Autophagy is elevated in metastatic tumors and is often associated with active epithelial-to-mesenchymal transition (EMT). However, the extent to which EMT is dependent on autophagy is largely unknown. This study aimed to identify the mechanisms by which autophagy facilitates EMT.
We employed a liquid chromatography-based metabolomic approach with kirsten rat sarcoma viral oncogene (KRAS) and liver kinase B1 (LKB1) gene co-mutated (KL) cells that represent an autophagy/EMT-coactivated invasive lung cancer subtype for the identification of metabolites linked to autophagy-driven EMT activation. Molecular mechanisms of autophagy-driven EMT activation were further investigated by quantitative real-time polymerase chain reaction (qRT-PCR), Western blotting analysis, immunoprecipitation, immunofluorescence staining, and metabolite assays. The effects of chemical and genetic perturbations on autophagic flux were assessed by two orthogonal approaches: microtubule-associated protein 1A/1B-light chain 3 (LC3) turnover analysis by Western blotting and monomeric red fluorescent protein-green fluorescent protein (mRFP-GFP)-LC3 tandem fluorescent protein quenching assay. Transcription factor EB (TFEB) activity was measured by coordinated lysosomal expression and regulation (CLEAR) motif-driven luciferase reporter assay. Experimental metastasis (tail vein injection) mouse models were used to evaluate the impact of calcium/calmodulin-dependent protein kinase kinase 2 (CAMKK2) or ATP citrate lyase (ACLY) inhibitors on lung metastasis using IVIS luciferase imaging system.
We found that autophagy in KL cancer cells increased acetyl-coenzyme A (acetyl-CoA), which facilitated the acetylation and stabilization of the EMT-inducing transcription factor Snail. The autophagy/acetyl-CoA/acetyl-Snail axis was further validated in tumor tissues and in autophagy-activated pancreatic cancer cells. TFEB acetylation in KL cancer cells sustained pro-metastatic autophagy in a mammalian target of rapamycin complex 1 (mTORC1)-independent manner. Pharmacological inhibition of this axis via CAMKK2 inhibitors or ACLY inhibitors consistently reduced the metastatic capacity of KL cancer cells in vivo.
This study demonstrates that autophagy-derived acetyl-CoA promotes Snail acetylation and thereby facilitates invasion and metastasis of KRAS-LKB1 co-mutated lung cancer cells and that inhibition of the autophagy/acetyl-CoA/acetyl-Snail axis using CAMKK2 or ACLY inhibitors could be a potential therapeutic strategy to suppress metastasis of KL lung cancer.