Abstract 1107: miR-29b acts as an oncogene or tumor suppressor gene depending on the external stimulus

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Abstract microRNAs (miRNAs), short regulatory sequences at the posttranscriptional level, are important mediators of signaling pathways that act as backups of transcriptional control. To identify miRNAs implicated in epidermal growth factor receptor (EGFR) signaling, transformed bronchial epithelial BEAS-2B cells were retrovirally transduced with KRASG12V and alterations in miRNA expression were assessed by microarray analysis. Here we show that miR-29b is significantly induced by mutant KRAS in bronchial epithelial and non-small cell lung cancer (NSCLC) cell lines as well as in primary NSCLC tissue. In agreement with these results, inhibitors of EGFR and MEK resulted in reduced levels of miR-29b while inhibitors of PI3K had no effect. KRASG12V-transduced BEAS-2B cells were significantly more protected from extrinsic apoptosis than control transduced cells, but co-transduction of cells with KRASG12V and anti-miR-29b constructs sensitized cells to apoptosis indicating that miR-29b is a mediator of KRAS-induced resistance to apoptosis. Protection from extrinsic apoptosis was due to enhanced nuclear factor κB (NF-κB) activity. The ubiquitin-editing enzyme tumor necrosis factor alpha-induced protein 3 (TNFAIP3/A20) is a negative regulator of NF-κB signaling. Enhanced NF-κB activity elicited by miR-29b was due to targeting TNFAIP3/A20. Overexpression of miR-29b-refractory TNFAIP3 restored NF-κB activity as well as extrinsic apoptosis, demonstrating that TNFAIP3 is a relevant target of miR-29b. Interestingly, miR-29b conferred sensitivity to cisplatin-induced intrinsic apoptosis by targeting Mcl-1. Thus, miR-29b tips the balance from extrinsic apoptosis towards intrinsic apoptosis. Our results indicate that miR-29b can act either as an oncogene or tumor suppressor gene depending on the external stimulus. Citation Format: Erik Vassella, Stephanie Langsch. miR-29b acts as an oncogene or tumor suppressor gene depending on the external stimulus. [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 1107.