Abstract 337: Expression of claudin-7 in colon cancer cells induces mesenchymal to epithelial transition (MET) and inhibits tumorigenesis

Background: The claudin family of proteins is integral to the structure and function of tight junction. However, studies have revealed roles of tight junction proteins including claudins in the regulation of proliferation, migration and epithelial differentiation in addition to their known role in epithelial barrier function. Recent studies support a key role of claudin-7 in the regulation of intestinal epithelial cell functioning and we have reported marked decreases in claudin-7 expression in colon cancer samples in a stage-specific manner. However, role of claudin-7 in the regulation of colon tumorigenesis remains poorly understood. Objective: To determine the role of claudin-7 expression in the regulation of colon cancer growth and progression. Methods: Full-length human claudin-7 cDNA was stably expressed in SW620 colon cancer cells (no detectable endogenous claudin-7 expression). In parallel, claudin-7 expression was stably inhibited in HT-29 colon cancer cells by RNA-interference using anti-human claudin-7 siRNA. Effect upon cell morphology, proliferation, apoptosis and migration was examined. Colony-forming and invasion assays were used to examine effect upon tumorigenic and/or invasive abilities of the cell lines used. Effect of claudin-7 expression upon tumor number/growth was examined using in vivo injection of the cells in nude athymic mice. Results: Claudin-7 expression in the poorly differentiated SW620 cells induced epithelial differentiation as SW620claudin-7 cells acquired epithelial morphology, showed increased transepithelial resistance (4-fold), decreased permeability (5-fold) and proliferated less (3-fold) compared to SW620vector cells. Additionally, claudin-7 expression induced E-cadherin expression while expression of Vimentin as well as claudin-1, a known colon tumor promoter was markedly decreased. Assays using growth in soft-agar (3-fold) and cell invasion (3-fold) further showed significant decreases in the tumorigenic ability of SW620claudin-7 cells versus SW620vector cells. In contrast, claudin-7 knockdown in HT-29 cells led to a decrease in E-cadherin expression, and increased Vimentin expression. Furthermore, Claudin-7 knockdown cells formed more colonies on softagar (4-fold) and invaded more (3-fold) when subjected to transwell-based invasion assay. Most, importantly, when inoculated into the athymic (nude) mice, SW620claudin-7 cells produced fewer tumors and of smaller size compared to the SW620vector cells while claudin-7 knockdown cells produced more tumors compared to the control cells. Conclusion: Taken together, outcome from our study suggests a colon tumor suppressive role for claudin-7 and thus claudin-7 may represent potential marker for colon cancer detection and a potential target for therapy. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 337. doi:1538-7445.AM2012-337