Search

Signal transducer and activator of transcription 3 (STAT3) is a transcription factor that is latent but constitutively activated in many types of cancers. It is well known that STAT3 plays a key role in inflammation-associated tumorigenesis. Curcumin is an anti-inflammatory natural compound isolated from the turmeric (Curcuma longa L., Zingiberaceae) that has been extensively used in a traditional medicine over the centuries. In the present study, we have found that curcumin inhibits STAT3 signaling that is persistently overactivated in H-Ras transformed breast epithelial cells (H-Ras MCF10A). Specific cysteine residues present in STAT3 appear to be critical for the activity as well as conformation of this transcription factor. We identified the cysteine residue 259 of STAT3 as a putative site for curcumin binding. Site-directed mutation of this cysteine residue abolished curcumin-induced inactivation of STAT3 and apoptosis in H-Ras MCF10A cells. The α,β-unsaturated carbonyl moiety of curcumin appears to be essential in its binding to STAT3 in H-Ras MCF10A cells. Tetrahydrocurcumin that lacks such electrophilic moiety failed to interact with STAT3 and to induce apoptosis in the same cell line. Taken together, our findings suggest that curcumin can abrogate aberrant activation of STAT3 through direct interaction, thereby inhibiting STAT3-mediated mammary carcinogenesis.

Multiple lines of evidence support an inverse association between consumption of garlic and the risk of cancer. Chemopreventive effects of garlic have been attributed to its oil-soluble sulfur ingredients, such as diallyl sulfide (DAS), diallyl disulfide (DADS), and diallyl trisulfide (DATS), but their underlying molecular mechanisms remain largely unresolved. In the present study, we found that DATS showed the most potent anti-proliferative effects in human breast cancer MCF-7 cells. MCF-7 cells treated with DATS underwent apoptotic death as revealed by a progressive increase in the proportion of the sub-G0/G1 cell population and a typical pattern of annexin V/propidium iodide staining. DATS induced phosphorylation of the antiapoptotic Bcl-2 and proteolytic cleavage of poly(ADP-ribose)polymerase (PARP) in MCF-7 cells. DATS treatment activated c-Jun N-terminal kinase (JNK). DATS-induced apoptosis was blunted in MCF-7 cells treated with a specific JNK inhibitor SP600125 or transiently transfected with dominant negative JNK. DATS treatment resulted in accumulation of reactive oxygen species (ROS). DATS-induced apoptosis as well as activation of JNK was abrogated by N-acetyl-l-cysteine (NAC). Furthermore, DATS induced phosphorylation and expression of c-Jun, which were attenuated by NAC. MCF-7 cells treated with DATS also exhibited increased DNA binding activity of AP-1, which was blocked by NAC and the JNK inhibitor. Proteolytic cleavage of PARP induced by DATS was abrogated in the cells transfected with c-jun siRNA. Oral administration of 5μmol/kg DATS to female Balb/c mice inhibited the growth of human MCF-7 cell tumor xenografts. These results suggest that DATS-induced apoptosis is mediated through ROS generation and subsequent activation of JNK and AP-1., (Copyright © 2012 Elsevier Inc. All rights reserved.)

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.

We previously reported that a novel alkylphospholipid type antitumor agent edelfosine (ET-18-O-CH3 ; 1-O-octadecyl-2-O-methyl-glycero-3-phosphocholine) induced apoptosis in human breast epithelial cells transfected with the H-ras oncogene (MCF10A-ras) which was causally linked to cyclooxygenase-2 (COX-2) up-regulation and production of 15-deoxy-Delta 12,14-prostaglandins J2 (15d-PGJ2). ET-18-O-CH3 treatment also enhanced the production of prostaglandin E2 (PGE2), a major COX-2 product. In this study, we found that ET-18-O-CH3 treatment resulted in elevated mRNA expression of the PGE2 receptor subunit, EP2 receptor. Exogenously added PGE2 inhibited the growth of MCF10A-ras cells and induced proteolytic cleavage of caspase 3. ET-18-O-CH3 also inhibited constitutive activation of ERK1/2, p38 MAPK, and Akt/protein kinase B, which was blunted by a selective COX-2 inhibitor SC58635. In addition, ET-18-O-CH3 inhibited DNA binding activity of NF-kappa B in MCF10A-ras cells, and this was again attenuated by SC58635. Based on these findings, it is likely that ET-18-O-CH3 inactivates ERK1/2, Akt, and NF-kappaB signaling via COX-2 induction in MCF10A-ras cells, thereby inducing apoptosis of these cells.

