TRIM21 - A potential novel therapeutic target in cancer

MYO1F in neutrophils is required for the response to immune checkpoint blockade therapy

Tumor-associated neutrophils (TANs) represent a significant barrier to the effectiveness of immune checkpoint blockade (ICB) therapy. A comprehensive understanding of TANs' regulatory mechanisms is therefore essential for predicting ICB efficacy and improving immunotherapy strategies. Our study reveals that MYO1F is selectively downregulated in neutrophils within both human cancers and murine tumor models, showing a negative correlation with ICB response. Mechanistically, MYO1F normally inhibits neutrophil immunosuppression and proliferation by restraining STAT3 activity. However, during tumorigenesis, tumor-derived TGF-β1 disrupts the binding of SPI1 to intron 8 of Myo1f via DNA methylation, thereby suppressing Myo1f transcription. The resultant decrease in MYO1F reprograms neutrophils into an immunosuppressive state through the STAT3-dependent signaling pathways. This immunosuppressive state further contributes to tumor microenvironment (TME) remodeling by inducing CTL exhaustion. These findings establish MYO1F as a critical regulator within TANs, highlighting its significant role in modulating ICB therapy efficacy.

RBMS3-loss impedes TRIM21-induced ubiquitination of ANGPT2 in an RNA-independent manner and drives sorafenib resistance in hepatocellular carcinoma

Sorafenib, a first-line targeted drug for advanced hepatocellular carcinoma (HCC), has limited clinical application due to intrinsic/acquired resistance. In this study, we have identified the RNA-binding protein RBMS3 as a pivotal regulator involved in sorafenib resistance among patients with HCC. Loss- and gain-of-function experiments further demonstrate that downregulation of RBMS3 promotes angiogenesis and confers resistance to sorafenib by augmenting the capacity of HCC cells to express and secrete ANGPT2, while upregulation of RBMS3 reverse these phenotypes.Through immunoprecipitation mass spectrometry experiments and co-immunoprecipitation (co-IP), we further verified that RBMS3 can facilitate the K48-linked ubiquitination and subsequent protein degradation of ANGPT2 by recruiting the ubiquitin E3 ligase TRIM21 in an RNA-independent manner.Additionally, RBMS3 is found to be deleted in HCC tissues and exhibits a significant positive correlation with angiogenesis and resistance to sorafenib treatment. Importantly, the combination of ANGPT2 antibody in RBMS3-deficient HCC cells restores sensitivity to sorafenib both in vitro and in vivo. These findings uncovered a novel molecular basis for post-translational upregulation of ANGPT2, suggesting that RBMS3-loss plays an oncogenic role in HCC by promoting angiogenesis and conferring resistance to sorafenib treatment.

Ubiquitin-conjugating enzyme UBE2N modulates proteostasis in immunoproteasome-positive acute myeloid leukemia

Altered protein homeostasis through proteasomal degradation of ubiquitinated proteins is a hallmark of many cancers. Ubiquitination, coordinated by E1, E2, and E3 enzymes, involves up to 40 E2-conjugating enzymes in humans to specify substrates and ubiquitin linkages. In a screen for E2 dependencies in acute myeloid leukemia (AML), ubiquitin conjugating enzyme E2 N (UBE2N) emerged as the top candidate. To investigate UBE2N's role in AML, we characterized an enzymatically defective mouse model of UBE2N, revealing UBE2N's requirement in AML without an impact on normal hematopoiesis. Unlike other E2s, which mediate lysine-48 (K48) polyubiquitination and degradation of proteins, UBE2N primarily synthesizes K63-linked chains, stabilizing or altering protein function. Proteomic analyses and a whole-genome CRISPR-activation screen in pharmacologically and genetically UBE2N-inhibited AML cells unveiled a network of UBE2N-regulated proteins, many of which are implicated in cancer. UBE2N inhibition reduced their protein levels, leading to increased K48-linked ubiquitination and degradation through the immunoproteasome and revealing UBE2N activity is enriched in immunoproteasome-positive AML. Furthermore, an interactome screen identified tripartite motif-containing protein 21 (TRIM21) as the E3 ligase partnering with activated UBE2N in AML to modulate UBE2N-dependent proteostasis. In conclusion, UBE2N maintains proteostasis in AML by stabilizing target proteins through K63-linked ubiquitination and prevention of K48 ubiquitin-mediated degradation by the immunoproteasome. Thus, inhibition of UBE2N catalytic function suppresses leukemic cells through selective degradation of critical proteins in immunoproteasome-positive AML.

Phospho-TRIM21 orchestrates RPA2 ubiquitination switch to promote homologous recombination and tumor radio/chemo-resistance

RPA2, a key component of the RPA complex, is essential for single-stranded DNA (ssDNA) binding and DNA repair. However, the regulation of RPA2-ssDNA interaction and the recruitment of repair proteins following DNA damage remain incompletely understood. Our study uncovers a novel mechanism by which phosphorylated TRIM21 (Phospho-TRIM21) regulates RPA2 ubiquitination, thereby modulating homologous recombination and tumor radio/chemo-resistance. In the absence of DNA damage, TRIM21 mediates K63-linked ubiquitination of RPA2, countering K6-linked ubiquitination. Upon DNA damage, ubiquitination-modified RPA2 binds ssDNA, stabilizing the DNA structure and facilitating ATRIP/ATR recruitment. ATR subsequently phosphorylates TRIM21 at Ser41, leading to the dissociation of the TRIM21-RPA2 complex and a shift in RPA2 ubiquitination from K63 to K6 linkage. This shift maintains RPA2 ubiquitination homeostasis and stabilizes the RPA2-ATRIP complex, which is crucial for efficient homologous recombination (HR) repair and enhanced tumor radio/chemo-resistance. We also demonstrate that TRIM21 is frequently upregulated in cancers, and its depletion sensitizes cancer cells to radio/chemotherapy, suggesting its potential as a therapeutic target. This study provides novel insights into TRIM21's role in the DNA damage response and its implications for cancer treatment.

Friend or foe of tripartite motif-containing protein 21 in cardiovascular disease: A review

As an E3 ubiquitin ligase and an Fc receptor, tripartite motif-containing protein 21 (TRIM21) plays a crucial role in immune defense, signal transduction, and cellular regulation. TRIM21 is widely expressed in various tissues, but it is particularly abundant in cardiovascular tissues and is involved in the pathogenesis of various cardiovascular diseases (CVDs). However, although TRIM21 is involved in the regulation of several key molecular pathways in the immune system, its specific role in CVD remains unclear. In this review, we comprehensively summarize the regulatory role of TRIM21 in signaling pathways and discuss the function of TRIM21 in CVD, to provide a systematic understanding of this important protein in CVD and offer insights for further research into the pathogenesis of CVD and its potential applications.

TRIM21-mediated ubiquitination and phosphorylation of ERK1/2 promotes cell proliferation and drug resistance in pituitary adenomas

BACKGROUND

Pituitary adenomas (PAs) are common intracranial tumors and the TRIM family plays a crucial role in cell proliferation and therapeutic resistance of tumors. However, the role of the TRIM family in PAs is not well recognized.

METHODS

CRISPR screening explored the role of the TRIM family in cell proliferation and drug resistance in PAs. In vitro and in vivo experiments were performed to evaluate the effects of Tripartite Motif Containing 21 (TRIM21). RNA-sequencing, mass spectrometry, immunoprecipitation, and ubiquitination experiments were performed to explore the molecular mechanism. NanoBiT assays were used to screen the drugs reducing TRIM21 expression.

RESULTS

CRISPR-Cas9 screens identified that TRIM21 facilitated cell proliferation and drug resistance in PAs. Mechanistically, TRIM21 interacted with ERK1/2 through PRY-SPRY domain, leading to ERK1/2 K27-linked ubiquitination. The ERK1/2 ubiquitination promotes the interaction between ERK1/2 and MEK1/2, thereby facilitating the phosphorylation of ERK1/2. However, an excess presence of TRIM21 suppressed the phosphorylation of ERK1/2 and cell proliferation via activating ERK1/2 negative feedback pathways. Importantly, TRIM21 was upregulated in dopamine-resistant prolactinomas and cabergoline-resistant MMQ cells. Furthermore, drug screening identified that Fimepinostat and Quisinostat, can reduce the protein levels of TRIM21, inhibit tumor progression, and increase drug sensitivity.

CONCLUSIONS

TRIM21 may represent a therapeutic target for tumors, and inhibiting TRIM21 could be a potential strategy for tumor treatment.

