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Esophageal cancer (EC) is a type of aggressive cancer without clinically relevant molecular subtypes, hindering the development of effective strategies for treatment. To define molecular subtypes of EC, we perform mass spectrometry-based proteomic and phosphoproteomics profiling of EC tumors and adjacent non-tumor tissues, revealing a catalog of proteins and phosphosites that are dysregulated in ECs. The EC cohort is stratified into two molecular subtypes—S1 and S2—based on proteomic analysis, with the S2 subtype characterized by the upregulation of spliceosomal and ribosomal proteins, and being more aggressive. Moreover, we identify a subtype signature composed of ELOA and SCAF4, and construct a subtype diagnostic and prognostic model. Potential drugs are predicted for treating patients of S2 subtype, and three candidate drugs are validated to inhibit EC. Taken together, our proteomic analysis define molecular subtypes of EC, thus providing a potential therapeutic outlook for improving disease outcomes in patients with EC. Proteomics can aid in the identification of molecular subtypes in cancers. Here, the authors perform proteomic profiling of 124 paired oesophageal cancer and adjacent non-tumour tissues and identify two subtypes that are associated with patient survival for therapeutic targeting.

Renal cell carcinoma (RCC) is the one of the most fatal and frequent form of urological malignancy worldwide. The von Hippel-Lindau (VHL) tumour suppressor gene is a critical component of the VHL-Cullin2-ElonginB/C (VCB) complex that regulates the ubiquitin-mediated proteasomal degradation of proteins with mutations consistently associated with the development of clear cell renal cell carcinoma (ccRCC). Despite extensive investigations conducted worldwide, there is a notable lack of data concerning VHL mutations in sporadic ccRCC patients from India. Our study aimed to investigate the sporadic VHL mutations within the tumours of 210 ccRCC patients without a familial history of VHL disease. We extracted genomic DNA from tumour and adjacent normal tissues, PCR amplified and sequenced the VHL gene. In silico tools were used assess the damaging potential of missense variants on pVHL structure and stability. Protein-protein docking and protein flexibility molecular docking simulation study were employed to study the interaction between wild-type and mutated VHL models with Elongin C. Sequence analysis revealed seven novel missense mutations in patient tumour tissues p.(Val170Phe), p.(Arg69Cys), p.(Phe76Leu), p.(Glu173Asp), p.(Leu201Val), p.(His208Leu), p.(Arg205Pro). I-Mutant 2.0 indicated these mutations reduced pVHL stability (ΔΔG < -0.5 kcal/mol). Protein Flexibility-Molecular Dynamic (MD) Simulation study indicated that mutations weaken the interaction of VHL with Elongin C, with V170F showing the most significant reduction in binding quality and stability. In conclusion, this study introduces novel genetic data from an understudied population and highlights the impact of VHL mutations on its interaction with Elongin C. These findings contribute to our understanding of the molecular basis of VHL-related pathologies and may guide future therapeutic strategies targeting these interactions.

Background Long noncoding RNAs (lncRNAs) have driven research focused on their effects as oncogenes or tumor suppressors involved in carcinogenesis. However, the functions and mechanisms of most lncRNAs in colorectal cancer (CRC) remain unclear. Methods The expression of DLGAP1-AS2 was assessed by quantitative RT-PCR in multiple CRC cohorts. The impacts of DLGAP1-AS2 on CRC growth and metastasis were evaluated by a series of in vitro and in vivo assays. Furthermore, the underlying mechanism of DLGAP1-AS2 in CRC was revealed by RNA pull down, RNA immunoprecipitation, RNA sequencing, luciferase assays, chromatin immunoprecipitation, and rescue experiments. Results We discovered that DLGAP1-AS2 promoted CRC tumorigenesis and metastasis by physically interacting with Elongin A (ELOA) and inhibiting its protein stability by promoting tripartite motif containing 21 (Trim21)-mediated ubiquitination modification and degradation of ELOA. In particular, we revealed that DLGAP1-AS2 decreases phospholysine phosphohistidine inorganic pyrophosphate phosphatase (LHPP) expression by inhibiting ELOA-mediated transcriptional activating of LHPP and thus blocking LHPP-dependent suppression of the AKT signaling pathway. In addition, we also demonstrated that DLGAP1-AS2 was bound and stabilized by cleavage and polyadenylation specificity factor (CPSF2) and cleavage stimulation factor (CSTF3). Conclusions The discovery of DLGAP1-AS2, a promising prognostic biomarker, reveals a new dimension into the molecular pathogenesis of CRC and provides a prospective treatment target for this disease.

