Hye-Kyung Na

(-)-Epigallocatechin gallate induces Nrf2-mediated antioxidant enzyme expression via activation of PI3K and ERK in human mammary epithelial cells.

The chemopreventive and chemoprotective activities of green tea have been attributed to the polyphenolic ingredient (-)-epigallocatechin-3-gallate (EGCG). Here, we report that treatment of human breast epithelial (MCF10A) cells with EGCG induces the expression of glutamate-cysteine ligase, manganese superoxide dismutase (MnSOD), and heme oxygenase-1 (HO-1). NF-E2-related factor (Nrf2) has been reported to regulate the antioxidant response element (ARE)-mediated expression of many antioxidant as well as detoxifying enzymes. The nuclear accumulation, ARE binding and transcriptional activity of Nrf2 were increased by EGCG treatment. Silencing of Nrf2 by siRNA gene knockdown rendered the MCF10A cells less sensitive to the EGCG-induced expression of HO-1 and MnSOD. Furthermore, EGCG activated Akt and extracellular signal-regulated protein kinase1/2 (ERK1/2). The pharmacologic inhibition of these kinases abrogated the nuclear translocation of Nrf2 induced by EGCG. These findings suggest that Nrf2 mediates EGCG-induced expression of some representative antioxidant enzymes, possibly via Akt and ERK1/2 signaling, which may provide the cells with acquired antioxidant defense capacity to survive the oxidative stress.

NF-κB and Nrf2 as prime molecular targets for chemoprevention and cytoprotection with anti-inflammatory and antioxidant phytochemicals

Cancer is a multifactorial heterogeneous disease characterized by multistage nature of pathogenesis. Over the past two or three decades, we have witnessed an enormous progress in the development of a vast variety of anticancer drugs and strategies. Nonetheless, we do not have magic bullets that can completely and selectively destroy malignant cells. Since neoplastic transformation, in general, is a relatively lengthy process that may take more than decades, there are ample opportunities to intervene in the pathogenesis of cancer, especially at early phases of oncogenesis. One such strategy is chemoprevention, an attempt to use either naturally occurring or synthetic substances, or their mixtures, to block, retard or even reverse the process of carcinogenesis. Numerous substances present in our daily diet, including fruits, vegetables, grains, spices, and seeds, have been shown to be effective in preventing cancer. Besides antioxidants, many plant-based organic chemical components, collectively called phytochemicals, retain pronounced chemopreventive potential. Currently, a series of human intervention trials are being considered with individual phytochemicals or their combination with known synthetic chemopreventive agents. However, precise assessment of underlying mechanisms of individual components is necessary before undertaking large-scale human trials. The chemopreventive effects that most edible phytochemicals exert are likely to be the sum of several distinct mechanisms. These include blockage of metabolic activation and/or DNA binding of carcinogens, stimulation of detoxification, repair of DNA damage, suppression of cell proliferation and metastasis or angiogenesis, induction of differentiation or apoptosis of precancerous or maliganant cells, etc. [1]. Given the great structural diversity of phytochemicals, it is not feasible to define structure–activity relationships or any other commonalities to deduce their underlying molecular mechanisms. In this context, one of the promising approaches employed in studying the mechanisms of chemopreventive phytochemicals includes assessment of their effects on the specific components of signal transduction network that becomes often deregulated—either amplified or repressed—in many cancerous or transformed cells. It has been known that a wide array of dietary phytochemicals act on the human genome, either directly or indirectly, to alter specific gene expression, thereby influencing the overall carcinogenic processes. Recently, much attention is being focussed on a new wave of nutrition research called ‘‘nutrigenomics’’. Nutrigenomics (or nutragenetics) can help understand how diseases such as cancer can be induced/aggravated or alleviated with dietary components by modulating specific gene expression. Nutrigenomic approaches are also applicable for the cancer chemoprevention studies.

Transcriptional regulation via cysteine thiol modification: A novel molecular strategy for chemoprevention and cytoprotection

Chemoprevention refers to the use of defined nontoxic chemical regimens to inhibit, reverse, or retard the process of multistage carcinogenesis that involves multiple signal transduction events. Identification of signaling molecules associated with carcinogenesis as prime targets of chemopreventive agents has become an area of great interest. Recent studies have implicated cysteine thiols present in various transcription factors, such as NF‐κB, AP‐1, and p53 as redox sensors in transcriptional regulation of many genes essential for maintaining cellular homeostasis. Some chemopreventive and cytoprotective agents have been found to target cysteine thiols present in key transcription factors or their regulators, thereby suppressing aberrant over‐activation of carcinogenic signal transduction or restoring/normalizing or even potentiating cellular defense signaling. The focus of this review is the oxidation or covalent modification of thiol groups present in key representative redox‐sensitive transcription factors and their regulating molecules as a unique strategy for molecular target‐based chemoprevention and cytoprotection.