Targeting the TRIM21-PD-1 axis potentiates immune checkpoint blockade and CAR-T cell therapy

Dysregulation of T cells is a major limitation for the clinical success of T cell-based cancer immunotherapies, such as immune checkpoint blockade and chimeric antigen receptor (CAR)-T cell therapy. Understanding the underlying mechanisms for regulating T cell functions can facilitate designing therapeutic strategies to improve immunotherapies. Here, we report that TRIM21 impairs CD8+ T cell activation and anti-tumor immunity. Mechanistically, TRIM21 catalyzes the K63-linked ubiquitination on programmed cell death-1 (PD-1) at K233, leading to stabilization of PD-1 through antagonizing its K48-linked ubiquitination and degradation. Thus, Trim21 knockout (KO) significantly decreases PD-1 expression and enhances the activation of cytotoxic CD8+ T cells, which sensitizes tumors to anti-CTLA-4 immunotherapy. Notably, Trim21 KO anti-CD19 CAR-T cells exhibit improved anti-tumor efficacy. These results reveal the molecular mechanism by which TRIM21-mediated K63-linked ubiquitination on PD-1 restrains the activation of CD8+ T cells, highlighting that targeting the TRIM21-PD-1 axis as a potential therapeutic strategy to potentiate cancer immunotherapy.

TRIM21 Promotes Endothelial Cell Activation via Accelerating SOCS3 Ubiquitination Degradation in Atherosclerosis

Activated endothelial cells play an important role in the beginning of atherosclerotic disease by secreting various proteins and inflammatory cytokines. Ubiquitination is one of the most common post-translational changes in cells. However, the role and mechanisms of ubiquitination in endothelial cell activation remain poorly understood. In this study, we identified TRIM21 as an E3 ubiquitin ligase with increased expression in atherosclerotic disease and activated endothelial cells. Knockdown of TRIM21 resulted in reduced secretion of inflammatory factors and attenuated the pyroptosis of endothelial cells, inhibiting the progression of atherosclerosis. Mechanistically, TRIM21 could bind and ubiquitinate SOCS3, thereby enhancing NLRP3-mediated pyroptosis. Taken together, we found that endothelial TRIM21 activated the JAK/STAT3 pathway by degrading SOCS3, which in turn promoted NLRP3-mediated pyroptosis and aggravated atherosclerosis, revealing that TRIM21 may be a promising treatment target for the medical management of atherosclerosis.

The Mechanism of TRIM21 Inhibiting the Invasion and Migration of ccRCC by Stabilizing ASS1

Clear cell renal cell carcinoma (ccRCC) is characterized by its aggressive invasion and metastasis, presenting significant clinical challenges. Gaining insights into the molecular mechanisms underlying its progression is crucial for the development of effective therapeutic strategies. Addressing a critical knowledge gap in understanding ccRCC tumorigenesis, this study aims to elucidate the expression patterns of TRIM21 in ccRCC, unravel its impact on ccRCC patient prognosis, and investigate the regulatory role of TRIM21 in ASS1 expression and urea cycle dysregulation within the context of ccRCC. The results demonstrate that TRIM21 is downregulated in ccRCC, and low expression of TRIM21 predicts an unfavorable prognosis for ccRCC patients. Furthermore, the upregulation of TRIM21 can inhibit the migration and invasion of ccRCC cells by regulating the ubiquitination modification of ASS1. This not only expands the functional role of TRIM21 in ccRCC tumorigenesis but also demonstrates its ability to reverse urea cycle dysregulation through stabilizing ASS1 expression. Specifically, abnormal downregulation of TRIM21 in ccRCC reduces K63 ubiquitination modification of ASS1, leading to decreased stability of the ASS1 protein, aggravated urea cycle dysregulation, and facilitated migration and invasion of ccRCC cells. Additionally, reduction in ASS1 reverses the depressed migration and invasion caused by overexpression of TRIM21 in ccRCC cells. In summary, our findings contribute to a deeper understanding of the functional role played by TRIM21 in ccRCC progression, pinpoint a unique and novel regulatory mechanism involving ectopic downregulation-mediated ASS1 ubiquitination modification and urea cycle dysfunction during ccRCC progression, and provide fresh insights for further investigation into the pathogenesis and metabolic reprogramming associated with ccRCC.

TRIM21-mediated PRMT1 degradation attenuates colorectal cancer malignant progression

Tripartite motif-containing 21 (TRIM21) plays a crucial role in antiviral responses and autoimmune diseases. While the impact of TRIM21 on cancer has been studied in various tumors, its role in colorectal cancer (CRC) remains unclear. In this study, we found that TRIM21 expression is reduced in primary CRC tissues. Low levels of TRIM21 in CRC are associated with unfavorable clinicopathological characteristics and shorter survival. Furthermore, we demonstrate that TRIM21 suppresses the proliferation, tumorigenesis, migration, and metastasis of CRC cells by promoting the ubiquitination-mediated degradation of PRMT1. These findings suggest that TRIM21 holds potential as a valuable predictive biomarker for assessing the prognosis of CRC patients.

Tanshinone T1/T2A inhibits non-small cell lung cancer through Lin28B-let-7-BORA/MYC regulatory network

BACKGROUND

Lung cancer is the leading cause of cancer-related deaths worldwide. Tanshinones are a group of compounds in Salvia miltiorrhiza. Although the effects of tanshinone I (T1) and tanshinone IIA (T2A) are widely concerned, the mechanisms of T1 and T2A in lung cancer is rarely studied.

EXPERIMENTAL PROCEDURE

Xenograft tumor growth was performed to detect the role of T1/T2A in vivo. Next-generation sequencing of miRNA expression profiles in T1/T2A-treated A549 cells showed that T1/T2A upregulated the expression of the let-7 family. Then, let-7a-5p and its downstream target gene BORA were identified as the research objects in this paper. Mechanistically, we examined the interplay between miR-let-7 and BORA through the dual-luciferase reporter assay. Finally, the potential regulatory role of T1/T2A on Lin28B and MYC was explored.

RESULTS

This study found that the let-7 family was significantly up-regulated via "Next-generation" sequencing (NGS) in the T1/T2A-treated A549 cell line, while BORA was downregulated. BORA was confirmed as a direct target of let-7. LncRNA MYCLo-5 was up-regulated after treatment with tanshinones. Knockdown of MYCLo-5 promoted the cell cycle and proliferation of non-small cell lung cancer (NSCLC) cells.

CONCLUSIONS

This study explored the effects of tanshinone T1 and T2A on NSCLC in vitro and in vivo, revealing the T1/T2A-let-7/BORA/MYCLo-5 regulatory pathway, which provided new insights for lung cancer treatment.

Trim21 modulates endoplasmic reticulum-associated degradation and sensitizes cancer cells to ER stress-induced apoptosis by inhibiting VCP/Npl4/UFD1 assembly

Endoplasmic reticulum-associated degradation (ERAD) serves as a crucial quality and quantity control system that removes misfolded or unassembled proteins from the Endoplasmic Reticulum (ER) through the cytoplasmic ubiquitin-proteasome system (UPS), which is critical for cell fate decision. ER stress arises when misfolded proteins accumulated within the ER lumen, potentially leading to cell death via proapoptotic unfolded protein response (UPR). UFD1 in associated with VCP-Npl4, is recognized as a key regulator of protein homeostasis in ERAD. However, the factors that control VCP complex assembly remain unclear. The study elucidates the function of Trim21, an E3 ubiquitin ligase, through its interaction with UFD1, facilitating K27-linkage ubiquitination of UFD1 and inhibiting its incorporation into the VCP complex. This results in the suppression of ERAD substrates degradation and the activation of a proapoptotic unfolded protein response in cancer cells. Additionally, Trim21 over-expression enhances ER stress response and promotes apoptosis upon expose to the ER inducer Tunicamycin. Notably, elevated Trim21 expression correlates with improved overall survival in various tumor types. Overall, the findings highlight the critical role of Trim21 in regulating ERAD progression and cell fate determination in cancer cells through modulation of VCP/Npl4/UFD1 complex assembly.

The Role of lncRNA FEZF1-AS1 in Colorectal Cancer Progression Via the P53 Signaling Pathway

Long noncoding RNAs (lncRNAs) have emerged as critical regulators in the development of colorectal cancer (CRC). Previous studies indicate that lncRNA FEZF1-AS1 is highly expressed in CRC, but its role in modulating CRC via the P53 signaling pathway remains unclear. In this study, we found that FEZF1-AS1 promotes the growth of the CRC cell line (HCT116) and drives epithelial-mesenchymal transition (EMT) through the P53 signaling pathway. Our data showed that FEZF1-AS1 expression is significantly upregulated in HCT116, and elevated levels of FEZF1-AS1 are associated with poor prognosis in patients with CRC. In addition, the knockdown of FEZF1-AS1 markedly inhibited the proliferation of HCT116 by inducing cell cycle arrest. Knockdown of FEZF1-AS1 depletion also led to apoptosis in CRC cells by suppressing the P53 signaling pathway and EMT, thereby reducing their viability, proliferation, migration, and invasion. In summary, this study confirmed that FEZF1-AS1 regulates the growth of junction HCT116 through P53 signaling pathway and inhibiting EMT, providing new insights for the potential therapeutic strategies against CRC.

