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.


CONCLUSIONS
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.
Ning
Li
L
Endocrine Surgery Research Laboratories, Department of Surgery, University of Wisconsin School of Medicine and Public Health, and the University of Wisconsin Paul P. Carbone Comprehensive Cancer Center, Madison, Wis, USA.
Kunnimalaiyaan
Muthusamy
M
Chen
Herbert
H
D018276:Carcinoma, Medullary / Q000378:metabolism / Q000503:physiopathology*; D002448:Cell Adhesion; D015815:Cell Adhesion Molecules / Q000096:biosynthesis*; D045744:Cell Line, Tumor; D002465:Cell Movement; D006801:Humans; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism*; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D015398:Signal Transduction; D013964:Thyroid Neoplasms / Q000378:metabolism / Q000503:physiopathology*; D048490:raf Kinases / Q000378:metabolism*
D015815:Cell Adhesion Molecules; D048490:raf Kinases; D020928:Mitogen-Activated Protein Kinases; D020929:Mitogen-Activated Protein Kinase Kinases