14–3-3 zeta homologoues genes: possible impact on Parkinson's disease?

A detailed mutation search in 303 sporadic and familial Parkinson's patients by Single Strand Conformation Polymorphism screening and sequence analysis revealed two missense mutations in 14–3-3 zeta homologous genes. 14–3-3 proteins, representing a family of ubiquitous cytoplasmic chaperones, are involved in cellular processes such as signal transduction, cell cycle control, stress response and apoptosis. They are known to act as adaptor molecules stimulating protein-protein interaction, regulate the subcellular localisation of proteins and activate or inhibit enzymes. 14–3-3 proteins share physical and functional homology with alpha-synuclein, which plays an important role in the pathogenesis of Parkinson's disease (PD) and other neurodegenerative diseases. Further, 14–3-3 proteins colocalize with Lewy bodies, the pathological hallmark of PD. We therefore investigated whether 14–3-3 proteins are also involved in the pathogenesis of PD.

In order to clarify the functional impact of these mutations, we established a chemical-inducible aggregation assay. The chaperone-like activity of 14–3-3 zeta-like is abolished in the case of the deletion protein. Cell stress experiments revealed 25–41% lower proliferation rate in the case of mutant cell line (25% mutation with amino acid exchange, 40% deletion protein) after hydrogenperoxid treatment compared with cells expressing wildtype protein. Expression of 14–3-3 zeta-like proteins in cell culture revealed that wildtyp protein is exclusivly in the cytoplasm whereas the deletion protein is predominantly nuclear localized. Inhibition of proteasome activity elicite the formation of juxtanuclear aggregates with characteristics of aggresomes including immunoreactivity for vimentin. We also observed disturbance of mitochondria that resulted in mitochondrial clustering, colocalizing with the 14–3-3 aggresomes. Similarly, mitochondrial pathology has been observed in an animal model with Parkin null mutants. In future studies we will concentrate on the nature of the aggresomes and their implication in cell function and neuronal cell death.

Functional changes, varying sensitivity to cellular stress, interaction with alpha-synuclein and the different cell localization in vitro assured the assumption that 14–3-3 proteins are implicated in the pathogenesis of Parkinson's disease.