Regulation of cell-cell contact molecules and the metastatic phenotype of medullary thyroid carcinoma by the Raf-1/MEK/ERK pathway

Background. Medullary thyroid carcinoma (MTC) is highly metastatic. We have recently reported that activation of the Raf-1/MEK/ERK signaling pathway in MTC cells results in morphologic changes. We hypothesized that Raf-1-induced morphologic changes could be associated with alterations in cell-cell contact molecules, thereby affecting the metastatic potential of MTC cells. Methods. An estradiol (E-2)-inducible Raf-1 MTC cell line (TT-raf) was utilized in this study. Western blot analysis was used to confirm the Raf-1/MEK/ERK pathway activation and to measure levels of essential cell-cell contact molecules. Assays for cell adhesion and migration, were performed to investigate the cell motility. Results. E-2 treatment of TT-raf cells resulted in the Raf-1/MEK/ERK pathway activation as evidenced by increased levels of phospho-MEK1/2 and -ERK1/2. This resulted in significant reductions in levels of essential cell-cell contact molecules including E-cadherin, beta-catenin, and occludin. Importantly, activation of the Raf-1/MEK/ERK pathway and the associated decrease in essential cell-cell contact molecules dramatically inhibited the abilities of adhesion and migration in MTC cells. Furthermore, treatment of Raf-1-activated cells with U0126, a specific inhibitor of MEK, abrogated these Raf-1-induced effects indicating that the suppression of the metastatic phenotype in MTC cells is a MEK-dependent pathway. Conclusion. These data suggest that. the Raf-1/MEK/ERK pathway regulates essential cell-cell contact molecules and metastatic phenotype of MTC cells. Thus, these findings provide further insight into the key steps in the metastatic progression of MTC. (Surgery 2008; 144:920-5.)