F-box/WD Repeat-containing Protein 7 Research Articles

Calcineurin-mediated dephosphorylation stabilizes E2F1 protein by suppressing binding of the FBXW7 ubiquitin ligase subunit

The transcription factor E2F1 serves as a regulator of the cell cycle and promotes cell proliferation. It is highly expressed in cancer tissues and contributes to their malignant transformation. Degradation by the ubiquitin-proteasome system may help to prevent such overexpression of E2F1 and thereby to suppress carcinogenesis. A detailed understanding of the mechanisms underlying E2F1 degradation may therefore inform the development of new cancer treatments. We here identified SCFFBXW7 as a ubiquitin ligase for E2F1 by comprehensive analysis. We found that phosphorylation of E2F1 at serine-403 promotes its binding to FBXW7 (F-box/WD repeat-containing protein 7) followed by its ubiquitination and degradation. Furthermore, calcineurin, a Ca2+/calmodulin-dependent serine-threonine phosphatase, was shown to stabilize E2F1 by mediating its dephosphorylation at serine-403 and thereby preventing FBXW7 binding. Treatment of cells with Ca2+ channel blockers resulted in downregulation of both E2F1 protein and the expression of E2F1 target genes, whereas treatment with the Ca2+ ionophore ionomycin induced upregulation of E2F1. Finally, the calcineurin inhibitor FK506 attenuated xenograft tumor growth in mice in association with downregulation of E2F1 in the tumor tissue. Impairment of the balance between the opposing actions of FBXW7 and calcineurin in the regulation of E2F1 abundance may therefore play an important role in carcinogenesis.

ASPM stabilizes the NOTCH intracellular domain 1 and promotes oncogenesis by blocking FBXW7 binding in hepatocellular carcinoma cells.

Notch signaling is aberrantly activated in approximately 30% of hepatocellular carcinoma (HCC), significantly contributing to tumorigenesis and disease progression. Expression of the major Notch receptor, NOTCH1, is upregulated in HCC cells and correlates with advanced disease stages, although the molecular mechanisms underlying its overexpression remain unclear. Here, we report that expression of the intracellular domain of NOTCH1 (NICD1) is upregulated in HCC cells due to antagonism between the E3-ubiquitin ligase F-box/WD repeat-containing protein 7 (FBXW7) and the large scaffold protein abnormal spindle-like microcephaly-associated protein (ASPM) isoform 1 (ASPM-i1). Mechanistically, FBXW7-mediated polyubiquitination and the subsequent proteasomal degradation of NICD1 are hampered by the interaction of NICD1 with ASPM-i1, thereby stabilizing NICD1 and rendering HCC cells responsive to stimulation by Notch ligands. Consistently, downregulating ASPM-i1 expression reduced the protein abundance of NICD1 but not its FBXW7-binding-deficient mutant. Reinforcing the oncogenic function of this regulatory module, the forced expression of NICD1 significantly restored the tumorigenic potential of ASPM-i1-deficient HCC cells. Echoing these findings, NICD1 was found to be strongly co-expressed with ASPM-i1 in cancer cells in human HCC tissues (P < 0.001). In conclusion, our study identifies a novel Notch signaling regulatory mechanism mediated by protein-protein interaction between NICD1, FBXW7, and ASPM-i1 in HCC cells, representing a targetable vulnerability in human HCC.

Targeted next-generation sequencing for the detection of cancer-associated somatic mutations in adenomyosis

