Search Results (3,215)

Immune checkpoint inhibitors (ICIs), including PD-L1 inhibitors, have been approved by the FDA for the treatment of cancers; however, only a small number of cancer patients benefit from these ICIs. Furthermore, the development of drug resistance to this type of treatment is often inevitable. The mechanisms of resistance to PD-L1 inhibitors can be attributed, in part, to an incomplete understanding of the regulation of PD-L1 protein expression. In this study, we identified the role of the E3 ligase GP78, also known as the Autocrine Motility Factor Receptor (AMFR), in the regulation of PD-L1 protein levels. We show that GP78 physically interacts with PD-L1, which is confirmed by IP and Western blotting and is supported by molecular modelling using AlphaFold2. Our modeling studies predict that the interface amino acids of the Ig1 domain of PD-L1 interact with the RING domain and a β-hairpin preceding the CUE domain of GP78. The crystal structure of the PD-1/PD-L1 complex reveals that the interaction with PD-1 is mediated by the Ig1 domain of PD-L1. Furthermore, proteasomal degradation of PD-L1 has been observed via GP78-mediated K48-linked ubiquitination, indicating a key regulatory role for GP78 in the downregulation of PD-L1. Because GP78 expression is inversely correlated with PD-L1 levels in cancer, these findings may have clinical implications for predicting tumor immune evasion and patient response to PD-1/PD-L1 blockade therapies. Taken together, these findings identify a previously unknown mechanism by which GP78 targets PD-L1 for ubiquitination and subsequent degradation in cancer cells, and suggest that blocking the interaction between PD-L1 and PD-1 by an E3 ligase is a novel strategy to improve immunotherapies for cancer patients. Full article

Spastic paraplegia 80 (SPG80), caused by mutations in ubiquitin-associated protein 1 (UBAP1), is a pure form of juvenile-onset hereditary spastic paraplegia (HSP) and leads to progressive motor dysfunction. Despite recent advances in the molecular analyses of HSP, disease-modifying therapy has not been established for HSP including SPG80. In the present study, we evaluated the therapeutic potential of 4-phenylbutyric acid (4-PBA), a chemical chaperone and histone deacetylase inhibitor, in Ubap1 knock-in (KI) mice expressing a disease-associated truncated UBAP1 variant. We found that 4-PBA administration significantly improved the motor performance of KI mice in the rotarod and beam walk tests, with maximal benefits achieved when given during pre- or early-symptomatic stages. Partial efficacy was also observed when treatment began after symptom onset in KI mice. Furthermore, 4-PBA attenuated spinal microglial activation and partially restored microglial morphology, although astrocytic reactivity remained unchanged. These findings support 4-PBA as a candidate therapeutic compound for SPG80 and highlight the potential of proteostasis-targeted interventions in HSPs. Full article

Porcine epidemic diarrhea virus (PEDV), a member of the genus Alpha coronavirus, is one of the main pathogens causing piglet diarrhea. PEDV can enhance its replication by regulating host protein function. The tyrosine phosphatase src homology 2 domain-containing PTP (SHP-1) acts as a host natural immune protein capable of influencing viral replication, but there are no studies on the regulation of virus replication by pig SHP-1. In this study, we expressed porcine SHP-1 protein and examined its interaction with PEDV as well as its potential role in PEDV infection. The results showed that SHP-1 overexpression in porcine kidney cells (PK15) significantly increased the mRNA level of viral S protein in a dose-dependent manner. In contrast, SHP-1 knockdown reduced S gene expression, indicating that SHP-1 promoted PEDV replication. Overexpression of SHP-1 had an inhibitory effect on IFN-β, TNF-α, ISG15, and CXCL10, while this inhibition was reduced as SHP-1 expression decreased. Furthermore, we found that SHP-1 interacted with TNF receptor-associated factor 3 (TRAF3) and inhibited its K63-linked ubiquitination, suppressing the expression of IFN-β and ISGs and facilitating PEDV replication. The study provided new insights for the prevention and control of porcine epidemic diarrhea. Full article

