ERK kinase phosphorylates and destabilizes the tumor suppressor FBW7 in pancreatic cancer

Molecular insights and clinical implications for the tumor suppressor role of SCFFBXW7 E3 ubiquitin ligase

FBXW7 is one of the most well-characterized F-box proteins, serving as substrate receptor subunit of SKP1-CUL1-F-box (SCF) E3 ligase complexes. SCFFBXW7 is responsible for the degradation of various oncogenic proteins such as cyclin E, c-MYC, c-JUN, NOTCH, and MCL1. Therefore, FBXW7 functions largely as a major tumor suppressor. In keeping with this notion, FBXW7 gene mutations or downregulations have been found and reported in many types of malignant tumors, such as endometrial, colorectal, lung, and breast cancers, which facilitate the proliferation, invasion, migration, and drug resistance of cancer cells. Therefore, it is critical to review newly identified FBXW7 regulation and tumor suppressor function under physiological and pathological conditions to develop effective strategies for the treatment of FBXW7-altered cancers. Since a growing body of evidence has revealed the tumor-suppressive activity and role of FBXW7, here, we updated FBXW7 upstream and downstream signaling including FBXW7 ubiquitin substrates, the multi-level FBXW7 regulatory mechanisms, and dysregulation of FBXW7 in cancer, and discussed promising cancer therapies targeting FBXW7 regulators and downstream effectors, to provide a comprehensive picture of FBXW7 and facilitate the study in this field.

LEPR/FOS/JUNB signaling pathway contributes to chronic restraint stress-induced tumor proliferation

BACKGROUND & AIMS

Psychosocial stress has become an unavoidable part of life, which was reported to promote tumor development. Chronic stress significantly promotes the norepinephrine (NE) secretion and the expression of leptin receptor (LEPR), leading to tumor invasion, metastasis, and proliferation. However, the mechanism of chronic stress-induced tumor proliferation remains unclear.

METHODS

To reveal the effect of chronic stress on tumor proliferation, subcutaneous tumor models combined with chronic restraint stress (CRS) were established. Combined with the transcript omics database of liver cancer patients, the target pathways were screened and further verified by in vitro experiments.

RESULTS

The results showed that the CRS with subcutaneous tumor transplantation (CRS + tumor) group exhibited significantly larger tumor sizes than the subcutaneous tumor transplantation (tumor) group. Compared with the tumor group, CRS obviously increased the mRNA levels of LEPR, FOS, and JUNB of tumor tissues in the CRS + tumor group. Furthermore, the treatment with norepinephrine (NE) significantly elevated the survival rate of H22 cells and enhanced the expression of LEPR, FOS, and JUNB in vitro. Silencing LEPR significantly reduced the expression of FOS and JUNB, accompanied by a decrease in H22 cell viability.

CONCLUSIONS

Our study demonstrated that CRS activates the LEPR-FOS-JUNB signaling pathway by NE, aggravating tumor development. These findings might provide a scientific foundation for investigating the underlying pathological mechanisms of tumors in response to chronic stress.

Transcription factor EB reprograms branched-chain amino acid metabolism and promotes pancreatic cancer progression via transcriptional regulation of BCAT1

Pancreatic cancer cells have a much higher metabolic demand than that of normal cells. However, the abundant interstitium and lack of blood supply determine the lack of nutrients in the tumour microenvironment. Although pancreatic cancer has been reported to supply extra metabolic demand for proliferation through autophagy and other means, the specific regulatory mechanisms have not yet been elucidated. In this study, we focused on transcription factor EB (TFEB), a key factor in the regulation of autophagy, to explore its effect on the phenotype and role in the unique amino acid utilisation pattern of pancreatic cancer cells (PCCs). The results showed that TFEB, which is generally highly expressed in pancreatic cancer, promoted the proliferation and metastasis of PCCs. TFEB knockdown inhibited the proliferation and metastasis of PCCs by blocking the catabolism of branched-chain amino acids (BCAAs). Concerning the mechanism, we found that TFEB regulates the catabolism of BCAAs by regulating BCAT1, a key enzyme in BCAA metabolism. BCAA deprivation alone did not effectively inhibit PCC proliferation. However, BCAA deprivation combined with eltrombopag, a drug targeting TFEB, can play a two-pronged role in exogenous supply deprivation and endogenous utilisation blockade to inhibit the proliferation of pancreatic cancer to the greatest extent, providing a new therapeutic direction, such as targeted metabolic reprogramming of pancreatic cancer.