Adenomyosis is a condition characterised by the invasion of endometrial tissues into the uterine myometrium, the molecular pathogenesis of which remains incompletely elucidated. Lesion profiling with next-generation sequencing (NGS) can lead to the identification of previously unanticipated causative genes and the detection of therapeutically actionable genetic changes. Using an NGS panel that included 275 cancer susceptibility genes, this study examined the occurrence and frequency of somatic mutations in adenomyotic tissue specimens collected from 17 women. Extracted DNA was enriched using targeted formalin-fixed paraffin-embedded tissue cores prior to the identification of lesion-specific variants. The results revealed that KRAS and AT-rich interactive domain 1A (ARID1A) were the two most frequently mutated genes (mutation frequencies: 24% and 12%, respectively). Notably, endometrial atypical hyperplasia did not involve adenomyotic areas. We also identified, for the first time, two potentially pathogenic mutations in the F-box/WD repeat-containing protein 7 (FBXW7) and cohesin subunit SA-2 (STAG2) genes. These findings indicate that mutations in the KRAS, ARID1A, FBXW7 and STAG2 genes may play a critical role in the pathogenesis of adenomyosis. Additional studies are needed to assess whether the utilisation of oncogenic driver mutations can inform the surveillance of patients with adenomyosis who had not undergone hysterectomy. Impact statement What is already known on this subject? Although somatic point mutations in the KRAS oncogene have been recently detected in adenomyosis, the molecular underpinnings of this condition remains incompletely elucidated. Lesion profiling with next-generation sequencing (NGS) can lead to the identification of previously unanticipated causative genes and the detection of therapeutically actionable genetic changes. What do the results of this study add? The results of NGS revealed that KRAS and AT-rich interactive domain 1A (ARID1A) were the two most frequently mutated genes (mutation frequencies: 24% and 12%, respectively). We also identified, for the first time, two potentially pathogenic mutations in the F-box/WD repeat-containing protein 7 (FBXW7) and cohesin subunit SA-2 (STAG2) genes. What are the implications of these findings for clinical practice and/or further research? The utilisation of oncogenic driver mutations has the potential to inform the surveillance of patients with adenomyosis who had not undergone hysterectomy.

FBXW7 Enhances Cisplatin-Induced Apoptosis in Oral Cancer Cell Lines

About one-third of patients with oral squamous cell carcinoma (OSCC) have a risk of occurrence and chemoresistance, making survival rates abysmal. We aim to evaluate the role of F-box/WD repeat-containing protein 7 (FBXW7) to further develop efficient treatment of chemoresistant OSCC. FBXW7 overexpression was induced in human OSCC cell lines including SCC9 and CAL27 by a lentiviral vector, Lv-FBXW7 or lv-NC (noncoding control), and overexpression efficiency was assessed using quantitative real-time polymerase chain reaction (qRT-PCR) and western blot of FBXW7. Cell viability was measured using MTT assay. The effects of FBXW7 overexpression on cell migration and invasion was evaluated by the colony formation assay and Matrigel assay. Apoptosis of cells with lv-FBXW7 transfection was measured by qRT-PCR and western blot analyses of BAX, BAK, MCL1, and BCL2 expression. Growth rate and cisplatin sensitivity of CAL27 xenografts with or without FBXW7 overexpression was monitored. Ki-67 and PCMA levels-which are biomarkers of intratumoural apoptosis-BAX, MCL1, Beclin1, and LC3I&II-which are autophagy biomarkers-were assessed. Transfection of lv-FBXW7 in SCC9 and CAL27 cells resulted in increased sensitivity to cisplatin treatment, as evidenced by slower cell proliferation, lower colony formation and invasion, higher apoptosis, and autophagy compared to those transfected with lv-NC. Mice with CAL27 xenografts overexpressing FBXW7 also demonstrated slower tumour growth and upregulation in Ki067 and PCNA. Tumours also showed higher apoptosis and autophagy activities. FBXW7 overexpression was herein shown to effectively sensitise OSCC cells to cisplatin treatment in vitro and in vivo.

FBXW7 affects autophagy through MCL1 in oral squamous cell carcinoma.

