Is an Epigenetically Regulated Tumor Suppressor Essential for Activation of the DNA Damage Response

Lung cancer is the leading cause of cancer-related death in the United States. Long noncoding RNAs (lncRNA) are a class of regulatory molecules whose role in lung carcinogenesis is poorly understood. In this study, we profiled lncRNA expression in lung adenocarcinoma (LUAD) cell lines, compared their expression with that of purified alveolar epithelial type II cells (the purported cell of origin for LUAD), cross-referenced these with lncRNAs altered in the primary human tumors, and interrogated for lncRNAs whose expression correlated with patient survival. We identified , a lncRNA with unknown function in LUAD, adjacent to the pioneering transcription factor FOXA2. Loss of was observed in multiple tumor types, including liver, breast, and gastric cancer. Reintroduction of into human LUAD cell lines inhibited cell migration and slowed proliferation by inducing G-M cell-cycle arrest, while upregulating DNA damage pathway genes and inducing phosphorylation-mediated activation of components of the DNA damage pathway. FOXA2 was able to induce expression, and the entire locus underwent hypermethylation in LUAD, leading to loss of expression. We have thus identified an epigenetically deregulated lncRNA, whose loss of expression in LUAD promotes the malignant phenotype and blocks activation of the DNA damage machinery, predisposing lung cells to cancer development. SIGNIFICANCE: These findings identify as a tumor suppressor that blocks cellular proliferation by activating the DNA damage response and suggest that epigenetic therapy to inhibit DNA methylation may enhance treatment of LUAD. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/79/12/3050/F1.large.jpg..