T-box (TBX) transcription factors are evolutionary conserved genes and master transcriptional regulators. In mammals, TBX2 subfamily (TBX2, TBX3, TBX4, and TBX5) genes are expressed in the developing lung bud and tracheae. Our group previously showed that the expression of TBX2 subfamily was significantly high in human normal lungs, but markedly suppressed in lung adenocarcinoma (LUAD). To further elucidate their role in LUAD pathogenesis, we first confirmed abundant expression of protein products of the four members by immunostaining in adult human normal lung tissues. We also found overall suppressed expression of these genes and their corresponding proteins in a panel of human LUAD cell lines. Transient over-expression of each of the genes in human (NCI-H1299), and mouse (MDA-F471) derived lung cancer cells was found to significantly inhibit growth and proliferation as well as induce apoptosis. Genome-wide transcriptomic analyses on NCI-H1299 cells, overexpressing TBX2 gene subfamily, unraveled novel regulatory pathways. These included, among others, inhibition of cell cycle progression but more importantly activation of the histone demethylase pathway. When using a pattern-matching algorithm, we showed that TBX's overexpression mimic molecular signatures from azacitidine treated NCI-H1299 cells which in turn are inversely correlated to expression profiles of both human and murine lung tumors relative to matched normal lung. In conclusion, we showed that the TBX2 subfamily genes play a critical tumor suppressor role in lung cancer pathogenesis through regulating its methylating pattern, making them putative candidates for epigenetic therapy in LUAD.
T-box (TBX) transcription factors are evolutionary conserved genes and master regulators of transcription repression and activation. In mammals, 18 members were described functionally and structurally, of which the TBX2 subfamily (TBX2, TBX3, TBX4, TBX5) genes were shown to be expressed early on in the developing lung bud and tracheae. Despite these insights into the role of the TBX2 subfamily in normal lung organogenesis, little is known about the role of these genes in pathological pulmonary conditions in humans; particularly lung cancer, an aggressive malignancy that is the leading cause of cancer-deaths worldwide. To fill this void, our group previously surveyed the expression of TBX2 subfamily in various publicly available datasets and found that all four members were preferentially and highly expressed in human normal lung, but markedly and consistently suppressed in lung adenocarcinoma (LUAD) the most common histological subtype of lung cancer. We also showed that the subfamily was also suppressed in preneoplastic lesions preceding the development of LUADs. Following the above and to further elucidate the role of the TBX2 subfamily in LUAD pathogenesis, we first probed and confirmed abundant expression of protein products of the four members by immunostaining in adult human normal lung tissues. On the other hand, quantitative real-time PCR and western blotting analyses demonstrated overall suppressed expression of the genes and corresponding proteins in a panel of human LUAD cell lines. Transient over-expression of each of the four genes in human LUAD cell lines (H1299 and H1944) was found to overall significantly inhibit cancer cell growth and proliferation. Additionally, over-expression of the four genes induced apoptosis, evidenced by sub-G0/G1 accumulation following cell cycle analysis, in both cell lines (ranging from 40% to 90% compared to control). To understand genome-wide effects of TBX2 subfamily in LUAD, we interrogated global expression programs downstream of these transcription factors by RNA-Seq in H1299 cells engineered to over-express the four members separately. We unraveled novel signaling cues signifying canonical pathways found in our analysis to be directly regulated by members of the TBX2 subfamily. These included, among others, inhibition of cell cycle progression and glycolysis, suppression of pathways mediated by epidermal growth factor (EGFR) and WNT signaling and activation of the major anti-tumor immune marker interferon gamma (IFNG). All in all, our findings point to tumor suppressor roles for TBX2 subfamily in human LUAD pathogenesis and suggest “oncophenotypes” downstream of these factors as putative targets for lung cancer therapy. Citation Format: Athar Khalil, Nehme El-Hachem, Batoul Dekmak, Humam Kadara, Georges Nemer. Role of the evolutionarily conserved TBX2 subfamily of transcription factors in the molecular pathogenesis of human lung adenocarcinoma [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 5513.
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