Active AKT2 stimulation of SREBP1/SCD1-mediated lipid metabolism boosts hepatosteatosis and cancer

Due to soared obesity population worldwide, hepatosteatosis is becoming a major risk factor for hepatocellular carcinoma (HCC). Undertaken molecular events during the progression of steatosis to liver cancer are thus under intensive investigation. In this study, we demonstrated that high-fat diet potentiated mouse liver AKT2. Hepatic AKT2 hyperactivation through gain-of-function mutation of Akt2 (Akt2E17K) caused spontaneous hepatosteatosis, injury, inflammation, fibrosis, and eventually HCC in mice. AKT2 activation also exacerbated lipopolysaccharide and D-galactosamine hydrochloride-induced injury/inflammation and N-Nitrosodiethylamine (DEN)-induced HCC. A positive correlation between AKT2 activity and SCD1 expression was observed in human HCC samples. Activated AKT2 enhanced the production of monounsaturated fatty acid which was dependent on SREBP1 upregulation of SCD1. Blockage of active SREBP1 and ablation of SCD1 reduced steatosis, inflammation, and tumor burden in DEN-treated Akt2E17K mice. Therefore, AKT2 activation is crucial for the development of steatosis-associated HCC which can be treated with blockage of AKT2-SREBP1-SCD1 signaling cascade.

Transcriptional Up-Regulation of FBXW7 by KCa1.1 K+ Channel Inhibition through the Nrf2 Signaling Pathway in Human Prostate Cancer LNCaP Cell Spheroid Model

The tumor suppressor gene F-box and WD repeat domain-containing (FBXW) 7 reduces cancer stemness properties by promoting the protein degradation of pluripotent stem cell markers. We recently demonstrated the transcriptional repression of FBXW7 by the three-dimensional (3D) spheroid formation of several cancer cells. In the present study, we found that the transcriptional activity of FBXW7 was promoted by the inhibition of the Ca2+-activated K+ channel, KCa1.1, in a 3D spheroid model of human prostate cancer LNCaP cells through the Akt-Nrf2 signaling pathway. The transcriptional activity of FBXW7 was reduced by the siRNA-mediated inhibition of the CCAAT-enhancer-binding protein C/EBP δ (CEBPD) after the transfection of miR223 mimics in the LNCaP spheroid model, suggesting the transcriptional regulation of FBXW7 through the Akt-Nrf2-CEBPD-miR223 transcriptional axis in the LNCaP spheroid model. Furthermore, the KCa1.1 inhibition-induced activation of FBXW7 reduced (1) KCa1.1 activity and protein levels in the plasma membrane and (2) the protein level of the cancer stem cell (CSC) markers, c-Myc, which is a molecule degraded by FBXW7, in the LNCaP spheroid model, indicating that KCa1.1 inhibition-induced FBXW7 activation suppressed CSC conversion in KCa1.1-positive cancer cells.

Arachidonic acid released by PIK3CA mutant tumor cells triggers malignant transformation of colonic epithelium by inducing chromatin remodeling

Key gene mutations are essential for colorectal cancer (CRC) development; however, how the mutated tumor cells impact the surrounding normal cells to promote tumor progression has not been well defined. Here, we report that PIK3CA mutant tumor cells transmit oncogenic signals and result in malignant transformation of intestinal epithelial cells (IECs) via paracrine exosomal arachidonic acid (AA)-induced H3K4 trimethylation. Mechanistically, PIK3CA mutations sustain SGK3-FBW7-mediated stability of the cPLA2 protein, leading to the synthetic increase in AA, which is transported through exosome and accumulated in IECs. Transferred AA directly binds Menin and strengthens the interactions of Menin and MLL1/2 methyltransferase. Finally, the combination of VTP50469, an inhibitor of the Menin-MLL interaction, and alpelisib synergistically represses PDX tumors harboring PIK3CA mutations. Together, these findings unveil the metabolic link between PIK3CA mutant tumor cells and the IECs, highlighting AA as the potential target for the treatment of patients with CRC harboring PIK3CA mutations.