Trim21 mediates metabolic reprogramming in renal tubular cells via PFKP ubiquitination to alleviate renal fibrosis

Chronic kidney disease (CKD), stemming from varied nephric impairments, manifests a steadily escalating global incidence. As a progressive pathological condition, CKD is typified by an intensification in the gravity of renal interstitium fibrotic transformations. Nonetheless, the intrinsic mechanisms underpinning nephric fibrosis remain elusive. In this context, we elucidated a marked augmentation in aerobic glycolysis within proximal tubular epithelial cells (TECs) of CKD patients, alongside unilateral ureteral obstruction (UUO) and ischemia-reperfusion injury (IRI) murine models, concomitant with deficiency of Trim21. Experimental investigations, both in vivo and in vitro, revealed that Trim21 deficiency aggravates the aberrantly heightened aerobic glycolysis, thereby exacerbating fibrotic reaction progression. Concomitantly, enhancive glycolytic flux paralleled an elevation in ATP genesis and reconstitution of cytoskeletal architecture. Mechanistically, we uncovered that Trim21 modulates aerobic glycolysis in TECs via ubiquitin-facilitated degradation of phosphofructokinase platelet (PFKP), thus attenuating nephric fibrosis. Collectively, our insights posit Trim21 as a prospective therapeutic target in the amelioration of renal fibrosis.

MDM4 inhibits ferroptosis in p53 mutant colon cancer via regulating TRIM21/GPX4 expression

MDM4 is one of the major regulators of p53. The biological effect of MDM4 on tumor is controversial, its role and molecular mechanism in colon cancer progression and prognosis are still unclear. In this study, we identify that MDM4 is significantly overexpressed in human colon cancer and high MDM4 expression was associated with poor prognosis of colon cancer with mutant p53. MDM4 inhibits the ubiquitination of the ferroptosis marker protein GPX4 at K167 and K191 by upregulating the protein expression level of the E3 ubiquitin ligase TRIM21, which promotes the polyubiquitination of GPX4 transfer from K48- to K63- linked ubiquitination. Thereby, MDM4 enhances the stability of GPX4 protein, inhibiting ferroptosis, increasing the resistance of colon cancer patients to chemotherapy, and promoting colon cancer progression. These findings elucidate the ferroptosis inhibition effect of MDM4 via regulating TRIM21/GPX4 on p53-mutated colon cancer and provide a potential therapeutic strategy for colon cancer therapy.

Chaperonin-containing TCP1 subunit 6A inhibition via TRIM21-mediated K48-linked ubiquitination suppresses triple-negative breast cancer progression through the AKT signalling pathway

BACKGROUND

Triple-negative breast cancer (TNBC) is distinguished by a significant likelihood of distant recurrence and an unfavourable prognosis. However, the underlying molecules and mechanisms have not been fully elucidated.

METHODS

We investigated the expression profile and clinical relevance of chaperonin-containing TCP1 subunit 6A (CCT6A) in TNBC. We performed cell function assays on TNBC cells with CCT6A knockdown or overexpression. To further explore the mechanism of action of CCT6A, RNA sequencing and co-immunoprecipitation-mass spectrometry analyses were utilized. Rescue and ubiquitination assays evaluated the impact of TRIM21-mediated CCT6A ubiquitination and degradation on TNBC progression in vitro and in vivo. Finally, we studied the potential of Ipatasertib, a pharmacological AKT inhibitor, and/or anti-PD1 therapy in inhibiting TNBC progression.

RESULTS

Elevated CCT6A expression in TNBC patients was associated with an adverse prognosis and lymph node metastasis. Mechanistically, CCT6A facilitated cell migration, invasion, epithelial-mesenchymal transition and proliferation by activating the phosphatidylinositol 3-kinase (PI3K)/AKT pathway. The TRIM21 RING domain is an E3 ligase, facilitating the K48-linked ubiquitination-mediated degradation of CCT6A, thereby impeding TNBC progression. Moreover, in the tumour tissues of the CCT6A-overexpressing mice, the quantity of CD8+ T cells and the concentration of secreted interferon-gamma were decreased, whereas in the group double-overexpression of CCT6A and TRIM21, they were elevated; the opposite was observed in the knockdown and double-knockdown groups. Ipatasertib demonstrated enhanced efficacy in inhibiting cell proliferation, invasion and migration in TNBC cells ectopically expressing CCT6A. When Ipatasertib and anti-PD1 therapies were combined, both the tumour volume and mass exhibited a notable reduction, while the expression of CD45+CD8+ T cells increased, and that of CD45+CD4+CTLA4+ and CD45+CD4+PD1+ T cells decreased.

CONCLUSIONS

Our findings indicate that TRIM21 inhibits TNBC progression by facilitating the K48-linked ubiquitination-mediated degradation of CCT6A via the PI3K/AKT signalling pathway. This highlights the potential of Ipatasertib and/or anti-PD1 as therapeutic strategies, particularly for TNBC patients overexpressing CCT6A.

KEY POINTS

Chaperonin TCP1 subunit 6A (CCT6A) plays an oncogenic role in triple-negative breast cancer (TNBC) through the AKT signaling pathway. TRIM21 facilitated K48-linked ubiquitination-mediated degradation of CCT6A, thereby impeding TNBC progression. Our study collectively underscores the potential of Ipatasertib in conjunction with anti-PD1 therapy as a promising strategy to counteract CCT6A/AKT hyperactivity-driven TNBC progression.

TRIM21 induces selective autophagic degradation of c-Myc and sensitizes regorafenib therapy in colorectal cancer

Kirsten rat sarcoma virus (KRAS) mutation is associated with malignant tumor transformation and drug resistance. However, the development of clinically effective targeted therapies for KRAS-mutant cancer has proven to be a formidable challenge. Here, we report that tripartite motif-containing protein 21 (TRIM21) functions as a target of extracellular signal-regulated kinase 2 (ERK2) in KRAS-mutant colorectal cancer (CRC), contributing to regorafenib therapy resistance. Mechanistically, TRIM21 directly interacts with and ubiquitinates v-myc avian myelocytomatosis viral oncogene homolog (c-Myc) at lysine 148 (K148) via K63-linkage, enabling c-Myc to be targeted to the autophagy machinery for degradation, ultimately resulting in the downregulation of enolase 2 expression and inhibition of glycolysis. However, mutant KRAS (KRAS/MT)-driven mitogen-activated protein kinase (MAPK) signaling leads to the phosphorylation of TRIM21 (p-TRIM21) at Threonine 396 (T396) by ERK2, disrupting the interaction between TRIM21 and c-Myc and thereby preventing c-Myc from targeting autophagy for degradation. This enhances glycolysis and contributes to regorafenib resistance. Clinically, high p-TRIM21 (T396) is associated with an unfavorable prognosis. Targeting TRIM21 to disrupt KRAS/MT-driven phosphorylation using the antidepressant vilazodone shows potential for enhancing the efficacy of regorafenib in treating KRAS-mutant CRC in preclinical models. These findings are instrumental for KRAS-mutant CRC treatment aiming at activating TRIM21-mediated selective autophagic degradation of c-Myc.

Deacetylation of GLUD1 maintains the survival of lung adenocarcinoma cells under glucose starvation by inhibiting autophagic cell death

Enhanced glutamine catabolism is one of the main metabolic features of cancer, providing energy and intermediate metabolites for cancer progression. However, the functions of glutamine catabolism in cancer under nutrient deprivation need to be further clarified. Here, we discovered that deacetylation of glutamate dehydrogenase 1 (GLUD1), one of the key enzymes in glutamine catabolism, maintains the survival of lung adenocarcinoma (LUAD) cells under glucose starvation by inhibiting autophagic cell death. We found that glucose starvation increased GLUD1 activity by reducing its acetylation on Lys84 and promoted its active hexamer formation. Besides, deacetylation of GLUD1 induced its cytoplasmic localization, where GLUD1 was ubiquitinated in K63-linkage by TRIM21, leading to the binding of GLUD1 with cytoplasmic glutaminase KGA. These two effects enhanced glutamine metabolism both in mitochondria and cytoplasm, increased the production of alpha-ketoglutarate (α-KG). Meanwhile, cytoplasmic GLUD1 also interacted with p62 and prevented its acetylation, leading to the inhibition of p62 body formation. All these effects blocked autophagic cell death of LUAD cells under glucose starvation. Taken together, our results reveal a novel function of GLUD1 under glucose deprivation in LUAD cells and provide new insights into the functions of glutamine catabolism during cancer progression.

EPDR1 promotes PD-L1 expression and tumor immune evasion by inhibiting TRIM21-dependent ubiquitylation of IkappaB kinase-β

While immune checkpoint blockade (ICB) has shown promise for clinical cancer therapy, its efficacy has only been observed in a limited subset of patients and the underlying mechanisms regulating innate and acquired resistance to ICB of tumor cells remain poorly understood. Here, we identified ependymin-related protein 1 (EPDR1) as an important tumor-intrinsic regulator of PD-L1 expression and tumor immune evasion. Aberrant expression of EPDR1 in hepatocellular carcinoma is associated with immunosuppression. Mechanistically, EPDR1 binds to E3 ligase TRIM21 and disrupts its interaction with IkappaB kinase-b, suppressing its ubiquitylation and autophagosomal degradation and enhancing NF-κB-mediated transcriptional activation of PD-L1. Further, we validated through a mouse liver cancer model that EPDR1 mediates exhaustion of CD8+ T cells and promotes tumor progression. In addition, we observed a positive correlation between EPDR1 and PD-L1 expression in both human and mouse liver cancer samples. Collectively, our study reveals a previously unappreciated role of EPDR1 in orchestrating tumor immune evasion and cancer progression.