Oral cancer is associated with high risk of morbidity and mortality. However, effective treatment for oral cancer is urgently required in clinics. In this study, we aimed to determine whether F-box/WD repeat-containing protein 7 (FBXW7), an essential tumor suppressor gene, can regulate autophagy and improve the prognosis in oral squamous cell carcinoma (OSCC). mRNA levels of FBXW7 and myeloid cell leukemia 1 (MCL-1) in OSCC tissues and adjacent normal tissues were measured by qRT-PCR. FBXW7 and MCL-1 were overexpressed in OSCC cell line using lentivirus containing FBXW7 and MCL-1, respectively. Protein expression was determined by Western blot. The mRNA and protein levels of FBXW7 were decreased in patients with OSCC, whereas the mRNA and protein levels of MCL-1 were increased. Moreover, the mRNA coding for autophagy proteins was reduced in patients with OSCC. Additionally, it was found that overexpression of FBXW7 significantly reduced MCL-1 expression and upregulated autophagy-related proteins, including Beclin1, autophagy related 7, and microtubule-associated protein light chain 3. Our results suggest that FBXW7 affects autophagy through MCL1 in OSCC.

FBXW7 induces apoptosis in glioblastoma cells by regulating HDAC7.

Glioblastoma is an aggressive type of brain cancer with an extremely poor prognosis. Additionally, the F-box WD repeat-containing protein 7 (FBXW7) is a component of the ubiquitin-proteasome system that has been widely implicated in human cancers. In this study, we investigated the role and mechanism of FBXW7 in glioblastoma. FBXW7 expression was analyzed in normal and glioblastoma tissue samples using The Cancer Genome Atlas Glioblastoma Multiforme (TCGA-GBM) database. Then, quantitative reverse transcription-polymerase chain reaction (RT-PCR) was used to examine mRNA expression, whereas, western blot analysis was conducted to determine protein levels of the samples. Furthermore, cell apoptosis was assessed using the Annexin V staining method, followed by flow cytometry analysis. Immunoprecipitation (IP) assay was conducted as well to test protein-protein interactions. Lastly, protein expression in tissues was examined by conducting immunohistochemistry (IHC). Results showed that the glioblastoma tissue samples displayed an FBXW7 downregulation compared with normal tissues. In vitro, the overexpression of FBXW7 in glioblastoma cells induced apoptosis, whereas, its knockdown displayed the opposite effect. Mechanistically, FBXW7 interacted with HDAC7 to promote HDAC7 ubiquitination, however, the overexpression of HDAC7 in glioblastoma cells blocked FBXW7-induced apoptosis. Finally, FBXW7 and HDAC7 displayed an inverse correlation in glioblastoma tissues in vivo. Therefore, our data demonstrated an important function of FBXW7 in promoting glioblastoma apoptosis by interacting with HDAC7 and promoting HDAC7 ubiquitination.

FBXW7 regulates epithelial barrier impairment in human bronchial epithelial cells in vitro by targeting apoptosis signal-regulating kinase1 via the p38 pathway

Bronchial asthma is a common chronic inflammatory disease characterized by airway hyperresponsiveness (AHR), inflammatory cell infiltration, and airway remodeling. F-box/WD repeat-containing protein 7 (FBXW7), an E3 ubiquiti... | Find, read and cite all the research you need on Tech Science Press

Alteration of FBXW7 is Associated with Worse Survival in Patients Undergoing Resection of Colorectal Liver Metastases

BackgroundFor patients undergoing resection of colorectal liver metastases (CLMs), the prognostic role of somatic gene alterations is increasingly recognized. F-box/WD repeat–containing protein 7 (FBXW7) is a tumor suppressor gene found in approximately 10% of patients with colorectal cancer. The aim of this study is to assess the association of FBXW7 with overall survival after CLM resection. MethodsPatients who underwent initial CLM resection during 2001–2016 and had genetic sequencing data were studied. Risk factors for overall survival (OS) were evaluated with Cox proportional hazards models using backward elimination. ResultsOf 2045 patients who underwent CLM resection during the study period, 476 were included. The majority (90.5%) underwent prehepatectomy chemotherapy. A total of 27 patients (5.7%) had FBXW7 alteration, along with 240 (50.4%) RAS, 337 (70.8%) TP53, 51 (10.7%) SMAD4, and 27 (5.7%) BRAF. Cox proportional hazards model analyses including 5 somatic gene alteration status and 12 clinicopathologic factors revealed FBXW7(hazard ratio [HR] 1.99, P = 0.015), BRAF (HR 2.47, P = 0.023), RAS (HR 2.42, P < 0.001), TP53 (HR 2.00, P < 0.001), and SMAD4 alterations (HR 1.90, P = 0.004) as significantly associated with OS, together with three clinicopathologic factors, prehepatectomy chemotherapy > 6 cycles (HR 1.51, P = 0.021), number of CLM (HR 1.05, P = 0.007), and largest liver metastasis diameter (HR 1.07, P = 0.023). The covariate-adjusted 5-year OS was significantly lower in patients with FBXW7 alteration than in patients with FBXW7 wild-type (40.4% vs.59.4%, P = 0.015). ConclusionsFBXW7 alterations are associated with worse survival after CLM resection. The information on multiple somatic gene alterations is imperative for risk stratification and patient selection for CLM resection.

