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The roles of Monoamine Oxidase-A and p38(MAPK) in breast cancer



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Monoamine oxidase-A (MAO-A) is an enzyme that has historically been linked to major depressive disorder (MDD). The prevalence of MDD among breast cancer patients is almost 25%, but realistically it is underdiagnosed within this patient population. Most breast cancer is deemed estrogen receptor positive [ER(+)] and is commonly treated with the anti-estrogenic chemotherapeutic compound tamoxifen. Resistance to tamoxifen has been associated with a paradoxical activation of the stress-associated kinase, p38(MAPK) (normally associated with cell death). Our research group has recently demonstrated that p38(MAPK) can regulate the function of MAO-A in glial cells. Taken together, MAO-A, depression and p38(MAPK) are all associated with a poor prognosis in breast cancer patients, particularly those with an ER(+) status. Several mechanisms have been proposed in each respect and we hope to further elucidate this relationship by focussing on the interaction between MAO-A and p38(MAPK) in the context of breast cancer. The hypothesis states that a functional interaction between the p38(MAPK) and MAO-A systems alters breast cancer cells in an ER-dependent manner. The proposed objectives of this project are to determine what might be influencing MAO-A function in breast cancer cells, and how changes in MAO-A function affect cell phenotype. Using pharmacological approaches (i.e. antidepressant drugs), we investigated the role of MAO-A and p38(MAPK) on selected characteristics of ER(+) (e.g. MCF-7) and ER(-) (e.g. MDA-MB-231) breast cancer cells under four treatment conditions, which include clorgyline (CLG), an antidepressant MAO-A inhibitor, and SB203580, an inhibitor of p38(MAPK). Our results indicate that the very high MAO-A activity in MDA-MB-231 (MB-231) cells was partly dependent on p38(MAPK) activity. The tumourigenic properties (e.g. anchorage-independent growth, migration) of MB-231 cells depended on both MAO-A and p38(MAPK) functions, although the effects were not additive suggesting that both inhibitors were exerting their respective effects via common signalling targets. The role of MAO-A and p38(MAPK) on MB-231 mitochondrial function and cell growth was negligible. In contrast, MAO-A and p38(MAPK) only influenced mitochondrial function in MCF-7 cells and did not affect any of the other tumourigenic properties measured. Immunocytochemical methods, supported by Western blotting, revealed an increase in E-cadherin expression in both cell lines. This suggested that MAO-A and p38(MAPK) could be influencing transitions between epithelial and mesenchymal phenotypes. Our in vitro findings suggest that MAO-A and p38(MAPK) might contribute to a common mechanism in breast cancer cell lines, but that their influence on cell phenotype is less dependent on the respective cell's ER status and perhaps more so dependent on the cell's metastatic potential. If this is the case, then the contribution of MAO-A and p38(MAPK) to [clinical] metastatic breast cancer should be duly considered. Our ongoing investigations are focussing on the influence of clinically relevant antidepressants on breast cancer cell phenotype in vitro.



Monoamine oxidase-A, p38(MAPK), breast cancer



Master of Science (M.Sc.)




Biological Psychiatry


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