FBXO4 loss facilitates carcinogen induced papilloma development in mice

FBXO38 deficiency promotes lysosome-dependent STING degradation and inhibits cGAS-STING pathway activation

F-box only protein 38 (FBXO38) is a member of the F-box family that mediates the ubiquitination and proteasome degradation of programmed death 1 (PD-1), and thus has important effects on T cell-related immunity. While its powerful role in adaptive immunity has attracted much attention, its regulatory roles in innate immune pathways remain unknown. The cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway is an important innate immune pathway that regulates type I interferons. STING protein is the core component of this pathway. In this study, we identified that FBXO38 deficiency enhanced tumor proliferation and reduced tumor CD8+ T cells infiltration. Loss of FBXO38 resulted in reduced STING protein levels in vitro and in vivo, further leading to preventing cGAS-STING pathway activation, and decreased downstream product IFNA1 and CCL5. The mechanism of reduced STING protein was associated with lysosome-mediated degradation rather than proteasomal function. Our results demonstrate a critical role for FBXO38 in the cGAS-STING pathway.

Inhibitors Targeting the F-BOX Proteins

F-box proteins are involved in multiple cellular processes through ubiquitylation and consequent degradation of targeted substrates. Any significant mutation in F-box protein-mediated proteolysis can cause human malformations. The various cellular processes F-box proteins involved include cell proliferation, apoptosis, invasion, angiogenesis, and metastasis. To target F-box proteins and their associated signaling pathways for cancer treatment, researchers have developed thousands of F-box inhibitors. The most advanced inhibitor of FBW7, NVD-BK M120, is a powerful P13 kinase inhibitor that has been proven to bring about apoptosis in cancerous human lung cells by disrupting levels of the protein known as MCL1. Moreover, F-box Inhibitors have demonstrated their efficacy for treating certain cancers through targeting particular mutated proteins. This paper explores the key studies on how F-box proteins act and their contribution to malignancy development, which fabricates an in-depth perception of inhibitors targeting the F-box proteins and their signaling pathways that eventually isolate the most promising approach to anti-cancer treatments.

Tumor suppressor mediated ubiquitylation of hnRNPK is a barrier to oncogenic translation

Heterogeneous Nuclear Ribonucleoprotein K (hnRNPK) is a multifunctional RNA binding protein (RBP) localized in the nucleus and the cytoplasm. Abnormal cytoplasmic enrichment observed in solid tumors often correlates with poor clinical outcome. The mechanism of cytoplasmic redistribution and ensuing functional role of cytoplasmic hnRNPK remain unclear. Here we demonstrate that the SCFFbxo4 E3 ubiquitin ligase restricts the pro-oncogenic activity of hnRNPK via K63 linked polyubiquitylation, thus limiting its ability to bind target mRNA. We identify SCFFbxo4-hnRNPK responsive mRNAs whose products regulate cellular processes including proliferation, migration, and invasion. Loss of SCFFbxo4 leads to enhanced cell invasion, migration, and tumor metastasis. C-Myc was identified as one target of SCFFbxo4-hnRNPK. Fbxo4 loss triggers hnRNPK-dependent increase in c-Myc translation, thereby contributing to tumorigenesis. Increased c-Myc positions SCFFbxo4-hnRNPK dysregulated cancers for potential therapeutic interventions that target c-Myc-dependence. This work demonstrates an essential role for limiting cytoplasmic hnRNPK function in order to maintain translational and cellular homeostasis.