Elongin is a heterotrimeric elongation factor for RNA polymerase (Pol) II transcription that is conserved among metazoa. Here, we report three cryo-EM structures of human Elongin bound to transcribing Pol II. The structures show that Elongin subunit ELOA binds the RPB2 side of Pol II and anchors the ELOB–ELOC subunit heterodimer. ELOA contains a ‘latch’ that binds between the end of the Pol II bridge helix and funnel helices, thereby inducing a conformational change near the polymerase active center. The latch is required for the elongation-stimulatory activity of Elongin, but not for Pol II binding, indicating that Elongin functions by allosterically regulating the conformational mobility of the polymerase active center. Elongin binding to Pol II is incompatible with association of the super elongation complex, PAF1 complex and RTF1, which also contain an elongation-stimulatory latch element. Using cryo-EM, here the authors structurally delineate the Elongin–RNA polymerase II holocomplex. They show that Elongin allosterically regulates the transcribing RNA polymerase II via a latch that affects its conformational mobility.

Radioresistance is a principal culprit for the failure of radiotherapy in hepatocellular carcinoma (HCC). Insights on the regulation genes of radioresistance and underlying mechanisms in HCC are awaiting for profound investigation. In this study, the suppressor of cytokine signaling 2 (SOCS2) were screened out by RNA-seq and bioinformatics analyses as a potential prognosis predictor of HCC radiotherapy and then were determined to promote radiosensitivity in HCC both in vivo or in vitro. Meanwhile, the measurements of ferroptosis negative regulatory proteins of solute carrier family 7 member 11 (SLC7A11) and glutathione peroxidase 4 (GPX4), intracellular lipid peroxidation and Fe2+ concentration suggested that a high level of ferroptosis contributed to the radiosensitization of HCC. Moreover, SOCS2 and SLC7A11 were expressed oppositely in HCC clinical tissues and tumour xenografts with different radiosensitivities. Mechanistically, the N-terminal domain of SLC7A11 was specifically recognized by the SH2-structural domain of SOCS2. While the L162 and C166 of SOCS2-BOX region could bind elongin B/C compound to co-form a SOCS2/elongin B/C complex to recruit ubiquitin molecules. Herein, SOCS2 served as a bridge to transfer the attached ubiquitin to SLC7A11 and promoted K48-linked polyubiquitination degradation of SLC7A11, which ultimately led to the onset of ferroptosis and radiosensitization of HCC. In conclusion, it was demonstrated for the first time that high-expressed SOCS2 was one of the biomarkers predicting radiosensitivity of HCC by advancing the ubiquitination degradation of SLC7A11 and promoting ferroptosis, which indicates that targeting SOCS2 may enhance the efficiency of HCC radiotherapy and improve the prognosis of patients.

The ubiquitin-proteasome system (UPS) represents an evolutionarily conserved machinery governing proteostasis through spatiotemporal regulation of protein degradation. While spermatogenesis involves multilayered regulatory mechanisms spanning translation to dynamic post-translational modifications (PTMs), the identity of UPS-associated E3 ligases orchestrating germ cell-specific protein turnover remains elusive. Here, we identify a testis-specific E3 ubiquitin ligase complex comprising elongin B/C, Cullin-2 (CUL2), RING-box protein-1 (RBX1), and SOCS box protein ASB9, designated ECS ASB9 . Genetic ablation of ECS ASB9 in mice via ubiquitous Asb9 knockout (KO) or spermatid-specific elongin B/C conditional KO disrupts spermiogenesis and compromises fertility. Mechanistic studies reveal that ECS ASB9 engages tubulin beta 4 A (TUBB4A) through substrate recognition, catalyzing K48-linked polyubiquitination at lysine 379 (K379) to promote proteasomal degradation. Notably, Tubb4a K379R knock-in (KI) mice phenocopy the spermiogenesis defects observed upon ECS ASB9 deficiency. Clinically, we identify three hemizygous missense variants in X-linked ASB9 among Chinese males with idiopathic infertility. Male mice bearing orthologous ASB9 variant exhibit oligoasthenoteratozoospermia (OAT) and subfertility, mirroring human phenotypes. Taken together, our findings establish ECS ASB9 as an important regulator of spermatogenic proteostasis and provide mechanistic insights into UPS-mediated tissue-specific degradation, while implicating ASB9 variants in male infertility pathogenesis. A testis-specific E3 ubiquitin ligase complex, ECSASB9, governs spermiogenesis by promoting TUBB4A degradation. Disruption of this pathway impairs male fertility, and pathogenic ASB9 variants are found in infertile men.

