Lectin reactivity of PNPF, a polyornithine-binding neurite-promoting factor

The fate of dissociated neurons from 8-day chick embryo ciliary ganglia, cultured in serum-containing media on polyornithine substrata, is influenced by two different macromolecular factors. The neurons will die within 24 h in the absence of CNTF, the eye-derived ciliary neuronotrophic factor. Even when supported by CNTF, however, ciliary neurons do not grow neurites unless the polyornithine substratum is coated with PNPF, a polyornithine-binding neurite-promoting factor. PNPF activity present in rat Schwannoma-conditioned medium has been shown to behave as a large, acidic, trypsin-sensitive molecule. In the experiments reported here the lectin reactivity of PNPF has been investigated. Using lectin affinity chromatography PNPF was found to bind to concanavalin A and wheat germ agglutinin from which it could be respectively eluted with the specific sugars alpha-methyl-D-mannoside and N-acetyl-D-glucosamine. PNPF did not bind to Ulex europaeus or Dolichus biflorus agglutinins. Pretreatment of polyornithine-bound PNPF with concanavalin A before cell seeding prevented neurite outgrowth from ciliary neurons in a dose-dependent manner, without affecting neuronal survival. This inhibitory effect of concanavalin A could be removed with alpha-methyl-D-mannoside. Wheat germ agglutinin failed to inhibit the neurite-promoting effects of polyornithine-bound PNPF.