Docosahexaenoic acid-induced apoptosis is mediated by activation of mitogen-activated protein kinases in human cancer cells
- Soyeon Jeong†1, 3,
- Kaipeng Jing†1, 3,
- Nayeong Kim†1, 3,
- Soyeon Shin1, 3,
- Soyeon Kim1, 3,
- Kyoung-Sub Song1,
- Jun-Young Heo1,
- Ji-Hoon Park1,
- Kang-Sik Seo1,
- Jeongsu Han1,
- Tong Wu4,
- Gi-Ryang Kweon1,
- Seung-Kiel Park1,
- Jong-Il Park1 and
- Kyu Lim1, 2, 3Email author
© Jeong et al.; licensee BioMed Central Ltd. 2014
Received: 21 November 2013
Accepted: 30 June 2014
Published: 3 July 2014
The role of omega-3 polyunsaturated fatty acids (ω3-PUFAs) in cancer prevention has been demonstrated; however, the exact molecular mechanisms underlying the anticancer activity of ω3-PUFAs are not fully understood. Here, we investigated the relationship between the anticancer action of a specific ω3-PUFA docosahexaenoic acid (DHA), and the conventional mitogen-activated protein kinases (MAPKs) including extracellular signal-regulated kinase (ERK), c-JUN N-terminal kinase (JNK) and p38 whose dysregulation has been implicated in human cancers.
MTT assays were carried out to determine cell viability of cancer cell lines (PA-1, H1299, D54MG and SiHa) from different origins. Apoptosis was confirmed by TUNEL staining, DNA fragmentation analysis and caspase activity assays. Activities of the conventional MAPKs were monitored by their phosphorylation levels using immunoblotting and immunocytochemistry analysis. Reactive oxygen species (ROS) production was measured by flow cytometry and microscopy using fluorescent probes for general ROS and mitochondrial superoxide.
DHA treatment decreased cell viability and induced apoptotic cell death in all four studied cell lines. DHA-induced apoptosis was coupled to the activation of the conventional MAPKs, and knockdown of ERK/JNK/p38 by small interfering RNAs reduced the apoptosis induced by DHA, indicating that the pro-apoptotic effect of DHA is mediated by MAPKs activation. Further study revealed that the DHA-induced MAPKs activation and apoptosis was associated with mitochondrial ROS overproduction and malfunction, and that ROS inhibition remarkably reversed these effects of DHA.
Together, these results indicate that DHA-induced MAPKs activation is dependent on its capacity to provoke mitochondrial ROS generation, and accounts for its cytotoxic effect in human cancer cells.
KeywordsDocosahexaenoic acid Reactive oxygen species Mitogen-activated protein kinases Apoptosis Cancer
Omega-3 polyunsaturated fatty acids (ω3-PUFAs) have the first double bond in the ω3 position (third carbon from the methyl end of the carbon chain) and are considered essential fatty acids because they cannot be synthesized by mammals . These PUFAs are able to regulate eicosanoid production , transcription events , formation of potent lipid peroxidation products , Wnt/β-catenin signaling [5, 6], and autophagy . Docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) are the main long chain ω3-PUFAs, and their anticancer effects have been demonstrated, with DHA showing a stronger effect than EPA because of the higher degree of unsaturation of the DHA molecule .
Various cellular metabolic processes are associated with the generation of reactive oxygen species (ROS) including hydrogen peroxide (H2O2), superoxide anion, and hydroxyl radicals as chemically reactive molecules . ROS regulate crucial cellular events, such as transcription factor activation, gene expression, and cell differentiation and proliferation . In mammalian cells, an important source of ROS generation is the mitochondrial electron transport chain . Overproduction of ROS induces cellular damage, such as the oxidation of cardiolipin in the mitochondrial membrane and a decrease in the mitochondrial membrane potential (MMP), which leads to apoptotic cell death [9, 11].
ROS activate the mitogen-activated protein kinases (MAPKs) families, which regulate many cellular processes, including cell growth, proliferation, differentiation, survival, and death . Mammals express at least three conventional MAPKs, extracellular signal-regulated kinase (ERK), c-JUN N-terminal kinase (JNK) and p38, and dysregulation of the conventional MAPKs is implicated in human cancers . While JNK and p38 activation is related to apoptosis under environmental stress conditions, especially oxidant injury, the activation of ERK induced by mitogens, growth factors and cytokines is generally believed to trigger pro-survival signals . However, recent studies suggest that ERK activation can also lead to apoptotic death of tumor cells in repsonse to various anticancer agents . For example, cisplatin-induced apoptosis in human cancer cells has been attributed to ERK activation, and inhibition of ERK markedly attenuates the pro-apoptotic effect of cisplatin .
