Loss of Aryl Hydrocarbon Receptor Favors K-Ras(G12D)-Driven Non-Small Cell Lung Cancer

SIMPLE SUMMARY: Non-small cell lung cancer (NSCLC) accounts for over 80% of the total number of lung cancers, thus having an important impact on human health worldwide. Despite the identification of different mutations in NSCLC patients, this cancer type has limited therapeutic approaches in part due to the existence of diverse mutational profiles among patients that challenges the application of effective treatments. The glycine to aspartic mutation (G to D) in the K-Ras oncogene (G12D) is a common genetic alteration considered relevant at the initial stages of NSCLC. The aryl hydrocarbon receptor Ahr, on the other hand, can either suppress or promote tumor development depending on the cell phenotype. We report here that Ahr expression can limit K-Ras(G12D)-induced NSCLC in vivo and that it does so by controlling the expansion of lung stem cells expressing pluripotency markers. Non-toxic physiological ligands for Ahr may be good tools to reduce the NSCLC burden in cases of K-Ras(G12D) activation. ABSTRACT: Non-small cell lung adenocarcinoma (NSCLC) bearing K-Ras(G12D) mutations is one of the most prevalent types of lung cancer worldwide. Aryl hydrocarbon receptor (AHR) expression varies in human lung tumors and has been associated with either increased or reduced lung metastasis. In the mouse, Ahr also adjusts lung regeneration upon injury by limiting the expansion of resident stem cells. Here, we show that the loss of Ahr enhances K-Ras(G12D)-driven NSCLC in mice through the amplification of stem cell subpopulations. Consistent with this, we show that K-Ras(G12D);Ahr(−/−) lungs contain larger numbers of cells expressing markers for both progenitor Clara (SCGB1A1 and CC10) and alveolar type-II (SFTPC) cells when compared to K-Ras(G12D);Ahr(+/+)-driven tumors. They also have elevated numbers of cells positive for pluripotent stem cells markers such as SOX2, ALDH1, EPCAM, LGR5 and PORCN. Typical pluripotency genes Nanog, Sox2 and c-Myc were also upregulated in K-Ras(G12D);Ahr(−/−) lung tumors as found by RNAseq analysis. In line with this, purified K-Ras(G12D/+);Ahr(−)/(−) lung cells generate larger numbers of organoids in culture that can subsequently differentiate into bronchioalveolar structures enriched in both pluripotency and stemness genes. Collectively, these data indicate that Ahr antagonizes K-Ras(G12D)-driven NSCLC by restricting the number of cancer-initiating stem cells. They also suggest that Ahr expression might represent a good prognostic marker to determine the progression of K-Ras(G12D)-positive NSCLC patients.