Investigation of the role of Endo180/urokinase-type plasminogen activator receptor-associated protein as a collagenase 3 (matrix metalloproteinase 13) receptor

Procollagenase 3 can be activated by interaction with and cleavage by the cell-associated membrane type I metalloproteinase (MT1 MMP; MMP 14). It has also been shown to bind to a specific receptor, and is subsequently internalized via the low-density lipoprotein-related receptor by osteoblast cell lines. The receptor was identified as a recycling glycoprotein of the macrophage mannose receptor family, Endo180. In order to ascertain whether there is a relationship between Endo180 binding and procollagenase 3 activation, we have compared procollagenase 3 activation by an HT1080 fibrosarcoma cell line overexpressing MT1 MMP, without and with overexpression of Endo180. No difference in procollagenase 3 activation was observed, and neither was the enzyme bound to the cells or internalized. In contrast, the osteoblast cell lines, MG63 and UMR-106, both bound and internalized procollagenase 3. However, immunolocalization studies showed that the Endo180 abundantly expressed by these cells did not co-localize with the procollagenase 3. In further biochemical studies we confirmed that procollagenase 3 did not bind to Endo180, using both ligand-blotting and immunoprecipitation techniques. We conclude that Endo180 is unlikely to be a receptor for collagenase 3 in relation to either its activation or cell binding and internalization, and that other interaction partners must be sought.