Peroxisome proliferator-activated receptor γ (PPARγ) ligands as bifunctional regulators of cell proliferation

Peroxisome proliferator-activated receptor gamma (PPARgamma), a member of the ligand-activated nuclear receptor superfamily, plays a key role in mediating differentiation of adipocytes and regulating fat metabolism. PPARgamma has been implicated in the pathophysiology of atherosclerosis, inflammation, obesity, diabetes, immune response, and ageing. Recently, it has been shown that activation of PPARgamma by J(2) series cyclopentenone prostaglandins (cyPGs), especially 15-deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)) or synthetic agents, such as antidiabetic thiazolidinediones, causes anti-proliferation, apoptosis, differentiation, and anti-inflammation of certain types of cancer cells. The anti-proliferative effects of PPARgamma activators are associated with de novo synthesis of proteins involved in regulating the cell cycle and cell survival/death. Anti-inflammatory effects of 15d-PGJ(2) are associated with interruption of nuclear factor-kappaB and subsequent blockade of inflammatory gene expression. Furthermore, 15d-PGJ(2) at nontoxic doses induce expression of phase II detoxification or stress-responding enzymes, which may confer cellular resistance or adaptation to oxidative stress. The presence of a reactive alpha,beta-unsaturated carbonyl moiety in the cyclopentenone ring of 15d-PGJ(2) is important for part of biological functions this cyPG has. Recently, attention has been focused on the anti-proliferative activity of nonsteroidal anti-inflammatory drugs (NSAIDs) in cancerous or transformed cells, which is mediated through interaction with PPARgamma irrespective of their ability to inhibit COX-2. Despite the fact that abnormally elevated COX-2 is associated with resistance to cell death, induction of apoptosis by certain NSAIDs is accompanied by up-regulation of COX-2 expression. This commentary focuses on dual effects of the typical PPARgamma agonist 15d-PGJ(2) on cell proliferation and growth, and its possible involvement in the NSAID-induced COX-2 expression and apoptosis.

Inhibition of Phorbol Ester–Induced COX-2 Expression by Epigallocatechin Gallate in Mouse Skin and Cultured Human Mammary Epithelial Cells

Green tea polyphenols are reported to possess substantial antiinflammatory and chemopreventive properties. However, the molecular mechanism of chemopreventive activity of green tea polyphenols is not fully understood. An abnormally elevated level of cyclooxygenase-2 (COX-2) is implicated in the pathogenesis of carcinogenesis. In the present study, we found that pretreatment of the green tea extract enriched with catechin and epigallocatechin gallate (EGCG) by gavage inhibited COX-2 expression induced by the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) in mouse skin. Similarly, EGCG downregulated COX-2 in TPA-stimulated human mammary epithelial cells (MCF-10A) in culture. To further elucidate the underlying mechanism of COX-2 inhibition by green tea extract and EGCG, we examined their effects on the activation of extracellular signal-regulated protein kinase (ERK) and p38 mitogen-activated protein kinase (MAPK), which are upstream enzymes known to regulate COX-2 expression in many cell types. Pretreatment with EGCG as well as green tea extract caused a decrease in the activation of ERK. In addition, EGCG inhibited the catalytic activity of ERK and p38 MAPK, suggesting that these signal-transducing enzymes could be potential targets for previously reported antitumor promoting activity of EGCG.

Role of Nrf2-mediated heme oxygenase-1 upregulation in adaptive survival response to nitrosative stress

Nitrosative stress caused by reactive nitrogen species such as nitric oxide and peroxynitrite overproduced during inflammation leads to cell death and has been implicated in the pathogenesis of many human ailments. However, relatively mild nitrosative stress may fortify cellular defense capacities, rendering cells tolerant or adaptive to ongoing and subsequent cytotoxic challenges, a phenomenon known as ‘preconditioning’ or ‘hormesis’. One of the key components of cellular stress response is heme oxygenase-1 (HO-1), the rate limiting enzyme in the process of degrading potentially toxic free heme into biliverdin, free iron and carbon monoxide. HO-1 is upregulated by a wide array of stimuli and has antioxidant, anti-inflammatory and other cytoprotective functions. This review is intended to provide readers with a welldocumented account of the research done in the area of cellular adaptive survival response against nitrosative stress with special focus on the role of HO-1 upregulation, especially through activation of the transcription factor, Nrf2.

Celecoxib induces apoptosis in cervical cancer cells independent of cyclooxygenase using NF-κB as a possible target

