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In vitro selection for multidrug resistance (MDR) and retroactive clinical studies have established an important role for both P-glycoprotein (P-gp) and the Multidrug Resistance-associated Protein (MRP) in conferring pleiotropic resistance to several structurally dissimilar hydrophobic drugs. Both P-gp and MRP are ABC transporters which when overexpressed in tumour cells are capable of enhancing drug efflux, resulting in a drug accumulation deficit. Paradoxically, acquisition of the MDR phenotype frequently results in newfound hypersensitivity to a different group of drugs. This thesis investigates the collateral sensitivity of the P-gp-bearing CHO cell line CH$ sp{ rm R}$ C5 to the calcium channel blocker, verapamil (VRP). In addition, the hypersensitivity of the MRP-bearing SCLC line H69AR to BSO, a depleter of glutathione (GSH), is herein examined. Although VRP clearly induced heightened levels of p53-independent apoptosis in CH$ sp{ rm R}$ C5 cells, blockage of calcium channels was not involved in the cytotoxicity of the drug. BSO clearly killed through depletion of GSH, apparently resulting in heightened levels of necrosis in H69AR cells. In both cases, decreased expression of the Bcl-2 gene appeared to result in hypersensitivity of MDR cells to the toxic effects of BSO and VRP.

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The mechanisms by which Angiopoietin-1 (Ang-1) modulates the survival of human endothelial cells were investigated. Ang-1 inhibited both TNFalpha-induced and serum deprivation-evoked apoptosis, an effect which was associated with attenuation of caspase activation, inhibition of Smac release from the mitochondria, up-regulation of Survivin-1 expression (IAPs member) and a significant activation of the pro-survival PI-3 kinase/AKT pathway. In addition, Ang-1 activated, in a time-dependent fashion, both the anti-apoptotic ERK1/2 and pro-apoptotic p38 MAP kinases. Ang-1-evoked ERK1/2 activation was mediated in part through the PI-3 kinase pathway, whereas both, the PI-3 kinase and ERK1/2 attenuated p38 MAP kinase activation. / We conclude that Ang-1 promotes endothelial cell survival through several pathways including the PI-3 kinase/AKT and ERK1/2 pathways, up-regulation of Survivin-1 as well as inhibition of Smac release and caspase activity. The preferential activation of these anti-apoptotic effects, as opposed to the activation of pro-apoptotic p38 MAP kinase, results in a net survival response.

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Graduate

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Properdin is a serum glycoprotein that upregulates the alternative pathway of complement by stabilizing the C3bBb complex. It also binds sulphated glycoconjugates, such as sulphatide, in vitro. Properdin is composed of cyclic dimers, trimers and tetramers of a 53 kDa monomeric subunit. The monomer contains an N-terminal region of no known homology and six thrombospondin type 1 repeats (TSRs) of approximately sixty amino acids. The sixth TSR of properdin contains an insertion of approximately 30 amino acids which corresponds to the position of an intron in the human properdin gene. In order to identify the regions of properdin important for function, human properdin, and mutant forms each lacking a single TSR, were expressed in Chinese Hamster Ovary cells. In addition, limited tryptic digestion yielded "nicked" properdin by the cleavage of one peptide bond in TSR5. The structural and functional properties of the normal and altered forms of properdin were investigated. Wild type recombinant properdin is similar to properdin purified from plasma in size, immunoreactivity, N-terminal sequence, possession of N-linked sugar, oligomerization (as determined by electron microscopy and gel exclusion chromatography), and functional activity in an alternative pathway haemolytic assay, and in C3b and sulphatide binding assays. Properdin "nicked" in TSR5 is unable to bind C3b, while retaining its overall structure and its ability to bind sulphatide. The removal of TSRS prevents C3b and sulphatide binding. Properdin lacking TSR4 is unable to stabilize the C3bBb complex, but is able to bind C3b and sulphatide, and shows the presence of monomers and dimers in the electron microscope. Properdin without TSR3 is able to stabilize the C3bBb complex, to bind CSb and sulphatide, and forms dimers, trimers and tetramers. Properdin lacking TSR6 is unable to form oligomers. The N-linked carbohydrate of properdin is not required for oligomerization or stabilization of the C3bBb complex. Monoclonal antibodies which bind to the N-terminal region, TSR1, or TSR2 are able to inhibit properdin binding to CSb. A monoclonal antibody which binds TSR4 is able to inhibit properdin binding to sulphatide, but not to CSb. The results confirm that TSRs are folded as independent units. The N-terminal end and TSR5 of properdin are implicated in CSb binding. The vertices of properdin oligomers may be important for interaction with CSb. TSR4 may also be involved in stabilization of the C3bBb complex. The sulphatide binding site is distinct from the CSb binding site, but TSR5, which contains many basic residues, may be important for both activities.