Identification of a new membrane-bound heparan sulphate proteoglycan

The morphological changes that occur during intestinal development have been extensively described, but the molecular basis of these changes is largely unknown. As a result of our efforts to identify molecules that play a role in intestinal morphogenesis during development, we have previously isolated a cDNA that is developmentally regulated in the intestine. This cDNA, named OCI-5, was recently shown to have 20-25% identity at the protein-sequence level with glypican and cerebroglycan, two heparan sulphate proteoglycans (HSPG) that are attached to the cell membrane by a glycosyl-phosphatidylinositol (GPI) anchor. Here we provide experimental evidence indicating that OCI-5 is also a GPI-linked HSPG. We demonstrate this by showing that OCI-5 can be labelled with radioactive sulphate and can be digested by heparitinase, but not by chondroitinase. We also show that treatment with phosphatidylinositol-specific phospholipase C releases OCI-5 from the cell surface of COS cells transfected with an OCI-5 expression vector. The identification of OCI-5 as a GPI-linked HSPG confirms that this proteoglycan belongs to the same family of HSPGs that include glypican and cerebroglycan.