FBXW7 Protein Research Articles

Deletion of Fbxw7 in oocytes causes follicle loss and premature ovarian insufficiency in mice.

Premature ovarian insufficiency (POI) is one of the important causes of female infertility. Yet the aetiology for POI is still elusive. FBXW7 (F-box with 7 tandem WD) is one of the important components of the Skp1-Cullin1-F-box (SCF) E3 ubiquitin ligase. FBXW7 can regulate cell growth, survival and pluripotency through mediating ubiquitylation and degradation of target proteins via triggering the ubiquitin-proteasome system, and is associated with tumorigenesis, haematopoiesis and testis development. However, evidence establishing the function of FBXW7 in ovary is still lacking. Here, we showed that FBXW7 protein level was significantly decreased in the ovaries of the cisplatin-induced POI mouse model. We further showed that mice with oocyte-specific deletion of Fbxw7 demonstrated POI, characterized with folliculogenic defects, early depletion of follicle reserve, disordered hormonal secretion, ovarian dysfunction and female infertility. Impaired oocyte-GCs communication, manifested as down-regulation of connexin 37, may contribute to follicular development failure in the Fbxw7-mutant mice. Furthermore, single-cell RNA sequencing and insitu hybridization results indicated an accumulation of Clu and Ccl2 transcripts, which may alter follicle microenvironment deleterious to oocyte development and accelerate POI. Our results establish the important role of Fbxw7 in folliculogenesis and ovarian function, and might provide valuable information for understanding POI and female infertility.

Role of F-box WD Repeat Domain Containing 7 in Type 1 Diabetes

Type I diabetes (T1DM) is a chronic immune system disease characterized by the devastation or injury of ß-cells in the Langerhans Island, resulting in insulin deficiency and hyperglycemia. This study determines the new marker F-box and WD repeat domain containing 7 (FBXW7). One hundred twenty type 1 diabetic patients from three different places (central child hospital, Alkindi center for diabetes and endocrinology, Children’s Education Hospital) in Iraq during the period from (20 December 2021 to 25 March 2022) an age ranges of (4-17) years. The patient group consisted of being derived to three groups: group one healthy patient group (33) was included as healthy patient, group two (20) newly diagnosed T1DM and (67) type 1 diabetic with insulin treatment. The quantitative enzyme-linked immunosorbent assay (ELISA) biochemical parameters were used to quantify the protein FBXW-7 levels. FBG, Cholesterol, Triglyceride, HDL, LDL, VLDL, HbA1c, GOT, GPT, Total Oxidant status, and Total Antioxidant status were measured through spectrophotometry. Serum FBXW-7 protein levels were considerably elevated noticeably (p-value = 0.00). In terms of FBXW7 protein, there was a significant variation between the new and therapy groups. There was no significant variation in protein levels between the new compared to healthy groups. Serum FBXW-7 protein was positively correlated with FBG, TG, cholesterol, GOT, GPT, LDL, and VLDL, and was negatively correlated with HDL in the patient group. According to ROC analysis, the cutoff value for FBXW-7 protein was (1.9) in the newly group and (2.1) in the treatment group. Levels of FBXW-7 protein are elevated in DM patients. FBXW-7 protein was significantly different in the treatment group but not different in the newly group when compared with the healthy group.

FBXW7 tumor suppressor regulation by dualspecificity tyrosine-regulated kinase 2

FBXW7 is a member of the F-box protein family, which functions as the substrate recognition component of the SCF E3 ubiquitin ligase. FBXW7 is a main tumor suppressor due to its ability to control proteasome-mediated degradation of several oncoproteins such as c-Jun, c-Myc, Cyclin E1, mTOR, and Notch1-IC. FBXW7 inactivation in human cancers results from a somatic mutation or downregulation of its protein levels. This work describes a novel regulatory mechanism for FBXW7 dependent on the serine/threonine protein kinase DYRK2. We show that DYRK2 interacts with and phosphorylates FBXW7 resulting in its proteasome-mediated degradation. DYRK2-dependent FBXW7 destabilization is independent of its ubiquitin ligase activity. The functional analysis demonstrates the existence of DYRK2-dependent regulatory mechanisms for key FBXW7 substrates. Finally, we provide evidence indicating that DYRK2-dependent regulation of FBXW7 protein accumulation contributes to cytotoxic effects in response to chemotherapy agents such as Doxorubicin or Paclitaxel in colorectal cancer cell lines and to BET inhibitors in T-cell acute lymphoblastic leukemia cell lines. Altogether, this work reveals a new regulatory axis, DYRK2/FBXW7, which provides an understanding of the role of these two proteins in tumor progression and DNA damage responses.

