Identification of a cell surface-binding protein for the core protein of the basement membrane proteoglycan

We have identified a protein(s) on the surface of hepatocytes that binds to the core protein of the heparan sulfate proteoglycan of basement membranes. These cells attached and spread on substrates prepared from the basement membrane heparan sulfate proteoglycan (HSPG) and its core protein (HSPG-core). Three proteins (Mr = 38,000, 36,000, and 26,000) were found to bind to a HSPG-core affinity column using extracts of iodinated hepatocytes, whereas proteins extracted from isolated membranes contained primarily the larger protein (Mr = 38,000). Similar results were obtained using a solid phase binding technique using labeled HSPG-core. Binding of HSPG-core to the protein (Mr = 38,000) was not altered by the presence of an excess of heparin, heparan sulfate, fibronectin, laminin, or collagen IV but was reduced by unlabeled HSPG-core. Similar studies showed that the binding protein (Mr = 3,0000) was present in extracts from the membranes of Engelbreth-Holm-Swarm tumor cells, Madin-Darby canine kidney cells, COS cells, melanoma cells, and rat kidney epithelial cells but not in fibroblasts. The protein was found in increased amounts in 3T3 cells treated with retinoic acid. These observations suggest that a variety of cells that contact basement membrane contain the proteoglycan-binding protein.