The BTB (broad-complex, tramtrack, and bric-à-brac) domain is a highly conserved protein interaction motif in eukaryotes. They are widely involved in transcriptional regulation, protein degradation and other processes. Recently, an increasing number of studies have shown that these genes play important roles in plant growth and development, biotic and abiotic stress processes. Here, we summarize the advances of these proteins ubiquitination-mediated development and abiotic stress responses in plants based on the protein structure, which may facilitate the study of this type of gene in plants.
Eukaryota ; Plant Development/genetics* ; Proteolysis ; Ubiquitination

OBJECTIVE: To observe the effects of herbal cake separated moxibustion on macrophage effector molecule T-cell immunoglobulin and mucin-domain containing-4 (Tim-4) and ubiquitination of programmed cell death protein 1 (PD-1) in rabbits with immunosuppression, and to explore the possible mechanism on herbal cake separated moxibustion in improving immunosuppression. METHODS: Thirty-two big-ear white rabbits were randomly divided into a normal group, a model group, a moxa stick moxibustion group and a herbal cake separated moxibustion group, 8 rabbits in each group. Except the normal group, the immunosuppression model was established by intraperitoneal injection of cyclophosphamide of60 mg/kg in the other 3 groups. "Shenque" (CV 8), "Shenshu" (BL 23), "Zusanli" (ST 36), etc. were selected in both the moxa stick moxibustion group and the herbal cake separated moxibustion group. Moxa stick moxibustion was applied in the moxa stick moxibustion group, one cone at each acupoint; herbal cake separated moxibustion was applied in the herbal cake separated moxibustion group, 5 cones at each acupoint. The intervention was given once every other day for 10 times in both groups. Leukocyte content in peripheral blood was detected by blood cell analyzer; the positive expression of PD-1 in CD⁺₄ T lymphocytes, CD⁺₈T lymphocytes and CD⁺₆₈ macrophages in peripheral blood was measured by flow cytometry, the serum levels of interleukin 2 (IL-2), CD₈, CD₆₈ and Tim-4 were detected by ELISA, and the expression of Tim-4 and F-box only protein 38 (FBXO38) in the liver and spleen tissues was measured by immunohistochemistry. RESULTS: Compared with the normal group, in the model group, white blood cell count (WBC) and percentage of neutrophils (NEU%) were decreased while percentage of lymphocyte (LYM%) was increased (P<0.01) in peripheral blood; the positive expression rates of PD-1 in CD⁺₄ T lymphocytes, CD⁺₈T lymphocytes and CD⁺₆₈ macrophages in peripheral blood were increased (P<0.01); the serum levels of IL-2, CD₆₈ and Tim-4 were increased (P<0.01), the serum level of CD₈ was decreased (P<0.01); the average optical density (AOD) of Tim-4 in the liver tissue and FBXO38 in the liver and spleen tissues was increased (P<0.01). Compared with the model group, in the moxa stick moxibustion group and the herbal cake separated moxibustion group, WBC and NEU% were increased (P<0.01); the positive expression rates of PD-1 in CD⁺₄ T lymphocytes, CD⁺₈T lymphocytes and CD⁺₆₈ macrophages in peripheral blood were decreased (P<0.01); the serum levels of IL-2, CD₆₈ and Tim-4 were decreased (P<0.01), the serum levels of CD₈ were increased (P<0.01); the AOD of Tim-4 and FBXO38 in the liver tissue and FBXO38 in the spleen tissue was decreased (P<0.01, P<0.05). Compared with the moxa stick moxibustion group, in the herbal cake separated moxibustion group, the positive expression rate of PD-1 in CD⁺₆₈ macrophages in peripheral blood was increased (P<0.05); serum level of Tim-4 was increased (P<0.01); AOD of Tim-4 in the liver tissue was decreased (P<0.05). CONCLUSION Herbal cake separated moxibustion can improve immunosuppression by regulating the expression of macrophage effector molecule Tim-4 and the FBXO38 mediated ubiquitination of PD-1, Tim-4 may be one of the specific indexes of immunomodulation involving with herbal cake separated moxibustion.
Animals ; Rabbits ; Interleukin-2/genetics* ; Moxibustion ; Programmed Cell Death 1 Receptor/genetics* ; Immunosuppression Therapy ; Ubiquitination

