Abstract 1309: The lineage-specific transcription factor ASCL1 defines a subtype of non-small cell lung cancer with poor prognosis
Authors: Augustyn Alexander , Tan Christopher , Sullivan James P. , Huffman Kenneth , Girard Luc , Borromeo Mark , Johnson Jane , Wistuba Ignacio , Xie Yang , Minna John D. 
Published: August 2012

Abstract
Introduction: Using genome-wide expression analyses several groups have identified a neuroendocrine subtype of NSCLC (NE-NSCLC), occurring in 5-8% of all NSCLC, which has a poorer prognosis than typical NSCLC. To determine a preclinical model for NE-NSCLC, we utilized whole-genome mRNA expression array data from 119 NSCLC cell lines to identify a class of NSCLC lines that fit the neuroendocrine phenotype. A gene expressed in all putative NE-NSCLC cell lines is the potent neural-specific transcription factor ASCL1. We found that ASCL1 is: necessary for the survival of NE-NSCLC cell lines; correlates with stem cell marker expression; and that an ASCL1-associated gene signature predicts for poor prognosis in NSCLC. Aims and Methods: We hypothesize that ASCL1 acts as a “lineage dependent oncogene” for NE-NSCLC and that associated with ASCL1's function in the molecular pathogenesis of these lung cancers will be a gene expression profile that contributes to the malignant phenotype, which will provide insight towards therapeutic targeting of this subset of NSCLC. To test this hypothesis we examined genome wide mRNA expression data from 119 NSCLC lines with validation of selected genes by qRT-PCR, ASLC1 ChIP-Seq data obtained on ASCL1 expressing NSCLC lines, the clinical outcome of a 275 resected NSCLCs characterized for ASCL1, and genome wide mRNA expression, performed functional analyses in NSCLC lines with siRNA mediated knockdown of ASCL1 and downstream target genes, and integrated this information using biostatistical and bioinformatics approaches. Results and Conclusions: We identified 11 out of 119 NSCLC cell lines (9.2%) that display a distinct neuroendocrine gene signature, and 24/275 resected NSCLCs with high ASCL1 expression. The NSCLCs expressing ASCL1 and the neuroendocrine gene signature had impaired prognosis compared to the other NSCLCs. Knockdown of ASCL1 in representative NSCLC lines reduced target gene expression, caused significant cell cycle defects, and induced apoptosis. NSCLC cell lines expressing ASCL1 demonstrate a cancer stem cell marker phenotype similar to that of small cell lung cancer, providing clues to the pathogenesis of the NE-NSCLC disease subset. ASCL1 ChIP-Seq data combined with genome wide mRNA expression data identified a subset of genes whose expression appears to be regulated by ASCL1. Our results suggest that neuroendocrine gene expression in NSCLC is of clinical relevance, that ASCL1 is required for survival of the NE-NSCLC disease subset, while the integrated ASCL1 ChIP-Seq and mRNA expression data provide a roadmap for systematically searching for therapeutic targets for this phenotype and their mechanistic role in a cancer stem cell (initiating cell) subpopulation within these tumors.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1309. doi:1538-7445.AM2012-1309