Tumor suppressor functions of FBW7 in cancer development and progression

Drugs targeting the particle for arrangement of quaternary structure (PAQosome) and protein complex assembly

INTRODUCTION

The PAQosome is a 12-subunit complex that acts as a co-factor of the molecular chaperones HSP90 and HSP70. This co-chaperone has been shown to participate in assembly and maturation of several protein complexes, including nuclear RNA polymerases, RNA processing factors, the ribosome, PIKKs, and others. Subunits of the PAQosome, adaptors, and clients have been reported to be involved in various diseases, making them interesting targets for drug discovery.

AREA COVERED

In this review, the authors cover the detailed mechanisms of PAQosome and chaperone function. Specifically, the authors summarize the status of the PAQosome and some related chaperones and co-chaperones as candidate targets for drug discovery. Indeed, a number of compounds are currently being tested for the development of treatments against diseases, such as cancers and neurodegenerative conditions.

EXPERT OPINION

Searching for new drugs targeting the PAQosome requires a better understanding of PAQosome subunit interactions and the discovery of new interaction partners. Thus, PAQosome subunit crystallization is an important experiment to initiate virtual screening against new target and the development of in silico tools such as AlphaFold-multimer could accelerate the search for new interaction partner and determine more rapidly the interaction pocket needed for virtual drug screening.

FBXW7 attenuates tumor drug resistance and enhances the efficacy of immunotherapy

FBXW7 (F-box and WD repeat domain containing 7) is a critical subunit of the Skp1-Cullin1-F-box protein (SCF), acting as an E3 ubiquitin ligase by ubiquitinating targeted protein. Through degradation of its substrates, FBXW7 plays a pivotal role in drug resistance in tumor cells and shows the potential to rescue the sensitivity of cancer cells to drug treatment. This explains why patients with higher FBXW7 levels exhibit higher survival times and more favorable prognosis. Furthermore, FBXW7 has been demonstrated to enhance the efficacy of immunotherapy by targeting the degradation of specific proteins, as compared to the inactivated form of FBXW7. Additionally, other F-box proteins have also shown the ability to conquer drug resistance in certain cancers. Overall, this review aims to explore the function of FBXW7 and its specific effects on drug resistance in cancer cells.

Pan-cancer analysis of FBXW family with potential implications in prognosis and immune infiltration

Background

The F-box and WD repeat domain containing (FBXW) family of SCF E3 complexes has 10 members that are responsible for ubiquitination and degradation of substrate proteins involved in cell cycle regulation and tumorigenesis. Among them, FBXW1 (also called b-TrCP1/BTRC) and FBXW7 are the central proteins in this category. However, there is still a lack of elaborate exploration of the contribution of FBXW family members, especially FBXW1 and FBXW7, in various tumor types.

Methods

In this present study, we preliminarily analyzed the genetic structure characteristics of the FBXW family, and systematically investigated their expression patterns and clinical correlations based on the TCGA pan-cancer data. Survival analysis of FBXWs was also conducted through the Kaplan-Meier method. In addition, we assessed their immune infiltration level through immune-related algorithms like Timer and xCell.

Results

There were obvious genetic heterogeneity and different clinical traits in FBXW family members. Moreover, we found that FBXW family genes may be useful in predicting prognosis and therapeutic efficacy using survival analysis. In addition, the immune infiltration of FBXW family was also clearly illustrated in this study. The results showed these genes were closely involved in immune components such as immune score, immune subtypes, tumor-infiltrating lymphocytes and immune checkpoints. Notedly, FBXW1 as an oncogene and FBXW7 as a tumor suppressor gene also show opposite relationships on immune cells.

Conclusion

Our results provided valuable strategies to guide the therapeutic orientation concerning the role of FBXW family genes in cancer.

MECP2 promotes the migration and invasion of gastric cancer cells by modulating the Notch1/c-Myc/mTOR signaling pathways by suppressing FBXW7 transcription

Methyl-CpG-binding protein 2 (MECP2), an epigenetic regulatory factor, promotes the carcinogenesis and progression of a number of cancers. However, its role in the migration and invasion of gastric cancer (GC), as well as the underlying molecular mechanisms, remain unclear. In this study, we found that MECP2 promoted the migration, invasion and metastasis of GC cells. Investigation of the molecular mechanism revealed that MECP2 repressed F-box and WD40 domain protein 7 (FBXW7) transcription in GC by binding to the methylated CpG sites in the FBXW7 promoter region. MECP2 expression was markedly negatively correlated with the FBXW7 level in GC tissues. FBXW7 expression was significantly downregulated in GC tissues and cell lines, and low FBXW7 expression was correlated with unfavorable clinicopathologic features. FBXW7 inhibited cell migration and invasion by regulating the Notch1/c-Myc/mTOR signaling pathways, and knockdown of FBXW7 reversed the effects of silencing MECP2. Moreover, MECP2 upregulated the Notch1/c-Myc/mTOR signaling pathways by inhibiting FBXW7 expression at the transcriptional level. This study demonstrates that MECP2 promotes the migration and invasion of GC cells by modulating the Notch1/c-Myc/mTOR signaling pathways via suppression of FBXW7 transcription. These findings suggest that MECP2 may be a novel effective therapeutic target in GC.

The functions of long noncoding RNAs on regulation of F-box proteins in tumorigenesis and progression

Accumulated evidence has revealed that F-box protein, a subunit of SCF E3 ubiquitin ligase complexes, participates in carcinogenesis and tumor progression via targeting its substrates for ubiquitination and degradation. F-box proteins could be regulated by cellular signaling pathways and noncoding RNAs in tumorigenesis. Long noncoding RNA (lncRNA), one type of noncoding RNAs, has been identified to modulate the expression of F-box proteins and contribute to oncogenesis. In this review, we summarize the role and mechanisms of multiple lncRNAs in regulating F-box proteins in tumorigenesis, including lncRNAs SLC7A11-AS1, MT1JP, TUG1, FER1L4, TTN-AS1, CASC2, MALAT1, TINCR, PCGEM1, linc01436, linc00494, GATA6-AS1, and ODIR1. Moreover, we discuss that targeting these lncRNAs could be helpful for treating cancer via modulating F-box protein expression. We hope our review can stimulate the research on exploration of molecular insight into how F-box proteins are governed in carcinogenesis. Therefore, modulation of lncRNAs is a potential therapeutic strategy for cancer therapy via regulation of F-box proteins.

Targeting matrix metalloproteinases by E3 ubiquitin ligases as a way to regulate the tumor microenvironment for cancer therapy

The tumor microenvironment (TME) plays an important role in neoplastic development. Matrix metalloproteinases (MMPs) are critically involved in tumorigenesis by modulation of the TME and degradation of the extracellular matrix (ECM) in a large variety of malignancies. Evidence has revealed that dysregulated MMPs can lead to ECM damage, the promotion of cell migration and tumor metastasis. The expression and activities of MMPs can be tightly regulated by TIMPs, multiple signaling pathways and noncoding RNAs. MMPs are also finely controlled by E3 ubiquitin ligases. The current review focuses on the molecular mechanism by which MMPs are governed by E3 ubiquitin ligases in carcinogenesis. Due to the essential role of MMPs in oncogenesis, they have been considered the attractive targets for antitumor treatment. Several strategies that target MMPs have been discovered, including the use of small-molecule inhibitors, peptides, inhibitory antibodies, natural compounds with anti-MMP activity, and RNAi therapeutics. However, these molecules have multiple disadvantages, such as poor solubility, severe side-effects and low oral bioavailability. Therefore, it is necessary to discover the novel inhibitors that suppress MMPs for cancer therapy. Here, we discuss the therapeutic potential of targeting E3 ubiquitin ligases to inhibit MMPs. We hope this review will stimulate the discovery of novel therapeutics for the MMP-targeted treatment of a variety of human cancers.

