Intersecting PTMS regulate clearance of pathogenic tau by the CHIP ubiquitin ligase

Abstract

AbstractBackgroundBiochemical and cellular models of tau post‐translational modifications (PTMs) were generated to understand how pathogenic tau species evade the protein quality control machinery during the pathogenesis of neurodegeneration.MethodA pathogenic fragment of 0N4R tau representing the species derived from caspase‐cleavage at Asp421 (tauC3) bearing native PTMs was purified from Sf9 insect cells, and its binding to the ubiquitin ligase CHIP was analyzed by ELISA. Differential scanning fluorimetry and fluorescence polarization assays were used to identify relevant sites of modification that alter the affinity of CHIP for tauC3. X‐ray crystallography was employed to define the molecular details of the interaction of the CHIP TPR domain with tauC3.ResultPhosphorylation of tauC3 was shown to reduce the affinity of the CHIP‐tauC3 interaction and attenuate ubiquitination of tauC3 by CHIP. Phosphorylation of tauC3 at Ser416 was shown to be sufficient to significantly reduce the affinity of CHIP‐tauC3 interaction and promote tauC3 accumulation in cells. Introducing specific mutations into CHIP rescued binding to phosphorylated tauC3 and improved ubiquitination and clearance of tauC3.ConclusionC‐terminal phosphorylation at Ser416 of caspase‐cleaved tau inhibits tau clearance by the CHIP ubiquitin ligase and represents a targetable modality to promote clearance of pathogenic tau species during the pathogenesis of neurodegenerative diseases.