Fbxw7 regulates lipid metabolism and cell fate decisions in the mouse liver

Molecular insights and clinical implications for the tumor suppressor role of SCFFBXW7 E3 ubiquitin ligase

FBXW7 is one of the most well-characterized F-box proteins, serving as substrate receptor subunit of SKP1-CUL1-F-box (SCF) E3 ligase complexes. SCFFBXW7 is responsible for the degradation of various oncogenic proteins such as cyclin E, c-MYC, c-JUN, NOTCH, and MCL1. Therefore, FBXW7 functions largely as a major tumor suppressor. In keeping with this notion, FBXW7 gene mutations or downregulations have been found and reported in many types of malignant tumors, such as endometrial, colorectal, lung, and breast cancers, which facilitate the proliferation, invasion, migration, and drug resistance of cancer cells. Therefore, it is critical to review newly identified FBXW7 regulation and tumor suppressor function under physiological and pathological conditions to develop effective strategies for the treatment of FBXW7-altered cancers. Since a growing body of evidence has revealed the tumor-suppressive activity and role of FBXW7, here, we updated FBXW7 upstream and downstream signaling including FBXW7 ubiquitin substrates, the multi-level FBXW7 regulatory mechanisms, and dysregulation of FBXW7 in cancer, and discussed promising cancer therapies targeting FBXW7 regulators and downstream effectors, to provide a comprehensive picture of FBXW7 and facilitate the study in this field.

The interplay of the circadian clock and metabolic tumorigenesis

The circadian clock and cell metabolism are both dysregulated in cancer cells through intrinsic cell-autonomous mechanisms and external influences from the tumor microenvironment. The intricate interplay between the circadian clock and cancer cell metabolism exerts control over various metabolic processes, including aerobic glycolysis, de novo nucleotide synthesis, glutamine and protein metabolism, lipid metabolism, mitochondrial metabolism, and redox homeostasis in cancer cells. Importantly, oncogenic signaling can confer a moonlighting function on core clock genes, effectively reshaping cellular metabolism to fuel cancer cell proliferation and drive tumor growth. These interwoven regulatory mechanisms constitute a distinctive feature of cancer cell metabolism.

Active AKT2 stimulation of SREBP1/SCD1-mediated lipid metabolism boosts hepatosteatosis and cancer

Due to soared obesity population worldwide, hepatosteatosis is becoming a major risk factor for hepatocellular carcinoma (HCC). Undertaken molecular events during the progression of steatosis to liver cancer are thus under intensive investigation. In this study, we demonstrated that high-fat diet potentiated mouse liver AKT2. Hepatic AKT2 hyperactivation through gain-of-function mutation of Akt2 (Akt2E17K) caused spontaneous hepatosteatosis, injury, inflammation, fibrosis, and eventually HCC in mice. AKT2 activation also exacerbated lipopolysaccharide and D-galactosamine hydrochloride-induced injury/inflammation and N-Nitrosodiethylamine (DEN)-induced HCC. A positive correlation between AKT2 activity and SCD1 expression was observed in human HCC samples. Activated AKT2 enhanced the production of monounsaturated fatty acid which was dependent on SREBP1 upregulation of SCD1. Blockage of active SREBP1 and ablation of SCD1 reduced steatosis, inflammation, and tumor burden in DEN-treated Akt2E17K mice. Therefore, AKT2 activation is crucial for the development of steatosis-associated HCC which can be treated with blockage of AKT2-SREBP1-SCD1 signaling cascade.

Protein neddylation and its role in health and diseases

NEDD8 (Neural precursor cell expressed developmentally downregulated protein 8) is an ubiquitin-like protein that is covalently attached to a lysine residue of a protein substrate through a process known as neddylation, catalyzed by the enzyme cascade, namely NEDD8 activating enzyme (E1), NEDD8 conjugating enzyme (E2), and NEDD8 ligase (E3). The substrates of neddylation are categorized into cullins and non-cullin proteins. Neddylation of cullins activates CRLs (cullin RING ligases), the largest family of E3 ligases, whereas neddylation of non-cullin substrates alters their stability and activity, as well as subcellular localization. Significantly, the neddylation pathway and/or many neddylation substrates are abnormally activated or over-expressed in various human diseases, such as metabolic disorders, liver dysfunction, neurodegenerative disorders, and cancers, among others. Thus, targeting neddylation becomes an attractive strategy for the treatment of these diseases. In this review, we first provide a general introduction on the neddylation cascade, its biochemical process and regulation, and the crystal structures of neddylation enzymes in complex with cullin substrates; then discuss how neddylation governs various key biological processes via the modification of cullins and non-cullin substrates. We further review the literature data on dysregulated neddylation in several human diseases, particularly cancer, followed by an outline of current efforts in the discovery of small molecule inhibitors of neddylation as a promising therapeutic approach. Finally, few perspectives were proposed for extensive future investigations.

FBXW7 polymorphism asserts susceptibility to colorectal cancer

FBXW7, belonging to the F-Box protein family, is considered a candidate cancer susceptibility gene. Our findings indicate that single nucleotide polymorphisms (SNPs) in the FBXW7 gene are linked to cancer risk, strengthening FBXW7's role in the pathogenesis of colorectal cancer. Our case-control study comprised of 450 patients diagnosed with colorectal cancer (CRC) and an equal number of 450 healthy subjects. FBXW7 SNPs rs2255137C>T and rs6842544C>T were genotyped using PCR-Restriction Fragment Length Polymorphism (PCR-RFLP) and Single-Stranded Conformation Polymorphism (SSCP) techniques and further cross-checked by direct sequencing. Linkage disequilibrium and haplotype analyses of these SNPs were also assessed. The in-silico approach was used to reveal the functional analysis between the nonsynonymous variation (rs6842544) and CRC followed by its validation at the protein level by western blotting and reverse transcription-PCR. A significant association of colorectal cancer was detected with rs6842544 SNP. However, there was no association between FBXW7 rs2255137 polymorphism and CRC. The homozygous individuals carrying the C variant in FBXW7 rs6842544 showed a slightly higher risk for colorectal cancer (OR = 1.590, 95%CI = 0.39 ∼ 2.89, p = 0.011). The haplotype CC identified in this study seemed to be associated with good prognosis (OR = 1.22, 95% CI = 1.00 ∼ 1.47, p = 0.0013) whereas the TT haplotype was found to reduce the CRC risk (OR = 0.642, 95%CI = 0.48 ∼ 0.84, p = 0.039). In-silico prediction proposed that the variant R133G is responsible for the lower expression of FBXW7. Additionally, the expression profiling of FBXW7 nonsynonymous SNP was significantly lower in primary CRC tissues than in the paired non-cancerous tissues at protein and mRNA levels. The study indicates that the FBXW7 rs6842544 is associated with the risk of development of CRC and could serve as a molecular biological marker to screen high-risk groups for CRC.

The critical role of BTRC in hepatic steatosis as an ATGL E3 ligase

Non-alcoholic fatty liver disease (NAFLD), characterized by hepatic steatosis, is one of the commonest causes of liver dysfunction. Adipose triglyceride lipase (ATGL) is closely related to lipid turnover and hepatic steatosis as the speed-limited triacylglycerol lipase in liver lipolysis. However, the expression and regulation of ATGL in NAFLD remain unclear. Herein, our results showed that ATGL protein levels were decreased in the liver tissues of high-fat diet (HFD)-fed mice, naturally obese mice, and cholangioma/hepatic carcinoma patients with hepatic steatosis, as well as in the oleic acid-induced hepatic steatosis cell model, while ATGL mRNA levels were not changed. ATGL protein was mainly degraded through the proteasome pathway in hepatocytes. Beta-transducin repeat containing (BTRC) was upregulated and negatively correlated with the decreased ATGL level in these hepatic steatosis models. Consequently, BTRC was identified as the E3 ligase for ATGL through predominant ubiquitination at the lysine 135 residue. Moreover, adenovirus-mediated knockdown of BTRC ameliorated steatosis in HFD-fed mouse livers and oleic acid-treated liver cells via upregulating the ATGL level. Taken together, BTRC plays a crucial role in hepatic steatosis as a new ATGL E3 ligase and may serve as a potential therapeutic target for treating NAFLD.

Regulation of lipid metabolism by E3 ubiquitin ligases in lipid-associated metabolic diseases

Previous studies have progressively elucidated the involvement of E3 ubiquitin (Ub) ligases in regulating lipid metabolism. Ubiquitination, facilitated by E3 Ub ligases, modifies critical enzymes in lipid metabolism, enabling them to respond to specific signals. In this review, we aim to present a comprehensive analysis of the role of E3 Ub ligases in lipid metabolism, which includes lipid synthesis and lipolysis, and their influence on cellular lipid homeostasis through the modulation of lipid uptake and efflux. Furthermore, it explores how the ubiquitination process governs the degradation or activation of pivotal enzymes, thereby regulating lipid metabolism at the transcriptional level. Perturbations in lipid metabolism have been implicated in various diseases, including hepatic lipid metabolism disorders, atherosclerosis, diabetes, and cancer. Therefore, this review focuses on the association between E3 Ub ligases and lipid metabolism in lipid-related diseases, highlighting enzymes critically involved in lipid synthesis and catabolism, transcriptional regulators, lipid uptake translocators, and transporters. Overall, this review aims to identify gaps in current knowledge, highlight areas requiring further research, offer potential targeted therapeutic approaches, and provide a comprehensive outlook on clinical conditions associated with lipid metabolic diseases.

