The role of PAF15 in the cell cycle of prostate cancer

Abstract

Prostate cancer (PCa) has the highest rate of diagnosis of all cancers in Australian males. Whilst also having the third highest mortality rate among cancers in Australian males. Due to its heterogeneous nature and improvements in screening patient's prostate specific antigen (PSA) early detection cases of low-risk PCa are becoming the larger proportion of cases. Over the course of their treatment around 30% of these patients deemed low-risk will have their PCa progress to a high-risk cancer that will require harsher treatment. Previous studies have noted the Ki-67 marker of proliferation as a method of measuring PCa that have progressed to a proliferative state, these cells are found in higher proportion in high-risk PCa. The other type of cell found in PCa are known as quiescent cells that remain in the G0 state of the cell cycle and are Ki-67 negative. The clinical problem that remains is the molecular mechanism that drives this progression from a quiescent cell type to a proliferative cell type remains unclear. The Proliferating cell nuclear antigen (PCNA) association factor (PAF15) is 15kDa that has known functions in DNA replication, DNA repair, cell survival, cell cycle regulation and proliferation. Studies have shown that PAF15 expression shows greater expression in cancerous cells compared to normal cells in PCa. This higher level of expression has shown implications with cancer progression and poorer prognosis in highly malignant cancers. Although, the molecular mechanisms that PAF15 may affect in the cell cycle are undetermined in prostate cancer. Therefore, this project aims to explore the role PAF15 expression has on the proportion of cancerous cell to quiescent cells in the G0 phase and thus on cancer proliferation. Furthermore, this project aims to investigate the potential mechanisms of proteins that PAF15 affects that pushes the changes in the proportion of quiescent cells. Using small interference RNA (siRNA) transfection to knockdown PAF15 expression, my study shows that silencing PAF15 expression decreased PCa proliferation which led to an amassing of cells at the G0 stage of the cell cycle. Protein levels of SKP2, PIRH2, C-MYC, PCNA and SPT16 were shown to be reduced by immunoblotting. Whereas, p27 protein levels were increased because of the treatment. Alongside these changes in protein levels Ki-67 and BrdU, markers of proliferation also showed reduced expression. This project has shown that PAF15 may potentially have an important role in the regulation of quiescent cells, which could be key for disease progression and future treatment development.

Date of Award	2017
Original language	English