PAK4 as a potential therapeutic target in pancreatic ductal adenocarcinoma (PDAC).

Abstract

e23139 Background: PDAC is an aggressive cancer and metastatic spread requires reorganization of the actin cytoskeleton, a process dependent on Rho family GTPases and their interaction with downstream effectors. p21 activated kinases (PAK1-6) are effectors of Rho GTPases Cdc42 and Rac, and play a key role in cell migration and survival. PAK4 can be amplified in PDAC and can reciprocally activate the PI3K pathway. Hepatocyte growth factor (HGF), via c-Met, is an established activator of PAK4 and the PI3K pathway and may promote PDAC invasion. We hypothesized that there is a link between PAK4 and PI3K downstream of HGF and thus PAK4 is a potential therapeutic target in PDAC. Methods: Several invasive PDAC cell lines were used including PaTu 8988T, PaTu 8988S, Capan 1, Panc 1 and PaTu 8902. SiRNA transfection allowed transient loss of PAK4 and cell migration was measured using 2D time lapse microscopy. An organotypic model consisting of PDAC and stromal cells within an extracellular gel of collagen was developed to assess 3D invasion. Immunofluorescence staining of cytokeratin and smooth muscle actin allowed analysis of depth of invasion. Protein expression was measured using western blotting and protein interaction by pulldown assays. Results: Treatment with the c-Met ligand HGF increased migration speed, persistence of direction and importantly PDAC invasion. HGF also stimulated the phosphorylation of several proteins within the PI3K pathway including AKT and PRAS40. Loss of PAK4 expression resulted in a concomitant loss in PI3K signalling. Moreover, PAK4 directly binds to the p85α subunit of PI3K in PDAC cells. Reduced PAK4 expression in PDAC cells suppressed HGF-induced migration, and PAK4 depletion significantly inhibited the invasion response to HGF. Conclusions: We demonstrate a novel link between PAK4, PI3K and AKT, and show the significant effects of PAK4 on PDAC cell polarity, migration and invasion. Our results strongly support further investigation of PAK4 as a therapeutic target in PDAC, particularly given the minimal impact of PI3K-AKT pathway inhibitors in PDAC to date.