FBXW7 and Its Downstream NOTCH Pathway Could be Potential Indicators of Organ-Free Metastasis in Colorectal Cancer

Colorectal cancer (CRC) is one of the leading causes of cancer-related deaths globally. Metastasis is associated with a poor prognosis, yet the underlying molecular mechanism(s) remained largely unknown. In this study, a total of 85 CRC patients were included and the primary tumor lesions were evaluated by next-generation sequencing using a targeted panel for genetic aberrations. Patients were sub-divided according to their metastasis pattern into the non-organ metastases (Non-OM) and organ metastases (OM) groups. By comparing the genetic differences between the two groups, we found that mutations in FBXW7 and alterations in its downstream NOTCH signaling pathway were more common in the Non-OM group. Moreover, correlation analysis suggested that FBXW7 mutations were independent of other somatic alterations. The negative associations of alterations in FBXW7 and its downstream NOTCH signaling pathway with CRC organ metastasis were validated in a cohort of 230 patients in the TCGA CRC dataset. Thus, we speculated that the genomic alterations of FBXW7/NOTCH axis might be an independent negative indicator of CRC organ metastases.

Mcl-1 inhibition overcomes BET inhibitor resistance induced by low FBW7 expression in breast cancer

While the promise of bromodomains and extraterminal (BET) protein inhibitors (BETis) is emerging in breast cancer (BC) therapy, resistance in these cells to BETis conspicuously curbs their therapeutic potential. FBW7 is an important tumour suppressor. However, the role of FBW7 in BC is not clear. In the current study, our data indicated that the low expression of FBW7 contributes to the drug resistance of BC cells upon JQ1 treatment. shRNA‐mediated FBW7 silencing in FBW7 WT BC cells suppressed JQ1‐induced apoptosis. Mechanistically, it was revealed that this diminished FBW7 level leads to Mcl‐1 stabilization, while Mcl‐1 upregulation abrogates the killing effect of JQ1. Mcl‐1 knockdown or inhibition resensitized the BC cells to JQ1‐induced apoptosis. Moreover, FBW7 knockdown in MCF7 xenografted tumours demonstrated resistance to JQ1 treatment. The combination of JQ1 with a Mcl‐1 inhibitor (S63845) resensitized the FBW7 knockdown tumours to JQ1 treatment in vivo. Our study paves the way for a novel therapeutic potential of BETis with Mcl‐1 inhibitors for BC patients with a low FBW7 expression.

The promotional effect of microRNA-103a-3p in cervical cancer cells by regulating the ubiquitin ligase FBXW7 function

MicroRNAs (miRNAs) have been reported to be involved in the initiation and progression of human tumors including cervical cancer (CC). However, the mechanisms underlying of their actions in CC remain to be fully elucidated. Herein, the differentially expressed miRNAs that were screened based on GSE55940 microarray data retrieved from Gene Expression Omnibus (GEO), and miR-103a-3p was significantly upregulated in CC tissues which was selected as the target miRNA for further research. We also found that high expression of miR-103a-3p was closely associated with histological grades, FIGO stage and distant metastasis as well as reflected poor overall survival. Moreover, miR-103a-3p inhibition decreased the growth capacity of SiHa and HeLa cells by inducing cell apoptosis. And F-box and WD repeat-domain containing protein 7 (FBXW7), a well-known tumor suppressor in many cancer types, was identified as a direct target of miR-103a-3p. It was further found that FBXW7 was significantly downregulated in CC tissues, and it was inversely correlated with miR-103a-3p expression levels. Further investigation demonstrated that FBXW7 upregulation could simulate the roles of miR-103a-3p knockdown in cell viability and apoptosis. Moreover, FBXW7 knockdown efficiently abrogated the influences of CC cells proliferation caused by miR-103a-3p inhibition. Notably, miR-103a-3p could block FBXW7 mediated the downstream transcription factor pathways. Taken together, these findings suggest that miR-103a-3p functions as an oncogene in CC by targeting FBXW7.

Tumor Suppressor FBXW7 and Its Regulation of DNA Damage Response and Repair

The proper DNA damage response (DDR) and repair are the central molecular mechanisms for the maintenance of cellular homeostasis and genomic integrity. The abnormality in this process is frequently observed in human cancers, and is an important contributing factor to cancer development. FBXW7 is an F-box protein serving as the substrate recognition component of SCF (SKP1-CUL1-F-box protein) E3 ubiquitin ligase. By selectively targeting many oncoproteins for proteasome-mediated degradation, FBXW7 acts as a typical tumor suppressor. Recent studies have demonstrated that FBXW7 also plays critical roles in the process of DDR and repair. In this review, we first briefly introduce the processes of protein ubiquitylation by SCF^FBXW7 and DDR/repair, then provide an overview of the molecular characteristics of FBXW7. We next discuss how FBXW7 regulates the process of DDR and repair, and its translational implication. Finally, we propose few future perspectives to further elucidate the role of FBXW7 in regulation of a variety of biological processes and tumorigenesis, and to design a number of approaches for FBXW7 reactivation in a subset of human cancers for potential anticancer therapy.

Upfront treatment with mTOR inhibitor everolimus in pediatric low-grade gliomas: A single-center experience

Pediatric low-grade gliomas (pLGGs) are the most frequent brain tumor in children. Adjuvant treatment, consisting in chemotherapy and radiotherapy, is often necessary if a complete surgical resection cannot be obtained. Traditional treatment approaches result in a significant long-term morbidity, with a detrimental impact on quality of life. Dysregulation of the mitogen-activated protein kinase (MAPK) pathway is the molecular hallmark of pLGGs and hyperactivation of the downstream mammalian target of rapamycin (mTOR) pathway is frequently observed. We report clinical and radiological results of front-line treatment with everolimus in 10 consecutive patients diagnosed with m-TOR positive pLGGs at the Bambino Gesù Children's Hospital in Rome, Italy. Median duration of treatment was 19 months (range from 13-60). Brain magnetic resonance imaging showed stable disease in 7 patients, partial response in 1 and disease progression in 2. Therapy-related adverse events were always reversible after dose reduction or temporary treatment interruption. To the best of our knowledge, this is the first report of everolimus treatment for chemo- and radiotherapy-naïve children with pLGG. Our results provide preliminary support, despite low sample size, for the use of everolimus as target therapy in pLGG showing lack of progression with a manageable toxicity profile.

The tumor suppressor archipelago E3 ligase is required for spermatid differentiation in Drosophila testis

The human orthologue of the tumor suppressor protein FBW7 is encoded by the Drosophila archipelago (ago) gene. Ago is an F-box protein that gives substrate specificity to its SCF ubiquitin ligase complex. It has a central role in multiple biological processes in a tissue-specific manner such as cell proliferation, cellular differentiation, hypoxia-induced gene expression. Here we present a previously unknown tissue-specific role of Ago in spermatid differentiation. We identified a classical mutant of ago which is semi-lethal and male-sterile. During the characterization of ago function in testis, we found that ago plays role in spermatid development, following meiosis. We confirmed spermatogenesis defects by silencing ago by RNAi in testes. The ago mutants show multiple abnormalities in elongating and elongated spermatids, including aberration of the cyst morphology, malformed mitochondrial structures, and individualization defects. Additionally, we determined the subcellular localization of Ago protein with mCherry-Ago transgene in spermatids. Our findings highlight the potential roles of Ago in different cellular processes of spermatogenesis, like spermatid individualization, and regulation of mitochondrial morphology.

