Ubiquitin-Specific Protease 14 Negatively Regulates Toll-Like Receptor 4-Mediated Signaling and Autophagy Induction by Inhibiting Ubiquitination of TAK1-Binding Protein 2 and Beclin 1

Usp14 deficiency removes α-synuclein by regulating S100A8/A9 in Parkinson's disease

Ubiquitin-proteasome system dysfunction triggers α-synuclein aggregation, a hallmark of neurodegenerative diseases, such as Parkinson's disease (PD). However, the crosstalk between deubiquitinating enzyme (DUBs) and α-synuclein pathology remains unclear. In this study, we observed a decrease in the level of ubiquitin-specific protease 14 (USP14), a DUB, in the cerebrospinal fluid (CSF) of PD patients, particularly females. Moreover, CSF USP14 exhibited a dual correlation with α-synuclein in male and female PD patients. To investigate the impact of USP14 deficiency, we crossed USP14 heterozygous mouse (USP14+/-) with transgenic A53T PD mouse (A53T-Tg) or injected adeno-associated virus (AAV) carrying human α-synuclein (AAV-hα-Syn) in USP14+/- mice. We found that Usp14 deficiency improved the behavioral abnormities and pathological α-synuclein deposition in female A53T-Tg or AAV-hα-Syn mice. Additionally, Usp14 inactivation attenuates the pro-inflammatory response in female AAV-hα-Syn mice, whereas Usp14 inactivation demonstrated opposite effects in male AAV-hα-Syn mice. Mechanistically, the heterodimeric protein S100A8/A9 may be the downstream target of Usp14 deficiency in female mouse models of α-synucleinopathies. Furthermore, upregulated S100A8/A9 was responsible for α-synuclein degradation by autophagy and the suppression of the pro-inflammatory response in microglia after Usp14 knockdown. Consequently, our study suggests that USP14 could serve as a novel therapeutic target in PD.

Mechanistic insights into the role of USP14 in adipose tissue macrophage recruitment and insulin resistance in obesity

Diet-induced obesity can cause metabolic syndromes. The critical link in disease progression is adipose tissue macrophage (ATM) recruitment, which drives low-level inflammation, triggering adipocyte dysfunction. It is unclear whether ubiquitin-specific proteinase 14 (USP14) affects metabolic disorders by mediating adipose tissue inflammation. In the present study, we showed that USP14 is highly expressed in ATMs of obese human patients and diet-induced obese mice. Mouse USP14 overexpression aggravated obesity-related insulin resistance by increasing the levels of pro-inflammatory ATMs, leading to adipose tissue inflammation, excessive lipid accumulation, and hepatic steatosis. In contrast, USP14 knockdown in adipose tissues alleviated the phenotypes induced by a high-fat diet. Co-culture experiments showed that USP14 deficiency in macrophages led to decreased adipocyte lipid deposition and enhanced insulin sensitivity, suggesting that USP14 plays an important role in ATMs. Mechanistically, USP14 interacted with TNF receptor-associated 6, preventing K48-linked ubiquitination as well as proteasome degradation, leading to increased pro-inflammatory polarization of macrophages. In contrast, the pharmacological inhibition of USP14 significantly ameliorated diet-induced hyperlipidemia and insulin resistance in mice. Our results demonstrated that macrophage USP14 restriction constitutes a key constraint on the pro-inflammatory M1 phenotype, thereby inhibiting obesity-related metabolic diseases.

Friend or foe? Reciprocal regulation between E3 ubiquitin ligases and deubiquitinases

Protein ubiquitination is a post-translational modification that entails the covalent attachment of the small protein ubiquitin (Ub), which acts as a signal to direct protein stability, localization, or interactions. The Ub code is written by a family of enzymes called E3 Ub ligases (∼600 members in humans), which can catalyze the transfer of either a single ubiquitin or the formation of a diverse array of polyubiquitin chains. This code can be edited or erased by a different set of enzymes termed deubiquitinases (DUBs; ∼100 members in humans). While enzymes from these distinct families have seemingly opposing activities, certain E3-DUB pairings can also synergize to regulate vital cellular processes like gene expression, autophagy, innate immunity, and cell proliferation. In this review, we highlight recent studies describing Ub ligase-DUB interactions and focus on their relationships.

Targeting autophagy and beyond: Deconvoluting the complexity of Beclin-1 from biological function to cancer therapy

Beclin-1 is the firstly-identified mammalian protein of the autophagy machinery, which functions as a molecular scaffold for the assembly of PI3KC3 (class III phosphatidylinositol 3 kinase) complex, thus controlling autophagy induction and other cellular trafficking events. Notably, there is mounting evidence establishing the implications of Beclin-1 in diverse tumorigenesis processes, including tumor suppression and progression as well as resistance to cancer therapeutics and CSC (cancer stem-like cell) maintenance. More importantly, Beclin-1 has been confirmed as a potential target for the treatment of multiple cancers. In this review, we provide a comprehensive survey of the structure, functions, and regulations of Beclin-1, and we discuss recent advances in understanding the controversial roles of Beclin-1 in oncology. Moreover, we focus on summarizing the targeted Beclin-1-regulating strategies in cancer therapy, providing novel insights into a promising strategy for regulating Beclin-1 to improve cancer therapeutics in the future.

Inhibition of USP14 enhances anti-tumor effect in vemurafenib-resistant melanoma by regulation of Skp2

BACKGROUND

The mutation of BRAF V600E often occurred in melanoma and results in tumorigenesis. BRAF mutation drives hyperactivation of the RAF-MAPK-ERK pathway. The acquired drug resistance upon prolonged use of BRAF inhibitors (such as vemurafenib) still remains the main obstacle. Previously, we have found that E3 ligase Skp2 over-expresses vemurafenib-resistant melanoma cells, and knockdown of Skp2 enhances the anti-tumor effect of vemurafenib. Interestingly, the literature has reported that the selective USP14/UCHL5 inhibitor b-AP15 displays great potential in melanoma therapy; however, the molecular mechanism still remains unknown.