MiR-25 enhances autophagy and promotes sorafenib resistance of hepatocellular carcinoma via targeting FBXW7.

Sorafenib resistance is a major challenge in the treatment of patients with advanced hepatocellular carcinoma (HCC). MicroRNAs (miRNAs) are a large family of non-coding RNA molecules, which is an important mechanism of drug resistance. We previously found that knockdown of miR-25 increased the sensitivity of TRAIL-induced apoptosis in liver cancer stem cells. We aimed to study the effects of miR-25 on sorafenib resistance of HCC and the underlying mechanisms. In the present study, we analyzed the expression of miR-25 between HCC and normal tissues and predicted miR-25 target genes through databases. After transfecting miR-25 mimics, inhibitor or FBXW7 Plasmid, CCK-8 and flow cytometry assay was performed to determine the sorafenib resistance. We performed LC3-dual-fluorescence assay and Western blotting to detect the autophagy levels. The expression of miR-25 was upregulated in human HCC tissues and was associated with tumor pathological grade, clinic staging, and lymphatic metastasis. MiR-25 enhanced sorafenib resistance of HCC cells and autophagy. FBXW7 is the direct target of miR-25. Overexpression of FBXW7 could reverse the increase of sorafenib resistance caused by miR-25 mimics. Our results suggested that miR-25 increased the sorafenib resistance of HCC via inducing autophagy. In addition, miR-25 decreases the expression of FBXW7 protein to regulate autophagy. Therefore, miR-25 may represent a novel therapeutic target for the treatment of HCC.

Tazarotene-induced gene 1 interacts with Polo-like kinase 2 and inhibits cell proliferation in HCT116 colorectal cancer cells.

Tazarotene-induced gene 1 (TIG1) is considered to be a tumor suppressor gene that is highly expressed in normal or well-differentiated colon tissues, while downregulation of TIG1 expression occurs in poorly differentiated colorectal cancer (CRC) tissues. However, it is still unclear how TIG1 regulates the tumorigenesis of CRC. Polo-like kinases (Plks) are believed to play an important role in regulating the cell cycle. The performance of PLK2 in CRC is negatively correlated with the differentiation status of CRC tissues. Here, we found that PLK2 can induce the growth of CRC cells and that TIG1 can prevent PLK2 from promoting the proliferation of CRC cells. We also found that the expression of PLK2 in CRC cells was associated with low levels of Fbxw7 protein and increased expression of cyclin E1. When TIG1 was coexpressed with PLK2, the changes in Fbxw7/cyclin E1 levels induced by PLK2 were reversed. In contrast, silencing TIG1 promoted the proliferation of CRC, and when PLK2 was also silenced, the proliferation of CRC cells induced by TIG1 silencing was significantly inhibited. The above research results suggest that TIG1 can regulate the tumorigenesis of CRC by regulating the activity of PLK2.

Blocking miR-27a-3p sensitises Taxol resistant osteosarcoma cells through targeting Fbxw7

Osteosarcoma (OS) is a human malignancy, which primarily affects the long bones and occurs in children and adolescent. Although advanced clinical approaches and the addition of neoadjuvant chemotherapy improved 5-year survival of OS patients, a large fraction of them developed chemoresistance. Thus, due to the high morbidity and mortality of OS, it is urgent to investigate effectively molecular targets against chemoresistant osteosarcoma. In this study, we aimed to evaluate the functions of miR-27a-3p in the Taxol sensitivity of osteosarcoma. From fifty-paired OS tumour tissues and adjacent normal bone tissues, we detected significantly upregulated miR-27a-3p expressions in osteosarcoma. In addition, expression of miR-27a-3p was remarkedly elevated in OS cancer cell lines compared with normal osteoblast cells, hFOB1.19. Blocking miR-27a-3p effectively suppressed OS cell growth and sensitised OS cells to Taxol. miRNA target prediction indicated Fbxw7 was a potential target of miR-27a-3p. We demonstrated Fbxw7 functioned as a tumour suppressor in osteosarcoma. Overexpression of miR-27a-3p significantly suppressed Fbxw7 protein expression in OS cells. The direct binding between miR-27a-3p and Fbxw7 3'UTR was validated by luciferase assay. Particularly, results from rescue experiments by inhibiting Fbxw7 expressions in miR-23a-3p-blocked OS cells demonstrated the miR-27a-3p-mediated Taxol resistance was through direct targeting Fbxw7. In summary, our findings report a new molecular mechanism for the miR-27a-3p-mediated Taxol resistance via targeting tumour suppressor, Fbxw7 in osteosarcoma. This study potentiates a miRNA-based therapeutic approach against Taxol resistant osteosarcoma.

