Interactions of gelatinases with soluble and immobilized fetuin and asialofetuin

We have analyzed the interactions of human and mouse gelatinases with fetuin and asialofetuin. The data showed that recombinant human gelatinase A (MMP-2) and B (MMP-9) were both specifically bound to asialofetuin and fetuin immobilized to activated agarose (affigel) with subsequent cleavage of the enzymes to lower molecular weight forms, which were likewise bound to asialofetuin/fetuin. The binding of gelatinases to immobilized forms of asialofetuin and fetuins was abrogated in the presence of either soluble fetuin or asialofetuin. Endogenous mouse macrophage gelatinases (mol wt 92 and approximately 52 kDa) were also specifically bound to immobilized asialofetuin upon which the two forms of the gelatinases were reduced to a approximately 45-kDa fragment. The binding of the approximately 45-kDa fragment to asialofetuin was also abrogated in the presence of either soluble fetuin or asialofetuin. Whereas only the activated MMP-2 bound to immobilized asialofetuin had significant gelatinolytic activity, both the zymogen and the activated forms of MMP-9 hydrolyzed soluble [3H]gelatin to the same extent while still bound to asialofetuin. Our data suggest that cell surface bound fetuin/asialofetuin could perform two functions: they could (a) act as cell surface receptors or anchors for MMP-2 and MMP-9 and (b) bind and activate MMP-9 on the cell surface.