Background: Ovarian carcinoma causes the highest mortality among all gynecological cancers. To improve the survival, discovery of novel therapeutic targets for ovarian carcinoma is worthy. p21-activated kinases (Paks) are vital signaling components in carcinogensis, thus may be potential molecular targets for cancer therapy. Pak4, a recently identified Pak family member, was found to play important roles in carcinogenesis. However, its involvement in ovarian carcinogensis is still poorly defined. In the present study, we aimed to characterize the expression of Pak4 and p-Pak4 (the activated form) during malignant progression of ovarian tumor and correlate it with clinical outcome of patients. The functional impact of Pak4 on migration and invasion of ovarian carcinoma cells were also determined.

Methods: Pak4 and p-Pak4 expression in 100 clinical samples of ovarian tumors including benign cystadenomas, borderline tumours, carcinomas of different histological subtypes as well as metastatic foci of ovarian carcinomas was evaluated by immunohistochemistry. By immunoblotting and fluorescence microscopy, Pak4 expression was also assessed in cell-lines of human normal ovarian epithelium (HOSE-6-3 and HOSE-17-1) and human ovarian carcinoma (SKOV-3, OVCAR-3, OVCA420, OVCA429 and OVCA433). The effects of Pak4 on migration and invasion of ovarian carcinoma cells were determined by wound healing assay and cell invasion assay with knock-down approach using siRNA against Pak4.

Results: Strong cytoplasmic staining of Pak4 was observed in ovarian cancer cells while immunoreactivity for p-Pak4 was predominantly found in the nucleus. In contrast, there was weak or no expression of Pak4 in borderline tumors and benign cystadenomas. Besides a statistically significant (P<0.001) increased expression observed with progression from benign cystadenoma to carcinoma, there was significant increase in Pak4 expression in the metastatic foci when compared with the primary ovarian carcinomas. Pak4 overexpression was also associated with shorter patient overall survival (P<0.05). Such overexpression was confirmed in ovarian carcinoma cell lines in contrast to its absent expression in HOSE. By wound healing assay and cell invasion assay, the motility and invasiveness of OVCA420 and OVCA433 transiently transfected with siRNA against Pak4 was found to be significantlyreduced when compared with that treated with control siRNA.

Conclusion: Our findings suggest that Pak4 overexpression was correlated with malignant progression of ovarian tumor as well as overall survival of patients with ovarian cancer. Pak4 also plays a significant role inovarian carcinoma migration and invasion. Nuclear localization of Pak4/p-Pak4 also suggested its possible role on gene transcription. Thus, Pak4 may act as a potentially reliable prognostic marker and therapeutic target in ovarian carcinoma.

98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA