Molecular targeting of prostate cancer invasion

Abstract

Prostate cancer (PCa) is the most common cancer in men and the second most common cause of cancer death in the UK. Most of the prostate cancer-related deaths are due to metastasis formation, yet there are no efficient anti-metastatic drugs available, as most chemotherapeutics are directed against cancer proliferation, rather than invasion. Therefore, understanding the mechanisms underlying the metastatic process of PCa is crucial to develop novel therapeutics. It is widely believed that degradation of the extracellular matrix is required to navigate the tumour stroma and can be achieved by cancer cells via the extension of invadopodia, actin-rich structures that protrude from the ventral surface and release metalloproteases at the interface with extracellular matrix (ECM). Invadopodia formation has been observed in-vitro and in-vivo in metastatic cell lines derived from multiple tumour types, and invadopodia are considered important drivers of tumour invasion, although there is less evidence in the prostate setting. The p-21 activated kinases (PAKs) have previously been associated with invadopodia dynamics, and PAK4 was found to be found to be localized within invadopodia in melanoma where it is thought to regulate RhoA activity via PDZ-RhoGEF. However, the molecular mechanisms underlying invadopodia activity in prostate cancer (PCa) remain to be elucidated as the classic PCa cell lines have not been reported to form invadopodia without external stimulation. This study aims to identify if prostate cancer cell lines derived from primary adenocarcinoma can be used to study invadopodia and elucidate the precise mechanism by which PAK4 regulates invadopodia. Characterisation of invasiveness potential revealed that all PCa cell lines tested were capable of spontaneous invadopodia formation and produced significant visible metastasis in Zebrafish dissemination assay. Protein depletion experiments demonstrated that PAK4 is essential for invadopodia formation and invadopodia-mediated matrix degradation in PCa cells. Moreover, we found evidence that PAK4 can regulate both metalloproteases and RhoA activity, possibly via direct phosphorylation of PDZ-RhoGEF. These findings indicate that PAK4 could play multiple roles in invadopodia lifecycle by regulating different downstream pathways, and could therefore constitute an interesting therapeutic target for the prevention of metastasis.

Date of Award	31 Jul 2021
Original language	English
Awarding Institution	King's College London
Supervisor	Claire Wells (Supervisor) & Sarah Rudman (Supervisor)