| Popis: |
p21-activated kinases (PAKs) are downstream targets of many Rho GTPases. They have been implicated as regulators of cell migration but little is known of their isoform-specific functions. PAK upregulation in some cancers suggests that they could play an important role in invasion and metastasis, making them potential therapeutic targets. In this study RNA interference (RNAi) was used to investigate the roles of PAK 1, PAK2 and PAK4 in DU145 and PC3 prostate cancer cells in response to hepatocyte growth factor (HGF), which stimulates cell migration. RNAi knockdown of PAK 1, PAK2, or PAK4 did not affect the speed of DU145 cell wound healing in vitro, but knockdown of PAK1 or PAK2 had distinct effects on DU145 morphology and scattering. PAK 1-deficient cells remained more spread and maintained more junctions than control cells following HGF stimulation. PAK2-deficient cells formed disorganised colonies and larger lamellipodia were observed after HGF treatment, which were enriched with ERK1/2 and GIT 1/2. Despite the cytoskeletal effects, PAK1 or PAK2 knockdown did not inhibit DU145 cell migration through transwells or invasion through Matrigel, and phosphorylation of many known PAK 1/2 substrates was unaffected. In PC3 cells, knockdown of PAK1 or PAK2 but not PAK4 slowed the speed of migration and PAK2 impaired the HGF-induced phosphorylation of Op 18 suggesting that decreased microtubule stability may lead to the associated phenotype. PAK2 depletion in DU145 or PC3 cells led to increased phosphorylation of PAK 1 at SI99/204, an autophosphorylation site which blocks PIX binding, whereas PAK1 knockdown had no effect on the phosphorylation of PAK2 at the homologous sites. These results show that PAK1, PAK2 and PAK4 play distinct roles in cytoskeletal regulation, probably through shared and isoform-specific substrates. Op 18 is shown to be a likely PAK2 target and a novel regulatory mechanism from PAK2 to PAK1 is identified for the first time. |
