MYC is a critical target of FBXW7

A microdeletion event at 19q13.43 in IDH-mutant astrocytomas is strongly correlated with MYC overexpression

MYC dysregulation is pivotal in the onset and progression of IDH-mutant gliomas, mostly driven by copy-number alterations, regulatory element alterations, or epigenetic changes. Our pilot analysis uncovered instances of relative MYC overexpression without alterations in the proximal MYC network (PMN), prompting a deeper investigation into potential novel oncogenic mechanisms. Analysing comprehensive genomics profiles of 236 "IDH-mutant 1p/19q non-co-deleted" lower-grade gliomas from The Cancer Genome Atlas, we identified somatic genomic alterations within the PMN. In tumours without PMN-alterations but with MYC-overexpression, genes correlated with MYC-overexpression were identified. Our analyses yielded that 86/236 of astrocytomas exhibited no PMN-alterations, a subset of 21/86 displaying relative MYC overexpression. Within this subset, we discovered 42 genes inversely correlated with relative MYC expression, all on 19q. Further analysis pinpointed a minimal common region at 19q13.43, encompassing 15 genes. The inverse correlations of these 15 genes with relative MYC overexpression were re-confirmed using independent scRNAseq data. Further, the micro-deleted astrocytoma subset displayed significantly higher genomic instability compared to WT cases, but lower instability compared to PMN-hit cases. This newly identified 19q micro-deletion represents a potential novel mechanism underlying MYC dysregulation in astrocytomas. Given the prominence of 19q loss in IDH-mutant gliomas, our findings bear significant implications for understanding gliomagenesis.

Topoisomerase 1 Inhibition in MYC-Driven Cancer Promotes Aberrant R-Loop Accumulation to Induce Synthetic Lethality

MYC is a central regulator of gene transcription and is frequently dysregulated in human cancers. As targeting MYC directly is challenging, an alternative strategy is to identify specific proteins or processes required for MYC to function as a potent cancer driver that can be targeted to result in synthetic lethality. To identify potential targets in MYC-driven cancers, we performed a genome-wide CRISPR knockout screen using an isogenic pair of breast cancer cell lines in which MYC dysregulation is the switch from benign to transformed tumor growth. Proteins that regulate R-loops were identified as a potential class of synthetic lethal targets. Dysregulated MYC elevated global transcription and coincident R-loop accumulation. Topoisomerase 1 (TOP1), a regulator of R-loops by DNA topology, was validated to be a vulnerability in cells with high MYC activity. Genetic knockdown of TOP1 in MYC-transformed cells resulted in reduced colony formation compared with control cells, demonstrating synthetic lethality. Overexpression of RNaseH1, a riboendonuclease that specifically degrades R-loops, rescued the reduction in clonogenicity induced by TOP1 deficiency, demonstrating that this vulnerability is driven by aberrant R-loop accumulation. Genetic and pharmacologic TOP1 inhibition selectively reduced the fitness of MYC-transformed tumors in vivo. Finally, drug response to TOP1 inhibitors (i.e., topotecan) significantly correlated with MYC levels and activity across panels of breast cancer cell lines and patient-derived organoids. Together, these results highlight TOP1 as a promising target for MYC-driven cancers.

SIGNIFICANCE

CRISPR screening reveals topoisomerase 1 as an immediately actionable vulnerability in cancers harboring MYC as a driver oncoprotein that can be targeted with clinically approved inhibitors.

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.

Ubiquitylation of unphosphorylated c-myc by novel E3 ligase SCFFbxl8

Overexpression of c-myc via increased transcription or decreased protein degradation is common to many cancer etiologies. c-myc protein degradation is mediated by ubiquitin-dependent degradation, and this ubiquitylation is regulated by several E3 ligases. The primary regulator is Fbxw7, which binds to a phospho-degron within c-myc. Here, we identify a new E3 ligase for c-myc, Fbxl8 (F-box and Leucine Rich Repeat Protein 8), as an adaptor component of the SCF (Skp1-Cullin1-F-box protein) ubiquitin ligase complex, for selective c-myc degradation. SCFFbxl8 binds and ubiquitylates c-myc, independent of phosphorylation, revealing that it regulates a pool of c-myc distinct from SCFFbxw7. Loss of Fbxl8 increases c-myc protein levels, protein stability, and cell division, while overexpression of Fbxl8 reduces c-myc protein levels. Concurrent loss of Fbxl8 and Fbxw7 triggers a robust increase in c-myc protein levels consistent with targeting distinct pools of c-myc. This work highlights new mechanisms regulating c-myc degradation.