Background/Objective: Proteotoxic stress induced by inhibitors of the ubiquitin–proteasome system has been successful in multiple myeloma but not in solid cancers such as prostate cancer. Our objective is to find a combination with proteasome inhibitors that increases apoptotic cell death in all types of prostate cancer without harming non-cancer cells. Methods: The effectiveness of rencofilstat, a pan-cyclophilin inhibitor, combined with the ixazomib proteasome inhibitor, was investigated in multiple prostate cancer and non-cancer cells. Inducible knockdown of stress response XBP1s and cyclophilins A/B and inducible expression of XBP1s and cyclophilin B were developed in prostate cancer to determine functional roles. Results: Rencofilstat + ixazomib increased apoptotic cell death in prostate cancer but not in non-cancer cells. We investigated the effects on XBP1s and PERK, important unfolded protein response factors required for cells to survive proteotoxic stress. The results revealed that XBP1s had a pro-survival role early, but maintenance at later times of rencofilstat + ixazomib treatment resulted in cell death. In addition, decreased PERK and phospho-eIF2α likely maintained protein synthesis to further enhance proteotoxic stress. In contrast, rencofilstat + ixazomib did not alter XBP1s or PERK in non-cancer cells. Additional genetic experiments showed that the RCF targets cyclophilins A, B, and D had protective effects. Rencofilstat increased extracellular secretion of cyclophilin B, but rencofilstat + ixazomib reduced glycosylation and, likely, the biological function of CD147 (CypB receptor) and decreased downstream ERK signaling. Conclusions: Rencofilstat + ixazomib may be a new strategy for increasing proteotoxic stress and apoptotic cell death in advanced prostate cancer cells with less toxic side effects. Full article

Usp21, a member of the ubiquitin protease family, plays a vital role in various biological functions. However, the effects of Usp21 dysfunction remain incompletely understood. In this study, we generated Usp21 knockout (KO) mice. Blood tests showed no impairment of liver function but did reveal elevated levels of total cholesterol (T-CHOL) and free fatty acid (FFA) in Usp21 KO mice compared to wild-type (WT) mice. Next, we performed RNA-sequencing (RNA-seq) to identify genes that Usp21 regulates. The results highlighted several candidate genes based on their biological relevance, and their expression levels were validated by RT-qPCR. The Usp21 KO mice exhibited significant elevations in the expression of the genes Fabp7, Nlrc5, and Ppargc1a, which play an important role in lipid metabolism, compared to WT. These data suggest that Usp21 may play roles in lipid metabolism in association with Fabp7, Nlrc5 and Ppargc1a. To clarify the involvement of USP21 in human hypercholesterolemia, we examined single-nucleotide polymorphisms (SNPs) around USP21 in non-hypercholesterolemic and hypercholesterolemic outpatients. We found that the rs11421 SNP downstream of USP21 was significantly associated with hypercholesterolemia. These data suggest that Usp21 plays a role in mice and human lipid metabolism and that its polymorphism may be a diagnostic marker for human hypercholesterolemia. Full article

Yield components are the most important breeding objectives, directly determining maize high-yield breeding. It is well known that these traits are controlled by a large number of quantitative trait loci (QTL). Therefore, deeply understanding the genetic basis of yield components and identifying key regulatory candidate genes can lay the foundation for maize marker-assisted selection (MAS) breeding. In this study, our aim was to identify the key genomic regions that regulate maize yield component formation through bioinformatic methods. Herein, 554 original QTLs related to 11 yield components, including ear length (EL), hundred-kernel weight (HKW), ear weight (EW), cob weight (CW), ear diameter (ED), cob diameter (CD), kernel row number (KRN), kernel number per row (KNR), kernel length (KL), grain weight per plant (GW), and kernel width (KW) in maize, were collected from the MaizeGDB, national center for biotechnology information (NCBI), and China national knowledge infrastructure (CNKI) databases. The consensus map was then constructed with a total length of 7154.30 cM. Approximately 80.32% of original QTLs were successfully projected on the consensus map, and they were unevenly distributed on the 10 chromosomes (Chr.). Moreover, 44 meta-QTLs (MQTLs) were identified by the meta-analysis. Among them, 39 MQTLs controlled two or more yield components, except for the MQTL4 in Chr. 1, which was associated with HKW; MQTL11 in Chr. 2, which was responsible for EL; MQTL19 in Chr. 3, which was related to KRN; MQTL26 in Chr. 5, which was involved in HKW; and MQTL36 in Chr. 7, which regulated EL. These findings were consistent with the Pearson correlation results, indicating that these traits exhibited co-linked heredity phenomena. Meanwhile, 159 candidate genes were found in all of the above MQTLs intervals, of which, 29 genes encoded E3 ubiquitin protein ligase, which was related with kernel size and weight. Other genes were involved in multiple metabolic processes, including plant hormones signaling transduction, plant growth and development, sucrose–starch synthesis and metabolism, and reproductive growth. Overall, the results will provide reliable genetic resources for high-yield molecular breeding in maize. Full article

