Abstract 1124: Expression of the lipocalin 2 oncogene in the development of smoking-associated and Kras mutant lung adenocarcinoma
Authors: Ochieng Joshua , Nunomura Sayuri , Lang Wenhua , Wei Jinsong , Xu Li , McDowell Christina , Ostrin Edwin , Arlinghaus Ralph , Fujimoto Junya , Kadara Humam 
Published: July 2016

There are more than 90 million smokers in the United States who are at elevated risk for lung adenocarcinoma (LUAD), the most common lung cancer subtype. LUADs in smokers frequently (greater than 25%) harbor activating mutations in the Kras oncogene. Kras mutant LUAD exhibits very poor prognosis warranting the need for new strategies to prevent and treat this fatal lung cancer subtype. Limiting these advances is a poor understanding of the earliest events that drive Kras mutant LUAD development in smokers and that would constitute targets for early treatment. The retinoic acid-inducible G-protein coupled receptor Gprc5a is preferentially expressed in normal lung and mice with knockout of the gene (Gprc5a-/-) develop late onset lung tumors spontaneously. In our data aimed at understanding smoking-associated lung cancer pathogenesis, we found that Gprc5a-/- mice, in contrast to wild type (WT) littermates, not only developed LUADs after tobacco carcinogen exposure but also that these lesions harbored somatic Kras mutations, the same variants thought to act as drivers of human LUAD in smokers. In the present study we construed that pinpointing early events preceding lung oncogenesis in Gprc5a-/- mice will help us comprehend how smoke-associated LUADs with Kras mutations evolve. Towards this, we performed RNA-sequencing, using the Ion Proton platform, of visually normal airway epithelia in Gprc5a-/- mice prior to tumor development compared to epithelia in WT mice. We noted distinctively marked up-regulation of the Lcn2 oncogene in normal airways of Gprc5a-/- mice. Functional pathways and gene set enrichment analyses revealed that Lcn2 up-regulation was associated with activation of mitogen activated protein kinase- and interleukin-associated pathways and with gene sets attributable to cigarette smoke. We then analyzed Lcn2 expression in murine cell lines we had derived and found that Lcn2 was significantly elevated in both Gprc5a-/- LUAD and airway cell lines compared to WT airway cells. Moreover, immunohistochemical expression of Lcn2 protein was elevated, compared to normal lung tissue, in early lesions (hyperplasias and adenomas) and in the LUADs of tobacco carcinogen exposed Gprc5a-/- mice. Of note, we also found that alternatively activated M2 macrophages surrounding all lesions were positive for Lcn2. We then analyzed human LCN2 expression in publicly available array datasets and found that the gene was significantly elevated in human KRAS mutant LUADs compared to wild type LUADs or normal lung (all P &lt; 0.05). Our preliminary findings suggest that elevated Lcn2 expression, in lung (airway and tumor) epithelia and in the protumorigenic inflammatory environment, may be implicated in the early development of smoking-associated Kras mutant LUAD. Efforts are underway to further probe this supposition in mice with knockout of Lcn2.

Citation Format: Joshua Ochieng, Sayuri Nunomura, Wenhua Lang, Jinsong Wei, Li Xu, Christina McDowell, Edwin Ostrin, Ralph Arlinghaus, Junya Fujimoto, Humam Kadara. Expression of the lipocalin 2 oncogene in the development of smoking-associated and Kras mutant lung adenocarcinoma. [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 1124.