Drivers of genomic loss of heterozygosity in leiomyosarcoma are distinct from carcinomas

Leiomyosarcoma (LMS) is a rare, aggressive, mesenchymal tumor. Subsets of LMS have been identified to harbor genomic alterations associated with homologous recombination deficiency (HRD); particularly alterations in BRCA2. Whereas genomic loss of heterozygosity (gLOH) has been used as a surrogate marker of HRD in other solid tumors, the prognostic or clinical value of gLOH in LMS (gLOH-LMS) remains poorly defined. We explore the genomic drivers associated with gLOH-LMS and their clinical import. Although the distribution of gLOH-LMS scores are similar to that of carcinomas, outside of BRCA2, there was no overlap with previously published gLOH-associated genes from studies in carcinomas. We note that early stage tumors with elevated gLOH demonstrated a longer disease-free interval following resection in LMS patients. Taken together, and despite similarities to carcinomas in gLOH distribution and clinical import, gLOH-LMS are driven by different genomic signals. Additional studies will be required to isolate and confirm the unique differences in biological factors driving these differences.

Aberrant SKP1 Expression: Diverse Mechanisms Impacting Genome and Chromosome Stability

The S-phase Kinase-Associated Protein 1 (SKP1) is a core component of the SKP1, Cullin 1, F-box protein (SCF) complex, an E3 ubiquitin ligase that serves to poly-ubiquitinate a vast array of protein targets as a signal for their proteasomal degradation, thereby playing a critical role in the regulation of downstream biological processes. Many of the proteins regulated by SKP1 and the SCF complex normally function within pathways that are essential for maintaining genome stability, including DNA damage repair, apoptotic signaling, and centrosome dynamics. Accordingly, aberrant SKP1 and SCF complex expression and function is expected to disrupt these essential pathways, which may have pathological implications in diseases like cancer. In this review, we summarize the central role SKP1 plays in regulating essential cellular processes; we describe functional models in which SKP1 expression is altered and the corresponding impacts on genome stability; and we discuss the prevalence of SKP1 somatic copy number alterations, mutations, and altered protein expression across different cancer types, to identify a potential link between SKP1 and SCF complex dysfunction to chromosome/genome instability and cancer pathogenesis. Ultimately, understanding the role of SKP1 in driving chromosome instability will expand upon our rudimentary understanding of the key events required for genome/chromosome stability that may aid in our understanding of cancer pathogenesis, which will be critical for future studies to establish whether SKP1 may be useful as prognostic indicator or as a therapeutic target.

The Connection between MicroRNAs and Oral Cancer Pathogenesis: Emerging Biomarkers in Oral Cancer Management

Oral cancer is a common human malignancy that still maintains an elevated mortality rate despite scientific progress. Tumorigenesis is driven by altered gene expression patterns of proto-oncogenes and tumor-suppressor genes. MicroRNAs, a class of short non-coding RNAs involved in gene regulation, seem to play important roles in oral cancer development, progression, and tumor microenvironment modulation. As properties of microRNAs render them stable in diverse liquid biopsies, together with their differential expression signature in cancer cells, these features place microRNAs at the top of promising biomarkers for diagnostic and prognostic values. In this review, we highlight eight expression levels and functions of the most relevant microRNAs involved in oral cancer development, progression, and microenvironment sustainability. Furthermore, we emphasize the potential of using these small RNA species as non-invasive biomarkers for the early detection of oral cancerous lesions. Conclusively, we highlight the perspectives and limitations of microRNAs as novel diagnostic tools, as well as therapeutic models.

The SCF Complex Is Essential to Maintain Genome and Chromosome Stability

The SKP1, CUL1, F-box protein (SCF) complex encompasses a group of 69 SCF E3 ubiquitin ligase complexes that primarily modify protein substrates with poly-ubiquitin chains to target them for proteasomal degradation. These SCF complexes are distinguishable by variable F-box proteins, which determine substrate specificity. Although the function(s) of each individual SCF complex remain largely unknown, those that have been characterized regulate a wide array of cellular processes, including gene transcription and the cell cycle. In this regard, the SCF complex regulates transcription factors that modulate cell signaling and ensures timely degradation of primary cell cycle regulators for accurate replication and segregation of genetic material. SCF complex members are aberrantly expressed in a myriad of cancer types, with altered expression or function of the invariable core SCF components expected to have a greater impact on cancer pathogenesis than that of the F-box proteins. Accordingly, this review describes the normal roles that various SCF complexes have in maintaining genome stability before discussing the impact that aberrant SCF complex expression and/or function have on cancer pathogenesis. Further characterization of the SCF complex functions is essential to identify and develop therapeutic approaches to exploit aberrant SCF complex expression and function.