Targeting the ubiquitin-proteasome system: a novel therapeutic strategy for neuroblastoma

Neuroblastoma (NB) stands as a common and formidable malignant tumor among children, characterized by marked tumor heterogeneity and resistance to conventional treatments. Central to the regulation of protein stability, localization, and function is the process of ubiquitination-a critical protein modification. The therapeutic potential of drugs that target deubiquitination, demonstrated in the treatment of refractory multiple myeloma, warrants investigation in the context of NB. This review endeavors to demystify the intricate biological implications of ubiquitination within NB pathology, synthesize the current landscape of preclinical studies focused on the inhibition of the ubiquitin-proteasome system in NB, and assess the viability of this strategy as an innovative therapeutic frontier.

NCAPH, ubiquitinated by TRIM21, promotes cell proliferation by inhibiting autophagy of cervical cancer through AKT/mTOR dependent signaling

Autophagy is closely related to the occurrence and development of human malignancies; however, the detailed mechanisms underlying autophagy in cervical cancer require further investigation. Previously, we found that the ectopic expression of NCAPH, a regulatory subunit of condensed protein complexes, significantly enhanced the proliferation of tumor cells; however, the underlying mechanisms were unclear. Here, we revealed that NCAPH is a novel autophagy-associated protein in cervical cancer that promotes cell proliferation by inhibiting autophagosome formation and reducing autophagy, with no effect on the cell cycle, apoptosis, or aging. Tripartite motif-containing protein 21 (TRIM21) is well known to be involved in inflammation, autoimmunity and cancer, mainly via its E3 ubiquitin ligase activity. Mass spectrometry and immunoprecipitation assays showed that TRIM21 interacted with NCAPH and decreased the protein stability of NCAPH via ubiquitination at the K11 lysine residue. Structural domain mutation analysis revealed that TRIM21 combined with NCAPH through its PRY/SPRY and CC domains and accelerated the degradation of NCAPH through the RING domain. Furthermore, TRIM21 promoted autophagosome formation and reduced cell proliferation by inhibiting NCAPH expression and the downstream AKT/mTOR pathway in cervical cancer cells. Immunohistochemical staining revealed that the protein expression of TRIM21 was negatively correlated with that of NCAPH and positively correlated with that of beclin-1 in cervical cancer tissues. Therefore, we provide evidence for the role of the TRIM21-NCAPH axis in cervical cancer autophagy and proliferation and the involvement of the AKT/mTOR signaling pathway in this process. These results deepen our understanding of the carcinogenesis of cervical cancer, broaden the understanding of the molecular mechanisms of TRIM21 and NCAPH, and provide guidance for individualized treatment of cervical cancer in the future.

Construction and validation of a SASP-related prognostic signature in patients with acute myeloid leukaemia

Acute myeloid leukaemia (AML) is a common and highly aggressive haematological malignancy in adults. Senescence-associated secretory phenotype (SASP) plays important roles in tumorigenesis and progression of tumour. However, the prognostic value of SASP in patients with AML has not been clarified. The present study aims to explore the prognostic value of SASP and develop a prognostic risk signature for AML. The RNA-sequencing data was collected from the TCGA, GTEx and TARGET databases. Subsequently, differentially expressed gene analysis, univariate Cox regression and LASSO regression were applied to identified prognostic SASP-related genes and construct a prognostic risk-scoring model. The risk score of each patient were calculated and patients were divided into high- or low-risk groups by the median risk score. This novel prognostic signature included 11 genes: G6PD, CDK4, RPS6KA1, UBC, H2BC12, KIR2DL4, HSF1, IFIT3, PIM1, RUNX3 and TRIM21. The patients with AML in the high-risk group had shorter OS, demonstrating that the risk score acted as a prognostic predictor, which was validated in the TAGET-AML dataset. Univariate and multivariate analysis revealed the risk score was an independent prognostic factor in patients with AML. Furthermore, the present study revealed that the risk score was associated with immune landscape, immune checkpoint gene expression and chemotherapeutic efficacy. In the present study, we constructed and validated a unique SASP-related prognostic model to assess therapeutic effect and prognosis in patients with AML, which might contribute to understanding the role of SASP in AML and guiding the treatment for AML.

PAK1 inhibition increases TRIM21-induced PD-L1 degradation and enhances responses to anti-PD-1 therapy in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDA) is a common malignancy with a 5-year survival <10 %. Immunosuppressive tumor microenvironment (TME) plays a critical role in the progression of PDA. In recent years, programmed death-ligand 1 (PD-L1)/programmed cell death protein-1 (PD-1) blockade has emerged as a potent anti-tumor immunotherapy, while is yet to achieve significant clinical benefits for PDA patients. P21-Activated kinase 1 (PAK1) is highly upregulated in PDA and has been reported to be involved in the regulation of anti-tumor immunity. This study aims to investigate the combined effect of PAK1 inhibition and anti-PD-1 therapy on PDA and the underlying mechanisms. We have shown that PAK1 expression positively correlated with PD-L1 in PDA patients, and that inhibition of PAK1 downregulated PD-L1 expression of PDA cells. More importantly, we have demonstrated that PAK1 competed with PD-L1 in binding to tripartite motif-containing protein 21 (TRIM21), a ubiquitin E3 ligase, resulting in less ubiquitination and degradation of PD-L1. Moreover, PAK1 inhibition promoted CD8+ T cells activation and infiltration. In a murine PDA model, the combination of PAK1 inhibition and anti-PD-1 therapy showed significant anti-tumor effects compared with the control or monotherapy. Our results indicated that the combination of PAK1 inhibition and anti-PD-1 therapy would be a more effective treatment for PDA patients.

TNKS1BP1 facilitates ubiquitination of CNOT4 by TRIM21 to promote hepatocellular carcinoma progression and immune evasion

Immune checkpoint inhibitors, particularly PD-1/PD-L1 blockades, have been approved for unresectable hepatocellular carcinoma (HCC). However, high resistance rates still limit their efficacy, highlighting the urgent need to understand the underlying mechanisms and develop strategies for overcoming the resistance. In this study, tankyrasel binding protein 1 (TNKS1BP1) was found to interact with tripartite motif containing 21 (TRIM21) and mediated the ubiquitination of CCR4-NOT transcription complex subunit 4 (CNOT4) at the K239 residue via K48 and K6 linkage, which was essential for its tumorigenesis function. Autophagy and lipid reprogramming were identified as two possible mechanisms underlying the pro-tumor effect of TNKS1BP1. Upregulated TNKS1BP1 inhibited autophagy while induced lipid accumulation by inhibiting the JAK2/STAT3 pathway upon the degradation of CNOT4 in HCC. Importantly, knocking down TNKS1BP1 synergized with anti-PD-L1 treatment by upregulating PD-L1 expression on tumor cells via the JAK2/STAT3 pathway, and remodeling the tumor microenvironment by increasing infiltration of tumor-infiltrating lymphocytes as well as augmenting the effect of cytotoxic T lymphocytes. In conclusion, this study identified TNKS1BP1 as a predictive biomarker for patient prognosis and a promising therapeutic target to overcome anti-PD-L1 resistance in HCC.

cGAS-STING pathway agonists are promising vaccine adjuvants

Adjuvants are of critical value in vaccine development as they act on enhancing immunogenicity of antigen and inducing long-lasting immunity. However, there are only a few adjuvants that have been approved for clinical use, which highlights the need for exploring and developing new adjuvants to meet the growing demand for vaccination. Recently, emerging evidence demonstrates that the cGAS-STING pathway orchestrates innate and adaptive immunity by generating type I interferon responses. Many cGAS-STING pathway agonists have been developed and tested in preclinical research for the treatment of cancer or infectious diseases with promising results. As adjuvants, cGAS-STING agonists have demonstrated their potential to activate robust defense immunity in various diseases, including COVID-19 infection. This review summarized the current developments in the field of cGAS-STING agonists with a special focus on the latest applications of cGAS-STING agonists as adjuvants in vaccination. Potential challenges were also discussed in the hope of sparking future research interests to further the development of cGAS-STING as vaccine adjuvants.

TRIM21-mediated ubiquitylation of TAT suppresses liver metastasis in gallbladder cancer

Liver metastasis is common in patients with gallbladder cancer (GBC), imposing a significant challenge in clinical management and serving as a poor prognostic indicator. However, the mechanisms underlying liver metastasis remain largely unknown. Here, we report a crucial role of tyrosine aminotransferase (TAT) in liver metastasis of GBC. TAT is frequently up-regulated in GBC tissues. Increased TAT expression is associated with frequent liver metastasis and poor prognosis of GBC patients. Overexpression of TAT promotes GBC cell migration and invasion in vitro, as well as liver metastasis in vivo. TAT knockdown has the opposite effects. Intriguingly, TAT promotes liver metastasis of GBC by potentiating cardiolipin-dependent mitophagy. Mechanistically, TAT directly binds to cardiolipin and leads to cardiolipin externalization and subsequent mitophagy. Moreover, TRIM21 (Tripartite Motif Containing 21), an E3 ubiquitin ligase, interacts with TAT. The histine residues 336 and 338 at TRIM21 are essential for this binding. TRIM21 preferentially adds the lysine 63 (K63)-linked ubiquitin chains on TAT principally at K136. TRIM21-mediated TAT ubiquitination impairs its dimerization and mitochondrial location, subsequently inhibiting tumor invasion and migration of GBC cells. Therefore, our study identifies TAT as a novel driver of GBC liver metastasis, emphasizing its potential as a therapeutic target.