Advances in the regulation of radiation-induced apoptosis by polysaccharides: A review

Polysaccharides are biomolecules composed of monosaccharides that are widely found in animals, plants and microorganisms and are of interest for their various health benefits. Cumulative studies have shown that the modulation of radiation-induced apoptosis by polysaccharides can be effective in preventing and treating a wide range of radiation injuries with safety and few side effects. Therefore, this paper summarizes the monosaccharide compositions, molecular weights, and structure-activity relationships of natural polysaccharides that regulate radiation-induced apoptosis, and also reviews the molecular mechanisms by which these polysaccharides modulate radiation-induced apoptosis, primarily focusing on promoting cancer cell apoptosis to enhance radiotherapy efficacy, reducing radiation damage to normal tissues, and inhibiting apoptosis in normal cells. Additionally, the role of gut microbiota in mediating the interaction between polysaccharides and radiation is discussed, providing innovative ideas for various radiation injuries, including hematopoiesis, immunity, and organ damage. This review will contribute to a better understanding of the value of natural polysaccharides in the field of radiation and provide guidance for the development of natural radioprotective agents and radiosensitizers.

Expanding the ubiquitin code in pancreatic cancer

The ubiquitin-proteasome system (UPS) is a fundamental regulatory mechanism in cells, vital for maintaining cellular homeostasis, compiling signaling transduction, and determining cell fates. These biological processes require the coordinated signal cascades of UPS members, including ubiquitin ligases, ubiquitin-conjugating enzymes, deubiquitinases, and proteasomes, to ubiquitination and de-ubiquitination on substrates. Recent studies indicate that ubiquitination code rewriting is particularly prominent in pancreatic cancer. High frequency mutation or aberrant hyperexpression of UPS members dysregulates ferroptosis, tumor microenvironment, and metabolic rewiring processes and contribute to tumor growth, metastasis, immune evasion, and acquired drug resistance. We conduct an in-depth overview of ubiquitination process in pancreatic cancer, highlighting the role of ubiquitin code in tumor-promoting and tumor-suppressor pathways. Furthermore, we review current UPS modulators and analyze the potential of UPS modulators as cancer therapy.

The m7G Reader NCBP2 Promotes Pancreatic Cancer Progression by Upregulating MAPK/ERK Signaling

PDAC is one of the most common malignant tumors worldwide. The difficulty of early diagnosis and lack of effective treatment are the main reasons for its poor prognosis. Therefore, it is urgent to identify novel diagnostic and therapeutic targets for PDAC patients. The m7G methylation is a common type of RNA modification that plays a pivotal role in regulating tumor development. However, the correlation between m7G regulatory genes and PDAC progression remains unclear. By integrating gene expression and related clinical information of PDAC patients from TCGA and GEO cohorts, m7G binding protein NCBP2 was found to be highly expressed in PDAC patients. More importantly, PDAC patients with high NCBP2 expression had a worse prognosis. Stable NCBP2-knockdown and overexpression PDAC cell lines were constructed to further perform in-vitro and in-vivo experiments. NCBP2-knockdown significantly inhibited PDAC cell proliferation, while overexpression of NCBP2 dramatically promoted PDAC cell growth. Mechanistically, NCBP2 enhanced the translation of c-JUN, which in turn activated MEK/ERK signaling to promote PDAC progression. In conclusion, our study reveals that m7G reader NCBP2 promotes PDAC progression by activating MEK/ERK pathway, which could serve as a novel therapeutic target for PDAC patients.

Role of CELF2 in ferroptosis: Potential targets for cancer therapy (Review)

Ferroptosis is a novel form of regulated cellular necrosis that plays a critical role in promoting cancer progression and developing drug resistance. The main characteristic of ferroptosis is iron‑dependent lipid peroxidation caused by excess intracellular levels of reactive oxygen species. CUGBP ELAV‑like family number 2 (CELF2) is an RNA‑binding protein that is downregulated in various types of cancer and is associated with poor patient prognoses. CELF2 can directly bind mRNA to a variety of ferroptosis control factors; however, direct evidence of the regulatory role of CELF2 in ferroptosis is currently limited. The aim of the present review was to summarise the findings of previous studies on CELF2 and its role in regulating cellular redox homeostasis. The present review may provide insight into the possible mechanisms through which CELF2 affects ferroptosis and to provide recommendations for future studies.

Nuclear receptor coactivator 6 (NCoA6) promotes cell proliferation, migration, and invasion in pancreatic cancer

BACKGROUND

Nuclear receptor coactivator 6 (NCoA6) is overexpressed in various cancers and considered a multifunctional coactivator of various transcription factors and nuclear receptors. However, the role of NCoA6 in pancreatic ductal adenocarcinoma (PDAC) remains unclear.