Transcription Factor ELF1 Activates MEIS1 Transcription and Then Regulates the GFI1/FBW7 Axis to Promote the Development of Glioma

Glioma is the most common malignancy in the central nervous system with no immediate prospect of a cure. Comprehensive understanding on the pathogenesis of the disorder contributes to a better outcome. Herein, we aimed to investigate whether transcription factors erythroblast transformation-specific (ETS) transcription factor (ELF1), myeloid ecotropic viral integration site 1 (MEIS1), and growth factor independence 1 (GFI1)/F-box/WD repeat-containing protein 7 (FBW7) mediate progression of glioma. ELF1, MEIS1, and GFI1 were upregulated in glioma cells and tissues, as ELF1 was correlated with poor prognosis. Bioinformatics analysis identified the binding between ELF1 and MEIS1 as well as between GFI1 and FBW7, confirmed by chromatin immunoprecipitation (ChIP) experiments. Functional experiment indicated that silencing of ELT1 decreased MEIS1 expression and that overexpression of MEIS1 increased GFI1 expression by activating GFI1 enhancer but decreased FBW7 expression. Importantly, silencing of ELF1 decreased the capacities of proliferation, migration, and invasion of glioma cells whereas it increased apoptosis, supported by increased capase-3 and decreased matrix metalloproteinase-9 (MMP-9) and proliferating cell nuclear antigen (PCNA) expression. Moreover, an in vivo experiment confirmed the inhibitory role of silenced ELF1 in tumor growth, with a decreased level of MEIS1 and GFI1. Taken together, our study elucidated a potential mechanism that ELF1 promoted cell progression by increasing GFI1 and METS1 as well as decreasing FBW7 expression in glioma.

MicroRNA‑92a promotes non‑small cell lung cancer cell growth by targeting tumor suppressor gene FBXW7.

MicroRNA (miRNA/miR)-92a has been identified as being significantly downregulated in non-small cell lung cancer (NSCLC) tissues using a miRNA array. However, its biological function and molecular mechanisms in NSCLC have not been fully elucidated. The aim of the present study was to determine the role of miR-92a in NSCLC and the mechanisms by which it affects NSCLC cells. The expression levels of miR-92a in NSCLC tissues and cell lines were analyzed using reverse transcription-quantitative PCR. Cell viability and cell apoptosis were determined using an MTT assay and flow cytometry, respectively. It was observed that miR-92a was significantly upregulated in NSCLC tissues and cell lines. Inhibition of miR-92a significantly suppressed viability of NSCLC cells, with concomitant downregulation of key proliferative genes, such as proliferating cell nuclear antigen and Ki-67. miR-92a downregulation induced apoptosis of NSCLC cells, as evidenced by flow cytometry and apoptosis-related protein detection. Luciferase assays confirmed that miR-92a could directly bind to the 3′-untranslated region of tumor suppressor F-box/WD repeat-containing protein 7 (FBXW7) and suppress its translation. Furthermore, small interfering RNA-mediated FBXW7 inhibition partially attenuated the tumor suppressive effect of an miR-92a inhibitor on NSCLC cells. Collectively, these findings demonstrated that miR-92a might function as an oncogene in NSCLC by regulating FBXW7. In conclusion, miR-92a could serve as a potential therapeutic target in NSCLC treatment.

