Autophagy suppresses Ras-driven epithelial tumourigenesis by limiting the accumulation of reactive oxygen species

Abstract

Activation of Ras signalling occurs in ~30% of human cancers; however, activated Ras alone is not sufficient for tumourigenesis. In a screen for tumour suppressors that cooperate with oncogenic Ras (RasV12) in Drosophila, we identified genes involved in the autophagy pathway. Bioinformatic analysis of human tumours revealed that several core autophagy genes, including GABARAP, correlate with oncogenic KRAS mutations and poor prognosis in human pancreatic cancer, supporting a potential tumour-suppressive effect of the pathway in Ras-driven human cancers. In Drosophila, we demonstrate that blocking autophagy at any step of the pathway enhances RasV12-driven epithelial tissue overgrowth via the accumulation of reactive oxygen species and activation of the Jun kinase stress response pathway. Blocking autophagy in RasV12 clones also results in non-cell-autonomous effects with autophagy, cell proliferation and caspase activation induced in adjacent wild-type cells. Our study has implications for understanding the interplay between perturbations in Ras signalling and autophagy in tumourigenesis, which might inform the development of novel therapeutics targeting Ras-driven cancers.

Tumor-promoting function of apoptotic caspases by an amplification loop involving ROS, macrophages and JNK in Drosophila

“…The ROS indicator dihydroethidium (DHE) strongly labels scrib −/− Ras V12 mutant clones in mosaic discs, while wild-type (wt), scrib −/− and Ras V12 -expressing clones are not labeled by DHE or very little ( Figure 1A–D’ ; quantified in Figure 1F ; see also Figure 2A,A’ ). Similar results were reported recently ( Katheder et al, 2017 ; Manent et al, 2017 ). A different ROS indicator, H 2 DCF-DA, confirms these results ( Figure 1—figure supplement 1A–C,G ).…”

A genome-wide Drosophila epithelial tumorigenesis screen identifies Tetraspanin 29Fb as an evolutionarily conserved suppressor of Ras-driven cancer

“…In these confirmation assays, downregulation of eighty out of the 100 retested genes resulted in increased hyperplasia of the eye epithelium, using an arbitrary cut off of an average score of 0.75 or above, specifically in the presence of constitutively activated dRas V12 ( Fig 3B and 3C ; S5 Table ). It should be noted that although some of the RNAi lines tested were KK RNAi lines (indicated by KK in S5 Table ), some of which may overexpress the tiptop ( tio ) gene and result in potentially aberrant effects [ 27 ], we have previously shown that tio overexpression does not modify the ey>dRas V12 phenotype [ 28 ]. Thus, the results from the KK lines tested, which mostly confirmed the results of GD lines, are valid.…”

“…Interestingly, several genes and pathways identified in our primary screen have an effect on oxidative stress levels or proper mitochondrial function: detoxifying enzymes such as Gutathione S Transferases or Wwox [ 64 ], and many mitochondrial genes, the loss of which can potentially impede proper mitochondrial function and generate oxidative stress. Interestingly, we have recently shown that increased oxidative stress levels induced by autophagy impairment can indeed cooperate with oncogenic Ras by triggering the JNK stress response pathway [ 28 ].…”

Autophagy inhibition specifically promotes epithelial-mesenchymal transition and invasion in RAS-mutated cancer cells

“…Autophagy has a double-edged sword effect in cancer [2,3]. Autophagy's tumor suppressive function is partly attributed to its ability to induce cell death via several mechanisms [4,5]; however, a positive role of autophagy in tumorigenesis has also been established. Emerging studies have shown that the RAS signalling pathway is one of the oncogenic pathways influenced by autophagic activity [6][7][8][9][10][11][12].…”