Identification and Validation of Lipid Metabolism Gene FASN-Associated miRNA in Wilms Tumor

miRNA has been a research hotspot in recent years and its scope of action is very wide, involving the regulation of cell proliferation, differentiation, apoptosis, and other biological behaviors. This study intends to explore the role of miRNA in the lipid metabolism and development of Wilms tumor (WT) by detecting and analyzing the differences in the expression profiles of miRNAs between the tumor and adjacent normal tissue. Gene detection was performed in tumor tissues and adjacent normal tissues of three cases of WT to screen differentially expressed miRNAs (DEMs). According to our previous research, FASN, which participates in the lipid metabolism pathway, may be a target of WT. The starBase database was used to predict FASN-targeted miRNAs. The above two groups of miRNAs were intersected to obtain FASN-targeted DEMs and then GO Ontology (GO) functional enrichment analysis of FASN-targeted DEMs was performed. Finally, the FASN-targeted DEMs were compared and further verified by qRT‒PCR. Through gene sequencing and differential analysis, 287 DEMs were obtained, including 132 upregulated and 155 downregulated miRNAs. The top ten DEMs were all downregulated. Fourteen miRNAs targeted by the lipid metabolism-related gene FASN were predicted by starBase. After intersection with the DEMs, three miRNAs were finally obtained, namely, miR-107, miR-27a-3p, and miR-335-5p. GO enrichment analysis was mainly concentrated in the Parkin-FBXW7-Cul1 ubiquitin ligase complex and response to prostaglandin E. Further experimental verification showed that miR-27a-3p was significantly correlated with WT (P = 0.0018). Imbalanced expression of miRNAs may be involved in the occurrence and development of WT through lipid metabolism. The expression of miR-27a-3p is related to the malignant degree of WT, and it may become the target of diagnosis, prognosis, and treatment of WT in the later stage.

Hepatocyte FBXW7-dependent activity of nutrient-sensing nuclear receptors controls systemic energy homeostasis and NASH progression in male mice

Nonalcoholic steatohepatitis (NASH) is epidemiologically associated with obesity and diabetes and can lead to liver cirrhosis and hepatocellular carcinoma if left untreated. The intricate signaling pathways that orchestrate hepatocyte energy metabolism and cellular stress, intrahepatic cell crosstalk, as well as interplay between peripheral tissues remain elusive and are crucial for the development of anti-NASH therapies. Herein, we reveal E3 ligase FBXW7 as a key factor regulating hepatic catabolism, stress responses, systemic energy homeostasis, and NASH pathogenesis with attenuated FBXW7 expression as a feature of advanced NASH. Multiomics and pharmacological intervention showed that FBXW7 loss-of-function in hepatocytes disrupts a metabolic transcriptional axis conjointly controlled by the nutrient-sensing nuclear receptors ERRα and PPARα, resulting in suppression of fatty acid oxidation, elevated ER stress, apoptosis, immune infiltration, fibrogenesis, and ultimately NASH progression in male mice. These results provide the foundation for developing alternative strategies co-targeting ERRα and PPARα for the treatment of NASH.

Cullin-associated and neddylation-dissociated 1 regulate reprogramming of lipid metabolism through SKP1-Cullin-1-F-boxFBXO11 -mediated heterogeneous nuclear ribonucleoprotein A2/B1 ubiquitination and promote hepatocellular carcinoma

BACKGROUND

Enhanced de novo lipogenesis is essential for hepatocellular carcinoma (HCC). Abnormally high cullin-associated and neddylation-dissociated 1 (CAND1) expression is associated with poor clinical prognosis in HCC. The SKP1-Cullin-1-F-box (SCF) complex consists of the SKP1, Cullin-1 and F-box proteins (FBPs) and performs multiple functions including adipogenesis. SCF complex was modulated by CAND1, but Whether and how the CAND1 promotes HCC by regulating SCF complex and lipogenesis are unknown.

METHODS

HCC samples were used to analyze the correlations between CAND1 expression and clinicopathological characteristics such as survival and prognosis. The in vitro functions of CAND1, FBXO11 and heterogeneous nuclear ribonucleoprotein A2/B1 (hnRNPA2B1) were measured by cell proliferation, colony formation and migration assays. The in vivo functions were tested in multiple mouse liver cancer models including patient-derived xenograft (PDX), cell line-derived xenograft and AKT/NRASV12-induced primary liver cancer models. Injections of adeno-associated virus targeting CAND1 (AAV-shCAND1) were performed to evaluate the therapeutic efficacy of targeting CAND1. RNA-Seq and lipidomic assays followed by serial biochemical experiments including mass spectrometry, immunoprecipitation and GST pull-down were performed to dissect the underlying mechanisms.

RESULTS

CAND1 promoted the expression of lipid synthesis genes by disrupting SCF complex assembly and lipid accumulation. Furthermore, we identified hnRNPA2B1 as a novel F-box protein 11 (FBXO11)-binding partner. FBXO11 directly bound to hnRNPA2B1 and promoted hnRNPA2B1 ubiquitination and subsequent degradation. Our evaluations of the therapeutic efficacy of AAV-shCAND1 injections confirmed that targeting the CAND1-SCFFBXO11 -hnRNPA2B1A signalling axis was therapeutically effective. CAND1 downregulation significantly reduced the tumour burden in a primary mouse liver cancer model and a PDX model.

CONCLUSIONS

Our results highlight that CAND1 is associated with poor prognosis in HCC and regulates lipid metabolic reprogramming by dissociating the SCF complex. Targeting the CAND1-SCFFBXO11 -hnRNPA2B1 axis may be a novel strategy for HCC treatment.

Neglected PTM in Animal Adipogenesis: E3-mediated Ubiquitination

Ubiquitination is a widespread post-transcriptional modification (PTM) that occurs during protein degradation in eukaryotes and participates in almost all physiological and pathological processes, including animal adipogenesis. Ubiquitination is a cascade reaction regulated by the activating enzyme E1, conjugating enzyme E2, and ligase E3. Several recent studies have reported that E3 ligases play important regulatory roles in adipogenesis. However, as a key influencing factor for the recognition and connection between the substrate and ubiquitin during ubiquitination, its regulatory role in adipogenesis has not received adequate attention. In this review, we summarize the E3s' regulation and modification targets in animal adipogenesis, explain the regulatory mechanisms in lipogenic-related pathways, and further analyze the existing positive results to provide research directions of guiding significance for further studies on the regulatory mechanisms of E3s in animal adipogenesis.

Biomedical importance of the ubiquitin-proteasome system in diabetes and metabolic transdifferentiation of pancreatic duct epithelial cells into β-cells

The ubiquitin-proteasome system (UPS) is a major pathway for cellular protein degradation. The molecular function of the UPS is the removal of damaged proteins, and this function is applied in many biological processes, including inflammation, proliferation, and apoptosis. Accumulating evidence also suggests that the UPS also has a key role in pancreatic β-cell transdifferentiation in diabetes and can be targeted for treatment of diabetic diseases. In this review, we summarized the mechanistic roles of the UPS in the biochemical activities of pancreatic β-cells, including the role of the UPS in insulin synthesis and secretion, as well as β-cell degradation. Also, we discuss how the UPS mediates the transdifferentiation of pancreatic duct epithelial cells into β-cells as the experimental basis for the development of new strategies for the treatment of diabetes in regenerative medicine.

FBXW7 alleviates hyperglycemia-induced endothelial oxidative stress injury via ROS and PARP inhibition

Diabetic retinopathy (DR) and other diabetic vascular complications are the leading cause of death and disability in patients with suboptimum glycemic control. In the pathogenesis of diabetic vascular diseases, hyperglycemia-induced oxidative stress, DNA damage, and poly-ADP-ribose-polymerase (PARP) hyperactivation play important roles in endothelial cell impairment. Adipose differentiation-related protein FBXW7 was reported to regulate PGC-1α stability and mitochondrial homeostasis. Here, we investigated the role and mechanism of FBXW7 in repairing endothelial oxidative stress injuries under hyperglycemic conditions. FBXW7 promoted the hampered activity of homologous recombination and non-homologues end joining pathway for repairing DNA double-strand breaks damage, an initiating factor for PARP hyperactivation and diabetic vascular complications. The abundant mobilization of DNA damage repair mediated by FBXW7 suppressed PARP activation, leading to downregulation of PARP expression and activity in both human endothelial cells and diabetic rat retinas. This provided a new method for PARP inhibition, superior to PARP inhibitors for treating diabetic vascular complication. Furthermore, FBXW7 rescued downregulated NAD+ levels and ameliorated mitochondrial dysfunction, thereby reducing superoxide production under hyperglycemic conditions. These effects reversed oxidative injury and vascular leakage in diabetic rat retina, providing a potential future treatment strategy.

