Poster Presentation 28th Lorne Cancer Conference 2016

Molecular Interactions of Polo-like kinase 1 (PLK1) in Colorectal Cancer (#220)

Wayne Ng 1 2 3 , Joo-Shik Shin 1 2 3 4 , Tao Yang 1 2 5 , Tara Roberts 3 6 , Bin Wang 7 , Jarrad Begg 8 9 , Soon C Lee 1 2 3 4
  1. Discipline of Pathology, Western Sydney University, Sydney, NSW, Australia
  2. Cancer Pathology and Cell Biology Laboratory, Ingham Institute for Applied Medical Research, Sydney, New South Wales, Australia
  3. Centre of Oncology Education and Research Translation (CONCERT), Sydney, New South Wales, Australia
  4. Molecular Medicine Research Group, School of Medicine, Western Sydney University, Sydney, New South Wales, Australia
  5. Sydney South West Pathology Service, Liverpool Hospital, Sydney, New South Wales, Australia
  6. Discipline of Medical Oncology, School of Medicine, Western Sydney University, Sydney, New South Wales, Australia
  7. South Western Sydney Clinical School, University of New South Wales, Sydney, New South Wales, Australia
  8. Department of Medical Physics, Liverpool and Macarthur Cancer Therapy Centre, Sydney, New South Wales, Australia
  9. Ingham Institute for Applied Medical Research, Sydney, New South Wales, Australia
Radiotherapy (RT) improves the local control of rectal cancer but patient responses to RT are variable. Biomarkers are needed to determine the radiosensitivity of these tumours. Microsatellite instability (MSI) accounts for 15% of colorectal cancer (CRC) cases and the associated proteins were shown to be involved in DNA damage responses (DDR). PLK1 promotes cell cycle progression and is also involved in recovery from DNA damage. Deregulation of PLK1 causes genetic instability due to G2-M checkpoint escape. PLK1 overexpression is associated with poor tumour prognosis. This study investigated the interactions between PLK1, MSI and ionising irradiation (IR) and explored the molecular mechanisms that lead to PLK1 deregulation in CRC. siRNA was used to deplete PLK1. The effects of the knockdown and IR were then analysed by real-time quantitative PCR, western blot, cell survival assays, caspase 3/7 assay, annexin V binding assay and cell cycle analysis. Sanger sequencing was performed to detect mutations in PLK1 gene. In MSI high cells (HCT116, SW48), PLK1 expression decreased post-IR whereas it remained unaffected in microsatellite stable (MSS) cells (Colo320DM, T84). MSI high cells were more radiosensitive than the MSS cells. PLK1 reduction resulted in substantial reduction of cell survival, as well as increased induction of apoptosis and G2/M blockage in Colo320DM, HCT116 and SW48 cells but not T84 cells. These effects were additive in the responsive cells when the treatment was combined with IR. Mutational studies showed that only secondary mutations were detected at the silencer region of PLK1 in HCT116 and SW48. In conclusion, MSI has an impact on PLK1 expression which in turns affects the cell survival after IR. Moreover, PLK1 knockdown additionally improved the effects of IR in some of the CRC cells, including some radioresistant cells. Lastly, sequencing concluded that mutation did not play a major role in PLK1 expression level in CRC.