Abstract 4056: Development of Kras mutant lung adenocarcinoma in tobacco carcinogen exposed mice with knockout of the airway lineage-specific G-protein coupled receptor Gprc5a
Authors: Fujimoto Junya , Nunomura Sayuri , Lang Wenhua , Liu Yihua , Wei Jinsong , Ochieng Joshua , Jakubek Yasminka , Ostrin Edwin , Petersen Jason , Davies Gareth , Darwiche Nadine , Ehli Erik , Fowler Jerry , Scheet Paul , Kadara Humam 
Published: July 2016

Abstract
Lung adenocarcinoma (LUAD) represents the most common lung cancer subtype in smokers. Despite the urgency for prevention in high-risk smokers, we still do not know the earliest changes that drive LUAD development and would thus be ideal targets for chemoprevention. Earlier work revealed that the retinoic acid-inducible G-protein coupled receptor, Gprc5a, is abundantly expressed in mouse normal lung relative to other normal tissues. Moreover, mice with knockout of Gprc5a develop spontaneous late onset lung tumors, including LUADs, suggesting a tumor suppressor role for this gene. In the present study, we sought to better understand the impact of Gprc5a expression on LUAD pathogenesis. We first examined the expression of human GPRC5A in publicly available datasets and found that GPRC5A was highest in human normal lung relative to other normal samples and was down-regulated in human LUADs. We then assessed expression patterns of Gprc5a within different mouse airway compartments and found that the gene was predominantly expressed in alveolar type I (AT1) cells pointing to potential airway lineage-specific functions for Gprc5a. Next we sought to analyze tobacco carcinogen-mediated lung oncogenesis as an attempt to emulate smoking-induced lung cancer in humans. In contrast to wild type littermates, Gprc5a-/- mice treated with the nicotine-specific carcinogen NNK developed LUADs by six months after carcinogen exposure. Following immunofluorescence analysis, these LUADs were found to express surfactant protein C (Sftpc) and lack the clara cell marker Ccsp suggesting that the cells of origin for these LUADs are alveolar type II (AT2) cells. We were then prompted to understand genomic alterations in the pathogenesis of the Gprc5a-/- LUADs. Using the Illumina HiSeq 2500 platform, we performed whole exome sequencing (WES) of five carcinogen-induced LUADs as well as two Gprc5a-/- tail veins and normal lung tissues to infer somatic variants. Of note, all LUADs exhibited somatic activating Kras mutations (p.G12D or p.Q61R), the same variants purported to act as drivers of human LUAD in smokers. The Kras mutations were also observed in premalignant lesions that developed prior to LUAD onset. Moreover, WES analysis revealed additional driver genes that were mutated (Apc, Atm, Kmt2d, Nf1, Trp53) or exhibited copy number alterations (CNAs) (gain of Kras, Met, Braf, Ezh2) in multiple Gprc5a-/- LUADs. Our data suggest that Gprc5a loss coupled with NNK exposure leads to AT2-derived Kras mutant LUADs with co-occurring mutations and CNAs in other driver oncogenes and tumor suppressors. Our findings also imply that the tobacco carcinogen exposed Gprc5a-/- model emulates the molecular pathology of human LUAD and offers unique opportunities to map the temporal evolution of Kras mutant LUAD and identify targets for chemoprevention of this fatal malignancy.
Citation Format: Junya Fujimoto, Sayuri Nunomura, Wenhua Lang, Yihua Liu, Jinsong Wei, Joshua Ochieng, Yasminka Jakubek, Edwin Ostrin, Jason Petersen, Gareth Davies, Nadine Darwiche, Erik Ehli, Jerry Fowler, Paul Scheet, Humam Kadara. Development of Kras mutant lung adenocarcinoma in tobacco carcinogen exposed mice with knockout of the airway lineage-specific G-protein coupled receptor Gprc5a. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4056.