The E3 Ubiquitin Ligase Fbxo4 Functions as a Tumor Suppressor: Its Biological Importance and Therapeutic Perspectives

Simple Summary

Fbxo4 is an E3 ubiquitin ligase that requires the formation of a complex with S-phase kinase-associated protein 1 and Cullin1 to catalyze the ubiquitylation of its substrates. Moreover, Fbxo4 depends on the existence of posttranslational modifications and/or co-factor to be activated to perform its biological functions. The well-known Fbxo4 substrates have oncogenic or oncogene-like activities, for example, cyclin D1, Trf1/Pin2, p53, Fxr1, Mcl-1, ICAM-1, and PPARγ; therefore, Fbxo4 is defined as a tumor suppressor. Biologically, Fbxo4 regulates cell cycle progression, DNA damage response, tumor metabolism, cellular senescence, metastasis and tumor cells’ response to chemotherapeutic compounds. Clinicopathologically, the expression of Fbxo4 is associated with patients’ prognosis depending on different tumor types. Regarding to its complicated regulation, more in-depth studies are encouraged to dissect the detailed molecular mechanisms to facilitate developing new treatment through targeting Fbxo4.

Abstract

Fbxo4, also known as Fbx4, belongs to the F-box protein family with a conserved F-box domain. Fbxo4 can form a complex with S-phase kinase-associated protein 1 and Cullin1 to perform its biological functions. Several proteins are identified as Fbxo4 substrates, including cyclin D1, Trf1/Pin2, p53, Fxr1, Mcl-1, ICAM-1, and PPARγ. Those factors can regulate cell cycle progression, cell proliferation, survival/apoptosis, and migration/invasion, highlighting their oncogenic or oncogene-like activities. Therefore, Fbxo4 is defined as a tumor suppressor. The biological functions of Fbxo4 make it a potential candidate for developing new targeted therapies. This review summarizes the gene and protein structure of Fbxo4, the mechanisms of how its expression and activity are regulated, and its substrates, biological functions, and clinicopathological importance in human cancers.

Bioinformatics analysis identifying FBXO45 gene as a potential oncogene in esophageal cancer

BACKGROUND

F-box protein 45 (FBXO45) is a member of the F-box protein family, and is reportedly involved in the progression of many diseases. However, its role in esophageal cancer (ESCA) remains unclear.

METHODS

The expression, clinical characteristics, gene function, pathway, and correlation between the infiltration of different immune cells were analyzed using public data. The pan-cancer expression of FBXO45 was assessed using the TIMER2 database. The expression of FBXO45 in different tumor stages and histology subtypes were evaluated using the UALCAN database. The protein-protein interaction (PPI) network was constructed using the STRING database. Immune cell infiltration data were downloaded from the ImmuCellAI database.

RESULTS

The top 300 genes most positively correlated with FBXO45 were screened into the enrichment analysis. The functional enrichment results showed that FBXO45 was mainly associated with proteasomal protein catabolic process and the regulation of DNA metabolic processing in the biological process (BP) category; spindle, chromosomal region, and focal adhesion in the cellular component category; and ATPase activity and ubiquitin-protein transferase activity terms in the molecular function category. FBXO45 was overexpressed in ESCA and other cancer types. FBXO45 expression was positively associated with the infiltration levels of immunosuppressive cells, such as CD8+ (cluster of differentiation 8+) T cells and NK (natural killer cell) cells, in ESCA. MYCBP2 and SKP1 were most associated with FBXO45.

CONCLUSIONS

Our results suggested that FBXO45 is a potential oncogene in ESCA. Elevated FBXO45 expression indicates a relatively immunosuppressive microenvironment.

Clinical Relevance of Secreted Small Noncoding RNAs in an Embryo Implantation Potential Prediction at Morula and Blastocyst Development Stages

