An Integrative Analysis of Transcriptome and Epigenome Features of ASCL1–Positive Lung Adenocarcinomas

Abstract

Introduction: A subgroup of lung adenocarcinoma shows neuroendocrine differentiation and expression of achaete-scute family bHLH transcription factor 1 (ASCL1), common to high-grade neuroendocrine tumors, small-cell lung cancer and large cell neuroendocrine carcinoma. Methods: The aim of this study was to characterize clinical and molecular features of ASCL1-positive lung adenocarcinoma by using recent transcriptome profiling in multiple patient cohorts and genome-wide epigenetic profiling including data from The Cancer Genome Atlas. Results: The ASCL1-positive subtype of lung adenocarcinoma developed preferentially in current or former smokers and usually did not harbor EGFR mutations. In transcriptome profiling, this subtype overlapped with the recently proposed proximal-proliferative molecular subtype. Gene expression profiling of ASCL1-positive cases suggested generally poor immune cell infiltration and none of the tumors were positive for programmed cell death ligand 1 protein expression. Genome-wide methylation analysis showed global DNA hypomethylation in ASCL1-positive cases. ASCL1 was associated with super-enhancers in ASCL1-positive lung adenocarcinoma cells, and ASCL1 silencing suppressed other super-enhancer-associated genes, suggesting that ASCL1 acts as a master transcriptional regulator. This was further reinforced by the essential roles of ASCL1 in cell proliferation, survival, and cell cycle control. Conclusions: These results suggest that ASCL1 defines a subgroup of lung adenocarcinoma with distinct molecular features by driving super-enhancer-mediated transcriptional programs.