Increase in synaptic vesicle proteins in synapsin-transfected NG108-15 cells: a subcellular fractionation study

We have examined the subcellular distribution of synapsins and synaptophysin in density gradients from synapsin- and vector-transfected NG108-15 cells, since we recently found that transfection of synapsin IIb cDNA into neuroblastoma x glioma hybrid cells (NG108-15) resulted in cell lines that had a more neuronal phenotype than controls. The increase in synapsins and synaptophysin in the transfected cells was maximal in the region of the gradient containing small synaptic vesicles. The transferrin receptor, a marker for early endosomes, did not increase in the synapsin-containing fractions in the transfected cells. Secretogranin I, a soluble protein stored in and secreted from large dense cored vesicles, showed a very pronounced increase in the dense regions of gradients from transfected cells. These subcellular fractionation data suggest a possible role for the synapsins in the regulation of synaptic vesicle function.