Despite the improvements in biotechnological approaches and the selection of controlled ovarian hyperstimulation protocols, the resulting pregnancy rate from in vitro fertilization (IVF) protocols still does not exceed 30-40%. In this connection, there is an acute question of the development of a non-invasive, sensitive, and specific method for assessing the implantation potential of an embryo. A total of 110 subfertile couples were included in the study to undergo the IVF/ICSI program. Obtained embryos for transfer into the uterine cavity of patient cohort 1 (n = 60) and cohort 2 (n = 50) were excellent/good-quality blastocysts, and small noncoding RNA (sncRNA) content in the corresponding spent culture medium samples at the morula stage (n = 43) or at the blastocyst stage (n = 31) was analyzed by deep sequencing followed by qRT-PCR in real time. Two logistic regression models were developed to predict the implantation potential of the embryo with 100% sensitivity and 100% specificity: model 1 at the morula stage, using various combinations of hsa_piR_022258, hsa-let-7i-5p, hsa_piR_000765, hsa_piR_015249, hsa_piR_019122, and hsa_piR_008112, and model 2 at the blastocyst stage, using various combinations of hsa_piR_020497, hsa_piR_008113, hsa-miR-381-3p, hsa_piR_022258, and hsa-let-7a-5p. Protein products of sncRNA potential target genes participate in the selective turnover of proteins through the ubiquitination system and in the organization of the various cell cytoskeleton and nucleoskeleton structures, regulating the activity of the Hippo signaling pathway, which determines the fate specification of the blastomers.

Downregulation of microRNA-3646 Through Direct Targeting of F-Box Protein 4 on Interleukin-17-Induced Lung Cancer Cell Migration and Invasion

IL-17 participates in the initiation and growth of malignant cancers, including lung cancer. The aberrant expression of miRNA is also related to tumor growth and metastasis. Studies have confirmed that high expression of miRNA-3646 can boost breast cancer cell invasion and migration, suggesting that miRNA-3646 is a tumor-promoting factor. However, the role of miRNA-3646 in the migration and invasion of IL-17-induced lung cancer cells is unclear. In this study, qRT-PCR was used to determine the level of miRNA-3646. We found that in lung cancer cells, miRNA-3646 levels exceeded those of normal bronchial epithelial 16HBE cells (P < 0.05). The level of miRNA-3646 in NCI-H1299 cells was higher than that in A549, NCI-H446, and SK-MES-1 cells (P < 0.05). After IL-17 treatment, the number of proliferating and migrating lung carcinoma NCI-H1299 cells increased, transport of vimentin increased, and transport of E-cadherin decreased (P < 0.05). After IL-17 treatment, the number of proliferating and migrating lung carcinoma NCI-H1299 cells transfected with miRNA-3646 inhibitor decreased, transport of vimentin decreased, and transport of E-cadherin increased (P < 0.05). FBXO4 siRNA reversed the inhibition of miRNA-3646 on the proliferation and migration of IL-17-induced lung carcinoma NCI-H1299 cells and the transport of E-cadherin and vimentin. Thus, downregulation of miRNA-3646 inhibited IL-17-induced lung carcinoma cell migration and proliferation by directly targeting FBXO4.

DNA polymerase β deficiency promotes the occurrence of esophageal precancerous lesions in mice

Esophageal mucosa undergoes mild, moderate, severe dysplasia, and other precancerous lesions and eventually develops into carcinoma in situ, and understanding the developmental progress of esophageal precancerous lesions is beneficial to prevent them from developing into cancer. DNA polymerase β (Polβ), a crucial enzyme of the base excision repair system, plays an important role in repairing damaged DNA and maintaining genomic stability. Abnormal expression or deletion mutation of Polβ is related to the occurrence of esophageal cancer, but the role of Polβ deficiency in the esophageal precancerous lesions is still unclear. Here, esophageal mucosa Polβ-knockout mice were used to explore the relationship of Polβ deficiency with esophageal precancerous lesions. First, we found the degree and number of esophageal precancerous lesions in Polβ-KO mice were more serious than those in Polβ-Loxp mice after N-nitrosomethylbenzylamine (NMBA) treatment. Whole exome sequencing revealed that deletion of Polβ increased the frequency of gene mutations. Gene expression prolife analysis showed that the expression of proteins correlated to cell proliferation and the cell cycle was elevated in Polβ-KO mice. We also found that deletion of Polβ promoted the proliferation and clone formation as well as accelerated cell cycle progression of human immortalized esophageal epithelial cell line SHEE treated with NMBA. Our findings indicate that Polβ knockout promotes the occurrence of esophageal precancerous lesions.

