Inhibition of AMPK-associated autophagy enhances caffeic acid phenethyl ester-induced cell death in C6 glioma cells.
An increasing number of studies show that AMP-activated protein kinase (AMPK) activation can inhibit apoptosis. To clarify the antitumor mechanism of caffeic acid phenethyl ester (CAPE) and achieve increased therapeutic efficiency, we investigated the potential roles of AMPK and autophagy in CAPE treatment against C6 glioma cells. The roles of AMPK and autophagy inhibition in CAPE's cytotoxic action were investigated. Phosphorylation of AMPK and mitogen-activated protein kinases (MAPKs) were observed in tumor cells following CAPE treatment. A combination of CAPE and the AMPK inhibitor, compound C, resulted in augmented cell death. Similar effects of compound C were observed in response to changes in the mitochondrial membrane potential ( ΔΨ(m)). Small interfering RNA-mediated AMPK downregulation increased CAPE-induced cell death. The results suggest that AMPK activation plays a role in diminishing apoptosis. CAPE treatment induced an increase in LC3 conversion as represented by the LC3-II/LC3-I ratio. Enlarged lysosomes and autophagosomes were present according to electron microscopy. The autophagy inhibitor, 3-MA, caused increased CAPE cytotoxicity, which suggests that autophagy induction protected glioma cells from CAPE. The combination of CAPE with autophagy and AMPK inhibitors markedly enhanced the cytotoxicity toward C6 glioma cells. Accordingly, CAPE-triggered activation of AMPK and the autophagic response protected tumor cells from apoptotic death. This provides new insights for combined therapy to enhance the therapeutic potential of cancer treatments.
Graduate Institute of Medical Sciences, Taipei Medical University, Taipei, Taiwan.
Szu-Hsu
SH
Yu
Yung-Ta
YT
Kao
Jui-Yu
JY
Wu
Shih-Hao
SH
Huang
Sheng-Tung
ST
Huang
Chi-Ming
CM
Lee
Kur-Ta
KT
Cheng
Chun-Mao
CM
Lin
D055372:AMP-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000187:drug effects / Q000378:metabolism*; D000225:Adenine / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D017209:Apoptosis; D001343:Autophagy / Q000187:drug effects / Q000502:physiology*; D002109:Caffeic Acids / Q000494:pharmacology*; D016923:Cell Death / Q000187:drug effects; D045744:Cell Line, Tumor; D015536:Down-Regulation; D004357:Drug Synergism; D005910:Glioma / Q000473:pathology; D006801:Humans; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects; D020928:Mitogen-Activated Protein Kinases / Q000187:drug effects / Q000378:metabolism; D018384:Oxidative Stress; D010626:Phenylethyl Alcohol / Q000031:analogs & derivatives* / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D011720:Pyrazoles / Q000494:pharmacology*; D011743:Pyrimidines / Q000494:pharmacology*; D034741:RNA, Small Interfering / Q000378:metabolism; D051381:Rats
D002109:Caffeic Acids; D011720:Pyrazoles; D011743:Pyrimidines; D034741:RNA, Small Interfering; C516138:dorsomorphin; C025946:3-methyladenine; D020928:Mitogen-Activated Protein Kinases; D055372:AMP-Activated Protein Kinases; C055494:caffeic acid phenethyl ester; D000225:Adenine; D010626:Phenylethyl Alcohol