Effects of tunicamycin on NGF binding and neurite outgrowth in PC12 cells

The effects of inhibition of glycosylation on nerve growth factor (NGF) binding and neurite outgrowth response of PC12 cells have been examined. Exposure to tunicamycin (1-10 micrograms/ml) for 24-36 hr eliminates the rapidly dissociating component of NGF binding and decreases the proportion of PC12 cells capable of elaborating neurites in a dose-dependent manner. These decreased cellular responses are probably due to an underglycosylation of the NGF receptor, since the effects of tunicamycin are correlated with a decrease in 3H-fucose incorporation rather than a general decline in cellular metabolism as measured by viability and protein synthesis. These results suggest that carbohydrate side chains are important for the function and/or orientation of the NGF receptor in PC12 cells and that the rapidly dissociating component of NGF binding may be associated with a minimum concentration of functional receptors per cell required for the full biologic response.