Elevated cholesterol levels play important mitogenic roles. Pseurotin A (PsA) is a fermentation product that has recently been reported as a dual inhibitor of proprotein convertase subtilisin/kexin type 9 (PCSK9) secretion and protein-protein interaction (PPI) with the LDLR. PsA showed a high acute safety profile and therapeutic potential against metastatic castration-resistant prostate cancer (mCRPC). The study aims to uncover the chronic safety, distribution, and anti-mCRPC genomic and molecular mechanistic insights of PsA. A 90-day chronic safety assessment of PsA up to 80 mg/kg in Swiss albino mice showed no signs of hematological, biochemical, or major organ toxicity. PsA demonstrated rapid intravenous distribution and elimination in Swiss albino mice. PsA is biodistributed to multiple key organs but was not detected in the brain, indicating its inability to cross the blood-brain barrier. PsA effectively suppressed the recurrence of nude mice xenografted mCRPC, which was subjected to a neoadjuvant docetaxel and enzalutamide regimen, followed by surgical excision. Collected PsA and vehicle control-treated recurrent tumors were subjected to RNA-sequencing and pathway enrichment analysis (PEA) of differentially expressed genes (DEGs). PsA-treated tumors revealed multiple significantly enriched pathways associated with promoting tumor apoptosis and inhibiting both invasion and migration. The PPI network analyses for the downregulated DEGs displayed prominent networks of genes associated with the ubiquitin-proteasome system. Results provide comprehensive mechanistic and preclinical validations for PsA’s potential as a novel PC recurrence suppressive lead entity. Full article

Ankyrin-repeat and SOCS-box protein 9 (ASB9) is a member of the ASB family of proteins, which act as a substrate recognition component of E3 ubiquitin ligases and regulate various reproductive processes. ASB9 was previously identified as being induced in bovine granulosa cells (GCs) by LH/hCG, and its binding partners, including protease-activated receptor 1 (PAR1), were reported. The aim of this study was to decipher ASB9’s mechanisms of action in GCs and determine whether ASB9 induction by LH/hCG is necessary for the regulation of PAR1 and the signaling pathways involved in GC function and activity. Cultured GCs were treated with different doses of FSH, LH, and thrombin. RT-qPCR analyses revealed that thrombin increased PAR1 expression, while FSH had no effect on PAR1. Treatment with LH significantly downregulated PAR1, even in the presence of thrombin, possibly via ASB9. The phosphorylation profile of MAPK3/1 in thrombin-treated GCs suggests PAR1-mediated control. ASB9 induction appeared to have a negative effect on the MAPK pathway, although thrombin treatment briefly (within an hour) blocked the negative effect of ASB9 on PAR1. Proliferation assays showed that ASB9 negatively regulated the GC number while increasing apoptosis. These data provide evidence of ASB9’s mode of action and its potent functional effects on PAR1 regulation, GC proliferation, and, potentially, the ovulatory process in bovine species. Full article

