title: Caffeine induces apoptosis by enhancement of autophagy via PI3K/Akt/mTOR/p70S6K inhibition.
abstract: Caffeine is one of the most frequently ingested neuroactive compounds. All known mechanisms of apoptosis induced by caffeine act through cell cycle modulation or p53 induction. It is currently unknown whether caffeine-induced apoptosis is associated with other cell death mechanisms, such as autophagy. Herein we show that caffeine increases both the levels of microtubule-associated protein 1 light chain 3-II and the number of autophagosomes, through the use of western blotting, electron microscopy and immunocytochemistry techniques. Phosphorylated p70 ribosomal protein S6 kinase (Thr389), S6 ribosomal protein (Ser235/236), 4E-BP1 (Thr37/46) and Akt (Ser473) were significantly decreased by caffeine. In contrast, ERK1/2 (Thr202/204) was increased by caffeine, suggesting an inhibition of the Akt/mTOR/p70S6K pathway and activation of the ERK1/2 pathway. Although insulin treatment phosphorylated Akt (Ser473) and led to autophagy suppression, the effect of insulin treatment was completely abolished by caffeine addition. Caffeine-induced autophagy was not completely blocked by inhibition of ERK1/2 by U0126. Caffeine induced reduction of mitochondrial membrane potentials and apoptosis in a dose-dependent manner, which was further attenuated by the inhibition of autophagy with 3-methyladenine or Atg7 siRNA knockdown. Furthermore, there was a reduced number of early apoptotic cells (annexin V positive, propidium iodide negative) among autophagy-deficient mouse embryonic fibroblasts treated with caffeine than their wild-type counterparts. These results support previous studies on the use of caffeine in the treatment of human tumors and indicate a potential new target in the regulation of apoptosis.
authors.affiliation: Department of Neurology, Juntendo University School of Medicine; Bunkyo, Tokyo, Japan.
authors.forename: Shinji
authors.initials: S
authors.lastname: Saiki
authors.forename: Yukiko
authors.initials: Y
authors.lastname: Sasazawa
authors.forename: Yoko
authors.initials: Y
authors.lastname: Imamichi
authors.forename: Sumihiro
authors.initials: S
authors.lastname: Kawajiri
authors.forename: Takahiro
authors.initials: T
authors.lastname: Fujimaki
authors.forename: Isei
authors.initials: I
authors.lastname: Tanida
authors.forename: Hiroki
authors.initials: H
authors.lastname: Kobayashi
authors.forename: Fumiaki
authors.initials: F
authors.lastname: Sato
authors.forename: Shigeto
authors.initials: S
authors.lastname: Sato
authors.forename: Ken-Ichi
authors.initials: K
authors.lastname: Ishikawa
authors.forename: Masaya
authors.initials: M
authors.lastname: Imoto
authors.forename: Nobutaka
authors.initials: N
authors.lastname: Hattori
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D001343:Autophagy / Q000187:drug effects*; D002110:Caffeine / Q000737:chemistry / Q000494:pharmacology*; D045744:Cell Line, Tumor; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D008247:Lysosomes / Q000187:drug effects / Q000378:metabolism; D008561:Membrane Fusion / Q000187:drug effects; D051379:Mice; D010588:Phagosomes / Q000187:drug effects / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors* / Q000378:metabolism; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000037:antagonists & inhibitors* / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors*
chemical_list: D002110:Caffeine; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D051057:Proto-Oncogene Proteins c-akt; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D020123:Sirolimus; D058570:TOR Serine-Threonine Kinases