Peptide-tiling screens of cancer drivers reveal oncogenic protein domains and associated peptide inhibitors

Gene fragments derived from structural domains mediating physical interactions can modulate biological functions. Utilizing this, we developed lentiviral overexpression libraries of peptides comprehensively tiling high-confidence cancer driver genes. Toward inhibiting cancer growth, we assayed ~66,000 peptides, tiling 65 cancer drivers and 579 mutant alleles. Pooled fitness screens in two breast cancer cell lines revealed peptides, which selectively reduced cellular proliferation, implicating oncogenic protein domains important for cell fitness. Coupling of cell-penetrating motifs to these peptides enabled drug-like function, with peptides derived from EGFR and RAF1 inhibiting cell growth at IC50s of 27-63 μM. We anticipate that this peptide-tiling (PepTile) approach will enable rapid de novo mapping of bioactive protein domains and associated interfering peptides.

Honokiol antagonizes doxorubicin resistance in human breast cancer via miR-188-5p/FBXW7/c-Myc pathway

BACKGROUND

Honokiol, a natural phenolic compound derived from Magnolia plants, is a promising anti-tumor compound that exerts a wide range of anti-cancer effects. Herein, we investigated the effect of honokiol on doxorubicin resistance in breast cancer.

METHODS

Doxorubicin-sensitive (MCF-7 and MDA-MB-231) and doxorubicin-resistant (MCF-7/ADR and MDA-MB-231/ADR) breast cancer cell lines were treated with doxorubicin in the absence or presence of honokiol; then, the following tests were performed: flow cytometry for cell apoptosis, WST-1 assay for cell viability, qPCR and western blot for the expression of miR-188-5p, FBXW7, and c-Myc. MiR-188-5p mimic, miR-188-5p inhibitor, siFBXW7, and c-Myc plasmids were transfected into cancer cells to evaluate whether miR-188-5p and FBXW7/c-Myc signaling are involved in the effect of honokiol on doxorubicin resistance in breast cancer. A dual luciferase reporter system was used to study the direct interaction between miR-188-5p and FBXW7.

RESULTS

Honokiol sensitized doxorubicin-resistant breast cancer cells to doxorubicin-induced apoptosis. Mechanically, upregulation of miR-188-5p was associated with doxorubicin resistance, and honokiol enhanced doxorubicin sensitivity by downregulating miR-188-5p. FBXW7 was confirmed to be a direct target gene of miR-188-5p. FBXW7/c-Myc signaling was involved in the chemosensitization effect of honokiol. Honokiol induced apoptosis in MCF-7/ADR and MDA-MB-231/ADR cells. However, FBXW7 silencing or c-Myc transfection resulted in resistance to the honokiol-induced apoptotic effect.

CONCLUSION

These findings suggest that downregulation of miR-188-5p by honokiol enhances doxorubicin sensitivity through FBXW7/c-Myc signaling in human breast cancer. Our study finds an important role of miR-188-5p in the development of doxorubicin resistance in breast cancer, and enriches our understanding of the mechanism of action of honokiol in cancer therapy.

The UVSSA complex alleviates MYC-driven transcription stress

Cancer cells develop strong genetic dependencies, enabling survival under oncogenic stress. MYC is a key oncogene activated across most cancers, and identifying associated synthetic lethality or sickness can provide important clues about its activity and potential therapeutic strategies. On the basis of previously conducted genome-wide screenings in MCF10A cells expressing MYC fused to an estrogen receptor fragment, we identified UVSSA, a gene involved in transcription-coupled repair, whose knockdown or knockout decreased cell viability when combined with MYC expression. Synthetic sick interactions between MYC expression and UVSSA down-regulation correlated with ATM/CHK2 activation, suggesting increased genome instability. We show that the synthetic sick interaction is diminished by attenuating RNA polymerase II (RNAPII) activity; yet, it is independent of UV-induced damage repair, suggesting that UVSSA has a critical function in regulating RNAPII in the absence of exogenous DNA damage. Supporting this hypothesis, RNAPII ChIP-seq revealed that MYC-dependent increases in RNAPII promoter occupancy are reduced or abrogated by UVSSA knockdown, suggesting that UVSSA influences RNAPII dynamics during MYC-dependent transcription. Taken together, our data show that the UVSSA complex has a significant function in supporting MYC-dependent RNAPII dynamics and maintaining cell survival during MYC addiction. While the role of UVSSA in regulating RNAPII has been documented thus far only in the context of UV-induced DNA damage repair, we propose that its activity is also required to cope with transcriptional changes induced by oncogene activation.

