Targeting Ribosomal Biogenesis in Prostate Cancer

项目摘要/摘要：肥胖与高级别PC术后复发风险增高有关

PROJECT SUMMARY/ABSTRACT: Obesity is linked with greater risk of high-grade PC, recurrence after therapy, metastases, and PC death. We exploited the link between obesity and aggressive PC to identify actionable targets. To this end, we performed a shRNA genomic screen in obese mice targeting the entire kinome. If kinase is essential for growth in obese hosts the subpopulation of cells expressing that shRNA will not survive. Our screen identified various kinases expected to be essential for growth in obese host such as insulin receptor and insulin like growth factor 1 receptor. Our screen also indentified Right Open Reading Frame Kinase 2 (RIOK2), a key ribosome assembly factor, as a promising PC target in obese mice and suggests that ribosomal biogenesis plays a role in PC. Ribosomes translate mRNA to protein and production of new ribosomes in the nucleolus is essential for increased for increased growth rates of cancer cells. In PC, enlargement or prominent nucleoli are a hallmark of invasive PC and ribosome components are found upregulated in primary PCs as the result of oncogenic signaling, or by loss of tumor suppressors. We established that oncogenic stimuli can also induce ribosomal stress and elicits cell cycle arrest a.k.a ribosomal stress checkpoint mediated by the tumor suppressor p53. Loss of this checkpoint unleashed ribosomal biogenesis and accelerated Myc-driven lymphomagenesis. In PC, Androgen Receptor (AR) and Myc oncogenes also induce ribosomal biogenesis and our preliminary data suggest they upregulate RIOK2 to maintain high rates of protein translation needed cell growth and division. RIOK2 is critical for new ribosome assembly and ensures ribosomes are fully functional before translating mRNA to avoid degradation by dedicated surveillance pathways which could be harmful to PC cells. In fact, RIOK2 loss inhibits protein translation and induces cell death in multiple PC cell lines independent of p53 status. This led us to hypothesize that the PC oncogenes Myc and AR increase ribosome biogenesis for PC growth, and that targeting RIOK2, a key ribosomal assembly factor, interrupts this process leading to a novel PC therapy. We have a unique set of genetic mouse models to assess if unrestricted ribosomal biogenesis via loss of ribosomal stress checkpoint accelerates AR or Myc-induced PC. We will evaluate if AR and Myc induced protein translation and PC cell growth are mediated by RIOK2 and determine the potential of targeting RIOK2 with small molecule inhibitors in PC xenografts in obese mice. Increased ribosomal biogenesis by PC oncogenes highlights a potential therapeutic target. Inhibiting ribosome biogenesis via RIOK2 would be relevant in AR and Myc driven PCs, which is ~70% of metastatic PCs. Current therapuetic strategies under investigation to target ribosome synthesis rely on functional p53, which is problematic since upwards of 50% of metastatic PCs have a mutated or deleted p53. Completion of these studies would provide a rationale for a new therapy in AR and/or Myc-driven PCs irrespective of p53 status.