Beta-galactoside binding protein (p-GBP) is a negative cell cycle regulator and an antiproliferative cytokine. The aim of this thesis is to define the molecular mechanisms whereby f3-GBP induces apoptosis in colon cancer cells. Three colon cancer cell lines were selected: SW480, derived from a primary tumour of the SW620 a metastatic derivative of SW 480 and Lo Vo a very aggressive drug resistant cell line. The results presented in this thesis demonstrate that f3-GBP can induce an early and complete inhibition of DNA synthesis and S phase arrest, paralleled with growth inhibition, which is followed by apoptosis in the p53 defective SW480 and SW620 colon cancer cells as well as in the p53 wild type Lo Vo cells. The molecular events leading to this response were examined by investigating cell cycle regulatory machinery and survival pathways. The observations as a consequence of treatment f3-GBP are following: cyclin E was persistently expressed and cyclin A was downregulated; E2F! transcription factor was persistently expressed before cell underwent apoptosis; phosphorylation of Chk2 was increased at an early stage before apoptosis occurred. f3-GBP was found to be an inhibitor of PI3K activity, however the downstream target Akt was found not to be decreased before the induction of apoptosis. Both ERK levels and Akt levels increased before both signallings were quenched as cells entered apoptosis. These findings suggest that f3-GBP can coordinate the cell cycle regulatory and different survival mechanism to arrest growth and induce apoptosis. The persistent expression of cyclin E and downregulation of cyc1in A may contribute to S phase arrest and apoptosis. The inhibition of DNA synthesis and activation ofERK may activate DNA checkpoints. The checkpoint kinase may playa critical role as f3-GBP induced activation of Chk2 could result in persistent expression of E2F! and therefore lead to p53-independent apoptosis. The ectopically expressed E2F! in S phase may playa crucial role because of the inherently different levels of E2F! between cancer cells and normal cells. The selective induction of apoptosis may be due to the integrated response of these mechanisms.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:504628 |
| Date | January 2007 |
| Creators | Shi, Dong-Yun |
| Publisher | King's College London (University of London) |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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