METHODS

In vitro, the effect of the combination regimen of vemurafenib (Vem, PLX4032) and b-AP15 on vem-sensitive and vem-resistant melanoma has been investigated by wound healing, colony formation, transwell invasion assay, flow cytometry, lysosome staining, and ROS detection. In vivo, the combination effect on vem-resistant melanoma has been evaluated with a nude mice xenograft tumor model. GST-pulldown and co-immunoprecipitation (co-IP) assays have been applied to investigate the interactions between USP14, UCHL5, and Skp2. Cycloheximide (CHX) assay and ubiquitination assays have been used to explore the effect of USP14 on Skp2 protein half-life and ubiquitination status.

RESULTS

In the present study, we have revealed that repression of USP14 sensitizes vemurafenib resistance in melanoma through a previously unappreciated mechanism that USP14 but not UCHL5 stabilizes Skp2, blocking its ubiquitination. K119 on Skp2 is required for USP14-mediated deubiquitination and stabilization of Skp2. Furthermore, the mutated catalytic activity amino acid cysteine (C) 114 on USP14 abrogates stabilization of Skp2. Stabilization of Skp2 is required for USP14 to negatively regulate autophagy. The combination regimen of Skp2 inhibitor vemurafenib and USP14/UCHL5 inhibitor b-AP15 dramatically inhibits cell viability, migration, invasion, and colony formation in vemurafenib-sensitive and vemurafenib-resistant melanoma. Vemurafenib and b-AP15 hold cells in the S phase thus leading to apoptosis as well as the formation of the autophagic vacuole in vemurafenib-resistant SKMEL28 cells. The enhanced proliferation effect of USP14 and Skp2 is mainly due to a more effective reduction of cell apoptosis and autophagy. Further evaluation of various protein alterations has revealed that the increased expression of cleaved-PARP, LC3, and decreased Ki67 are more obvious in the combination of vemurafenib and b-AP15 treatment than those in single-drug treatment. Moreover, the co-treatment of vemurafenib and b-AP15 dramatically inhibits the growth of vemurafenib-resistant melanoma xenograft in vivo. Collectively, our findings have demonstrated that the combination of Skp2 inhibitor and USP14 inhibitor provides a new solution for the treatment of BRAF inhibitor resistance melanoma.

USP14 Positively Modulates Head and Neck Squamous Carcinoma Tumorigenesis and Potentiates Heat Shock Pathway through HSF1 Stabilization

The ubiquitin-proteasome system is a pivotal intracellular proteolysis process in posttranslational modification. It regulates multiple cellular processes. Deubiquitinating enzymes (DUBs) are a stabilizer in proteins associated with tumor growth and metastasis. However, the link between DUBs and HNSCC remains incompletely understood. In this study, therefore, we identified USP14 as a tumor proliferation enhancer and a substantially hyperactive deubiquitinase in HNSCC samples, implying a poor prognosis prediction. Silencing USP14 in vitro conspicuously inhibited HNSCC cell proliferation and migration. Consistently, defective USP14 in vivo significantly diminished HNSCC tumor growth and lung metastasis compared to the control group. Luciferase assays indicated that HSF1 was downstream from USP14, and an evaluation of the cellular effects of HSF1 overexpression in USP14-dificient mice tumors showed that elevated HSF1 reversed HNSCC growth and metastasis predominantly through the HSF1-HSP pathway. Mechanistically, USP14 encouraged HSF1 expression by deubiquitinating and stabilizing HSF1, which subsequently orchestrated transcriptional activation in HSP60, HSP70, and HSP90, ultimately leading to HNSCC progression and metastasis. Collectively, we uncovered that hyperactive USP14 contributed to HNSCC tumor growth and lung metastasis by reinforcing HSF1-depedent HSP activation, and our findings provided the insight that targeting USP14 could be a promising prognostic and therapeutic strategy for HSNCC.

β-arrestin 2 negatively regulates lung cancer progression by inhibiting the TRAF6 signaling axis for NF-κB activation and autophagy induced by TLR3 and TLR4

β-arrestin 2 (ARRB2) is functionally implicated in cancer progression via various signaling pathways. However, its role in lung cancer remains unclear. To obtain clinical insight on its function in lung cancer, microarray data from lung tumor tissues (LTTs) and matched lung normal tissues (mLNTs) of primary non-small cell lung cancer (NSCLC) patients (n = 37) were utilized. ARRB2 expression levels were markedly decreased in all 37 LTTs compared to those in matched LNTs of NSCLC patients. They were significantly co-related to enrichment gene sets associated with oncogenic and cancer genes. Importantly, Gene Set Enrichment Analysis (GSEA) between three LTTs with highly down-regulated ARRB2 and three LTTs with lowly down-regulated ARRB2 revealed significant enrichments related to toll-like receptor (TLR) signaling and autophagy genes in three LTTs with highly down-regulated ARRB2, suggesting that ARRB2 was negatively involved in TLR-mediated signals for autophagy induction in lung cancer. Biochemical studies for elucidating the molecular mechanism revealed that ARRB2 interacted with TNF receptor-associated factor 6 (TRAF6) and Beclin 1 (BECN1), thereby inhibiting the ubiquitination of TRAF6-TAB2 to activate NF-κB and TRAF6-BECN1 for autophagy stimulated by TLR3 and TLR4, suggesting that ARRB2 could inhibit the TRAF6-TAB2 signaling axis for NF-κB activation and TRAF6-BECN1 signaling axis for autophagy in response to TLR3 and TLR4. Notably, ARRB2-knockout (ARRB2KO) lung cancer cells exhibited marked enhancements of cancer migration, invasion, colony formation, and proliferation in response to TLR3 and TLR4 stimulation. Altogether, our current data suggest that ARRB2 can negatively regulate lung cancer progression by inhibiting TLR3- and TLR4-induced autophagy.