LSD1 Promotes Prostate Cancer Cell Survival by Destabilizing FBXW7 at Post-Translational Level

Prostate cancer (PCa) is the most common cancer in men and the fifth leading cause of cancer death worldwide. Unfortunately, castration-resistant prostate cancer (CRPCa) is incurable with surgical treat and prone to drug resistance. Therefore, it is of great importance to find a new target for treatment. LSD1 is up-regulated in PCa and related with prognosis. The high-expression LSD1 has been shown to be a potential target for treatment and is widely studied for its demethylase-activity. However, its demethylation-independent function remains to be elusive in PCa. Recent study shows that LSD1 can destabilize cancer suppressor protein FBXW7 without demethylation-function. Hence, we hope to investigate the impact of non-canonical function of LSD1 on PCa cell survival. We over-expressed FBXW7 gene through plasmid vector in LNCaP and PC3 cell lines and the result shows that up-regulated FBXW7 can suppress the viability of PC cell through suppressing oncoproteins, such as c-MYC, NOTCH-1. After FBXW7 function experiment on PC cell, we knock-down LSD1 gene in the same kinds of cell lines. In western blot assay, we detected that down-regulation of LSD1 will cause the increasing of FBXW7 protein level and decreasing of its targeting oncoproteins. And mRNA level of FBXW7 did not change significantly after LSD1 knock-down, which means LSD1 may destabilize FBXW7 by protein-protein interactions. Moreover, exogenous wild type LSD1 and catalytically deficient mutant K661A both can abrogate previous effect of LSD1 knock-down. Consequently, LSD1 may promote PC cell survival by destabilizing FBXW7 without its demethylase-activity. Next, we compared two kinds inhibitors, and found that SP-2509 (Allosteric inhibitor) treatment suppress the cancer cell survival by blocking the LSD1–FBXW7 interaction, which is an effect that GSK-2879552 (catalytic inhibitor) cannot achieve. This work revealed a pivotal function of LSD1 in PCa, and indicated a new direction of LSD1 inhibitor research for PCa treatment.

A case-control study to determination FBXW7 and Fetuin-A levels in patients with type 2 diabetes in Iraq.

diabetes mellitus (type 2) is a chronic disease characterized by hyperglycemia resulting either from a deficiency of insulin, or decrease insulin action or both. This study focused on determining the new marker F- box and WD repeat domain containing protein 7 (FBXW7) as well as Fetuin -A and their correlation with other parameters in Diabetes mellitus type 2. Sixty diabetes type2 patients were recruited from (National diabetes Center for treatment and Research) at Al Mustansriya University in Iraq during the period (from November 2018-March 2019) with an age range (37-69) years. The patient group was subdivided into two groups: group I (30) newly diagnosed T2DM and group II (30) T2DM (on metformin monotherapy), for comparison, 30 healthy individuals were included as a control. The protein levels (FBXW7, and Fetuin-A) were estimated using quantitative enzyme-linked immunesorbent assay (ELISA). Biochemical parameters; fasting serum glucose (FSG), and lipid profile were measured through spectrophotometrically. Insulin was determined using ELISA kit finally, HbA1c was determined using HPLC. Serum levels of FBXW7 protein were significantly higher (p-value = 0.01), whereas, there was no significant difference (p ˃ 0.05) in the level of Fetuin-A in group I as compared to control group. There was no significant difference (p ˃ 0.05) in the levels of both proteins who group II was compared with the control group. On the other hand, FBXW7 level were significantly lower in group II as compared to group I. Fasting blood sugar FSG, glycated hemoglobin HbA1c, body mass index BMI, waist- to-height ratio WHtR, and lipid profile were significantly elevated, except for high density lipoproteins, HDL was decreased in Group I as compared to control group, whereas insulin appeared non-significant (P > 0.05). FBXW7 Protein was negatively correlated to Fetuin -A, HOMA-IR, Insulin concentration, and BMI, whereas positive correlate to FSG, HbA1c, lipid profile, and atherogenic index. According to ROC analysis, the optimal cutoff value for FBXW7 protein was (1.455) ng/ml. Levels of FBXW7 and Fetuin-A proteins in sera of Diabetic patients were elevated. FBXW7 was significantly correlated with newly diagnosed patients. Metformin reduces FBXW7 and Fetuin-A levels.