Loss of the Fbw7 tumor suppressor rewires cholesterol metabolism in cancer cells leading to activation of the PI3K-AKT signalling axis

The sterol regulatory-element binding proteins (SREBPs) are transcription factors controlling cholesterol and fatty acid synthesis and metabolism. There are three SREBP proteins, SREBP1a, SREBP1c and SREBP2, with SREBP1a being the strongest transcription factor. The expression of SREBP1a is restricted to rapidly proliferating cells, including cancer cells. The SREBP proteins are translated as large, inactive precursors bound to the endoplasmic reticulum (ER) membranes. These precursors undergo a two-step cleavage process that releases the amino terminal domains of the proteins, which translocate to the nucleus and function as transcription factors. The nuclear forms of the SREBPs are rapidly degraded by the ubiquitin-proteasome system in a manner dependent on the Fbw7 ubiquitin ligase. Consequently, inactivation of Fbw7 results in the stabilization of active SREBP1 and SREBP2 and enhanced expression of target genes. We report that the inactivation of Fbw7 in cancer cells blocks the proteolytic maturation of SREBP2. The same is true in cells expressing a cancer-specific loss-of-function Fbw7 protein. Interestingly, the activation of SREBP2 is restored in response to cholesterol depletion, suggesting that Fbw7-deficient cells accumulate cholesterol. Importantly, inactivation of SREBP1 in Fbw7-deficient cells also restores the cholesterol-dependent regulation of SREBP2, suggesting that the stabilization of active SREBP1 molecules could be responsible for the blunted activation of SREBP2 in Fbw7-deficient cancer cells. We suggest that this could be an important negative feedback loop in cancer cells with Fbw7 loss-of-function mutations to protect these cells from the accumulation of toxic levels of cholesterol and/or cholesterol metabolites. Surprisingly, we also found that the inactivation of Fbw7 resulted in the activation of AKT. Importantly, the activation of AKT was dependent on SREBP1 and on the accumulation of cholesterol. Thus, we suggest that the loss of Fbw7 rewires lipid metabolism in cancer cells to support cell proliferation and survival.

Physiological Functions of FBW7 in Metabolism

FBW7 is the recognition subunit of the SCF (Skp1-Cullin1-F-box proteins) E3 ubiquitin ligase complex, and it determines the specificity of the SCF substrate. SCFFBW7 is a recognized tumor suppressor because of its ability to degrade many proto-oncogenic substrates. Recent studies have shown that FBW7 plays a key role in metabolism by targeting the degradation of critical regulators involved in cellular metabolism in a ubiquitin-dependent manner. Here, we review recent studies, which highlight the important role of FBW7 in metabolism.

Germline variants in tumor suppressor FBXW7 lead to impaired ubiquitination and a neurodevelopmental syndrome

Neurodevelopmental disorders are highly heterogenous conditions resulting from abnormalities of brain architecture and/or function. FBXW7 (F-box and WD-repeat-domain-containing 7), a recognized developmental regulator and tumor suppressor, has been shown to regulate cell-cycle progression and cell growth and survival by targeting substrates including CYCLIN E1/2 and NOTCH for degradation via the ubiquitin proteasome system. We used a genotype-first approach and global data-sharing platforms to identify 35 individuals harboring de novo and inherited FBXW7 germline monoallelic chromosomal deletions and nonsense, frameshift, splice-site, and missense variants associated with a neurodevelopmental syndrome. The FBXW7 neurodevelopmental syndrome is distinguished by global developmental delay, borderline to severe intellectual disability, hypotonia, and gastrointestinal issues. Brain imaging detailed variable underlying structural abnormalities affecting the cerebellum, corpus collosum, and white matter. A crystal-structure model of FBXW7 predicted that missense variants were clustered at the substrate-binding surface of the WD40 domain and that these might reduce FBXW7 substrate binding affinity. Expression of recombinant FBXW7 missense variants in cultured cells demonstrated impaired CYCLIN E1 and CYCLIN E2 turnover. Pan-neuronal knockdown of the Drosophila ortholog, archipelago, impaired learning and neuronal function. Collectively, the data presented herein provide compelling evidence of an F-Box protein-related, phenotypically variable neurodevelopmental disorder associated with monoallelic variants in FBXW7.

Integrative Analysis of RNA Expression and Regulatory Networks in Mice Liver Infected by Echinococcus multilocularis

The larvae of Echinococcus multilocularis causes alveolar echinococcosis, which poses a great threat to the public health. However, the molecular mechanisms underlying the host and parasite interactions are still unclear. Exploring the transcriptomic maps of mRNA, miRNA and lncRNA expressed in the liver in response to E. multilocularis infection will help us to understand its pathogenesis. Using liver perfusion, different cell populations including the hepatic cells, hepatic stellate cells and Kupffer cells were isolated from mice interperitoneally inoculated with protoscoleces. Their transcriptional profiles including lncRNAs, miRNAs and mRNAs were done by RNA-seq. Among these cell populations, the most differentially-expressed (DE) mRNA, lncRNAs and miRNAs were annotated and may involve in the pathological processes, mainly including metabolic disorders, immune responses and liver fibrosis. Following the integrative analysis of 38 differentially-expressed DEmiRNAs and 8 DElncRNAs, the lncRNA-mRNA-miRNA networks were constructed, including F63-miR-223-3p-Fbxw7/ZFP36/map1b, F63-miR-27-5p-Tdrd6/Dip2c/Wdfy4 and IFNgAS1-IFN-γ. These results unveil the presence of several potential lncRNA-mRNA-miRNA axes during E. multilocularis infection, and further exploring of these axes may contribute to better understanding of the pathogenic mechanisms.

Fbw7 Inhibits the Progression of Activated B-Cell Like Diffuse Large B-Cell Lymphoma by Targeting the Positive Feedback Loop of the LDHA/lactate/miR-223 Axis

Background

F-box and WD repeat domain-containing 7 (Fbw7) is well known as a tumor suppressor and ubiquitin ligase which targets a variety of oncogenic proteins for proteolysis. We previously reported that Fbw7 promotes apoptosis in diffuse large B-cell lymphoma (DLBCL) through Fbw7-mediated ubiquitination of Stat3. This study aimed to identify the mechanism of Fbw7-mediated aerobic glycolysis reprogramming in DLBCL.

Methods

Expression levels of Fbw7 and Lactate Dehydrogenase A (LDHA) in human DLBCL samples were evaluated by immunohistochemistry. Crosstalk between Fbw7 and LDHA signaling was analyzed by co-immunoprecipitation, ubiquitination assay, western blotting and mRNA quanlitative analyses. In vitro and in vivo experiments were used to assess the effect of the Fbw7-mediated LDHA/lactate/miR-223 axis on DLBCL cells growth.

Results

Fbw7 could interact with LDHA to trigger its ubiquitination and degradation. Inversely, lactate negatively regulated Fbw7 via trigging the expression of miR-223, which targeted Fbw7 3’-UTR to inhibit its expression. In vivo and in vitro experiments revealed that miR-223 promoted tumor growth and that the effects of miR-223 on tumor growth were primarily related to the inhibition of Fbw7-mediated LDHA’s ubiquitination.

Conclusions

We demonstrated that the ubiquitin-ligase Fbw7 played a key role in LDHA-related aerobic glycolysis reprogramming in DLBCL. Our study uncovers a negative functional loop consisting of a Fbw7-mediated LDHA/lactate/miR-223 axis, which may support the future ABC-DLBCL therapy by targeting LDHA-related inhibition.

Skp2 stabilizes Mcl-1 and confers radioresistance in colorectal cancer

Overexpression of Skp2 plays a critical role in tumorigenesis and correlates with poor prognosis in human malignancies. Thus, Skp2 has been proposed as an attractive target for anti-tumor interventions. The expression of Skp2 in human colorectal cancer (CRC) and the role of Skp2 in tumorigenic properties and irradiation sensitivities of CRC cells were examined by anchorage-dependent and -independent growth assays, immunoblot, flow cytometry, immunohistochemical staining, ubiquitination analysis, co-immunoprecipitation assay, CRISPR-Cas9-based gene knockout, and xenograft experiments. Skp2 is highly expressed in CRC patient tissues. Blocking Skp2 expression reduces the tumorigenic properties of CRC cells in vitro and in vivo. Depletion of Skp2 confers sensitivity to irradiation of CRC cells. Skp2 deficiency enhances irradiation-induced intrinsic apoptosis by facilitating E3 ligase FBW7-mediated Mcl-1 ubiquitination and degradation. Knockout of Skp2 sensitizes CRC cells to irradiation treatments in vivo. Our findings indicate that Skp2 stabilizes Mcl-1, and targeting Skp2 in combination with traditional radiotherapy might be efficacious in treating CRC.

FBXW7 gene polymorphism is associated with type 2 diabetes in the Uygur population in Xinjiang, China

Background

FBXW7 gene expression is positively correlated with glycolipid metabolism and is associated with diabetes in animal models. In the current study, we focused on exploring whether genetic variants of the FBXW7 gene were associated with type 2 diabetes (T2DM) and the risk factors for T2DM in Uygur people in Xinjiang, China.

