In contrast, after pre-treatment of Jurkat cells with the proteasome inhibitors Carfilzomib (CFZ) and MG-132, degradation of PDE by bifunctional compound 5 was abrogated, suggesting that the proteasome might be involved in the degradation (Fig. ). Proteasomal degradation mediated by Cullin-Ring Ubiquitin ligases (CRLs) is dependent on modification with NEDD8 on the cullin backbone. In the presence of the neddylation inhibitor MLN4924 , degradation of PDE did not occur (Fig. ). Similar results were obtained when degraders 6 with GW5074 as a LC3B ligand and deltasonamide-derived bifunctional degrader 7 were employed (Fig. and Supplementary Fig. ). These findings indicate that degradation of PDE induced by bifunctional modalities 5, 6 and 7 does not occur by means of macroautophagy but rather proceeds through the UPS and is mediated by a CRL E3 ligase.