Synapsin I in PC12 cells. I. Characterization of the phosphoprotein and effect of chronic NGF treatment.

PC12 cells contain a synapsin I-like molecule. Several serum and monoclonal antibodies raised against bovine brain synapsin I bind to and precipitate this molecule, demonstrating immunochemical similarity between the brain and PC12 species. PC12 synapsin I, like brain synapsin I, is a phosphoprotein: It is phosphorylated in intact cells and, when partially purified, serves as a substrate for several synapsin I kinases. PC12 cell synapsin I is structurally similar to brain synapsin I as shown by peptide mapping of 35S-methionine-and 32P-phosphate-labeled molecules from the 2 sources. Chronic NGF treatment of the cells induces a significant increase in the amount of synapsin I relative to total cell protein, measured either by immunolabeling or incorporation of 35S-methionine. The synapsin I present in untreated PC12 cells migrates predominantly as a singlet and that present in cells treated chronically with NGF as a doublet in SDS-PAGE.