The 14-3-3 protein family, which includes the isoforms η, γ, ε, θ, β, and ζ, is essential for controlling a number of pathways linked to DNA and RNA viruses, including HIV, influenza A virus (IAV), measles virus, HRSV, and double-stranded DNA viruses. TRIM32, an E3 ubiquitin ligase, has been reported to target IAV’s PB1 polymerase for species-specific degradation via ubiquitination. Notably, 14-3-3η binds to phosphorylated TRIM32, preventing its autoubiquitylation and forming soluble but inactive cytoplasmic aggregates that regulate TRIM32 levels. However, the functional link between 14-3-3η, TRIM32, and PB1 during viral infection remains unclear. In this study, we establish a mechanistic connection between 14-3-3η–TRIM32 and TRIM32–PB1 interactions in IAV (H1N1) infection. We demonstrate that 14-3-3η directly interacts with PB1, influencing viral replication. Using transient knockdown models, we show that 14-3-3η deficiency alters influenza virus-induced cytotoxicity, cell death, immune responses, and reactive oxygen species (ROS) production. Additionally, we observe a significant reduction in the soluble TRIM32 levels in 14-3-3η-deficient cells, which leads to increased PB1 accumulation and thus suggests a critical regulatory role for 14-3-3η in PB1 stability. Our findings reveal a novel function of 14-3-3η in influenza virus infection, demonstrating its role in PB1 regulation via TRIM32 and its impact on innate immune activation. This study highlights 14-3-3η as a possible target for antiviral treatments against influenza and offers fresh insights into the host–virus relationship. Full article

Background: Gastric cancer is one of the most prevalent malignancies worldwide and the fourth leading cause of cancer-related mortality. Protein ubiquitination and deubiquitination regulate protein stability as post-translational modifications, playing essential roles in tumorigenesis. Although UCHL1, a deubiquitinating enzyme (DUB), is implicated in the progression of several cancer types, its role in gastric cancer remains unclear. Methods: Kaplan–Meier analysis and gastric cancer patient tissues were used to assess UCHL1 expression. Cell viability assay, colony-forming assay, and transwell migration and invasion assay were performed to evaluate cell growth. Immunoprecipitation and Western blotting analyzed protein expression and interactions. Results: This study demonstrates that UCHL1 expression is markedly upregulated in gastric cancer tissues compared to normal tissues. Elevated UCHL1 expression is associated with poor patient prognosis, supporting its potential role as an oncogenic factor. Reduced UCHL1 expression suppressed cell proliferation, migration, and invasion in gastric cancer cell lines. As the underlying mechanism, we identified CIP2A, a known oncogenic regulator of c-Myc, as a downstream effector of UCHL1. UCHL1 knockdown reduced CIP2A protein levels via deubiquitination, attenuated c-Myc signaling, and decreased expression of key cell cycle regulators. Furthermore, UCHL1 knockdown significantly downregulated cyclin D1 expression, arresting the cell cycle in the G1 phase and inhibiting cell proliferation. Conclusions: Collectively, our findings reveal that UCHL1 promotes gastric cancer progression, highlighting it as a potential therapeutic target. Full article

The COP9 signalosome (CSN) is a highly conserved eukaryotic protein complex that plays a crucial role in plant growth, development, and stress responses by modulating the ubiquitination pathway. Emerging evidence underscores its significance in plant immunity, where it orchestrates diverse defense mechanisms, including hormone signaling, reactive oxygen species (ROS), homeostasis, and secondary metabolite (SM) biosynthesis. As a key regulator, CSN influences multiple layers of immune responses, such as pattern-triggered immunity (PTI), effector-triggered immunity (ETI), and systemic acquired resistance (SAR). However, the intricate interplay between CSN and immune regulatory networks remains incompletely understood, and a comprehensive model of its mechanistic framework is still lacking. This review systematically consolidates current knowledge on CSN-mediated immune regulation in plant–pathogen interactions and highlights its role in disease resistance. Full article

Background: The ubiquitin–proteasome system plays a critical role in plant antiviral defense, with HECT-type E3 ubiquitin ligases serving as key regulators of protein turnover. To explore the potential involvement of the HECT gene family in host resistance against tomato yellow leaf curl virus (TYLCV), a comprehensive analysis was conducted in Nicotiana benthamiana. Methods: In this study, the HECT gene family in N. benthamiana was systematically investigated using a genome-wide bioinformatic analysis. The potential roles of these genes in the response to TYLCV infection were further examined using a virus-induced gene silencing (VIGS) technique. Results: Using a Hidden Markov Model approach, 18 NbHECT genes were identified that phylogenetically clustered into four subfamilies with distinct structural features. Chromosomal location and synteny analyses indicated that these genes were unevenly distributed across 11 chromosomes, with 10 instances of segmental duplication identified. Tissue-specific expression profiling demonstrated that 17 NbHECTs were constitutively expressed, with Group III members showing the highest expression in reproductive tissues. Following TYLCV infection, NbHECT6 was significantly downregulated while NbHECT13 was upregulated in both inoculated and systemic leaves. Functional validation through the VIGS approach revealed that suppression of NbHECT6 and NbHECT13 increased host susceptibility, as evidenced by exacerbated symptom severity and enhanced viral DNA accumulation compared to controls. Conclusions: These findings establish NbHECT6 and NbHECT13 as critical components of the plant antiviral response, providing new insights into ubiquitin-mediated defense mechanisms against geminiviruses. Full article

