HERC3 promotes YAP/TAZ stability and tumorigenesis independently of its ubiquitin ligase activity

PPARα regulates YAP protein levels and activity by affecting its ubiquitination modification

BACKGROUND

Peroxisome proliferator-activated receptor α (PPARα) plays a crucial role in liver physiological and pathological processes. Yes-associated protein (YAP) is a key effector in regulating cell growth and organ size. Ubiquitination is known to modulate YAP protein expression, stability, and nuclear localization. Our previous study demonstrated that PPARα activation promotes hepatomegaly and liver regeneration via YAP activation. However, the underlying molecular mechanisms by which PPARα regulates YAP are unclear. In this study, PPARα was activated by the classical agonist WY-14643, and its effects on YAP ubiquitination were examined using plasmid transfection and immunoprecipitation. The ubiquitination of YAP was further investigated through mutant YAP plasmids, gene knockdown, and immunofluorescence staining. YAP mRNA and protein expression were measured via qRT-PCR and western blotting.

RESULTS

The results demonstrated that PPARα activation upregulated YAP protein levels and enhanced its activity, while reducing overall YAP ubiquitination. Specifically, PPARα activation inhibited K48-linked ubiquitination while promoting K63-linked ubiquitination of YAP. Mutations at the K252, K321, and K497 residues of YAP markedly reduced the capacity of PPARα activation to facilitate YAP nuclear translocation. Furthermore, knockdown of the E3 ligase TRAF6 abolished the PPARα-induced K63-linked ubiquitination of YAP and the upregulation of its downstream target genes.

CONCLUSIONS

These findings highlight the pivotal role of ubiquitination in regulating YAP through PPARα activation, providing novel insights for future studies on the post-translational regulation of YAP by PPARα activation.

The deubiquitinating enzyme ATXN3 promotes hepatocellular carcinoma progression by stabilizing TAZ

Hepatocellular carcinoma (HCC) was a primary cause of cancer-related morbidity and mortality in China. ATXN3 was a deubiquitinase (DUB) associated with spinocerebellar ataxia, widely expressed in the cytoplasm and nucleus of cells in the central nervous system and other tissues. The crucial role of the Hippo pathway in tumorigenesis has been established, among which TAZ served as one of the key molecules. However, the mechanisms underlying the deubiquitinase and TAZ in HCC remained largely unknown. In the present study, we explored that ATXN3 was overexpressed in HCC. ATXN3 promoted the proliferation, migration, invasion, and tumorigenic ability of HCC in vitro and in vivo. Besides, we explored that ATXN3 was positively associated with TAZ in HCC. ATXN3 could interact with, stabilize, and deubiquitylate TAZ in a deubiquitylase-dependent manner. Specifically, this interaction was primarily mediated by the C-terminal domain of TAZ and Josephin domain of ATXN3, thereby inhibiting the K48-linked ubiquitin chain on TAZ. Furthermore, we demonstrated that ATXN3 promoted the occurrence and development of HCC by regulating TAZ. Therefore, our study revealed the oncogenic function of ATXN3 and an interesting deubiquitination mechanism of ATXN3 and TAZ in HCC, providing new insights into the diagnosis and treatment of HCC.

OPN-Mediated Crosstalk Between Hepatocyte E4BP4 and Hepatic Stellate Cells Promotes MASH-Associated Liver Fibrosis