Trim21 deficiency in mice increases HCC carcinogenesis in a NASH context and is associated with immune checkpoint upregulation

The global pandemic of metabolic diseases has increased the incidence of hepatocellular carcinoma (HCC) in the context of non-alcoholic steatohepatitis (NASH). The downregulation of the E3 ubiquitin ligase TRIM21 has been linked to poor prognosis in different cancers including HCC. In order to investigate the role of TRIM21 in liver cancer progression on NASH, Trim21+/+ and Trim21-/- male mice were injected with streptozotocin at the neonatal stage. The hypoinsulinemic mice were then fed with a high-fat high-cholesterol diet (HFHCD) for 4, 8 or 12 weeks. All mice developed NASH which systematically resulted in HCC progression. Interestingly, compared to the Trim21+/+ control mice, liver damage was worsened in Trim21-/- mice, with more HCC nodules found after 12 weeks on HFHCD. Immune population analysis in the spleen and liver revealed a higher proportion of CD4+PD-1+ and CD8+PD-1+ T cells in Trim21-/- mice. The liver and HCC tumors of Trim21-/- mice also exhibited an increase in the number of PD-L1+ and CD68+ PD-L1+ cells. Thus, TRIM21 limits the emergence of HCC nodules in mice with NASH by potentially restricting the expression of PD-1 in lymphocytes and PD-L1 in tumors.

TRIM26 inhibits clear cell renal cell carcinoma progression through destabilizing ETK and thus inactivation of AKT/mTOR signaling

BACKGROUND

Tripartite motif-containing 26 (TRIM26), a member of the TRIM protein family, exerts dual function in several types of cancer. Nevertheless, the precise role of TRIM26 in clear cell renal cell carcinoma (ccRCC) has not been investigated.

METHODS

The expression of TRIM26 in ccRCC tissues and cell lines were examined through the use of public resources and experimental validation. The impacts of TRIM26 on cell proliferation, migration, invasion, and epithelial-mesenchymal transition (EMT) process were determined via CCK-8, colony formation, EdU incorporation, wound healing, Transwell invasion, Western blot, and Immunofluorescence assays. RNA-seq followed by bioinformatic analyses were used to identify the downstream pathway of TRIM26. The interaction between TRIM26 and ETK was assessed by co-immunoprecipitation, qRT-PCR, Western blot, cycloheximide (CHX) chase, and in vivo ubiquitination assays.

RESULTS

We have shown that TRIM26 exhibits a downregulation in both ccRCC tissues and cell lines. Furthermore, this decreased expression of TRIM26 is closely linked to unfavorable overall survival and diseases-free survival outcomes among ccRCC patients. Gain- and loss-of-function experiments demonstrated that increasing the expression of TRIM26 suppressed the proliferation, migration, invasion, and EMT process of ccRCC cells. Conversely, reducing the expression of TRIM26 had the opposite effects. RNA sequencing, coupled with bioinformatic analysis, revealed a significant enrichment of the mTOR signaling pathway in the control group compared to the group with TRIM26 overexpression. This finding was then confirmed by a western blot assay. Subsequent examination revealed that TRMI26 had a direct interaction with ETK, a non-receptor tyrosine kinase. This interaction facilitated the ubiquitination and degradation of ETK, resulting in the deactivation of the AKT/mTOR signaling pathway in ccRCC. ETK overexpression counteracted the inhibitory effects of TRIM26 overexpression on cell proliferation, migration, and invasion.

CONCLUSION

Our results have shown a novel mechanism by which TRIM26 hinders the advancement of ccRCC by binding to and destabilizing ETK, thus leading to the deactivation of AKT/mTOR signaling. TRIM26 shows promise as both a therapeutic target and prognostic biomarker for ccRCC patients.

TRIM21 is critical in regulating hepatocellular carcinoma growth and response to therapy by altering the MST1/YAP pathway

Liver cancer is the sixth most common cancer and the third leading cause of cancer-related death globally. Despite efforts being made in last two decades in cancer diagnosis and treatment, the 5-year survival rate of liver cancer remains extremely low. TRIM21 participates in cancer metabolism, glycolysis, immunity, chemosensitivity and metastasis by targeting various substrates for ubiquitination. TRIM21 serves as a prognosis marker for human hepatocellular carcinoma (HCC), but the mechanism by which TRIM21 regulates HCC tumorigenesis and progression remains elusive. In this study, we demonstrated that TRIM21 protein levels were elevated in human HCC. Elevated TRIM21 expression was associated with HCC progression and poor survival. Knockdown of TRIM21 in HCC cell lines significantly impaired cell growth and metastasis and enhanced sorafenib-induced toxicity. Mechanistically, we found that knockdown of TRIM21 resulted in cytosolic translocation and inactivation of YAP. At the molecular level, we further identified that TRIM21 interacted and induced ubiquitination of MST1, which resulted in MST1 degradation and YAP activation. Knockdown of MST1 or overexpression of YAP reversed TRIM21 knockdown-induced impairment of HCC growth and chemosensitivity. Taken together, the current study demonstrates a novel mechanism that regulates the Hippo pathway and reveals TRM21 as a critical factor that promotes growth and chemoresistance in human HCC.

TRIM21 silencing inhibits the apoptosis and expedites the osteogenic differentiation of dexamethasone‑induced MC3T3‑E1 cells by activating the Keap1/Nrf2 pathway

Steroid-induced osteonecrosis of the femoral head (ONFH) is a serious complication caused by long-term or excessive use of glucocorticoids. The present study aimed to ascertain the effects of tripartite motif-containing protein 21 (TRIM21) on the process of steroid-induced ONFH and its hidden action mechanism. TRIM21 expression in dexamethasone (Dex)-treated mouse MC3T3-E1 preosteoblast cells was examined using reverse transcription-quantitative PCR and western blotting. The Cell Counting Kit-8 (CCK-8) method and lactate dehydrogenase release assay were used to respectively measure cell viability and injury. Flow cytometry analysis was used to assay cell apoptosis. Caspase 3 activity was evaluated using a specific assay, while alkaline phosphatase and Alizarin red S staining were used to evaluate osteogenesis. 2,7-dichloro-dihydrofluorescein diacetate fluorescence probe was used to estimate reactive oxygen species generation. Specific assay kits were used to appraise oxidative stress levels. In addition, the expression of apoptosis-, osteogenic differentiation- and Kelch-like ECH-associated protein 1 (Keap1)/nuclear factor erythroid 2-related factor 2 (Nrf2) signaling-associated proteins was assessed using western blotting. In Nrf2 inhibitor (ML385)-pretreated MC3T3-E1 cells exposed to Dex, cell apoptosis, osteogenesis and oxidative stress were detected again as aforementioned. Results revealed that TRIM21 expression was raised in Dex-induced MC3T3-E1 cells and TRIM21 deletion improved the viability and osteogenic differentiation, whereas it hampered the oxidative stress and apoptosis in MC3T3-E1 cells with Dex induction. In addition, silencing of TRIM21 activated Keap1/Nrf2 signaling. Moreover, ML385 partially abrogated the effects of TRIM21 depletion on the oxidative stress, apoptosis and osteogenic differentiation in MC3T3-E1 cells exposed to Dex. In conclusion, TRIM21 silencing might activate Keap1/Nrf2 signaling to protect against steroid-induced ONFH.

Viral infection and spread are inhibited by the polyubiquitination and downregulation of TRPV2 channel by the interferon-stimulated gene TRIM21

Interferon (IFN) contributes to the host's antiviral response by inducing IFN-stimulated genes (ISGs). However, their functional targets and the mechanism of action remain elusive. Here, we report that one such ISG, TRIM21, interacts with and degrades the TRPV2 channel in myeloid cells, reducing its expression and providing host protection against viral infections. Moreover, viral infection upregulates TRIM21 in paracrine and autocrine manners, downregulating TRPV2 in neighboring cells to prevent viral spread to uninfected cells. Consistently, the Trim21-/- mice are more susceptible to HSV-1 and VSV infection than the Trim21+/+ littermates, in which viral susceptibility is rescued by inhibition or deletion of TRPV2. Mechanistically, TRIM21 catalyzes the K48-linked ubiquitination of TRPV2 at Lys295. TRPV2K295R is resistant to viral-infection-induced TRIM21-dependent ubiquitination and degradation, promoting viral infection more profoundly than wild-type TRPV2 when reconstituted into Lyz2-Cre;Trpv2fl/fl myeloid cells. These findings characterize targeting the TRIM21-TRPV2 axis as a conducive strategy to control viral spread to bystander cells.