A Regulatory Loop of FBXW7-MYC-PLK1 Controls Tumorigenesis of MYC-Driven Medulloblastoma

Simple Summary

Group 3 medulloblastoma (MB) is often accompanied by MYC amplification and has a poor prognosis. FBXW7, a critical tumor suppressor in many types of cancer, regulates the proteasome-mediated degradation of oncoproteins including MYC. However, the role of FBXW7 in the tumorigenesis of group 3 MB has not been well studied. In this study, we show that FBXW7 is downregulated in group 3 MB patient samples, and FBXW7 stabilization is crucial for inhibiting c-MYC. We identified a FBXW7-MYC-PLK1 regulatory loop in MYC-driven MB, which provides a mechanism of using protein kinase inhibitors for translation in the future.

Abstract

Polo-like kinase 1 (PLK1) is highly expressed in group 3 medulloblastoma (MB), and it has been preclinically validated as a cancer therapeutic target in medulloblastoma. Here, we demonstrate that PLK1 inhibition with PCM-075 or BI6727 significantly reduces the growth of MB cells and causes a decrease of c-MYC mRNA and protein levels. We show that MYC activates PLK1 transcription, while the inhibition of PLK1 suppresses MB tumor development and causes a decrease in c-MYC protein level by suppressing FBXW7 auto poly-ubiquitination. FBXW7 physically interacts with PLK1 and c-MYC, facilitating their protein degradation by promoting ubiquitination. These results demonstrate a PLK1-FBXW7-MYC regulatory loop in MYC-driven medulloblastoma. Moreover, FBXW7 is significantly downregulated in group 3 patient samples. The overexpression of FBXW7 induced apoptosis and suppressed proliferation in vitro and in vivo, while constitutive phosphorylation mutation attenuated its tumor suppressor function. Altogether, these findings demonstrated that PLK1 inhibition stabilizes FBXW7 in MYC-driven MB, thus revealing an important function of FBXW7 in suppressing medulloblastoma progression.

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

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

Regulation of cell cycle drivers by Cullin-RING ubiquitin ligases

The last decade has revealed new roles for Cullin-RING ubiquitin ligases (CRLs) in a myriad of cellular processes, including cell cycle progression. In addition to CRL1, also named SCF (SKP1-Cullin 1-F box protein), which has been known for decades as an important factor in the regulation of the cell cycle, it is now evident that all eight CRL family members are involved in the intricate cellular pathways driving cell cycle progression. In this review, we summarize the structure of CRLs and their functions in driving the cell cycle. We focus on how CRLs target key proteins for degradation or otherwise alter their functions to control the progression over the various cell cycle phases leading to cell division. We also summarize how CRLs and the anaphase-promoting complex/cyclosome (APC/C) ligase complex closely cooperate to govern efficient cell cycle progression.

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

Background

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

Methods

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

Results

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

Conclusion

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

Computational approach to target USP28 for regulating Myc

Myc is a crucial player in cellular proliferation and a known regulator of cancer pathobiology. Modulation of Myc expression targeting the Myc Protein-Protein Interactors (PPIs) like Myc-Max has till now been the most explored approach. However, this approach threatens the normal cells where Myc expression is required for proliferation. This demands the need for a new strategy to indirectly modulate Myc expression. Indirect modulation can be achieved by regulating Myc turnover. FBXW7 mediates the ubiquitination and subsequent degradation of Myc which is reversed by USP28. In this study, the interaction of USP28 with FBXW7 as well as with its substrate, Ubiquitin (Ub) were used as targets. Computation based high-throughput screening of bioactive small chemicals using molecular docking method was implemented to predict USP28 inhibitors. For the two regions, docking study with AutoDock Vina gave top 10 best scoring drugs which were identified and tabulated. The two regions defined in the study as FBXW7 binding and Ub binding also encompass the areas in which USP28 differed from USP25, a homologue with a different role. Out of these the best scoring drugs were explored for their role in cancer, if any. This study was performed keeping in mind re-purposing of these known drugs for possible alternative anti-Myc cancer therapy.

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

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

Modelling the MYC-driven normal-to-tumour switch in breast cancer

The potent MYC oncoprotein is deregulated in many human cancers, including breast carcinoma, and is associated with aggressive disease. To understand the mechanisms and vulnerabilities of MYC-driven breast cancer, we have generated an in vivo model that mimics human disease in response to MYC deregulation. MCF10A cells ectopically expressing a common breast cancer mutation in the phosphoinositide 3 kinase pathway (PIK3CA^H1047R) led to the development of organised acinar structures in mice. Expressing both PIK3CA^H1047R and deregulated MYC led to the development of invasive ductal carcinoma. Therefore, the deregulation of MYC expression in this setting creates a MYC-dependent normal-to-tumour switch that can be measured in vivo. These MYC-driven tumours exhibit classic hallmarks of human breast cancer at both the pathological and molecular level. Moreover, tumour growth is dependent upon sustained deregulated MYC expression, further demonstrating addiction to this potent oncogene and regulator of gene transcription. We therefore provide a MYC-dependent model of breast cancer, which can be used to assay invivo tumour signalling pathways, proliferation and transformation from normal breast acini to invasive breast carcinoma. We anticipate that this novel MYC-driven transformation model will be a useful research tool to better understand the oncogenic function of MYC and for the identification of therapeutic vulnerabilities.

