiation inducer of HL-60 cells into the monocytic lineage. Silibinin enhanced protein kinase C (PKC) activity and increased protein levels of both PKCalpha and PKCbeta in 1,25-(OH)(2)D(3)-treated HL-60 cells. PKC and extracellular signal-regulated kinase (ERK) inhibitors significantly inhibited HL-60 cell differentiation induced by silibinin alone or in combination with 1,25-(OH)(2)D(3), indicating that PKC and ERK may be involved in silibinin-induced HL-60 cell differentiation.

IL-32γ Induces the Maturation of Dendritic Cells with Th1- and Th17-Polarizing Ability through Enhanced IL-12 and IL-6 Production

IL-32, a newly described multifunctional cytokine, has been associated with a variety of inflammatory diseases, including rheumatoid arthritis, vasculitis, and Crohn’s disease. In this study, we investigated the immunomodulatory effects of IL-32γ on bone marrow-derived dendritic cell (DC)-driven Th responses and analyzed the underlying signaling events. IL-32γ–treated DCs exhibited upregulated expression of cell-surface molecules and proinflammatory cytokines associated with DC maturation and activation. In particular, IL-32γ treatment significantly increased production of IL-12 and IL-6 in DCs, which are known as Th1- and Th17-polarizing cytokines, respectively. This increased production was inhibited by the addition of specific inhibitors of the activities of phospholipase C (PLC), JNK, and NF-κB. IL-32γ treatment increased the phosphorylation of JNK and the degradation of both IκBα and IκBβ in DCs, as well as NF-κB binding activity to the κB site. The PLC inhibitor suppressed NF-κB DNA binding activity and JNK phosphorylation increased by IL-32γ treatment, thereby indicating that IL-32γ induced IL-12 and IL-6 production in DCs via a PLC/JNK/NF-κB signaling pathway. Importantly, IL-32γ–stimulated DCs significantly induced both Th1 and Th17 responses when cocultured with CD4+ T cells. The addition of a neutralizing anti–IL-12 mAb abolished the secretion of IFN-γ in a dose-dependent manner; additionally, the blockage of IL-1β and IL-6, but not of IL-21 or IL-23p19, profoundly inhibited IL-32γ–induced IL-17 production. These results demonstrated that IL-32γ could effectively induce the maturation and activation of immature DCs, leading to enhanced Th1 and Th17 responses as the result of increased IL-12 and IL-6 production in DCs.

Resveratrol induces the suppression of tumor-derived CD4+CD25+ regulatory T cells

CD4+CD25+ regulatory T cells (Treg cells) are negative regulator of the immune system and main obstacles to cancer immunotherapy in tumor-bearing hosts. Resveratrol is a natural product found in grapes with both immunomodulatory and anticancer effects, which can be controlled by Treg cells. Therefore, to determine whether resveratrol performs these actions via Treg cells, we investigated changes in Treg cell population and immunomodulatory cytokines in EG7 tumor-bearing C57BL/6 mice. In the present study, CD4+CD25+ cell population among CD4+ cells was inhibited ex vivo by resveratrol treatment in a dose-dependent manner. FoxP3+ expressing cells among CD4+CD25+ population were significantly reduced after resveratrol treatment ex vivo in intracellular FACS analysis. Single intraperitoneal administration of 4 mg/kg resveratrol suppressed the CD4+CD25+ cell population among CD4+ cells and downregulated secretion of TGF-beta, an immunosuppressive cytokine, measured from the spleens of tumor-bearing mice. Furthermore, resveratrol enhanced IFN-gamma expression in CD8+ T cells both ex vivo and in vivo,leading to immune stimulation. Taken together, these results suggest that resveratrol has a suppressive role on CD4+CD25+ cell population and makes peritumoral microenvironment unfavorable to tumor in tumor-bearing mice. Thus, resveratrol can be considered as possible adjuvant material for vaccination-based cancer therapy.

Air pollution and skin diseases: Adverse effects of airborne particulate matter on various skin diseases.

Environmental air pollution encompasses various particulate matters (PMs). The increased ambient PM from industrialization and urbanization is highly associated with morbidity and mortality worldwide, presenting one of the most severe environmental pollution problems. This article focuses on the correlation between PM and skin diseases, along with related immunological mechanisms. Recent epidemiological studies on the cutaneous impacts of PM showed that PM affects the development and exacerbation of skin diseases. PM induces oxidative stress via production of reactive oxygen species and secretion of pro-inflammatory cytokines such as TNF-α, IL-1α, and IL-8. In addition, the increased production of ROS such as superoxide and hydroxyl radical by PM exposure increases MMPs including MMP-1, MMP-2, and MMP-9, resulting in the degradation of collagen. These processes lead to the increased inflammatory skin diseases and skin aging. In addition, environmental cigarette smoke, which is well known as an oxidizing agent, is closely related with androgenetic alopecia (AGA). Also, ultrafine particles (UFPs) including black carbon and polycyclic aromatic hydrocarbons (PAHs) enhance the incidence of skin cancer. Overall, increased PM levels are highly associated with the development of various skin diseases via the regulation of oxidative stress and inflammatory cytokines. Therefore, anti-oxidant and anti-inflammatory drugs may be useful for treating PM-induced skin diseases.