This study aims to investigate the effect and mechanism of hydnocarpin(HC) in treating triple negative breast cancer(TNBC). Cell counting kit-8(CCK-8), xCELLigence real-time cellular analysis(RTCA), and colony formation assay were employed to determine the effects of HC on the proliferation of two TNBC cell lines: MDA-MB-231 and MDA-MB-436. The effects of HC on the migration and invasion of TNBC cells were detected by high-content analysis, wound-healing assay, and Transwell assay. The changes in the epithelial-mesenchymal transition(EMT) and the expression of invasion-and migration-associated proteins [E-cadherin, vimentin, Snail, matrix metalloproteinase-2(MMP-2), and MMP-9] were detected by Western blot. Western blot and RT-qPCR were employed to determine the protein and mRNA levels of Yes-associated protein(YAP) and downstream targets(CTGF and Cyr61). TNBC cells were transfected with Flag-YAP for the overexpression of YAP, and the role of YAP as a key target for HC to inhibit TNBC malignant progression was examined by CCK-8 assay, Transwell assay, and wound-healing assay. The pathway of HC-induced YAP degradation was detected by the co-treatment of proteasome inhibitor with HC and ubiquitination assay. The binding of HC to YAP and the E3 ubiquitin ligase Ccr4-not transcription complex subunit 4(CNOT4) was detected by microscale thermophoresis(MST) assay and drug affinity responsive target stability(DARTS) assay. The results showed that HC significantly inhibited the proliferation, colony formation, invasion, and EMT of TNBC cells. HC down-regulated the protein and mRNA levels of CTGF and Cyr61. HC down-regulated the total protein level of YAP, while it had no effect on the mRNA level of YAP. The overexpression of YAP antagonized the inhibitory effects of HC on the proliferation, migration, and invasion of TNBC cells. HC promoted the degradation of YAP through the proteasome pathway and up-regulated the ubiquitination level of YAP. The results of MST and DARTS demonstrated direct binding between HC, YAP, and CNOT4. The above results indicated that HC inhibited the malignant progression of TNBC via CNOT4-mediated degradation and ubiquitination of YAP.
Humans ; Triple Negative Breast Neoplasms/metabolism* ; Matrix Metalloproteinase 2/metabolism* ; Cell Line, Tumor ; Cell Proliferation ; Cell Movement ; Ubiquitination ; RNA, Messenger/metabolism* ; Epithelial-Mesenchymal Transition ; Transcription Factors/metabolism*

The ubiquitin-proteasome system plays an important role in protein degradation. The process of ubiquitination requires ubiquitin activating enzyme E1, ubiquitin-conjugating enzyme E2, and ubiquitin ligase E3 to complete the coordination. Our previous studies have shown that HUWE1 (HECT, UBA and WWE domain containing 1), as an E3 ubiquitin ligase, can degrade epidermal growth factor receptor (EGFR) to inhibit renal tubulointerstitial fibrosis. However, E2 ubiquitin-conjugating enzymes binding to HUWE1 are still unclear. The aim of the present study was to identify E2 ubiquitin-conjugating enzymes of HUWE1. Real-time PCR was used to identify E2 ubiquitin-conjugating enzyme that may interact with HUWE1. The expression of E2 ubiquitin-conjugating enzyme was detected in kidney of unilateral ureteral obstruction (UUO) mice and HK-2 cells treated with transforming growth factor-β (TGF-β). The results showed that the expressions of E2 ubiquitin-conjugating enzyme UBE2Q2 were significantly down-regulated at both RNA and protein levels in UUO kidneys. The expression of UBE2Q2 was also down-regulated in HK-2 cells stimulated with TGF-β, which was consistent with the change in the expression of HUWE1. These findings indicated that UBE2Q2 expression was synergistic with HUWE1 in the injured kidney. Co-immunoprecipitation (Co-IP) experiments showed that HUWE1 interacted with UBE2Q2 in HK-2 cells. The co-localization of UBE2Q2 and HUWE1 was confirmed by cell immunofluorescence staining. After knocking down UBE2Q2 by siRNA, ubiquitin binding to HUWE1 and EGFR was decreased. In sum, our results demonstrated that UBE2Q2, ubiquitin-conjugating enzyme, works with HUWE1 to mediate ubiquitination and degradation of target protein in kidney.
Animals ; Cell Line ; Fibrosis ; Humans ; Kidney Diseases ; Mice ; Ubiquitin-Conjugating Enzymes/metabolism* ; Ubiquitin-Protein Ligases/metabolism* ; Ubiquitination

