Systematic In Vivo Inactivation of Chromatin-Regulating Enzymes Identifies Setd2 as a Potent Tumor Suppressor in Lung Adenocarcinoma

Chromatin-modifying genes are frequently mutated in human lung adenocarcinoma, but the functional impact of these mutations on disease initiation and progression is not well understood. Using a CRISPR-based approach, we systematically inactivated three of the most commonly mutated chromatin regulatory genes in two KrasG12D-driven mouse models of lung adenocarcinoma to characterize the impact of their loss. Targeted inactivation of SWI/SNF nucleosome–remodeling complex members Smarca4 (Brg1) or Arid1a had complex effects on lung adenocarcinoma initiation and progression. Loss of either Brg1 or Arid1a were selected against in early-stage tumors, but Brg1 loss continued to limit disease progression over time, whereas loss of Arid1a eventually promoted development of higher grade lesions. In contrast to these stage-specific effects, loss of the histone methyltransferase Setd2 had robust tumor-promoting consequences. Despite disparate impacts of Setd2 and Arid1a loss on tumor development, each resulted in a gene expression profile with significant overlap. Setd2 inactivation and subsequent loss of H3K36me3 led to the swift expansion and accelerated progression of both early- and late-stage tumors. However, Setd2 loss per se was insufficient to overcome a p53-regulated barrier to malignant progression, nor establish the prometastatic cellular states that stochastically evolve during lung adenocarcinoma progression. Our study uncovers differential and context-dependent effects of SWI/SNF complex member loss, identifies Setd2 as a potent tumor suppressor in lung adenocarcinoma, and establishes model systems to facilitate further study of chromatin deregulation in lung cancer. Cancer Res; 77(7); 1719–29. ©2017 AACR.

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