Discovery of a Keap1-dependent peptide PROTAC to knockdown Tau by ubiquitination-proteasome degradation pathway

Induced protein degradation by PROTACs has emerged as a promising strategy to target nonenzymatic proteins inside the cell. The aim of this study was to identify Keap1, a substrate adaptor protein for ubiquitin E3 ligase involved in oxidative stress regulation, as a novel candidate for PROTACs that can be applied in the degradation of the nonenzymatic protein Tau. A peptide PROTAC by recruiting Keap1-Cul3 ubiquitin E3 ligase was developed and applied in the degradation of intracellular Tau. Peptide 1 showed strong in vitro binding with Keap1 and Tau. With proper cell permeability, peptide 1 was found to colocalize with cellular Keap1 and resulted in the coimmunoprecipitation of Tau and Keap1. The results of flow cytometry and western blotting assays showed that peptide 1 can downregulate the intracellular Tau level in both time- and concentration-dependent manner. The application of Keap1 siRNA silencing and the proteasome inhibitor MG132 confirmed that peptide 1 could promote the Keap1-dependent poly-ubiquitination and proteasome-dependent degradation of Tau. The results suggested that using PROTACs to recruit Keap1 to induce the degradation of Tau may show promising character in the treatment of neurodegenerative disease. Besides, our research demonstrated that Keap1 should be a promising E3 ligase adaptor to be used in the design of novel PROTACs.