Methods

A total of 2164 Chinese Uygur subjects (673 T2DM patients and 1491 controls) were recruited for our case–control study, and four SNPs (rs10033601, rs2255137, rs2292743 and rs35311955) of the FBXW7 gene were genotyped using the improved multiplex ligation detection reaction (iMLDR) technique.

Results

Our study showed that the genotypes using the overdominant model (GA vs AA + GG) of rs10033601 and using the overdominant model (TA vs TT + AA) of rs2292743 were significantly different between T2DM patients and the controls (P = 0.005 and P = 0.012, respectively). After multivariate adjustments for confounders, the rs10033601 and rs2292743 SNPs were still independent risk factors for T2DM [GA vs AA + GG: odds ratio = 1.35, 95% confidence interval (CI) = 1.12–1.64, P = 0.002; TA vs TT + AA: OR = 1.28, 95% CI = 1.06–1.55, P = 0.011]. Participants within the Chinese Uygur populations and who with the GA genotype of rs10033601 and the TA genotype of rs2292743 were associated with significantly elevated glucose levels.

Conclusions

Our study revealed that both rs10033601 and rs2292743 of the FBXW7 gene were associated with T2DM in the Uygur populations in Xinjiang.

The FBXW7-NOTCH interactome: A ubiquitin proteasomal system-induced crosstalk modulating oncogenic transformation in human tissues

BACKGROUND

Ubiquitin ligases or E3 ligases are well programmed to regulate molecular interactions that operate at a post-translational level. Skp, Cullin, F-box containing complex (or SCF complex) is a multidomain E3 ligase known to mediate the degradation of a wide range of proteins through the proteasomal pathway. The three-dimensional domain architecture of SCF family proteins suggests that it operates through a novel and adaptable "super-enzymatic" process that might respond to targeted therapeutic modalities in cancer.

RECENT FINDINGS

Several F-box containing proteins have been characterized either as tumor suppressors (FBXW8, FBXL3, FBXW8, FBXL3, FBXO1, FBXO4, and FBXO18) or as oncogenes (FBXO5, FBXO9, and SKP2). Besides, F-box members like βTrcP1 and βTrcP2, the ones with context-dependent functionality, have also been studied and reported. FBXW7 is a well-studied F-box protein and is a tumor suppressor. FBXW7 regulates the activity of a range of substrates, such as c-Myc, cyclin E, mTOR, c-Jun, NOTCH, myeloid cell leukemia sequence-1 (MCL1), AURKA, NOTCH through the well-known ubiquitin-proteasome system (UPS)-mediated degradation pathway. NOTCH signaling is a primitive pathway that plays a crucial role in maintaining normal tissue homeostasis. FBXW7 regulates NOTCH protein activity by controlling its half-life, thereby maintaining optimum protein levels in tissue. However, aberrations in the FBXW7 or NOTCH expression levels can lead to poor prognosis and detrimental outcomes in patients. Therefore, the FBXW7-NOTCH axis has been a subject of intense study and research over the years, especially around the interactome's role in driving cancer development and progression. Several studies have reported the effect of FBXW7 and NOTCH mutations on normal tissue behavior. The current review attempts to critically analyze these mutations prognostic value in a wide range of tumors. Furthermore, the review summarizes the recent findings pertaining to the FBXW7 and NOTCH interactome and its involvement in phosphorylation-related events, cell cycle, proliferation, apoptosis, and metastasis.

CONCLUSION

The review concludes by positioning FBXW7 as an effective diagnostic marker in tumors and by listing out recent advancements made in cancer therapeutics in identifying protocols targeting the FBXW7-NOTCH aberrations in tumors.

FBW7-NRA41-SCD1 axis synchronously regulates apoptosis and ferroptosis in pancreatic cancer cells

FBW7 functions as a tumor suppressor by targeting oncoproteins for degradation. Our previous study found FBW7 was low expressed in pancreatic cancer due to sustained activation of Ras-Raf-MEK-ERK pathway, which destabilized FBW7 by phosphorylating at Thr205. MicroPET/CT imaging results revealed that FBW7 substantially decreased 18F-fluorodeoxyglucose uptake in xenograft tumors. Mechanistically, FBW7 inhibited glucose metabolism via c-Myc/TXNIP axis. But in these studies, we observed FBW7 down-regulated genes were widely involved in redox reaction and lipid metabolism. Here we reanalyzed previous gene expression profiling and conducted targeted cell metabolites analysis. Results revealed that FBW7 regulated lipid peroxidation and promoted ferroptosis, a non-apoptotic form of cell death. Mechanistically, we found FBW7 inhibited the expression of stearoyl-CoA desaturase (SCD1) via inhibiting nuclear receptor subfamily 4 group A member 1 (NR4A1). SCD1 was reported to inhibit both ferroptosis and apoptosis, which was consistent with the function of FBW7 and NR4A1, another FBW7 down-regulated gene in the gene expression profiling. Moreover, FBW7 potentiated cytotoxic effect of gemcitabine via activating ferroptosis and apoptosis. Combination ferroptosis inducers and apoptosis activators could also significantly potentiated cytotoxic effect of gemcitabine in pancreatic cancer. Therefore, our findings might provide new strategies for the comprehensive treatment of pancreatic cancer.

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Ferroptosis possesses great potential in pancreatic cancer therapy.

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FBW7 synchronously induces apoptosis and ferroptosis.

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Activation of apoptosis and ferroptosis potentiates cytotoxic effect of gemcitabine.

Loss of Fbxw7 Impairs Development of and Induces Heterogeneous Tumor Formation in the Mouse Mammary Gland

Fbxw7 is an F-box protein that contributes to regulation of cell proliferation and cell fate determination as well as to tumor suppression in various tissues. In this study, we generated mice with mammary gland-specific ablation of Fbxw7 (Blg-Cre/Fbxw7 ^F/F mice) and found that most neonates born to mutant dams die soon after birth as a result of defective maternal lactation. The mammary gland of mutant dams was markedly atrophic and manifested both excessive cell proliferation and apoptosis in association with the accumulation of Notch1 and p63. Despite the hypoplastic nature of the mutant mammary gland, Blg-Cre/Fbxw7 ^F/F mice spontaneously developed mammary tumors that resembled basal-like carcinoma with marked intratumoral heterogeneity. Additional inactivation of Trp53 in Blg-Cre/Fbxw7 ^F/F mice further promoted onset and development of mammary tumors, suggesting that spontaneous mutation of Trp53 may facilitate transition of hypoplastic mammary lesions to aggressive cancer in mice lacking Fbxw7. RNA-sequencing analysis of epithelial- and mesenchymal-like cell lines from a Blg-Cre/Fbxw7 ^F/F mouse tumor revealed an increased mutation rate and structural alterations in the tumor and differential expression of upstream transcription factors including known targets of Fbxw7. Together, our results implicate Fbxw7 in the regulation of cell differentiation and in tumor suppression in the mammary gland. Loss of Fbxw7 increases mutation rate and chromosome instability, activates signaling pathways governed by transcription factors regulated by Fbxw7, and triggers the development of mammary tumors with prominent heterogeneity. SIGNIFICANCE: Mammary gland-specific ablation of Fbxw7 in mice results in defective gland development and spontaneous mammary tumor formation reminiscent of human basal-like carcinoma with intratumoral heterogeneity. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/80/24/5515/F1.large.jpg.

Diverse and pivotal roles of neddylation in metabolism and immunity

Neddylation is one type of protein post-translational modification by conjugating a ubiquitin-like protein neural precursor cell-expressed developmentally downregulated protein 8 to substrate proteins via a cascade involving E1, E2, and E3 enzymes. The best-characterized substrates of neddylation are cullins, essential components of cullin-RING E3 ubiquitin-ligase complexes. The discovery of noncullin neddylation targets indicates that neddylation may have diverse biological functions. Indeed, neddylation has been implicated in various cellular processes including cell cycle progression, metabolism, immunity, and tumorigenesis. Here, we summarized the reported neddylation substrates and also discuss the functions of neddylation in the immune system and metabolism.

Myeloid FBW7 deficiency disrupts redox homeostasis and aggravates dietary-induced insulin resistance

The E3 ubiquitin ligase FBW7 plays critical roles in multiple pathological and physiological processes. Here, we report that after high-fat diet (HFD) feeding for 16 weeks, myeloid-specific FBW7-deficient mice demonstrate increased redox stress, inflammatory responses and insulin resistance. Macrophages activation under FBW7 deficiency decreases substrate flux through the pentose phosphate pathway (PPP) to produce less equivalents (NADPH and GSH) and aggravate the generation of intracellular reactive oxygen species (ROS) in macrophages, thereby over-activating proinflammatory reaction. Mechanistically, we identify that pyruvate kinase muscle isozyme M2 (PKM2) is a new bona fide ubiquitin substrate of SCF^FBW7. While challenged with HFD stress, pharmacological inhibition of PKM2 protects FBW7-deficient macrophages against production of ROS, proinflammatory reaction and insulin resistance. Intriguingly, we further find an inverse correlation between FBW7 level and relative higher H₂O₂ level and the severity of obesity-related diabetes. Overall, the results suggest that FBW7 can play a crucial role in modulating inflammatory response through maintaining the intracellular redox homeostasis during HFD insults.