Summary: We present a MYC-driven transformation model of breast cancer that recapitulates the disease in vivo and which can be used to identify MYC-dependent cancer vulnerabilities.

FBXW7 Mutations Promote Cell Proliferation, Migration, and Invasion in Cervical Cancer

Aim: Cervical cancer is the most common gynecological cancer. Recent studies have revealed that the F-box and WD repeat domain containing 7 (FBXW7) gene, which encodes a subunit of Skp1-Cul1-F-box protein (SCF) ubiquitin ligase, is frequently mutated in cervical squamous cell carcinomas. In this study, we investigated whether Chinese cervical cancer cells also harbor these mutations. Methods: Using PCR and sequencing assays, a total of 190 specimens from Han Chinese patients with cervical cancer were analyzed for FBXW7 mutations. Results: Two FBXW7 mutations (p.R479P and p.L443H), were identified from a study of 145 (1.4%) cervical squamous cell carcinomas. The p.L443H somatic mutation has not been previously reported. Functional assays showed that both of these FBXW7 mutations could promote cell proliferation, migration, and invasion. Conclusion: A low frequency (1.4%) of cervical squamous cell carcinomas were identified with FBXW7 mutations. We did, however, identify a novel FBXW7 mutation. Our results also demonstrated that the identified FBXW7 mutations could promote cell proliferation, migration, and invasion in cervical cancer cells.

CEP55 is a determinant of cell fate during perturbed mitosis in breast cancer

The centrosomal protein, CEP55, is a key regulator of cytokinesis, and its overexpression is linked to genomic instability, a hallmark of cancer. However, the mechanism by which it mediates genomic instability remains elusive. Here, we showed that CEP55 overexpression/knockdown impacts survival of aneuploid cells. Loss of CEP55 sensitizes breast cancer cells to anti‐mitotic agents through premature CDK1/cyclin B activation and CDK1 caspase‐dependent mitotic cell death. Further, we showed that CEP55 is a downstream effector of the MEK1/2‐MYC axis. Blocking MEK1/2‐PLK1 signaling therefore reduced outgrowth of basal‐like syngeneic and human breast tumors in in vivo models. In conclusion, high CEP55 levels dictate cell fate during perturbed mitosis. Forced mitotic cell death by blocking MEK1/2‐PLK1 represents a potential therapeutic strategy for MYC‐CEP55‐dependent basal‐like, triple‐negative breast cancers.

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.

Analysis on GENIE reveals novel recurrent variants that affect molecular diagnosis of sizable number of cancer patients

Background

Significant numbers of variants detected in cancer patients are often left labeled only as variants of unknown significance (VUS). In order to expand precision medicine to a wider population, we need to extend our knowledge of pathogenicity and drug response in the context of VUS’s.

Methods

In this study, we analyzed variants from AACR Project GENIE Consortium APG (Cancer Discov 7:818-831, 2017) and compared them to the COSMIC database Forbes et al. (Nucleic Acids Res 43:D805-811, 2015) to identify recurrent variants that would merit further study. We filtered out known hotspot variants, inactivating variants in tumor suppressors, and likely benign variants by comparing with COSMIC and ExAC Lee et al. (Science 337:967-971, 2012).

Results

We have identified 45,933 novel variants with unknown significance unique to GENIE. In our analysis, we found on average six variants per patient where two could be considered as pathogenic or likely pathogenic and the majority are VUS’s. More importantly, we have discovered 730 recurrent variants that appear more than 3 times in GENIE but less than 3 in COSMIC. If we combine the recurrences of GENIE and COSMIC for all variants, 2586 are newly identified as occurring more than 3 times than when using COSMIC alone.

Conclusions

Although it would be inappropriate to blindly accept these recurrent variants as pathogenic, they may warrant higher priority than other observed VUS’s. These newly identified recurrent variants might affect the molecular profiles of approximately 1 in 6 patients. Further analysis and characterization of these variants in both research and clinical contexts will improve patient treatments and the development of new therapeutics.

Electronic supplementary material

The online version of this article (10.1186/s12885-019-5313-1) contains supplementary material, which is available to authorized users.