F-Box Proteins and Cancer

Controlled protein degradation is essential for the operation of a variety of cellular processes including cell division, growth, and differentiation. Identification of the relations between ubiquitin ligases and their substrates is key to understanding the molecular basis of cancer development and to the discovery of novel targets for cancer therapeutics. F-box proteins function as the substrate recognition subunits of S-phase kinase-associated protein 1 (SKP1)−Cullin1 (CUL1)−F-box protein (SCF) ubiquitin ligase complexes. Here, we summarize the roles of specific F-box proteins that have been shown to function as tumor promoters or suppressors. We also highlight proto-oncoproteins that are targeted for ubiquitylation by multiple F-box proteins, and discuss how these F-box proteins are deployed to regulate their cognate substrates in various situations.

F-box proteins and cancer: an update from functional and regulatory mechanism to therapeutic clinical prospects

E3 ubiquitin ligases play a critical role in cellular mechanisms and cancer progression. F-box protein is the core component of the SKP1-cullin 1-F-box (SCF)-type E3 ubiquitin ligase and directly binds to substrates by various specific domains. According to the specific domains, F-box proteins are further classified into three sub-families: 1) F-box with leucine rich amino acid repeats (FBXL); 2) F-box with WD 40 amino acid repeats (FBXW); 3) F-box only with uncharacterized domains (FBXO). Here, we summarize the substrates of F-box proteins, discuss the important molecular mechanism and emerging role of F-box proteins especially from the perspective of cancer development and progression. These findings will shed new light on malignant tumor progression mechanisms, and suggest the potential role of F-box proteins as cancer biomarkers and therapeutic targets for future cancer treatment.

Cyclin D degradation by E3 ligases in cancer progression and treatment

D cyclins include three isoforms: D1, D2, and D3. D cyclins heterodimerize with cyclin-dependent kinase 4/6 (CDK4/6) to form kinase complexes that can phosphorylate and inactivate Rb. Inactivation of Rb triggers the activation of E2F transcription factors, which in turn regulate the expression of genes whose products drive cell cycle progression. Because D-type cyclins function as mitogenic sensors that link growth factor signaling directly with G₁ phase progression, it is not surprising that D cyclin accumulation is dysregulated in a variety of human tumors. Elevated expression of D cyclins results from gene amplification, increased gene transcription and protein translation, decreased microRNA levels, and inefficiency or loss of ubiquitylation-mediated protein degradation. This review focuses on the clinicopathological importance of D cyclins, how dysregulation of Ubiquitin-Proteasome System (UPS) contributes to the overexpression of D cyclins, and the therapeutic potential through targeting D cyclin-related machinery in human tumors.

The Establishment of Esophageal Precancerous Lesion Model by Using p53 Conditional Knockout Mouse in Esophageal Epithelium

Understanding the molecular mechanisms of precancerous lesion of esophageal cancer is beneficial for early diagnosis and early treatment. The deletion of p53 gene is common in esophageal cancer, but its pathogenesis is still unclear. An animal model is urgently needed to study the mechanisms of esophageal cancer and p53 deficiency. KO mice (p53^flox/flox.ED-L2-Cre^+/−) and the corresponding control Loxp mice (p53^flox/flox.ED-L2-Cre^−/−) were obtained by crossing between the p53^flox/flox mice and ED-L2-Cre^+/− mice. Methylbenzylnitrosamine (NMBA) was injected subcutaneously to induce esophageal precancerous lesion of these two groups of mice. Hematoxylin and eosin staining analysis was performed to evaluate the number and extent of esophageal precancerous lesions in KO mice and Loxp mice at the 16th and 48th weeks. Immunohistochemistry analysis was used to detect the change of Ki67, P21, Bcl-2, and Bax proteins. The number and extent of esophageal precancerous lesions in KO mice were significantly increased compared with the control at the 16th and 48th weeks under the induction of NMBA. The Ki67, P21, Bcl-2, and Bax proteins also had cancer-related pathological characteristics. These results suggest that the esophageal precancerous lesion model was established under the combined effect of p53 gene deletion in esophageal epithelium and NMBA, which could provide a new esophageal precancerous lesion model to explore the mechanism of precancerous lesions.

