Journal
AUTOPHAGY
Volume 14, Issue 6, Pages 958-971Publisher
TAYLOR & FRANCIS INC
DOI: 10.1080/15548627.2018.1434471
Keywords
ATG7; autophagy; caspase-9; HSP90; lung cancer
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Funding
- US Department of Veterans Affairs Biomedical Laboratory Research and Development [I01 BX002307]
- Department of Defense Grant [W81XWH-15-1-0048, W81XWH-16-1-0213]
- NIH [R21 CA187466]
- LUNGevity Foundation
- [UPCI LUNG SPORE CDA P50CA090440]
- [P30CA047904]
- NATIONAL CANCER INSTITUTE [P30CA047904, R21CA187466] Funding Source: NIH RePORTER
- Veterans Affairs [I01BX002307] Funding Source: NIH RePORTER
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Macroautophagy/autophagy has emerged as a resistance mechanism to anticancer drug treatments that induce metabolic stress. Certain tumors, including a subset of KRAS-mutant NSCLCs have been shown to be addicted to autophagy, and potentially vulnerable to autophagy inhibition. Currently, autophagy inhibition is being tested in the clinic as a therapeutic component for tumors that utilize this degradation process as a drug resistance mechanism. The current study provides evidence that HSP90 (heat shock protein 90) inhibition diminishes the expression of ATG7, thereby impeding the cellular capability of mounting an effective autophagic response in NSCLC cells. Additionally, an elevation in the expression level of CASP9 (caspase 9) prodomain in KRAS-mutant NSCLC cells surviving HSP90 inhibition appears to serve as a cell survival mechanism. Initial characterization of this survival mechanism suggests that the altered expression of CASP9 is mainly ATG7 independent; it does not involve the apoptotic activity of CASP9; and it localizes to a late endosomal and pre-lysosomal phase of the degradation cascade. HSP90 inhibitors are identified here as a pharmacological approach for targeting autophagy via destabilization of ATG7, while an induced expression of CASP9, but not its apoptotic activity, is identified as a resistance mechanism to the cellular stress brought about by HSP90 inhibition.
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