Haploid genetic screens identify genetic vulnerabilities to microtubule-targeting agents

The absence of biomarkers to accurately predict anticancer therapy response remains a major obstacle in clinical oncology. We applied a genome‐wide loss‐of‐function screening approach in human haploid cells to characterize genetic vulnerabilities to classical microtubule‐targeting agents. Using docetaxel and vinorelbine, two well‐established chemotherapeutic agents, we sought to identify genetic alterations sensitizing human HAP1 cells to these drugs. Despite the fact that both drugs act on microtubules, a set of distinct genes were identified whose disruption affects drug sensitivity. For docetaxel, this included a number of genes with a function in mitosis, while for vinorelbine we identified inactivation of FBXW7,RB1, and NF2, three frequently mutated tumor suppressor genes, as sensitizing factors. We validated these genes using independent knockout clones and confirmed FBXW7 as an important regulator of the mitotic spindle assembly. Upon FBXW7 depletion, vinorelbine treatment led to decreased survival of cells due to defective mitotic progression and subsequent mitotic catastrophe. We show that haploid insertional mutagenesis screens are a useful tool to study genetic vulnerabilities to classical chemotherapeutic drugs by identifying thus far unknown sensitivity factors. These results provide a rationale for investigating patient response to vinca alkaloid‐based anticancer treatment in relation to the mutational status of these three tumor suppressor genes, and could in the future lead to the establishment of novel predictive biomarkers or suggest new drug combinations based on molecular mechanisms of drug sensitivity.

The ubiquitin ligase SCFFBXW7α promotes GATA3 degradation

GATA3 is a key transcription factor in cell fate determination and its dysregulation has been implicated in various types of malignancies. However, how the abundance and function of GATA3 are regulated remains unclear. Here, we report that GATA3 is physically associated with FBXW7α, and FBXW7α destabilizes GATA3 through assembly of a SKP1-CUL1-F-box E3 ligase complex. Importantly, we showed that FBXW7α promotes GATA3 ubiquitination and degradation in a GSK3 dependent manner. Furthermore, we demonstrated that FBXW7α inhibits breast cancer cells survival through destabilizing GATA3, and the expression level of FBXW7α is negatively correlated with that of GATA3 in breast cancer samples. This study indicated that FBXW7α is a critical negative regulator of GATA3 and revealed a pathway for the maintenance of GATA3 abundance in breast cancer cells.

The importance of regulatory ubiquitination in cancer and metastasis

Ubiquitination serves as a degradation mechanism of proteins, but is involved in additional cellular processes such as activation of NFκB inflammatory response and DNA damage repair. We highlight the E2 ubiquitin conjugating enzymes, E3 ubiquitin ligases and Deubiquitinases that support the metastasis of a plethora of cancers. E3 ubiquitin ligases also modulate pluripotent cancer stem cells attributed to chemotherapy resistance. We further describe mutations in E3 ubiquitin ligases that support tumor proliferation and adaptation to hypoxia. Thus, this review describes how tumors exploit members of the vast ubiquitin signaling pathways to support aberrant oncogenic signaling for survival and metastasis.

Potential effect of spliceosome inhibition in small cell lung cancer irrespective of the MYC status

Small cell lung cancer (SCLC) is a highly aggressive malignancy with few therapeutic advances in the treatment in recent decades. Based on a recent study that identified the spliceosome as a therapeutic vulnerability in MYC-driven breast cancers, we evaluated the efficacy of a spliceosome inhibitor in SCLC cell lines and analyzed the correlation with MYC status. Among 23 SCLC cell lines examined, eight showed high MYC protein expression (> 80% positive cells) by immunohistochemistry (IHC), while 10 cell lines demonstrated no staining for MYC. The remaining five cell lines showed weak staining (< 40% positive cells). All four cell lines that were previously demonstrated to have MYC gene amplification were positive for MYC by IHC. Four cell lines with high MYC expression and four with low MYC expression were used in further analysis. A spliceosome inhibitor, pladienolide B, showed high efficacy (IC₅₀ < 12nM) in all eight cell lines tested, irrespective of the MYC IHC or MYC gene amplification status. We observed that the four cell lines with higher sensitivity to the spliceosome inhibitor were established from patients with prior chemotherapy. Therefore we chronically treated H1048 cells, that were established from a treatment-naïve patient, with cisplatin for 4 weeks, and found that H1048-cisplatin treated cells became more sensitive to pladienolide B. In conclusion, our in vitro results indicate that spliceosome inhibitors would be promising molecular target drugs in SCLC irrespective of the MYC status, especially in the second-line settings after an effective front-line chemotherapy.

