Introduction

Paternally expressed gene-10 (PEG10) is required for placental development. There is currently intense interest in the reactivation of placental and developmental genes in cancer, given the inherently ‘‘oncogenic’’ tissue invasion and immune evasion properties of the placenta. Although transposon ability was lost 120 million years ago, PEG10 retains the ability to self-cleave, in an apparently homologous manner, to HIV. We have recently identified that PEG10 promotes cell cycle progression in the context of TP53 and RB1 loss in neuroendocrine prostate cancer. Based on the evidence that TP53 mutations and RB1 inactivation are more prevalent in muscle invasive bladder cancer (MIBC), we hypothesized that PEG10 may be concerned to the poor prognosis of MIBC. To test this hypothesis, we characterized PEG10 function in bladder cancer and evaluated if PEG10 can be a novel therapeutic target for bladder cancer. We also investigated whether Ritonavir, which is an antiretroviral medication used to treat HIV/AIDS, suppresses the expression of PEG10 and induced growth suppression in T24 cells.

Methods

PEG10 gene expression of tumor samples was analyzed using the cancer genome atlas (TCGA) cohort. The PEG10 expression in several bladder cancer cell lines was assessed by Western blot analysis and quantitative reverse transcription-PCR (qRT-PCR). Silencing of PEG10 in vitro was achieved using siRNA. The in vivo effect of PEG10 antisense oligonucleotide (ASO) treatment was assessed in the T24 orthotopic bladder cancer model.

Results

Higher mRNA level of PEG10 was significantly associated with poorer disease-free survival after cystectomy in 131 patients in the TCGA, Nature 2014 cohort. We examined PEG10 expression in a panel of 12 bladder cancer cell lines by Western blot. UM-UC14 showed the highest PEG10 expression, and T24 showed higher PEG10 expression than the other bladder cancer cell lines. Similar results were confirmed by qRT-PCR. PEG10 transient knockdown using two independent siRNAs resulted in significant growth suppression in UM-UC14 (RB1inactivatedTP53mut) and T24 (RB1wtTP53mut) cells. PEG10 knockdown induced higher expression of key cell cycle dependent kinase inhibitors p21 and p27 than observed in the control cells. Conversely, forced PEG10 RF1b/2 isoform over-expression induced cell growth in UC14 and T24 cells. Furthermore, UM-UC14 cell invasion was significantly decreased with PEG10 transient knockdown. Using the BrdU incorporation assay after cell cycle synchronization by double-thymidine block, we found that PEG10 drives cell cycle progression from G0/G1. In the orthotopic bladder cancer model, systemic PEG10-ASO administration to athymic nude mice delayed tumor progression in T24 cells. Surprisingly, Ritonavir suppressed the expression of PEG10 and induced growth suppression in T24 cells.

Conclusions

We have demonstrated that PEG10 promotes bladder cancer progression. Inhibition of PEG10 may be a novel treatment strategy for a subset of bladder cancer.

Funding

none