Abstract
Earlier studies suggested that there is a specific activity in mammalian serum and plasma that supports epidermal (epithelial) cell movement. This activity was shown to be nondialyzable and heat labile. In the studies reported here, using standard biochemical procedures--i.e., ammonium sulfate fractionation, ion-exchange and gel filtration chromatography, isoelectric precipitation, and preparative polyacrylamide gel electrophoresis--we have purified a factor from human plasma that supports epidermal cell movement. The factor travels as an apparent single band on disc gel electrophoresis and corresponds to a glycosylated single-chain protein of approximately 65,000 +/- 3,000 daltons. The purified fraction is necessary and sufficient for dissociated epidermal cells, (ii) outgrowth of epithelial sheets from skin explants, and (iii) epiboly, epithelial sheet movement over a floating skin explant. The purified fraction is active at a concentration of 1-2 micrograms/ml of growth medium. It is destroyed by trypsin and its activity is augmented more than 10-fold by a second, as yet unpurified, fraction of plasma. These studies support the notion that a single protein of plasma supports epidermal cell movement and that this protein may play an important role in wound closure. Because it supports epiboly, the most biologically relevant of the assays, it has been named epibolin.