Emerging roles of F-box proteins in cancer drug resistance

Chemotherapy continues to be a major treatment strategy for various human malignancies. However, the frequent emergence of chemoresistance compromises chemotherapy efficacy leading to poor prognosis. Thus, overcoming drug resistance is pivotal to achieve enhanced therapy efficacy in various cancers. Although increased evidence has revealed that reduced drug uptake, increased drug efflux, drug target protein alterations, drug sequestration in organelles, enhanced drug metabolism, impaired DNA repair systems, and anti-apoptotic mechanisms, are critically involved in drug resistance, the detailed resistance mechanisms have not been fully elucidated in distinct cancers. Recently, F-box protein (FBPs), key subunits in Skp1-Cullin1-F-box protein (SCF) E3 ligase complexes, have been found to play critical roles in carcinogenesis, tumor progression, and drug resistance through degradation of their downstream substrates. Therefore, in this review, we describe the functions of FBPs that are involved in drug resistance and discuss how FBPs contribute to the development of cancer drug resistance. Furthermore, we propose that targeting FBPs might be a promising strategy to overcome drug resistance and achieve better treatment outcome in cancer patients. Lastly, we state the limitations and challenges of using FBPs to overcome chemotherapeutic drug resistance in various cancers.

Targeting glutamine-addiction and overcoming CDK4/6 inhibitor resistance in human esophageal squamous cell carcinoma

The dysregulation of Fbxo4-cyclin D1 axis occurs at high frequency in esophageal squamous cell carcinoma (ESCC), where it promotes ESCC development and progression. However, defining a therapeutic vulnerability that results from this dysregulation has remained elusive. Here we demonstrate that Rb and mTORC1 contribute to Gln-addiction upon the dysregulation of the Fbxo4-cyclin D1 axis, which leads to the reprogramming of cellular metabolism. This reprogramming is characterized by reduced energy production and increased sensitivity of ESCC cells to combined treatment with CB-839 (glutaminase 1 inhibitor) plus metformin/phenformin. Of additional importance, this combined treatment has potent efficacy in ESCC cells with acquired resistance to CDK4/6 inhibitors in vitro and in xenograft tumors. Our findings reveal a molecular basis for cancer therapy through targeting glutaminolysis and mitochondrial respiration in ESCC with dysregulated Fbxo4-cyclin D1 axis as well as cancers resistant to CDK4/6 inhibitors.

The RNA-binding protein FXR1 modulates prostate cancer progression by regulating FBXO4

This paper is to characterize the expression status of Fragile X Mental Retardation, Autosomal Homolog 1 (FXR1) in prostate cancer cells and understand its mechanistic involvement in the tumor biology of prostate cancer. The relative expression of FXR1 in prostate cancer cells was determined by real-time polymerase chain reaction and Western blotting. Cell proliferation in FXR1-deficient cells was evaluated by cell counting and MTT assays. The migrative and invasive capacities were measured by transwell assay. The potential regulatory effect of FXR1 on FBXO4 was interrogated using luciferase reporter assay. The direct bind of FXR1 with FBXO4 transcripts was analyzed by RNA immunoprecipitation and RNA pull-down assay. We observed aberrant overexpression of FXR1 in prostate cancer cells at both transcript and protein levels. FXR1 deficiency was associated with inhibited cell proliferation/viability and compromised migration/invasion in prostate cancer cells. Mechanistically, FXR1 negatively regulated FBXO4 transcripts via direct association with its 3'UTR and promoted mRNA degradation. FBXO4 knockdown predominantly rescued the tumor-suppressive phenotype in FXR1-deficient cells. We uncovered the oncogenic role of FXR1 in prostate cancer cells and further demonstrated its dependence on FBXO4. Our data highlight the importance of FXR1-FBXO4 signaling in prostate cancer.