In the present study, we investigated the cell death mode induced by DHA in four cancer cell lines derived from different types of cancers, and explored the relationship between conventional MAPKs and the cytotoxic effect of DHA. Our results show that DHA induces apoptotic cell death via ROS-regulated MAPK activation. These results have important implications for the chemoprevention and treatment of human cancer using ω3-PUFAs.
Chemicals and antibodies
DHA (Cayman Chemical, Ann Arbor, MI, USA) and tetramethylrhodamine ethyl ester (TMRE, Invitrogen, Camarillo, CA, USA) dissolved in absolute ethanol, Dihydroethidium (DHE, Invitrogen), PD98059 (Calbiochem, Cambridge, UK), SP600125 (Calbiochem), SB600125 (Calbiochem) and MitoSOX Red (Invitrogen) dissolved in dimethyl sulfoxide (Sigma, ST Louis, MO, USA), N-acetyl-L-cystein (NAC, Sigma) dissolved in phosphate buffered saline and H2O2 (MERCK, Darmstadt, Germany) dissolved in distilled water were stored at -20°C before use.
The antibodies used and their sources are as follows. Caspase-3, JNK, p38, phospho-p38 (Thr180/Tyr182) and XIAP antibodies were purchased from Cell signaling Technology (Beverly, MA, USA); antibodies against PARP-1/2 (H-250), phospho-ERK (E-4), ERK1 (K-23), Survivin and actin (I-19)-R were from Santa Cruz (CA, USA); goat anti-rabbit and goat anti-mouse secondary antibodies were from Calbiochem; and phospho-JNK1&2 (pT183/pY185) antibodies and secondary antibodies (goat anti-rabbit and goat anti-mouse) conjugated with TRITC were from Invitrogen.
Cell cultures and chemical treatment
Human ovarian cancer PA-1 cells, human lung cancer H1299 cells, and human cervical cancer SiHa cells were purchased from American Type Cell Culture Collection (Rockville, MD, USA). Human glioblastoma D54MG cells were provided by Dr. Binger (Duke University Medical Center, Durham, NC, USA). PA-1 cells were maintained in Minimum Essential Medium (MEM, GIBCO, Grand Island, NY, USA); H1299 and SiHa cells were maintained in Dulbecco’s Modified Eagle Medium (DMEM); and D54MG cells were maintained in RPMI 1640 medium (GIBCO). The media were supplemented with 10% heat-inactivated fetal bovin serum (FBS, GIBCO), penicillin and streptomycin. The cells were cultured in a humidified 5% CO2 atmosphere at 37°C.
Cells grown to 70% confluency were switched into serum-free media, and the cultures (H1299, D54MG and SiHa) were allowed to expand for 24 h before giving any treatment. For PA-1 cells, the serum-free culture condition was used at 12 h, as an incubation time longer than 12 h resulted in slight loss of cell viability (data not shown).
Cell viability assay
Cells were plated onto 96-well plates at seeding densities of 6.5 × 103 cells per well for PA-1, H1299 and SiHa cells and 7 × 103 cells per well for D54MG cells. The cell viability after treatment with appropriate agents was measured using Thiazolyl Blue Tetrazolium Bromide (MTT, Sigma) as previously described . Concentrations of DHA that produced 50% inhibition in cell survival (IC50) following a 24 h exposure, were manually derived from dose–response curves generated by the Microsoft Excel 2010 edition.
Measurement of oxygen consumption rate (OCR)
Cellular oxygen consumption was measured using a Seahorse bioscience XF24 analyzer (Seahorse Bioscience Inc., North Billerica, MA, USA) in 24-well plates at 37°C, with correction for positional temperature variations adjusted from four empty wells evenly distributed within the plate. PA-1 cells were seeded at 4 × 104 cells per well 18 h prior to the analysis, and each experimental condition was performed on 4 biological replicates. Immediately before the measurement, cells were switched to 1% FBS contained MEM for 4 h. Then cells were washed and 590 μL of non-buffered media (sodium bicarbonate free, pH 7.4 DMEM) was added to each well. After 15 min equilibration period, three successive 2 min measurements were performed at 3 min intervals with inter-measurement mixing to homogenize oxygen concentration in the medium and each condition was measured in independent walls. Concentrated compounds (10X) were injected into each well using the internal injector of the cartridge and three successive 2 min measurements were performed at 3 min intervals with inter-measurement mixing.