The transcriptome of HTLV-1-infected primary cells following reactivation reveals changes to host gene expression central to the proviral life cycle

Infections by Human T cell Leukaemia Virus type 1 (HTLV-1) persist for the lifetime of the host by integrating into the genome of CD4+ T cells. Proviral gene expression is essential for proviral survival and the maintenance of the proviral load, through the pro-proliferative changes it induces in infected cells. Despite their role in HTLV-1 infection and a persistent cytotoxic T lymphocyte response raised against the virus, proviral transcripts from the sense-strand are rarely detected in fresh cells extracted from the peripheral blood, and have recently been found to be expressed intermittently by a small subset of cells at a given time. Ex vivo culture of infected cells prompts synchronised proviral expression in infected cells from peripheral blood, allowing the study of factors involved in reactivation in primary cells. Here, we used bulk RNA-seq to examine the host transcriptome over six days in vitro, following proviral reactivation in primary peripheral CD4+ T cells isolated from subjects with non-malignant HTLV-1 infection. Infected cells displayed a conserved response to reactivation, characterised by discrete stages of gene expression, cell division and subsequently horizontal transmission of the virus. We observed widespread changes in Polycomb gene expression following reactivation, including an increase in PRC2 transcript levels and diverse changes in the expression of PRC1 components. We hypothesize that these transcriptional changes constitute a negative feedback loop that maintains proviral latency by re-deposition of H2AK119ub1 following the end of proviral expression. Using RNAi, we found that certain deubiquitinases, BAP1, USP14 and OTUD5 each promote proviral transcription. These data demonstrate the detailed trajectory of HTLV-1 proviral reactivation in primary HTLV-1-carrier lymphocytes and the impact on the host cell.

FFAR2 antagonizes TLR2- and TLR3-induced lung cancer progression via the inhibition of AMPK-TAK1 signaling axis for the activation of NF-κB

BACKGROUND

Free fatty acid receptors (FFARs) and toll-like receptors (TLRs) recognize microbial metabolites and conserved microbial products, respectively, and are functionally implicated in inflammation and cancer. However, whether the crosstalk between FFARs and TLRs affects lung cancer progression has never been addressed.

METHODS

We analyzed the association between FFARs and TLRs using The Cancer Genome Atlas (TCGA) lung cancer data and our cohort of non-small cell lung cancer (NSCLC) patient data (n = 42), and gene set enrichment analysis (GSEA) was performed. For the functional analysis, we generated FFAR2-knockout (FFAR2KO) A549 and FFAR2KO H1299 human lung cancer cells and performed biochemical mechanistic studies and cancer progression assays, including migration, invasion, and colony-formation assays, in response to TLR stimulation.

RESULTS

The clinical TCGA data showed a significant down-regulation of FFAR2, but not FFAR1, FFAR3, and FFAR4, in lung cancer, and a negative correlation with TLR2 and TLR3. Notably, GSEA showed significant enrichment in gene sets related to the cancer module, the innate signaling pathway, and the cytokine-chemokine signaling pathway in FFAR2^DownTLR2^UpTLR3^Up lung tumor tissues (LTTs) vs. FFAR2^upTLR2^DownTLR3^Down LTTs. Functionally, treatment with propionate (an agonist of FFAR2) significantly inhibited human A549 or H1299 lung cancer migration, invasion, and colony formation induced by TLR2 or TLR3 through the attenuation of the cAMP-AMPK-TAK1 signaling axis for the activation of NF-κB. Moreover, FFAR2KO A549 and FFAR2KO H1299 human lung cancer cells showed marked increases in cell migration, invasion, and colony formation in response to TLR2 or TLR3 stimulation, accompanied by elevations in NF-κB activation, cAMP levels, and the production of C-C motif chemokine ligand (CCL)2, interleukin (IL)-6, and matrix metalloproteinase (MMP) 2 cytokines.

CONCLUSION

Our results suggest that FFAR2 signaling antagonized TLR2- and TLR3-induced lung cancer progression via the suppression of the cAMP-AMPK-TAK1 signaling axis for the activation of NF-κB, and its agonist might be a potential therapeutic agent for the treatment of lung cancer.

A review of deubiquitinases and thier roles in tumorigenesis and development

Ubiquitin is a small protein that can be added onto target protein for inducing target degradation, thereby modulating the activity and stability of protein. Relatively, deubiquitinases (DUBs), a class catalase that can remove ubiquitin from substrate protein, provide a positive regulation of the protein amount at transcription level, post-translational modification, protein interaction, etc. The reversible and dynamic ubiquitination-deubiquitination process plays an essential role in maintaining protein homeostasis, which is critical to almost all the biological processes. Therefore, the metabolic dysregulation of deubiquitinases often lead to serious consequences, including the growth and metastasis of tumors. Accordingly, deubiquitinases can be served as key drug targets for the treatment of tumors. The small molecule inhibitors targeting deubiquitinases has become one of the hot spots of anti-tumor drug research areas. This review concentrated on the function and mechanism of deubiquitinase system in the proliferation, apoptosis, metastasis and autophagy of tumor cells. The research status of small molecule inhibitors of specific deubiquitinases in tumor treatment is introduced, aiming to provide reference for the development of clinical targeted drugs.

Dihydromyricetin inhibits Hepatitis B virus replication by activating NF-κB, MAPKs, and autophagy in HepG2.2.15 cells

BACKGROUND

Hepatitis B virus (HBV) infection is a severe global health problem, and there has been no effective method to eliminate HBV. This study was designed to explore the pharmacological mechanism of Dihydromyricetin (DHM) treatment on HBV replication in vitro.

METHODS AND RESULTS

DHM is a flavonoid compound from Ampelopsis grossedentata. Using HepG2.2.15 cells, which can stably express HBV in vitro, we demonstrated that DHM treatment dramatically reduced HBV replication and secretions of HBsAg and HBeAg. Meanwhile, DHM inhibited mRNA expression of HBV RNAs in HepG2.2.15 cells, including Total HBV RNA, HBV pregenomic RNA (pgRNA), and HBV precore mRNA (pcRNA). Also, DHM elevated the mRNA expressions of inflammatory cytokines and antiviral effectors. In contrast, DHM decreased the mRNA level of HNF4α, which positively correlated with HBV replication. Further studies show that the activation of nuclear factor-kappa B (NF-κB) and mitogen-activated protein kinase (MAPK) signaling pathway played a critical role in DHM-initiated inhibition of HBV replication in HepG2.2.15 cells. Besides, activated autophagy was another contributor that may accelerate the clearance of HBV components.

CONCLUSION

In summary, DHM could suppress HBV replication by activating NF-κB, MAPKs, and autophagy in HepG2.2.15 cells. Our studies shed light on the future application of DHM for the clinical treatment of HBV infection.