RASA1 inhibits the progression of renal cell carcinoma by decreasing the expression of miR-223-3p and promoting the expression of FBXW7.

RAS p21 protein activator 1 (RASA1), also known as p120-RasGAP, is a RasGAP protein that functions as a signaling scaffold protein, regulating pivotal signal cascades. However, its biological mechanism in renal cell carcinoma (RCC) remains unknown. In the present study, RASA1, F-box/WD repeat-containing protein 7 (FBXW7), and miR-223-3p expression were assessed via quantitative reverse transcription-polymerase chain reaction (qRT-PCR) and Western blot. Then, the targeted correlations of miR-223-3p with FBXW7 and RASA1 were verified via a dual-luciferase reporter gene assay. CCK-8, flow cytometry, and Transwell assays were implemented independently to explore the impact of RASA1 on cell proliferation, apoptosis, migration, and cell cycle progression. Finally, the influence of RASA1 on tumor formation in RCC was assessed in vivo through the analysis of tumor growth in nude mice. Results showed that FBXW7 and RASA1 expression were decreased in RCC tissues and cell lines, while miR-223-3p was expressed at a higher level. Additionally, FBXW7 and RASA1 inhibited cell proliferation but facilitated the population of RCC cells in the G0/G1 phase. Altogether, RASA1 may play a key role in the progression of RCC by decreasing miR-223-3p and subsequently increasing FBXW7 expression.

MiR-223 regulates autophagy associated with cisplatin resistance by targeting FBXW7 in human non-small cell lung cancer

BackgroundCisplatin is widely used as a first-line treatment for non-small cell lung cancer (NSCLC), but chemoresistance remains a major clinical obstacle for efficient use. As a microRNA, miR-223 was reported to promote the doxorubicin resistance of NSCLC. However, whether miR-223 is also involved in cisplatin resistance of NSCLC and the mechanism miR-223 involved in drug resistance is unclear. Accumulated evidence has shown that abnormal autophagy is associated with tumor chemoresistance. The study aimed to study the role of miR-223 on cisplatin sensitivity in NSCLC and uncover the potential mechanisms.MethodsNSCLC cells transfected with mimic or inhibitor for miR-223 was assayed for chemoresistance in vitro. MiR-223 expression was assessed by quantitative real-time PCR (qRT-PCR). Western blot were used to study the expression level of F-box/WD repeat-containing protein 7 (FBXW7) and autophagy-related protein. The effect of miR-223 on cisplatin sensitivity was examined by using CCK-8, EdU assays and Autophagic flux assay. Luciferase assays, EdU assays and small interfering RNA were performed to identify the targets of miR-223 and the mechanism by which it promotes treatment resistance. Xenograft models were established to investigate the effect of mir-223 on cisplatin sensitivity.ResultsIn the present study, we found that the level of miR-223 was significantly positively correlated with cisplatin resistance. MiR-223 overexpression made NSCLC cells resistant to cisplatin treatment. We further found that autophagy mediated miR-223-mediated cisplatin resistance in NSCLC cells. Further mechanistic research demonstrated that miR-223 directly targeted FBXW7. The overexpression of miR-223 could inhibit the level of FBXW7 protein expression, thus promoting autophagy and making NSCLC cells resistant to cisplatin. Finally, we confirmed the increased effect of cisplatin sensitivity by miR-223 Antagomir in xenograft models of NSCLC.ConclusionsOur results demonstrate that miR-223 could enhance autophagy by targeting FBXW7 in NSCLC cells. Inhibition of autophagy by miR-223 knockdown provides a novel treatment strategy to alleviate cisplatin resistance in NSCLC.

Function and regulation of F-box/WD repeat-containing protein 7.