Western blot, immunocytochemistry and apoptosis assays
Western blot, immunocytochemistry and apoptosis assays were done as described previously in reference .
Determination of intracellular ROS and MMP
ROS production was measured using fluorescent probes DHE, and MitoSOX. Cells seeded onto 6-well plates were first stained with either DHE (10 μM) or MitoSOX (5 μM) in Hanks’ balanced salt solution (HBSS) for 30 min (15 min in case of MitoSOX) at 37°C. After washing away unbound probes, cells were switched into serum-free media, pretreated with or without 5 mM of NAC for 1 h and exposed to DHA for 4 h. Direct imaging of ROS in probe-stained cells was performed using a fluorescence microscope (Olympus iX70, Japan), and images were captured with a DP Controller software. All images were taken under identical exposure conditions to assess the intensity of the probe fluorescence accurately. Alternatively, the probe-stained cells were detached with trypsin-EDTA, washed and fluorescence intensity was measured within 60 min by flow cytometry. For each sample, at least 10,000 events were acquired and analyzed using the BD FACS-Calibur (BD Bioscience, San Diego, CA, USA). MMP levels were evaluated using fluorescent probes, TMRE. In brief, cells were stained with TMRE at a concentration of 25 nM for 15 min at 37°C in HBSS, washed twice, and then preincubated with or without 5 mM of NAC for 1 h in serum-free media before DHA exposure. After incubation with DHA for 4 h, the fluorescence of the cells stained with TMRE was monitored by flow cytometry as described above.
Small interfering RNAs (siRNAs)
siRNAs for human ERK1/2, JNK1/2 and p38 were purchased from Bioneer (Daejeon, Korea). For transfection, 25 nM siRNAs were added to 9 × 105 cells in a 100 mm dish using Lipofectamine RNAiMAX (Invitrogen) as recommended by the vendor. Control cells were transfected with a negative control siRNA with no known mRNA target (5’-ACG UGA CAC GUU CGG AGA AUU-3’) designed by Bioneer. After 18 h of transfection, cells were switched into serum-free media for 24 h (12 h in case of PA-1 cells) and then treated with DHA. The siRNAs sequences used were: ERK1 (5′-GAC CGG AUG UUA ACC UUU A-3′), ERK2 (5′-CCA AAG CUC UGG ACU UAU-U-3′), JNK1 (5′-CUG GUA UGA UCC UUC UGA A-3′), JNK2 (5′-CUG UAA CUG UUG AGA UGU A-3′) and p38 (5′-CAA AUU CUC CGA GGU CUA A -3′).
Student’s t test was performed for statistical analyses. In all analyses, the level of statistical significance was more than the 95% confidence level (P < 0.05). *** means P < 0.001.
DHA inhibits cell viability and induces apoptosis in human cancer cells
To determine whether the observed reduction in cell viability was caused by apoptosis, DHA-treated cells were first examined for cleavage of the apoptosis marker PARP and expression levels of Bcl-2 family proteins, which play critical roles in the apoptotic process . While DHA increased the expression levels of cleaved PARP and pro-apoptotic Bax, it attenuated the expression level of anti-apoptotic Bcl-2 (Figure 1B). In addition, DHA induced the formation of DNA strand breaks/hypodipliod nuclei (a typical characteristic of apoptotic cells ) as evidenced by an increased number of TUNEL positive cells (Figure 1C) and the cells with Sub-G1 DNA content (Figure 1D and Additional file 2: Figure S2). Notably, the elevated Sub-G1 population was directly paralleled by diminished proportions of D54MG (Figure 1D) and PA-1 cells (Additional file 2: Figure S2A) in each cell-cycle phase. However, a transient increase in the cell populations in G2/M phase was detected 6 h after 30 μM DHA treatment in H1299 and SiHa cell lines (Additional file 2: Figure S2B-S2C), implying that DHA may also interfere with cell-cycle distribution. Next, we measured the activity and cleavage formation of caspase-3, an executor caspase that is activated through both intrinsic and extrinsic apoptosis pathways , using PA-1 cells. Our results showed that DHA dose-dependently activated caspase-3 (Figure 1E, left), and upregulated the level of cleaved caspase-3 (Figure 1E, right and Additional file 1: Figure S1B). It is known that the inhibitor of apoptosis proteins (IAPs) are able to suppress apoptosis by inhibiting caspase-3 . We thus also determined the effect of DHA on expression of two well-documented IAP family members, Survivin and XIAP (Figure 1E, right). Levels of Survivin and XIAP were decreased markedly after DHA treatment. These results indicate that DHA induces apoptosis, which contributes to the inhibitory effect of DHA on cancer cell growth.
