Autophagy suppression sensitizes glioma cells to IMP dehydrogenase inhibition-induced apoptotic death.
We investigated the role of autophagy, a process of controlled self-digestion, in the in vitro anticancer action of the inosine monophosphate dehydrogenase (IMPDH) inhibitor ribavirin. Ribavirin-triggered oxidative stress, caspase activation, and apoptotic death in U251 human glioma cells were associated with the induction of autophagy, as confirmed by intracellular acidification, appearance of autophagic vesicles, conversion of microtubule associated protein 1 light chain 3 (LC3)-I to autophagosome-associated LC3-II, and degradation of autophagic target p62/sequestosome 1. Ribavirin downregulated the activity of autophagy-inhibiting mammalian target of rapamycin complex 1 (mTORC1), as indicated by a decrease in phosphorylation of the mTORC1 substrate ribosomal p70S6 kinase and reduction of the mTORC1-activating Src/Akt signaling. Guanosine supplementation inhibited, while IMPDH inhibitor tiazofurin mimicked ribavirin-mediated autophagy induction, suggesting the involvement of IMPDH blockade in the observed effect. Autophagy suppression by ammonium chloride, bafilomycin A1, or RNA interference-mediated knockdown of LC3 sensitized glioma cells to ribavirin-induced apoptosis. Ribavirin also induced cytoprotective autophagy associated with Akt/mTORC1 inhibition in C6 rat glioma cells. Our data demonstrate that ribavirin-triggered Akt/mTORC1-dependent autophagy counteracts apoptotic death of glioma cells, indicating autophagy suppression as a plausible therapeutic strategy for sensitization of cancer cells to IMPDH inhibition.
Institute of Medical and Clinical Biochemistry, School of Medicine, University of Belgrade, Pasterova 2, Belgrade, Serbia.
Andjelka M
AM
Isakovic
Institute of Medical and Clinical Biochemistry, School of Medicine, University of Belgrade, Pasterova 2, Belgrade, Serbia.
Marija
M
Dulovic
Institute of Medical and Clinical Biochemistry, School of Medicine, University of Belgrade, Pasterova 2, Belgrade, Serbia.
Ivanka
I
Markovic
Institute of Histology and Embryology, School of Medicine, University of Belgrade, Visegradska 26, 11000 Belgrade, Serbia.
Tamara
T
Kravic-Stevovic
Institute of Histology and Embryology, School of Medicine, University of Belgrade, Visegradska 26, 11000 Belgrade, Serbia.
Vladimir
V
Bumbasirevic
Institute of Microbiology and Immunology, School of Medicine, University of Belgrade, Dr. Subotica 1, 11000 Belgrade, Serbia. Electronic address: vtrajkovic@med.bg.ac.rs.
Vladimir
V
Trajkovic
Institute of Medical and Clinical Biochemistry, School of Medicine, University of Belgrade, Pasterova 2, Belgrade, Serbia. Electronic address: aisakovic@med.bg.ac.rs.
Aleksandra
A
Isakovic
D017209:Apoptosis / Q000187:drug effects*; D001343:Autophagy / Q000187:drug effects*; D045744:Cell Line, Tumor; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005910:Glioma / Q000201:enzymology* / Q000235:genetics / Q000473:pathology; D006801:Humans; D007168:IMP Dehydrogenase / Q000037:antagonists & inhibitors*; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D034622:RNA Interference; D012254:Ribavirin / Q000031:analogs & derivatives / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects
D004791:Enzyme Inhibitors; D012254:Ribavirin; D007168:IMP Dehydrogenase; D051057:Proto-Oncogene Proteins c-akt; C033706:tiazofurin
Akt; Apoptosis; Autophagy; IMP dehydrogenase; Ribavirin; mTOR