MBRS-65. FBXW7 ACTS A TUMOR SUPPRESSOR IN MYC-DRIVEN MEDULLOBLASTOMA BY CONTROLLING A FEED-FORWARD REGULATORY LOOP OF PLK1 AND MYC

Group 3 medulloblastoma (MB) is often accompanied by MYC amplification and has a higher rate of metastatic disease. So, it is critical to have more effective therapies for high MYC expressing sub-groups. Here we report that FBXW7, a substrate recognition component of the SKP1-CUL1-Fbox (SCF) E3 ligase, interacts with and targets c-MYC for polyubiquitination and proteasomal degradation. FBXW7 shows lower expression level in MYC-driven MB compared with other MB subgroups suggesting activity as a tumor suppressor. Genomic deletion or mutation of Fbxw7 has frequently been identified in many human cancers but not in MB. We demonstrate that overexpression of Fbxw7 in MB cells induces apoptosis and suppresses proliferation in vitro and in vivo. Both phospho-deficient (T205A) and phosphomimetic aspartic acid (T205D) mutants deactivate its tumor suppressor function suggesting a conformational change of its protein structure. Mechanistically, PLK1 kinase specifically phosphorylates FBXW7 and promotes its auto-polyubiquitination and proteasomal degradation, counteracting FBXW7-mediated degradation of oncogene substrates, including c-MYC and PLK1. Chip-Seq results show stabilized c-MYC in turn directly activates PLK1 and FBXW7 transcription, constituting a feedforward regulatory loop. Co-immunoprecipitation demonstrates that FBXW7 directly binds to PLK1 and c-MYC, facilitating their protein degradation by promoting the ubiquitination of both proteins. Furthermore, we show that FBXW7 protein can be stabilized by various kinase inhibitors, proposing a mechanism of kinase-targeted agents to treat MYC-driven MB. These results collectively demonstrate how kinase inhibition stabilizes the tumor suppressor FBXW7 in MYC-driven MB, thus revealing an important function of FBXW7 in suppressing MB progression.

Abstract LB-047: CHMP5 dependency is a therapeutic vulnerability of T cell acute lymphoblastic leukemia

Abstract T-cell acute lymphoblastic leukemia (T-ALL) is a very aggressive hematologic malignancy that results from the transformation of immature T-cell progenitors. Aberrant cell growth and proliferation is sustained by strong oncogenic drivers, notably NOTCH1 and MYC, whose activation is present in more than half of all T-ALL cases. However, although it is known that post-translational modifications, such as ubiquitination by the E3-ligase FBXW7, regulate NOTCH1 and MYC protein stability and activity, regulatory proteins involved in their stability remain unestablished. The Charged multivesicular body protein 5 (CHMP5), an accessory protein of the ESCRT (endosomal sorting complex required for transport) pathway, has been shown to regulate the stability of client proteins in thymocytes through the recruitment of de-ubiquitinating enzymes. Here, we report that CHMP5 protein is not only highly expressed in T-ALL cells, but also promotes the stability of transactivating intracellular NOTCH1 (ICN1) and MYC. We found that depletion of CHMP5 significantly reduced the abundance of ICN1 and MYC, and the transcription of their target genes in vitro, as well as suppressed the development of T-ALL in vivo in a murine model of NOTCH1 driven T-ALL. Additionally, loss of CHMP5 restored T-ALL cell susceptibility to chemotherapeutic agents, including glucocorticoids and gamma secretase inhibitors, resistance to which contributes to disease relapse in patients. We further reveal CHMP5 as an adaptor protein required to orchestrate T-ALL client protein deubiquitination and stability. Altogether, our data suggest that CHMP5 is a non-oncogenic dependency of T-ALL and its depletion may be an effective therapeutic strategy for T-ALL. Citation Format: Katharine Umphred-Wilson, Stanley Adoro. CHMP5 dependency is a therapeutic vulnerability of T cell acute lymphoblastic leukemia [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr LB-047.

