靶向蛋白质降解是药物发现的突破性模式；然而，监管机制仍不完全清楚。在这里，我们确定了调节由基于 CRL2VHL 或 CRL4CRBN 的 PROTAC 诱导的抗癌靶点 BRD4 以及相关新底物 BRD2/3 和 CDK9 的靶向降解的细胞信号传导途径。被确定为降解增强剂的化学物质包括细胞信号传导途径的抑制剂，例如聚 ADP 核糖基化（PARG 抑制剂 PDD00017273）、未折叠蛋白反应（PERK 抑制剂 GSK2606414）和蛋白质稳定化（HSP90 抑制剂 luminespib）。从机制上讲，PARG 抑制通过促进 BRD4 染色质解离和 BRD4-PROTAC-CRL2VHL 三元复合物的形成，促进 TRIP12 介导的 BRD4 K29/K48 连接分支泛素化；相比之下，HSP90 抑制会在泛素化步骤后促进 BRD4 降解。因此，这些信号抑制剂使细胞对 PROTAC 诱导的细胞凋亡敏感。这些结果表明，各种细胞固有的信号传导途径在多个步骤中自发地抵消化学诱导的靶标降解，这些降解可以通过特定的抑制剂释放。© 2024。作者。

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.© 2024. The Author(s).