The role of post-translational modifications in the regulation of MCL1

Apoptosis is an evolutionarily conserved form of programed cell death (PCD) that has a vital effect on early embryonic development, tissue homeostasis and clearance of damaged cells. Dysregulation of apoptosis can lead to many diseases, such as Alzheimer's disease, cancer, AIDS and heart disease. The anti-apoptotic protein MCL1, a member of the BCL2 family, plays important roles in these physiological and pathological processes. Its high expression is closely related to drug resistances in the treatment of tumor. This review summarizes the structure and function of MCL1, the types of post-translational modifications of MCL1 and their effects on the functions of MCL1, as well as the treatment strategies targeting MCL1 in cancer therapy. The research on the fine regulation of MCL1 will be favorable to the provision of a promising future for the design and screening of MCL1 inhibitors.

Expression levels of FBXW7 and MDM2 E3 ubiquitin ligases and their c-Myc and p53 substrates in patients with dysplastic nevi or melanoma

E3 ubiquitin ligases are of interest as drug targets due to their involvement in the regulation of the functions and interactions of several proteins. Various E3 ligase complexes are considered oncogenes or tumor suppressors associated with the development of melanoma. These proteins regulate the functions of various signaling pathways and proteins, such as p53 and Notch. The aim of the present study was to determine the expression levels of F-box and WD repeat domain-containing 7 (FBXW7), c-Myc, MDM2 and p53 proteins in samples from patients with dysplastic nevi or melanoma, and to evaluate their association with clinicopathological parameters and prognosis of the disease. Paraffin blocks with postoperative material from 100 patients diagnosed with dysplastic moles or melanoma were used in the present study. Tissue microarrays and immunohistochemistry were used to examine FBXW7, c-Myc, MDM2 and p53 protein expression. The results revealed that there was significantly lower FBXW7 expression in advanced melanoma compared with dysplastic nevus, melanoma in situ and stage pT1 melanoma (P<0.001). Additionally, there was a statistically significant association between the expression levels of FBXW7 and the morphological type of the tumor (P<0.001). In addition, there was a strong positive association between FBXW7 expression and the changes in c-Myc expression (P<0.02), and a strong trend was observed between decreased FBXW7 expression and a higher risk of death in patients, with the major factor in patient mortality being the stages of melanoma. Additionally, p53 expression was associated with the depth of melanoma invasion and the morphological type of the tumor. In summary, FBXW7 expression exhibited the highest statistically significant prognostic value and associations with advanced melanoma. As the majority of FBXW7 substrates are oncoproteins, their degradation by FBXW7 may highlight these proteins as potential targets for the treatment of melanoma.

Substitution of Thr572 to Ala in mouse c-Myb attenuates progression of early erythroid differentiation

The expression level of transcription factor c-Myb oscillates during hematopoiesis. Fbw7 promotes ubiquitin-mediated degradation of c-Myb, which is dependent on phosphorylation of Thr572. To investigate the physiological relevance of Fbw7-mediated c-Myb degradation, we generated mutant mice carrying c-Myb-T572A (TA). Homozygous mutant (TA/TA) mice exhibited a reduction in the number of peripheral red blood cells and diminished erythroblasts in bone marrow, presumably as a result of failure during erythroblast differentiation. We found that c-Myb high-expressing cells converged in the Lin^-CD71⁺ fraction, and the expression of c-Myb was higher in TA/TA mice than in wild-type mice. Moreover, TA/TA mice had an increased proportion of the CD71⁺ subset in Lin^- cells. The c-Myb level in the Lin^-CD71⁺ subset showed three peaks, and the individual c-Myb level was positively correlated with that of c-Kit, a marker of undifferentiated cells. Ultimately, the proportion of c-Myb^hi subgroup was significantly increased in TA/TA mice compared with wild-type mice. These results indicate that a delay in reduction of c-Myb protein during an early stage of erythroid differentiation creates its obstacle in TA/TA mice. In this study, we showed the T572-dependent downregulation of c-Myb protein is required for proper differentiation in early-stage erythroblasts, suggesting the in vivo significance of Fbw7-mediated c-Myb degradation.

Anti-tumor Drug Targets Analysis: Current Insight and Future Prospect

The incidence and mortality of malignant tumors are on the rise, which has become the second leading cause of death in the world. At present, anti-tumor drugs are one of the most common methods for treating cancer. In recent years, with the in-depth study of tumor biology and related disciplines, it has been gradually discovered that the essence of cell carcinogenesis is the infinite proliferation of cells caused by the disorder of cell signal transduction pathways, followed by a major shift in the concept of anti-tumor drugs research and development. The focus of research and development is shifting from traditional cytotoxic drugs to a new generation of anti-tumor drugs targeted at abnormal signaling system targets in tumor cells. In this review, we summarize the targets of anti-tumor drugs and analyse the molecular mechanisms of their effects, which lay a foundation for subsequent treatment, research and development.

Role of PI3K/AKT pathway in cancer: the framework of malignant behavior

Given that the PI3K/AKT pathway has manifested its compelling influence on multiple cellular process, we further review the roles of hyperactivation of PI3K/AKT pathway in various human cancers. We state the abnormalities of PI3K/AKT pathway in different cancers, which are closely related with tumorigenesis, proliferation, growth, apoptosis, invasion, metastasis, epithelial-mesenchymal transition, stem-like phenotype, immune microenvironment and drug resistance of cancer cells. In addition, we investigated the current clinical trials of inhibitors against PI3K/AKT pathway in cancers and found that the clinical efficacy of these inhibitors as monotherapy has so far been limited despite of the promising preclinical activity, which means combinations of targeted therapy may achieve better efficacies in cancers. In short, we hope to feature PI3K/AKT pathway in cancers to the clinic and bring the new promising to patients for targeted therapies.

The FBXW7-SHOC2-Raptor Axis Controls the Cross-Talks between the RAS-ERK and mTORC1 Signaling Pathways

FBXW7 is a tumor suppressive E3 ligase, whereas RAS-ERK and mechanistic target of rapamycin kinase (mTORC1) are two major oncogenic pathways. Whether and how FBXW7 regulates these two oncogenic pathways are unknown. Here, we showed that SHOC2, a RAS activator, is a FBXW7 substrate. Growth stimuli trigger SHOC2 phosphorylation on Thr⁵⁰⁷ by the mitogen-activated protein kinase (MAPK) signal, which facilitates FBXW7 binding for ubiquitylation and degradation. FBXW7-mediated SHOC2 degradation terminates the RAS-MAPK signals and inhibits proliferation. Furthermore, SHOC2 selectively binds to Raptor to competitively inhibit the Raptor-mTOR binding to inactivate mTORC1 and induce autophagy, whereas Raptor binding of SHOC2 inhibits the SHOC2-RAS binding to block the MAPK pathway and proliferation. Finally, SHOC2 is overexpressed in pancreatic cancer, which correlated with poor patient survival. SHOC2 mutations were found in lung cancer tissues with gain-of-function activity. Collectively, the SHOC2-Raptor interaction triggers negative cross-talk between RAS-ERK and mTORC1 pathways, whereas FBXW7 regulates both pathways by targeting SHOC2 for ubiquitylation and degradation.

Examination of the expression levels of MACC1, Filamin A and FBXW7 genes in colorectal cancer patients

OBJECTIVE:

Colorectal cancer (CRC) is the third most common type of cancer observed in cancer-related mortality because it has a high metastasis ratio. This study aims to investigate the expression levels of several genes, including metastasis-related colon cancer 1 (MACC1), Filamin A (FLNA), F-box/WD repeat-containing protein 7 (FBXW7), which has an important role in cell signaling, migration and adhesion through the remodeling of the cell skeleton.