DHA leads toMAPK activation
DHA induces mitochondrial ROSproduction
DHA-induced MAPKs activation is required for apoptosis
DHA-induced ROS production is responsible for the MAPKs activation
To verify the above findings, we used a different approach. PA-1 cells were first treated with exogenous ROS, H2O2, in the presence or absence of NAC. Then, cell viability and the levels of cleaved PARP and phospho-MAPKs were analyzed by MTT assays (Figure 5C, top) and western blotting (Figure 5C, bottom), respectively. H2O2 decreased cell viability and increased the expression levels of cleaved PARP as well as phospho-MAPKs; and NAC remarkably reversed these effects of H2O2. Furthermore, H2O2 also significantly increased the nuclear staining levels of phospho-ERK/JNK/p38, which could be prevented by NAC pretreatment (Additional file 3: Figure S3D-S3F). Together, these findings demonstrated that excessive ROS production is responsible for the activation of MAPKs, and that DHA-induced apoptosis is linked to the ROS-mediated MAPKs activation in cancer cells.
The ω3-PUFA, DHA prevents cancer through regulating multiple targets implicated in various stages of cancer progression, and one aspect of its antitumor effect involves inhibition of cell growth . It has been shown that the growth-inhibitory effect of DHA is attributed to apoptosis and/or cell-cycle arrest, depending on the cell line studied [23, 24]. In agreement with this, our results showed that the apoptosis induced by DHA is accompanied by cell-cycle arrest in H1299 and SiHa cells but not in PA-1 and D54MG cells. Although the identification of molecular determinant controlling either apoptosis or cell-cycle arrest as alternative modes of DHA-induced growth inhibition requires further investigation, these inconsistent observations indicate that detailed mechanistic events underlying the growth-inhibitory effect of DHA may be also cell type specific.
One major finding of this study is that the activation of conventional MAPKs (ERK, JNK and p38) is critical for the induction of apoptosis in tumor cells exposed to DHA. This finding confirms the results from previous studies [25–27], showing that DHA-induced apoptosis involves p38 activation. Meanwhile, it extends these studies by demonstrating that ERK and JNK activation is also required for the apoptosis in cells treated with DHA. The detailed mechanism by which activation of conventional MAPKs promotes DHA-induced apoptosis is still uncertain. We found that the apoptosis triggered by DHA was associated with altered protein levels of Bax and Bcl-2. Since conventional MAPKs activation has been shown to promote the expression and phosphorylation of pro-apoptotic Bax, and to disrupt anti-apoptotic Bcl-2 function, thereby resulting in apoptosis [20, 28, 29], it is reasonable to assume that Bax and Bcl-2 may act downstream of MAPKs activation to induce apoptosis in tumor cells treated with DHA. Notably, our data contrast with the findings of previous studies [30–33] which show that inactivation of ERK/p38 by DHA accounts for the apoptotic death of MCF-7, A549 and HCT-116 cancer cells. The reason for such disparate regulation of MAPKs activity in response to DHA is unclear, but might be related to the distinct genetic background (e.g., the prodeath or prosurvival role of basal MAPKs activity) of different types of cancer cells [13, 14].
Previous studies suggest that the apoptosis inducing effect of DHA is at least partially attributed to its capacity to trigger mitochondrial ROS overproduction and malfunction [1, 4, 17, 34]. Mitochondria are the major cellular organelles producing ROS and within mitochondria, the primary site of ROS generation is electron transport chain . Therefore, our results that upon DHA exposure, the ROS, especially mitochondrial superoxide overproduced, and the OCR dramatically decreased with an increase in extracellular acidification rate (Figure 3 and data not shown), implying that DHA may cause a metabolic shift from oxidative phosphorylation to glycolysis and the disruption of electron transport chain.
