A heparin-binding growth factor, midkine, binds to a chondroitin sulfate proteoglycan, PG-M/versican

Midkine is a heparin-binding growth factor with survival-promoting and migr ation-enhancing activities. In order to understand the regulation of midkin e signaling, we isolated midkine-binding proteoglycans from day 13 mouse em bryos, when midkine is intensely expressed. Deglycosylation followed by SDS /PAGE revealed various protein bands; one of these was identified as PG-M/v ersican by in gel trypsin digestion and sequencing the resulting peptides. PG-M/versican isolated from day 13 mouse embryos bound midkine with a K-d o f 1.0 nm. Pleiotrophin/heparin-binding growth-associated molecule, which ha s a structure related to midkine, was also bound similarly. Digestion with chondroitinase ABC, AC-I or B abolished the binding to midkine. Heparin as well as chondroitin sulfate D and E inhibited the binding. After chondroiti nase ABC digestion, the midkine-binding PG-M/versican released 4-sulfated, 6-sulfated, 2,6-disulfated and 4,6-disulfated unsaturated disaccharides. Th ese results suggest that midkine binds to a polysulfated domain in the chon droitin sulfate chain with a region of dermatan sulfate structure. This pro teoglycan may modulate the midkine activity, as binding to midkine can enha nce midkine action by concentrating it to the cell periphery or inhibit the action by competing with the binding to a signaling receptor.