The description of the crystal structure of the Brd4 PROTAC compound MZ1 in complex with the human E3 ubiquitin ligase VHL and the Brd4 bromodomain shines new light onto how PROTACs work and enables design of degraders with increased selectivity for Brd4. Inducing macromolecular interactions with small molecules to activate cellular signaling is a challenging goal. PROTACs (proteolysis-targeting chimeras) are bifunctional molecules that recruit a target protein in proximity to an E3 ubiquitin ligase to trigger protein degradation. Structural elucidation of the key ternary ligase–PROTAC–target species and its impact on target degradation selectivity remain elusive. We solved the crystal structure of Brd4 degrader MZ1 in complex with human VHL and the Brd4 bromodomain (Brd4 BD2 ). The ligand folds into itself to allow formation of specific intermolecular interactions in the ternary complex. Isothermal titration calorimetry studies, supported by surface mutagenesis and proximity assays, are consistent with pronounced cooperative formation of ternary complexes with Brd4 BD2 . Structure-based-designed compound AT1 exhibits highly selective depletion of Brd4 in cells. Our results elucidate how PROTAC-induced de novo contacts dictate preferential recruitment of a target protein into a stable and cooperative complex with an E3 ligase for selective degradation.

Rpb1, the largest subunit of RNA polymerase II (RNAPII), is rapidly polyubiquitinated and degraded in response to DNA damage; this process is considered to be a “mechanism of last resort” employed by cells. The underlying mechanism of this process remains elusive. Here, we uncovered a previously uncharacterized multistep pathway in which the polymerase-associated factor 1 (Paf1) complex (PAF1C, composed of the subunits Ctr9, Paf1, Leo1, Cdc73, and Rtf1) is involved in regulating the RNAPII pool by stimulating Elongin-Cullin E3 ligase complex-mediated Rpb1 polyubiquitination and subsequent degradation by the proteasome following DNA damage. Mechanistically, Spt5 is dephosphorylated following DNA damage, thereby weakening the interaction between the Rtf1 subunit and Spt5, which might be a key step in initiating Rpb1 degradation. Next, Rad26 is loaded onto stalled RNAPII to replace the Spt4/Spt5 complex in an RNAPII-dependent manner and, in turn, recruits more PAF1C to DNA lesions via the binding of Rad26 to the Leo1 subunit. Importantly, the PAF1C, assembled in a Ctr9-mediated manner, coordinates with Rad26 to localize the Elongin-Cullin complex on stalled RNAPII, thereby inducing RNAPII removal, in which the heterodimer Paf1/Leo1 and the subunit Cdc73 play important roles. Together, our results clearly revealed a new role of the intact PAF1C in regulating the RNAPII pool in response to DNA damage.

The ankyrin (ANK) SOCS box (ASB) family, encompassing ASB1-18, is the largest group of substrate receptors of cullin 5 Ring E3 ubiquitin ligase. Nonetheless, the mechanism of substrate recognition by ASB family proteins has remained largely elusive. Here we present the crystal structure of ASB7-Elongin B-Elongin C ternary complex bound to a conserved helical degron. ASB7 employs its ANK3-6 to form an extended groove, effectively interacting with the internal α-helix-degron through a network of side-chain-mediated electrostatic and hydrophobic interactions. Our structural findings, combined with biochemical and cellular analyses, identify the key residues of the degron motif and ASB7 required for their recognition. This will facilitate the identification of additional physiological substrates of ASB7 by providing a defined degron motif for screening. Furthermore, the structural insights provide a basis for the rational design of compounds that can specifically target ASB7 by disrupting its interaction with its cognate degron.

The Cullin 5 (CUL5) Ring E3 ligase uses adaptors Elongins B and C (ELOB/C) to bind different SOCS-box-containing substrate receptors, determining the substrate specificity of the ligase. The 18-member ankyrin and SOCS box (ASB) family is the largest substrate receptor family. Here we report cryo-EM data for the substrate, creatine kinase (CKB) bound to ASB9-ELOB/C, and for full-length CUL5 bound to the RING protein, RBX2, which binds various E2s. To date, no full structures are available either for a substrate-bound ASB nor for CUL5. Hydrogen–deuterium exchange (HDX-MS) mapped onto a full structural model of the ligase revealed long-range allostery extending from the substrate through CUL5. We propose a revised allosteric mechanism for how CUL-E3 ligases function. ASB9 and CUL5 behave as rigid rods, connected through a hinge provided by ELOB/C transmitting long-range allosteric crosstalk from the substrate through CUL5 to the RBX2 flexible linker. Multi-subunit Cullin (CUL)-RING ligases (CRL) form the largest family of E3 ligases and are composed of a substrate receptor, a CUL, and a RING-box (RBX) protein. Here, the authors use cryo-EM and HDX-MS to characterise the ASB9 CUL-RING E3 ligase and present the structure of ASB9-ELOB/C bound to the substrate creatine kinase and the full-length CUL5 structure in complex with RBX2, and they propose a revised allosteric mechanism for CUL-E3 ligase function.