Flavonoids have a variety of biological activities and have important applications in food, medicine, cosmetics, and many other fields. Naringenin is a platform chemical for the biosynthesis of many important flavonoids. Ubiquitination plays a pivotal role in the post-translational modification of proteins and participates in the regulation of cellular activities. Ubiquitinated proteins can be degraded by the ubiquitin-protease system, which is important for maintaining the physiological activities of cells, and may also exert a significant impact on the expression of exogenous proteins. In this study, a real-time in-situ detection system for ubiquitination modification has been established in Saccharomyces cerevisiae by using a fluorescence bimolecular complementation approach. The ubiquitination level of protein was characterized by fluorescence intensity. By using the approach, the potential ubiquitination sites of proteins involved in the naringenin biosynthesis pathway have been obtained. The lysine residues of the relevant ubiquitination sites were mutated to arginine to reduce the ubiquitination level. The mutants of tyrosine ammonia-lyase (FjTAL) and chalcone synthase (SjCHS, SmCHS) showed decreased fluorescence, suggested that a decreased ubiquitination level. After fermentation verification, the S. cerevisiae expressing tyrosine ammonia-lyase FjTAL mutant FjTAL-K487R accumulated 74.2 mg/L p-coumaric acid at 72 h, which was 32.3% higher than that of the original FjTAL. The strains expressing chalcone synthase mutants showed no significant change in the titer of naringenin. The results showed that mutation of the potential ubiquitination sites of proteins involved in the naringenin biosynthesis pathway could increase the titer of p-coumaric acid and have positive effect on naringenin biosynthesis.
Biosynthetic Pathways ; Flavanones/metabolism* ; Saccharomyces cerevisiae/metabolism* ; Ubiquitination

OBJECTIVE: To observe the expression of c-Myc protein in cervical cancer HeLa cells and explore the effect of juglone on the proliferation and apoptosis of HeLa cells by affecting c-Myc ubiquitination. METHODS: HeLa cells treated with different concentrations (0, 10, 20, or 50 μmol/L) of juglone or with 20 μmol/L juglone for different time lengths were examined for expression of c-Myc protein with Western blotting. The half-life of c-Myc protein was determined using cycloheximide (CHX) and c-Myc protein degradation was detected using coimmunoprecipitation. We also assessed the effects of 20 μmol/L juglone combined with 0, 1.0 or 2.0 μmol/L MG132 (a proteasome inhibitor) on c-Myc expression. The effects of 20 μmol/L juglone on the proliferation and apoptosis of HeLa cells with RNA interference-mediated knockdown of c-Myc were evaluated with MTT assay and flow cytometry. RESULTS: Treatment with juglone significantly lowered c-Myc protein expression in HeLa cells in a concentration-and time-dependent manner (P < 0.05). Juglone obviously shortened the half-life of c-Myc protein, and the addition of MG132 significantly up-regulated the expression level of c-Myc protein (P < 0.05). Juglone treatment also promoted ubiquitination of c-Myc protein in HeLa cells. Compared with the cells transfected with a negative control construct, the cells transfected with si-c-Myc showed significantly decreased proliferation inhibition and a lowered cell rate with early apoptosis after juglone treatment (P < 0.05). CONCLUSION Juglone inhibits proliferation and promotes apoptosis of HeLa cells by affecting the ubiquitination of c-Myc protein.
Apoptosis ; Cell Proliferation ; Female ; HeLa Cells ; Humans ; Naphthoquinones ; Ubiquitination ; Uterine Cervical Neoplasms/genetics*

Ubiquitination is a post-translational modification of proteins in eukaryotes, which mediates the specific degradation and signal transduction of proteins to regulate a variety of life processes and thus affects functions of the body. The disorder and imbalance of ubiquitination network is a major cause of serious human diseases. Ubiquitin molecules can form eight homogeneous ubiquitin chains with different topological structures, which vary greatly in abundance and function. At present, the classical ubiquitin chains K48 and K63 with high abundance and rich substrates have been intensively studied, while other atypical ubiquitin chains with low content remain to be studied. However, it has been proved that atypical ubiquitin chains play a key role in intracellular regulation. K6 is an important atypical ubiquitin chain, which is similar to K48 chain and has a tight spatial structure. It plays a role in DNA damage repair, mitochondrial quality control, the occurrence and development of tumor, and the pathogenesis of Parkinson's disease. Due to the lack of specific antibodies and effective enrichment methods for K6, little is known about its substrate and regulatory mechanism. This paper systematically reviews the structural characteristics, regulatory mechanism, biological functions, and relevant diseases of atypical K6 linkages, aiming to provide reference for the functional study of K6.
Humans ; Protein Processing, Post-Translational ; Signal Transduction ; Ubiquitin/chemistry* ; Ubiquitination

