GSE208372
Repurposing E3 ubiquitin ligases as cell surface protein degraders using Proteolysis Targeting Antibodies
The majority of current therapeutics targeting plasma membrane receptors function by antagonizing ligand binding or enzymatic activities. Typical mammalian proteins, however, consist of multiple domains executing discrete but coordinated activities, and saturating inhibition of one functional domain often incompletely suppresses the totality of the protein's function. Recent work on targeted protein degradation technologies including Proteolysis Targeting Chimeras (PROTACs) has highlighted clinically important distinctions between target inhibition and target degradation. However, the generation of heterobifunctional compounds requiring linkage of two small molecules, each with high affinity for their targets, is highly complex, particularly with respect to achieving oral bioavailability. Here we describe the development of Proteolysis Targeting Antibodies (PROTABs) that tether cell-surface E3 ubiquitin ligases to transmembrane proteins, resulting in target ubiquitination and subsequent degradation. PROTAB-mediated degradation drives deeper pathway inhibition than inhibitory antibodies and is functional in vivo. The scope of this technology is also demonstrated through the identification  of additional cell surface E3 ubiquitin ligases that can function as “on demand” degraders of various cell surface proteins. The generality of this approach enables tissue-selective degradation, as suggested by the Wnt-responsive ligases RNF43 and ZNRF3. Furthermore, through engineering of various optimized antibody formats, we offer insights on the ground rules governing optimal target degradation. Taken together, this work describes a strategy for the rapid development of potent, bioavailable and tissue selective degradation of cell surface proteins. Overall design: As a prototypical model of aberrant Wnt signaling, we generated mouse intestinal organoids and used CRISPR/Cas9 to introduce a frame shift truncation in the Adenomatous Polyposis Coli (APC) gene, which leads to Wnt pathway hyperactivation and colon cancer initiation. We performed RNA seq and compared expression of genes in normal and APC mutant colon murine organoids.