Phosphorylation of the 105-kDa Heat Shock Proteins, HSP105α and HSP105β, by Casein Kinase II

The 105-kDa heat shock protein α (HSP105α) and HSP105β are mammalian heat shock proteins that belong to the HSP105/HSP110 family. Both HSP105α and HSP105β consist of acidic and basic isoforms. Here we report that the acidic isoforms are serine phosphorylated HSP105α or HSP105β. Furthermore, using an in-gel kinase assay with HSP105α or HSP105β as the substrate, the protein kinase that phosphorylates HSP105α and HSP105β was identified as casein kinase II. Since phosphorylated HSP105α is especially prominent in the brain compared to other tissues of mice and rats, the phosphorylation of HSP105α by casein kinase II may be biologically significant.