herbimycin and Spinocerebellar-Ataxias

Amyloid and amyloid-like protein aggregations are hallmarks of multiple, varied neurodegenerative disorders, including Alzheimer's and Parkinson's diseases. We previously reported that spinocerebellar ataxia type 14 (SCA14), a dominant-inherited neurodegenerative disease that affects cerebellar Purkinje cells, is characterized by the intracellular formation of neurotoxic amyloid-like aggregates of genetic variants of protein kinase Cγ (PKCγ). A number of protein chaperones, including heat shock protein 70 (Hsp70), promote the degradation and/or refolding of misfolded proteins and thereby prevent their aggregation. Here, we report that, in various SCA14-associated, aggregating PKCγ variants, endogenous Hsp70 is incorporated into aggregates and that expression of these PKCγ mutants up-regulates Hsp70 expression. We observed that PKCγ binds Hsp70 and that this interaction is enhanced in the SCA14-associated variants, mediated by the kinase domain that is involved in amyloid-like fibril formation as well as the C2 domain of PKCγ. Pharmacological up-regulation of Hsp70 by the Hsp90 inhibitors celastrol and herbimycin A attenuated the aggregation of mutant PKCγ in primary cultured Purkinje cells. Up-regulation of Hsp70 diminished net PKCγ aggregation by preventing aggregate formation, resulting in decreased levels of apoptotic cell death among primary cultured Purkinje cells expressing the PKCγ variant. Of note, herbimycin A also ameliorated abnormal dendritic development. Extending our

Topics: Animals; Cell Line; Cerebellum; Detergents; Heat-Shock Proteins; Humans; Mutation; Protein Kinase C; Rifabutin; Solubility; Spinocerebellar Ataxias; Up-Regulation