Project description:Similar to ubiquitin, SUMO forms chains, but the identity of SUMO-chain-modified factors and the purpose of this modification remain largely unknown. Here, we identify budding yeast SUMO protease Ulp2, able to disassemble SUMO chains, as a DDK interactor enriched at replication origins that promotes DNA replication initiation. Replication-engaged DDK is SUMOylated on chromatin, becoming a degradation-prone substrate when Ulp2 no longer protects it against SUMO-chain assembly. Specifically, SUMO chains channel DDK for SUMO-targeted ubiquitin ligase Slx5/Slx8-mediated and Cdc48 segregase-assisted proteasomal degradation. Importantly, the SUMOylation-defective ddk-KR mutant rescues inefficient replication onset and MCM activation in cells lacking Ulp2, suggesting that SUMO chains time DDK degradation. Using two unbiased proteomic approaches, we further identify subunits of the MCM helicase and other factors as SUMO-chain-modified degradation-prone substrates of Ulp2 and Slx5/Slx8. We thus propose SUMO-chain-/Ulp2-protease-regulated proteasomal degradation as a mechanism that times the availability of functionally-engaged SUMO-modified protein pools during replication and beyond.
Project description:The protein ubiquitylation is under the equilibrium between ubiquitin conjugation and deconjugation. How substrates stabilized by deubiquitylation are directed for degradation remains unclear. Branched ubiquitin chains promote substrate degradation through the proteasome, but the underlying mechanisms are not fully understood. TRIP12 and UBR5 are HECT-type E3s specific for the K29 and K48 linkages, respectively. Here, we show that the deubiquitylase (DUB) OTUD5 is cooperatively modified by TRIP12 and UBR5, resulting in the conjugation of K29/K48 branched ubiquitin chains and accelerated proteasomal degradation. The TRIP12–OTUD5 antagonism regulates TNF-–induced NF-B signaling. Mechanistically, although OTUD5 readily cleaves K48 linkages, K29 linkages are resistant against OTUD5 activity. Consequently, K29 linkages overcome OTUD5 DUB activity to facilitate UBR5-dependent K48-linked chain branching. This mechanism is applicable to other TRIP12 substrates associated with OTUD5. These results reveal a unique cellular strategy in which the combination of DUB-resistant and proteasome-targeting ubiquitin linkages efficiently promotes the degradation of substrates protected by deubiquitylation, underscoring the role of branched ubiquitin chains in shifting the ubiquitin conjugation/deconjugation equilibrium.
Project description:Ubiquitin-mediated proteolysis play a significant role in various biological processes including transcription, DNA repair and cell cycle progression. The identification of Set8 and Set8b (a splice isoform) histone H4K20 methyl transferase as a substrate for the cullin-based ubiquitin ligase (CRL4-Cdt2) demonstrate that this pathway plays a significant role in promoting cell cycle progression, specifically promoting G2 progression. This study investigate the effect of failure to degrade Set8 in S-phase of the cell cycle via CRL4-Cdt2 on gene expression. We used microarrays to detail the effect of the expression of stable form of Set8b H4K20 mono-methyl transferase (Set8b_deltaPIP2) on gene expression Human osteosarcoma-derived human cells were transduced with retroviruses encoding either wt-Set8b or a mutant of Setb8 which is resistant to degradation via CRL4-Cdt2 ubiquitin ligase complex (Set8b_deltaPIP2) or with an a control pMSCV empty virus. 5 days after transduction, cells were harvested and the RNA was extracted by Trizol (Invitrogen) and hybridized to the affymetrix chips array.
Project description:Reversibility of protein ubiquitylation play essential roles in cellular protein homeostasis. How substrates stabilized by deubiquitylation are directed for degradation remains largely elusive. Here, we show that the branched ubiquitin chains promote the degradation of the deubiquitylase (DUB) OTUD5. OTUD5 is sequentially modified by TRIP12 and UBR5, E3s specific for the K29 and K48 linkages, respectively, resulting in the conjugation of K29/K48 branched ubiquitin chains. The TRIP12-OTUD5 antagonism regulates TNF--induced NF-B signaling. Mechanistically, while OTUD5 readily cleaves K48-linkages, K29-linkages are resistant against OTUD5 activity. Consequently, K29-linkages overcome OTUD5 DUB activity to facilitate UBR5-dependent K48-linked chain branching. Regarding generality, this mechanism adopts to other TRIP12 substrates associated with OTUD5. These results uncover a cellular unique strategy in which the sequential addition of DUB-resistant and proteasome-targeting ubiquitin linkages efficiently promote degradation of substrates protected by deubiquitylation, underscoring the role of branched ubiquitin chains in the quality control of hard-to-degrade substrates.
