Functional protein kinase arrays reveal inhibition of p-21-activated kinase 4 by alpha-synuclein oligomers.

There is increasing evidence that aggregation of alpha-synuclein contributes to the functional and structural deterioration in the CNS of Parkinson's disease patients and transgenic animal models. alpha-Synuclein binds to various cellular proteins and aggregated alpha-synuclein species may affect their physiological function. In the present study, we used protein arrays spotted with 178 active human kinases for a large-scale analysis of the effects of recombinant alpha-synuclein on kinase activities. Incubation with globular alpha-synuclein oligomers significantly inhibited autophosphorylation of p21-activated kinase (PAK4) compared to treatment with monomeric alpha-synuclein or beta-synuclein. A concentration-dependent inhibition was also observed in a solution-based kinase assay. To show in vivo relevance, we analyzed brainstem protein extracts from alpha-synuclein (A30P) transgenic mice where accumulation of alpha-synuclein oligomers has been demonstrated. By immunoblotting using a phospho-specific antibody, we detected a significant decline in phosphorylation of LIM kinase 1, a physiological substrate for PAK4. Suppression of PAK activity by amyloid-beta oligomers has been reported in Alzheimer's disease. Thus, PAKs may represent a target for various neurotoxic protein oligomers, and signaling deficits may contribute to the behavioral defects in chronic neurodegenerative diseases.