CLDN1 and neoplasm: Reduced CLDN1 Expression Inhibits Tumor Growth in Mice. To test the importance of CLDN1 to tumors in vivo, we injected female athymic nude mice with SKOV3 cells that had been transduced with a control shRNA or CLDN1-specific shRNA along with a GFP construct (GFP+/shCLDN1 or GFP+/shControl (shCON), respectively).