Stressed hepatocytes promote liver fibrosis through communications with hepatic stellate cells (HSCs) during chronic liver injury. However, intra-hepatocyte players that facilitate such cell-to-cell communications are largely undefined. It is previously reported that hepatocyte E4BP4 is potently induced by ER stress and hepatocyte deletion of E4bp4 protects mice from high-fat diet-induced liver steatosis. Here how hepatocyte E4bp4 deficiency impacts the activation of HSCs and the progression toward MASH-associated liver fibrosis is examined. Hepatic E4BP4 is increased in mouse models of NASH diet- or CCl4-induced liver fibrosis. Hepatocyte-specific E4bp4 deletion protected mice against NASH diet-induced liver injury, inflammation, and fibrosis without impacting liver steatosis. Hepatocyte E4BP4 overexpression activated HSCs in a medium transfer experiment, whereas hepatocyte E4bp4 depletion did the opposite. RNA-Seq analysis identified the pro-fibrogenic factor OPN as a critical target of E4BP4 within hepatocytes. Antibody neutralization or shRNA depletion of Opn abrogated hepatocyte E4BP4-induced HSC activation. E4BP4 interacted with and stabilized YAP, an established activator of OPN. Loss of hepatic Yap blocked OPN induction in the liver of Ad-E4bp4-injected mice. Hepatocyte E4BP4 induces OPN via YAP to activate HSCs and promote liver fibrosis during diet-induced MASH. Inhibition of the hepatocyte E4BP4-OPN pathway could offer a novel therapeutic avenue for treating MASLD/MASH.

DAPK enhances DDX20 protein stability via suppression of TRIM25-mediated ubiquitination-based DDX20 degradation

We have previously found that the DAPK-DDX20 signaling axis exerts an anti-cancer activity in hepatocellular carcinoma (HCC) by inhibiting the GTPase activity of CDC42, thereby reducing the invasive and migratory capabilities of cancer cells without affecting cell proliferation. DDX20 serves as an intermediate protein regulated by DAPK in the control of CDC42. Specifically, DAPK enhances DDX20 protein levels by suppressing DDX20 degradation. However, the mechanism underlying DAPK regulation of DDX20 remains unclear. In the current study, we discovered that DDX20 is degraded through the ubiquitin-proteasome pathway and identified TRIM25 as the E3 ubiquitin ligase of DDX20. TRIM25 mediates the proteasomal degradation of DDX20 by binding to, and ubiquitinating the 1-244 amino acid region of DDX20. Moreover, DAPK interacts with this 1-244 segment of DDX20, inhibiting its ubiquitination and enhancing its stability, despite the lack of direct physical interaction between DAPK and the 1-244 region of DDX20. Remarkably, DAPK, TRIM25, and DDX20 form a ternary protein complex in cells, and knockdown of TRIM25 leads to a reduction in the cellular levels of the binary DAPK-DDX20 complex, suggesting that TRIM25 acts as an important intermediate protein linking DAPK and DDX20. TRIM25 functions as an oncogene in liver cancer, as shRNA-mediated silencing of TRIM25 inhibits cell migration and invasion. Therefore, these novel findings of the interaction among these three proteins not only enhances our knowledge of the downstream molecular network of DAPK and its possible role in the development of HCC, but also provides potential druggable targets for the future development of novel anticancer drug therapeutics.

Pancreatic ductal adenocarcinoma cells reshape the immune microenvironment: Molecular mechanisms and therapeutic targets

Pancreatic ductal adenocarcinoma (PDAC) is a digestive system malignancy characterized by challenging early detection, limited treatment alternatives, and generally poor prognosis. Although there have been significant advancements in immunotherapy for hematological malignancies and various solid tumors in recent decades, with impressive outcomes in recent preclinical and clinical trials, the effectiveness of these therapies in treating PDAC continues to be modest. The unique immunological microenvironment of PDAC, especially the abnormal distribution, complex composition, and variable activation states of tumor-infiltrating immune cells, greatly restricts the effectiveness of immunotherapy. Undoubtedly, integrating data from both preclinical models and human studies helps accelerate the identification of reliable molecules and pathways responsive to targeted biological therapies and immunotherapies, thereby continuously optimizing therapeutic combinations. In this review, we delve deeply into how PDAC cells regulate the immune microenvironment through complex signaling networks, affecting the quantity and functional status of immune cells to promote immune escape and tumor progression. Furthermore, we explore the multi-modal immunotherapeutic strategies currently under development, emphasizing the transformation of the immunosuppressive environment into an anti-tumor milieu by targeting specific molecular and cellular pathways, providing insights for the development of novel treatment strategies.