USP14 promotes colorectal cancer progression by targeting JNK for stabilization

MAPK/JNK signaling is pivotal in carcinogenesis. However, ubiquitin-mediated homeostasis of JNK remains to be verified. Here, with results from RNA sequencing (RNA-seq) and luciferase reporter pathway identification, we show that USP14 orchestrates MAPK/JNK signaling and identify USP14 as a deubiquitinase that interacts and stabilizes JNK. USP14 is elevated in colorectal cancer patients and is positively associated with JNK protein and downstream gene expression. USP14 ablation reduces cancer cell proliferation in vitro and colorectal tumorigenesis in vivo by downregulating MAPK/JNK pathway activation. Moreover, USP14 expression is induced by TNF-α, forming a feedback loop with JNK and leading to tumor amplification. Our study suggests that elevated expression of USP14 promotes MAPK/JNK signaling by stabilizing JNK, which in turn augments colorectal carcinogenesis, indicating a potential therapeutic target for colorectal cancer patients with increased USP14 expression.

USP13 Deficiency Impairs Autophagy and Facilitates Age-related Lung Fibrosis

Idiopathic pulmonary fibrosis (IPF) is an age-related disease. Failure of the proteostasis network with age, including insufficient autophagy, contributes to the pathology of IPF. Mechanisms underlying autophagy disruption in IPF are unclear and may involve regulation of USP (ubiquitin-specific protease) by post-translational modifications. To expand our previous observation of low USP13 expression in IPF, this study evaluated the role of USP13 in age-related lung fibrosis. Here, we demonstrated that Usp13-deficient aged mice exhibited impaired autophagic activity and increased vulnerability to bleomycin-induced fibrosis. Mechanistically, USP13 interacted with and deubiquitinated Beclin 1, and Beclin 1 overexpression abolished the effects of USP13 disruption. In addition, Beclin 1 inhibition resulted in insufficient autophagy and more severe lung fibrosis after bleomycin injury, consistent with the phenotype of aged Usp13-deficient mice. Collectively, we show a protective role of USP13 in age-related pulmonary fibrosis. Aging-mediated USP13 loss impairs autophagic activity and facilitates lung fibrosis through Beclin 1 deubiquitination. Our findings support the notion that age-dependent dysregulation of autophagic regulators enhances vulnerability to lung fibrosis.

Intersections of Ubiquitin-Proteosome System and Autophagy in Promoting Growth of Glioblastoma Multiforme: Challenges and Opportunities

Glioblastoma multiforme (GBM) is a brain tumor notorious for its propensity to recur after the standard treatments of surgical resection, ionizing radiation (IR), and temozolomide (TMZ). Combined with the acquired resistance to standard treatments and recurrence, GBM is an especially deadly malignancy with hardly any worthwhile treatment options. The treatment resistance of GBM is influenced, in large part, by the contributions from two main degradative pathways in eukaryotic cells: ubiquitin-proteasome system (UPS) and autophagy. These two systems influence GBM cell survival by removing and recycling cellular components that have been damaged by treatments, as well as by modulating metabolism and selective degradation of components of cell survival or cell death pathways. There has recently been a large amount of interest in potential cancer therapies involving modulation of UPS or autophagy pathways. There is significant crosstalk between the two systems that pose therapeutic challenges, including utilization of ubiquitin signaling, the degradation of components of one system by the other, and compensatory activation of autophagy in the case of proteasome inhibition for GBM cell survival and proliferation. There are several important regulatory nodes which have functions affecting both systems. There are various molecular components at the intersections of UPS and autophagy pathways that pose challenges but also show some new therapeutic opportunities for GBM. This review article aims to provide an overview of the recent advancements in research regarding the intersections of UPS and autophagy with relevance to finding novel GBM treatment opportunities, especially for combating GBM treatment resistance.

MF-094 nanodelivery inhibits oral squamous cell carcinoma by targeting USP30

BACKGROUND

Oral squamous cell carcinoma (OSCC) is a common head and neck cancer, and the incidence of OSCC is increasing. As the mortality of OSCC keeps increasing, it is crucial to clarify its pathogenesis and develop new therapeutic strategies.

METHODS

Confocal laser scanning microscopy was used to evaluate the uptake of nanoparticles (NPs). The potential functions of USP30 were evaluated by cell counting kit (CCK)-8, flow cytometry, biochemical assay, coimmunoprecipitation, qRT-PCR, and immunoblotting. The antitumor effect of NP-loaded USP30 inhibitor MF-094 was evaluated in vitro and in vivo.

RESULTS

In this study, increased USP30 expression was found in OSCC specimens and cell lines through qRT-PCR and immunoblotting. CCK-8, flow cytometry, and biochemical assay revealed that the deubiquitylated catalytic activity of USP30 contributed to cell viability and glutamine consumption of OSCC. Subsequently, USP30 inhibitor MF-094 was loaded in ZIF-8-PDA and PEGTK to fabricate ZIF-8-PDA-PEGTK nanoparticles, which exhibited excellent inhibition of cell viability and glutamine consumption of OSCC, both in vitro and in vivo.

CONCLUSION

The results indicated the clinical significance of USP30 and showed that nanocomposites provide a targeted drug delivery system for treating OSCC.

USP15 negatively regulates lung cancer progression through the TRAF6-BECN1 signaling axis for autophagy induction

TNF receptor-associated factor 6 (TRAF6)-BECN1 signaling axis plays a pivotal role in autophagy induction through ubiquitination of BECN1, thereby inducing lung cancer migration and invasion in response to toll-like receptor 4 (TLR4) stimulation. Herein, we provide novel molecular and cellular mechanisms involved in the negative effect of ubiquitin-specific peptidase 15 (USP15) on lung cancer progression. Clinical data of the TCGA and primary non-small cell lung cancer (NSCLC) patients (n = 41) revealed that the expression of USP15 was significantly downregulated in lung cancer patients. Importantly, USP15-knockout (USP15KO) A549 and USP15KO H1299 lung cancer cells generated with CRISPR-Cas9 gene-editing technology showed increases in cancer migration and invasion with enhanced autophagy induction in response to TLR4 stimulation. In addition, biochemical studies revealed that USP15 interacted with BECN1, but not with TRAF6, and induced deubiquitination of BECN1, thereby attenuating autophagy induction. Notably, in primary NSCLC patients (n = 4) with low expression of USP15, 10 genes (CCNE1, MMP9, SFN, UBE2C, CCR2, FAM83A, ETV4, MYO7A, MMP11, and GSDMB) known to promote lung cancer progression were significantly upregulated, whereas 10 tumor suppressor genes (FMO2, ZBTB16, FCN3, TCF21, SFTPA1B, HPGD, SOSTDC1, TMEM100, GDF10, and WIF1) were downregulated, providing clinical relevance of the functional role of USP15 in lung cancer progression. Taken together, our data demonstrate that USP15 can negatively regulate the TRAF6-BECN1 signaling axis for autophagy induction. Thus, USP15 is implicated in lung cancer progression.

