Nayeong Kim

Docosahexaenoic acid induces autophagy through p53/AMPK/mTOR signaling and promotes apoptosis in human cancer cells harboring wild-type p53

Docosahexaenoic acid (DHA) has been reported to induce tumor cell death by apoptosis. However, little is known about the effects of DHA on autophagy, another complex well-programmed process characterized by the sequestration of cytoplasmic material within autophagosomes. Here, we show that DHA increased both the level of microtubule-associated protein light-chain 3 and the number of autophagic vacuoles without impairing autophagic vesicle turnover, indicating that DHA induces not only apoptosis but also autophagy. We also observed that DHA-induced autophagy was accompanied by p53 loss. Inhibition of p53 increased DHA-induced autophagy and prevention of p53 degradation significantly led to the attenuation of DHA-induced autophagy, suggesting that DHA-induced autophagy is mediated by p53. Further experiments showed that the mechanism of DHA-induced autophagy associated with p53 attenuation involved an increase in the active form of AMP-activated protein kinase and a decrease in the activity of mammalian target of rapamycin. In addition, compelling evidence for the interplay between autophagy and apoptosis induced by DHA is supported by the findings that autophagy inhibition suppressed apoptosis and further autophagy induction enhanced apoptosis in response to DHA treatment. Overall, our results demonstrate that autophagy contributes to the cytotoxicity of DHA in cancer cells harboring wild-type p53.

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

Docosahexaenoic acid (DHA) induces autophagy-associated apoptotic cell death in wild-type p53 cancer cells via regulation of p53. The present study investigated the effects of DHA on PC3 and DU145 prostate cancer cell lines harboring mutant p53. Results show that, in addition to apoptosis, DHA increased the expression levels of lipidated form LC3B and potently stimulated the autophagic flux, suggesting that DHA induces both autophagy and apoptosis in cancer cells expressing mutant p53. DHA led to the generation of mitochondrial reactive oxygen species (ROS), as shown by the mitochondrial ROS-specific probe mitoSOX. Similarly, pretreatment with the antioxidant N-acetyl-cysteine (NAC) markedly inhibited both the autophagy and the apoptosis triggered by DHA, indicating that mitochondrial ROS mediate the cytotoxicity of DHA in mutant p53 cells. Further, DHA reduced the levels of phospho-Akt and phospho-mTOR in a concentration-dependent manner, while NAC almost completely blocked that effect. Collectively, these findings present a novel mechanism of ROS-regulated apoptosis and autophagy that involves Akt-mTOR signaling in prostate cancer cells with mutant p53 exposed to DHA.

Docosahexaenoic acid-induced apoptosis is mediated by activation of mitogen-activated protein kinases in human cancer cells

BackgroundThe 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.MethodsMTT 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.ResultsDHA 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.ConclusionTogether, 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.

Docosahexaenoic Acid Induces Cell Death in Human Non-Small Cell Lung Cancer Cells by Repressing mTOR via AMPK Activation and PI3K/Akt Inhibition

The anticancer properties and mechanism of action of omega-3 polyunsaturated fatty acids (ω3-PUFAs) have been demonstrated in several cancers; however, the mechanism in lung cancer remains unclear. Here, we show that docosahexaenoic acid (DHA), a ω3-PUFA, induced apoptosis and autophagy in non-small cell lung cancer (NSCLC) cells. DHA-induced cell death was accompanied by AMP-activated protein kinase (AMPK) activation and inactivated phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) signaling. Knocking down AMPK and overexpressing Akt increased mTOR activity and attenuated DHA-induced cell death, suggesting that DHA induces cell death via AMPK- and Akt-regulated mTOR inactivation. This was confirmed in Fat-1 transgenic mice, which produce ω3-PUFAs. Lewis lung cancer (LLC) tumor cells implanted into Fat-1 mice showed slower growth, lower phospho-Akt levels, and higher levels of apoptosis and autophagy than cells implanted into wild-type mice. Taken together, these data suggest that DHA-induced apoptosis and autophagy in NSCLC cells are associated with AMPK activation and PI3K/Akt inhibition, which in turn lead to suppression of mTOR; thus ω3-PUFAs may be utilized as potential therapeutic agents for NSCLC treatment.

