Targeting the FACT complex in understanding the regulation of quiescent cancer cells

  • Iman Sohail

Western Sydney University thesis: Master's thesis

Abstract

Prostate cancer (PCa) is the most commonly diagnosed cancer among Australian males and the third most common cancer-related mortality in Australia. The heterogeneous nature of PCa as well as the increased clinical use of prostate-specific antigen (PSA) testing has led to a dramatic shift towards the diagnosis of low-risk and low-grade PCa. Nearly 30% of low-risk PCa patients subsequently experience cancer progression after active surveillance or primary treatments such as radiation or surgery. The presence of quiescent cancer cells, which are defined as Ki-67 negative and at a reversible arrest at the G0 phase, has been observed in PCa. Additionally, the proportion of quiescent cancer cells is low in low-risk PCa but increases in high-risk or metastatic PCa. Therefore, PCa progression may be potentially influenced by the cell's transition from a quiescent to proliferative state. However, an understanding of the biological mechanisms involved in an increased proportion of quiescent over proliferative cells is currently elusive. The Facilitates Chromatin Transcription (FACT) complex is a highly conserved histone chaperone that is known to play major roles in ordered nucleosome assembly and reassembly, chromatin integrity, DNA replication and repair. FACT's role in transcription regulation is also selective to a subset of genes involved in cell maintenance and cell growth function. As a higher level of FACT is documented in cancer cells, FACT has recently been implicated in cancer progression and associated with the poor prognosis of aggressive cancers. Moreover, an increased expression of FACT was evident in metastatic PCa and lower levels of FACT facilitated a G1 arrest to reduce cell proliferation. However, what is currently undetermined is the potential role or mechanism FACT may facilitate in the distribution of PCa cells in the cell cycle. Additionally, research on FACT and its effect on the G0 population is vastly ambiguous. Thus, the aim of this project was to define the effect of FACT expression on the proportion of quiescent cells at the G0 phase in PCa cells. Additionally, the project aimed to investigate the mechanism underlying FACT action on the increased proportion of quiescent PCa cells. Using a doxycycline-controlled shRNA to silence each of FACT's subunits, SPT16 and SSRP1, my study indicated that the silencing of FACT decreased cell proliferation and led to an accumulation of PCa cells at the G0 phase. Decreased levels of SKP2 and PIRH2 and increased levels of p27, all of which are G0 regulatory proteins, was revealed through immunoblotting. Concomitantly, a similar pattern by the G0 regulatory proteins was determined at the mRNA level through RT-qPCR. Overall, this project has revealed that FACT may potentially play an important role in the regulation of G0 cells, which could be important in disease progression and future treatment.
Date of Award2017
Original languageEnglish

Keywords

  • prostate
  • cancer
  • prostate-specific antigen
  • cell proliferation

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