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Myeloid FBW7 deficiency aggravates HFD-induced oxidative stress, inflammation and insulin resistance.

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PKM2 is a new bona fide ubiquitin substrate of SCF^FBW7.

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FBW7 divert glycolysis to combat oxidative stress via PKM2 in macrophages.

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FBW7 expression inversely correlates with ROS level to govern obesity-related metabolic disorder.

FBXW7 promotes pathological cardiac hypertrophy by targeting EZH2-SIX1 signaling

F-box and WD repeat domain-containing 7 (FBXW7) is an E3-ubiquitin ligase, which serves as one of the components of the SKP1, CUL1, and F-box protein type ubiquitin ligase (SCF) complex. Previous studies reveal that FBXW7 participates in cancer, inflammation and Parkinson's disease. FBXW7 also contributes to angiogenesis of endothelial cells. However, the function of FBXW7 in cardiac homeostasis remains to elucidate. Here we identified the critical role of FBXW7 during cardiac hypertrophy in humans and rodents. Quantitative real-time PCR (qRT-PCR) and Western blot revealed that the mRNA and protein levels of FBXW7 were upregulated significantly in hypertrophic hearts in human and mouse as well as Angiotensin II (Ang II)-induced hypertrophic neonatal rat cardiomyocytes (NRCM). Gain-of-function (adenovirus) and loss-of-function (siRNA) experiments provided evidence that FBXW7 promoted Ang II-induced cardiomyocyte hypertrophy as demonstrated by the increase in the size of cardiomyocytes and overexpression of hypertrophic fetal genes myosin heavy chain 7 (Myh7) natriuretic peptide a (Nppa), brain natriuretic peptide (Nppb). Further mechanism study revealed that FBXW7 promoted the expression of sine oculis homeobox homolog 1 (SIX1) in cardiomyocytes, which relied on regulation of the stability of the histone methyltransferase EZH2 (Enhancer of zeste homolog 2). Previous work revealed the pro-hypertrophic role of the EZH2-SIX1 axis in rodents. Indeed, our genetic and pharmacological evidence showed that the EZH2-SIX1 signaling was critically involved in FBXW7 functions in Ang II-induced cardiomyocyte hypertrophy. Therefore, we identified FBWX7 as an important regulator of cardiac hypertrophy via modulating the EZH2-SIX1 axis.

Recent insight into the role of FBXW7 as a tumor suppressor

FBXW7 (also known as Fbw7, Sel10, hCDC4, or hAgo) is a tumor suppressor and the most frequently mutated member of the F-box protein family in human cancers. FBXW7 functions as the substrate recognition component of an SCF-type E3 ubiquitin ligase. It specifically controls the proteasome-mediated degradation of many oncoproteins such as c-MYC, NOTCH, KLF5, cyclin E, c-JUN, and MCL1. In this review, we summarize the molecular and biological features of FBXW7 and its substrates as well as the impact of mutations of FBXW7 on cancer development. We also address the clinical potential of anticancer therapy targeting FBXW7.

Regulation of Stem Cells by Cullin-RING Ligase

Stem cells can remain quiescent, self-renewal, and differentiate into many types of cells and even cancer stem cells. The coordination of these complex processes maintains the homeostasis of the organism. Ubiquitination is an important posttranslational modification process that regulates protein stability and activity. The ubiquitination levels of stem cell-associated proteins are closely related with stem cell characteristics. Cullin-RING Ligases (CRLs) are the largest family of E3 ubiquitin ligases, accounting for approximately 20% of proteins degraded by proteasome. In this review, we discuss the role of CRLs in stem cell homeostasis, self-renewal, and differentiation and expound their ubiquitination substrates. In addition, we also discuss the effect of CRLs on the formation of cancer stem cells that may provide promising therapy strategies for cancer.

Knockout Mouse Models Provide Insight into the Biological Functions of CRL1 Components

The CRL1 complex, also known as the SCF complex, is a ubiquitin ligase that in mammals consists of an adaptor protein (SKP1), a scaffold protein (CUL1), a RING finger protein (RBX1, also known as ROC1), and one of about 70 F-box proteins. Given that the F-box proteins determine the substrate specificity of the CRL1 complex, the variety of these proteins allows the generation of a large number of ubiquitin ligases that promote the degradation or regulate the function of many substrate proteins and thereby control numerous key cellular processes. The physiological and pathological functions of these many CRL1 ubiquitin ligases have been studied by the generation and characterization of knockout mouse models that lack specific CRL1 components. In this chapter, we provide a comprehensive overview of these mouse models and discuss the role of each CRL1 component in mouse physiology and pathology.

Targeting SCF E3 Ligases for Cancer Therapies

SKP1-cullin-1-F-box-protein (SCF) E3 ubiquitin ligase complex is responsible for the degradation of proteins in a strictly regulated manner, through which it exerts pivotal roles in regulating various key cellular processes including cell cycle and division, apoptosis, and differentiation. The substrate specificity of the SCF complex largely depends on the distinct F-box proteins, which function in either tumor promotion or suppression or in a context-dependent manner. Among the 69 F-box proteins identified in human genome, FBW7, SKP2, and β-TRCP have been extensively investigated among various types of cancer in respective of their roles in cancer development, progression, and metastasis. Moreover, several specific inhibitors have been developed to target those E3 ligases, and their efficiency in tumors has been determined. In this review, we provide a summary of the roles of SCF E3 ligases in cancer development, as well as the potential application of miRNA or specific inhibitors for cancer therapy.

F-box/WD Repeat-Containing Protein 5 Mediates the Ubiquitination of Apoptosis Signal-Regulating Kinase 1 and Exacerbates Nonalcoholic Steatohepatitis in Mice

Inhibition of apoptosis signal-regulating kinase 1 (ASK1) activation has emerged as a promising target for the treatment of nonalcoholic steatohepatitis (NASH). Multiple forms of posttranslational modifications determine the activity of ASK1. In addition to phosphorylation, recent studies revealed that ubiquitination is essential for ASK1 activation. However, the endogenous factor that regulates ASK1 ubiquitination and activation remains poorly defined. In this study, we identified the E3 ligase Skp1-Cul1-F-box (SCF) protein F-box/WD repeat-containing protein 5 (FBXW5) as a key endogenous activator of ASK1 ubiquitination. FBXW5 is the central component of the SCF complex (SCF^Fbxw5 ) that directly interacts with and ubiquitinates ASK1 in hepatocytes during NASH development. An in vivo study showed that hepatocyte-specific overexpression of FBXW5 exacerbated diet-induced systemic and hepatic metabolic disorders, as well as the activation of ASK1-related mitogen-activated protein kinase (MAPK) signaling in the liver. Conversely, hepatocyte-specific deletion of FBXW5 significantly prevented the progression of these abnormalities. Mechanically, FBXW5 facilitated the addition of Lys63-linked ubiquitin to ASK1 and thus exacerbated ASK1-c-Jun N-terminal kinase/p38 MAPK signaling, inflammation, and lipid accumulation. Furthermore, we demonstrated that the N-terminus (S1) and C-terminus (S3) of FBXW5 respectively and competitively ablate the function of FBXW5 on ASK1 activation and served as effective inhibitors of NASH progression. Conclusion: This evidence strongly suggests that SCF^Fbxw5 is an important activator of ASK1 ubiquitination in the context of NASH. The development of FBXW5(S1) or FBXW5(S3)-mimicking drugs and screening of small-molecular inhibitors specifically abrogating ASK1 ubiquitination-dependent activation are viable approaches for NASH treatment.

The epigenetic regulator SIRT6 protects the liver from alcohol-induced tissue injury by reducing oxidative stress in mice

BACKGROUND & AIMS

As a nicotinamide adenine dinucleotide-dependent deacetylase and a key epigenetic regulator, sirtuin 6 (SIRT6) has been implicated in the regulation of metabolism, DNA repair, and inflammation. However, the role of SIRT6 in alcohol-related liver disease (ALD) remains unclear. The aim of this study was to investigate the function and mechanism of SIRT6 in ALD pathogenesis.

METHODS

We developed and characterized Sirt6 knockout (KO) and transgenic mouse models that were treated with either control or ethanol diet. Hepatic steatosis, inflammation, and oxidative stress were analyzed using biochemical and histological methods. Gene regulation was analyzed by luciferase reporter and chromatin immunoprecipitation assays.