K48/K63-linked polyubiquitination of ATG9A by TRAF6 E3 ligase regulates oxidative stress-induced autophagy

Excessive generation and accumulation of highly reactive oxidizing molecules causes oxidative stress and oxidative damage to cellular components. Accumulating evidence indicates that autophagy diminishes oxidative damage in cells and maintains redox homeostasis by degrading and recycling intracellular damaged components. Here, we show that TRAF6 E3 ubiquitin ligase and A20 deubiquitinase coordinate to regulate ATG9A ubiquitination and autophagy activation in cells responding to oxidative stress. The ROS-dependent TRAF6-mediated non-proteolytic, K48/63-linked ubiquitination of ATG9A enhances its association with Beclin 1 and the assembly of VPS34-UVRAG complex, thereby stimulating autophagy. Notably, expression of the ATG9A ubiquitination mutants impairs ROS-induced VPS34 activation and autophagy. We further find that lipopolysaccharide (LPS)-induced ROS production also stimulates TRAF6-mediated ATG9A ubiquitination. Ablation of ATG9A causes aberrant TLR4 endosomal trafficking and decreases IRF-3 phosphorylation in LPS-stimulated macrophages. Our findings provide important insights into how K48/K63-linked ubiquitination of ATG9A contributes to the regulation of oxidative stress-induced autophagy.

USP8 regulates liver cancer progression via the inhibition of TRAF6-mediated signal for NF-κB activation and autophagy induction by TLR4

Herein, we aimed to elucidate the molecular and cellular mechanism in which ubiquitin-specific protease 8 (USP8) is implicated in liver cancer progression via TRAF6-mediated signal. USP8 induces the deubiquitination of TRAF6, TAB2, TAK1, p62, and BECN1, which are pivotal roles for NF-κB activation and autophagy induction. Notably, the LIHC patient with low USP8 mRNA expression showed markedly shorter survival time, whereas there was no significant difference in the other 18-human cancers. Importantly, the TCGA data analysis on LIHC and transcriptome analysis on the USP8 knockout (USP8KO) SK-HEP-1 cells revealed a significant correlation between USP8 and TRAF6, TAB2, TAK1, p62, and BECN1, and enhanced NF-κB-dependent and autophagy-related cancer progression/metastasis-related genes in response to LPS stimulation. Furthermore, USP8KO SK-HEP-1 cells showed an increase in cancer migration and invasion by TLR4 stimulation, and a marked increase of tumorigenicity and metastasis in xenografted NSG mice. The results demonstrate that USP8 is negatively implicated in the LIHC progression through the regulation of TRAF6-mediated signal for the activation of NF-κB activation and autophagy induction. Our findings provide useful insight into the LIHC pathogenesis of cancer progression.

Ubiquitin-specific protease 3 attenuates interleukin-1β-mediated chondrocyte senescence by deacetylating forkhead box O-3 via sirtuin-3

Osteoarthritis (OA) affects approximately 12% of the aging Western population. The sirtuin/forkhead box O (SIRT/FOXO) signaling pathway plays essential roles in various biological processes. Despite it has been demonstrated that ubiquitin-specific protease 3 (USP3) inhibits chondrocyte apoptosis induced by interleukin (IL)-1β, the role of USP3/SIRT3/FOXO3 in the senescence of chondrocytes in OA is unclear. This study initially isolated articular chondrocytes and investigated the role of USP3 in IL-1β-induced senescence of chondrocytes. After USP3 was overexpressed or silenced by lentivirus, expressions of genes and proteins were detected using quantitative polymerase chain reaction and immunoblotting, respectively. Cell cycle analysis was performed using flow cytometry. Reactive oxygen species (ROS) levels and senescence were analyzed. Then, SIRT3 was inhibited or overexpressed to explore the underlying mechanism. We found that overexpression of USP3 hindered IL-1β-mediated cell cycle arrest, ROS generation, and chondrocyte senescence. The inhibition of SIRT3 blocked the protective effect of USP3 on cell senescence, whereas the overexpression of SIRT3 abolished USP3-silencing-induced cell senescence. Furthermore, SIRT3 attenuated cell senescence, probably by deacetylating FOXO3. USP3 upregulated SIRT3 to deacetylate FOXO3 and attenuated IL-1β-induced chondrocyte senescence. This study demonstrated that USP3 probably attenuated IL-1β-mediated chondrocyte senescence by deacetylating FOXO3 via SIRT3.

Inhibiting USP14 ameliorates inflammatory responses in trophoblast cells by suppressing MAPK/NF-κB signaling

Background

Preeclampsia can cause severe consequences for pregnant women and infants, and developing effective medicine or methods to prevent or treat patients with preeclampsia is urgently needed. Ubiquitin‐specific protease 14 (USP14) has emerged as a critical regulator in the development of human cancers and neurodegenerative diseases. However, its role in preeclampsia remains elusive.

Methods

The expression of USP14 in placental tissues from healthy donors and preeclampsia patients were determined by quantitative reverse transcription PCR assay. The protein levels of targeted genes were evaluated by Western blotting assay. Small interfering RNA‐mediated gene knockdown was used to reduce USP14 expression in trophoblast cell lines.

Results

The expression levels of USP14 and proinflammatory cytokine were substantially upregulated in placental tissues from preeclampsia patients. Knockdown or inhibition of USP14 significantly abrogated hypoxia/reoxygenation‐induced upregulation of nuclear factor kappa B (NF‐κB) activation and proinflammatory cytokine production.

Conclusion

Our results suggested that USP14 promotes proinflammatory cytokine production through activation of NF‐κB. Developing drugs targeting USP14 may be beneficial for the prevention or treatment of patients with preeclampsia.

