Purification and biological characterization of epitaxin, a fibroblast-derived motility factor for epithelial cells

We have identified a motility factor in conditioned medium of human fibroblasts that stimulates the migration of HepG2 cells in the Boyden chamber assay. This factor, termed epitaxin, was purified to homogeneity by ammonium sulfate precipitation, hydrophobic interaction chromatography on phenyl-Sepharose, and a series of reverse phase high performance liquid chromatography. Under a nonreducing condition, purified epitaxin migrated as a 36-kDa band, and the biological activity was recovered from the area in the gel coinciding with this band. Purified epitaxin stimulates the motility of HepG2 cells in the concentrations above 1 ng/ml with half-maximal activity at 4.2 ng/ml, and its mode of action is mainly chemotactic. Epitaxin slightly stimulates DNA synthesis of HepG2 cells, while scatter factor/hepatocyte growth factor which also stimulates the motility of HepG2 cells showed a growth-inhibitory effect. Epitaxin increases the motility of a wide variety of epithelially derived tumor cell lines, but none of the tested fibroblast lines responded to epitaxin. These results define epitaxin as a novel fibroblast-derived factor that affects the migration, and possibly the invasion, of epithelially derived tumor cells.