The cysteine-rich domain of human ADAM 12 supports cell adhesion through syndecans and triggers signaling events that lead to beta 1 integrin-dependent cell spreading

The ADAMs (a disintegrin and metalloprotease) family of proteins is involve d in a variety of cellular interactions, including cell adhesion and ectodo main shedding. Here we show that ADAM 12 binds to cell surface syndecans. T hree forms of recombinant ADAM 12 were used in these experiments: the cyste ine-rich domain made in Escherichia coli (rADAM 12-cys), the disintegrin-li ke and cysteine-rich domain made in insect cells (rADAM 12-DC), and full-le ngth human ADAM 12-S tagged with green fluorescent protein made in mammalia n cells (rADAM 12-GFP). Mesenchymal cells specifically and in a dose-depend ent manner attach to ADAM 12 via members of the syndecan family. After bind ing to syndecans. mesenchymal cells spread and form focal adhesions and act in stress fibers, Integrin pi was responsible for cell spreading because fu nction-blocking monoclonal antibodies completely inhibited cell spreading, and chondroblasts lacking pi integrin attached but did not spread. These da ta suggest that mesenchymal cells use syndecans as the initial receptor for the ADAM 12 cysteine-rich domain-mediated cell adhesion, and then the pi i ntegrin to induce cell spreading. Interestingly, carcinoma cells attached b ut did not spread on ADAM 12. However, spreading could be efficiently induc ed by the addition of either 1 mM Mn2+ or the pi integrin-activating monocl onal antibody 12G10, suggesting that in these carcinoma cells, the ADAM 12- syndecan complex fails to modulate the function of pi integrin.