METHODS

NCoA6 expression data in PDAC were extracted from TCGA and GTEx databases, and their correlation with survival outcomes were analyzed using the Kaplan-Meier plotter database. NCoA6 protein expression in PDAC tissues was evaluated using immunohistochemistry. RNA-sequencing technology was used to sequence the transcriptome of NCoA6-silenced PANC-1 cells, followed by differential expression, GO/KEGG and GSEA analyses. The effects of NCoA6 on cell proliferation, migration, invasion, cell cycle, and apoptosis were determined in two representative cell lines (PANC-1 and SW1990). Western blotting, qPCR, and co-immunoprecipitation were performed to explore the mechanism of action of NCoA6 in PDAC cells.

RESULTS

NCoA6 expression was markedly increased in PDAC tissues, and high NCoA6 expression was associated with poor survival prognosis. However, there was no significant relationship between NCoA6 expression and metastasis in PDAC patients. Our RNA-sequencing data analysis found 1194 significant differentially expressed genes between the control and NCoA6-silenced PANC-1 cells. GO/KEGG analysis results mainly focused on cytokine production, cytokine activity, and cytokine-cytokine receptor interactions. GSEA results showed that the knockdown of NCoA6 affected the expression of histone deacetylase 1 (HDAC1) targeted genes. NCoA6 knockdown suppressed proliferation, migration, and invasion of PDAC cells. Finally, western blotting, qPCR, and co-immunoprecipitation results showed that NCoA6 interacted with HDAC1 and that NCoA6 expression was negatively correlated with F-box and WD repeat domain-containing 7 (FBW7) and caudal-related homeobox transcription factor 2 (CDX2) expression in pancreatic cancer.

CONCLUSIONS

NCoA6 has a profound effect on cell proliferation, migration, invasion, and prognosis of PDAC and is potentially related to the expression of HDAC1, FBW7, and CDX2. Our results may provide novel therapeutic strategies for PDAC patients.

The Role of FBXW7 in Gynecologic Malignancies

The F-Box and WD Repeat Domain Containing 7 (FBXW7) protein has been shown to regulate cellular growth and act as a tumor suppressor. This protein, also known as FBW7, hCDC4, SEL10 or hAGO, is encoded by the gene FBXW7. It is a crucial component of the Skp1-Cullin1-F-box (SCF) complex, which is a ubiquitin ligase. This complex aids in the degradation of many oncoproteins, such as cyclin E, c-JUN, c-MYC, NOTCH, and MCL1, via the ubiquitin-proteasome system (UPS). The FBXW7 gene is commonly mutated or deleted in numerous types of cancer, including gynecologic cancers (GCs). Such FBXW7 mutations are linked to a poor prognosis due to increased treatment resistance. Hence, detection of the FBXW7 mutation may possibly be an appropriate diagnostic and prognostic biomarker that plays a central role in determining suitable individualized management. Recent studies also suggest that, under specific circumstances, FBXW7 may act as an oncogene. There is mounting evidence indicating that the aberrant expression of FBXW7 is involved in the development of GCs. The aim of this review is to give an update on the role of FBXW7 as a potential biomarker and also as a therapeutic target for novel treatments, particularly in the management of GCs.

FBXW7 loss of function promotes esophageal squamous cell carcinoma progression via elevating MAP4 and ERK phosphorylation

BACKGROUND

Increasing evidence suggests that FBXW7 has a high frequency of mutations in esophageal squamous cell carcinoma (ESCC). However, the function of FBXW7, especially the mutations, is not clear. This study was designed to investigate the functional significance of FBXW7 loss of function and underlying mechanism in ESCC.

METHODS

Immunofluorescence was applied to clarify the localization and main isoform of FBXW7 in ESCC cells. Sanger sequencing were performed to explore mutations of FBXW7 in ESCC tissues. Proliferation, colony, invasion and migration assays were performed to examine the functional roles of FBXW7 in ESCC cells in vitro and in vivo. Real-time RT-PCR, immunoblotting, GST-pulldown, LC-MS/MS and co-immunoprecipitation assay were used to explore the molecular mechanism underlying the actions of FBXW7 functional inactivation in ESCC cells. Immunohistochemical staining were used to explore the expression of FBXW7 and MAP4 in ESCC tissues.

