Autophagy provides metabolic substrates to maintain energy charge and nucleotide pools in Ras-driven lung cancer cells
- Jessie Yanxiang Guo1,2,3,6,
- Xin Teng4,6,
- Saurabh V. Laddha1,
- Sirui Ma1,
- Stephen C. Van Nostrand1,
- Yang Yang1,
- Sinan Khor1,
- Chang S. Chan1,2,
- Joshua D. Rabinowitz1,4 and
- Eileen White1,5
- 1Rutgers Cancer Institute of New Jersey, New Brunswick, New Jersey 08903, USA;
- 2Department of Medicine, Rutgers Robert Wood Johnson Medical School, New Brunswick, New Jersey 08901, USA;
- 3Department of Chemical Biology, Rutgers Ernest Mario School of Pharmacy, Piscataway, New Jersey 08854, USA;
- 4Department of Chemistry, Princeton University, Princeton, New Jersey 08544, USA;
- 5Department of Molecular Biology and Biochemistry, Rutgers University, Piscataway, New Jersey 08854, USA
- Corresponding authors: epwhite{at}cinj.rutgers.edu, yanxiang{at}cinj.rutgers.edu
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↵6 These authors contributed equally to this work.
Abstract
Autophagy degrades and is thought to recycle proteins, other macromolecules, and organelles. In genetically engineered mouse models (GEMMs) for Kras-driven lung cancer, autophagy prevents the accumulation of defective mitochondria and promotes malignancy. Autophagy-deficient tumor-derived cell lines are respiration-impaired and starvation-sensitive. However, to what extent their sensitivity to starvation arises from defective mitochondria or an impaired supply of metabolic substrates remains unclear. Here, we sequenced the mitochondrial genomes of wild-type or autophagy-deficient (Atg7−/−) Kras-driven lung tumors. Although Atg7 deletion resulted in increased mitochondrial mutations, there were too few nonsynonymous mutations to cause generalized mitochondrial dysfunction. In contrast, pulse-chase studies with isotope-labeled nutrients revealed impaired mitochondrial substrate supply during starvation of the autophagy-deficient cells. This was associated with increased reactive oxygen species (ROS), lower energy charge, and a dramatic drop in total nucleotide pools. While starvation survival of the autophagy-deficient cells was not rescued by the general antioxidant N-acetyl-cysteine, it was fully rescued by glutamine or glutamate (both amino acids that feed the TCA cycle and nucleotide synthesis) or nucleosides. Thus, maintenance of nucleotide pools is a critical challenge for starving Kras-driven tumor cells. By providing bioenergetic and biosynthetic substrates, autophagy supports nucleotide pools and thereby starvation survival.
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Footnotes
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Supplemental material is available for this article.
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Article published online ahead of print. Article and publication date are online at http://www.genesdev.org/cgi/doi/10.1101/gad.283416.116.
- Received June 28, 2016.
- Accepted July 22, 2016.
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