Aberrant regulation and function of Src family tyrosine kinases: their potential contributions to glutamate-induced neurotoxicity

Excitotoxicity, a major cause of neuronal death in acute and chronic neurodegenerative diseases and conditions such as stroke and Parkinson's disease, is initiated by overstimulation of glutamate receptors, leading to calcium overload in affected neurons. The sustained high concentration of intracellular calcium constitutively activates a host of enzymes, notably the calcium-activated proteases calpains, neuronal nitric oxide synthase (nNOS) and NADPH oxidase (NOX), to antagonise the cell survival signalling pathways and induce cell death. Upon overactivation by calcium, calpains catalyse limited proteolysis of specific cellular proteins to modulate their functions; nNOS produces excessive amounts of nitric oxide (NO), which, in turn, covalently modifies specific enzymes by S-nitrosylation; and NOX produces excessive amounts of reactive oxygen species (ROS) to inflict damage to key metabolic enzymes. Presumably, key regulatory enzymes governing cell survival and cell death are aberrantly modified and regulated by calpains, NO and ROS in affected neurons; these aberrantly modified enzymes then cooperate to induce the death of affected neurons. c-Src, an Src family kinase (SFK) member, is one of the aberrantly regulated enzymes involved in excitotoxic neuronal death. Herein we review how SFKs are functionally linked to the glutamate receptors and the biochemical and structural basis of the aberrant regulation of SFKs. Results in the literature suggest that SFKs are aberrantly activated by calpain-mediated truncation and S-nitrosylation. Thus, the aberrantly activated SFKs are targets for therapeutic intervention to reduce the extent of brain damage caused by stroke.