Sin-Ting Wang1, Shi-Wei Huang1, Jun-Kai Kao2, Shu-Mei Liang3, Yi-Ju Chen4, Yu-Yu Chen1, Chun-Ying Wu5, Jeng-Jer Shieh6. 1. Institute of Biomedical Sciences, National Chung Hsing University, Taichung, Taiwan. 2. Institute of Biomedical Sciences, National Chung Hsing University, Taichung, Taiwan; Department of Pediatrics, Children's Hospital, Changhua Christian Hospital, Changhua, Taiwan. 3. Agricultural Biotechnology Research Center, Academia Sinica, Taipei, Taiwan. 4. Department of Dermatology, Taichung Veterans General Hospital, Taichung, Taiwan. 5. Division of Gastroenterology and Hepatology, Taichung Veterans General Hospital, Taichung, Taiwan. Electronic address: chun@vghtc.gov.tw. 6. Institute of Biomedical Sciences, National Chung Hsing University, Taichung, Taiwan; Department of Education and Research, Taichung Veterans General Hospital, Taichung, Taiwan; Rong Hsing Research Center for Translational Medicine, National Chung Hsing University, Taichung, Taiwan. Electronic address: shiehjj@vghtc.gov.tw.
Abstract
BACKGROUND: AMP-activated protein kinase (AMPK), a principal intracellular energy sensor, plays a crucial role in cell growth, proliferation, apoptosis and autophagy. Imiquimod (IMQ) directly exhibits anti-tumor activity through the induction of apoptosis and autophagic cell death. OBJECTIVE: To evaluate the role of AMPK in IMQ-induced apoptosis and autophagy. METHODS: The phosphorylation of AMPK and its substrates was detected by immunoblotting. ATP contents were analyzed by an ATP bioluminescence assay. The upstream signaling for AMPK activation was dissected by examination of TLR7/8 expression, over-expression of TLR7/8, the addition of AMPK kinase inhibitors, and the genetic silencing of Myd88 and LKB1. The role of AMPK activation in IMQ-induced autophagy and apoptosis was assessed by inhibiting AMPK, genetically silencing AMPK and over-expressing AMPK dominant-negative mutants. Autophagy and apoptosis were evaluated by a DNA content assay, immunoblotting, EGFP-LC3 puncta detection and acridine orange staining. RESULTS: IMQ could activate AMPK and autophagy in cancer cells not expressing TLR7/8. IMQ caused ATP depletion and induced LKB1-mediated AMPK activation. The down-regulation of AMPK activity via pharmacological inhibition and genetic silencing resulted in reduced IMQ-induced apoptosis but did not influence autophagy, and this rescue effect was associated with the retention of translation factor activity and anti-apoptotic Bcl-2 family member Mcl-1 protein expression levels. CONCLUSION: IMQ induces AMPK activation independent of TLR7/8 expression, resulting in translation inhibition and subsequent apoptosis through ATP depletion and LKB1 signaling, in skin tumor cells.
BACKGROUND:AMP-activated protein kinase (AMPK), a principal intracellular energy sensor, plays a crucial role in cell growth, proliferation, apoptosis and autophagy. Imiquimod (IMQ) directly exhibits anti-tumor activity through the induction of apoptosis and autophagic cell death. OBJECTIVE: To evaluate the role of AMPK in IMQ-induced apoptosis and autophagy. METHODS: The phosphorylation of AMPK and its substrates was detected by immunoblotting. ATP contents were analyzed by an ATP bioluminescence assay. The upstream signaling for AMPK activation was dissected by examination of TLR7/8 expression, over-expression of TLR7/8, the addition of AMPK kinase inhibitors, and the genetic silencing of Myd88 and LKB1. The role of AMPK activation in IMQ-induced autophagy and apoptosis was assessed by inhibiting AMPK, genetically silencing AMPK and over-expressing AMPK dominant-negative mutants. Autophagy and apoptosis were evaluated by a DNA content assay, immunoblotting, EGFP-LC3 puncta detection and acridine orange staining. RESULTS:IMQ could activate AMPK and autophagy in cancer cells not expressing TLR7/8. IMQ caused ATP depletion and induced LKB1-mediated AMPK activation. The down-regulation of AMPK activity via pharmacological inhibition and genetic silencing resulted in reduced IMQ-induced apoptosis but did not influence autophagy, and this rescue effect was associated with the retention of translation factor activity and anti-apoptotic Bcl-2 family member Mcl-1 protein expression levels. CONCLUSION:IMQ induces AMPK activation independent of TLR7/8 expression, resulting in translation inhibition and subsequent apoptosis through ATP depletion and LKB1 signaling, in skin tumor cells.
Authors: Amanda L Patchett; Richard Wilson; Jac C Charlesworth; Lynn M Corcoran; Anthony T Papenfuss; Bruce A Lyons; Gregory M Woods; Cesar Tovar Journal: Oncotarget Date: 2018-03-23