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Investigating the importance of PAK1 kinase activity during breast cancer cell spreading and migration

Student thesis: Doctoral ThesisDoctor of Philosophy

Breast cancer is a primary cause of cancer lethality in women due to its ability to metastasise to other organs. Currently there are no therapeutic interventions specifically targeting breast cancer metastasis. p-21 activated kinases (PAK 1-6) are recognised regulators of cell morphology and thus promotion of migration. Therefore, these proteins have been implicated in driving metastasis and many pharmaceutical companies have developed PAK programmes.
In particular PAK1 is associated with breast cancer. The PAK1 gene is located in a genomic region which is frequently amplified in many breast cancers. Indeed, PAK1 is reported to be overexpressed and/or hyperactivated in over 50% of human breast cancers. However, the importance of PAK1 kinase activity over PAK1 protein interactions is not well established. This is crucial given many drug discovery programmes are focused on kinase inhibition. Furthermore, the downstream targets of PAK1 specifically in breast cancer are not fully described; especially those proteins most important for cell spreading. This project focuses on the role PAK1 plays in breast cancer cell spreading and migration, with an emphasis on unravelling the kinase dependent pathways.
PAK1 depletion via shRNA and CRISPR-Cas9 technology in a triple negative breast cancer cell line caused a decrease in both cell spread area and cell migration. These findings were replicated using a pharmacological inhibitor of PAK1 kinase activity. The importance of PAK1 kinase activity in breast cancer cell migration was confirmed where pharmacological inhibition or depletion of PAK1 lead to a decrease in in vitro cell invasion and in vivo cell migration. Using an inducible system to stimulate PAK1 kinase activity a specific role in cell spreading was observed. Induction of cell spreading via PAK1 activation was associated with the serine 910 phosphorylation of FAK and serine 189 phosphorylation of ERK3. These are novel pathways in breast cancer. Taken together these results place PAK1 at the centre of cell spreading and migration and suggest that kinase activity is essential for these cellular responses. Thus, findings in this thesis support pharmaceutical inhibition of kinase activity as a valid therapeutic approach.
Original languageEnglish
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Award date2019

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