miR-367 promotes the proliferation and invasion of non-small cell lung cancer via targeting FBXW7

The involvement of miR-367 in lung cancer development remains unclear. In the present study, we analyzed the expression of miR-367 in tumor and adjacent tissue samples from 113 patients with non-small cell lung cancer (NSCLC) utilizing real-time PCR. miR-367 expression was significantly upregulated in the cancer tissues compared with non-cancer controls. Based on the median value of the miR-367 expression level, we divided the NSCLC patients into miR-367 high-expression and miR-367 low-expression groups. Overexpression of miR-367 was correlated with a poorer prognosis of NSCLC patients Chi-square (χ2) test showed a significant statistical correlation between tumor size, tumor stage, metastasis and miR-367 expression. Additionally, miR-367 expression was found to be negatively correlated with FBXW7 expression. Based on the above correlations, we performed a series of functional experiments to further confirm the effect of miR-367 on NSCLC. Our results indicated that miR-367 may be involved in the development and progression of NSCLC by promoting proliferation and invasion and impeding apoptosis in NSCLC cells. Furthermore, FBXW7 was identified as a potential target of miR-367, and FBXW7 silencing partially compromised the invasive, proliferative and migratory capacities in the cells with low miR-367 expression. Thus, the miR-367/FBXW7 axis may be involved in the development and progression of NSCLC and may be valuable as a therapeutic target for the treatment of human NSCLC, especially cancers with high invasive potential.

PIM1 kinase inhibition as a targeted therapy against triple-negative breast tumors with elevated MYC expression

Triple-negative breast cancer (TNBC), in which cells lack expression of the estrogen receptor (ER), the progesterone receptor (PR) and the ERBB2 (also known as HER2) receptor, is the breast cancer subtype with the poorest outcome. No targeted therapy is available against this subtype of cancer owing to a lack of validated molecular targets. We previously reported that signaling involving MYC-an essential, pleiotropic transcription factor that regulates the expression of hundreds of genes-is disproportionally higher in triple-negative (TN) tumors than in receptor-positive (RP) tumors. Direct inhibition of the oncogenic transcriptional activity of MYC has been challenging to achieve. Here, by conducting a shRNA screen targeting the kinome, we identified PIM1, a non-essential serine-threonine kinase, in a synthetic lethal interaction with MYC. PIM1 expression was higher in TN tumors than in RP tumors and was associated with poor prognosis in patients with hormone- and HER2-negative tumors. Small-molecule PIM kinase inhibitors halted the growth of human TN tumors with elevated MYC expression in patient-derived tumor xenograft (PDX) and MYC-driven transgenic mouse models of breast cancer by inhibiting the oncogenic transcriptional activity of MYC and restoring the function of the endogenous cell cycle inhibitor, p27. Our findings warrant clinical evaluation of PIM kinase inhibitors in patients with TN tumors that have elevated MYC expression.

27-Hydroxycholesterol increases Myc protein stability via suppressing PP2A, SCP1 and FBW7 transcription in MCF-7 breast cancer cells

27-hydroxycholesterol (27-HC), the most abundant metabolite of cholesterol, is a risk factor for breast cancer. It can increase the proliferation of breast cancer cells and promote the metastasis of breast tumours in mouse models. Myc is a critical oncoprotein overexpressed in breast cancer. However, whether 27-HC affects Myc expression has not been reported. In the current study, we aimed to investigate the effects of 27-HC on Myc and the underlying mechanisms in MCF-7 breast cancer cells. Our data demonstrated that 27-HC activated Myc via increasing its protein stability. Three key negative modulators of Myc protein stability, PP2A, SCP1 and FBW7, were suppressed by 27-HC at the transcriptional level. We performed a data-mining analysis of the chromatin immunoprecipitation with next-generation DNA sequencing (ChIP-Seq) data in the ChIPBase, and discovered that a number of putative transcription factors (TFs), including Myc itself, were involved in the transcriptional regulation of PP2A, SCP1 and FBW7. Our results provide a novel mechanistic insight into the activation of Myc by 27-HC via transcriptional repression of PP2A, SCP1 and FBW7 to increase Myc protein stability in breast cancer cells.

Drugging the addict: non-oncogene addiction as a target for cancer therapy

Historically, cancers have been treated with chemotherapeutics aimed to have profound effects on tumor cells with only limited effects on normal tissue. This approach was followed by the development of small‐molecule inhibitors that can target oncogenic pathways critical for the survival of tumor cells. The clinical targeting of these so‐called oncogene addictions, however, is in many instances hampered by the outgrowth of resistant clones. More recently, the proper functioning of non‐mutated genes has been shown to enhance the survival of many cancers, a phenomenon called non‐oncogene addiction. In the current review, we will focus on the distinct non‐oncogenic addictions found in cancer cells, including synthetic lethal interactions, the underlying stress phenotypes, and arising therapeutic opportunities.

