BACKGROUND - Mutations in oncogenic Ras contribute to colorectal tumorigenesis. Loss of the cell adhesion protein E-cadherin is associated with tumor invasion and metastasis.
METHODS - Expression of oncogenic Ras was induced in intestinal epithelial cells. Changes in cell morphology, E-cadherin protein expression, and E-cadherin localization were examined by light microscopy, Western blot, and immunofluorescence respectively. Expression of E-cadherin in human colorectal tumors was examined by immunohistochemistry.
RESULTS - Induction of oncogenic Ras results in an epithelial to mesenchymal transformation with loss of membranous E-cadherin expression and mis-localization to the cytoplasm. Removal of Ras stimulus or blockade of the MAP kinase pathway allowed reversion to a normal cellular phenotype and return of E-cadherin to the cell membrane. Loss of or decreased expression of E-cadherin was observed in seven of eight colorectal tumors.
CONCLUSIONS - Oncogenic Ras contributes to malignant transformation and altered E-cadherin expression in intestinal epithelial cells. Similar dysregulation of E-cadherin is found in human colorectal tumors. Ras effects on E-cadherin are critical to malignant transformation in our in-vitro model and may be an important event in human colorectal tumors.