Carcinoma cells activate AMP-activated protein kinase-dependent autophagy as survival response to kaempferol-mediated energetic impairment.
Kaempferol, a dietary cancer chemopreventive polyphenol, has been reported to trigger apoptosis in several tumor histotypes, but the mechanism underlying this phenomenon is not fully understood. Here, we demonstrate that in HeLa cells, kaempferol induces energetic failure due to inhibition of both glucose uptake and Complex I of the mitochondrial respiratory chain. As adaptive response, cells activate autophagy, the occurrence of which was established cytofluorometrically, upon acridine orange staining, and immunochemically, by following the increase of the autolysosome-associated form of the microtubule-associated protein light chain 3 (LC3-II). Autophagy is an early and reversible process occurring as survival mechanisms against apoptosis. Indeed, chemical inhibition of autophagy, by incubations with monensin, wortmannin, 3-methyladenine, or by silencing Atg5, significantly increases the extent of apoptosis, which takes place via the mitochondrial pathway, and shortens the time in which the apoptotic markers are detectable. We also demonstrate that autophagy depends on the early activation of the AMP-activated protein kinase (AMPK)/mTOR-mediated pathway. The overexpression of dominant negative AMPK results in a decrease of autophagic cells, a decrement of LC3-II levels, and a significant increase of apoptosis. Experiments performed with another carcinoma cell line yielded the same results, suggesting for kaempferol a unique mechanism of action.
Filomeni
Giuseppe
G
Department of Biology, University of Rome Tor Vergata, Rome, Italy.
Desideri
Enrico
E
Cardaci
Simone
S
Graziani
Ilaria
I
Piccirillo
Sara
S
Rotilio
Giuseppe
G
Ciriolo
Maria R
MR
D055372:AMP-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism*; D001343:Autophagy / Q000502:physiology*; D049109:Cell Proliferation / Q000187:drug effects; D019069:Cell Respiration / Q000187:drug effects; D002470:Cell Survival; D004734:Energy Metabolism / Q000187:drug effects*; D004789:Enzyme Activation; D005947:Glucose / Q000378:metabolism; D006367:HeLa Cells / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D044949:Kaempferols / Q000494:pharmacology*; D008928:Mitochondria / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D010085:Oxidative Phosphorylation / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism; D058570:TOR Serine-Threonine Kinases
D047908:Intracellular Signaling Peptides and Proteins; D044949:Kaempferols; D017382:Reactive Oxygen Species; C006552:kaempferol; C546842:MTOR protein, human; D017346:Protein Serine-Threonine Kinases; D058570:TOR Serine-Threonine Kinases; D020928:Mitogen-Activated Protein Kinases; D055372:AMP-Activated Protein Kinases; D005947:Glucose