Abstract B62: Assessing the relationship between Mucin 16 and Membrane-type I Matrix Metalloproteinase in intra-peritoneal metastatic events

The process of epithelial ovarian cancer (EOC) metastasis is unique in that epithelial cells detach from the primary tumor and shed into the peritoneal cavity as single cells and multicellular aggregates (MCA), which adhere intraperitoneally and invade the interstitial collagen-rich submesothelial matrix, where they proliferate to anchor secondary lesions. Mucin 16 (MUC16), clinically referred to as cancer antigen 125 (CA125), is a giant mucin-like glycoprotein which is undetected in the epithelium of normal ovaries but highly expressed on the ovarian tumor cell surface. Interestingly, MUC16 tends to shed from tumors, releasing soluble proteolytic fragments into the bloodstream; 90% of women with advanced EOC have elevated blood serum levels of CA125. The catalyst(s) for this shedding is unknown. Membrane-type 1 matrix metalloproteinase (MT1-MMP), an extracellular matrix degrading transmembrane protease, has been implicated in a number of pro-metastatic events. The overexpression of MT1-MMP in EOC tumors relative to the normal ovary, with enhanced expression in metastases relative to primary tumors, suggests that it may be the protease facilitating MUC16 shedding. Immunofluorescence and flow-cytometric detection of MUC16 in ovarian cancer (ovca) cells engineered to overexpress MT1-MMP indicate that MT1-MMP overexpressors have lower surface levels of MUC16. As recent studies suggest that MUC16 binds selectively to mesothelin (potentially mediating the cell-to-cell adhesion inherent in metastasis), we tested the hypothesis that cells that overexpress MT1-MMP (and thus shed MUC16) will be less adherent to mesothelial cells. Examination of the adherence of MT1-MMP overexpressing ovca cells to a live mesothelial cell monolayer indicated decreased cell-to-cell adhesion compared to controls. We have previously shown that up-regulation of MT1-MMP promotes a collagen invasive phenotype in ovarian carcinomas. As the sub-mesothelial matrix is rich in interstitial collagen, we further investigated the potential for MT1-MMP overexpressors to invade a live mesothelial cell monolayer. To assay invasion, a modified transwell “mesothelial mimetic” assay was utilized consisting of a three dimensional collagen type I matrix atop an 8μm filter and overlaid with a confluent layer of mesothelial cells. Seeding of ovca cells +/- MT1-MMP overexpression followed by quantitation of migrating/invading cells indicates a role for MT1-MMP in sub-mesothelial anchoring. These results intimate that MUC16 expression may be key for initial cell-to-mesothelial cell contact and suggest that MT1-MMP overexpression contributes to sub-mesothelial anchoring of EOC cells. Citation Format: Lana Y. Bruney, M. Sharon Stack. Assessing the relationship between Mucin 16 and Membrane-type I Matrix Metalloproteinase in intra-peritoneal metastatic events. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research: From Concept to Clinic; Sep 18-21, 2013; Miami, FL. Philadelphia (PA): AACR; Clin Cancer Res 2013;19(19 Suppl):Abstract nr B62.