Amino-terminal processing of cell surface heparin-binding epidermal growth factor-like growth factor up-regulates its juxtacrine but not its paracrine growth factor activity.

Human heparin-binding epidermal growth factor (EGF)-like growth factor (HB-EGF) expressed on Chinese hamster ovary (CHO) cells is synthesized as a 19-kDa major, and 22- and 27-kDa minor, membrane-anchored precursors (proHB-EGF). In contrast, the 27-kDa species is major and the 19- and 22-kDa ones are minor in mouse proHB-EGF. The juxtacrine growth factor activities of human and mouse proHB-EGFs on CHO cells toward EP170.7 cells in co-culture are significantly different. To investigate the relationship between the juxtacrine growth factor activities and the molecular species, we prepared human-mouse chimeras. Chimeras that have the human amino-terminal sequence with a mouse EGF-like domain showed approximately 8-fold up-regulation of the juxtacrine growth factor activity and the predominance of a 19-22-kDa major species. In contrast, chimeras that have the mouse amino-terminal sequence with a human EGF-like domain showed approximately 5-fold down-regulation of the juxtacrine activity and the predominance of the 27-kDa major species. A Gly32.HB-EGF (117-amino acid form), which is amino-terminally extended, induced the same mitogenic activity as that of Arg73.HB-EGF (75-amino acid form), which is amino-terminally truncated. These results strongly suggested that amino-terminal processing of human proHB-EGF would be required for up-regulation of its juxtacrine growth factor activity, but not for its paracrine activity.