The ubiquitin-proteasome system is an important post-translational modification system involved in numerous biological processes, such as cell cycle regulation, gene transcription, signal transduction, apoptosis, differentiation and development. F-box/WD repeat-containing protein 7 (FBXW7) is one of the most studied F-box (FBX) proteins, serving as substrate recognition component of S phase kinase-associated protein 1-Cullin 1-FBX protein complexes. As a tumor suppressor, FBXW7 recognizes numerous proto-oncoproteins and promotes their ubiquitination and subsequent proteasomal degradation. FBXW7 is regulated at different levels, leading to tunable and specific control of the activity and abundance of its substrates. Therefore, genetic mutations or decreases in its expression serve an important biological role in tumor development. In-depth studies and identification of additional substrates targeted by FBXW7 have suggested a signaling network regulated by FBXW7, including its tumor-inhibitory role. The present review focused on the role of FBXW7 in tumor suppression and its application in cancer therapy.

FBW7 regulates HIF-1α/VEGF pathway in the IL-1β induced chondrocytes degeneration.

The aim of the study was to observe the effect of F-box/WD repeat-containing protein 7 (FBW7) on hypoxia-inducible factor-1α (HIF-1α)/vascular endothelial growth factor (VEGF) pathway in chondrocytes (CHs) under IL-1β induced degeneration. We explored the levels of FBW7, HIF-1α, and VEGF in degenerated cartilage from osteoarthritis (OA) and chondrocytes (CHs) treated by IL-1β. Meanwhile, we regulated HIF-1α and FBW7 expression in IL-1β treated CHs and observed the effects FBW7 of the HIF-1α/VEGF pathway. FBW7 expression was significantly decreased along with the increased HIF-1α and VEGF expression both in OA cartilage and IL-1β induced degenerated CHs. Additionally, suppression of HIF-1α decreased VEGF level, which contributed to the production of collagen II, aggrecan and SOX-9, and inhibited collagen I and Runx-2 expression. Furthermore, FBW7 suppressed HIF-1α/VEGF pathway and promoted the integration of collagen II, aggrecan, and SOX-9, but inhibited the collagen I and Runx-2 expression. FBW7 negatively regulates HIF-1α/VEGF pathway and plays a protective role in the IL-1β induced CHs degeneration.

The F-box protein FBXL16 up-regulates the stability of C-MYC oncoprotein by antagonizing the activity of the F-box protein FBW7

F-box proteins, such as F-box/WD repeat-containing protein 7 (FBW7), are essential components of the SKP1-CUL1-F-box (SCF) E3 ubiquitin ligases. They bind to S-phase kinase-associated protein 1 (SKP1) through the F-box motif and deliver their protein substrate to the E3 ligase complex for ubiquitination and subsequent degradation. F-box and leucine-rich repeat protein 16 (FBXL16) is a poorly studied F-box protein. Because it does not interact with the scaffold protein cullin 1 (CUL1), we hypothesized that FBXL16 might not form a functional SCF-E3 ligase complex. In the present study, we found that FBXL16 up-regulates the levels of proteins targeted by SCF-E3 ligases, such as C-MYC, β-catenin, and steroid receptor coactivator 3 (SRC-3). Focusing on C-MYC, a well-known oncoprotein overexpressed in most human cancers, we show that FBXL16 stabilizes C-MYC by antagonizing FBW7-mediated C-MYC ubiquitination and degradation. Further, we found that, although FBXL16 does not interact with CUL1, it interacts with SKP1 via its N-terminal F-box domain and with its substrate C-MYC via its C-terminal leucine-rich repeats (LRRs) domain. We found that both the F-box domain and the LRR domain are important for FBXL16-mediated C-MYC stabilization. In line with its role in up-regulating the levels of the C-MYC and SRC-3 oncoproteins, FBXL16 promoted cancer cell growth and migration and colony formation in soft agar. Our findings reveal that FBXL16 is an F-box protein that antagonizes the activity of another F-box protein, FBW7, and thereby increases C-MYC stability, resulting in increased cancer cell growth and invasiveness.

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

BackgroundDysregulation 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.MethodsThe 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.ResultsIt 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.ConclusionThe 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.