RESULTS

The main FBXW7 isoform in ESCC cells was the β transcript in the cytoplasm. Functional inactivation of FBXW7 led to activation of the MAPK signaling pathway and upregulation of the downstream MMP3 and VEGFA, which enhanced tumor proliferation cell invasion and migration. Among the five mutation forms screened, S327X (X means truncated mutation) had an effect similar to the FBXW7 deficiency and led to the inactivation of FBXW7 in ESCC cells. Three other point mutations, S382F, D400N and R425C, attenuated but did not eliminate FBXW7 function. The other truncating mutation, S598X, which was located outside of the WD40 domain, revealed a tiny attenuation of FBXW7 in ESCC cells. Notably, MAP4 was identified as a potential target of FBXW7. The threonine T521 of MAP4, which was phosphorylated by CHEK1, played a key role in the FBXW7-related degradation system. Immunohistochemical staining indicated that FBXW7 loss of function was associated with tumor stage and shorter survival of patients with ESCC. Univariate and multivariate Cox proportional hazards regression analyses showed that high FBXW7 and low MAP4 was an independent prognostic indicator and prospective longer survival. Moreover, a combination regimen that included MK-8353 to inhibit the phosphorylation of ERK and bevacizumab to inhibit VEGFA produced potent inhibitory effects on the growth of FBXW7 inactivation xenograft tumors in vivo.

CONCLUSIONS

This study provided evidence that FBXW7 loss of function promoted ESCC via MAP4 overexpression and ERK phosphorylation, and this novel FBXW7/MAP4/ERK axis may be an efficient target for ESCC treatment.

Ferroptosis in gastrointestinal cancer: From mechanisms to implications

Ferroptosis is a form of regulated cell death that is initiated by excessive lipid peroxidation that results in plasma membrane damage and the release of damage-associated molecular patterns. In recent years, ferroptosis has gained significant attention in cancer research due to its unique mechanism compared to other forms of regulated cell death, especially caspase-dependent apoptotic cell death. Gastrointestinal (GI) cancer encompasses malignancies that arise in the digestive tract, including the stomach, intestines, pancreas, colon, liver, rectum, anus, and biliary system. These cancers are a global health concern, with high incidence and mortality rates. Despite advances in medical treatments, drug resistance caused by defects in apoptotic pathways remains a persistent challenge in the management of GI cancer. Hence, exploring the role of ferroptosis in GI cancers may lead to more efficacious treatment strategies. In this review, we provide a comprehensive overview of the core mechanism of ferroptosis and discuss its function, regulation, and implications in the context of GI cancers.

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.

SMYD2 Promotes Hepatocellular Carcinoma Progression by Reprogramming Glutamine Metabolism via c-Myc/GLS1 Axis

Metabolic reprogramming, such as alterations in glutamine metabolism or glycolysis, is the hallmark of hepatocellular carcinoma (HCC). However, the underlying mechanisms are still incompletely elucidated. Previous studies have identified that methyltransferase SET and MYND domain-containing protein 2(SMYD2) is responsible for the pathogenesis of numerous types of cancer. Here, we innovatively uncover how SMYD2 regulates glutamine metabolism in HCC cells and promotes HCC progression. We identified that SMYD2 expression is upregulated in HCC tissues, which correlates with unfavorable clinical outcomes. Our in vitro and in vivo results showed that the depletion of SMYD2 inhibits HCC cell growth. Mechanistically, c-Myc methylation by SMYD2 increases its protein stability through the ubiquitin-proteasome system. We showed SMYD2 depletion destabilized c-Myc protein by increasing the conjugated K48-linked polyubiquitin chain. SMYD2 increased c-Myc expression and further upregulated glutaminase1 (GLS1), a crucial enzyme that catalyzes the conversion of glutamine to glutamic acid, in HCC cells. GLS1 plays an important role in SMYD2-mediated HCC progression and glutamine metabolism regulation. The knockdown of SMYD2 inhibited glutamine metabolism in HCC cells and overcame their chemoresistance to sorafenib. Collectively, our findings demonstrated a novel mechanism of how SMYD2 promotes HCC progression by regulating glutamine metabolism through the c-Myc/GLS1signaling, implicating the therapeutic potential of targeting SMYD2 in HCC patients.