Another question we addressed in the present study is the relationship between ROS, MARKs activation and apoptosis induced by DHA. ROS mediate MAPKs and the ROS-regulated ERK/JNK/p38 signaling in governing apoptosis under oxidative conditions have been widely investigated . Although many studies have provided a general view that activation of the ERK pathway delivers a survival signal under oxidative stress, which counteracts the pro-apoptotic signaling associated with JNK and p38 activation , it is also reported that ROS-mediated ERK activation can induce apoptosis . Our observations that DHA induced conventional MAPKs activation and apoptosis, which could be blocked by antioxidants are in agreement with the view that ROS-mediated activation of ERK/JNK/p38 in DHA-treated cancer cells is pro-apoptotic. Then, how do DHA-induced ROS result in the simultaneous activation of ERK/JNK/p38? One of potential molecules that may mediate this process is ASK1 (apoptosis signal-regulating kinase 1). ASK1 is substantially activated in response to a variety of ROS inducers, and has been shown to induce the activation of not only p38, but also ERK and JNK [35, 36]. Thus, it is foreseen that DHA-induced ROS would simultaneously activate all three conventional MAPKs via upregulation of ASK1.
Apoptosis signal-regulating kinase 1
Dulbecco’s modified eagle medium
Extracellular signal-regulated kinase
Inhibitor of apoptosis proteins
c-jun N-terminal kinase
Mitogen-activated protein kinases
Minimum essential medium
Mitochondrial membrane potential
Thiazolyl Blue Tetrazolium Bromide
Oxygen consumption rate
Polyunsaturated fatty acid
Reactive oxygen species
Small interfering RNA
Tetramethylrhodamine, ethyl ester
- TUNEL assays:
Terminal deoxynucleotidyl transferase dUTP nick end labeling assays.
This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MEST) (2007–0054932).
- Jing K, Wu T, Lim K: Omega-3 polyunsaturated fatty acids and cancer. Anticancer Agents Med Chem. 2013, 13: 1162-1177.View ArticlePubMedGoogle Scholar
- Calder PC: Dietary modification of inflammation with lipids. Proc Nutr Soc. 2002, 61: 345-358.View ArticlePubMedGoogle Scholar
- Jump DB: Dietary polyunsaturated fatty acids and regulation of gene transcription. Curr Opin Lipidol. 2002, 13: 155-164.View ArticlePubMedGoogle Scholar
- Siddiqui RA, Harvey K, Stillwell W: Anticancer properties of oxidation products of docosahexaenoic acid. Chem Phys Lipids. 2008, 153: 47-56.View ArticlePubMedGoogle Scholar
- Lim K, Han C, Dai Y, Shen M, Wu T: Omega-3 polyunsaturated fatty acids inhibit hepatocellular carcinoma cell growth through blocking beta-catenin and cyclooxygenase-2. Mol Cancer Ther. 2009, 8: 3046-3055.View ArticlePubMedPubMed CentralGoogle Scholar
- Lim K, Han C, Xu L, Isse K, Demetris AJ, Wu T: Cyclooxygenase-2-derived prostaglandin E2 activates beta-catenin in human cholangiocarcinoma cells: evidence for inhibition of these signaling pathways by omega 3 polyunsaturated fatty acids. Cancer Res. 2008, 68: 553-560.View ArticlePubMedGoogle Scholar
- Jing K, Song KS, Shin S, Kim N, Jeong S, Oh HR, Park JH, Seo KS, Heo JY, Han J, Park JI, Han C, Wu T, Kweon GR, Park SK, Yoon WH, Hwang BD, Lim K: Docosahexaenoic acid induces autophagy through p53/AMPK/mTOR signaling and promotes apoptosis in human cancer cells harboring wild-type p53. Autophagy. 2011, 7: 1348-1358.View ArticlePubMedPubMed CentralGoogle Scholar