Purpose Recently, many studies have shown that celecoxib induces apoptosis in various cancer cells by different mechanisms depending on the cell type. This study examined the apoptotic effect of celecoxib in cervical cancer cells and its mechanism.Methods Cell viability was measured by MTT assay and apoptosis was examined by DNA fragmentation and flow cytometry. Western blotting and immunoprecipitation were used to explore various mechanisms of celecoxib-induced apoptosis. The activation of NF-κB was confirmed by EMSA.Results Celecoxib induced apoptosis independent of COX-2 activity. This event accompanied the activation of caspase-8 and -9 with Bid cleavage and the loss of mitochondrial membrane potential. The protective effect of caspase-8 and -9 inhibitors on celecoxib-induced apoptosis suggests the importance of caspase-8 and -9 activation in this apoptotic pathway. Fas/FADD-mediated apoptotic pathway was detected only in C33A cells, demonstrated by the immunoprecipitation of Fas-FADD in celecoxib-treated cells and the protective effect of FADD dominant negative mutant. Finally, NF-κB appeared to be involved in celecoxib-induced apoptosis, as revealed by increased NF-kB DNA binding activity in a time-dependent manner and attenuation of its proapoptotic effect by N-tosyl-L-phenylalanyl-chloromethyl ketone, an NF-kB blocker.Conclusions These data show that caspase-8 and -9 are involved in the apoptotic effect of celecoxib in cervical cancer cells. This requires the FADD-dependent pathway in a cell type-specific manner. In addition, NF-κB may play a key role in celecoxib-induced apoptosis.

15-Deoxy-Δ12,14-prostaglandin J2 rescues PC12 cells from H2O2-induced apoptosis through Nrf2-mediated upregulation of heme oxygenase-1: Potential roles of Akt and ERK1/2

Oxidative stress induced by reactive oxygen intermediates has been implicated in a variety of human diseases including rheumatoid arthritis and neurodegenerative disorders. 15-Deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)), a terminal dehydration product of prostaglandin D(2), is an endogenous ligand of peroxisome proliferator-activated receptor-gamma and exhibits a number of biological activities including the proapoptotic activity. Recent studies have revealed that this cyclopentenone prostaglandin, at non-toxic concentrations, can also exert antiapoptotic or cytoprotective effects. In this study, the underlying mechanisms involved in the protective effects of 15d-PGJ(2) on the H2O2-induced cytotoxicty were explored using cultured rat pheochromocytoma (PC12) cells. PC12 cells treated with H2O2 underwent apoptosis, which was attenuated by pretreatment with non-toxic concentrations of 15d-PGJ(2). Treatment of the PC12 cells with 15d-PGJ(2) resulted in increased nuclear translocation, DNA-binding and transcriptional activity of NF-E2-related factor 2 (Nrf2), leading to upregulation of heme oxygenase-1 (HO-1) expression, which provided an adaptive survival response against the H2O2-derived oxidative cytotoxicity. Transfection of PC12 cells with dominant-negative Nrf2 gene abolished the 15d-PGJ(2)-derived induction of HO-1 expression. Moreover, the 15d-PGJ(2)-mediated increases in Nrf2-ARE binding and ARE luciferase activity were suppressed by the dominant-negative mutation as well as the pharmacological inhibition of Akt/protein kinase B or extracellular signal-regulated kinase 1/2 (ERK1/2). Taken together, these findings suggest that 15d-PGJ(2) augments cellular antioxidant defense capacity through activation of Akt and ERK signal pathways that leads to Nrf2 activation, and subsequently HO-1 induction, thereby protecting the PC12 cells from H2O2-induced oxidative cell death.

Ginger-derived phenolic substances with cancer preventive and therapeutic potential.

Ginger, the rhizomes of Zingiber officinale Roscoe (Zingiberaceae), has widely been used as a spice and condiment in different societies. Besides its food-additive functions, ginger has a long history of medicinal use for the treatment of a variety of human ailments including common colds, fever, rheumatic disorders, gastrointestinal complications, motion sickness, diabetes, cancer, etc. Ginger contains several nonvolatile pungent principles viz. gingerols, shogaols, paradols and zingerone, which account for many of its health beneficial effects. Studies conducted in cultured cells as well as in experimental animals revealed that these pungent phenolics possess anticarcinogenic properties. This chapter summarizes updated information on chemopreventive and chemotherapeutic effects of ginger-derived phenolic substances and their underlying mechanisms.

Resveratrol and Piceatannol Inhibit iNOS Expression and NF-κ B Activation in Dextran Sulfate Sodium-Induced Mouse Colitis

Inflammatory tissue injury has been implicated in tumor promotion and progression. 3,5,4′-trihydroxy-trans-stilbene (resveratrol) and 3,4,3′, 5′-tetrahydroxy-trans-stilbene (piceatannol), 2 structurally related plant polyphenols, have been reported to possess antioxidant, anti-inflammatory, and chemopreventive properties. This study was aimed at investigating the possible protective effects of resveratrol and piceatannol against dextran sulfate sodium (DSS)-induced inflammation in mouse colonic mucosa. Administration of DSS (2.5%) in drinking water for 7 days to male ICR mice resulted in colitis and elevated expression of inducible nitric oxide synthase (iNOS) and activation of nuclear factor-kappa B (NF-κB), a major transcription factor known to upregulate proinflammatory gene expression. Phosphorylation of extracellular signal-regulated kinase (ERK) and signal transducer and activator of transcription-3 (STAT3) was also enhanced after DSS treatment. Oral administration of resveratrol or piceatannol (10 mg/kg body weight each) for 7 constitutive days attenuated the DSS-induced inflammatory injury, upregulation of iNOS expression, and activation of NF-κB, STAT3, and ERK.