The Emerging Role of Deubiquitinases in Radiosensitivity

Radiation therapy is a primary treatment for cancer, but radioresistance remains a significant challenge in improving efficacy and reducing toxicity. Accumulating evidence suggests that deubiquitinases (DUBs) play a crucial role in regulating cell sensitivity to ionizing radiation. Traditional small-molecule DUB inhibitors have demonstrated radiosensitization effects, and novel deubiquitinase-targeting chimeras (DUBTACs) provide a promising strategy for radiosensitizer development by harnessing the ubiquitin-proteasome system. This review highlights the mechanisms by which DUBs regulate radiosensitivity, including DNA damage repair, the cell cycle, cell death, and hypoxia. Progress on DUB inhibitors and DUBTACs is summarized, and their potential radiosensitization effects are discussed. Developing drugs targeting DUBs appears to be a promising alternative approach to overcoming radioresistance, warranting further research into their mechanisms.

FGF19 promotes nasopharyngeal carcinoma progression by inducing angiogenesis via inhibiting TRIM21-mediated ANXA2 ubiquitination

PURPOSE

Nasopharyngeal carcinoma (NPC) has characteristics of high invasion and early metastasis. Most NPC patients present with locoregionally advanced illness when first diagnosed. Therefore, it is urgent to discover NPC biomarkers. Fibroblast growth Factor 19 (FGF19) plays a role in various physiological or pathological processes, including cancer. In this research, we discovered the importance of FGF19 in NPC, and clarified its role in tumour angiogenesis.

METHODS

Western blotting, immunohistochemistry and ELISA were used to investigate FGF19 expression in NPC. Then we took CCK8, colony formation, Transwell and wound healing assays to identify the influence of FGF19 on NPC malignant behaviours. The proliferative and metastatic capacity of FGF19 were evaluated in nude mice and zebrafish. The role of FGF19 in angiogenesis was investigated by tube formation and Matrigel plug angiogenesis assays. We then evaluated the variation in Annexin A2(ANXA2) levels with the treatment of FGF19. Lastly, co-immunoprecipitation and ubiquitination assays were performed to identify the mechanisms involved.

RESULTS

FGF19 levels were elevated in tissues and serum of NPC patients and were associated with poor clinical stages. High expression of FGF19 promoted NPC malignant behaviours. In particular, FGF19 expression was correlated with microvessel density in tissues and NPC-derived FGF19 could accelerate angiogenesis in vitro and in vivo. Mechanistically, FGF19 influenced ANXA2 expression to promote angiogenesis. Moreover, tripartite motif-containing 21(TRIM21) interacted with ANXA2 and was responsible for ANXA2 ubiquitination.

CONCLUSION

FGF19 promoted NPC angiogenesis by inhibiting TRIM21-mediated ANXA2 ubiquitination. It may serve as a noninvasive biomarker for NPC and provides new insights for therapy.

A ubiquitination-related risk model for predicting the prognosis and immunotherapy response of gastric adenocarcinoma patients

Ubiquitination is crucial for the growth of cancer. However, the role of ubiquitination-related genes (URGs) in stomach adenocarcinoma (STAD) remains unclear. Differentially expressed URGs (DE-URGs) were examined in the whole TCGA-STAD dataset, and the prognosis-related genes were discovered from the The Cancer Genome Atlas (TCGA) training set. Prognostic genes were discovered using selection operator regression analysis and absolute least shrinkage (LASSO). A multivariate Cox analysis was further employed, and a polygene-based risk assessment system was established. Signatures were verified using the Gene Expression Omnibus (GEO) database record GSE84433 and the TCGA test set. Using the MEXPRESS dataset, a detailed analysis of gene expression and methylation was carried out. Using the DAVID database, DE-URG function and pathway enrichment was examined. The identified 163 DE-URGs were significantly associated with pathways related to protein ubiquitination, cell cycle, and cancer. A prognostic signature based on 13 DE-URGs was constructed, classifying patients into two risk groups. Compared to low-risk patients, people at high risk had considerably shorter survival times. Cox regression analyses considered prognostic parameters independent of age and risk score and were used to generate nomograms. Calibration curves show good agreement between nomogram predictions and observations. Furthermore, the results of the MEXPRESS analysis indicated that 13 prognostic DE-URGs had an intricate methylation profile. The enhanced Random Forest-based model showed greater efficacy in predicting prognosis, mutation, and immune infiltration. The in vitro validation, including CCK8, EdU, Transwell, and co-culture Transwell, proved that RNF144A was a potent oncogene in STAD and could facilitate the migration of M2 macrophages. In this research, we have created a genetic model based on URGs that can appropriately gauge a patient's prognosis and immunotherapy response, providing clinicians with a reliable tool for prognostic assessment and supporting clinical treatment decisions.

Targeting lipid biosynthesis on the basis of conventional treatments for clear cell renal cell carcinoma: A promising therapeutic approach

A variety of cancer cells exhibit dysregulated lipid metabolism, characterized by excessive intracellular lipid accumulation, and clear cell renal cell carcinoma (ccRCC) is the most typical disease with these characteristics. As the most common malignancy of all renal cell carcinomas (RCCs), ccRCC is typically characterized by a large accumulation of lipids and glycogen in the cytoplasm and a nucleus that is squeezed by the accumulated lipid droplets and localized to the marginal areas within the cytoplasm. This lipid accumulation has been found to be critically involved in the maintenance of malignant features observed in various cancers. Firstly, it maintains the persistent proliferative and metastasis properties of cancer cells. Secondly, it acts as a buffer against lipid peroxidation, preventing lipid peroxidation-induced ferroptosis. Moreover, lipids can diminish the sensitivity of cancer cells to radiotherapy. As ccRCC is a type of cancer with high lipid synthesis, targeting lipid synthesis-related genes in cancer cells may be a promising therapeutic modality for single treatment or in combination with radiotherapy, chemotherapy, and immunotherapy. This may revolutionize the choice of treatment modality for ccRCC patients. In this review, we concentrate on the current status and progress of research on lipid biosynthesis in ccRCC and the potential applications of targeting lipid synthesis to treat ccRCC. At last, we propose perspective and future research directions for targeting inhibition of lipid biosynthesis in combination with conventional therapeutic approaches for the treatment of ccRCC, which will help to evolve the therapeutic model.

A Interacting Model: How TRIM21 Orchestrates with Proteins in Intracellular Immunity

Tripartite motif-containing protein 21 (TRIM21), identified as both a cytosolic E3 ubiquitin ligase and FcR (Fragment crystallizable receptor), primarily interacts with proteins via its PRY/SPRY domains and promotes their proteasomal degradation to regulate intracellular immunity. But how TRIM21 involves in intracellular immunity still lacks systematical understanding. Herein, it is probed into the TRIM21-related literature and raises an interacting model about how TRIM21 orchestrates proteins in cytosol. In this novel model, TRIM21 generally interacts with miscellaneous protein in intracellular immunity in two ways: For one, TRIM21 solely plays as an E3, ubiquitylating a glut of proteins that contain specific interferon-regulatory factor, nuclear transcription factor kappaB, virus sensors and others, and involving inflammatory responses. For another, TRIM21 serves as both E3 and specific FcR that detects antibody-complexes and facilitates antibody destroying target proteins. Correspondingly delineated as Fc-independent signaling and Fc-dependent signaling in this review, how TRIM21's interactions contribute to intracellular immunity, expecting to provide a systematical understanding of this important protein and invest enlightenment for further research on the pathogenesis of related diseases and its prospective application is elaborated.

Mutual regulation between TRIM21 and TRIM8 via K48-linked ubiquitination

Tripartite motif (TRIM)-containing proteins, one of the largest subfamilies of the RING type E3 ubiquitin ligases, control important biological processes such as cell apoptosis, autophagy, signal transduction, innate immunity and tumorigenesis. So far, the mutual regulation between TRIM family members has rarely been reported. Here, we found for the first time that there was a direct mutual regulation between TRIM21 and TRIM8 in lung and renal cancer cells, mechanistically by activating their proteasome pathway via Lys48 (K48)- linked ubiquitination. Subsequent studies verified that negatively correlated expressions existed in clinical non-small cell lung cancer (NSCLC) and renal cell carcinoma (RCC) tissues, which were closely related to tumor progression. Our findings highlighted a possible homeostasis between TRIM21 and TRIM8 that might possibly affect cell stemness and was expected to provide a new idea for cancer therapy.

The interconnected roles of TRIM21/Ro52 in systemic lupus erythematosus, primary Sjögren's syndrome, cancers, and cancer metabolism

Protein tripartite motif-containing 21 (TRIM21/Ro52), an E3 ubiquitin ligase, is an essential regulator of innate immunity, and its dysregulation is closely associated with the development of autoimmune diseases, predominantly systemic lupus erythematosus (SLE) and primary Sjögren's syndrome (pSS). TRIM21 /Ro52 also features anti-cancer and carcinogenic functions according to different malignancies. The interconnected role of TRIM21/Ro52 in regulating autoimmunity and cell metabolism in autoimmune diseases and malignancies is implicated. In this review, we summarize current findings on how TRIM21/Ro52 affects inflammation and tumorigenesis, and investigate the relationship between TRIM21/Ro52 expression and the formation of lymphoma and breast cancer in SLE and pSS populations.