FBXO22 Suppresses Metastasis in Human Renal Cell Carcinoma via Inhibiting MMP-9-Mediated Migration and Invasion and VEGF-Mediated Angiogenesis

F-box only protein 22 (FBXO22), a substrate receptor of the SKP1-Cullin 1-F-box protein (SCF) E3 ubiquitin ligase that targets key regulators of cellular activities for ubiquitylation and degradation, plays important roles in the progression of human cancer. However, little is known about the role of FBXO22 in renal cell carcinoma (RCC). This study aims to explore the biological function of FBXO22 in RCC progression and its specific regulation mechanism. We performed immunohistochemistry analysis and found that the expression level of FBXO22 was significantly lower in RCC tissues than in normal renal tissues. Reduced FBXO22 expression in RCC tissues is related to tumor size and TNM stage and to worse overall and disease-free survival. Through an in vitro assay, we demonstrated that FBXO22 has no effect on renal cancer cells proliferation, whereas FBXO22 remarkably restricted RCC cell migration and invasion, thereby reversing EMT transition and elevating the activity of tissue inhibitor of matrix metalloproteinase-1, which subsequently inhibited metalloproteinase-9 (MMP-9) expression and activity in vitro. We also found that FBXO22 suppresses tube formation by disrupting the secretion of vascular endothelial growth factor. Meanwhile, in vivo studies verified that FBXO22 suppresses RCC metastasis. These findings suggested that FBXO22 is a novel prognostic indicator and plays an important role in RCC metastasis.

Prognostic values of F-box members in breast cancer: an online database analysis and literature review

Introduction: F-box proteins are the substrate-recognizing subunits of SKP1 (S-phase kinase-associated protein 1)–cullin1–F-box protein (SCF) E3 ligase complexes that play pivotal roles in multiple cellular processes, including cell proliferation, apoptosis, angiogenesis, invasion, and metastasis. Dysregulation of F-box proteins may lead to an unbalanced proteolysis of numerous protein substrates, contributing to progression of human malignancies. However, the prognostic values of F-box members, especially at mRNA levels, in breast cancer (BC) are elusive. Methods: An online database, which is constructed based on the gene expression data and survival information downloaded from GEO (http://www.ncbi.nlm.nih.gov/geo/), was used to investigate the prognostic values of 15 members of F-box mRNA expression in BC. Results: We found that higher mRNA expression levels of FBXO1, FBXO31, SKP2, and FBXO5 were significantly associated with worse prognosis for BC patients. While FBXO4 and β-TrCP1 were found to be correlated to better overall survival (OS). Conclusion: The associated results provide new insights into F-box members in the development and progression of BC. Further researches to explore the F-box protein-targetting reagents for treating BC are needed.

Fbxo4-mediated degradation of Fxr1 suppresses tumorigenesis in head and neck squamous cell carcinoma

The Fbxo4 tumour suppressor is a component of an Skp1-Cul1-F-box E3 ligase for which two substrates are known. Here we show purification of SCFFbxo4 complexes results in the identification of fragile X protein family (FMRP, Fxr1 and Fxr2) as binding partners. Biochemical and functional analyses reveal that Fxr1 is a direct substrate of SCFFbxo4. Consistent with a substrate relationship, Fxr1 is overexpressed in Fbxo4 knockout cells, tissues and in human cancer cells, harbouring inactivating Fbxo4 mutations. Critically, in head and neck squamous cell carcinoma, Fxr1 overexpression correlates with reduced Fbxo4 levels in the absence of mutations or loss of mRNA, suggesting the potential for feedback regulation. Direct analysis reveals that Fbxo4 translation is attenuated by Fxr1, indicating the existence of a feedback loop that contributes to Fxr1 overexpression and the loss of Fbxo4. Ultimately, the consequence of Fxr1 overexpression is the bypass of senescence and neoplastic progression.