Mechanism of Anti-Invasive Action of Docosahexaenoic Acid in SW480 Human Colon Cancer Cell

Colon cancer is one of the most common malignancies in the western world and the second leading cause of cancer death in Korea. Epidemiology studies have shown a reduced incidence of colon cancer among populations consuming a large quantity of ω3-polyunsaturated fatty acids (ω3-PUFA) of ma- rine origin. Recently, it has been found that ω 3-PUFA has an antineoplastic effect in several cancers. This study was designed to investigate the mechanism of the anti-invasive effect of ω3-PUFA in colon cancer. ω3-PUFA, docosahexaenoic acids (DHA) and eicosapentaenoic acid ( EPA) treatment resulted in a dose-dependent inhibition of cell growth in SW480 human colon cancer cells. In contrast, arach- idonic acid (AA), a ω6-PUFA, exhibited no significant effect. This action likely involves apoptosis, giv- en that DHA treatment increased apoptotic cells in TUNEL assay. Moreover, invasiveness of SW480 cells was inhibited following treatment of DHA in a dose-dependent manner; in contrast, AA had no effect. The levels of MMP-9 and MMP-2 mRNA decreased after DHA pretreatment. MMP-9 and MMP-2 promoter activities were also inhibited by DHA treatment. The levels of NF-kB and p-IkB pro- tein were down-regulated by DHA pretreatment in a dose dependent manner. In addition, DHA in- hibited NF-kB promoter reporter activities. These findings suggest that ω3-PUFA may inhibit cancer cell invasion by inhibition of MMPs via reduction of NF-kB in colon cancer. In conclusion, ω3-PUFA could be used for chemoprevention and treatment of human colon cancer.

138 Inhibition of MTor Through AMPK Activation and PI3K/Akt Inhibition is Important to Docosahexaenoic Acid-induced Cell Death in Human Non-small Cell Lung Cancer Cells

Introduction: Reactive oxygen species (ROS) produced by docosahexaenoic acid (DHA) have an important function in cancer cell death. However, the exact mechanism of ROS production, after DHA stimulation, is not clearly understood. Here, we determined that elevated levels of ROS generated by mitochondrial respiration is directly associated with DHA-induced cervical cancer cell death. Material and Method: The effects of DHA on cell proliferation and cell cycle were examined by MTT assay and FACS. DHA-induced apoptosis was analyzed using the TUNEL assay, caspase activity assay, and western blot. Dihydroethidium (DHE) was used for reactive oxygen species (ROS) measurement in cytosol. MitoSox was performed for ROS measurement in mitochondria. Results and Discussion: The levels of caspase 3 activity, TUNELpositive staining cells and Sub-G1 portion were markedly increased in DHA-treated cancer cells, suggesting that apoptosis is responsible for the DHA-induced cervical cancer cell death. Furthermore, DHA was able to induce both mitochondrial complex I substrateand complex II substratesupported mitochondrial ROS production in isolated mitochondria from rodent liver. Meanwhile, a reduction in oxygen consumption rate and an increase in mitochondrial ROS production as measured by MitoSOX, were also observed in DHA-treated cancer cells, indicating that DHA can directly act on mitochondrial respiration and enhance ROS generation. The role of DHA-induced mitochondrial ROS production in apoptosis was further identified by the findings that DHA reduced the mitochondrial membrane potential, resulting in cardiolipin oxidation and cytochrome c release from mitochondria, and that N-acetylcysteine, an antioxidant almost completely blocked these processes as well as ROS production occurred in mitochondria and remarkably reversed the apoptotic cell death triggered by DHA. Conclusion: From the results presented here, we conclude that mitochondria actively participate in the DHA-induced apoptotic cell death by the generation of mitochondrial ROS. This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Ministry of Education, Science and Technology (2011– 0006232 and 2011–0003060).