METHODS:

In this study, 21 patients with a precise diagnosis of CRC and 21 controls were included. Gene expressions were examined using the RT-PCR technique. To define the relationship of the genes with metastasis, blood samples were collected from all patients with colon/rectal cancer diagnosis without metastasis at six months before and after the medication with Xelox.

RESULTS:

Our findings showed that no significant difference was observed in the pre-treatment values compared to the control group, whereas FLNA (p=0.001) expression was observed to be significantly increased following treatment with Xelox.

CONCLUSION:

To our knowledge, our study is the first study to investigate the effects of Xelox treatment on the expression levels of MACC1, FBXW7 and FLNA genes in non-metastatic colorectal cancer patients in Turkey.

Cell-Nonautonomous Regulation of Proteostasis in Aging and Disease

The functional health of the proteome is determined by properties of the proteostasis network (PN) that regulates protein synthesis, folding, macromolecular assembly, translocation, and degradation. In eukaryotes, the PN also integrates protein biogenesis across compartments within the cell and between tissues of metazoans for organismal health and longevity. Additionally, in metazoans, proteome stability and the functional health of proteins is optimized for development and yet declines throughout aging, accelerating the risk for misfolding, aggregation, and cellular dysfunction. Here, I describe the cell-nonautonomous regulation of organismal PN by tissue communication and cell stress-response pathways. These systems are robust from development through reproductive maturity and are genetically programmed to decline abruptly in early adulthood by repression of the heat shock response and other cell-protective stress responses, thus compromising the ability of cells and tissues to properly buffer against the cumulative stress of protein damage during aging. While the failure of multiple protein quality control processes during aging challenges cellular function and tissue health, genetic studies, and the identification of small-molecule proteostasis regulators suggests strategies that can be employed to reset the PN with potential benefit on cellular health and organismal longevity.

Long non-coding RNA FER1L4 inhibits prostate cancer progression via sponging miR-92a-3p and upregulation of FBXW7

Background

Dysregulation of long non-coding RNAs (lncRNAs) is involved in development of prostate cancer. However, the molecular mechanisms of many lncRNAs in prostate cancer have not been studied yet.

Methods

The lncRNA Fer-1-like protein 4 (FER1L4) expression was explored in prostate tumors and normal prostate tissues by RT-qPCR and bioinformatic analysis. Overexpression of FER1L4 was performed to evaluate its role in prostate cancer cell proliferation and survival. The molecular mechanism of FER1L4 was investigated by dual luciferase reporter assay, RNA pull down assay, western blotting and RT-qPCR.

Results

It was found that FER1L4 was lower in prostate cancer tissues than normal tissues. Higher expression of FER1L4 was associated with prostate cancer tissues of early stage (AJCC stage I/II). Overexpression of FER1L4 inhibited cell proliferation and promoted cell apoptosis in prostate cancer cells. Bioinformatic analysis, RT-qPCR, RNA pull down assay and dual luciferase assay showed that FER1L4 upregulated F-box/WD repeat-containing protein 7 (FBXW7) tumor suppressor via sponging miR-92a-3p. Silencing of FBXW7 reversed the cell phenotypes caused by FER1L4 overexpression in prostate cancer cells.

Conclusion

The data demonstrated that FER1L4, a downregulated lncRNA in prostate cancer, was pivotal for cell proliferation and survival of prostate cancer. The study provided new sights into understanding of the signaling network in prostate cancer and implied that FER1L4 might be a biomarker for patients with prostate cancer.

MiR-182 promotes glioma progression by targeting FBXW7

OBJECTIVE

MicroRNAs (miRNAs) are widely considered to play an important role in the tumor progression. In this study, we aimed to investigate the potential biological effects of miR-182 and its target FBXW7 on glioma development.

METHODS

Expression data of glioma were procured from TCGA database. Differential analysis was performed to identify the potential differentially expressed miRNA (DEmiRNA), and bioinformatics databases were utilized for target genes prediction. qRT-PCR was conducted to detect miR-182 and western blot was performed to test FBXW7 in protein level. Then the cells were processed for proliferation determination by CCK-8, migration test through wound healing assay, invasion detection via Transwell and apoptosis measurement by flow cytometry. In addition, dual-luciferase reporter gene assay was carried out for evaluation of the targeted relationship between the miR-182 and FBXW7.

RESULTS

MiR-182 was found to be up-regulated in glioma cells while FBXW7 was down-regulated. Besides, miR-182 was predicted to targeted bind with FBXW7 on 3'UTR via bioinformatics methods, and their targeted relationship was further validated by dual-luciferase assay. MiR-182 mimic could significantly promote cell proliferation, migration, invasion and inhibit cell apoptosis, while miR-182 inhibitor had the negative effect. Moreover, FBXW7 knockdown could reverse the inhibitory effect of miR-182 inhibitor on glioma cells.

CONCLUSION

MiR-182 promotes cell proliferation, migration, invasion and inhibits cell apoptosis in glioma by targeting FBXW7.

Regulation of the p53 Family Proteins by the Ubiquitin Proteasomal Pathway

The tumor suppressor p53 and its homologues, p63 and p73, play a pivotal role in the regulation of the DNA damage response, cellular homeostasis, development, aging, and metabolism. A number of mouse studies have shown that a genetic defect in the p53 family could lead to spontaneous tumor development, embryonic lethality, or severe tissue abnormality, indicating that the activity of the p53 family must be tightly regulated to maintain normal cellular functions. While the p53 family members are regulated at the level of gene expression as well as post-translational modification, they are also controlled at the level of protein stability through the ubiquitin proteasomal pathway. Over the last 20 years, many ubiquitin E3 ligases have been discovered that directly promote protein degradation of p53, p63, and p73 in vitro and in vivo. Here, we provide an overview of such E3 ligases and discuss their roles and functions.

FBXW7-mediated stability regulation of signal transducer and activator of transcription 2 in melanoma formation

The physiological relevance of STAT2 (a member of STAT family) in melanoma formation is clearly shown using a human skin tissue array. Moreover, FBXW7-mediated STAT2 protein stability regulation via ubiquitination is shown to play an essential role in melanoma cell proliferation in monolayer and anchorage-independent 3D culture systems. The molecular mechanisms that regulate STAT2 protein stability by FBXW7 include the interaction between CCD and DBD domains of STAT2 and the WD40 domain of FBXW7. STAT2 phosphorylation at the putative degron motifs that contain Ser381, Thr385, and Ser393 might be mediated by GSK3β. These serve as critical amino acids that form hydrogen bonds with the WD40 domain of FBXW7. Thus, the FBXW7–STAT2 signaling axis is an important target for melanoma treatment.

In this study, we provide critical evidence that STAT2 stability regulation plays an essential role in melanoma cell proliferation and colony growth. We found that the interaction of FBXW7 and STAT2 induced STAT2 destabilization via a ubiquitination-mediated proteasomal degradation pathway. Notably, GSK3β-mediated STAT2 phosphorylation facilitated STAT2–FBXW7 interactions via the DNA binding domain of STAT2 and domains 1, 2, 6, and 7 of FBXW7 WD40. Importantly, the inverse correlation between protein levels of STAT2 and FBXW7 were observed not only in human melanoma cells but also in a human skin cancer tissue array. The relationship between protein levels of STAT2 and FBXW7, cell proliferation, and colony growth were similarly observed in the melanoma cell lines SK-MEL-2, -5, and -28. Moreover, STAT2 knockdown in melanoma cells suppressed melanoma cell proliferation and colony formation. These data demonstrated that FBXW7-mediated STAT2 stability regulation plays an essential role in melanoma cell proliferation and cancer growth.

