Immunopurification and characterization of a neuronal heparan sulfate proteoglycan

We have identified a unique heparan sulfate (HeS) proteoglycan synthesized by the neuronal-like cell line PC12. The proteoglycan, purified with monoclonal antibodies from medium conditioned by PC12 cells, has an apparent molecular weight of 350,000, and it contains a Mr 80,000 core protein and HeS side chains of Mr 15,000 each. The purified molecule has the same apparent size and density as it has in conditioned medium. HeS proteoglycans that are indistinguishable antigenically but very difficult to solubilize are found on the external surface and in the interior of PC12 cells and neurons. Mild proteolysis converts the surface proteoglycan into a molecule closely resembling that found in the medium. The same surface antigens are also present on a subpopulation of T-cells and on a non-neuronal accessory cell found in dorsal root ganglion cultures. The PC12 cell line and the non-neuronal dorsal root ganglion cells secrete a factor into medium that, after adsorption to polylysine-coated surfaces, induces rapid neurite out-growth by primary sympathetic neurons. The monoclonal antibodies used to purify the neuronal HeS proteoglycan from PC12 cells are capable of depleting this conditioned medium of its neurite-promoting activity. These studies suggest that a HeS proteoglycan synthesized and secreted by neurons and certain accessory cells plays a role in regulating neurite outgrowth.