Osteoblastic interstitial collagenase receptor is a member of the low-density lipoprotein scavenger receptor superfamily

We have previously identified a specific receptor for collagenase on UMR 106-01 rat osteosarcoma cells which is responsible for removal, internalization and degradation of PTH-induced extracellular collagenase. The present work shows that this is a member of aie low-density lipoprotein (LDL) receptor superfamily. The intracellular receptor associated protein (RAP) prevents ligand binding by three members of this family, the lipoprotein receptor related protein (LRP), gp330 and the VLDL receptor. RAP efficiently competed for binding of collagenase to UMR cells indicating that the collagenase receptor is another member of the LDL receptor superfamily. We have eliminated the possibility that the collagenase receptor is the LRP since equivalent collagenase binding was observed on LRP-null mouse embryo fibroblasts as on wild-type cells. Ligand blots of membranes from kidney, liver and UMR cells using 125I-RAP or collagenase show that the UMR membranes contain a similar receptor to LRP (liver) and gp330 (kidney) which is about 600kDa. Western blots using antiserum to rat gp330 suggest that the UMR collagenase receptor is not gp330. We have shown that normal rat osteoblasts and rat embryo fibroblasts also bind collagenase and endocytose and degrade the ligand. Our results suggest that the collagenase receptor is a member of the LDL receptor superfamily and is possibly a new member of mis family.