Tetrahydropapaveroline (THP), a dopaminergic isoquinoline neurotoxin, has been reported to contribute to neurodegeneration in parkinsonism. As THP bears two catechol moieties, it undergoes autooxidation or enzymatic oxidation to produce reactive oxygen species (ROS), which may contribute to the THP-induced cell death. Although ROS are cytotoxic, the initial accumulation of ROS may provoke a survival response. In this study, treatment of PC12 cells with THP increased expression of heme oxygenase-1 (HO-1) as an adaptive survival response. Furthermore, THP-induced cytotoxicity was attenuated by the HO-1 inducer (SnCl2) and exacerbated by the HO-1 inhibitor (ZnPP). To elucidate the molecular mechanisms underlying THP-mediated HO-1 expression, we examined the possible involvement of NF-E2-related factor 2 (Nrf2), which plays an important role in the transcriptional regulation of detoxifying/antioxidant genes. THP treatment elevated nuclear translocation of Nrf2 and subsequent binding to antioxidant response element (ARE). PC12 cells transfected with dominant-negative Nrf2 exhibited increased cytotoxicity and decreased HO-1 expression after THP treatment. Moreover, U0126 and LY294002, which are pharmacologic inhibitors of extracellular signal-regulated kinase1/2 and phosphoinositide 3-kinase, respectively, attenuated HO-1 expression as well as Nrf2-ARE binding activity. Taken together, these findings suggest that HO-1 induction via Nrf2 activation may confer a cellular adaptive response against THP-mediated cell death.

We show here that Ca(2+) and reactive oxygen species (ROS) are involved in the up-regulation of c-Jun NH(2)-terminal kinase 1 (JNK1) activity during apoptosis induced by ginsenoside Rh2 (G-Rh2) in HeLa, MCF10A-ras, and MCF7 cells. Addition of antioxidants such as N-acetyl-l-cysteine or catalase attenuates G-Rh2-induced ROS generation, JNK1 activation, and apoptosis. The overexpression of catalase down-regulates caspase-3 and JNK1 activities. G-Rh2 treatment of cells results in mitochondrial depolarization, second mitochondrial activator of caspase release, and translocation of Bax into the mitochondria, and these events are inhibited by antioxidants. Ca(2+) is also involved in mitochondrial depolarization during G-Rh2-induced apoptosis. These results suggest that ROS and Ca(2+) are important signaling intermediates leading to stress-activated protein kinase/extracellular signal-regulated kinase kinase 1/JNK1 activation and depolarization of the mitochondrial membrane potential in G-Rh2-induced apoptosis.

Abnormally elevated expression of cyclooxygenase-2 (COX-2) has been frequently observed in transformed or malignant cells, and certain non-steroidal anti-inflammatory drugs with COX-2 inhibitory activity exert anti-neoplastic or chemopreventive effects. Contrary to this notion, we have found that a novel alkylphospholipid type antitumor agent ET-18-O-CH3 (1-O-octadecyl-2-O-methyl-glycero-3-phosphocholine) induces COX-2 expression in H-ras transformed human breast epithelial cells (MCF10A-ras) while it causes apoptosis at the same concentration range. The addition of a selective COX-2 inhibitor SC-58635 and COX-2 gene knock down with the siRNA blocked ET-18-O-CH3-induced apoptosis, suggesting that COX-2 induction by this drug is causally linked to its apoptosis inducing activity. ET-18-O-CH3 enhanced the transcriptional activities of cyclic AMP response element which is a key regulator of COX-2 expression. 15-Deoxy-Delta(12,14) prostaglandin J2 is, an endogenous ligand for peroxisome proliferator-activated receptor gamma (PPARgamma), has been known to possess proapoptotic potential in diverse cell types. ET-18-O-CH3 treatment resulted in elevated release of 15d-PGJ2 and DNA binding and transcriptional activity of PPARgamma. Based on these findings, it is likely that ET-18-O-CH3 induces COX-2 expression and production of 15d-PGJ2 which may mediate the ET-18-O-CH3-induced apoptosis in MCF10A-ras cells.

Catechol estrogens, the hydroxylated metabolites of 17beta-estradiol (E2), have been considered to be implicated in estrogen-induced carcinogenesis. 4-Hydroxyestradiol (4-OHE2), an oxidized metabolite of E2 formed preferentially by cytochrome P450 1B1, reacts with DNA to form depurinating adducts thereby exerting genotoxicity and carcinogenicity. 4-OHE2 undergoes 2-electron oxidation to quinone via semiquinone, and during this process, reactive oxygen species (ROS) can be generated to cause DNA damage and cell death. In the present study, 4-OHE2 was found to elicit cytotoxicity in cultured human mammary epithelial (MCF-10A) cells, which was blocked by the antioxidant trolox. MCF-10A cells treated with 4-OHE2 exhibited increased intracellular ROS accumulation and 8-oxo-7,8-dihydroxy-2'-deoxyguanosine formation, and underwent apoptosis as determined by poly(ADP-ribose)polymerase cleavage and disruption of mitochondrial transmembrane potential. The redox-sensitive transcription factor nuclear factor kappaB (NF-kappaB) was transiently activated by 4-OHE2 treatment. Cotreatment of MCF-10A cells with the NF-kappaB inhibitor, L-1-tosylamido-2-phenylethyl chloromethyl ketone, exacerbated 4-OHE2-induced cell death. 4-OHE2 also caused transient activation of extracellular signal-regulated protein kinases (ERK) involved in transmitting cell survival or death signals. A pharmacological inhibitor of ERK aggravated the 4-OHE2-induced cytotoxicity, supporting the pivotal role of ERK in protecting against catechol estrogen-induced oxidative cell death.