Decreased expression of FBXW7 by ERK1/2 activation in drug-resistant cancer cells confers transcriptional activation of MDR1 by suppression of ubiquitin degradation of HSF1

The acquisition of MDR1-mediated chemoresistance poses a major obstacle to the success of conventional chemotherapeutic agents. HSF1 is also involved in chemoresistance, and several studies have demonstrated the relationship between HSF1 and MDR1 but without any consistent results. Paclitaxel- and doxorubicin-resistant cancer cells showed higher expression of MDR1 and HSF1. Depletion of HSF1 decreased mdr1 expression at mRNA level, and HSF1 directly interacted with the promoter site of mdr1, suggesting its role as a transcriptional regulator of MDR1. Phosphorylation of Ser303/307, which was involved in protein stability of HSF1 by FBXW7-mediated degradation, was found to be important for transcriptional activation of mdr1. Drug-resistant cells showed decreased expression of FBXW7, which was mediated by the activation of ERK1/2, thus indicating that over-activation of ERK1/2 in drug-resistant cells decreased FBXW7 protein stability, which finally inhibited protein degradation of pHSF1 at Ser303/307. There was a positive correlation between immunofluorescence data of pHSF1 at Ser303/307 and MDR1 in carcinogen-induced rat mammary tumors and human lung cancers. These findings identified the post-translational mechanisms of HSF1 transcription in MDR1 regulation of drug resistance development.

BI6727, a polo-like kinase 1 inhibitor with promising efficacy on Burkitt lymphoma cells

ObjectiveBI6727, an ATP-competitive PLK1 inhibitor, has been shown to cause cell death in multi-tumors. This study aimed to investigate the anti-tumor effect and potential molecular mechanism of BI6727 in human Burkitt lymphoma (BL) cell lines.MethodsWe assessed polo-like kinase 1 (PLK1) expression in BL patient tissues and cells, also investigated the cytotoxic effect using CCK8 assay and flow cytometry. In addition, western blotting and real-time polymerase chain reaction (RT-PCR) assays were used to explore the molecular mechanisms of BI6727 in human BL cell lines.ResultsPLK1 was overexpressed in BL cells compared with normal cells. The PLK1 inhibitor BI6727 reduced activated PLK1 expression and caused mitotic arrest in BL cells. Additionally, BI6727 suppressed cellular proliferation and induced apoptosis in BL cell lines. BI6727 treatment also decreased C-MYC protein and mRNA expression, blocked the PI3K/AKT/mTOR signaling pathway, and stabilized the FBXW7 protein.ConclusionsOur findings explained a potential molecular mechanism of BI6727 in BL cells and suggested that BI6727 might be a new therapeutic agent for BL in the future.

FBXO45-MYCBP2 regulates mitotic cell fate by targeting FBXW7 for degradation

Cell fate decision upon prolonged mitotic arrest induced by microtubule-targeting agents depends on the activity of the tumor suppressor and F-box protein FBXW7. FBXW7 promotes mitotic cell death and prevents premature escape from mitosis through mitotic slippage. Mitotic slippage is a process that can cause chemoresistance and tumor relapse. Therefore, understanding the mechanisms that regulate the balance between mitotic cell death and mitotic slippage is an important task. Here we report that FBXW7 protein levels markedly decline during extended mitotic arrest. FBXO45 binds to a conserved acidic N-terminal motif of FBXW7 specifically under a prolonged delay in mitosis, leading to ubiquitylation and subsequent proteasomal degradation of FBXW7 by the FBXO45-MYCBP2 E3 ubiquitin ligase. Moreover, we find that FBXO45-MYCBP2 counteracts FBXW7 in that it promotes mitotic slippage and prevents cell death in mitosis. Targeting this interaction represents a promising strategy to prevent chemotherapy resistance.

Endocrinological characterization of pancreatic ducts in HFD and HGD fed mice.

