The Amyloid Precursor Protein and Cell Viability in Diseases of the Ageing Brain.

Gough, Mallory (2013) The Amyloid Precursor Protein and Cell Viability in Diseases of the Ageing Brain. PhD thesis, Lancaster University.

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Abstract

The amyloid precursor protein (APP) has been extensively studied in relation to Alzheimer's disease, but the physiological function of the protein has yet to be determined. One possible role for APP may be to protect cells against the detrimental effects of excess copper. In the current study I have investigated which regions of the APP molecule participate in this putative function. I have used both Du145 and SH-SY5Y mammalian cell systems to explore this question, relating the generated results to both cancer and Alzheimer's Disease. Initial studies using western blotting showed that a range of prostate cancer cell lines express APP, and that increased APP expression levels may represent a more advanced stage of cancer progression. Exogenous copper altered the expression levels of APP in Du145 cells, immediately indicating the intricate relationship between APP and copper. Subsequently, using MTS assays, I found that APP can indeed enhance cell viability in the face of copper, in both of the cell systems stated above. This role is isoform dependent, being specific to the APP695 isoform, which is predominantly found in the brain. N-terminal copper binding and copper binding within the Abeta region of the APP holoprotein appeared to be a prerequisite for this action. The intracellular domain was also required in order to enhance cell viability, and the importance of this region was assigned to specific tyrosine residues within the domain. APP over-expression in Du145 cells also appeared to induce a partial epithelial to mesenchymal transition of the cells. Along with suggesting a possible physiological function for APP, these data suggest that prostate cancer epithelial cells metastasising to the brain might utilise APP to protect them against the increased copper levels found in this organ.