Extracts of Artemisia asiatica Nakai (Asteraceae) possess anti-inflammatory and antioxidative activities. Eupatilin (5,7-dihydroxy-3',4', 6-trimethoxyflavone), one of the pharmacologically active ingredients derived from A. asiatica was shown to induce apoptosis in human promyelocytic leukemia (HL-60) cells. In the present study, we examined the ability of eupatilin to induce apoptosis in human gastric cancer (AGS) cells. Eupatilin induced the apoptosis of AGS cells as revealed by a decrease in the ratio of pro-apoptotic Bax and anti-apoptotic Bcl-2, as well as the cleavage of caspase-3 and poly(ADP-ribose)polymerase (PARP). The pro-apoptotic effects of eupatilin were further verified by its perturbation of the mitochondrial transmembrane potential (DeltaPsim). In addition, eupatilin treatment led to an elevated expression of p53 and p21. Eupatilin inhibited the activation of ERK1/2 and Akt, which are important components of cell-survival pathways.

Catechol estrogens, the hydroxylated metabolites of 17beta-estradiol (E2), have been considered to be implicated in estrogen-induced carcinogenesis. 2-Hydroxyestradiol (2-OHE2), a major oxidized metabolite of E2 formed preferentially by cytochrome P-450 1A1, reacts with DNA to form stable adducts and exerts genotoxicity. 2-OHE2 can be oxidized to quinone, which is accompanied by generation of reactive oxygen species (ROS). In the present study, 2-OHE2 induced strand scission in phiX174 phage DNA and oxidative base modifications in calf thymus DNA in the presence of cupric ion. In cultured human mammary epithelial (MCF-10A) cells, 2-OHE2 treatment produced ROS accumulation, 8-oxo-7,8-dihydroxy-2'-deoxyguanosine formation, cytotoxicity, and disruption of mitochondrial transmembrane potential, all of which were prevented by N-acetylcysteine. These findings, taken together, suggest that 2-OHE2-induced oxidative DNA damage and apoptosis in MCF-10A cells might be mediated by ROS generated via the redox cycling of this catechol estrogen.

Nitrosative stress with subsequent inflammatory cell death has been associated with many neurodegenerative disorders. Expression of inducible nitric-oxide synthase and production of nitric oxide (NO) have been frequently elevated in many inflammatory disorders. NO can rapidly react with superoxide anion, producing more reactive peroxynitrite. In the present study, exposure of rat pheochromocytoma (PC12) cells to the peroxynitrite donor 3-morpholinosydnonimine hydrochloride (SIN-1) induced apoptosis, which accompanied depletion of intracellular glutathione (GSH), c-Jun N-terminal kinase activation, mitochondrial membrane depolarization, the cleavage of poly(ADP-ribose)polymerase, and DNA fragmentation. During SIN-1-induced apoptotic cell death, expression of inducible cyclooxygenase (COX-2), and peroxisome proliferator-activated receptor-gamma (PPARgamma) was elevated. SIN-1 treatment resulted in elevated production of 15-deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)), an endogenous PPARgamma activator. Preincubation with 15d-PGJ(2) rendered PC12 cells resistant to nitrosative stress induced by SIN-1. 15d-PGJ(2) fortified an intracellular GSH pool through up-regulation of glutamylcysteine ligase, thereby preventing cells from SIN-1-induced GSH depletion. The above findings suggest that 15d-PGJ(2) may act as a survival mediator capable of augmenting cellular thiol antioxidant capacity through up-regulation of the intracellular GSH synthesis in response to the nitrosative insult.

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-kappaB 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-kappaB 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-kappaB may play a key role in celecoxib-induced apoptosis.

COX-2 expression has been reported to be elevated in several forms of human cancer. The presence of oncogenic ras has been associated with constitutive induction of COX-2, which confers resistance to apoptosis. Contrary to the above notion, we have found that H-ras-transformed human breast epithelial (MCF10A-ras) cells treated with the anticancer drug ET-18-O-CH(3) exhibit an increased expression of COX-2, while they still undergo apoptosis. To determine whether the induction of COX-2 by ET-18-O-CH(3) could contribute to apoptosis in MCF10A-ras cells, the selective COX-2 inhibitor celecoxib (SC-58635) was used. Celecoxib treatment attenuated ET-18-O-CH(3)-induced cell death. Taken together, the above findings suggest that COX-2 up-regulation does not necessarily confer the resistance to apoptosis in ras-transformed cells, but rather may sensitize these cells to apoptotic death.