N4BP1 mediates RAM domain-dependent notch signaling turnover during neocortical development

Notch signaling pathway activity, particularly fluctuations in the biologically active effector fragment NICD, is required for rapid and efficient dynamic regulation of proper fate decisions in stem cells. In this study, we identified NEDD4-binding protein 1 (N4BP1), which is highly expressed in the developing mouse cerebral cortex, as a negative modulator of Notch signaling dynamics in neural progenitor cells. Intriguingly, N4BP1 regulated NICD stability specifically after Notch1 S3 cleavage through ubiquitin-mediated degradation that depended on its RAM domain, not its PEST domain, as had been extensively and previously described. The CoCUN domain in N4BP1, particularly the "Phe-Pro" motif (862/863 amino acid), was indispensable for mediating NICD degradation. The Ring family E3 ligase Trim21 was, in contrast to other NEDD4 family members, required for N4BP1-regulated NICD degradation. Overexpression of N4BP1 in cortical neural progenitors promoted neural stem cell differentiation, whereas neural progenitor cells lacking N4BP1 were sensitized to Notch signaling, resulting in the maintenance of stem-like properties in neural progenitor cells and lower production of cortical neurons.

TRIM21 of Micropterus salmoides exerts antiviral roles against largemouth bass ulcer syndrome virus

Tripartite motif 21 (TRIM21), a member of the TRIM family, plays an important role in apoptosis, autophagy and ubiquitination in human, and has been proven to play antiviral roles in different organisms. In this study, the TRIM21 gene of Micropterus salmoides (MsTRIM21) was cloned, and it encoded 376 amino acids, which showed 89.3% similarity with Micropterus dolomieu and 38.3% with homo sapiens. Bioinformatics analysis revealed MsTRIM21 contained four domains: C4HC3-type RING-variant (RINGv), coiled coil, PRY and SPRY. The high expression level of MsTRIM21 could be detected in liver, stomach and muscle of healthy Micropterus salmoides, and it was significantly upregulated in head kidney, muscle, gill and brain and significantly down-regulated in the stomach of Micropterus salmoides infected with largemouth bass ulcer syndrome virus (LBUSV). The overexpression of MsTRIM21 could significantly inhibit the viral replication in vitro, evidenced by the reduction of CPE severity and the downregulation of the viral gene transcription. In addition, the overexpression of MsTRIM21 could significantly increase the expression level of interferon regulatory factor (IRF) 3, IRF7, myxovirus resistance 1 (Mx1), interferon stimulated gene 15 (ISG15), double-stranded RNA-activated protein kinase (PKR) and tumor necrosis factor α (TNF-α) in vitro, indicating the enhancement of innate immune response and inflammatory response, which may directly affect the replication of LBUSV. Thus, these results provide new lights on the roles of fish TRIM21 in innate immune response against iridovirus.

TRIM21 mediates the synergistic effect of Olaparib and Sorafenib by degrading BRCA1 through ubiquitination in TNBC

Triple-negative breast cancer (TNBC) is a heterogeneous and aggressive type of breast cancer with a poor prognosis and a high recurrence rate. Chemotherapy is still the mainstay of treatment for cancer patients without a genetic BRCA mutation, despite the approval of Olaparib, an inhibitor of the poly (ADP-ribose) polymerase (PARP) enzyme. Tripartite motif containing-21 (TRIM21) is one of the TRIM family members that has been investigated in various types of cancer. Here, we found that a low TRIM21 expression level was correlated with poor overall survival of TNBC patients. Knockout of TRIM21 promoted the proliferation of TNBC cells in vivo and in vitro, as well as migratory and invasive capabilities in vitro. Importantly, breast cancer susceptibility gene 1 (BRCA1) was identified as a ubiquitination substrate of TRIM21. It was confirmed that BRCA1 was upregulated after Olaparib treatment, which may explain the relative resistance of BRCA1-proficient TNBC cells to Olaparib. Moreover, Sorafenib, a standard treatment for hepatocellular carcinoma, increased the sensitivity of TNBC cells to Olaparib by promoting TRIM21-mediated ubiquitination degradation of BRCA1. Thus, a synergic effect of Olaparib and Sorafenib was found in vitro and in vivo. This combined treatment also aggravated DNA damage, cell cycle arrest, and apoptosis of TNBC cells. In summary, the findings verified the synergistic effect of Olaparib and Sorafenib and revealed TRIM21 as a potential target for TNBC therapy.

Regulation of hPCL3 isoforms' ubiquitination by TRIM21 in non-small cell lung cancer progression

Non-small cell lung cancer (NSCLC) is the main subtype of lung cancer. The role of hPCL3 isoforms, hPCL3S and hPCL3L, remains ambiguous. This study examines the functional implications of these isoforms in NSCLC, using lung cancer cell lines A549 and NCI-H226c for in vivo and in vitro analyses. The results indicate that elevated expression of both hPCL3S and hPCL3L correlates with diminished overall survival, although only hPCL3S levels are augmented in clinical NSCLC specimens. Inhibition of either isoform leads to reduced cell proliferation, invasion, and migration, with hPCL3S knockdown displaying superior effectiveness. Moreover, the findings reveal that TRIM21 interacts with both isoforms and mediates hPCL3S degradation through K48-linked ubiquitination in NSCLC cells. Conversely, TRIM21 does not facilitate hPCL3L degradation, despite forming K63-linked polyubiquitin chains. These observations highlight the divergent roles of hPCL3 isoforms in NSCLC and underscore the potential therapeutic value of targeting hPCL3S.

TRIM21-Promoted FSP1 Plasma Membrane Translocation Confers Ferroptosis Resistance in Human Cancers

Ferroptosis, an iron-dependent form of regulated cell death driven by excessive accumulation of lipid peroxides, has become a promising strategy in cancer treatment. Cancer cells exploit antioxidant proteins, including Ferroptosis Suppressor Protein 1 (FSP1), to prevent ferroptosis. In this study, it is found that the E3 ubiquitin ligase TRIM21 bound to FSP1 and mediated its ubiquitination on K322 and K366 residues via K63 linkage, which is essential for its membrane translocation and ferroptosis suppression ability. It is further verified the protective role of the TRIM21-FSP1 axis in RSL3-induced ferroptosis in cancer cells and a subcutaneous tumor model. Moreover, TRIM21 is highly expressed in multiple gastrointestinal (GI) tumors, and its expression is further stimulated upon ferroptosis induction in cancer cells and the KPC mouse model. In summary, This study identifies TRIM21 as a negative regulator of ferroptosis through K63 ubiquitination of FSP1, which can serve as a therapeutic target to enhance the chemosensitivity of tumors based on ferroptosis induction.

TRIM21 promotes tumor progression and cancer stemness in cervical squamous cell carcinoma

BACKGROUND

The ubiquitin ligase family member triplex motif protein 21 (TRIM21), which is involved in the proliferation, metastasis, and selective death of tumor cells, is crucial in the ubiquitination of a number of tumor marker proteins. As research progresses, more studies demonstrate that TRIM21 expression levels can be used to predict cancer prognosis. However, it is unclear how exactly TRIM21 contributes to cervical squamous carcinoma.

METHODS

Immunohistochemistry, Western Blot, and q-PCR were utilized to determine the expression level of TRIM21 in 113 patients with CESC removed by stage I surgery at Xijing Hospital from 2018 to 2023 using paraffin-embedded tumor tissues and 12 pairs of fresh tumor tissues and their paracancerous tissues. Log-rank analysis using SPSS 23.0 was performed for prognosis and survival analysis using univariate/multifactorial analysis. CCK-8, wound-healing and Scratch assay verified that TRIM21 promoted cell proliferation, migration and invasion. The effect of overexpression and knockdown of TRIM21 on tumor stemness was examined using sphere-forming assay and Western Blot. Finally, we constructed a xenograft model to observe the effect of TRIM21 on tumorigenesis in Si Ha cell lines in vivo.

RESULTS

TRIM21 expression is greater in CESC tissues than in paracancerous tissues, according to immunohistochemical data. Similarly, at the protein and mRNA levels, we verified this conclusion using Western-Blotting and q-PCR. Prognostic and OS analysis showed that TRIM21 expression levels are associated with individual prognostic factors. CCK-8, Wound healing, Transwell, and Sphere-forming tests all demonstrated that TRIM21 overexpression enhances Ca Ski cell proliferation, migration, invasion, and stemness. TRIM21 knockdown in Si Ha inhibited tumor cell proliferation, migration, invasion, and stemness. The experimental results of xenograft models demonstrated that TRIM21 knockdown in Si Ha cells inhibited tumor development.

CONCLUSION

TRIM21 is a poor predictor of prognosis for cervical squamous cell carcinoma and might open up new avenues for investigation into therapeutic targets.