TRIM48 is a human-specific tripartite motif (TRIM) family protein with E3 ubiquitin ligase activity that plays a significant role in the oxidative stress response and tumor suppression. However, the mechanisms regulating TRIM48 expression remain unknown. In this study, we demonstrate that TRIM48 is targeted for ubiquitination-dependent degradation by S-phase kinase-associated protein 1 (Skp1)-Cullin1 (Cul1)-F-box protein (SCF) ubiquitin ligase complex, containing F-box protein 22 (FBXO22) as a substrate recognition subunit. We found that TRIM48 is a rapid turnover protein, as evidenced by the fast and drastic decrease in its protein expression level in the presence of a protein synthesis inhibitor cycloheximide, which was suppressed by knocking down either Skp1, Cul1 or FBXO22. Exogenous FBXO22 expression promoted K48-linked polyubiquitination and degradation of TRIM48. FBXO22 deficiency accelerated oxidative stress-induced activation of apoptosis signal-regulating kinase 1 (ASK1) and cell death, which was reversed by additional TRIM48 knockdown. Collectively, our findings identify the FBXO22 SCF complex as a key negative regulator of TRIM48-driven ASK1-activation and cell death under oxidative stress. The dysregulation of this axis may underlie human-specific pathologies, such as tumorigenesis and oxidative stress-associated disorders, highlighting its potential as a target for novel therapeutic interventions. Full article

Proteolysis-targeting chimeras (PROTACs) are a transformative therapeutic modality that co-opts the ubiquitin-proteasome system for selective protein degradation. To date, the development of PROTACs has been overwhelmingly dominated by the recruitment of four canonical E3 ligases: CRBN, VHL, MDM2, and IAP. This limited repertoire represents a critical bottleneck, restricting the scope of degradable proteins and potential therapeutic applications. Addressing this challenge, recent years have witnessed a surge in the successful recruitment of novel E3 ligases. This review provides a dedicated and comprehensive summary of this progress, focusing exclusively on the emerging E3 ligases and their cognate ligands reported for PROTAC technology outside of the well-established quartet. We detail their discovery and strategic application, highlighting how this rapidly expanding toolbox promises to overcome existing limitations and unlock the full potential of targeted protein degradation. Full article

Alzheimer’s disease (AD) is the most common cause of dementia worldwide, and there are still no strategies to slow or prevent its clinical progression. Significant financial and research resources have been invested into studying the pathology of AD. However, its pathogenesis is not fully understood. This review provides a comprehensive analysis of current understanding of AD pathogenesis, including classical hypotheses (amyloid cascade, tau pathology, neuroinflammation, oxidative stress), emerging mechanisms (cellular senescence, endoplasmic reticulum stress, ubiquitin-proteasome system dysfunction), and alternative mechanisms (cholinergic dysfunction, glutamate excitotoxicity, disruption of the microbiota–gut–brain axis, and autophagy). Schematic illustrations summarize the relationships between the hypotheses and their role in the pathogenesis of AD. Particular attention is paid to the systematization of promising biological targets and the analysis of modern ligands of various nature, including small molecules, peptides, antibodies and their fragments, natural compounds, as well as innovative hybrid and multifunctional structures. A separate section is devoted to radiopharmaceuticals for PET imaging (Florbetaben, Flortaucipir, etc.) and promising therapeutic agents. Thus, in this review we (1) systematize modern concepts of AD pathogenesis, including classical, emerging mechanisms and alternative hypotheses; (2) conduct a comparative analysis of ligand classes (small molecules, peptides, antibodies, etc.) and their therapeutic potential; and (3) discuss the clinical prospects of radiopharmaceuticals for PET imaging and targeted therapy. The work provides a comprehensive analysis of modern approaches, which can help in the development of more effective drugs against AD. Full article