UBR1 promotes anaplastic thyroid carcinoma progression via stabilizing YAP through monoubiquitylation

Anaplastic thyroid carcinoma (ATC) is a highly aggressive human malignancy without effective treatment. Yes-associated protein (YAP) is a critical effector of the Hippo pathway, which is essential in thyroid carcinogenesis. However, the underlying mechanisms of aberrant YAP expression in ATC are not completely understood. Ubiquitylation-related enzyme siRNA screening identified the ubiquitin protein ligase E3 component n-recognin 1 (UBR1) as a stabilizer of YAP in ATC cells. UBR1 deficiency reduced YAP protein levels and its target gene expression. UBR1 directly interacted with YAP and promoted its monoubiquitylation, competitively suppressing its polyubiquitylation and resulting in extended protein half-life. UBR1 depletion reduced ATC cell proliferation and migration in vitro. Xenograft tumor studies also suggested that UBR1 knockdown suppressed ATC cell growth in vivo. Furthermore, exogenous YAP expression partially reversed the inhibitive effects of UBR1 depletion on ATC cell proliferation and migration. Our studies demonstrated that UBR1 directly interacts with YAP and stabilized it in a monoubiquitylation-dependent manner, consequently promoting ATC tumorigenesis, suggesting that UBR1 might be a potentially therapeutic target for ATC treatment.

TRIM58 downregulation maintains stemness via MYH9-GRK3-YAP axis activation in triple-negative breast cancer stem cells

TRIM58 is a member of the TRIM protein family, which possess with E3 ubiquitin ligase activities. Studies have revealed that low expression of TRIM58 plays key roles, has been implicated in the tumor progression of tumor formation due to its reduced expression. However, its role in regulating the stemness of breast cancer stem cells (CSCs) remains unexplored. Here, we found that TRIM58 was underexpressed in TNBC tissues and cells compared to adjacent mucosa tissue, and its downregulation was significantly associated with shorter survival. Overexpression of TRIM58 reduced the proportion of CD44 + /CD24- cells, upregulated differentiation genes, and inhibited stemness-related gene expression in TNBC CSCs. In vitro and in vivo experiments revealed that TRIM58 overexpression in CSCs suppressed tumor sphere formation and tumorigenic capacity. Co-IP results indicated direct interaction between TRIM58 and MYH9, with TRIM58 inducing MYH9 degradation via ubiquitination in differentiated cells. Label-free quantitative proteomics identified GRK3 and Hippo-YAP as downstream targets and signaling pathways of MYH9. TIMER database analysis, immunohistochemistry, western blotting, DNA-protein pulldown experiments, and dual luciferase reporter assays demonstrated that MYH9 regulated GRK3 transcriptional activation in CSCs. In conclusion, elevated TRIM58 expression in CSCs downregulates MYH9 protein levels by promoting ubiquitin-mediated degradation, thereby inhibiting downstream GRK3 transcription, inactivating the YAP stemness pathway, and ultimately promoting CSC differentiation.

A deep insight into ferroptosis in lung disease: facts and perspectives

In the last decade, ferroptosis has received much attention from the scientific research community. It differs from other modes of cell death at the morphological, biochemical, and genetic levels. Ferroptosis is mainly characterized by non-apoptotic iron-dependent cell death caused by iron-dependent lipid peroxide excess and is accompanied by abnormal iron metabolism and oxidative stress. In recent years, more and more studies have shown that ferroptosis is closely related to the occurrence and development of lung diseases. COPD, asthma, lung injury, lung fibrosis, lung cancer, lung infection and other respiratory diseases have become the third most common chronic diseases worldwide, bringing serious economic and psychological burden to people around the world. However, the exact mechanism by which ferroptosis is involved in the development and progression of lung diseases has not been fully revealed. In this manuscript, we describe the mechanism of ferroptosis, targeting of ferroptosis related signaling pathways and proteins, summarize the relationship between ferroptosis and respiratory diseases, and explore the intervention and targeted therapy of ferroptosis for respiratory diseases.

