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

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.