Wheat Germ Agglutinin Inhibits the Effects of Nerve Growth Factor on the Phosphorylation of Proteins in PC12h Cells

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Abstract
Treatment of PC12h cells in tissue culture with nerve growth factor (NGF) led to an increased incorporation of [32P]orthophosphoric acid into specific proteins. The increased phosphorylation of 60,000-dalton and 20,000-dalton proteins in the 0.2% Triton X-100 detergent-soluble fraction, of 35,000-dalton protein in the 0.2% Triton X-100 detergent-insoluble fraction, and of slow migrating protein (SMP) in the nonhistone nuclear fraction was observed upon NGF treatment. Wheat germ agglutinin (WGA) treatment of PC12h cells induced a slightly decreased phosphorylation of these NGF-responsive proteins. Incubation of cell-free extracts from PC12h cells with [.gamma.-32P]ATP led to the phosphorylation of a 100,000-dalton protein. In extracts from cells treated with NGF, the labeling of the 100,000-dalton protein was substantially and selectively reduced. Treatment of PC12h cells with WGA led to an increased phosphorylation of the 100,000-dalton protein in cell-free extracts. NGF and WGA showed opposite effect on the phosphorylation of specific proteins in both intact cells and cell-free extracts. It was also observed in both systems that pre- and posttreatment of PCS12 h cels and WGA abolished the effects of NGF on the phosphorylation and produced a phosphorylation pattern similar to that from PC12h cells treated only with WGA. In parent PC12 cells, it has been reported that the treatment of cells with WGA inhibits NGF binding to its receptor and converts the rapidly dissociating receptors to slowly dissociating receptors. WGA in conjunction with NGF, results in the practical disappearance of rapidly dissociating receptors on cells. The NGF-induced alteration of the phosphorylation of proteins in PC12h cells may be linked to the rapidly dissociating receptor.