Induction of interleukin-12 production in mouse macrophages by berberine, a benzodioxoloquinolizine alkaloid, deviates CD4+ T cells from a Th2 to a Th1 response

In this study we investigated whether berberine‐mediated induction of interleukin‐12 (IL‐12) production in antigen‐presenting cells could regulate a cytokine profile of antigen‐primed CD4+ T helper (Th) cells. Pretreatment with berberine induced IL‐12 production in both macrophages and dendritic cells, and significantly increased the levels of IL‐12 production in lipopolysaccharide‐stimulated macrophages and in CD40 ligand‐stimulated dendritic cells. Importantly, berberine pretreatment of macrophages increased their ability to induce interferon‐γ (IFN‐γ) and reduced their ability to induce IL‐4 in antigen‐primed CD4+ T cells. Berberine did not influence the macrophage cell surface expression of the class II major histocompatibility complex molecule, the co‐stimulatory molecules CD80 and CD86, and intracellular adhesion molecule‐1. Addition of neutralizing anti‐IL‐12p40 monoclonal antibody to cultures of berberine‐pretreated macrophages and CD4+ T cells restored IL‐4 production in antigen‐primed CD4+ T cells. The in vivo administration of berberine resulted in the enhanced induction of IL‐12 production by macrophages when stimulated in vitro with lipopolysaccharide or heat‐killed Listeria monocytogenes, leading to the inhibition of the Th type 2 cytokine profile (decreased IL‐4 and increased IFN‐γ production) in antigen‐primed CD4+ T cells. These findings may point to a possible therapeutic use of berberine or medicinal plants containing berberine in the Th type 2 cell‐mediated immune diseases such as allergic diseases.

L-ascorbic acid (vitamin C) induces the apoptosis of B16 murine melanoma cells via a caspase-8-independent pathway.

Abstractl-Ascorbic acid (vitamin C) has been reported to play a role in the treatment and prevention of cancer. However, its specific mechanistic pathways remain obscure. This study was carried out to identify the sodium ascorbate–induced apoptotic pathway in B16F10 murine melanoma cells. Sodium ascorbate was found to induce the apoptosis of B16F10 murine melanoma in a time- and dose-dependent manner, and this was prevented by pretreatment with N-acetyl-l-cysteine (NAC), a well-known antioxidant. In fact, sodium ascorbate–treated B16F10 melanoma cells showed increased intracellular reactive oxygen species generation (ROS) levels. These results indicate that sodium ascorbate induced apoptosis in B16F10 murine melanoma cells by acting as a prooxidant. We examined the involvement of caspase-8 using a specific caspase-8 inhibitor (z-IETD-fmk) on the sodium ascorbate–induced apoptotic pathway. Cell death was found not to be inhibited by z-IETD-fmk treatment, indicating that sodium ascorbate–induced apoptosis is not mediated by caspase-8. In addition, we detected a reduction in the mitochondrial membrane potential during apoptosis and confirmed cytochrome-c release from mitochondria by immunoblotting. Taken together, it appears that the induction of a prooxidant state by sodium ascorbate and a subsequent reduction in mitochondrial membrane potential are involved in the apoptotic pathway of B16F10 murine melanoma cells, and that this occurs in a caspase-8–independent manner.

l-Kynurenine-induced apoptosis in human NK cells is mediated by reactive oxygen species

Recent studies have shown that indoleamine 2,3-dioxygenase (IDO) plays a pivotal role in the modulation of immune response against tumor and virus infection. Here we demonstrate the pro-apoptotic effect of L-kynurenine, a tryptophan catabolite of IDO, on human NK cell line, NK92 MI. Treatment with L-kynurenine dose-dependently induced growth inhibition and apoptosis in NK92 MI cells. Treatment with the antioxidant NAC completely protected cells from L-kynurenine-induced apoptosis. Moreover, we found that treatment with Z-VAD-fmk and ZB4 slightly inhibited L-kynurenine-induced apoptosis, suggesting that L-kynurenine-induced apoptosis in NK cells occurs primarily through an ROS mediated pathway. We observed that the presence of NAC blocks cytochrome c release and activation of caspase-3 during L-kynurenine-induced apoptosis. Overall, we conclude that L-kynurenine resulting from IDO can cause cell death via ROS pathway in NK cells. Our findings provide a new insight into the interaction between NK cells and IDO positive cancer cells in regulating immune responses.