Ubiquitination is one of the reversible protein post-translational modifications, in which ubiquitin molecules bind to the target protein in a cascade reaction of ubiquitin activating enzymes, ubiquitin conjugating enzymes, and ubiquitin ligases. The deubiquitinating enzymes (DUBs) remove ubiquitin residues from the substrates, which play key roles in the formation of mature ubiquitin, the removal and trimming of ubiquitin chains, as well as the recycling of free ubiquitin chains. Ubp14, a member of the ubiquitin specific proteases family in Saccharomyces cerevisiae, is mainly responsible for the recycling of intracellular free ubiquitin chains. To investigate its global biological function, a ubp14∆ mutant was constructed by homologous recombination technique. The growth rate of ubp14∆ mutant was lower than that of the wild-type (WT) strain. Using stable isotope labeling by amino acids in cell culture (SILAC) combined with deep coverage proteomics analysis, the differentially expressed proteins of ubp14∆ mutant relative to the wild-type strain were systematically analyzed. A total of 3 685 proteins were identified in this study, and 109 differentially expressed proteins were filtered out by statistical analysis. Gene ontology analysis found that differentially expressed proteins caused by Ubp14 loss were mainly involved in amino acid metabolism, REDOX, heat shock stress and etc, which shed light on the broad biological function of this DUB. This study provides highly reliable proteomic data for further exploring the biological functions of the deubiquitination enzyme Ubp14, and further understanding the relationship between the free ubiquitin homeostasis and biological process regulation.
Saccharomyces cerevisiae/metabolism* ; Proteomics ; Endopeptidases/metabolism* ; Ubiquitin/metabolism* ; Ubiquitination ; Proteins/metabolism* ; Deubiquitinating Enzymes/metabolism* ; Biological Phenomena

Ubiquitin-proteasome system (UPS) plays an essential role in eukaryotic protein cycle,the dysregulation of which can lead to tumorigenesis.Increased activities of UPS have been observed in the patients with cancers including leukemia.UPS inhibitors can kill cancer cells by affecting ubiquitin-ligating enzyme E3,deubiquitinase,and protein degradation active sites of UPS.Therefore,UPS inhibitors have emerged as an important therapy for treating hematological malignancies,while they are rarely applied in the treatment of acute myeloid leukemia.This paper summarizes the research progress in the inhibitors affecting the protein ubiquitination at different stages of acute myeloid leukemia,aiming to provide new clues for the clinical treatment of acute myeloid leukemia.
Humans ; Proteasome Inhibitors/therapeutic use* ; Ubiquitin/metabolism* ; Proteasome Endopeptidase Complex/metabolism* ; Ubiquitination ; Leukemia, Myeloid, Acute/drug therapy*

OBJECTIVE: To explore the role of TRIM21 in modulating the invasive phenotype of hepatocellular carcinoma (HCC) cells and its mechanism of action. METHODS: RNA interference technique was used to knock down the expression of TRIM21 and β-catenin, alone or in combination, in HCC cell lines 97H and LM3, and the interfering efficiency and the activity of closely related pathways were determined using Western blotting. The two cells with TRIM21 knockdown (siTRIM21 97H and siTRIM21 LM3 cells) were assessed for their invasion ability in vitro using Transwell invasion assay, and the lung metastasis capacity of siTRIM21 LM3 cells following tail vein injection was evaluated in nude mice. The binding of TRIM21 with β-catenin and the ubiquitylation level of β-catenin in TRIM21-overexpressing HEK293 cells were determined with Western blotting and co-immunoprecipitation assay. We also compared the overall survival of patients with CTNNB1^highTRIM21^high and CTNNB1^highTRIM21^low HCC subtypes using Kaplan-Meier method based on filtrated and grouped HCC clinical data from TCGA database. RESULTS: TRIM21 knockdown significantly enhanced the invasion ability of 97H and LM3 cells in vitro (P < 0.01 or 0.05) and the lung metastasis ability of LM3 cells in nude mice (P < 0.01), and simultaneous knockdown of β -catenin obviously suppressed the in vitro invasiveness of the cells (P < 0.0001 or 0.05). Co-immunoprecipitation assay showed that TRIM21 was capable of directly binding with β-catenin protein to accelerate the ubiquitination and degradation of the latter, leading to inhibition of nuclear translocation of β-catenin and hence reduced invasiveness of HCC cells. Bioinformatic analysis showed that compared patients with CTNNB1^highTRIM21^low HCC subtype where Wnt pathway was activated, the patients with CTNNB1^highTRIM21^high HCC subtype had a significantly better survival outcomes (P < 0.05). CONCLUSION A high expression of TRIM21 suppresses the invasion of HCC cells by promoting β-catenin ubiquitylation and degradation, which possibly explains the poor prognosis of CTNNB1^highTRIM21^low HCC patients.
Animals ; Carcinoma, Hepatocellular/pathology* ; Cell Line, Tumor ; Cell Proliferation ; Gene Expression Regulation, Neoplastic ; HEK293 Cells ; Humans ; Liver Neoplasms/pathology* ; Mice ; Mice, Nude ; Ribonucleoproteins/genetics* ; Ubiquitination ; Wnt Signaling Pathway ; beta Catenin/metabolism*