Phosphorylation of Synaptophysin by the c-src Encoded Protein Tyrosin Kinase pp60 c-src

Abstract

The phosphorylation and dephosphorylation of proteins plays an essential role in the regulation of cellular proliferation and differentiation processes. Within the central nervous system (CNS) protein phosphorylation is considered to be involved in various aspects of neuronal function including neurotransmitter uptake, storage, metabolism and release. A possible regulatory role of tyrosine phosphorylation in neurotransmission is supported by the recent observation that synaptophysin, a major synaptic vesicle protein is phosphorylated by the c-src encoded protooncogene product pp6O c-src (Barnekow et al., 1990). Expression of pp60 c-src , the first well defined protooncogene product, is developmentally regulated and tissue-specific, with neuronal tissues displaying high amounts of the c-src encoded pp60 c-src kinase activity (Barnekow and Bauer, 1984; Schartl and Barnekow, 1984). In the CNS pp60 c-src is preferentially expressed in regions characterized by a high content of grey matter and elevated density of nerve terminals (Sudol, 1988). The physiological function of pp60 c-src is still unclear and specific target proteins need to be identified in order to obtain a better understanding of the role this protein plays in cellular differentiation processes.