Abstract 952: Genome-wide enhancer analysis identifies PVT1 as an oncogenic enhancer of MYC
Authors: Shigeyasu Kunitoshi , Toden Shusuke , Nagasaka Takeshi , Fujiwara Toshiyoshi , Boland C. Richard , Goel Ajay 
Published: July 2016

Introduction: An enhancer is a short stretch of DNA that can be targeted by specific proteins to activate gene transcription, and recent evidence suggests that enhancers can act as key regulators of oncogenes in cancer. Recently, the FANTOM5 project comprehensively characterized enhancer activities in various cell types. Interestingly, several enhancers coding for lncRNAs were commonly up-regulated in multiple cancer types, suggesting that these enhancers may play an important oncogenic role through enhancer-promoter-lncRNA interaction, and may help mediate chemoresistance. However, specific lncRNAs with oncogenic enhancer function and their clinical significance in colorectal cancer (CRC) remains unexplored.

Aims: We analyzed genome-wide cancer-specific enhancer activation in multiple cancers to identify potential oncogenic lncRNAs, and assessed their clinical significance in two independent patient cohorts with CRC. We thereafter evaluated the functional role of candidate enhancer lncRNAs in CRC.

Methods: Using the FANTOM5 enhancer database, cancer-specific enhancer activity was analyzed in cancers of the colon, stomach, lung, prostate and melanoma. LncRNA candidates that encode these cancer-specific enhancers were identified. We then screened these lncRNAs in two independent CRC cohorts, as well as the APC(Min/+) mouse model. The functional role of target lncRNAs was assessed in parental and chemoresistant CRC cell lines. The oncogenic enhancer activity was confirmed using the chromatin conformation capture (3C) assay.

Results: We identified ten lncRNA candidates with consistent enhancer activities in all five cancer types. In particular, PVT1 appeared to have one of the highest enhancer activities. Using two independent CRC cohorts, we confirmed upregulation of PVT1 in cancer tissues. Patients with high-PVT1 expression had shorter overall survival in Stage II and III CRCs, suggesting that the PVT1 expression could discriminate high-risk patients, and identify those who may benefit from adjuvant chemotherapy. Intriguingly, we discovered that PVT1 was also upregulated in human colorectal adenomas as well as adenomas isolated from APC(Min/+) mice, indicating that PVT1 may be involved in the early stages of the adenoma-carcinoma sequence. The expression level of PVT1 significantly correlated with c-MYC expression in CRC specimens and the 3C assay showed that the enhancer region in PVT1 can target c-MYC. Finally, we demonstrated that PVT1 and c-MYC were co-overexpressed in several chemoresistant CRC cell lines, and that suppression of PVT1 led to a significant reduction in proliferation of chemoresistant cells, further suggesting that PVT1 may play a key role in chemoresistance.

Conclusion: PVT1 acts as an oncogenic enhancer of c-MYC in CRC. High expression of PVT1 served as a predictive marker for identifying high-risk Stage II and III CRC patients. PVT1 could serve as a potential therapeutic target in chemoresistant CRCs.

Citation Format: Kunitoshi Shigeyasu, Shusuke Toden, Takeshi Nagasaka, Toshiyoshi Fujiwara, C. Richard Boland, Ajay Goel. Genome-wide enhancer analysis identifies PVT1 as an oncogenic enhancer of MYC. [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 952.