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The tumor suppressor in lung cancer 1 (TSLC1/IGSF4) encodes an immunoglobulin-like cell adhesion molecule whose cytoplasmic domain contains a protein 4.1-binding motif (protein 4.1-BM) and a PDZ-binding motif (PDZ-BM). Loss of TSLC1 expression is frequently observed in advanced cancers implying its involvement in tumor invasion and/or metastasis. Using Mardin-Darby canine kidney (MDCK) cells expressing a full-length TSLC1 or various cytoplasmic deletion mutants of TSLC1, we examined the role of TSLC1 in epithelial mesenchymal transitions (EMT) during the hepatocyte growth factor (HGF)-induced tubulogenesis and cell scattering. In a three-dimensional (3D) culture, the full-length TSLC1, which was localized to the lateral membrane of MDCK cysts, inhibited HGF-induced tubulogenesis. In contrast, the mutants lacking either the protein 4.1-BM or the PDZ-BM abolished the inhibitory effect on tubulogenesis. In addition, these mutants showed aberrant subcellular localization indicating that lateral localization is correlated with the effect of TSLC1. In a two-dimensional (2D) culture, the full-length TSLC1, but not the mutants lacking the protein 4.1-BM or the PDZ-BM, suppressed HGF-induced cell scattering. Furthermore, the cells expressing full-length TSLC1 retained E-cadherin-based cell-cell adhesion even after being treated with HGF. These cells showed prolonged activation of Rac and low activity of Rho, whereas the HGF-treated parental cells induced transient activation of Rac and sustained activation of Rho. Prolonged Rac activation caused by the expression of TSLC1 required its cytoplasmic tail. These findings, taken together, suggest that TSLC1 plays a role in suppressing induction of EMT by regulating the activation of small Rho GTPases.

[Proc Amer Assoc Cancer Res, Volume 47, 2006]