Our previous findings show that insulin-produced cells are found in human pancreatic ducts. However, the underlying molecular mechanism of transdifferentiation in pancreatic ductal cells is not yet totally uncovered. High-fat diet (HFD) and high-glucose diet (HGD) fed mice were subjected to the biochemical tests in sera. And the pancreatic samples were used for immunostaining and immunoblotting assays, respectively. These serological findings showed that fasting blood glucose, insulin, blood lipids (triglyceride, total cholesterol), liver functional enzymes (glutamic-oxaloacetic transaminase, glutamic-pyruvic transaminase) were increased in HFD fed mice. Immunostaining observations showed that insulin protein was positively expressed in pancreatic islets and ducts, characterized with elevated immunoreactive cells of insulin, neurogenin-3, poly (ADP-ribose) polymerase (PARP), and reduced F-box/WD repeat-containing protein 7-positive cells in pancreatic islets and ducts of HFD and HGD fed mice. Interestingly, immunoblotting assays suggested that intrapancreatic expressions of insulin, Krüppel-like Factor 2, PARP, p42/44MAPK proteins were upregulated in HFD and HGD exposed mice, while Fbxw7 protein content in pancreas samples were reduced. Taken together, the current findings reveal that there may be potential transdifferentiation of insulin-producing cells in pancreatic ducts through inducing a pathway of intracellular Fbxw7 ubiquitination.

FBXW7 in Cancer: What Has Been Unraveled Thus Far?

The FBXW7 (F-box with 7 tandem WD40) protein encoded by the gene FBXW7 is one of the crucial components of ubiquitin ligase called Skp1-Cullin1-F-box (SCF) complex that aids in the degradation of many oncoproteins via the ubiquitin-proteasome system (UPS) thus regulating cellular growth. FBXW7 is considered as a potent tumor suppressor as most of its target substrates can function as potential growth promoters, including c-Myc, Notch, cyclin E, c-JUN, and KLF5. Its regulators include p53, C/EBP-δ, Numb, microRNAs, Pin 1, Hes-5, BMI1, Ebp2. Mounting evidence has indicated the involvement of aberrant expression of FBXW7 for tumorigenesis. Moreover, numerous studies have also shown its role in cancer cell chemosensitization, thereby demonstrating the importance of FBXW7 in the development of curative cancer therapy. This comprehensive review emphasizes on the targets, functions, regulators and expression of FBXW7 in different cancers and its involvement in sensitizing cancer cells to chemotherapeutic drugs.

TINCR suppresses proliferation and invasion through regulating miR-544a/FBXW7 axis in lung cancer

BackgroundLong noncoding RNAs (LncRNAs) play critical roles in multiple biological processes implicated in the development and progression of cancers. Terminal differentiation-induced lncRNA (TINCR) has been demonstrated to be associated with the carcinogenesis of several cancers. However, little is known about the function and mechanism of TINCR in lung cancer. MethodsqRT-PCR was performed to measure the expression of TINCR, miR-544a or FBXW7 mRNA in lung cancer tissues or cells. FBXW7 protein level was detected via western blot analysis. Cell Counting Kit-8 (CCK-8) and transwell invasion analysis were used to assess the proliferative and invasive ability of lung cancer cells. Bioinformatic softwares, luciferase reporter assay, and RNA immunoprecipitation (RIP) were employed to explore the relationship between TINCR, miR-544a and FBXW7. ResultsTINCR expression was downregulated while miR-544a expression was upregulated in lung cancer tissues and cells. TINCR overexpression suppressed proliferation and invasion in lung cancer cells. Moreover, TINCR was confirmed as a molecular sponge of miR-544a. We further validated that miR-544a facilitated proliferation and invasion, and miR-544a could reverse TINCR-mediated anti-proliferation and anti-invasion effect in lung cancer cells. TINCR acted as a competing endogenous RNA (ceRNA) to sequester miR-544a from its target gene FBXW7. Finally, FBXW7 suppressed proliferation and invasion, and FBXW7 knockdown abolished the inhibition of TINCR on proliferation and invasion in lung cancer cells. ConclusionTINCR suppressed proliferation and invasion through regulating miR-544a/FBXW7 axis in lung cancer, indicating that it might be a potential target for the therapy of lung cancer.

C-MYC and Its Main Ubiquitin Ligase, FBXW7, Influence Cell Proliferation and Prognosis in Adult T-cell Leukemia/Lymphoma.

