title: Imiquimod-induced AMPK activation causes translation attenuation and apoptosis but not autophagy.
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.
  
  
  CONCLUSIONS
  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.affiliation: Institute of Biomedical Sciences, National Chung Hsing University, Taichung, Taiwan.
authors.forename: Sin-Ting
authors.initials: ST
authors.lastname: Wang
authors.affiliation: Institute of Biomedical Sciences, National Chung Hsing University, Taichung, Taiwan.
authors.forename: Shi-Wei
authors.initials: SW
authors.lastname: Huang
authors.affiliation: Institute of Biomedical Sciences, National Chung Hsing University, Taichung, Taiwan; Department of Pediatrics, Children's Hospital, Changhua Christian Hospital, Changhua, Taiwan.
authors.forename: Jun-Kai
authors.initials: JK
authors.lastname: Kao
authors.affiliation: Agricultural Biotechnology Research Center, Academia Sinica, Taipei, Taiwan.
authors.forename: Shu-Mei
authors.initials: SM
authors.lastname: Liang
authors.affiliation: Department of Dermatology, Taichung Veterans General Hospital, Taichung, Taiwan.
authors.forename: Yi-Ju
authors.initials: YJ
authors.lastname: Chen
authors.affiliation: Institute of Biomedical Sciences, National Chung Hsing University, Taichung, Taiwan.
authors.forename: Yu-Yu
authors.initials: YY
authors.lastname: Chen
authors.affiliation: Division of Gastroenterology and Hepatology, Taichung Veterans General Hospital, Taichung, Taiwan. Electronic address: chun@vghtc.gov.tw.
authors.forename: Chun-Ying
authors.initials: CY
authors.lastname: Wu
authors.affiliation: 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.
authors.forename: Jeng-Jer
authors.initials: JJ
authors.lastname: Shieh
mesh_terms: D000091162:AMP-Activated Protein Kinase Kinases; D055372:AMP-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D000634:Aminoquinolines / Q000494:pharmacology*; D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D001343:Autophagy / Q000187:drug effects; D002280:Basal Cell Carcinoma / Q000188:drug therapy / Q000378:metabolism*; D002294:Carcinoma, Squamous Cell / Q000188:drug therapy / Q000378:metabolism*; D045744:Cell Line, Tumor; D015536:Down-Regulation; D004789:Enzyme Activation / Q000187:drug effects; D020868:Gene Silencing; D006801:Humans; D000077271:Imiquimod; D008545:Melanoma / Q000188:drug therapy / Q000378:metabolism*; D064549:Myeloid Cell Leukemia Sequence 1 Protein / Q000235:genetics / Q000378:metabolism; D053594:Myeloid Differentiation Factor 88 / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D014176:Protein Biosynthesis / Q000187:drug effects*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D015398:Signal Transduction; D012878:Skin Neoplasms / Q000188:drug therapy / Q000378:metabolism*; D051199:Toll-Like Receptor 7 / Q000378:metabolism; D051200:Toll-Like Receptor 8 / Q000378:metabolism
chemical_list: D000634:Aminoquinolines; D000970:Antineoplastic Agents; C579095:MCL1 protein, human; C507779:MYD88 protein, human; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D053594:Myeloid Differentiation Factor 88; C495348:TLR7 protein, human; C495349:TLR8 protein, human; D051199:Toll-Like Receptor 7; D051200:Toll-Like Receptor 8; D000255:Adenosine Triphosphate; D017346:Protein Serine-Threonine Kinases; C109790:STK11 protein, human; D000091162:AMP-Activated Protein Kinase Kinases; D055372:AMP-Activated Protein Kinases; D000077271:Imiquimod
keywords: AMPK; Apoptosis; Autophagy; Imiquimod