AbstractBladder cancer is the most common malignancy of the urinary tract in humans with a high incidence and rate of recurrence. Poor prognoses are associated with disease progression including the development of resistance to chemotherapy. Epithelial-to-mesenchymal transition (EMT) and high insulin-like growth factor (IGF)-activity have been reported to facilitate tumour development in many cancer types including bladder. Insulin-like growth factor binding protein 2 (IGFBP-2), a member of the IGF system as well as the second most abundant IGFBP in human serum, can exert effects that either promote or suppress cancer progression in an IGF-dependent and/or -independent way. In this thesis, the levels of IGFBP-2, its regulation, role and the mechanisms underlying its actions were investigated in bladder cancer cell lines. The relationship between IGF/IGFBP-2-activity and their involvement in EMT was also assessed.
We observed that the epithelial-like RT4 cells had abundant levels of IGFBP-2 whereas the mesenchymal-like T24 and TCCSUP bladder cancer cells lines were null for IGFBP-2. We determined that IGFBP-2 was epigenetically silenced in the mesenchymal cell lines via DNA methylation, suggesting a reduction in IGFBP-2 was associated with more aggressive disease.
We found that silencing IGFBP-2 in RT4 cells led to increased cell proliferation, cell invasion, as well as colony formation: along this was associated with a decrease in the levels of E-cadherin (an epithelial marker) and the nuclear translocation of the β-catenin. Adding exogenous IGFBP-2 to T24 and TCCSUP cells had the opposite effects on all cell phenotypes that were associated with an increase in the levels of N-cadherin (a mesenchymal marker). The cell lines with higher levels of endogenous IGFBP-2 were also found to be more sensitive to cisplatin. As the data suggested that IGFBP-2 could act in both an IGF-dependent and independent manner, we also examined the actions of IGF-I and found that IGF-I induced an increase in cell proliferation, invasion, migration, colony formation and EMT-related cancer progression in both RT4 and T24 bladder cancer cell lines that appeared to involve the IGF-IR/PI3K/Akt signalling pathway.
IGFBP-2 appears to play an inhibitory role in the progression of bladder cancer by decreasing proliferation, invasion, migration, colony-formation and by modifying markers of EMT. We also observed that IGFBP-2 may represent a biomarker for chemo-sensitivity. IGFBP-2 achieves its effects on cell actions in both IGF-dependent and independent ways and as anticipated the addition of IGF-I alone had a stimulatory effect in all cell lines, on all cell phenotypes to promote bladder cancer progression.
|Date of Award
|23 Jan 2019
|Claire M Perks (Supervisor) & Jeff M. P. Holly (Supervisor)