Smoldering-type and chronic-type adult T-cell leukemia/lymphomas (ATLL) patients have relatively indolent clinical courses, but often progress into aggressive lymphoma-type and acute-type disease. We examined the roles of transcription factor C-MYC and its ubiquitin ligase FBXW7 in tumor tissues from 137 patients with ATLL. Immunohistochemical tests showed ≥50% of lymphoma cells in 78.7% (48/61) of lymphoma-type, and 64.9% (24/37) of acute-type samples expressed C-MYC, significantly higher than was seen in smoldering-type (3.6%) and chronic-type (9.1%) samples (P<0.01). Real-time polymerase chain reaction showed C-MYC mRNA expression in lymphoma-type and acute-type samples were significantly higher than in smoldering-type (P<0.01). C-MYC expression was highly correlated with its mRNA levels (ρ=0.65, P<0.0001), chromosomal amplification and duplication (ρ=0.3, P=0.045) and MIB1 labeling index (ρ=0.69, P<0.0001). Expression of FBXW7 protein and mRNA in lymphoma-type samples were significantly lower than those of smoldering-type (P<0.01 for each), and both were inversely correlated with C-MYC (protein: ρ=-0.4, P=0.0002; mRNA: ρ=-0.31, P=0.015). Seven patients with smoldering-type or chronic-type ATLL converted to acute-type, in 4 of whom C-MYC expression increased from <50% to ≥50%. Patients with ≥50% C-MYC or MIB1 had significantly worse prognosis than those with <50% C-MYC (P=0.0004) or MIB1 (P<0.0001), as did those with ≥7.5 C-MYC mRNA scores (P=0.033); whereas significantly better prognosis was associated with ≥50% FBXW7 protein (P=0.0006) or ≥0.17 FBXW7 mRNA (P=0.016). C-MYC and FBXW7 affect ATLL proliferation and progression, and low FBXW7 may increase C-MYC expression. C-MYC was a critical prognostic factor in ATLL patients.

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.

MicroRNA-32 promotes cell proliferation, migration and suppresses apoptosis in breast cancer cells by targeting FBXW7

BackgroundMicroRNAs are a class of small non-coding RNAs that are involved in many important physiological and pathological processes by regulating gene expression negatively. The purpose of this study was to investigate the effect of miR-32 on cell proliferation, migration and apoptosis and to determine the functional connection between miR-32 and FBXW7 in breast cancer.MethodsIn this study, quantitative RT-PCR was used to evaluate the expression levels of miR-32 in 27 breast cancer tissues, adjacent normal breast tissues and human breast cancer cell lines. The biological functions of miR-32 in MCF-7 breast cancer cells were determined by cell proliferation, apoptosis assays and wound-healing assays. In addition, the regulation of FBXW7 by miR-32 was assessed by qRT-PCR, Western blot and luciferase reporter assays.ResultsMiR-32 was frequently overexpressed in breast cancer tissue samples and cell lines as was demonstrated by qRT-PCR. Moreover, the up-regulation of miR-32 suppressed apoptosis and promoted proliferation and migration, whereas down-regulation of miR-32 showed an opposite effect. Dual-luciferase reporter assays showed that miR-32 binds to the 3′-untranslated region of FBXW7, suggesting that FBXW7 is a direct target of miR-32. Western blot analysis showed that over-expression of miR-32 reduced FBXW7 protein level. Furthermore, an inverse correlation was found between the expressions of miR-32 and FBXW7 mRNA levels in breast cancer tissues. Knockdown of FBXW7 promoted proliferation and motility and suppressed apoptosis in MCF-7 cells.ConclusionsTaken together, the present study suggests that miR-32 promotes proliferation and motility and suppresses apoptosis of breast cancer cells through targeting FBXW7.

MiR‑223‑3p regulates cell growth and apoptosis via FBXW7 suggesting an oncogenic role in human testicular germ cell tumors.

miR-223-3p is deregulated in several tumor types and plays an important role in tumorigenesis and progression. However, its role in the pathogenesis of testicular germ cell tumor (TGCT) remains uncharacterized. We previously demonstrated that miR-223-3p expression was increased in TGCTs compared with normal testes (NT), suggesting that miR-223-3p may have an oncogenic role in TGCT. Using published dataset and The Cancer Genome Atlas database, we validated higher miR-223-3p expression in TGCTs than NT, and found a negative correlation between miR-223-3p and FBXW7 mRNA expression levels. Using both gain- and loss-of-function experiments, we show that miR-223-3p regulates FBXW7 protein expression, cell growth and apoptosis in TGCT cell lines. Additionally, we demonstrate that ectopic expression of the full-length coding sequence of FBXW7 could rescue the cell growth and apoptotic effects mediated by miR-223-3p. Our findings suggest an oncogenic role for miR-223-3p in TGCT, which promotes cell growth and inhibits apoptosis through repression of FBXW7.