Abstract
Cytoskeletal regulation in tumour invasion and metastasis involves Ras-related small GTPases and their effectors, such as PAKs. PAK isoforms have been found to be overexpressed in many tumours and are generally associated with poorer prognosis. PAK1 overexpression has been associated with bladder tumour recurrence and progression but the roles for other PAKs are unclear. We found that PAK5 has a distinct expression profile in bladder cancer. We proceeded to characterise the role of PAK5 in the cell biology of bladder cancer.Bladder cancer cell-lines of invasive and non-invasive origins were screened for the expression of PAK5 using isoform-specific antibody. Confocal microscopy and co-immunoprecipitation were used to characterise the subcellular localisation and interacting partners of PAK5. Functional studies were performed using recombinant PAK5 and siRNA. PAK5 mRNA expression in patient samples was screened by quantitative RT-PCR.
We found that PAK5 protein is differentially expressed in bladder cancer cell lines, with higher expression levels in non-invasive bladder cancer cells. In tissue samples, PAK5 expression was also higher in normal bladder tissues, and reduced in tumours. Endogenous PAK5 co-localises with adherens junction proteins such as E-cadherin and P120-catenin, and their interactions were confirmed by co-immunoprecipitation. Silencing of PAK5 in RT4 cell using siRNA technology affected the cell morphology resulting in smaller and more rounded cells. Silencing of PAK5 also affected the protein level of E-cadherin and the integrity of cell-cell adherens junction.
Our results have indicated that PAK5 expression is associated with non-invasive tumours and cell morphology. We found that in bladder cancer cells, PAK5 is a component of the adherens junction complex. We hypothesise that PAK5 contributes to maintain the adherens junction stability. Further research investigating the mechanism of interaction of PAK5 within the adherens junctions will assess the prognostic and therapeutic utility of PAK5 in bladder cancer.
| Date of Award | 2015 |
|---|---|
| Original language | English |
| Awarding Institution |
|
| Supervisor | Claire Wells (Supervisor) & Prokar Dasgupta (Supervisor) |