TRIM21 ameliorates hepatic glucose and lipid metabolic disorders in type 2 diabetes mellitus by ubiquitination of PEPCK1 and FASN

Hepatic glucose and lipid metabolism disorders promote the development and progression of type 2 diabetes mellitus (T2DM), yet the underlying mechanisms are not fully understood. Here, we identify tripartite motif-containing protein 21 (TRIM21), a class IV TRIM family member, as a pivotal regulator of hepatic metabolism in T2DM for the first time. Bioinformatic analysis suggests that TRIM21 expression is significantly reduced in T2DM patients. Intriguingly, in a mouse model of obese diabetes, TRIM21 expression is predominantly reduced in the liver rather than in other metabolic organs. It is further demonstrated that hepatic overexpression of TRIM21 significantly ameliorates glucose intolerance, insulin resistance, hepatic steatosis, and dyslipidemia in obese diabetic mice. In contrast, the knockdown of TRIM21 promotes glucose intolerance, insulin resistance, and triglyceride accumulation. Mechanistically, both phosphoenolpyruvate carboxykinase 1 (PEPCK1) and fatty acid synthase (FASN) are the hepatic targets of TRIM21. We revealed that TRIM21 promotes the degradation of PEPCK1 and FASN through a direct protein-protein interaction mediated K48-linked ubiquitination. Notably, overexpression of PEPCK1 and FASN essentially abolished the beneficial effects achieved by TRIM21 overexpression in obese diabetic mice. Overall, our data demonstrate that TRIM21 is a novel regulator of hepatic metabolic disorder, and suggest TRIM21 as a promising therapeutic target for T2DM.

TRIM21 ubiquitylates GPX4 and promotes ferroptosis to aggravate ischemia/reperfusion-induced acute kidney injury

AIMS

This study aims to verify the molecular mechanism that Tripartite motif containing 21 (TRIM21) promotes ubiquitination degradation of glutathione peroxidase 4 (GPX4) by regulating ferroptosis, and to discuss the feasibility of TRIM21 as a new therapeutic target for acute kidney injury (AKI).

MATERIALS AND METHODS

Ischemia-reperfusion (I/R)-AKI model was constructed using Trim21+/+ and Trim21-/- mice, and the expression of markers associated with kidney injury and ferroptosis were evaluated. HK-2 cells were treated by RSL3 and Erastin, and a hypoxia/reoxygenation (H/R) model was constructed to simulate I/R injury in vivo.

KEY FINDINGS

In vivo, TRIM21 is highly expressed in I/R kidney tissues. Loss of TRIM21 alleviated I/R-AKI and improved renal function. The upregulation of GPX4, a key ferroptosis regulator, and the mild mitochondrial damage suggested that loss of TRIM21 had a negative regulation of ferroptosis. In vitro, TRIM21 was highly expressed in H/R models, and overexpression of TRIM21 in HK-2 cells increased ROS production, promoted intracellular iron accumulation, and boosted cellular sensitivity to RSL3 and Erastin. Mechanistically, we confirmed that GPX4 is a substrate of TRIM21 and can be degraded by TRIM21-mediated ubiquitination, suggesting that inhibiting TRIM21 attenuates ferroptosis. A JAK2 inhibitor Fedratinib downregulated TRIM21 expression and reduced damage both in vivo and in vitro, which is correlated with the upregulation of GPX4.

SIGNIFICANCE

Our study showed that loss of TRIM21 could alleviate ferroptosis induced by I/R, revealed the mechanism of ubiquitination degradation of GPX4 by TRIM21 and suggested TRIM21 is a potential target for the treatment of AKI.

The E3 Ubiquitin Ligase TRIM21 Regulates Basal Levels of PDGFRβ

Activation of platelet-derived growth factor (PDGF) receptors α and β (PDGFRα and PDGFRβ) at the cell surface by binding of PDGF isoforms leads to internalization of receptors, which affects the amplitude and kinetics of signaling. Ubiquitination of PDGF receptors in response to ligand stimulation is mediated by the Casitas b-lineage lymphoma (Cbl) family of ubiquitin ligases, promoting internalization and serving as a sorting signal for vesicular trafficking of receptors. We report here that another E3 ligase, i.e., tripartite motif-containing protein 21 (TRIM21), contributes to the ubiquitination of PDGFRβ in human primary fibroblasts AG1523 and the osteosarcoma cell line U2OS and regulates basal levels of PDGFRβ. We found that siRNA-mediated depletion of TRIM21 led to decreased ubiquitination of PDGFRβ in response to PDGF-BB stimulation, while internalization from the cell surface and the rate of ligand-induced degradation of the receptor were not affected. Moreover, induction of TRIM21 decreased the levels of PDGFRβ in serum-starved cells, and even more in growing cells, in the absence of PDGF stimulation. Consistently, siRNA knockdown of TRIM21 caused accumulation of the total amount of PDGFRβ, both in the cytoplasm and on the cell surface, without affecting mRNA levels of the receptor. We conclude that TRIM21 acts post-translationally and maintains basal levels of PDGFRβ, thus suggesting that ubiquitination of PDGFRβ by TRIM21 may direct a portion of receptor for degradation in growing cells in a ligand-independent manner.

Berberine promotes IGF2BP3 ubiquitination by TRIM21 to induce G1/S phase arrest in colorectal cancer cells

The increasing incidence of colorectal cancer (CRC) has become a major global public health burden. The natural drug Berberine (BBR) has shown potential in preventing CRC, and IGF2 mRNA binding protein 3 (IGF2BP3) may be a target of BBR. This study aims to investigate the mechanisms of BBR acting on IGF2BP3 to improve CRC. The results showed that IGF2BP3 played an important role in the development of CRC. BBR down-regulated IGF2BP3 expression and inhibited CRC growth in mice. Cell thermodynamic stability analysis (CETSA) and drug affinity responsive target stability (DARTS) analysis showed BBR may bind to IGF2BP3. BBR may induce structural changes in IGF2BP3 and decrease its protein stability in cytoplasm. The results from Co-Immunoprecipitation (Co-IP) suggested that BBR promoted the ubiquitination of IGF2BP3 by tripartite motif-containing protein 21 (TRIM21). Through RNA binding protein Immunoprecipitation (RIP) assay, it was found BBR inhibited the stabilization of CDK4/CCND1 mRNA by IGF2BP3 and promoted G1/S phase arrest in CRC cells. Overexpression of IGF2BP3 in vitro and in vivo attenuated the inhibition of CRC growth by BBR. This work demonstrated the potential of BBR targeting to IGF2BP3 in improving CRC and provided a new strategy for clinical treatment on CRC as well as novel anticancer drug design based on IGF2BP3 and TRIM21.

TRIM21 inhibits irradiation-induced mitochondrial DNA release and impairs antitumour immunity in nasopharyngeal carcinoma tumour models

Although radiotherapy can promote antitumour immunity, the mechanisms underlying this phenomenon remain unclear. Here, we demonstrate that the expression of the E3 ubiquitin ligase, tumour cell-intrinsic tripartite motif-containing 21 (TRIM21) in tumours, is inversely associated with the response to radiation and CD8⁺ T cell-mediated antitumour immunity in nasopharyngeal carcinoma (NPC). Knockout of TRIM21 modulates the cGAS/STING cytosolic DNA sensing pathway, potentiates the antigen-presenting capacity of NPC cells, and activates cytotoxic T cell-mediated antitumour immunity in response to radiation. Mechanistically, TRIM21 promotes the degradation of the mitochondrial voltage-dependent anion-selective channel protein 2 (VDAC2) via K48-linked ubiquitination, which inhibits pore formation by VDAC2 oligomers for mitochondrial DNA (mtDNA) release, thereby inhibiting type-I interferon responses following radiation exposure. In patients with NPC, high TRIM21 expression was associated with poor prognosis and early tumour relapse after radiotherapy. Our findings reveal a critical role of TRIM21 in radiation-induced antitumour immunity, providing potential targets for improving the efficacy of radiotherapy in patients with NPC.

Decoding the Role of MDM2 as a Potential Ubiquitin E3 Ligase and Identifying the Therapeutic Efficiency of Alkaloids against MDM2 in Combating Glioblastoma

Glioblastomas (GBMs) represent the most aggressive form of brain tumor arising from the malignant transformation of astrocytes. Despite various advancements, treatment options remain limited to chemotherapy and radiotherapy followed by surgery giving an overall survival of 14-15 months. These therapies are somewhere restricted in giving a better survival and cure. There is a need for new therapeutics that could potentially target GBM based on molecular pathways and pathology. Here, ubiquitin E3 ligases can be used as targets as they bind a wide array of substrates and therefore can be attractive targets for new inhibitors. Through this study, we have tried to sort various ubiquitin E3 ligases based on their expression, pathways to which these ligases are associated, and mutational frequencies, and then we tried to screen potent inhibitors against the most favorable E3 ligase as very few studies are available concerning inhibition of E3 ligase in GBM. Our study found MDM2 to be the most ideal E3 ligase and further we tried to target MDM2 against various compounds under the alkaloid class. Molecular Docking and MD simulations combined with ADMET properties and BBB scores revealed that only evodiamine and sanguinarine were effective in inhibiting MDM2. We also tried to give a proposed mechanism of how these inhibitors mediate the p53 signaling in GBM. Therefore, the new scaffolds predicted by the computational approach could help in designing promising therapeutic agents targeting MDM2 in glioblastoma.