The intricate interplay between HIFs, ROS, and the ubiquitin system in the tumor hypoxic microenvironment

Alterations in protein ubiquitination and hypoxia-inducible factor (HIF) signaling both contribute to tumorigenesis and tumor progression. Ubiquitination is a dynamic process that is coordinately regulated by E3 ligases and deubiquitinases (DUBs), which have emerged as attractive therapeutic targets. HIF expression and transcriptional activity are usually increased in tumors, leading to poor clinical outcomes. Reactive oxygen species (ROS) are upregulated in tumors and have multiple effects on HIF signaling and the ubiquitin system. A growing body of evidence has shown that multiple E3 ligases and UBDs function synergistically to control the expression and activity of HIF, thereby allowing cancer cells to cope with the hypoxic microenvironment. Conversely, several E3 ligases and DUBs are regulated by hypoxia and/or HIF signaling. Hypoxia also induces ROS production, which in turn modulates the stability or activity of HIF, E3 ligases, and DUBs. Understanding the complex networks between E3 ligase, DUBs, ROS, and HIF will provide insights into the fundamental mechanism of the cellular response to hypoxia and help identify novel molecular targets for cancer treatment. We review the current knowledge on the comprehensive relationship between E3 ligase, DUBs, ROS, and HIF signaling, with a particular focus on the use of E3 ligase or DUB inhibitors in cancer.

Jwa participates the maintenance of intestinal epithelial homeostasis via ERK/FBXW7-mediated NOTCH1/PPARγ/STAT5 axis and acts as a novel putative aging related gene

The intestinal epithelium is a rapid self-renewal and regenerated tissue of which the structural integrity is beneficial for maintaining health. The integrity of intestinal epithelium depends on the balance of cell proliferation, differentiation, migration, and the function of intestinal stem cells, which declines due to genetic defect or aging. Jwa participates in multiple cellular processes; it also responds to oxidative stress and repairs DNA damage. However, whether Jwa plays a role in maintaining the homeostasis of intestinal renewal and regeneration is not clear. In the present study, we firstly described that the deletion of Jwa disturbed the homeostasis of intestinal epithelial renewal and regeneration. Jwa deficiency promoted NOTCH1 degradation in the ERK/FBXW7-mediated ubiquitin-proteasome pathway, thus disturbing the PPARγ/STAT5 axis. These mechanisms might partially contribute to the reduction of intestinal stem cell function and alteration of intestinal epithelial cell lineage distribution, finally suppressing the renewal and regeneration of intestinal epithelium. Moreover, our results also revealed that Jwa was a novel putative aging related gene.

Present Status, Challenges, and Prospects of Dihydromyricetin in the Battle against Cancer

Dihydromyricetin (DHM) is a natural flavonoid compound extracted from Ampelopsis grossedentata that has been used for centuries in traditional Chinese medicine. DHM has attracted intensive attention due to its numerous beneficial activities, such as hepatoprotection, cardioprotection, antioxidant, and anti-inflammation. In addition, DHM inhibits the progression of cancers such as lung cancer, hepatocellular cancer, breast cancer, melanoma, and malignant reproductive systems through multiple mechanisms, including antiangiogenesis, antiproliferation, apoptosis, and inhibition of invasion and migration. Notably, DHM also activates autophagy at different levels, exerting a dual-regulatory effect on cancers. Mechanistically, DHM can effectively regulate mammalian target of rapamycin (mTOR), noncoding RNA-mediated signaling, phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) pathway, nuclear factor-κB (NF-κB), p53, and endoplasmic reticulum stress (ER stress)-driven signaling in different types of cancers. DHM has also been shown to have inhibitory effects on various regulators that trigger epithelial–mesenchymal transition (EMT). Furthermore, DHM exhibits a remarkable anticancer reversal ability when used in combination with drugs such as adriamycin, nedaplatin, and other drugs. However, the low bioavailability of DHM limits its potential applications, which are improved through structural modification and the exploration of novel dosage forms. Therefore, DHM may become a promising candidate for treating malignancies alone or combined with conventional anticancer strategies used in clinical practice.

Chromatin Ubiquitination Guides DNA Double Strand Break Signaling and Repair

Chromatin is the context for all DNA-based molecular processes taking place in the cell nucleus. The initial chromatin structure at the site of the DNA damage determines both, lesion generation and subsequent activation of the DNA damage response (DDR) pathway. In turn, proceeding DDR changes the chromatin at the damaged site and across large fractions of the genome. Ubiquitination, besides phosphorylation and methylation, was characterized as an important chromatin post-translational modification (PTM) occurring at the DNA damage site and persisting during the duration of the DDR. Ubiquitination appears to function as a highly versatile “signal-response” network involving several types of players performing various functions. Here we discuss how ubiquitin modifiers fine-tune the DNA damage recognition and response and how the interaction with other chromatin modifications ensures cell survival.