YAP1-CPNE3 positive feedback pathway promotes gastric cancer cell progression

Hippo-Yes-associated protein 1 (YAP1) plays an important role in gastric cancer (GC) progression; however, its regulatory network remains unclear. In this study, we identified Copine III (CPNE3) was identified as a novel direct target gene regulated by the YAP1/TEADs transcription factor complex. The downregulation of CPNE3 inhibited proliferation and invasion, and increased the chemosensitivity of GC cells, whereas the overexpression of CPNE3 had the opposite biological effects. Mechanistically, CPNE3 binds to the YAP1 protein in the cytoplasm, inhibiting YAP1 ubiquitination and degradation mediated by the E3 ubiquitination ligase β-transducin repeat-containing protein (β-TRCP). Thereby activating the transcription of YAP1 downstream target genes, which creates a positive feedback cycle to facilitate GC progression. Immunohistochemical analysis demonstrated significant upregulation of CPNE3 in GC tissues. Survival and Cox regression analyses indicated that high CPNE3 expression was an independent prognostic marker for GC. This study elucidated the pivotal involvement of an aberrantly activated CPNE3/YAP1 positive feedback loop in the malignant progression of GC, thereby uncovering novel prognostic factors and therapeutic targets in GC.

UBE3C Facilitates the ER-Associated and Peripheral Degradation of Misfolded CFTR

The ubiquitin E3 ligase UBE3C promotes the proteasomal degradation of cytosolic proteins and endoplasmic reticulum (ER) membrane proteins. UBE3C is proposed to function downstream of the RNF185/MBRL ER-associated degradation (ERAD) branch, contributing to the ERAD of select membrane proteins. Here, we report that UBE3C facilitates the ERAD of misfolded CFTR, even in the absence of both RNF185 and its functional ortholog RNF5 (RNF5/185). Unlike RNF5/185, UBE3C had a limited impact on the ubiquitination of misfolded CFTR. UBE3C knockdown (KD) resulted in an additional increase in the functional ∆F508-CFTR channels on the plasma membrane when combined with the RNF5/185 ablation, particularly in the presence of clinically used CFTR modulators. Interestingly, although UBE3C KD failed to attenuate the ERAD of insig-1, it reduced the ERAD of misfolded ∆Y490-ABCB1 and increased cell surface expression. UBE3C KD also stabilized the mature form of ∆F508-CFTR and increased the cell surface level of T70-CFTR, a class VI CFTR mutant. These results suggest that UBE3C plays a vital role in the ERAD of misfolded CFTR and ABCB1, even within the RNF5/185-independent ERAD pathway, and it may also be involved in maintaining the peripheral quality control of CFTR.

The deubiquitinating enzyme USP19 facilitates hepatocellular carcinoma progression through stabilizing YAP

Hippo pathway plays a crucial role in the progression of hepatocellular carcinoma (HCC), and yes-associated protein (YAP) is one of the major factors of the Hippo pathway. However, the mechanism of abnormal YAP activation in HCC has not been well elucidated. Here, we screened a Deubiquitinating enzymes' (DUB) siRNA library targeting DUBs, and identified Ubiquitin Specific Peptidase 19 (USP19) as a specific deubiquitinating enzyme of YAP in HCC, which could stabilize YAP at K76 and K90 sites via removing the K48- and K11-linked ubiquitin chains. USP19 knockdown decreased the expression of YAP protein and its target gene (CTGF, CYR61, ANKRD1) expression. Through substantial in vivo and in vitro experiments, we prove that USP19 facilities the proliferation and migration of HCC. More importantly, we found that USP19 was upregulated in HCC tissues and associated with poor prognosis. In general, our research revealed a novel post-translational mechanism between USP19 and YAP in HCC, suggesting that USP19 may be a pivotal therapeutic target for HCC treatment.

Control of TGFβ signalling by ubiquitination independent function of E3 ubiquitin ligase TRIP12