Abstract 2071: Docosahexaenoic acid-induced apoptosis is directly linked to mitochondria-mediated reactive oxygen species production in human cervical cancer cells

Reactive oxygen species (ROS) produced by docosahexaenoic acid (DHA) have an important function in cancer cell death. However, the exact mechanism of ROS production, after DHA stimulation, is not clearly understood. Here, we determined that elevated levels of ROS generated by mitochondrial respiration is directly associated with DHA-induced cervical cancer cell death. The levels of caspase 3 activity, TUNEL-positive staining cells and Sub-G1 portion were markedly increased in DHA-treated cancer cells, suggesting that apoptosis is responsible for the DHA-induced cervical cancer cell death. Furthermore, DHA was able to induce both mitochondrial complex I substrate- and complex II substrate-supported mitochondrial ROS production in isolated mitochondria from rodent liver. Meanwhile, a reduction in oxygen consumption rate and an increase in mitochondrial ROS production as measured by MitoSOX, were also observed in DHA-treated cancer cells, indicating that DHA can directly act on mitochondrial respiration and enhance ROS generation. The role of DHA-induced mitochondrial ROS production in apoptosis was further identified by the findings that DHA reduced the mitochondrial membrane potential, resulting in cardiolipin oxidation and cytochrome c release from mitochondria, and that N-acetylcysteine, an antioxidant almost completely blocked these processes as well as ROS production occurred in mitochondria and remarkably reversed the apoptotic cell death triggered by DHA. From the results presented here, we conclude that mitochondria actively participate in the DHA-induced apoptotic cell death by the generation of mitochondrial ROS. (This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Ministry of Education, Science and Technology (2011-0006232 and 2011-0003060)). Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2071. doi:1538-7445.AM2012-2071

Abstract 2274: Docosahexaenoic acid-induced cell death may be related to inhibition of mTOR through AMPK activation and PI3K/Akt inhibition in human non-small cell lung cancer cells

Proceedings: AACR 103rd Annual Meeting 2012‐‐ Mar 31‐Apr 4, 2012; Chicago, IL Over 80% of the lung cancer patients have non-small cell lung cancer (NSCLC). Although the anticancer mechanisms of omega-3 polyunsaturated fatty acids (≥3-PUFAs) have been reported in several cancers, it is still unclear in lung cancer. In this study, we have identified a novel anticancer effect of docosahexaenoic acid (DHA), a α3-PUFAs, on NSCLC. DHA induced cytotoxicity and morphology change in A549 and H1299 NSCLC cells and was confirmed that apoptosis and autophagy are responsible for the cytotoxicity induced by DHA. DHA increased AMPK activity and inhibited PI3K/Akt signaling as well as mTOR signaling molecules. Knockdown AMPK using small interfering RNAs specific for AMPK and overexpression Akt significantly enhanced the mTOR activity and attenuated the cell death caused by DHA treatment, indicating that DHA induces NSCLC cell death via the AMPK- and Akt-regulated mTOR inactivation. We also confirmed this effect of α3-PUFAs in vivo using Fat-1 transgenic mice that are capable of producing α3-PUFAs. When mouse lung cancer LLC cells were subcutaneously implanted into Fat-1 mice, the growth of tumor was markedly inhibited with decrease the level of p-Akt as well as increases in TUNEL-positive staining cells and autophagic levels, compared to wild-type mice. Taken together, these data suggest that the apoptosis and autophagy induced by DHA may be related to mTOR inhibition through AMPK activation and PI3K/Akt inhibition in NSCLC. Therefore, utilization of DHA may represent a potential effective therapy for the chemoprevention and treatment of human non-small cell lung cancer. [This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Ministry of Education, Science and Technology (2011-0013263 and 2011-0006232)] Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2274. doi:1538-7445.AM2012-2274