Recent Insight on Regulations of FBXW7 and Its Role in Immunotherapy

SCF^FBXW7 E3 ubiquitin ligase complex is a crucial enzyme of the ubiquitin proteasome system that participates in variant activities of cell process, and its component FBXW7 (F-box and WD repeat domain–containing 7) is responsible for recognizing and binding to substrates. The expression of FBXW7 is controlled by multiple pathways at different levels. FBXW7 facilitates the maturity and function maintenance of immune cells via functioning as a mediator of ubiquitination-dependent degradation of substrate proteins. FBXW7 deficiency or mutation results in the growth disturbance and dysfunction of immune cell, leads to the resistance against immunotherapy, and participates in multiple illnesses. It is likely that FBXW7 coordinating with its regulators and substrates could offer potential targets to improve the sensitivity and effects of immunotherapy. Here, we review the mechanisms of the regulation on FBXW7 and its tumor suppression role in immune filed among various diseases (mostly cancers) to explore novel immune targets and treatments.

Neddylation inhibition induces glutamine uptake and metabolism by targeting CRL3SPOP E3 ligase in cancer cells

Abnormal neddylation activation is frequently observed in human cancers and neddylation inhibition has been proposed as a therapy for cancer. Here, we report that MLN4924, a small-molecule inhibitor of neddylation activating enzyme, increases glutamine uptake in breast cancer cells by causing accumulation of glutamine transporter ASCT2/SLC1A5, via inactivation of CRL3-SPOP E3 ligase. We show the E3 ligase SPOP promotes ASCT2 ubiquitylation, whereas SPOP itself is auto-ubiquitylated upon glutamine deprivation. Thus, SPOP and ASCT2 inversely regulate glutamine uptake and metabolism. SPOP knockdown increases ASCT2 levels to promote growth which is rescued by ASCT2 knockdown. Adding ASCT2 inhibitor V-9302 enhances MLN4924 suppression of tumor growth. In human breast cancer specimens, SPOP and ASCT2 levels are inversely correlated, whereas lower SPOP with higher ASCT2 predicts a worse patient survival. Collectively, our study links neddylation to glutamine metabolism via the SPOP-ASCT2 axis and provides a rational drug combination for enhanced cancer therapy.

Neddylation inhibition has been reported as a therapy for cancer. Here, the authors show that neddylation inhibition increases glutamine metabolism by stabilizing glutamine transporter ASCT2, therefore targeting ASCT2 improves the anti-cancer effect of neddylation inhibitors.

Clinical significance of FBXW7 loss of function in human cancers

FBXW7 (F-Box and WD Repeat Domain Containing 7) (also referred to as FBW7 or hCDC4) is a component of the Skp1-Cdc53 / Cullin-F-box-protein complex (SCF/β-TrCP). As a member of the F-box protein family, FBXW7 serves a role in phosphorylation-dependent ubiquitination and proteasome degradation of oncoproteins that play critical role(s) in oncogenesis. FBXW7 affects many regulatory functions involved in cell survival, cell proliferation, tumor invasion, DNA damage repair, genomic instability and telomere biology. This thorough review of current literature details how FBXW7 expression and functions are regulated through multiple mechanisms and how that ultimately drives tumorigenesis in a wide array of cell types. The clinical significance of FBXW7 is highlighted by the fact that FBXW7 is frequently inactivated in human lung, colon, and hematopoietic cancers. The loss of FBXW7 can serve as an independent prognostic marker and is significantly correlated with the resistance of tumor cells to chemotherapeutic agents and poorer disease outcomes. Recent evidence shows that genetic mutation of FBXW7 differentially affects the degradation of specific cellular targets resulting in a distinct and specific pattern of activation/inactivation of cell signaling pathways. The clinical significance of FBXW7 mutations in the context of tumor development, progression, and resistance to therapies as well as opportunities for targeted therapies is discussed.

