Collagenase-3 binds to a specific receptor and requires the low density lipoprotein receptor-related protein for internalization

We have previously identified a specific receptor for collagenase-3 that me diates the binding, internalization, and degradation of this ligand in UMR 106-01 rat osteoblastic osteosarcoma cells. In the present study, we show t hat collagenase-3 binding is calcium-dependent and occurs in a variety of c ell types, including osteoblastic and fibroblastic cells. We also present e vidence supporting a two-step mechanism of collagenase-3 binding and intern alization involving both a specific collagenase-3 receptor and the low dens ity lipoprotein receptor-related protein. Ligand blot analysis shows that I -125-collagenase-3 binds specifically to two proteins (similar to 170 kDa a nd similar to 600 kDa) present in UMR 106-01 cells. Western blotting identi fied the 600-kDa protein as the low density lipoprotein receptor-related pr otein. Our data suggest that the 170-kDa protein is a specific collagenase- 3 receptor. Low density lipoprotein receptor-related protein-null mouse emb ryo fibroblasts bind but fail to internalize collagenase-3, whereas UMR 106 -01 and wildtype mouse embryo fibroblasts bind and internalize collagenase- 3. Internalization, but not binding, is inhibited by the 39-kDa receptor-as sociated protein. We conclude that the internalization of collagenase-3 req uires the participation of the low density lipoprotein receptor-related pro tein and propose a model in which the cell surface interaction of this liga nd requires a sequential contribution from two receptors, with the collagen ase-3 receptor acting as a high affinity primary binding site and the low d ensity lipoprotein receptor-related protein mediating internalization.