TAK1-TABs Complex: A Central Signalosome in Inflammatory Responses

Transforming growth factor-β (TGF-β)-activated kinase 1 (TAK1) is a member of the MAPK kinase kinase (MAPKKK) family and has been implicated in the regulation of a wide range of physiological and pathological processes. TAK1 functions through assembling with its binding partners TAK1-binding proteins (TAB1, TAB2, and TAB3) and can be activated by a variety of stimuli such as tumor necrosis factor α (TNFα), interleukin-1β (IL-1β), and toll-like receptor ligands, and they play essential roles in the activation of NF-κB and MAPKs. Numerous studies have demonstrated that post-translational modifications play important roles in properly controlling the activity, stability, and assembly of TAK1-TABs complex according to the indicated cellular environment. This review focuses on the recent advances in TAK1-TABs-mediated signaling and the regulations of TAK1-TABs complex by post-translational modifications.

AMPKα1 Regulates Lung and Breast Cancer Progression by Regulating TLR4-Mediated TRAF6-BECN1 Signaling Axis

Simple Summary

TRAF6-BECN1 signaling axis in TLR4 signal plays an essential role for the autophagy induction, thereby it regulates cancer migration and invasion. Here we show that AMPKα1, one of the isoforms of AMPK, is functionally involved in autophagy induction by regulating the TRAF6-BECN1 signaling axis. In this context, AMPKα1-knockout lung or breast cancer cells exhibited the attenuation of cancer cell migration and invasion induced by TLR4 simulation. Additionally, we could find that the expression of AMPKα1 is positively associated with gene expressions related to autophagy, migration, and metastasis of cancer cells in primary non-small cell lung cancers (NSCLCs). These findings demonstrate that AMPKα1 plays a pivotal role in cancer progression by regulating the TRAF6-BECN1 signaling axis for autophagy induction.

Abstract

TRAF6-BECN1 signaling axis is critical for autophagy induction and functionally implicated in cancer progression. Here, we report that AMP-activated protein kinase alpha 1 (AMPKα1, PRKAA1) is positively involved in autophagy induction and cancer progression by regulating TRAF6-BECN1 signaling axis. Mechanistically, AMPKα1 interacted with TRAF6 and BECN1. It also enhanced ubiquitination of BECN1 and autophagy induction. AMPKα1-knockout (AMPKα1KO) HEK293T or AMPKα1-knockdown (AMPKα1KD) THP-1 cells showed impaired autophagy induced by serum starvation or TLR4 (Toll-like receptor 4) stimulation. Additionally, AMPKα1KD THP-1 cells showed decreases of autophagy-related and autophagosome-related genes induced by TLR4. AMPKα1KO A549 cells exhibited attenuation of cancer migration and invasion induced by TLR4. Moreover, primary non-small cell lung cancers (NSCLCs, n = 6) with low AMPKαl levels showed markedly decreased expression of genes related to autophagy, cell migration and adhesion/metastasis, inflammation, and TLRs whereas these genes were significantly upregulated in NSCLCs (n = 5) with high AMPKαl levels. Consistently, attenuation of cancer migration and invasion could be observed in AMPKα1KO MDA-MB-231 and AMPKα1KO MCF-7 human breast cancer cells. These results suggest that AMPKα1 plays a pivotal role in cancer progression by regulating the TRAF6-BECN1 signaling axis for autophagy induction.

IU1 suppresses proliferation of cervical cancer cells through MDM2 degradation

Previous studies have demonstrated that the antitumor potential of IU1 (a pharmacological compound), which was mediated by selective inhibition of proteasome-associated deubiquitinase ubiquitin-specific protease 14 (USP14). However, the underlying molecular mechanisms remain elusive. It has been well established that mdm2 (Murine double minute 2) gene was amplified and/or overexpressed in a variety of human neoplasms, including cervical cancer. Furthermore, MDM2 is critical to cervical cancer development and progression. Relatively studies have reported that USP15 and USP7 stabilized MDM2 protein levels by removing its ubiquitin chain. In the current study, we studied the cell proliferation status after IU1 treatment and the USP14-MDM2 protein interaction in cervical cancer cells. This study experimentally revealed that IU1 treatment reduced MDM2 protein expression in HeLa cervical cancer cells, along with the activation of autophagy-lysosomal protein degradation and promotion of ubiquitin-proteasome system (UPS) function, thereby blocked G0/G1 to S phase transition, decreased cell growth and triggered cell apoptosis. Thus, these results indicate that IU1 treatment simultaneously targets two major intracellular protein degradation systems, ubiquitin-proteasome and autophagy-lysosome systems, which leads to MDM2 degradation and contributes to the antitumor effect of IU1.

The Roles of Ubiquitin in Mediating Autophagy

Ubiquitination, the post-translational modification essential for various intracellular processes, is implicated in multiple aspects of autophagy, the major lysosome/vacuole-dependent degradation pathway. The autophagy machinery adopted the structural architecture of ubiquitin and employs two ubiquitin-like protein conjugation systems for autophagosome biogenesis. Ubiquitin chains that are attached as labels to protein aggregates or subcellular organelles confer selectivity, allowing autophagy receptors to simultaneously bind ubiquitinated cargos and autophagy-specific ubiquitin-like modifiers (Atg8-family proteins). Moreover, there is tremendous crosstalk between autophagy and the ubiquitin-proteasome system. Ubiquitination of autophagy-related proteins or regulatory components plays significant roles in the precise control of the autophagy pathway. In this review, we summarize and discuss the molecular mechanisms and functions of ubiquitin and ubiquitination, in the process and regulation of autophagy.

The potential roles of deubiquitinating enzymes in brain diseases

Most proteins undergo posttranslational modification such as acetylation, methylation, phosphorylation, biotinylation, and ubiquitination to regulate various cellular processes. Ubiquitin-targeted proteins from the ubiquitin-proteasome system (UPS) are degraded by 26S proteasome, along with this, deubiquitinating enzymes (DUBs) have specific activity against the UPS through detaching of ubiquitin on ubiquitin-targeted proteins. Balancing between protein expression and degradation through interplay between the UPS and DUBs is important to maintain cell homeostasis, and abnormal expression and elongation of proteins lead to diverse diseases such as cancer, diabetes, and autoimmune response. Therefore, development of DUB inhibitors as therapeutic targets has been challenging. In addition, understanding of the roles of DUBs in neurodegeneration, specifically brain diseases, has emerged gradually. This review highlights recent studies on the molecular mechanisms for DUBs, and discusses potential therapeutic targets for DUBs in cases of brain diseases.

