Abstract 5185: Squamous cell cancers and chronic obstructive pulmonary disease share polycomb repressive cComplex 2 dysregulation
Authors: Aria L. Byrd, Christine F. Brainson
Journal: Cancer Research (2019)

Abstract Non-small cell lung cancers often share the aberrant differentiation patterns observed in the bronchiolar epithelium of chronic obstructive pulmonary disease (COPD), including squamous and mucinous phenotypes. Additionally, smokers with COPD are 3.5 times more likely to develop squamous lung cancer than smokers with pathologically normal lung epithelium. The Polycomb Repressive Complex 2 (PRC2), which contains the methyltransferase EZH2, mediates proper cell differentiation via tri-methylation of histone H3 at lysine 27 (H3K27me3), leading to epigenetic silencing of genomic regions. Our previous data demonstrate that squamous lung cancers often have low H3K27me3. Therefore, we hypothesized that loss of proper PRC2-mediated gene repression changes lung epithelial cell fate and drives squamous and mucinous phenotypes in COPD as well. To examine this hypothesis, we stained lung tissue from healthy patients and patients with COPD for H3K27me3 and observed that areas of squamous and mucinous metaplasia had a significantly decreased abundance of nuclear H3K27me3 stain. To demonstrate that this effect was due to loss of EZH2 activity, EZH2 transcripts were knocked down with short hairpins in human bronchiolar epithelial cells. When grown in air-liquid-interface cultures, shEZH2 cells had significantly more goblet cells and significantly fewer club cells than control cultures. We also tested this hypothesis in genetically engineered mice in which we could conditionally delete Ezh2. To examine growth, differentiation and self-renewal potentials of different lung epithelial cells, we FACS-isolated distal lung bronchioalveolar stem cells (BASCs) and cultured them as organoids. We observed a 2-fold decrease in organoid number of Ezh2 null vs wild type bronchiolar cells and a significant difference in organoid diameter between Ezh2 wild type, heterozygous and null bronchiolar cells. Organoids with squamous morphology were only seen in the Ezh2 null genotype. Lastly, we performed Gene Set Enrichment Analysis and found that genes up-regulated in human COPD patients relative to healthy smokers were also up-regulated in murine EZH2 knock-out adenocarcinoma cells. Together, these data suggest that loss of proper PRC2-mediated gene silencing is a shared epigenetic state in COPD and squamous lung cancers. Our laboratory is actively investigating the mechanisms through which EZH2 activity is lost in bronchiolar epithelium and plan to use our knowledge in attempt to ‘renormalize’ dysregulated epithelium to a more normal epigenetic state. Funded by American Cancer Society IRG-85-001-25, K22 CA20103 and Molecular Mechanisms of Toxicity Training Grant T32ES07266 Citation Format: Aria L. Byrd, Christine F. Brainson. Squamous cell cancers and chronic obstructive pulmonary disease share polycomb repressive cComplex 2 dysregulation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 5185.