A role for a 70-kDa amino-terminal fibronectin fragment in supporting soluble gelatin interactions with rat peritoneal macrophages.

Seventy-kilodalton amino-terminal and 180-kDa cell-binding fibronectin fragments were used to determine which fibronectin domains support soluble gelatin interactions with macrophages. At each time measured, intact and 180-kDa fibronectin supported significantly larger quantities of cell-associated gelatin than control levels (P < 0.05). Throughout the time course fibronectin supported more binding than 180 kDa. Seventy kilodalton did not augment gelatin binding until 2 h, but by 6 h 70 kDa supported more binding than intact fibronectin (P < 0.01). This appeared to result from a cellular response initiated by 70-kDa-gelatin interactions with the macrophages. Within 4 h the majority of gelatin associated with cells under control conditions, and in the presence of fibronectin or 180 kDa, was internalized. Seventy-kilodalton-mediated binding remained localized primarily to the cell surfaces at all times. The macrophages partially degraded the internalized and external gelatin fractions. These results demonstrate that intact fibronectin and specific fibronectin fragments support soluble gelatin interactions with macrophages.