FILIP1L INHIBITS OVARIAN CANCER METASTASIS THROUGH INHIBITION OF WNT SIGNALING

Ovarian cancers are often diagnosed at an advanced stage with a 5-year survival rate below 25%. Identifying key mediators of ovarian cancer progression is crucial to overcoming this deadly disease. WNT signaling mediates progression of many types of cancer, and growing evidence suggests that this pathway also plays a critical role in ovarian cancer invasion and metastasis. We have shown that a novel tumor suppressor-like protein, filamin A interacting protein 1-like (FILIP1L), inhibits ovarian cancer invasion and metastasis and inhibits WNT signaling. Importantly, we demonstrated that FILIP1L localizes in centrosomes, which also comprise proteasomes and components of the beta-catenin destruction complex -- beta-catenin is a central transcriptional activator in the WNT pathway. Thus, inhibiting beta-catenin-mediated transcription will block downstream pathways that are regulated by its transcriptional targets. We hypothesize that FILIP1L facilitates beta-catenin degradation in centrosomes and the resulting downregulation of beta-catenin targets reverses the metastatic phenotype of ovarian cancer cells. Our published and unpublished work supports our hypothesis: (1) Using an ovarian orthotopic model, we showed that FILIP1L significantly inhibits ovarian peritoneal metastasis. (2) FILIP1L inhibits the epithelial-to-mesenchymal transition (EMT), which enhances cell invasion and metastasis. (3) FILIP1L decreases levels of active beta-catenin and increases inactive beta-catenin, which is slated for proteasomal degradation. This results in loss of nuclear beta-catenin and beta-catenin-directed transcriptional activity. Together, our preliminary findings show that by downregulating beta-catenin, FILIP1L inhibits canonical WNT signaling, which modulates EMT. These processes are essential to invasiveness and metastasis. We now propose to further explore the role of FILIP1L in ovarian cancer by the completion of the following specific aims and study design.Aim 1: To investigate the mechanism by which FILIP1L enhances proteasome-mediated beta-catenin degradation and how this modulates the canonical WNT pathway.Using FILIP1L deletion mutants that we have already generated, we will identify the domains required for centrosomal localization and association with the beta-catenin destruction complex. Loss-of-function mutants as well as dominant-negative mutants of FILIP1L will be identified by Topflash activity. We will also determine the role of FILIP1L in phospho-beta-catenin degradation by the ubiquitin-proteasome system.Aim 2: To determine whether EMT downregulation by FILIP1L inhibits invasion and metastasis in ovarian cancer.We will determine whether FILIP1L modulation of EMT markers correlates with inhibition of ovarian cancer invasion and metastasis. Primary and metastatic tumors from orthotopic injections in mice will be examined for the expression of FILIP1L, beta-catenin, and EMT markers. Similar analyses will be performed in human ovarian cancer tissue microarrays. An inverse correlation between FILIP1L expression and these markers will support the central hypothesis. Further, we will modify our FILIP1L-expressing cell lines to overexpress or knock down mesenchymal markers such as SNAIL and determine if EMT inhibition by FILIP1L is reversed by modulating the expression of mesenchymal markers.Impact: Treatment strategies for ovarian cancer urgently need new targets. Here we propose that FILIP1L could be the basis for novel and innovative therapies for this deadly disease. FILIP1L expression was inversely correlated with an invasive/aggressive phenotype and like many other tumor suppressors, is downregulated by promoter hyper-methylation in cancer cells of various histologies including ovarian, prostate, breast, colon, lung, and pancreatic. Completion of the proposed studies will provide immediate and important insights into the role of FILIP1L in regulating the metastatic phenotype of ovarian cancer. As a long-range outcome, compounds mimicking FILIP1L activity or specifically inducing its expression could therefore be developed as novel therapeutics for ovarian cancer. As an increasing number of women are members of all branches of our military, cancers that affect women present a risk to our national defense. As ovarian cancer metastases are a major source of patient mortality, the outcome of the proposed research will likely benefit active duty Service members, Veterans, and their dependents.