57144

PAK7

The p21-activated kinase 5 (PAK5) is overexpressed in advanced cancer and the transcription factor E47 is a direct repressor of E-cadherin and inducer of epithelial-mesenchymal transition (EMT). However, the relationship between PAK5 and E47 has not been explored. In this study, we found that PAK5-mediated E47 phosphorylation promoted EMT in advanced colon cancer. PAK5 interacted with E47 and phosphorylated E47 on Ser39 under hepatocyte growth factor (HGF) stimulation, which decreased cell-cell cohesion, increased cell migration and invasion in vitro and promoted metastasis in a xenograft model. Furthermore, phosphorylation of E47 facilitated its accumulating in nucleus in an importin alpha-dependent manner, and enhanced E47 binding to E-cadherin promoter directly, leading to inhibition of E-cadherin transcription. In contrast, PAK5-knockdown resulted in blockage of HGF-induced E47 phosphorylation, attenuated association of E47 with importin alpha and decreased E47 binding to E-cadherin promoter. In addition, we demonstrated a close correlation between PAK5 and phospho-Ser39 E47 expression in colon cancer specimens. More importantly, high expression of phospho-E47 was associated with an aggressive phenotype of colon cancer and nuclear phospho-E47 staining was found in certain cases of colon cancer with metastasis. Collectively, E47 is a novel substrate of PAK5, and PAK5-mediated phosphorylation of E47 promotes EMT and metastasis of colon cancer, suggesting that phosphorylated E47 on Ser39 may be a potential therapeutic target in progressive colon cancer.

Ovarian cancer is the most lethal gynecologic cancer and currently ranks fifth in causing cancer-related deaths among women. P21(cdc42/rac1)-activated kinase 5 (PAK5) is a newly identified protein that has been indicated to have oncogenic potential. The present study investigated the expression level of PAK5 in clinical ovarian cancer and the functional roles of PAK5 in ovarian cancer progression. It was initially found that PAK5 was highly expressed in ovarian cancer tissues, particularly in patients with distant metastasis. Higher expression of PAK5 predicted poor survival fates in patients with ovarian cancer (p = 0.008). Knockdown of PAK5 in SKOV3 cells caused epithelial cell phenotypes, whereas overexpression of PAK5 led to remarkable mesenchymal cell phenotypes in A2780 cells. When PAK5 was depleted from SKOV3 cells, cells exhibited impaired wound recovery abilities. Cell migration and invasion abilities were also significantly inhibited. On the contrary, when PAK5 was overexpressed in A2780 cells, the wound recovery ability was enhanced by 68%. Cell migration and invasion abilities were consistently increased to approximately 2-fold. After knockdown of PAK5, the phosphorylation levels of PI3K p85 at Tyr458 and its downstream AKT at Ser473 were both decreased. The total protein of PI3K and AKT as well as the phosphorylation level of AKT at Thr308 remained unaffected. These data suggested that PI3K induced epithelial-to-mesenchymal transition and promoted cell migration and invasion by activating the PI3K/AKT pathway in ovarian cancer. The oncogenic potential of PAK5 in ovarian cancer might suggest that any therapeutic strategies targeting PAK5 had the promising value for ovarian cancer treatment.