Sang-Hun Kim1, Kyo-Min Son2, Kwang-Youn Kim3, Sun-Nyoung Yu1, Sul-Gi Park1, Young-Wook Kim1, Hyo-Won Nam1, Jeung-Tak Suh4, Jae-Hoon Ji5, Soon-Cheol Ahn6. 1. Department of Microbiology & Immunology, Pusan National University School of Medicine, Yangsan, Republic of Korea. 2. Department of Orthopedic Surgery, Hana Hospital, Changwon, Republic of Korea. 3. Department of Herbal Formula, Medical Research Center (MRC-GHF), College of Oriental Medicine, Daegu Haany University, Gyeongsan, Republic of Korea. 4. Department of Orthopedic Surgery, Pusan National University School of Medicine, Busan, Republic of Korea. 5. Genomic Instability Research Center, Ajou University School of Medicine, Suwon, Republic of Korea. Electronic address: jij@ajou.ac.kr. 6. Department of Microbiology & Immunology, Pusan National University School of Medicine, Yangsan, Republic of Korea; Immunoregulatory Therapeutics Group in Brain Busan 21 Project, Pusan National University, Yangsan, Republic of Korea. Electronic address: ahnsc@pusan.ac.kr.
Abstract
BACKGROUND: A natural compound deoxypodophyllotoxin (DPT) possesses potent anti-proliferative and anti-tumor properties on several cancer types. It triggers cell cycle arrest followed by apoptosis through various cellular processes. However, it is limited to the action mechanism of DPT-mediated cell death modes via apoptosis and autophagy. METHODS: Cell viability assay, morphological changes, annexin-V/propidium iodide (PI) assay, reactive oxygen species (ROS), acridine orange staining, and Western blot analyses were evaluated. RESULTS: We demonstrated that DPT induced both apoptosis and autophagy via production of mitochondrial reactive oxygen species (ROS). DPT suppressed the PI3K/AKT/mTOR signaling cascades to lead autophagy process, resulting from conversion of light chain 3-I (LC3-I) into LC3-II and acidic vesicular organelles (AVOs) formation. Even if DPT-induced ROS were occurred in both apoptosis and autophagy, inhibition of ROS generation enhanced cell viability. Otherwise, 3-methyladeine (3-MA) impeding on autophagy accelerated an apoptotic response caused by DPT. Therefore, these findings suggest that DPT triggers cytoprotective autophagy against cytotoxic apoptosis. CONCLUSION: Autophagy is required for cell survival by inhibition of apoptosis through down-regulation of PI3K/AKT/mTOR pathway against DPT-induced apoptosis in U2OS cells.
BACKGROUND: A natural compound deoxypodophyllotoxin (DPT) possesses potent anti-proliferative and anti-tumor properties on several cancer types. It triggers cell cycle arrest followed by apoptosis through various cellular processes. However, it is limited to the action mechanism of DPT-mediated cell death modes via apoptosis and autophagy. METHODS: Cell viability assay, morphological changes, annexin-V/propidium iodide (PI) assay, reactive oxygen species (ROS), acridine orange staining, and Western blot analyses were evaluated. RESULTS: We demonstrated that DPT induced both apoptosis and autophagy via production of mitochondrial reactive oxygen species (ROS). DPT suppressed the PI3K/AKT/mTOR signaling cascades to lead autophagy process, resulting from conversion of light chain 3-I (LC3-I) into LC3-II and acidic vesicular organelles (AVOs) formation. Even if DPT-induced ROS were occurred in both apoptosis and autophagy, inhibition of ROS generation enhanced cell viability. Otherwise, 3-methyladeine (3-MA) impeding on autophagy accelerated an apoptotic response caused by DPT. Therefore, these findings suggest that DPT triggers cytoprotective autophagy against cytotoxic apoptosis. CONCLUSION: Autophagy is required for cell survival by inhibition of apoptosis through down-regulation of PI3K/AKT/mTOR pathway against DPT-induced apoptosis in U2OS cells.