Transforming growth factor β (TGFβ) pathway is a master regulator of cell proliferation, differentiation, and death. Deregulation of TGFβ signalling is well established in several human diseases including autoimmune disorders and cancer. Thus, understanding molecular pathways governing TGFβ signalling may help better understand the underlying causes of some of those conditions. Here, we show that a HECT domain E3 ubiquitin ligase TRIP12 controls TGFβ signalling in multiple models. Interestingly, TRIP12 control of TGFβ signalling is completely independent of its E3 ubiquitin ligase activity. Instead, TRIP12 recruits SMURF2 to SMAD4, which is most likely responsible for inhibitory monoubiquitination of SMAD4, since SMAD4 monoubiquitination and its interaction with SMURF2 were dramatically downregulated in TRIP12-/- cells. Additionally, genetic inhibition of TRIP12 in human and murine cells leads to robust activation of TGFβ signalling which was rescued by re-introducing wildtype TRIP12 or a catalytically inactive C1959A mutant. Importantly, TRIP12 control of TGFβ signalling is evolutionary conserved. Indeed, genetic inhibition of Drosophila TRIP12 orthologue, ctrip, in gut leads to a reduced number of intestinal stem cells which was compensated by the increase in differentiated enteroendocrine cells. These effects were completely normalised in Drosophila strain where ctrip was co-inhibited together with Drosophila SMAD4 orthologue, Medea. Similarly, in murine 3D intestinal organoids, CRISPR/Cas9 mediated genetic targeting of Trip12 enhances TGFβ mediated proliferation arrest and cell death. Finally, CRISPR/Cas9 mediated genetic targeting of TRIP12 in MDA-MB-231 breast cancer cells enhances the TGFβ induced migratory capacity of these cells which was rescued to the wildtype level by re-introducing wildtype TRIP12. Our work establishes TRIP12 as an evolutionary conserved modulator of TGFβ signalling in health and disease.

E2 enzyme Bruce negatively regulates Hippo signaling through POSH-mediated expanded degradation

The Hippo pathway is a master regulator of organ growth, stem cell renewal, and tumorigenesis, its activation is tightly controlled by various post-translational modifications, including ubiquitination. While several E3 ubiquitin ligases have been identified as regulators of Hippo pathway, the corresponding E2 ubiquitin-conjugating enzymes (E2s) remain unknown. Here, we performed a screen in Drosophila to identify E2s involved in regulating wing overgrowth caused by the overexpression of Crumbs (Crb) intracellular domain and identified Bruce as a critical regulator. Loss of Bruce downregulates Hippo target gene expression and suppresses Hippo signaling inactivation induced tissue growth. Unexpectedly, our genetic data indicate that Bruce acts upstream of Expanded (Ex) but in parallel with the canonical Hippo (Hpo) -Warts (Wts) cascade to regulate Yorkie (Yki), the downstream effector of Hippo pathway. Mechanistically, Bruce synergizes with E3 ligase POSH to regulate growth and ubiquitination-mediated Ex degradation. Moreover, we demonstrate that Bruce is required for Hippo-mediated malignant tumor progression. Altogether, our findings unveil Bruce as a crucial E2 enzyme that bridges the signal from the cell surface to regulate Hippo pathway activation in Drosophila.

CAMK2D serves as a molecular scaffold for RNF8-MAD2 complex to induce mitotic checkpoint in glioma

MAD2 is a spindle assembly checkpoint protein that participates in the formation of mitotic checkpoint complex, which blocks mitotic progression. RNF8, an established DNA damage response protein, has been implicated in mitotic checkpoint regulation but its exact role remains poorly understood. Here, RNF8 proximity proteomics uncovered a role of RNF8-MAD2 in generating the mitotic checkpoint signal. Specifically, RNF8 competes with a small pool of p31comet for binding to the closed conformer of MAD2 via its RING domain, while CAMK2D serves as a molecular scaffold to concentrate the RNF8-MAD2 complex via transient/weak interactions between its p-Thr287 and RNF8's FHA domain. Accordingly, RNF8 overexpression impairs glioma stem cell (GSC) mitotic progression in a FHA- and RING-dependent manner. Importantly, low RNF8 expression correlates with inferior glioma outcome and RNF8 overexpression impedes GSC tumorigenicity. Last, we identify PLK1 inhibitor that mimics RNF8 overexpression using a chemical biology approach, and demonstrate a PLK1/HSP90 inhibitor combination that synergistically reduces GSC proliferation and stemness. Thus, our study has unveiled a previously unrecognized CAMK2D-RNF8-MAD2 complex in regulating mitotic checkpoint with relevance to gliomas, which is therapeutically targetable.