Project description:E3 ubiquitin ligases of the Cullin RING Ligase (CRL) family assemble into multiprotein complexes to diversify substrate adaptors and ensure selectivity in substrate engagement for degradation. Here we show a novel mechanism whereby mutations in substrate adaptors can drive neo-substrate degradation in cancer. KBTBD4 is a CRL3 substrate adaptor harbouring recurrent indel mutations in a subset of non-WNT/non-SHH medulloblastomas. We show that these mutations, arising in the substrate recognition domain of KBTBD4, promote the recruitment and ubiquitylation of the REST Corepressor (CoREST), which forms a complex to modulate chromatin accessibility and transcriptional programmes. We observe that this neomorphic activity of KBTBD4 mutants induces changes in epigenetic markers and significant alterations in transcription, diverting normal cellular programmes towards increased stemness. These results highlight mutation-driven neomorphic E3 ligase activity as a previously unrecognised mechanism in tumorigenesis, with implications for medulloblastoma pathogenesis and treatment.
Project description:MicroRNAs (miRNAs) associate with Argonaute (AGO) proteins to direct widespread post-transcriptional gene repression. Although association with AGO typically protects miRNAs from nucleases, extensive pairing to some unusual target RNAs can trigger miRNA degradation. Here we found that this target-directed miRNA degradation (TDMD) required the ZSWIM8 Cullin-RING E3 ubiquitin ligase. This and other findings suggested and supported a mechanistic model of TDMD in which target-directed proteolysis of AGO by the ubiquitin–proteasome pathway exposes the miRNA for degradation. Moreover, loss-of-function studies indicated that the ZSWIM8 Cullin-RING ligase accelerates degradation of numerous miRNAs in cells of mammals, flies, and nematodes, thereby specifying the half-lives of most short-lived miRNAs. These results elucidate the mechanism of TDMD and expand the inferred role of TDMD in shaping miRNA levels in bilaterian animals.
Project description:MicroRNAs (miRNAs) associate with Argonaute (AGO) proteins to direct widespread post-transcriptional gene repression. Although association with AGO typically protects miRNAs from nucleases, extensive pairing to some unusual target RNAs can trigger miRNA degradation. Here we found that this target-directed miRNA degradation (TDMD) required the ZSWIM8 Cullin-RING E3 ubiquitin ligase. This and other findings suggested and supported a mechanistic model of TDMD in which target-directed proteolysis of AGO by the ubiquitin–proteasome pathway exposes the miRNA for degradation. Moreover, loss-of-function studies indicated that the ZSWIM8 Cullin-RING ligase accelerates degradation of numerous miRNAs in cells of mammals, flies, and nematodes, thereby specifying the half-lives of most short-lived miRNAs. These results elucidate the mechanism of TDMD and expand the inferred role of TDMD in shaping miRNA levels in bilaterian animals.
Project description:MicroRNAs (miRNAs) associate with Argonaute (AGO) proteins to direct widespread post-transcriptional gene repression. Although association with AGO typically protects miRNAs from nucleases, extensive pairing to some unusual target RNAs can trigger miRNA degradation. Here we found that this target-directed miRNA degradation (TDMD) required the ZSWIM8 Cullin-RING E3 ubiquitin ligase. This and other findings suggested and supported a mechanistic model of TDMD in which target-directed proteolysis of AGO by the ubiquitin–proteasome pathway exposes the miRNA for degradation. Moreover, loss-of-function studies indicated that the ZSWIM8 Cullin-RING ligase accelerates degradation of numerous miRNAs in cells of mammals, flies, and nematodes, thereby specifying the half-lives of most short-lived miRNAs. These results elucidate the mechanism of TDMD and expand the inferred role of TDMD in shaping miRNA levels in bilaterian animals.