The central regulator p62 between ubiquitin proteasome system and autophagy and its role in the mitophagy and Parkinson's disease

The ubiquitin-proteasome system (UPS) and autophagy are two major degradative pathways of proteins in eukaryotic cells. As about 30% of newly synthesized proteins are known to be misfolded under normal cell conditions, the precise and timely operation of the UPS and autophagy to remove them as well as their tightly controlled regulation, is so important for proper cell function and survival. In the UPS, target proteins are labeled by small proteins called ubiquitin, which are then transported to the proteasome complex for degradation. Alternatively, many greatly damaged proteins are believed to be delivered to the lysosome for autophagic degradation. Although these autophagy and UPS pathways have not been considered to be directly related, many recent studies proposed their close link and dynamic interconversion. In this review, we’ll focus on the several regulatory molecules that function in both UPS and autophagy and their crosstalk. Among the proposed multiple modulators, we will take a closer look at the so-called main connector of UPS-autophagy regulation, p62. Last, the functional role of p62 in the mitophagy and its implication for the pathogenesis of Parkinson’s disease, one of the major neurodegenerative diseases, will be briefly reviewed.

p62 is Negatively Implicated in the TRAF6-BECN1 Signaling Axis for Autophagy Activation and Cancer Progression by Toll-Like Receptor 4 (TLR4)

Toll-like receptors (TLRs) induce the activation of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) and autophagy through the TNF (Tumor necrosis factor) receptor-associated factor 6 (TRAF6)-evolutionarily conserved signaling intermediate in Toll pathways (ECSIT) and TRAF6-BECN1 signaling axes, respectively. Having shown that p62 negatively regulates Toll-like receptor 4 (TLR4)-mediated signaling via TRAF6-ECSIT signaling axis, we herein investigated whether p62 is functionally implicated in the TRAF6-BECN1 signaling axis, thereby regulating cancer cell migration and invasion. p62 interacted with TRAF6 and BECN1, to interrupt the functional associations required for TRAF6-BECN1 complex formation, leading to inhibitions of BECN1 ubiquitination and autophagy activation. Importantly, p62-deficient cancer cells, such as p62-knockdown (p62^KD) SK-HEP-1, p62^KD MDA-MB-231, and p62-knockout (p62^KO) A549 cells, showed increased activation of autophagy induced by TLR4 stimulation, suggesting that p62 negatively regulates autophagy activation. Moreover, these p62-deficient cancer cells exhibited marked increases in cell migration and invasion in response to TLR4 stimulation. Collectively, these results suggest that p62 is negatively implicated in the TRAF6-BECN1 signaling axis, thereby inhibiting cancer cell migration and invasion regulated by autophagy activation in response to TLR4 stimulation.

The deubiquitinating enzyme Usp14 controls ciliogenesis and Hedgehog signaling

Primary cilia are hair-like organelles that play crucial roles in vertebrate development, organogenesis and when dysfunctional result in pleiotropic human genetic disorders called ciliopathies, characterized by overlapping phenotypes, such as renal and hepatic cysts, skeletal defects, retinal degeneration and central nervous system malformations. Primary cilia act as communication hubs to transfer extracellular signals into intracellular responses and are essential for Hedgehog (Hh) signal transduction in mammals. Despite the renewed interest in this ancient organelle of growing biomedical importance, the molecular mechanisms that trigger cilia formation, extension and ciliary signal transduction are still not fully understood. Here we provide, for the first time, evidence that the deubiquitinase ubiquitin-specific protease-14 (Usp14), a major regulator of the ubiquitin proteasome system (UPS), controls ciliogenesis, cilia elongation and Hh signal transduction. Moreover, we show that pharmacological inhibition of Usp14 positively affects Hh signal transduction in a model of autosomal dominant polycystic kidney disease. These findings provide new insight into the spectrum of action of UPS in cilia biology and may provide novel opportunities for therapeutic intervention in human conditions associated with ciliary dysfunction.

Phosphorylated Heat Shock Protein 27 Inhibits Lipopolysaccharide-Induced Inflammation in Thp1 Cells by Promoting TLR4 Endocytosis, Ubiquitination, and Degradation

The aims of this study were to investigate the effect of Hsp27 on LPS-induced inflammation and identify the precise mechanisms about how Hsp27 regulates LPS-induced TLR4 signaling in Thp1 cells. Thp1 cells were transfected with Flag-Hsp27 or pcDNA3.1, and then treated with LPS for indicated time. TNF-α, IL-1β, and IL-6 were determined by ELISA. The protein levels of Hsp27, p-Hsp27 (Ser15, Ser78, and Ser82), and TLR4 were measured by Western blotting. In vitro study showed that over-expression of Hsp27 downregulated the release of TNF-α, IL-1β, and IL-6 and suppressed the activation of TLR4 signals after stimulated by LPS. The location of TLR4 and RAB5 was detected by confocal microscopy. Immunoprecipitation was used to determine the ubiquitination and degradation of TLR4 and interaction between Hsp27 and TLR4. Results showed that Hsp27 could promote TLR4 endocytosis and ubiquitination and degradation. Further research revealed that Hsp27 was phosphorylated after LPS, only phosphorylated Hsp27 can interact with TLR4 and inhibit the activation of TLR4 signaling, which was demonstrated by inhibition of Hsp27 phosphorylation with inhibitors or transfection of Hsp27 mutants into Thp1 cells. Phosphorylated Hsp27 reduced the release of TNF-α, IL-1β, and IL-6, and suppressed the activation of TLR4 signaling by promoting TLR4 endocytosis, ubiquitination, and degradation.

AMPK, a Regulator of Metabolism and Autophagy, Is Activated by Lysosomal Damage via a Novel Galectin-Directed Ubiquitin Signal Transduction System

AMPK is a central regulator of metabolism and autophagy. Here we show how lysosomal damage activates AMPK. This occurs via a hitherto unrecognized signal transduction system whereby cytoplasmic sentinel lectins detect membrane damage leading to ubiquitination responses. Absence of Galectin 9 (Gal9) or loss of its capacity to recognize lumenal glycans exposed during lysosomal membrane damage abrogate such ubiquitination responses. Proteomic analyses with APEX2-Gal9 have revealed global changes within the Gal9 interactome during lysosomal damage. Gal9 association with lysosomal glycoproteins increases whereas interactions with a newly identified Gal9 partner, deubiquitinase USP9X, diminishes upon lysosomal injury. In response to damage, Gal9 displaces USP9X from complexes with TAK1 and promotes K63 ubiquitination of TAK1 thus activating AMPK on damaged lysosomes. This triggers autophagy and contributes to autophagic control of membrane-damaging microbe Mycobacterium tuberculosis. Thus, galectin and ubiquitin systems converge to activate AMPK and autophagy during endomembrane homeostasis.