RESULTS

The Sirt6 KO mice developed severe liver injury characterized by a remarkable increase of oxidative stress and inflammation, whereas the Sirt6 transgenic mice were protected from ALD via normalization of hepatic lipids, inflammatory response, and oxidative stress. Our molecular analysis has identified a number of novel Sirt6-regulated genes that are involved in antioxidative stress, including metallothionein 1 and 2 (Mt1 and Mt2). Mt1/2 genes were downregulated in the livers of Sirt6 KO mice and patients with alcoholic hepatitis. Overexpression of Mt1 in the liver of Sirt6 KO mice improved ALD by reducing hepatic oxidative stress and inflammation. We also identified a critical link between SIRT6 and metal regulatory transcription factor 1 (Mtf1) via a physical interaction and functional coactivation. Mt1/2 promoter reporter assays showed a strong synergistic effect of SIRT6 on the transcriptional activity of Mtf1.

CONCLUSIONS

Our data suggest that SIRT6 plays a critical protective role against ALD and it may serve as a potential therapeutic target for ALD.

LAY SUMMARY

The liver, the primary organ for ethanol metabolism, can be damaged by the byproducts of ethanol metabolism, including reactive oxygen species. In this study, we have identified a key epigenetic regulator SIRT6 that plays a critical role in protecting the liver from oxidative stress-induced liver injury. Thus, our data suggest that SIRT6 may be a potential therapeutic target for alcohol-related liver disease.

Ubiquitin Ligases Involved in the Regulation of Wnt, TGF-β, and Notch Signaling Pathways and Their Roles in Mouse Development and Homeostasis

The Wnt, TGF-β, and Notch signaling pathways are essential for the regulation of cellular polarity, differentiation, proliferation, and migration. Differential activation and mutual crosstalk of these pathways during animal development are crucial instructive forces in the initiation of the body axis and the development of organs and tissues. Due to the ability to initiate cell proliferation, these pathways are vulnerable to somatic mutations selectively producing cells, which ultimately slip through cellular and organismal checkpoints and develop into cancer. The architecture of the Wnt, TGF-β, and Notch signaling pathways is simple. The transmembrane receptor, activated by the extracellular stimulus, induces nuclear translocation of the transcription factor, which subsequently changes the expression of target genes. Nevertheless, these pathways are regulated by a myriad of factors involved in various feedback mechanisms or crosstalk. The most prominent group of regulators is the ubiquitin-proteasome system (UPS). To open the door to UPS-based therapeutic manipulations, a thorough understanding of these regulations at a molecular level and rigorous confirmation in vivo are required. In this quest, mouse models are exceptional and, thanks to the progress in genetic engineering, also an accessible tool. Here, we reviewed the current understanding of how the UPS regulates the Wnt, TGF-β, and Notch pathways and we summarized the knowledge gained from related mouse models.

Mouse Models for Diseases in the Cholangiocyte Lineage

Cholangiopathies are an important group of liver diseases affecting the biliary system, and the purpose of this review is to describe how diseases in the biliary system can be studied in mouse models. A particular focus is placed on mouse models for Alagille syndrome, a cholangiopathy with a strong genetic link to dysfunctional Notch signaling. Recently, a number of different genetic mouse models based on various manipulations of the Notch signaling pathway have been generated to study Alagille syndrome, and we discuss the resulting phenotypes, and possible causes for the phenotypic heterogeneity among the various models. In the final section, we provide a more general discussion on how well mouse models can be expected to mimic human liver disease, as well as an outlook toward the need for new technologies that can help us to gain new insights from mouse models for liver disease.

Exposure to PM2.5 affects blood lipid levels in asthmatic rats through notch signaling pathway

BACKGROUND

Epidemiological studies have confirmed atmospheric PM_2.5 could affect asthma, and dyslipidemia may be related to pathogenesis of asthma. Recent studies show Notch ligands had lipid combination domains which are responsible for regulating lipid levels. However, the effect of PM_2.5 on asthmatic rats' lipid levels and the role of Notch signaling pathway is unclear.

METHODS

Rats were treat with ovalbumin (OVA) to establish asthma models. Notch signaling pathway inhibitor (DAPT) was injected intraperitoneally. Asthmatic and healthy rats were exposed to different concentrations of PM_2.5. Lung tissues were collected and the expression of Hes1 protein was detected by Western Blot. Blood samples were collected to detect the serum lipid levels.

RESULTS

Hes1 expression levels in healthy and asthma pathway inhibition groups were lower than those in control groups. Compared with control group, rats exposed to PM_2.5 in middle and high dose, the levels of TG and TC were decreased. Similar results were observed after exposure to the same concentration of PM_2.5 in asthmatic rats. Rats, which were exposed to PM_2.5 after being established the asthma model successfully, could exhibit more significant dyslipidemia than those with direct exposure. After Notch signaling pathway inhibited, TC and LDL in asthma pathway inhibition group were lower than those in healthy group.

CONCLUSIONS

PM_2.5 can affect the lipid levels of asthmatic rats through the Notch signaling pathway.

Fbxw7 increases CCL2/7 in CX3CR1hi macrophages to promote intestinal inflammation

Resident and inflammatory mononuclear phagocytes (MPh) with functional plasticity in the intestine are critically involved in the pathology of Inflammatory Bowel Diseases (IBD), in which the mechanism remains incompletely understood. In the present study, we found that increased expression of E3 ligase FBXW7 in the inflamed intestine was significantly correlated to IBD severity in both human diseases and mice model. Myeloid-Fbxw7 deficiency protected mice from dextran sodium sulfate (DSS) and 2,6,4-trinitrobenzene sulfonic acid (TNBS) induced colitis. Fbxw7 deficiency resulted in decreased production of chemokines CCL2 and CCL7 by colonic CX3CR1hi resident macrophages and reduced accumulation of CX3CR1int pro-inflammatory MPh in colitis colon tissue. Mice received AAV-shFbxw7 administration showed significantly improved survival rate and alleviated colitis. Mechanisms screening demonstrated that FBXW7 suppresses H3K27me3 modification and promotes Ccl2 and Ccl7 expression via degradation of histone-lysine N-methyltransferase EZH2 in macrophages. Taken together, our results indicate that FBXW7 degrades EZH2 and increases Ccl2/Ccl7 in CX3CR1hi macrophages, which promotes the recruiting CX3CR1int pro-inflammatory MPh into local colon tissues with colitis. Targeting FBXW7 might represent a potential therapeutic approach for intestine inflammation intervention.

FBXW7 suppresses HMGB1-mediated innate immune signaling to attenuate hepatic inflammation and insulin resistance in a mouse model of nonalcoholic fatty liver disease

Background

Innate immune dysfunction contributes to the development and progression of nonalcoholic fatty liver disease (NAFLD), however, its pathogenesis is still incompletely understood. Identifying the key innate immune component responsible for the pathogenesis of NAFLD and clarifying the underlying mechanisms may provide therapeutic targets for NAFLD. Recently, F-box- and WD repeat domain-containing 7 (FBXW7) exhibits a regulatory role in hepatic glucose and lipid metabolism. This study aims to investigate whether FBXW7 controls high-mobility group box 1 protein (HMGB1)-mediated innate immune signaling to improve NAFLD and the mechanism underlying this action.

Methods

Mice were fed a high-fat diet (HFD) for 12 or 20 weeks to establish NAFLD model. Hepatic overexpression or knockdown of FBXW7 was induced by tail-vein injection of recombinant adenovirus. Some Ad-FBXW7-injected mice fed a HFD were injected intraperitoneally with recombinant mouse HMGB1 to confirm the protective role of FBXW7 in NAFLD via inhibition of HMGB1.

Results

FBXW7 improves NAFLD and related metabolic parameters without remarkable influence of body weight and food intake. Moreover, FBXW7 markedly ameliorated hepatic inflammation and insulin resistance in the HFD-fed mice. Furthermore, FBXW7 dramatically attenuated the expression and release of HMGB1 in the livers of HFD-fed mice, which is associated with inhibition of protein kinase R (PKR) signaling. Thereby, FBXW7 restrains Toll-like receptor 4 (TLR4) and receptor for advanced glycation end products (RAGE) signaling in HFD-fed mouse livers. In addition, exogenous HMGB1 treatment abolished FBXW7-mediated inhibition of hepatic inflammation and insulin resistance in HFD-fed mouse livers.

Conclusions

Our results demonstrate a protective role of FBXW7 in NAFLD by abating HMGB1-mediated innate immune signaling to suppress inflammation and consequent insulin resistance, suggesting that FBXW7 is a potential target for therapeutic intervention in NAFLD development.

Electronic supplementary material

The online version of this article (10.1186/s10020-019-0099-9) contains supplementary material, which is available to authorized users.

The subunit assembly state of the Mediator complex is nutrient-regulated and is dysregulated in a genetic model of insulin resistance and obesity

The Mediator complex plays a critical role in the regulation of transcription by linking transcription factors to RNA polymerase II. By examining mouse livers, we have found that in the fasted state, the Mediator complex exists primarily as an approximately 1.2-MDa complex, consistent with the size of the large Mediator complex, whereas following feeding, it converts to an approximately 600-kDa complex, consistent with the size of the core Mediator complex. This dynamic change is due to the dissociation and degradation of the kinase module that includes the MED13, MED12, cyclin-dependent kinase 8 (CDK8), and cyclin C (CCNC) subunits. The dissociation and degradation of the kinase module are dependent upon nutrient activation of mTORC1 that is necessary for the induction of lipogenic gene expression because pharmacological or genetic inhibition of mTORC1 in the fed state restores the kinase module. The degradation but not dissociation of the kinase module depends upon the E3 ligase, SCFFBW7 In addition, genetically insulin-resistant and obese db/db mice in the fasted state displayed elevated lipogenic gene expression and loss of the kinase module that was reversed following mTORC1 inhibition. These data demonstrate that the assembly state of the Mediator complex undergoes physiologic regulation during normal cycles of fasting and feeding in the mouse liver. Furthermore, the assembly state of the Mediator complex is dysregulated in states of obesity and insulin resistance.

