Activation of a transfected FGFR‐1 receptor in Madin‐Darby epithelial cells results in a reversible loss of epithelial properties

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Abstract
Basic fibroblast growth factor (bFGF) is a potent mitogen for a wide variety of cell types derived from mesoderm and neuroectoderm. The activity of bFGF is mediated by several types of closely related receptors belonging to the tyrosine‐kinase family of receptors. We have found that Madin‐Darby epithelial cells (MDCK) do not seem to produce bFGF or bFGF receptors. High level expression of human bFGF cDNA in these cells did not produce any mitogenic or morphological effects. Expression of the mouse‐derived cDNA encoding FGF receptor‐1 (FGFR‐1) in MDCK cells resulted in the acquisition of a fibroblast‐like morphology when the transfected cells were cultured at low density in the presence of 0.6% fetal calf serum and 20 ng/ml bFGF. Acidic fibroblast growth factor (aFGF) also induced these morphological changes but not keratinocyte growth factor. The morphological effect was not accompanied by increased bFGF‐induced cell proliferation and did not result in the loss of epithelial cell markers such as cytokeratins. However, the morphological transition was accompanied by changes in the intracellular distribution of actin. In spite of these changes the transfected cells formed monolayers even in the presence of bFGF. Coexpression of bFGF and FGFR‐1 in the MDCK cells resulted in similar morphological effects that were not dependent upon exogenous bFGF. These morphological effects were mimicked by exposure of MDCK cells to either orthovanadate or phorbol ester. Parental and FGFR‐1 ‐expressing MDCK cells formed monolayers tht displayed high electrical resistance. Incubation of monolayers of FGFR‐1‐transfected cells with bFGF resulted in the loss of trans‐epithelial resitance. Monolayers of parental MDCK cells did not lose their trans‐epithelial resistance in response to bFGF, although exposure to phorbol ester did result in the loss of their trans‐epithelial resistance, indicating that the effects on the trans‐epithelial resistance are mediated by protein kinase C activation. Interestingly, orthovanadate did not cause a loss of transepithelial resistance, suggesting that the loss of trans‐epithelial resistance is separable from the morphological transition.

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