A novel transthyretin/STAT4/miR-223-3p/FBXW7 signaling pathway affects neovascularization in diabetic retinopathy

MicroRNAs (miRNAs) are small RNAs without protein-coding functions that negatively regulate target genes and play important roles in physiological and pathological processes. The aim of this work was to reveal a novel miRNA/gene pathway in diabetic retinopathy (DR). A microarray was used to screen miRNAs in samples from nondiabetic controls and patients with DR, and miR-223-3p was screened as a potential candidate. Quantitative real-time PCR (qRT-PCR) revealed that the level of miR-223-3p was frequently overexpressed in DR samples and human retinal endothelial cells (hRECs) in hyperglycemia, but it was decreased in hyperglycemia after the addition of transthyretin (TTR). In addition, according to cell proliferation, tube formation, and wound healing assays, the downregulation of miR-223-3p suppressed cell migration and proliferation, whereas miR-223-3p upregulation showed the opposite effects. Furthermore, luciferase assays identified F-box and WD repeat domain-containing 7 (FBXW7) as a target mRNA of miR-223-3p. High glucose conditions facilitated the recruitment of signal transducer and activator of transcription 4 (STAT4) and promoted the transcription of miR-223-3p. In hRECs, in a hyperglycemic environment, TTR inhibited STAT4 expression, downregulated the level of miR-223-3p, and finally promoted FBXW7 expression. This study found a novel mechanism whereby TTR might affect neovascularization through a newly identified STAT4/miR-223-3p/FBXW7 cascade in DR.

MicroRNAs and their involvement in T-ALL: A brief overview

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive malignancy in which the transformed clone is arrested during T-cell development. Several genetic and epigenetic events have been implicated in this transformation. MicroRNAs (miRNAs) are small, non-coding RNAs that primarily function as endogenous translational repressors of protein-coding genes. The involvement of miRNAs in the regulation of cancer progression is well-established, namely by down-regulating the expression of key oncogenes or tumor suppressors and thereby preventing or promoting tumorigenesis, respectively. Similar to other cancers, several miRNA genes have been identified and implicated in the context of T-ALL. In this review we focused on the most studied microRNAs associated with T-ALL pathogenesis.

Pseudophosphatase STYX promotes tumor growth and metastasis by inhibiting FBXW7 function in colorectal cancer

Serine/threonine/tyrosine interacting protein (STYX), a member of protein tyrosine phosphatases, has recently been reported as a potential oncogene. However, the role of STYX in colorectal cancer (CRC) remains unknown. In this study, we found that STYX was highly expressed in CRC tissues and closely correlated with tumor development and survival of CRC patients. In vitro studies showed that overexpression of STYX promoted proliferation, migration, invasion, and epithelial-mesenchymal transition (EMT) and inhibited apoptosis in CRC cells, while STYX knockdown had the opposite effects. Consistently, in vivo experiments showed that overexpression of STYX promoted tumor growth and lung metastasis. Mechanically, STYX bound to the F-box and WD repeat domain-containing7 (FBXW7) protein and inhibited its function. Co-regulation of STYX and FBXW7 expression reversed the biological changes mediated by regulation of STYX expression alone in CRC cells. Additionally, FBXW7 expression was negatively associated with STYX expression in CRC tissues, and low STYX levels accompanying high FBXW7 levels predicted favorable prognosis of CRC patients. In conclusion, our results suggest that STYX plays an oncogenic role by inhibiting FBXW7 and represents a potential therapeutic target and prognostic biomarker in CRC.

F-box/WD-40 repeat-containing protein 7: A potential target in the progression and treatment of gastrointestinal malignancy

Cancer is a principal cause of human morbidity and mortality, with gastrointestinal malignancies, in particular, resulting in a marked number of tumor-associated mortalities. The progression of gastrointestinal malignancy is regulated by a variety of aberrantly expressed proteins, a number of which facilitate tumor progression, whereas, others function as tumor suppressors. The detection of such proteins not only contributes to the early diagnosis of cancer, they may additionally serve as potential therapeutic targets. In normal tissues, numerous proteins encoded by proto-oncoproteins are degraded by ubiquitylation enzymes, consisting of F-box/WD-40 repeat-containing protein 7 (Fbw7) and other proteins, thus avoiding tumorigenesis and maintaining homeostasis. In tumor tissues, the downregulation of Fbw7, caused by various factors, leads to disorders in ubiquitinase synthesis, which may induce tumor progression and chemoresistance, particularly in gastrointestinal malignancy. Therefore, an in-depth study of the regulatory mechanisms involved in disorders of Fbw7 expression and the role of Fbw7 in chemoresistance of gastrointestinal tumors may suggest improvements for early diagnostic screening and targeted therapy.

It takes a team: a gain-of-function story of p53-R249S

Gain-of-function (GOF), the most malicious oncogenic activity of a cancer-promoting protein, is well illustrated to three hotspot p53 mutations at R248, R175, and R273 with distinct molecular mechanisms. Yet, less is known about another hotspot p53 mutant, R249S (p53-R249S). p53-R249S is the sole hotspot mutation in hepatocellular carcinoma (HCC) that is highly associated with chronic hepatitis B virus (HBV) infection and dietary exposure to aflatoxin B1 (AFB1). Its GOF is suggested by the facts that this mutant is associated with earlier onset of HCC and poorer prognosis of cancer patients and that its overexpression drives HCC proliferation and tumorigenesis. By contrast, simply knocking in this mutant in normal mice did not show apparent GOF activity. Hence, the GOF activity for p53-R249S and its underlying mechanisms have been elusive until recent findings offered some new insights. This review will discuss these findings as well as their clinical significance and implications for the development of a strategy to target multiple molecules as a therapy for p53-R249S-harboring HCC.

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.

A negative feedback loop between XBP1 and Fbw7 regulates cancer development

In cancer, activation of X-box binding protein (XBP1) has a critical role in tumorigenesis and cancer progression. Transcriptional regulatory mechanism of XBP1 in cancer development has been well known, however, regulation of ubiquitination and degradation of XBP1 has not been elucidated yet. Here we show that Fbw7, a substrate recognition component of the SKP1-Cullin-F-box-type E3 ligase, interacts with XBP1 in a phosphorylation-dependent manner, and facilitates XBP1 ubiquitination and protein degradation. Moreover, Fbw7 inhibits oncogenic pathways including NF-κB, AP1, and Myc induced by XBP1. Interestingly, XBP1 negatively regulates transcription of Fbw7 via a feedback mechanism through NF-κB/E2F-1 axis signaling pathway, suggesting that overexpression of XBP1s may contribute to low level of Fbw7 expression in human cancers. Therefore, a negative feedback loop between Fbw7 and XBP1 contributes to the regulation of tumor development and can be an attractive target for novel therapy in cancers.

SPOP Promotes Nanog Destruction to Suppress Stem Cell Traits and Prostate Cancer Progression

Frequent SPOP mutation defines the molecular feature underlying one of seven sub-types of human prostate cancer (PrCa). However, it remains largely elusive how SPOP functions as a tumor suppressor in PrCa. Here, we report that SPOP suppresses stem cell traits of both embryonic stem cells and PrCa cells through promoting Nanog poly-ubiquitination and subsequent degradation. Mechanistically, Nanog, but not other pluripotency-determining factors including Oct4, Sox2, and Klf4, specifically interacts with SPOP via a conservative degron motif. Importantly, cancer-derived mutations in SPOP or at the Nanog-degron (S68Y) disrupt SPOP-mediated destruction of Nanog, leading to elevated cancer stem cell traits and PrCa progression. Notably, we identify the Pin1 oncoprotein as an upstream Nanog regulator that impairs its recognition by SPOP and thereby stabilizes Nanog. Thus, Pin1 inhibitors promote SPOP-mediated destruction of Nanog, which provides the molecular insight and rationale to use Pin1 inhibitor(s) for targeted therapies of PrCa patients with wild-type SPOP.

