Midkine, a heparin-binding growth/differentiation factor, exhibits nerve cell adhesion and guidance activity for neurite outgrowth in vitro

By means of a baculovirus expression system, a large amount of mouse midkine (MK) was produced. The protein was purified to homogeneity by heparin-Sepharose column chromatography. The purified protein was of a mature type; the signal peptide was cleaved fit the expected site. To examine the neurite-guiding activity of MK, rat embryonic brain cells (embryonic days 17-18) were cultured on plates coated with purified MK in a grid pattern. The cells attached to and extended their neurites along the substrate pattern. This interaction was strongly inhibited by heparin, but not by other glycosaminoglycans. Treatment of the cells with heparitinase was effective for inhibiting their adhesion to the substrate. These data suggest that the heparin-like domain on cell surface heparan sulfate proteoglycan is the primary site for MK binding upon interaction with nerve cells.