Role of FBXW7 in the quiescence of gefitinib-resistant lung cancer stem cells in EGFR-mutant non-small cell lung cancer.

Several recent studies suggest that cancer stem cells (CSCs) are involved in intrinsic resistance to cancer treatment. Maintenance of quiescence is crucial for establishing resistance of CSCs to cancer therapeutics. F-box/WD repeat-containing protein 7 (FBXW7) is a ubiquitin ligase that regulates quiescence by targeting the c-MYC protein for ubiquitination. We previously reported that gefitinib-resistant persisters (GRPs) in EGFR-mutant non-small cell lung cancer (NSCLC) cells highly expressed octamer-binding transcription factor 4 (Oct-4) as well as the lung CSC marker CD133, and they exhibited distinctive features of the CSC phenotype. However, the role of FBXW7 in lung CSCs and their resistance to epidermal growth factor receptor (EGFR)-tyrosine kinase inhibitors in NSCLC is not fully understood. In this study, we developed GRPs from the two NSCLC cell lines PC9 and HCC827, which express an EGFR exon 19 deletion mutation, by treatment with a high concentration of gefitinib. The GRPs from both PC9 and HCC827 cells expressed high levels of CD133 and FBXW7, but low levels of c-MYC. Cell cycle analysis demonstrated that the majority of GRPs existed in the G0/G1 phase. Knockdown of the FBXW7 gene significantly reduced the cell number of CD133-positive GRPs and reversed the cell population in the G0/G1-phase. We also found that FBXW7 expression in CD133-positive cells was increased and c-MYC expression was decreased in gefitinib-resistant tumors of PC9 cells in mice and in 9 out of 14 tumor specimens from EGFR-mutant NSCLC patients with acquired resistance to gefitinib. These findings suggest that FBXW7 plays a pivotal role in the maintenance of quiescence in gefitinib-resistant lung CSCs in EGFR mutation-positive NSCLC.

PRMT5 enhances tumorigenicity and glycolysis in pancreatic cancer via the FBW7/cMyc axis

BackgroundThe epigenetic factor protein arginine methyltransferase 5 (PRMT5) has been reported to play vital roles in a wide range of cellular processes, such as gene transcription, genomic organization, differentiation and cell cycle control. However, its role in pancreatic cancer remains unclear. Our study aimed to investigate the roles of PRMT5 in pancreatic cancer prognosis and progression and to explore the underlying molecular mechanism.MethodsReal-time PCR, immunohistochemistry and analysis of a dataset from The Cancer Genome Atlas (TCGA) were performed to study the expression of PRMT5 at the mRNA and protein levels in pancreatic cancer. Cell proliferation assays, including cell viability, colony formation ability and subcutaneous mouse model assays, were utilized to confirm the role of PRMT5 in cell proliferation and tumorigenesis. A Seahorse extracellular flux analyzer, a glucose uptake kit, a lactate level measurement kit and the measurement of 18F-FDG (fluorodeoxyglucose) uptake by PET/CT (positron emission tomography/computed tomography) imaging were used to verify the role of PRMT5 in aerobic glycolysis, which sustains cell proliferation. The regulatory effect of PRMT5 on cMyc, a master regulator of oncogenesis and aerobic glycolysis, was explored by quantitative PCR and protein stability measurements.ResultsPRMT5 expression was significantly upregulated in pancreatic cancer tissues compared with that in adjacent normal tissues. Clinically, elevated expression of PRMT5 was positively correlated with worse overall survival in pancreatic cancer patients. Silencing PRMT5 expression inhibited the proliferation of pancreatic cancer cells both in vitro and in vivo. Moreover, PRMT5 regulated aerobic glycolysis in vitro in cell lines, in vivo in pancreatic cancer patients and in a xenograft mouse model used to measure 18F-FDG uptake. We found that mechanistically, PRMT5 posttranslationally regulated cMyc stability via F-box/WD repeat-containing protein 7 (FBW7), an E3 ubiquitin ligase that controls cMyc degradation. Moreover, PRMT5 epigenetically regulated the expression of FBW7 in pancreatic cancer cells.ConclusionsThe present study demonstrated that PRMT5 epigenetically silenced the expression of the tumor suppressor FBW7, leading to increased cMyc levels and the subsequent enhancement of the proliferation of and aerobic glycolysis in pancreatic cancer cells. The PRMT5/FBW7/cMyc axis could be a potential therapeutic target for the treatment of pancreatic cancer.