E3 ligase FBXW7 aggravates TMPD-induced systemic lupus erythematosus by promoting cell apoptosis

Systemic lupus erythematosus (SLE) is a systemic autoimmune disease, and the pathogenesis of SLE has not been fully elucidated. The E3 ubiquitin ligase FBXW7 has been well characterized in cancer as a tumor suppressor that can promote the ubiquitination and subsequent degradation of various oncoproteins; however, the potential role of FBXW7 in autoimmune diseases is unclear. In the present study, we identified that FBXW7 is a crucial exacerbating factor for SLE development and progression in a mouse model induced by 2, 6, 10, 14-tetramethylpentadecane (TMPD). Myeloid cell-specific FBXW7-deficient (Lysm⁺FBXW7^f/f) C57BL/6 mice showed decreased immune complex accumulation, glomerulonephritis, glomerular mesangial cell proliferation, and base-membrane thickness in the kidney. Lysm⁺FBXW7^f/f mice produced fewer anti-Sm/RNP and anti-ANA autoantibodies and showed a decreased MHC II expression in B cells. In Lysm⁺FBXW7^f/f mice, we observed that cell apoptosis was reduced and that fewer CD11b⁺Ly6C^hi inflammatory monocytes were recruited to the peritoneal cavity. Consistently, diffuse pulmonary hemorrhage (DPH) was also decreased in Lysm⁺FBXW7^f/f mice. Mechanistically, we clarified that FBXW7 promoted TMPD-induced cell apoptosis by catalyzing MCL1 degradation through K48-linked ubiquitination. Our work revealed that FBXW7 expression in myeloid cells played a crucial role in TMPD-induced SLE progression in mice, which may provide novel ideas and theoretical support for understanding the pathogenesis of SLE.

The prognostic significance of FBXO2 expression in colorectal cancer

Colorectal cancer is the third most frequently diagnosed malignancy, and the prognosis at advanced tumor stages remains poor. FBXO2, a member of the F-box protein family, is a cytoplasmic protein and an ubiquitin ligase. The aim of this study was to investigate the role of FBXO2 in colorectal cancer. The expression levels of Ki67, N-cadherin and FBXO2 were detected in 195 pairs of primary CRC tissues using immunohistochemistry (IHC). The associations among Ki67, N-cadherin, and FBXO2 expression, as well as the clinicopathological parameters, were analyzed. Survival curves were calculated with the Kaplan-Meier method. Univariate and multivariate analyses were performed to explore the prognostic significance of Ki67, N-cadherin, and FBXO2 expression. We found that the positive rates of Ki67, N-cadherin and FBXO2 expression in CRC tissue samples were 55.9%, 65.1%, 62.6%, respectively. The high expression levels of Ki67 and N-cadherin were significantly correlated with CRC size (P = 0.01) and metastasis (P = 0.01), respectively. The high expression level of FBXO2 was significantly correlated with CRC metastasis (P = 0.04) and AJCC stage (P = 0.029). A Cox regression analysis revealed that FBXO2 is an independent prognostic factor for CRC patients (HR 1.817, 95% CI 1.106-2.983, P = 0.018). FBXO2 may serve as a biomarker for metastasis and a reliable predictor for poor prognosis in CRC patients.

Cross Talk Networks of Mammalian Target of Rapamycin Signaling With the Ubiquitin Proteasome System and Their Clinical Implications in Multiple Myeloma

Multiple myeloma (MM) is the second most common hematological malignancy and results from the clonal amplification of plasma cells. Despite recent advances in treatment, MM remains incurable with a median survival time of only 5-6years, thus necessitating further insights into MM biology and exploitation of novel therapeutic approaches. Both the ubiquitin proteasome system (UPS) and the PI3K/Akt/mTOR signaling pathways have been implicated in the pathogenesis, and treatment of MM and different lines of evidence suggest a close cross talk between these central cell-regulatory signaling networks. In this review, we outline the interplay between the UPS and mTOR pathways and discuss their implications for the pathophysiology and therapy of MM.

Emerging roles of Myc in stem cell biology and novel tumor therapies

The pathophysiological roles and the therapeutic potentials of Myc family are reviewed in this article. The physiological functions and molecular machineries in stem cells, including embryonic stem (ES) cells and induced pluripotent stem (iPS) cells, are clearly described. The c-Myc/Max complex inhibits the ectopic differentiation of both types of artificial stem cells. Whereas c-Myc plays a fundamental role as a "double-edged sword" promoting both iPS cells generation and malignant transformation, L-Myc contributes to the nuclear reprogramming with the significant down-regulation of differentiation-associated genetic expression. Furthermore, given the therapeutic resistance of neuroendocrine tumors such as small-cell lung cancer and neuroblastoma, the roles of N-Myc in difficult-to-treat tumors are discussed. N-Myc and p53 exhibit the co-localization in the nucleus and alter p53-dependent transcriptional responses which are necessary for DNA repair, anti-apoptosis, and lipid metabolic reprogramming. NCYM protein stabilizes N-Myc, resulting in the stimulation of Oct4 expression, while Oct4 induces both N-Myc and NCYM via direct transcriptional activation of N-Myc, [corrected] thereby leading to the enhanced metastatic potential. Importantly enough, accumulating evidence strongly suggests that c-Myc can be a promising therapeutic target molecule among Myc family in terms of the biological characteristics of cancer stem-like cells (CSCs). The presence of CSCs leads to the intra-tumoral heterogeneity, which is mainly responsible for the therapeutic resistance. Mechanistically, it has been shown that Myc-induced epigenetic reprogramming enhances the CSC phenotypes. In this review article, the author describes two major therapeutic strategies of CSCs by targeting c-Myc; Firstly, Myc-dependent metabolic reprogramming is closely related to CD44 variant-dependent redox stress regulation in CSCs. It has been shown that c-Myc increases NADPH production via enhanced glutaminolysis with a finely-regulated mechanism. Secondly, the dormancy of CSCs due to FBW7-depedent c-Myc degradation pathway is also responsible for the therapeutic resistance to the conventional anti-tumor agents, the action points of which are largely dependent on the operation of the cell cycle. That is why the loss-of-functional mutations of FBW7 gene are expected to trigger "awakening" of dormant CSCs in the niche with c-Myc up-regulation. Collectively, although the further research is warranted to develop the effective anti-tumor therapeutic strategy targeting Myc family, we cancer researchers should always catch up with the current advances in the complex functions of Myc family in highly-malignant and heterogeneous tumor cells to realize the precision medicine.

