Autophagy modulates lipid metabolism in Liver Kinase B1 (LKB1)‐deficient Kras‐driven lung tumorigenesis

Abstract

Tumor suppressor liver kinase B1 (LKB1) activates 5′‐adenosine monophosphate protein kinase (AMPK) to maintain energy homeostasis. LKB1 mutations are the third most frequent mutation detected in non‐small cell lung cancer (NSCLC). Compared to p53 mutation, mutations in LKB1 causes more aggressive tumor growth and resistance to chemotherapy as well as immunotherapy. Thus, identifying a novel target to improve LKB1‐deficient NSCLC treatment is urgently needed. Autophagy degrades and recycles macromolecules for cells to survive starvation. Using genetically engineered mouse models for NSCLC with Kras activation and LKB1 loss (KL), we found that autophagy (Atg7) deficiency prevents tumor initiation, reduced tumor growth and extended the mouse lifespan compared to mice bearing Atg7 wild‐type (WT) tumors. Most importantly, tumor growth inhibition by Atg7 deficiency was much more dramatic in KL than Kras/p53 (KP) lung tumors. Furthermore, we generated mouse tumor‐derived cell lines (TDCLs) and found that Atg7 null TDCLs were more sensitive to starvation‐induced cell death than Atg7 WT TDCLs, which can be rescued by palmitate supplementation, indicating that autophagy is required to maintain free fatty acid (FA) level for cells to survive starvation. We further performed 13C glucose tracing study and found that Atg7 deletion increased de novo FA synthesis and reduced FAs elongation. Fasnall, a selective FA synthase inhibitor, inhibited Atg7 null cell proliferation. Treatment with Orlistat, a lipase inhibitor, did not impact cell proliferation in nutrient‐rich conditions but accelerated starvation‐induced Atg7 null cell death, indicating that lipase‐medicated lipid degradation compensates for autophagy loss to provide free FAs in starvation. A carnitine palmitoyltransferase I inhibitor, Etomoxir treatment, accelerated the starvation‐induced Atg7 null cell death and reduced oxygen consumption rate (OCR) of Atg7 null cells in starvation, compared with Atg7 WT cells, indicating that autophagy‐deficient cells rely more on FA oxidation for energy production in nutrient deprivation. To probe the significance of autophagy in human lung cancer cell lines with LKB1 mutation, we knocked down ATG7 using siRNA. ATG7 knockdown (KD) inhibited clonogenic survival of LKB1 mutant cells in starvation but had no effect in LKB1 WT cells. Supplementation of glutamine or palmitate rescued the survival of LKB1 mutant cells with ATG7 KD in starvation and maintained OCR, demonstrating that KRAS‐driven human lung cancer cells with mutant LKB1 rely on autophagy to maintain mitochondrial metabolism to survive energy crises. Taken together, our results demonstrate that autophagy modulates lipid metabolism for KL cells to survive metabolic stress. Thus, a combination of autophagy inhibition with interruption of lipid metabolism could be a novel therapeutic strategy to specifically treat LKB1‐deficient NSCLC.Support or Funding InformationThis research has been supported by the research funds from K22 CA190521 (NIH) grant, American Cancer Society Early Investigator Pilot Award, Lung Cancer Research Foundation grant and startup funding from Rutgers Cancer Institute of New Jersey.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.