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Abstract Targeted protein degradation is a groundbreaking modality in drug discovery; however, the regulatory mechanisms are still not fully understood. Here, we identify cellular signaling pathways that modulate the targeted degradation of the anticancer target BRD4 and related neosubstrates BRD2/3 and CDK9 induced by CRL2VHL- or CRL4CRBN -based PROTACs. The chemicals identified as degradation enhancers include inhibitors of cellular signaling pathways such as poly-ADP ribosylation (PARG inhibitor PDD00017273), unfolded protein response (PERK inhibitor GSK2606414), and protein stabilization (HSP90 inhibitor luminespib). Mechanistically, PARG inhibition promotes TRIP12-mediated K29/K48-linked branched ubiquitylation of BRD4 by facilitating chromatin dissociation of BRD4 and formation of the BRD4–PROTAC–CRL2VHL ternary complex; by contrast, HSP90 inhibition promotes BRD4 degradation after the ubiquitylation step. Consequently, these signal inhibitors sensitize cells to the PROTAC-induced apoptosis. These results suggest that various cell-intrinsic signaling pathways spontaneously counteract chemically induced target degradation at multiple steps, which could be liberated by specific inhibitors.

Genetic variants of proteasome subunit genes have been shown to associate with perturbed immune function. Here authors show that a heterozygous missense variant of the immunoproteasome subunit β-type 9 causes an autoinflammatory/immune deficiency syndrome in humans and in a mouse model.

In the proteasome, Rpn2 provides the docking site for substrate receptor Rpn13. Here the authors present the structure of human Rpn13 Pru domain bound to its binding site in Rpn2 and provide insights into the mode of action for Rpn13-targeting molecule RA190, which has anticancer properties.

Foxn1 is involved in thymic epithelial cell (TEC) and CD8+T cell development. Here the authors show this development requires Foxn1 binding proximal to, and inducing transcription of, the gene encoding β5t in cortical TECs.