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 CK1α-SACK1(A-H) (formerly known as FAM83A-H) complexes initiated by molecular glue degraders primarily designed to target Ser/Thr kinase CK1α. We demonstrate that lenalidomide-derived degraders DEG-77 and SJ3149, which selectively target the CK1α isoform, co-degrade multiple SACK1(A-H) proteins. We show that the degradation of SACK1(A-H) proteins by DEG-77 and SJ3149 requires CK1α, the CUL4A(CRBN) E3 ligase complex and the proteasome. In cells derived from palmoplantar keratoderma patients harbouring the CK1α-binding deficient SACK1G(R265P) mutation, DEG-77 targets CK1α and mitotic SACK1D but not SACK1G(R265P), highlighting the requirement for CK1α-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.