Overexpression of αPIX contributes to ovarian cancer metastasis, increased chemoresistance and poor prognosis

Abstract

Background: Ovarian cancer is a lethal gynecological malignancy worldwide. Genes governing metastasis and chemosensitivity are crucial for the development of novel prognostic and therapeutic targets. Alpha PAK interactive exchange factor (αPIX/Cool2) functions as guanine nucleotide exchange factor which activates Rho GTPases, Rac1 and Cdc42. αPIX is involved in various biological functions, ranging from the formation of cytoskeletal-membrane complex and focal adhesion structures to X-linked metal retardation. However, the study of αPIX in cancer has been very limited. In this study, we aimed to investigate the expression, prognostic significance and functional roles of αPIX in ovarian cancer. Methods: The expression of αPIX in 143 clinical samples of ovarian tumors including inclusion cysts, benign cystadenomas, borderline tumors, carcinomas of different histological subtypes as well as metastatic foci of ovarian cancers was analyzed by immunohistochemistry and real-time PCR. αPIX expression was also assessed in cell-lines of human normal ovarian epithelium (HOSE 11-12 and HOSE 17-1) and ovarian carcinoma (SKOV3, OVCAR3, OVCA420, OVCA429, OVCA433, ES2, A2780S and A2780CP) by real-time PCR and immunoblotting. The effects of αPIX on migration and invasion of ovarian carcinoma cells were determined by Transwell migration and invasion assays. Results: By immunohistochemistry, strong cytoplasmic αPIX immunoreactivity was observed in ovarian cancer samples. In contrast, there was moderate staining of αPIX in borderline tumors and weak or no staining in benign cystadenomas/inclusion cysts. We demonstrated a significant association between higher αPIX expression with metastasis of ovarian cancers (P=0.035), advanced stage (P=0.04), high grade cancer (P=0.045), serous/clear cell histological subtypes (P=0.004), reduced chemosensitivity (P=0.036), and shorter overall and disease-free survival (P<0.001). Cox’s regression analysis showed that αPIX expression was an independent prognostic factor (P=0.016). Real-time PCR showed similar results (P<0.05). αPIX mRNA and protein overexpression was also observed in various ovarian cancer cell-lines compared with normal ovarian surface epithelial cell-lines. Consistent with results of immunohistochemistry, an increase in αPIX mRNA and protein expression was detected in A2780CP, a chemoresistant cell lines, than its parental chemosensitive cell line, A2780S. Transwell migration and invasion assays revealed that ectopic αPIX overexpression in OVCA420 enhanced cell migration and invasion. Conversely, transient knockdown of αPIX in OVCAR3 and ES2 led to reduced cell migration and invasion. Conclusion: αPIX was correlated with ovarian cancer progression and metastasis, and the development of chemoresistance. αPIX expression was an independent prognostic marker and might be a therapeutic target in ovarian cancer.