Abstract 528: Identification of MYC as a novel repressor of miR-29 in pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is a lethal malignant disease with a dismal 5-year survival rate of 8%. The lack of effective therapies reinforces the need to better understand molecular mechanisms in PDAC. In our previous work, we found that downregulation of miR-29 is a common phenomenon of PDAC, and its restored expression had a potent tumor-suppressive effect in pancreatic cancer cells. However, the mechanism associated with the loss of miR-29 in PDAC has yet to be elucidated. In our initial work, using PDAC cell lines, we found that miR-29 is downregulated independent of KRAS. In an effort to understand the transcriptional factors mediating miR-29 repression, we selected several transcription factors that have a role in PDAC pathogenesis and binding sites in the miR-29 promoter region. siRNA mediated knockdown (KD) of three candidate transcription factors, SMAD4, MYC, and Gli3 revealed that the KD of MYC resulted in the highest gain of miR-29 expression (2-fold increase). Furthermore, MYC nuclear localization negatively correlates with miR-29 expression in various pancreatic cancer cell lines, and treatment of pancreatic cancer cells with small-molecule MYC inhibitor resulted in a dosage-dependent increase of miR-29 expression. miR-29a/b1 locus located on human chromosome 7 has two canonical MYC binding motifs upstream of the miR-29 transcription start site, which were functionally validated via luciferase assay. Finally, autophagy has been shown to be upregulated by MYC and is known to mitigate stressors of the integrated stress response (ISR) pathway in cancer. In our previous work, we showed that miR-29 blocks autophagy in pancreatic cancer cells. Consistently, we found miR-29 overexpression led to decreased cancer cell viability in combination with gemcitabine and induced the ISR as indicated by increased phospho-eIF2α. Taken together, our results demonstrate that MYC plays a key role in the regulation of miR-29 expression in pancreatic cancer. Furthermore, our data indicate the potential use of miR-29 as a novel therapeutic agent for PDAC, and these results could help form the basis for future studies to develop a more targeted approach of miR-29 therapeutic administration. Citation Format: Jason Kwon, Kayla Quirin, Tricia Factora, Janaiah Kota. Identification of MYC as a novel repressor of miR-29 in pancreatic ductal 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 528.