Neurite-promoting activity from fetal skeletal muscle: immunological comparison with laminin

Polycation-binding neurite-promoting factor (PNPF) from skeletal muscle of bovine fetuses has been compared to mouse tumor laminin by an immunological approach. Antiserum prepared against PNPF blocked the neurite-promoting activity in a dose-dependent manner. The anti-PNPF antiserum bound to Mr = 200,000-195,000 bands as well as several components of higher molecular weight, as detected in immunoblots of reduced PNPF. The anti-PNPF antiserum did not inhibit the neurite-promoting activity of mouse laminin, although it did bind to native laminin. Antilaminin antiserum bound to PNFP and identified the same Mr = 200,000-195,000 bands and two other higher-molecular-weight bands, as did the anti-PNPF antiserum. The activity of PNPF was confirmed to be sensitive to treatment with heparitinase. It is concluded that PNPF from bovine fetal muscle contains a complex of heparan sulfate and high-molecular-weight components, particularly of Mr = 200,000-195,000, which share antigenic determinants with mouse laminin. However antilaminin antiserum fails to inhibit the activity of PNPF, suggesting that the active site, and/or adjacent regions, of PNPF are antigenically different from the neurite-promoting site of purified mouse tumor laminin.