Login to Access Video or Poster Abstract: MP99-18
Sources of Funding: American Cancer Society 125627-RSG-14-074-01-TBG _x000D_ NIH/NCI 1R01CA200643-01A1 _x000D_ Institute of Prostate and Urological Cancer_x000D_ Masonic Cancer Center, University of Minnesota_x000D_

Introduction

Though gain of 8q24.21 is a common mutation in human cancers, its functional annotation is limited to studying myelocytomatosis (MYC), the prominent oncogene in the amplicon. However, MYC is co-gained with an adjacent long non-coding RNA gene plasmacytoma variant translocation 1 (PVT1), CCDC26 and gasdermin C (Gsdmc). Whether copy number gain of one or more of these genes drives neoplasia is unknown.

Methods

We developed chromosome engineered mouse strains with an extra copy of 1) Myc, 2) Pvt1, Ccdc26, Gsdmc, and 3) Myc, Pvt1, Ccdc26, Gsdmc. These mice were crossed with transgenic mice harboring rat Neu was introduced to test the change in the latency in mammary tumor development. We also used genetically engineered human cancer cell lines to identify the molecular basis of co-operation between MYC and PVT1 in human cancer.

Results

Only the mice with an extra copy of Myc, Pvt1, Ccdc26, Gsdmc developed adenocarcinomas, suggesting that may co-operate with Pvt1, Ccdc26 or Gsdmc to promote cancer. Si-RNA mediated knockdown of Pvt1/PVT1 reduced the proliferation rates in the tumors. Ablation of PVT1 decreased MYC protein levels, suggesting a PVT1-dependence of MYC protein in MYC amplified cancer cells. These data suggests that PVT1 can potentiate MYC in human cancers. CRISPR-cas9 mediated deletion of PVT1 in HCT116 impaired tumor formation in xenografts, and significantly reduced MYC levels. Additionally, we have identified the putative functional domain of PVT1 which confers its oncogenic potential. We have recently discovered that the exon 2 of PVT1 can undergo ‘backsplicing’ and form circular RNA of 410 bases (CircPVT1). This CircPVT1 is more abundant in MYC-driven cancer cell lines. Though PVT1 is known as a long non-coding RNA, we found that CircPVT1 can form an open reading frame (ORF) of 104 amino acids, which we have annotated as PVT1 encoded protein upon circularization (PEPc). While CRISPR-Cas9 mediated deletion of PVT1 exon 2 results into decreased MYC levels and reduced transformation potential in MYC-driven cancer cells, PEPc can independently augment MYC when added exogenously to LNCaP cells, and increase their transformation potential.

Conclusions

These results suggest that PEPc may play a key role in boosting MYC levels in metastatic prostate cancers. We propose that the dependence of high levels of MYC on PVT1 provides a much-needed therapeutic window against MYC protein, known to be refractory to small molecule inhibition.

Funding

American Cancer Society 125627-RSG-14-074-01-TBG _x000D_ NIH/NCI 1R01CA200643-01A1 _x000D_ Institute of Prostate and Urological Cancer_x000D_ Masonic Cancer Center, University of Minnesota_x000D_