FBXW7 mutation is associated with decreased survival following hepatectomy for metastatic colorectal cancer

Introduction: Improved understanding of tumor genomics has transformed the treatment of colorectal liver metastases (CLM). F-box/WD repeat-containing protein 7 (FBXW7) is a tumor suppressor gene recognized in the degradation of mediators of cell cycle progression. We have previously reported the effect of frequently mutations in the setting of CLM, however the role of FBXW7 in the progression of this disease is underreported. We aimed to evaluate the impact of FBXW7 mutation on survival following hepatectomy for CLM. Method: Clinicopathologic data was abstracted for patients with documented mutational analysis who underwent hepatectomy from 2001-2016. Kaplan-Meier analysis was performed for overall survival (OS) and compared by log-rank test. Risk factors for overall survival were determined by Cox proportional hazards model. Result: In total, 462 patients were included with a median age of 55 years (IQR 46-62 years). Most had colon primary tumors (68.5%), were ≥T3 (87.5%), and had lymph node-positive primary disease (70.9%). Synchronous metastasis occurred in 76.5%, yet the minority had extrahepatic metastases (16.6%). Most (90.5%) underwent neoadjuvant chemotherapy, with 71% of these receiving concomitant targeted therapy. Few patients (20.4%) underwent R1 resection. The most common mutation associated with survival was TP53 (prevalence: 70.7%,HR:2.0, 95%CI 1.4-3.0, p<0.001), followed byRAS (50.4%, HR:2.4, 95%CI 1.7-3.5, p<001). Mutation in FBXW7 was found in 5.7% of patients, and it was a strong negative prognostic factor for OS (HR 1.99, p=0.015). BRAF was the least common mutation, found in 2.3%, but it was the strongest negative prognostic factor for OS (HR 2.47, p=0.023). Conclusion: Mutation of FBXW7 is a strong negative predictor of OS and is detected more frequently than other accepted mutations used for prognostication following hepatectomy for CLM. Further analyses of FBXW7 in combination with additional mutations and clinical factors may refine risk stratification and treatment decisions for patients with CLM.

Sorting Nexin 5 Controls Head and Neck Squamous Cell Carcinoma Progression by Modulating FBW7

Head and neck squamous cell carcinoma (HNSCC) is the sixth most prevalent cancer worldwide. Long-term survival rates in patients with HNSCC have not increased significantly in the past 30 years. Therefore, looking for novel molecular targets that control HNSCC progression is urgently required to improve the treatment of HNSCC. Here, we identified Sorting Nexin 5 (SNX5) as a new regulator that plays an oncogenic function in HNSCC progression. Analyzing HNSCC patients' data from the Cancer Genome Atlas (TCGA) indicates that the expression levels of SNX5 in HNSCC are significantly elevated compared to normal tissues. Furthermore, higher SNX5 expression correlates with a worse prognosis for HNSCC patients. These results suggest that SNX5 has an oncogenic role. Consistently, loss of SNX5 in HNSCC cells dramatically reduces colony formation and significantly decreases tumor growth in xenograft mouse models. SNX5 interacts with the tumor suppressor F-box/WD repeat-containing protein 7 (FBW7), an E3 ubiquitin ligase that mediates ubiquitination and degradation of oncoproteins such as c-Myc, NOTCH1, and Cyclin E1. By interacting with FBW7, SNX5 inhibits FBW7-mediated oncoproteins ubiquitination. In this way, SNX5 decreases the FBW7-mediated oncoproteins degradation to promote HNSCC progression.