The role of RalA in biology and therapy of ovarian cancer.

The Ral (Ras-like) GTP-binding proteins (RalA and RalB), as effectors of the proto-oncogene Ras, play an important role in the molecular pathology of human malignancies. However, the role of Ral in ovarian cancer has not been studied before. Here, we report that RalA was found to be activated in human ovarian cancer cells and tissues as compared to non-malignant ovarian surface epithelial cells or non-malignant ovarian tissues. The RalA downstream effectors (RalBP1 and CDC42-GTP) and regulators (RalGDS, PP2A and Aurora Kinase A) were deregulated in ovarian cancer cells in a manner consistent with overactivation of this signaling pathway. Inhibition of RalA expression with an anti-RalA lentivirus caused a significant reduction in the proliferation and invasiveness of ovarian cancer cells. Similarly, pharmacological inhibition of RalA by GGTI-2147 or inhibition of Aurora Kinase A (an activator of RalA) also suppressed ovarian cancer cell growth in vitro, and suppressed their tumorigenic capabilities in subcutaneous nude mouse model in vivo. Additionally, an increase in the levels of RalA activation was detected in a syngeneic mouse model for ovarian cancer. Finally, we were interested in investigating the status of RalA activation in ovarian cancer stem cells. RalA was found to be active at higher levels in ovarian cancer cells expressing CD24 (a marker for ovarian cancer stem cells). Together, our findings indicate the important role of RalA in the development of ovarian cancer, and shows its potentially significant ramifications in detection, prevention, and therapy of this deadly malignancy.Significance Statement: Our work reveals, for the first time, that RalA is an important contributor to the biology of ovarian cancer. The research delineates the inhibition of RalA as a potential strategy to impede the growth and invasiveness of ovarian cancer. Additionally, the overactivation of RalA is reported in a syngeneic mouse model for ovarian cancer and ovarian cancer stem cells. Therefore, this work increases our understanding of ovarian cancer and provides a novel platform for development of therapies against this deadly disease.