PHD finger protein 1 (PHF1) is a novel reader for histone H4R3 symmetric dimethylation and coordinates with PRMT5-WDR77/CRL4B complex to promote tumorigenesis

Histone post-translational modifications regulate chromatin structure and function largely through interactions with effector proteins that often contain multiple histone-binding domains. PHF1 [plant homeodomain (PHD) finger protein 1], which contains two kinds of histone reader modules, a Tudor domain and two PHD fingers, is an essential factor for epigenetic regulation and genome maintenance. While significant progress has been made in characterizing the function of the Tudor domain, the roles of the two PHD fingers are poorly defined. Here, we demonstrated that the N-terminal PHD finger of PHF1 recognizes symmetric dimethylation of H4R3 (H4R3me2s) catalyzed by PRMT5-WDR77. However, the C-terminal PHD finger of PHF1, instead of binding to modified histones, directly interacts with DDB1, the main component of the CUL4B-Ring E3 ligase complex (CRL4B), which is responsible for H2AK119 mono-ubiquitination (H2AK119ub1). We showed that PHF1, PRMT5-WDR77, and CRL4B reciprocally interact with one another and collaborate as a functional unit. Genome-wide analysis of PHF1/PRMT5/CUL4B targets identified a cohort of genes including E-cadherin and FBXW7, which are critically involved in cell growth and migration. We demonstrated that PHF1 promotes cell proliferation, invasion, and tumorigenesis in vivo and in vitro and found that its expression is markedly upregulated in a variety of human cancers. Our data identified a new reader for H4R3me2s and provided a molecular basis for the functional interplay between histone arginine methylation and ubiquitination. The results also indicated that PHF1 is a key factor in cancer progression, supporting the pursuit of PHF1 as a target for cancer therapy.

Mcl-1 Phosphorylation without Degradation Mediates Sensitivity to HDAC Inhibitors by Liberating BH3-Only Proteins

Mcl-1, a prosurvival Bcl-2 family protein, is frequently overexpressed in cancer cells and plays a critical role in therapeutic resistance. It is well known that anticancer agents induce phosphorylation of Mcl-1, which promotes its binding to E3 ubiquitin ligases and subsequent proteasomal degradation and apoptosis. However, other functions of Mcl-1 phosphorylation in cancer cell death have not been well characterized. In this study, we show in colon cancer cells that histone deacetylase inhibitors (HDACi) induce GSK3β-dependent Mcl-1 phosphorylation, but not degradation or downregulation. The in vitro and in vivo anticancer effects of HDACi were dependent on Mcl-1 phosphorylation and were blocked by genetic knock-in of a Mcl-1 phosphorylation site mutant. Phosphorylation-dead Mcl-1 maintained cell survival by binding and sequestering BH3-only Bcl-2 family proteins PUMA, Bim, and Noxa, which were upregulated and necessary for apoptosis induction by HDACi. Resistance to HDACi mediated by phosphorylation-dead Mcl-1 was reversed by small-molecule Mcl-1 inhibitors that liberated BH3-only proteins. These results demonstrate a critical role of Mcl-1 phosphorylation in mediating HDACi sensitivity through a novel and degradation-independent mechanism. These results provide new mechanistic insights on how Mcl-1 maintains cancer cell survival and suggest that Mcl-1-targeting agents are broadly useful for overcoming therapeutic resistance in cancer cells.Significance: These findings present a novel degradation-independent function of Mcl-1 phosphorylation in anticancer therapy that could be useful for developing new Mcl-1-targeting agents to overcome therapeutic resistance. Cancer Res; 78(16); 4704-15. ©2018 AACR.

FBW7 suppresses metastasis of colorectal cancer by inhibiting HIF1α/CEACAM5 functional axis

F-box and WD repeat domain-containing 7 (FBW7) functions as a major tumor suppressor by targeting oncoproteins for degradations. FBW7 has been reported to be one of the most frequently mutated genes in colorectal cancer (CRC). However, its roles and possible mechanisms in the development of CRC are still unclear. In the present study, we adopted immunohistochemistry staining in tissue microarray (TMA), consisting of 276 samples from stage I-IV CRC patients, and analyzed the correlation between FBW7 expression and clinicopathological parameters, as well as overall survival (OS) and disease-free survival (DFS). The impact of FBW7 on migration was further validated in vitro. Whole-genome expression microarray (GEO,accession numbers GSE76443), was then analyzed to find the possible target of FBW7. The results were verified by functional experiments in vitro and IHC staining of TMA. Finally, luciferase and chromatin immunoprecipitation (ChIP) assays were carried out to identify the possible mechanisms. The expression level of FBW7 in TMA was negatively correlated with serum CEA level, venous invasion, N stage and M stage, and positively associated with the survival of CRC patients(P<0.05). Ectopic FBW7 expression significantly suppressed migration of colon cancer cells in vitro. GEO analysis revealed that decreased FBW7 significantly correlated with increased level of CEACAM5, which encoded CEA. The correlation was verified by IHC of TMA and silencing CEACAM5 inhibited migration in vitro. Mechanistically, we demonstrated that CEACAM5 was a HIF1α target gene and that FBW7 regulated CEACAM5 in a HIF1α-dependent manner. In conclusion, our results revealed that FBW7 suppressed migration through regulation of the HIF1α/CEACAM5 axis in colorectal cancer. Therefore, our study sheds novel lights on the impact of FBW7 on HIF1α/CEACAM5 signaling axis and constitutes potential prognostic predictors and therapeutic targets for CRC.

Ubiquitin-Dependent Regulation of the Mammalian Hippo Pathway: Therapeutic Implications for Cancer

The Hippo pathway serves as a key barrier for oncogenic transformation. It acts by limiting the activity of the proto-oncogenes YAP and TAZ. Reduced Hippo signaling and elevated YAP/TAZ activities are frequently observed in various types of tumors. Emerging evidence suggests that the ubiquitin system plays an important role in regulating Hippo pathway activity. Deregulation of ubiquitin ligases and of deubiquitinating enzymes has been implicated in increased YAP/TAZ activity in cancer. In this article, we review recent insights into the ubiquitin-mediated regulation of the mammalian Hippo pathway, its deregulation in cancer, and possibilities for targeting the Hippo pathway through the ubiquitin system.

Histone deacetylase 6 controls Notch3 trafficking and degradation in T-cell acute lymphoblastic leukemia cells

Several studies have revealed that endosomal sorting controls the steady-state levels of Notch at the cell surface in normal cells and prevents its inappropriate activation in the absence of ligands. However, whether this highly dynamic physiologic process can be exploited to counteract dysregulated Notch signaling in cancer cells remains unknown. T-ALL is a malignancy characterized by aberrant Notch signaling, sustained by activating mutations in Notch1 as well as overexpression of Notch3, a Notch paralog physiologically subjected to lysosome-dependent degradation in human cancer cells. Here we show that treatment with the pan-HDAC inhibitor Trichostatin A (TSA) strongly decreases Notch3 full-length protein levels in T-ALL cell lines and primary human T-ALL cells xenografted in mice without substantially reducing NOTCH3 mRNA levels. Moreover, TSA markedly reduced the levels of Notch target genes, including pTα, CR2, and DTX-1, and induced apoptosis of T-ALL cells. We further observed that Notch3 was post-translationally regulated following TSA treatment, with reduced Notch3 surface levels and increased accumulation of Notch3 protein in the lysosomal compartment. Surface Notch3 levels were rescued by inhibition of dynein with ciliobrevin D. Pharmacologic studies with HDAC1, 6, and 8-specific inhibitors disclosed that these effects were largely due to inhibition of HDAC6 in T-ALL cells. HDAC6 silencing by specific shRNA was followed by reduced Notch3 expression and increased apoptosis of T-ALL cells. Finally, HDAC6 silencing impaired leukemia outgrowth in mice, associated with reduction of Notch3 full-length protein in vivo. These results connect HDAC6 activity to regulation of total and surface Notch3 levels and suggest HDAC6 as a potential novel therapeutic target to lower Notch signaling in T-ALL and other Notch3-addicted tumors.