Inhibition of mTOR-kinase destabilizes MYCN and is a potential therapy for MYCN-dependent tumors

MYC oncoproteins deliver a potent oncogenic stimulus in several human cancers, making them major targets for drug development, but efforts to deliver clinically practical therapeutics have not yet been realized. In childhood cancer, aberrant expression of MYC and MYCN genes delineates a group of aggressive tumours responsible for a major proportion of pediatric cancer deaths. We designed a chemical-genetic screen that identifies compounds capable of enhancing proteasomal elimination of MYCN oncoprotein. We isolated several classes of compound that selectively kill MYCN expressing cells and we focus on inhibitors of PI3K/mTOR pathway in this study. We show that PI3K/mTOR inhibitors selectively killed MYCN-expressing neuroblastoma tumor cells, and induced significant apoptosis of transgenic MYCN-driven neuroblastoma tumors concomitant with elimination of MYCN protein in vivo. Mechanistically, the ability of these compounds to degrade MYCN requires complete blockade of mTOR but not PI3 kinase activity and we highlight NVP-BEZ235 as a PI3K/mTOR inhibitor with an ideal activity profile. These data establish that MYCN expression is a marker indicative of likely clinical sensitivity to mTOR inhibition, and provide a rationale for the selection of clinical candidate MYCN-destabilizers likely to be useful for the treatment of MYCN-driven cancers.

Analysis of the transcriptional regulation of cancer-related genes by aberrant DNA methylation of the cis-regulation sites in the promoter region during hepatocyte carcinogenesis caused by arsenic

Liver is the major organ for arsenic methylation metabolism and may be the potential target of arsenic-induced cancer. In this study, normal human liver cell was treated with arsenic trioxide, and detected using DNA methylation microarray. Some oncogenes, tumor suppressor genes, transcription factors (TF), and tumor-associated genes (TAG) that have aberrant DNA methylation have been identified. However, simple functional studies of genes adjacent to aberrant methylation sites cannot well reflect the regulatory relationship between DNA methylation and gene transcription during the pathogenesis of arsenic-induced liver cancer, whereas a further analysis of the cis-regulatory elements and their trans-acting factors adjacent to DNA methylation can more precisely reflect the relationship between them. MYC and MAX (MYC associated factor X) were found to participating cell cycle through a bioinformatics analysis. Additionally, it was found that the hypomethylation of cis-regulatory sites in the MYC promoter region and the hypermethylation of cis-regulatory sites in the MAX promoter region result in the up-regulation of MYC mRNA expression and the down-regulation of MAX mRNA, which increased the hepatocyte carcinogenesis tendency.

microRNA-25 Inhibits Cell Apoptosis of Human Gastric Adenocarcinoma Cell Line AGS via Regulating CCNE1 and MYC

BACKGROUND Gastric carcinoma is the second leading cause of cancer death. microRNAs play vital roles in regulating expression of related oncogenes. microRNA-25 (miR-25) has been found to be up-regulated in gastric carcinoma. However, its roles in affecting cell apoptosis of gastric carcinoma and the related mechanism remain elusive. This study aimed to uncover the influences of miR-25 on gastric carcinoma cell apoptosis and the possible functional mechanisms involved. MATERIAL AND METHODS Human gastric adenocarcinoma cell line AGS was used and transfected with lentivirus containing miR-25-specifc inhibitor sponge or expression vector to analyze the effects of miR-25. RESULTS miR-25 had higher expression in AGS than in human gastric epithelial cell line GES-1 (P<0.01). Inhibition of miR-25 by its sponge in AGS cells resulted in suppressed cell viability (P<0.01) and promoted cell apoptosis (P<0.01), while overexpression of miR-25 abrogated these effects (P<0.01 and P<0.05), indicating that miR-25 can promote cell viability and inhibit cell apoptosis in AGS cells. Expression analysis of related factors by Western blot showed that inhibiting miR-25 led to the up-regulation of F-box and WD repeat domain-containing 7 (FBXW7, P<0.01) and the down-regulation of FBXW7 substrates, cyclin E1 (CCNE1, P<0.01), and v-myc avian myelocytomatosis viral oncogene homolog (MYC, P<0.001). CONCLUSIONS These results indicate that miR-25 has anti-apoptosis roles in AGS cells, possibly via inhibiting FBXW7 and thus promoting oncogenes, such as CCNE1 and MYC. This study provides basic evidence for using miR-25 as a possible therapeutic target in treating gastric carcinoma.