- Gorjao R, Azevedo-Martins AK, Rodrigues HG, Abdulkader F, Arcisio-Miranda M, Procopio J, Curi R: Comparative effects of DHA and EPA on cell function. Pharmacol Ther. 2009, 122: 56-64.View ArticlePubMedGoogle Scholar
- D’Autreaux B, Toledano MB: ROS as signalling molecules: mechanisms that generate specificity in ROS homeostasis. Nat Rev Mol Cell Biol. 2007, 8: 813-824.View ArticlePubMedGoogle Scholar
- Thannickal VJ, Fanburg BL: Reactive oxygen species in cell signaling. Am J Physiol Lung Cell Mol Physiol. 2000, 279: L1005-L1028.PubMedGoogle Scholar
- Zhang DX, Gutterman DD: Mitochondrial reactive oxygen species-mediated signaling in endothelial cells. Am J Physiol Heart Circ Physiol. 2007, 292: H2023-H2031.View ArticlePubMedGoogle Scholar
- McCubrey JA, Lahair MM, Franklin RA: Reactive oxygen species-induced activation of the MAP kinase signaling pathways. Antioxid Redox Signal. 2006, 8: 1775-1789.View ArticlePubMedGoogle Scholar
- Wagner EF, Nebreda AR: Signal integration by JNK and p38 MAPK pathways in cancer development. Nat Rev Cancer. 2009, 9: 537-549.View ArticlePubMedGoogle Scholar
- Wada T, Penninger JM: Mitogen-activated protein kinases in apoptosis regulation. Oncogene. 2004, 23: 2838-2849.View ArticlePubMedGoogle Scholar
- Cagnol S, Chambard JC: ERK and cell death: mechanisms of ERK-induced cell death–apoptosis, autophagy and senescence. FEBS J. 2010, 277: 2-21.View ArticlePubMedGoogle Scholar
- Wang X, Martindale JL, Holbrook NJ: Requirement for ERK activation in cisplatin-induced apoptosis. J Biol Chem. 2000, 275: 39435-39443.View ArticlePubMedGoogle Scholar
- Shin S, Jing K, Jeong S, Kim N, Song KS, Heo JY, Park JH, Seo KS, Han J, Park JI, Kweon GR, Park SK, Wu T, Hwang BD, Lim K: The omega-3 polyunsaturated fatty acid DHA induces simultaneous apoptosis and autophagy via mitochondrial ROS-mediated Akt-mTOR signaling in prostate cancer cells expressing mutant p53. Biomed Res Int. 2013, 2013: 568671-View ArticlePubMedPubMed CentralGoogle Scholar
- Kroemer G, El-Deiry WS, Golstein P, Peter ME, Vaux D, Vandenabeele P, Zhivotovsky B, Blagosklonny MV, Malorni W, Knight RA, Piacentini M, Nagata S, Melino G: Classification of cell death: recommendations of the Nomenclature Committee on Cell Death. Cell Death Differ. 2005, 12 (Suppl 2): 1463-1467.View ArticlePubMedGoogle Scholar
- Deveraux QL, Reed JC: IAP family proteins–suppressors of apoptosis. Genes Dev. 1999, 13: 239-252.View ArticlePubMedGoogle Scholar
- Zhuang S, Schnellmann RG: A death-promoting role for extracellular signal-regulated kinase. J Pharmacol Exp Ther. 2006, 319: 991-997.View ArticlePubMedGoogle Scholar
- Guyton KZ, Liu Y, Gorospe M, Xu Q, Holbrook NJ: Activation of mitogen-activated protein kinase by H2O2. Role in cell survival following oxidant injury. J Biol Chem. 1996, 271: 4138-4142.View ArticlePubMedGoogle Scholar
- Kroemer G, Galluzzi L, Brenner C: Mitochondrial membrane permeabilization in cell death. Physiol Rev. 2007, 87: 99-163.View ArticlePubMedGoogle Scholar
- Albino AP, Juan G, Traganos F, Reinhart L, Connolly J, Rose DP, Darzynkiewicz Z: Cell cycle arrest and apoptosis of melanoma cells by docosahexaenoic acid: association with decreased pRb phosphorylation. Cancer Res. 2000, 60: 4139-4145.PubMedGoogle Scholar
- Brown I, Cascio MG, Wahle KW, Smoum R, Mechoulam R, Ross RA, Pertwee RG, Heys SD: Cannabinoid receptor-dependent and -independent anti-proliferative effects of omega-3 ethanolamides in androgen receptor-positive and -negative prostate cancer cell lines. Carcinogenesis. 2010, 31: 1584-1591.View ArticlePubMedPubMed CentralGoogle Scholar
