Cartwright, T. | bioRxiv Science

bioRxiv2026

Targeted dephosphorylation of Tau at the endogenous level promotes its association with microtubules.

Hyperphosphorylation of Tau is a contributory factor for Tauopathies, which constitute a spectrum of neurodegenerative disorders including Alzheimer's disease (AD). Inhibitors of Tau kinases or activators of the Tau phosphatase PP2A to reverse Tau hyperphosphorylation have shown limited therapeutic promise, due primarily to a lack of Tau selectivity. An innovative strategy to potentially circumvent these limitations would be to selectively target the dephosphorylation of phospho-residues on Tau. In this study, we provide evidence for targeted dephosphorylation of phospho-Tau at the endogenous level, including those known to promote Tau aggregation. By recruiting PPP1CA and PPP2CA Affinity-directed (Ad)-Phosphatases to Tau, we demonstrate highly selective targeted dephosphorylation of multiple phospho-residues on Tau in SK-N-MC neuroblastoma cells, leading to its stabilization in microtubules. Moreover, by using a heterobifunctional molecule termed BDPIC (bromoTAG-dTAG proximity-inducing chimera) in cells harbouring bromoTAG and dTAG knockins on Tau and PPP2CA, respectively, we demonstrate highly selective dephosphorylation phospho-residues on Tau.

neuroscience↗

bioRxiv2025

The contribution of native protein complexes to targeted protein degradation

Targeted protein degradation (TPD) destroys proteins of interest (POIs) by hijacking the cellular proteolytic machinery. Most proteins in cells exist and function as part of multi-protein or macromolecular complexes, thereby allowing a single protein to control multiple biological processes. Therefore, when a small molecule degrader induces proximity between an E3 ligase and the POI, the macromolecular context of the POI potentially influences the degradation outcomes of the POI and of the complex components. Here, we explore degradation of the eight CK1-SACK1(A-H) (formerly known as FAM83A-H) complexes initiated by molecular glue degraders primarily designed to target Ser/Thr kinase CK1. We demonstrate that lenalidomide-derived degraders DEG-77 and SJ3149, which selectively target the CK1 isoform, co-degrade multiple SACK1(A-H) proteins. We show that the degradation of SACK1(A-H) proteins by DEG-77 and SJ3149 requires CK1, the CUL4ACRBN E3 ligase complex and the proteasome. In cells derived from palmoplantar keratoderma patients harbouring the CK1-binding deficient SACK1GR265P mutation, DEG-77 targets CK1 and mitotic SACK1D but not SACK1GR265P, highlighting the requirement for CK1-SACK1(A-H) interaction to achieve co-degradation. Our study underscores the importance of POI context in TPD and reinforces the potential for selectively targeting specific protein complexes for degradation.

cell biology↗