Notch pathway deactivation mediated by F-box/WD repeat domain-containing 7 ameliorates hydrogen peroxide-induced apoptosis in rat periodontal ligament stem cells

OBJECTIVE

To investigate the protective role of F-box/WD repeat domain-containing 7 in rat periodontal ligament stem cells under oxidative stress.

MATERIALS AND METHODS

The apoptosis of rat periodontal ligament stem cells was induced by exposure to various concentrations of hydrogen peroxide for 24 h, after which cell viability and the cleaved caspase-3 and -9 levels were determined. The levels of proteins in the Notch signaling pathway were determined by western blotting.

RESULTS

The overexpression of F-box/WD repeat domain-containing 7 increased cell viability following hydrogen peroxide administration and suppressed the activation of caspases-3 and -9. The overexpression of F-box/WD repeat domain-containing 7 inhibited Notch signaling. Furthermore, the protective effect of F-box/WD repeat domain-containing 7 could be resumed by PF-03084014, a Notch-specific inhibitor.

CONCLUSIONS

These observations suggest a protective role of F-box/WD repeat domain-containing 7 against hydrogen peroxide-induced oxidative stress in rat periodontal ligament stem cells. These findings will facilitate the in vitro culturing of periodontal ligament stem cell for clinical usage and promote stem cell-based therapy for periodontal tissue regeneration.

FBXW7 regulates endothelial barrier function by suppression of the cholesterol synthesis pathway and prenylation of RhoB

Rho GTPases control both the actin cytoskeleton and adherens junction stability and are recognized as essential regulators of endothelial barrier function. They act as molecular switches and are primarily regulated by the exchange of GDP and GTP. However, posttranslational modifications such as phosphorylation, prenylation, and ubiquitination can additionally alter their localization, stability, and activity. F-box proteins are involved in the recognition of substrate proteins predestined for ubiquitination and subsequent degradation. Given the importance of ubiquitination, we studied the effect of the loss of 62 members of the F-box protein family on endothelial barrier function in human umbilical vein endothelial cells. Endothelial barrier function was quantified by electrical cell impedance sensing and macromolecule passage assay. Our RNA interference–based screen identified FBXW7 as a key regulator of endothelial barrier function. Mechanistically, loss of FBXW7 induced the accumulation of the RhoB GTPase in endothelial cells, resulting in their increased contractility and permeability. FBXW7 knockdown induced activation of the cholesterol biosynthesis pathway and changed the prenylation of RhoB. This effect was reversed by farnesyl transferase inhibitors and by the addition of geranylgeranyl pyrophosphate. In summary, this study identifies FBXW7 as a novel regulator of endothelial barrier function in vitro. Loss of FBXW7 indirectly modulates RhoB activity via alteration of the cholesterol biosynthesis pathway and, consequently, of the prenylation status and activity of RhoB, resulting in increased contractility and disruption of the endothelial barrier.

Hdac1 Regulates Differentiation of Bipotent Liver Progenitor Cells During Regeneration via Sox9b and Cdk8

BACKGROUND & AIMS

Upon liver injury in which hepatocyte proliferation is compromised, liver progenitor cells (LPCs), derived from biliary epithelial cells (BECs), differentiate into hepatocytes. Little is known about the mechanisms of LPC differentiation. We used zebrafish and mouse models of liver injury to study the mechanisms.

METHODS

We used transgenic zebrafish, Tg(fabp10a:CFP-NTR), to study the effects of compounds that alter epigenetic factors on BEC-mediated liver regeneration. We analyzed zebrafish with disruptions of the histone deacetylase 1 gene (hdac1) or exposed to MS-275 (an inhibitor of Hdac1, Hdac2, and Hdac3). We also analyzed zebrafish with mutations in sox9b, fbxw7, kdm1a, and notch3. Zebrafish larvae were collected and analyzed by whole-mount immunostaining and in situ hybridization; their liver tissues were collected for quantitative reverse transcription polymerase chain reaction. We studied mice in which hepatocyte-specific deletion of β-catenin (Ctnnb1^flox/flox mice injected with Adeno-associated virus serotype 8 [AAV8]-TBG-Cre) induces differentiation of LPCs into hepatocytes after a choline-deficient, ethionine-supplemented (CDE) diet. Liver tissues were collected and analyzed by immunohistochemistry and immunoblots. We performed immunohistochemical analyses of liver tissues from patients with compensated or decompensated cirrhosis or acute on chronic liver failure (n = 15).

RESULTS

Loss of Hdac1 activity in zebrafish blocked differentiation of LPCs into hepatocytes by increasing levels of sox9b mRNA and reduced differentiation of LPCs into BECs by increasing levels of cdk8 mRNA, which encodes a negative regulator gene of Notch signaling. We identified Notch3 as the receptor that regulates differentiation of LPCs into BECs. Loss of activity of Kdm1a, a lysine demethylase that forms repressive complexes with Hdac1, produced the same defects in differentiation of LPCs into hepatocytes and BECs as observed in zebrafish with loss of Hdac1 activity. Administration of MS-275 to mice with hepatocyte-specific loss of β-catenin impaired differentiation of LPCs into hepatocytes after the CDE diet. HDAC1 was expressed in reactive ducts and hepatocyte buds of liver tissues from patients with cirrhosis.

CONCLUSIONS

Hdac1 regulates differentiation of LPCs into hepatocytes via Sox9b and differentiation of LPCs into BECs via Cdk8, Fbxw7, and Notch3 in zebrafish with severe hepatocyte loss. HDAC1 activity was also required for differentiation of LPCs into hepatocytes in mice with liver injury after the CDE diet. These pathways might be manipulated to induce LPC differentiation for treatment of patients with advanced liver diseases.

Sex-specific differences in hepatic steatosis in obese spontaneously hypertensive (SHROB) rats

Background

Patients with metabolic syndrome, who are characterized by co-existence of insulin resistance, hypertension, hyperlipidemia, and obesity, are also prone to develop non-alcoholic fatty liver disease (NAFLD). Although the prevalence and severity of NAFLD is significantly greater in men than women, the mechanisms by which gender modulates the pathogenesis of hepatic steatosis are poorly defined. The obese spontaneously hypertensive (SHROB) rats represent an attractive model of metabolic syndrome without overt type 2 diabetes. Although pathological manifestation caused by the absence of a functional leptin receptor has been extensively studied in SHROB rats, it is unknown whether these animals elicited sex-specific differences in the development of hepatic steatosis.

Methods

We compared hepatic pathology in male and female SHROB rats. Additionally, we examined key biochemical and molecular parameters of signaling pathways linked with hyperinsulinemia and hyperlipidemia. Finally, using methods of quantitative polymerase chain reaction (qPCR) and western blot analysis, we quantified expression of 45 genes related to lipid biosynthesis and metabolism in the livers of male and female SHROB rats.

Results

We show that all SHROB rats developed hepatic steatosis that was accompanied by enhanced expression of SREBP1, SREBP2, ACC1, and FASN proteins. The livers of male rats also elicited higher induction of Pparg, Ppara, Slc2a4, Atox1, Skp1, Angptl3, and Pnpla3 mRNAs. In contrast, the livers of female SHROB rats elicited constitutively higher levels of phosphorylated JNK and AMPK and enhanced expression of Cd36.

Conclusion

Based on these data, we conclude that the severity of hepatic steatosis in male and female SHROB rats was mainly driven by increased de novo lipogenesis. Moreover, male and female SHROB rats also elicited differential severity of hepatic steatosis that was coupled with sex-specific differences in fatty acid transport and esterification.

Electronic supplementary material

The online version of this article (10.1186/s13293-018-0202-x) contains supplementary material, which is available to authorized users.

Hepatic F-Box Protein FBXW7 Maintains Glucose Homeostasis Through Degradation of Fetuin-A

Type 2 diabetes mellitus (T2DM) has become one of the most serious and long-term threats to human health. However, the molecular mechanism that links obesity to insulin resistance remains largely unknown. Here, we show that F-box and WD repeat domain-containing 7 (FBXW7), an E3 ubiquitin protein ligase, is markedly downregulated in the liver of two obese mouse models and obese human subjects. We further identify a functional low-frequency human FBXW7 coding variant (p.Ala204Thr) in the Chinese population, which is associated with elevated blood glucose and T2DM risk. Notably, mice with liver-specific knockout of FBXW7 develop hyperglycemia, glucose intolerance, and insulin resistance even on a normal chow diet. Conversely, overexpression of FBXW7 in the liver not only prevents the development of high-fat diet-induced insulin resistance but also attenuates the disease signature of obese mice. Mechanistically, FBXW7 directly binds to hepatokine fetuin-A to induce its ubiquitination and subsequent proteasomal degradation, comprising an important mechanism maintaining glucose homeostasis. Thus, we provide evidence showing a beneficial role of FBXW7 in glucose homeostasis.