Molecular Mechanisms Driving Cholangiocarcinoma Invasiveness: An Overview

The acquisition of invasive functions by tumor cells is a first and crucial step toward the development of metastasis, which nowadays represents the main cause of cancer-related death. Cholangiocarcinoma (CCA), a primary liver cancer originating from the biliary epithelium, typically develops intrahepatic or lymph node metastases at early stages, thus preventing the majority of patients from undergoing curative treatments, consistent with their very poor prognosis. As in most carcinomas, CCA cells gradually adopt a motile, mesenchymal-like phenotype, enabling them to cross the basement membrane, detach from the primary tumor, and invade the surrounding stroma. Unfortunately, little is known about the molecular mechanisms that synergistically orchestrate this proinvasive phenotypic switch. Autocrine and paracrine signals (cyto/chemokines, growth factors, and morphogens) permeating the tumor microenvironment undoubtedly play a prominent role in this context. Moreover, a number of recently identified signaling systems are currently drawing attention as putative mechanistic determinants of CCA cell invasion. They encompass transcription factors, protein kinases and phosphatases, ubiquitin ligases, adaptor proteins, and miRNAs, whose aberrant expression may result from either stochastic mutations or the abnormal activation of upstream pro-oncogenic pathways. Herein we sought to summarize the most relevant molecules in this field and to discuss their mechanism of action and potential prognostic relevance in CCA. Hopefully, a deeper knowledge of the molecular determinants of CCA invasiveness will help to identify clinically useful biomarkers and novel druggable targets, with the ultimate goal to develop innovative approaches to the management of this devastating malignancy.

Natural Compound Methyl Protodioscin Suppresses Proliferation and Inhibits Glycolysis in Pancreatic Cancer

Methyl protodioscin (MPD) is one of the main bioactive components in the plant of Dioscoreaceae. MPD has been demonstrated to possess antitumor activities. However, its role in pancreatic cancer and the underlying molecular mechanisms are poorly defined. In the present study, we demonstrated that MPD inhibited proliferation and promoted apoptosis of pancreatic cancer. Furthermore, our results demonstrated that MPD decreased oncogene c-Myc in protein level and resulted in concomitant reduction in glycolysis. In vivo assays with xenograft mouse model further confirmed the in vitro observations, which indicated that MPD inhibited 18FDG uptake in tumors formed by subcutaneously injection of MIA PaCa-2 cells. Collectively, our present study uncovered novel antitumor functions of MPD in pancreatic cancer and provided the possible molecular mechanism.

Fbxw7 haploinsufficiency loses its protection against DNA damage and accelerates MNU-induced gastric carcinogenesis

Fbxw7, a subunit of the SCF E3 ubiquitin ligase, recognizes oncoprotein substrates and leads to their proteasomal degradation. Fbxw7 acts as a tumor suppressor via inducing apoptosis and growth arrest in various kinds of tumors. To clarify the initiating role in gastric carcinogenesis as well as the histologic characterization of tumor in Fbxw7 allele haploinsufficient mice, we generated Fbxw7 heterozygous knockout mice (Fbxw7^+/−) and treated them with chemical carcinogen N-methyl-N-nitrosourea (MNU) at 5–6 weeks of age. We also treated mouse embryo fibroblasts (MEFs) from Fbxw7^+/− and Fbxw7^+/+ mice with MNU and examined cell DNA damage via comet assay. The protein expression of Fbxw7 and its substrate c-Myc from mouse tumors, as well as human tumors sampled from six patients, were detected by Western blot. As results, the tumor incidence was obviously higher in Fbxw7^+/− mice (13/20) than in Fbxw7^+/+ mice (6/20) after 35-week observation. Intestinal metaplasia (P = 0.013) and dysplasia (P = 0.036) were more severe in Fbxw7^+/− mice than in Fbxw7^+/+ mice. The repair potential of DNA damage was suppressed in MEFs from Fbxw7^+/− mice after MNU exposure. Increased c-Myc expression was accompanied by decreased Fbxw7 protein expression in tumor tissues from mouse and patients. In conclusion, Fbxw7 haploinsufficiency increased the risk of gastric carcinogenesis induced by MNU, which is associated with the accumulation of DNA damage as well as c-Myc oncoprotein.

EglN2 contributes to triple negative breast tumorigenesis by functioning as a substrate for the FBW7 tumor suppressor

EglN2 contributes to ERα-positive breast tumorigenesis by acting as an estrogen-inducible gene. However, the detailed molecular mechanism(s) underlying the post-transcriptional regulation of EglN2 and its potential role in Triple Negative Breast Cancer (TNBC) remains largely unclear. By using C3Tag transgenic mice and tumor-derived C3Tag cell line, here we report that EglN2 contributes to TNBC tumor progression and genetic knockout of EglN2 improves C3Tag mice survival from tumor progression. Mechanistically, we further show that FBW7, an E3 ligase complex component that is frequently downregulated in TNBC, negatively regulates EglN2 protein stability. As such, depletion of FBW7 in breast cell lines leads to upregulation of EglN2 and other canonical FBW7 substrates. Conversely, FBW7 overexpression leads to EglN2 downregulation in a GSK3β-dependent manner. Furthermore, we identified some potential serine or threonine residues on the C-terminal of EglN2 that may mediate its binding and potential regulation by FBW7. Together, our study reveals that EglN2 might act as an FBW7 ubiquitin ligase substrate contributing to TNBC.

Fbxw7 regulates renal cell carcinoma migration and invasion via suppression of the epithelial-mesenchymal transition

F-box and WD repeat domain containing 7 (Fbxw7) is an F-box protein that belongs to the SKP1-CUL1-F-box protein E3 ligase complex and is responsible for transferring the ubiquitin molecule to the substrate, which results in its recognition and subsequent degradation by proteasomes. Furthermore, it can identify a network of signaling proteins that function in cell growth, diversion and apoptosis. In the present study, Fbxw7 was downregulated in renal cell carcinoma (RCC) tissues compared with the adjacent non-tumor tissues and its expression was significantly associated with the tumor-node-metastasis stage, lymph node metastasis and distant metastasis in patients with RCC. Furthermore, multivariate Cox regression analyses indicated that Fbxw7 expression was an independent factor for the prediction of the overall survival of patients with RCC. A functional study demonstrated that downregulation of Fbxw7 facilitated tumor cell migration and invasion via the epithelial-mesenchymal transition (EMT). Therefore, the results of the current study indicted that Fbxw7 is an anti-oncogene that serves a notable function in RCC development by suppressing RCC metastasis and the EMT, indicating the potential therapeutic value of Fbxw7 in inhibiting metastasis in RCC.

FBW7 regulates DNA interstrand cross-link repair by modulating FAAP20 degradation

Mutations that deregulate protein degradation lead to human malignancies. The SCF ubiquitin E3 ligase complex degrades key oncogenic regulators, thereby limiting their oncogenic potential. FBW7 is a substrate recognition subunit of SCF^FBW7 and is among the most commonly mutated ubiquitin-proteasome system proteins in cancer. FBW7-mutated cancer cells display increased genome instability, but the molecular mechanism by which FBW7 preserves genome integrity remains elusive. Here, we demonstrate that SCF^FBW7 regulates the stability of FAAP20, a critical component of the Fanconi anemia (FA) DNA interstrand cross-link (ICL) repair pathway. Phosphorylation of the FAAP20 degron motif by GSK3β provides a platform for recognition and polyubiquitination of FAAP20 by FBW7, and its subsequent degradation by the proteasome. Accordingly, enhanced GSK3β-FBW7 signaling disrupts the FA pathway. In cells expressing non-phosphorylatable FAAP20 mutant, the turnover of its binding partner, FANCA, is deregulated in the chromatin during DNA ICL repair, and the FA pathway is compromised. We propose that FAAP20 degradation, which is prompted by its phosphorylation, controls the dynamics of the FA core complex required for completing DNA ICL repair. Together, this study provides insights into how FBW7-mediated proteolysis regulates genome stability and how its deregulation is associated with tumorigenesis.