- Diep QN, Touyz RM, Schiffrin EL: Docosahexaenoic acid, a peroxisome proliferator-activated receptor-alpha ligand, induces apoptosis in vascular smooth muscle cells by stimulation of p38 mitogen-activated protein kinase. Hypertension. 2000, 36: 851-855.View ArticlePubMedGoogle Scholar
- Slagsvold JE, Pettersen CH, Storvold GL, Follestad T, Krokan HE, Schonberg SA: DHA alters expression of target proteins of cancer therapy in chemotherapy resistant SW620 colon cancer cells. Nutr Cancer. 2010, 62: 611-621.View ArticlePubMedGoogle Scholar
- Toit-Kohn JL, Louw L, Engelbrecht AM: Docosahexaenoic acid induces apoptosis in colorectal carcinoma cells by modulating the PI3 kinase and p38 MAPK pathways. J Nutr Biochem. 2009, 20: 106-114.View ArticlePubMedGoogle Scholar
- Kim BJ, Ryu SW, Song BJ: JNK- and p38 kinase-mediated phosphorylation of Bax leads to its activation and mitochondrial translocation and to apoptosis of human hepatoma HepG2 cells. J Biol Chem. 2006, 281: 21256-21265.View ArticlePubMedGoogle Scholar
- Lei K, Nimnual A, Zong WX, Kennedy NJ, Flavell RA, Thompson CB, Bar-Sagi D, Davis RJ: The Bax subfamily of Bcl2-related proteins is essential for apoptotic signal transduction by c-Jun NH(2)-terminal kinase. Mol Cell Biol. 2002, 22: 4929-4942.View ArticlePubMedPubMed CentralGoogle Scholar
- Fasano E, Serini S, Piccioni E, Toesca A, Monego G, Cittadini AR, Ranelletti FO, Calviello G: DHA induces apoptosis by altering the expression and cellular location of GRP78 in colon cancer cell lines. Biochim Biophys Acta. 1822, 2012: 1762-1772.Google Scholar
- Lu IF, Hasio AC, Hu MC, Yang FM, Su HM: Docosahexaenoic acid induces proteasome-dependent degradation of estrogen receptor alpha and inhibits the downstream signaling target in MCF-7 breast cancer cells. J Nutr Biochem. 2010, 21: 512-517.View ArticlePubMedGoogle Scholar
- Serini S, Trombino S, Oliva F, Piccioni E, Monego G, Resci F, Boninsegna A, Picci N, Ranelletti FO, Calviello G: Docosahexaenoic acid induces apoptosis in lung cancer cells by increasing MKP-1 and down-regulating p-ERK1/2 and p-p38 expression. Apoptosis. 2008, 13: 1172-1183.View ArticlePubMedGoogle Scholar
- Sun H, Hu Y, Gu Z, Owens RT, Chen YQ, Edwards IJ: Omega-3 fatty acids induce apoptosis in human breast cancer cells and mouse mammary tissue through syndecan-1 inhibition of the MEK-Erk pathway. Carcinogenesis. 2011, 32: 1518-1524.View ArticlePubMedPubMed CentralGoogle Scholar
- Watkins SM, Carter LC, German JB: Docosahexaenoic acid accumulates in cardiolipin and enhances HT-29 cell oxidant production. J Lipid Res. 1998, 39: 1583-1588.PubMedGoogle Scholar
- Tobiume K, Matsuzawa A, Takahashi T, Nishitoh H, Morita K, Takeda K, Minowa O, Miyazono K, Noda T, Ichijo H: ASK1 is required for sustained activations of JNK/p38 MAP kinases and apoptosis. EMBO Rep. 2001, 2: 222-228.View ArticlePubMedPubMed CentralGoogle Scholar
- Yang TC, Lai CC, Shiu SL, Chuang PH, Tzou BC, Lin YY, Tsai FJ, Lin CW: Japanese encephalitis virus down-regulates thioredoxin and induces ROS-mediated ASK1-ERK/p38 MAPK activation in human promonocyte cells. Microbes Infect. 2010, 12: 643-651.View ArticlePubMedGoogle Scholar
- The pre-publication history for this paper can be accessed here:http://www.biomedcentral.com/1471-2407/14/481/prepub
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