The deubiquitinase USP9X regulates FBW7 stability and suppresses colorectal cancer

The tumor suppressor FBW7 targets oncoproteins such as c-MYC for ubiquitylation and is mutated in several human cancers. We noted that in a substantial percentage of colon cancers, FBW7 protein is undetectable despite the presence of FBW7 mRNA. To understand the molecular mechanism of FBW7 regulation in these cancers, we employed proteomics and identified the deubiquitinase (DUB) USP9X as an FBW7 interactor. USP9X antagonized FBW7 ubiquitylation, and Usp9x deletion caused Fbw7 destabilization. Mice lacking Usp9x in the gut showed reduced secretory cell differentiation and increased progenitor proliferation, phenocopying Fbw7 loss. In addition, Usp9x inactivation impaired intestinal regeneration and increased tumor burden in colitis-associated intestinal cancer. c-Myc heterozygosity abrogated increased progenitor proliferation and tumor burden in Usp9x-deficient mice, suggesting that Usp9x suppresses tumor formation by regulating Fbw7 protein stability and thereby reducing c-Myc. Thus, we identify a tumor suppressor mechanism in the mammalian intestine that arises from the posttranslational regulation of FBW7 by USP9X independent of somatic FBW7 mutations.

Degradation of the endoplasmic reticulum-anchored transcription factor MyRF by the ubiquitin ligase SCFFbxw7 in a manner dependent on the kinase GSK-3

The ubiquitin-proteasome system regulates the abundance of many cellular proteins by mediating their targeted degradation. We previously developed a method-differential proteomics-based identification of ubiquitylation substrates (DiPIUS)-for the comprehensive identification of substrates for a given F-box protein subunit of SCF-type ubiquitin ligases. We have now applied DiPIUS to the F-box protein Fbxw7 in three cell lines (mHepa, Neuro2A, and C2C12) and thereby identified myelin regulatory factor (MyRF), an endoplasmic reticulum-anchored transcription factor that is essential for myelination of nerves in the central nervous system, as a candidate substrate of Fbxw7 specifically in mHepa cells. Co-immunoprecipitation analysis confirmed that the NH₂-terminal cytoplasmic domain of MyRF interacted with Fbxw7 in these cells. Furthermore, an in vitro ubiquitylation assay revealed that MyRF undergoes polyubiquitylation in the presence of purified recombinant SCF^Fbxw7 In addition, the stability of MyRF in mHepa cells was increased by mutation of a putative phosphodegron sequence or by exposure of the cells to an inhibitor of glycogen synthase kinase-3 (GSK-3). We found that MyRF mRNA is not restricted to the central nervous system but is instead distributed widely among mouse tissues. Furthermore, with the use of RNA sequencing in mHepa cells overexpressing or depleted of MyRF, we identified many novel potential target genes of MyRF. Our results thus suggest that Fbxw7 controls the transcription of MyRF target genes in various tissues through regulation of MyRF protein stability in a manner dependent on MyRF phosphorylation by GSK-3.

Physiological functions of FBW7 in cancer and metabolism

FBW7 is one of the most well characterized F-box proteins that serve as substrate recognition subunits of SCF (Skp1-Cullin 1-F-box proteins) E3 ubiquitin ligase complexes. SCF^FBW7 plays key roles in regulating cell cycle progression, differentiation, and stem cell maintenance largely through targeting a broad range of oncogenic substrates for proteasome-dependent degradation. The identification of an increasing number of FBW7 substrates for ubiquitination, and intensive in vitro and in vivo studies have revealed a network of signaling components controlled by FBW7 that contributes to metabolic regulation as well as its tumor suppressor role. Here we mainly focus on recent findings that highlight a critical role for FBW7 in cancer and metabolism.

Establishment and analysis of a novel mouse line carrying a conditional knockin allele of a cancer-specific FBXW7 mutation

F-box and WD40 domain protein 7 (FBXW7) is a component of the SKP1-CUL1-F-box protein (SCF) complex that mediates the ubiquitination of diverse oncogenic target proteins. The exploration of FBXW7 mutations in human primary cancer has revealed three mutation hotspots at conserved arginine residues (Arg⁴⁶⁵, Arg⁴⁷⁹, and Arg⁵⁰⁵) in the WD40 domain, which are critical for substrate recognition. To study the function of human FBXW7^R465C, the most frequent mutation in human malignancies, we generated a novel conditional knockin mouse line of murine Fbxw7^R468C corresponding to human FBXW7^R465C. Systemic heterozygous knockin of the Fbxw7^R468C mutation resulted in perinatal lethality due to defects in lung development, and occasionally caused an eyes-open at birth phenotype and cleft palate. Furthermore, mice carrying liver-specific heterozygous and homozygous Fbxw7^R468C alleles cooperated with an oncogenic Kras mutation to exhibit bile duct hyperplasia within 8 months of birth and cholangiocarcinoma-like lesions within 8 weeks of birth, respectively. In addition, the substrates affected by the mutant Fbxw7 differed between the embryos, embryonic fibroblasts, and adult liver. This novel conditional knockin Fbxw7^R468C line should be useful to gain a more profound understanding of carcinogenesis associated with mutation of FBXW7.

Association of lipid metabolism relevant gene FBXW7 polymorphism with coronary artery disease in Uygur Chinese population in Xinjiang, China: a case-control

BACKGROUND

Hyperlipidemia is a major risk factor for coronary artery disease (CAD). As F-box and WD repeat domain-containing 7 (FBXW7) gene is an important regulating factor for lipid metabolism, the aim of the present study is to assess the association between human FBXW7 gene polymorphisms and CAD among Han Chinese and Uygur Chinese populations in Xinjiang, China.

METHODS

A total of 1,312 Han Chinese (650 CAD patients and 662 controls) and 834 Uygur Chinese (414 CAD patients and 420 controls) were enrolled in this case-control study. Three single nucleotide polymorphisms (SNPs) rs2255137 T>C, rs2292743 A>T, rs35311955 G>C of FBXW7 were selected and genotyped using the improved multiplex ligase detection reaction (iMLDR) method.

RESULTS

We found that the rs2255137 CC genotype was very common in the CAD patients compared with the control subjects in the Uygur Chinese populations. After adjustments for several confounders: age, gender, smoking, drinking, hypertension, diabetes, TG, TC, HDL-C and LDL-C, this association remained significant. Furthermore, we investigated the relationships between rs2255137 genotypes and the circulating serum lipid levels and found that people carrying the C allele of rs2255137 may have higher serum lipid levels in the Uygur Chinese populations.

CONCLUSION

Our results indicate that rs2255137 in FBXW7 gene is associated with CAD in the Uygur Chinese population in China.

Association of genetic variations in the lipid regulatory pathway genes FBXW7 and SREBPs with coronary artery disease among Han Chinese and Uygur Chinese populations in Xinjiang, China

Background

Hyperlipidemia is a major risk factor for coronary artery disease (CAD). The current study was designed to explore the possible correlation between single nucleotide polymorphisms (SNPs) in the lipid homeostasis regulatory genes F-box and WD repeat domain-containing 7 (FBXW7) and sterol regulatory element-binding proteins (SREBPs) with CAD among Han Chinese and Uygur Chinese populations in Xinjiang, China.

Results

In the Uygur Chinese population, rs9902941 in SREBP-1 and rs10033601 in FBXW7 were found to be associated with CAD in a recessive model (TT vs. CT + CC, P = 0.032; GG vs. AG + AA, P = 0.010, respectively), and rs7288536 in SREBP-2 was found to be associated with CAD in an additive model (CT vs. CC + TT, P = 0.045). The difference was statistically significant in the Uygur Chinese population after multivariate adjustments [Odds ratio (OR) = 1.803, 95% confidence interval (CI): 1.036~3.137, P = 0.037; OR = 1.628, 95% CI: 1.080~2.454, P = 0.020; OR = 1.368; and 95% CI: 1.018~1.837, P = 0.037, respectively]. There were also significant interactions between the above-mentioned models in the Uygur Chinese population. However, these relationships were not observed before or after multivariate adjustment in the Han Chinese population.

Materials and Methods

A total of 1,312 Han Chinese (650 CAD patients and 662 controls) and 834 Uygur Chinese (414 CAD patients and 420 controls) were enrolled in this case-control study. Three SNPs (rs9902941 in SREBP-1, rs7288536 in SREBP-2 and rs10033601 in FBXW7) were selected and genotyped using the improved multiplex ligase detection reaction (iMLDR) method.

Conclusions

The results of this study indicate that variations in the lipid regulatory pathway genes FBXW7 and SREBPs (rs9902941 in SREBP-1, rs7288536 in SREBP-2 and rs10033601 in FBXW7) are associated with CAD in the Uygur Chinese population in Xinjiang, China.