Constitutive Overexpression of Nrf2-dependent Heme Oxygenase-1 in A549 Cells Contributes to Resistance to Apoptosis Induced by Epigallocatechin 3-Gallate

Abstract

Epigallocatechin 3-gallate (EGCG), the major polyphenol found in green tea, exerts antiproliferative and proapoptotic effects in many cancer cells. However, we found that among many cancer cells human lung adenocarcinoma A549 cells are markedly resistant to apoptosis induction by EGCG (even at 100 M for 72 h). Heme oxygenase-1 (HO-1) induced by stress stimuli represents a prime cellular defense mechanism, but it may be associated with enhanced cell proliferation and chemoresistance in some cancer cells. Because we found that A549 cells constitutively overexpress HO-1 and its associated transcription factor Nrf2, we tested an hypothesis that EGCG resistance in these cells may be linked with Nrf2-mediated HO-1 overexpression. HO-1 inhibition with tin-protoporphyrin IX and silencing with RNA interference rendered cells more sensitive to apoptosis induction by EGCG and classical prooxidants. Interestingly, EGCG at high concentration (>200 M) induced apoptosis by suppressing expression of HO-1 protein and mRNA, and this effect correlated with a decrease in both Nrf2-ARE binding and HO-1-ARE-luciferase activity, suggesting Nrf2-driven transcriptional activation of ho-1. Because we observed notably high levels of phosphorylated protein kinase C␣ and its suppression by EGCG and deferoxamine (an iron chelator), a possible mechanism involving phosphorylated protein kinase C␣ and iron in Nrf2-HO-1 activation was further investigated. Collectively, our findings suggest that Nrf2-mediated HO-1 overexpression confers resistance to apoptosis induction by EGCG; therefore, its inactivation may be a target for overcoming the resistance to chemoprevention and chemotherapy.Epigallocatechin 3-gallate (EGCG), 2 the major polyphenol found in green tea, is a widely studied cancer chemopreventive agent with potential anticancer activity. The major mechanism of EGCG-mediated anticancer effects is considered to be related to induction of apoptosis (1, 2). Studies have shown differential sensitivity among different tumor cells or tumor cells versus normal cells to EGCG (1, 2). In particular, in many cancer cells EGCG has been shown to modulate multiple and often different signal transduction pathways. The reason for these observed differences is not clear but may be because of the differential oxidative status imposed by EGCG in various cell types or cell type-specific expression of endogenous antioxidant defense enzymes.Heme oxygenase-1 (HO-1) is known to be highly induced by a variety of stress stimuli and many cancer chemopreventive agents, and it represents a prime cellular defense mechanism against oxidative stress via antioxidant function of its catalytic products like bilirubin and carbon monoxide (CO) with concomitant induction of iron sequestering ferritin (3, 54). On the contrary, its overexpression in human cancers may offer cancer cells a growth advantage and cellular resistance against chemotherapy and photodynamic therapy (4, 5). Because the growth of most tumors depends on HO-1 (6), it is also considered as a target for canc...

High-dose green tea polyphenols induce nephrotoxicity in dextran sulfate sodium-induced colitis mice by down-regulation of antioxidant enzymes and heat-shock protein expressions

“…In fact, formation of EGCG-thiol conjugates was detected only at high doses (400 mg/kg) following intraperitoneal injection in mice (Sang et al 2005). Meanwhile, high-dose EGCG reduced the expressions of antioxidant enzymes, including HO-1, SOD, and catalase (Kweon et al 2006;Kim et al 2010). Along a similar line, our present results revealed that 1% GTPs dramatically decreased the mRNA expressions of HO-1 and NQO1 in the kidneys and livers of nontreated mice (Fig.…”

Effects of theanine on growth of human lung cancer and leukemia cells as well as migration and invasion of human lung cancer cells

“…The mechanisms of action of theanine against the migration and invasion of A549 cells require further investigation. It should be mentioned that theanine has displayed an anticancer activity comparable to EGCG in the suppression of some kinds of cancer cells such as A549 and hepatoma AH109A cells in vitro and/or in in vivo models (Kweon et al 2006;Zhang et al 2002). This is the first time to report that theanine significantly reduces cell viability of human nonsmall cell lung cancer and leukemia cells as well as cell migration and invasion of human lung cancer cells.…”

4-Methoxychalcone Enhances Cisplatin-Induced Oxidative Stress and Cytotoxicity by Inhibiting the Nrf2/ARE-Mediated Defense Mechanism in A549 Lung Cancer Cells

“…Many anti-cancer drugs induce apoptosis by producing reactive oxygen species (ROS) in cancer cells; therefore, its antioxidant and cytoprotective potential could be considered the 'dark side' of Nrf2 signaling as regards the therapeutic action of these drugs. This perspective is corroborated by reports demonstrating that up-regulation of Nrf2 downstream genes including heme oxygenase-1 (HO-1) and NAD(P)H:quinone oxidoreductase 1 (NQO1) is related to the resistance of cancer cells to chemotherapy (Kweon et al, 2006), and that down-regulation of Nrf2 causes radiosensitization (Singh et al, 2010). Therefore, Nrf2/ARE regulators are needed for a new therapeutic approach against cancer as adjuvant chemotherapeutic drugs.…”