Abstract 5509: Early suppression of the TBX2 subfamily of transcription factors during in vivo tobacco carcinogen-mediated lung adenocarcinoma development
Authors: Khalil Athar , Fujimoto Junya , McDowell Tina , Scheet Paul , Nemer Georges , Kadara Humam 
Published: August 2018

Abstract
Targets for early treatment of lung adenocarcinoma (LUAD), the leading cause of cancer mortality among smokers, are far and few largely due to the paucity in our knowledge of the molecular pathogenesis of the malignancy. In our efforts to address this glaring gap in knowledge, we previously surveyed the expression of members of the T-box 2 subfamily of transcription factors (TBXs 2, 3, 4 and 5) in normal and malignant lung tissues owing to their evolutionarily conserved expression and function in normal lung organogenesis,. We found that all four members were profoundly suppressed in human premalignant lesions and malignant LUADs. While these findings showed that the TBX2 subfamily of transcription factors is suppressed in overt LUADs, their role in the molecular and temporal oncogenesis of the malignancy in smokers is still elusive. To fill this void, we first surveyed the expression of these genes in a mouse model of LUAD we had developed comprised of knockout of the airway-lineage specific gene Gprc5a (Gprc5a-/-) and exposure to the tobacco-specific carcinogen nicotine-derived nitrosamine ketone (NNK). We had previously found that NNK-exposed Gprc5a-/- mice developed adenomas and LUADs that harbored somatic activating mutations (p.G12D and p.Q61R) in the Kras oncogene – the same variants posited to function as drivers of LUAD in human smokers. In ongoing RNA-Seq efforts cataloging expression in frozen-fixed temporally collected (up to seven months post-NNK) Gprc5a-/- normal tissues, adenomas and LUADs, we found that all four TBX genes were markedly down-regulated (all P &lt; 0.05) in all lesions and across all time points following exposure, relative to normal lung tissues. Concurrent analysis of canonical genes directly activated or repressed by the TBX2 subfamily were found to be consistently down-regulated or elevated, respectively, in the same NNK-exposed lung lesions relative to normal lung. We employed a mouse LUAD cell line (mF471 cells) we had previously derived from an NNK-exposed Gprc5a-/- mouse tumor to further functionally probe the role of TBX2 subfamily in LUAD oncogenesis. Transient over-expression of each of the four TBX2 subfamily members in the mF471 LUAD cells significantly inhibited cell proliferation and growth evidenced by trypan blue dye exclusion, MTT and cell cycle analyses. Over-expression of each of the four TBX2 subfamily members yielded similar anti-growth effects with significant increases in sub-G0 phase of the cell cycle indicating cell cycle arrest (up to 35%) 48 hours following transfection. These findings suggest that the TBX2 subfamily genes are suppressed at early stages in the development of smoking-associated Kras-mutant LUAD and play key tumor suppressor roles in the molecular pathogenesis of this common and fatal malignancy.
Citation Format: Athar Khalil, Junya Fujimoto, Tina McDowell, Paul Scheet, Georges Nemer, Humam Kadara. Early suppression of the TBX2 subfamily of transcription factors during in vivo tobacco carcinogen-mediated lung adenocarcinoma development [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5509.