Dual cyclin-dependent kinase 4/6 inhibition by PD-0332991 induces apoptosis and senescence in oesophageal squamous cell carcinoma cells

BACKGROUND AND PURPOSE

Aberrant activation of the cyclin D1-cyclin-dependent kinase 4/6 (CDK4/6)-Rb signalling pathway is common in oesophageal squamous cell carcinoma (ESCC). PD-0332991, a highly specific inhibitor of CDK4/6, has potent antitumour activity against many types of cancer. The purpose of this study was to examine the in vitro and in vivo antineoplastic effect of PD-0332991 against the growth and metastasis of ESCC cells.

EXPERIMENTAL APPROACH

Cell viability and any synergy between PD-0332991 and 5-fluorouracil or cisplatin were measured by MTS assay and CalcuSyn software respectively. Cell migration and invasion were detected by wound healing and transwell assays. Apoptosis was evaluated by flow cytometry after staining annexin V-FITC/PI. Cellular senescence was assessed by measuring SA-β-gal activity. Nude mouse xenograft models of ESCC were employed to determine the in vivo activity of PD-0332991 against tumour growth and lung metastasis.

KEY RESULTS

PD-0332991 inhibited cellular growth and induced mitochondrial-dependent apoptosis in ESCC cells. PD-0332991 also suppressed migration, invasion and the expression of MMP-2 in ESCC cells. Furthermore, PD-0332991 treatment caused cell senescence in a FOXM1-dependent manner. In addition, there was synergy between PD-0332991 and cisplatin or 5-fluorouracil. Importantly, the xenografted tumour experiments demonstrated that PD-0332991 potently inhibits ESCC cell growth and lung metastasis.

CONCLUSIONS AND IMPLICATIONS

PD-0332991 can elicit a strong antitumour activity against ESCC growth and metastasis and may be a promising candidate drug for the treatment of patients with ESCC. Our results warrant a clinical trial to further evaluate the efficacy of PD-0332991 in ESCC patients, even those with metastasis.

Recent advances in SCF ubiquitin ligase complex: Clinical implications

F-box proteins, which are subunit recruiting modules of SCF (SKP1-Cullin 1-F-box protein) E3 ligase complexes, play critical roles in the development and progression of human malignancies through governing multiple cellular processes including cell proliferation, apoptosis, invasion and metastasis. Moreover, there are emerging studies that lead to the development of F-box proteins inhibitors with promising therapeutic potential. In this article, we describe how F-box proteins including but not restricted to well-established Fbw7, Skp2 and β-TRCP, are involved in tumorigenesis. However, in-depth investigation is required to further explore the mechanism and the physiological contribution of undetermined F-box proteins in carcinogenesis. Lastly, we suggest that targeting F-box proteins could possibly open new avenues for the treatment and prevention of human cancers.

Involvement of F-box proteins in esophageal cancer (Review)

The F-box proteins (FBPs) in esophageal tumorigenesis are pivotal as they govern a broad array of basic physiological responses including cell growth, cell death and DNA damage repair. Esophageal cancer (EC) is a common and highly aggressive cancer worldwide. Aberrant stabilization of crucial proteins participates in esophageal tumorigenesis. Recently, growing evidence has shown that FBPs play a critical role in oncogenesis, invasion, metastasis and prognosis assessment of EC. In this review we summarized published data on the roles of known FBPs, their respective substrates and the key signaling pathways, in the development of EC, aiming to uncover new ways for the rational design of targeted therapies in EC.

Deregulation of F-box proteins and its consequence on cancer development, progression and metastasis

F-box proteins are substrate receptors of the SCF (SKP1-Cullin 1-F-box protein) E3 ubiquitin ligase that play important roles in a number of physiological processes and activities. Through their ability to assemble distinct E3 ubiquitin ligases and target key regulators of cellular activities for ubiquitylation and degradation, this versatile group of proteins is able to regulate the abundance of cellular proteins whose deregulated expression or activity contributes to disease. In this review, we describe the important roles of select F-box proteins in regulating cellular activities, the perturbation of which contributes to the initiation and progression of a number of human malignancies.