USP15 potentiates NF-κB activation by differentially stabilizing TAB2 and TAB3

Tumor necrosis factor α (TNFα)- and interleukin 1β (IL-1β)-induced nuclear factor-κB (NF-κB) activation play key roles in inflammation, immunity, and cancer development. Here, we identified one of the deubiquitinating enzymes (DUBs), ubiquitin-specific protease 15 (USP15), as a positive regulator in both TNFα- and IL-1β-induced NF-κB activation. Overexpression of USP15 potentiated TNFα- or IL-1β-triggered NF-κB activation and downstream gene transcription, whereas knockdown of USP15 had opposite effects. Mechanistically, upon TNFα stimulation, USP15 showed an enhanced interaction with transforming growth factor-β activated kinase-1 (TAK1)-TAK1 binding protein (TAB) complex to inhibit the proteolysis of TAB2/3 by different pathways. Apart from deubiquitination dependently inducing cleavage of lysine 48-linked TAB2 ubiquitination, USP15 also DUB independently inhibited lysosome-associated TAB2 degradation, thus enhanced TAB2 stabilization. For TAB3, USP15 inhibited NBR1-mediated selective autophagic TAB3 degradation independent of its deubiquitinating activity. Together, our results reveal a novel USP15-mediated mechanism through which efficient NF-κB activation is achieved by differentially maintaining the TAB2/3 stability.

The Proteasome and Its Network: Engineering for Adaptability

The proteasome, the most complex protease known, degrades proteins that have been conjugated to ubiquitin. It faces the unique challenge of acting enzymatically on hundreds and perhaps thousands of structurally diverse substrates, mechanically unfolding them from their native state and translocating them vectorially from one specialized compartment of the enzyme to another. Moreover, substrates are modified by ubiquitin in myriad configurations of chains. The many unusual design features of the proteasome may have evolved in part to endow this enzyme with a robust ability to process substrates regardless of their identity. The proteasome plays a major role in preserving protein homeostasis in the cell, which requires adaptation to a wide variety of stress conditions. Modulation of proteasome function is achieved through a large network of proteins that interact with it dynamically, modify it enzymatically, or fine-tune its levels. The resulting adaptability of the proteasome, which is unique among proteases, enables cells to control the output of the ubiquitin-proteasome pathway on a global scale.

USP14 Inhibition Regulates Tumorigenesis by Inducing Autophagy in Lung Cancer In Vitro

The ubiquitin–proteasome system is an essential regulator of several cellular pathways involving oncogenes. Deubiquitination negatively regulates target proteins or substrates linked to both hereditary and sporadic forms of cancer. The deubiquitinating enzyme ubiquitin-specific protease 14 (USP14) is associated with proteasomes where it trims the ubiquitin chain on the substrate. Here, we found that USP14 is highly expressed in patients with lung cancer. We also demonstrated that USP14 inhibitors (IU1-47 and siRNA-USP14) significantly decreased cell proliferation, migration, and invasion in lung cancer. Remarkably, we found that USP14 negatively regulates lung tumorigenesis not only through apoptosis but also through the autophagy pathway. Our findings suggest that USP14 plays a crucial role in lung tumorigenesis and that USP14 inhibitors are potent drugs in lung cancer treatment.

p62 Negatively Regulates TLR4 Signaling via Functional Regulation of the TRAF6-ECSIT Complex

Sequestosome 1 (SQSTM1, p62), a ubiquitin binding protein, plays a role in cell signaling, oxidative stress, and autophagy. However, its functional role in inflammatory signaling is controversial. Recent studies have shown that p62 is negatively implicated in inflammatory responses. But, the precise molecular mechanisms by which p62 regulates inflammatory responses remain unclear. In this study, we report on a new regulatory role for p62 in TLR4-mediated signaling. p62 overexpression led to the suppression of NF-κB activation and the production of pro-inflammatory cytokines, TNF-α, IL-6, and IL-1β in response to TLR4 stimulation. In contrast, p62^−/− mouse embryonic fibroblast (MEF) cells exhibited marked enhancement of NF-κB activation and production of pro-inflammatory cytokines by TLR4 stimulation, compared to p62^+/+ MEF cells. Additionally, the TLR4-induced activation of signal transduction was significantly augmented in p62^−/− MEF cells, indicating that p62 was negatively implicated in TLR4-mediated signaling. Biochemical studies revealed that p62 interacted with the internal domain of evolutionarily conserved signaling intermediate in Toll pathways (ECSIT), which is critical for associating with the TNF receptor associated factor 6 (TRAF6)-ECSIT complex to activate NF-κB in TLR4 signaling. Interestingly, p62-ECSIT interaction inhibited the interaction between TRAF6 and ECSIT and attenuated the ubiquitination of ECSIT. Furthermore, upon LPS challenge, the mortality of p62^−/− (p62-knockout) mice was markedly enhanced compared to p62^+/+ (p62 wild-type) mice. Taken together, our data demonstrate that p62 negatively regulated TLR4 signaling via functional regulation of the TRAF6-ECSIT complex.

Deubiquitinating Enzymes Related to Autophagy: New Therapeutic Opportunities?

Autophagy is an evolutionary conserved catabolic process that allows for the degradation of intracellular components by lysosomes. This process can be triggered by nutrient deprivation, microbial infections or other challenges to promote cell survival under these stressed conditions. However, basal levels of autophagy are also crucial for the maintenance of proper cellular homeostasis by ensuring the selective removal of protein aggregates and dysfunctional organelles. A tight regulation of this process is essential for cellular survival and organismal health. Indeed, deregulation of autophagy is associated with a broad range of pathologies such as neuronal degeneration, inflammatory diseases, and cancer progression. Ubiquitination and deubiquitination of autophagy substrates, as well as components of the autophagic machinery, are critical regulatory mechanisms of autophagy. Here, we review the main evidence implicating deubiquitinating enzymes (DUBs) in the regulation of autophagy. We also discuss how they may constitute new therapeutic opportunities in the treatment of pathologies such as cancers, neurodegenerative diseases or infections.