Abstract 4175: Reactive oxygen species-dependent ERK and JNK activation is important to docasahexaenoic acid-induced cell cytotoxicity in human ovarian cancer cells

Proceedings: AACR 103rd Annual Meeting 2012‐‐ Mar 31‐Apr 4, 2012; Chicago, IL Although abundant experimental evidences show that the Omega-3 polyunsaturated fatty acids (≥3-PUFAs) prevent carcinogenesis, the exact molecular mechanisms of the anti-cancer actions of α3-PUFAs in ovarian cancer remain incompletely understood. In the present study, the effectiveness of docosahexaenoic acid (DHA), a α3-PUFA, against ovarian cancer cells was investigated. We found that DHA induced cell cytotoxicity in three ovarian cancer cells including PA-1, MDAH2774 and ID8. DHA treatment inhibited the cell proliferation of PA-1 cells in a dose- and time-dependent manner. Meanwhile, DHA-treated ovarian cancer cells showed increased levels of caspase-3 activity, Annexin-V staining positive cells, TUNEL-positive cells and the portion of sub-G1 cells, suggesting that DHA-induced cell death is mainly associated with apoptosis. Western blot and immunocytochemistry assays revealed that DHA also remarkably increased the levels of phospho-ERK and phospho-JNK in both cytosol and nucleus. Moreover, knockdown ERK and JNK by small interfering RNAs partially attenuated the apoptosis induced by DHA, indicating that ERK and JNK activation is responsible for the apoptosis in DHA-treated ovarian cancer cells. In addition, we determined that the activation of ERK and JNK was associated with the reactive oxygen species (ROS) production induced by DHA. ROS scavenger, N-acetyl-L-cysteine (NAC), almost completely blocked the ERK and JNK phosphorylation as well as the apoptosis triggered by DHA. Together, these results indicate that DHA induces ROS and the ROS-dependent ERK and JNK activation is important to DHA-induced cell cytotoxicity in human ovarian cancer cells. [This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2011-0006232 and 2011-0003060)]. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4175. doi:1538-7445.AM2012-4175

Abstract 4654: Docosahexaenoic acid induces autophagy through reactive oxygen species /mTOR pathway in p53 mutant cancer cells

Our previous studies reported that docosahexaenoic acid (DHA) induces autophagy through p53 inhibition in the wild-type p53 cancer cells. This study attempts to elucidate the molecular mechanism underlying DHA-induced autophagy in PC3 and DU145 prostate cancer cells harboring mutant p53. DHA increased both the level of microtubule-associated protein light-chain 3 (LC3) and the number of autophagic vacuoles. Autophagic flux assay confirmed that DHA-induced increase in LC3-II and autophagic vesicles was an outcome of autophagic process activation, indicating that DHA also induces autophagy in p53 mutant cancer cells. DHA treatment also increased the level of reactive oxygen species (ROS) as measured by dihydroethidine staining, and pretreatment of an antioxidant, N-acetylcysteine (NAC), significantly inhibited the ROS production as well as autophagy induced by DHA, suggesting that ROS regulates the autophagic process triggered by DHA. Further experiments showed that the mechanism of DHA-induced autophagy associated with ROS production was related to a decrease in the activity of mammalian target of rapamycin (mTOR). NAC remarkably restored the decreases in the levels of phospho-mTOR and 4EBP, an mTOR downstream molecule, induced by DHA as analyzed by the Western blot assay. Furthermore, the level of phospho-AMPK, which negatively regulates mTOR was increased, while phospho-Akt was reduced during the DHA-induced autophagy, indicating the involvement of AMPK and Akt signalings. Collectively, our results demonstrate that DHA induces autophagy through the ROS-mediated mTOR inactivation in p53 mutant prostate cancer cells. This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MEST) (No. 2011-0006232]. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4654. doi:1538-7445.AM2012-4654