PDCD4 as a prognostic factor and a modulator of cell proliferation, migration and invasion in ovarian cancer

Abstract

Programmed cell death 4 (Pdcd4), a novel gene and originally identified as the neoplastic transformation inhibitor, is down regulated in human colon, breast and lung cancer cells and considered as a diagnostic and prognostic marker in lung cancer. It has been shown to have tumor suppressor properties such as inhibition of cell invasion and proliferation, as well as induction of apoptosis. However, those properties of Pdcd4 are tissue specific. The mechanisms of function of Pdcd4 are largely unknown and its function and modulation in ovarian cancer is still elusive. The objectives of our present study are firstly to investigate the expression of Pdcd4 in normal and malignant ovarian tissues and the role of Pdcd4 in ovarian carcinogenesis; and secondly, to study the function of Pdcd4 in the regulation of cell proliferation, migration and invasion and modulation of Pdcd4 in ovarian cancer. Using both western blot and real-time quantitative PCR analyses, we demonstrated that Pdcd4 expression was continuously down-regulated in the sequence of normal-borderline-malignant ovarian tissue samples. Higher Pdcd4 expression was found to be associated with longer disease-free survival (p=0.037). Using immunohistochemical staining approach, we found the subcellular localization of Pdcd4 differed in the way that, normal ovarian tissues showed distinctive nuclear localization while malignant ovarian tissues showed mainly cytoplasmic staining. To further explore the function of Pdcd4 in ovarian cancer cells, we developed Pdcd4 over-expression stable clones in ovarian cancer cell lines. Our in vitro studies demonstrated that ectopic Pdcd4 expression significantly inhibited ovarian cancer cell proliferation by inducing cell cycle arrest at G0/G1 stage and the upregulation of cell cycle regulators p27 and p21. The induction of p21 by Pdcd4 was not mediated through p53. Using wound healing, transwell migration and invasion assay, we demonstrated Pdcd4 significantly inhibited ovarian cancer cell migration and invasion. In conclusion, loss of Pdcd4 was a common abnormality at molecular level in ovarian cancer and it might be a potential prognostic factor in ovarian cancer patients. In addition, our results also provided first evidence for the tumor suppressor properties of Pdcd4 in inhibition of cell proliferation by inducing cell cycle arrest and modulating cell cycle regulators, as well as inhibition of cell migration and invasion in ovarian cancer cells.