TGF-β1-induced RAP2 regulates invasion in pancreatic cancer

Pancreatic cancer is highly lethal due to its aggressive invasive properties and capacity for metastatic dissemination. Additional therapeutic targets and effective treatment options for patients with tumours of high invasive capacity are required. Ras-related protein-2a (RAP2) is a member of the GTP-binding proteins. RAP2 has been reported to be widely upregulated in many types of cancers via regulating cytoskeleton reorganization, cell proliferation, migration, and adhesion, as well as inflammation. As a member of the RAS oncogene family, which has been demonstrated to drive pancreatic cancer oncogenesis and many other malignancies, the physiological roles of RAP2 in pancreatic cancer have seldom been discussed. In the present study, we explored the correlation between RAP2 expression and the prediction of overall survival of pancreatic cancer patients. Mechanistic studies were carried out to shed light on the role of RAP2 in pancreatic cancer invasion and how RAP2 is regulated in the invasive process. Our results demonstrated that patients with higher RAP2 expression showed unfavourable prognoses. studies demonstrated that silencing of inhibited the invasion of pancreatic cancer cells. Moreover, our results demonstrated that transforming growth factor-β1 (TGF-β1), an inducer of the metastatic potential of pancreatic cancer cells, regulates the expression of RAP2 via the transcription factor c-Myc. In conclusion, the present study uncovered RAP2 as a novel predictive marker and therapeutic target for pancreatic cancer.

Pevonedistat Suppresses Pancreatic Cancer Growth via Inactivation of the Neddylation Pathway

Background

The neddylation pathway is aberrantly overactivated in multiple human cancers and has been indicated as an effective target for anticancer therapy in clinical trials. We aimed to study whether the neddylation pathway is upregulated in pancreatic cancer and whether pevonedistat, a first-in-class anticancer agent specifically targeting this pathway, will suppress cancer tumorigenesis and progression.

Methods

We evaluated the expression pattern of neddylation pathway components in 179 pancreatic adenocarcinoma (PAAD) compared with 171 normal tissues from The Cancer Genome Atlas (TCGA) dataset and further assessed PAAD patient prognosis with high neddylation pathway expression via Gene Expression Profiling Interactive Analysis (GEPIA). We then analyzed malignant cancer phenotypes both in vitro and in vivo, as well as intrinsic molecular mechanisms upon pevonedistat treatment.

Results

We found that the neddylation pathway was hyperactivated in pancreatic cancer. Patients with high neddylation pathway expression exhibited worse prognoses. Pevonedistat significantly inhibited the cancer cell cycle, cell growth, and proliferation; increased cell apoptosis; and decreased cancer cell xenografts in a mouse model. Mechanistically, pevonedistat treatment and the siRNA knockdown neddylation pathway were able to remarkably induce the accumulation of Wee1, p27, and p21. Further mechanistic studies revealed that pevonedistat mainly impaired the ubiquitination level and delayed the protein degradation of Wee1, p27, and p21.

Conclusions

Our results showed that pevonedistat targeted the overexpression of the neddylation pathway in pancreatic cancer to induce cell growth suppression by inducing the accumulation of the cell cycle regulators Wee1, p27, and p21, which provides sound evidence for the clinical trial of pevonedistat for pancreatic cancer therapy.

Loss of FBXW7 Correlates with Increased IDH1 Expression in Glioma and Enhances IDH1-Mutant Cancer Cell Sensitivity to Radiation

F-box and WD repeat domain containing 7 (FBXW7) is a substrate receptor of the ubiquitin ligase SKP1-Cullin1-F-box complex and a potent tumor suppressor that prevents unregulated cell growth and tumorigenesis. However, little is known about FBXW7-mediated control of cell metabolism and related functions in cancer therapy. Here, we report that FBXW7 expression inversely correlates with the expression levels of the key metabolic enzyme isocitrate dehydrogenase 1 (IDH1) in patients with glioma and public glioma datasets. Deletion of FBXW7 significantly increased both wild-type (WT) and mutant IDH1 expression, which was mediated by blocking degradation of sterol regulatory element binding protein 1 (SREBP1). The upregulation of neomorphic mutant IDH1 by FBXW7 deletion stimulated production of the oncometabolite 2-hydroxyglutarate at the expense of increasing pentose phosphate pathway activity and NADPH consumption, limiting the buffering ability against radiation-induced oxidative stress. In addition, FBXW7 knockout and IDH1 mutations induced nonhomologous end joining and homologous recombination defects, respectively. In vitro and in vivo, loss of FBXW7 dramatically enhanced the efficacy of radiation treatment in IDH1-mutant cancer cells. Taken together, this work identifies FBXW7 deficiency as a potential biomarker representing both DNA repair and metabolic vulnerabilities that sensitizes IDH1-mutant cancers to radiotherapy. SIGNIFICANCE: Deficiency of FBXW7 causes defects in DNA repair and disrupts NADPH homeostasis in IDH1-mutant glioma cells, conferring high sensitivity to radiotherapy.

Glycometabolic rearrangements-aerobic glycolysis in pancreatic ductal adenocarcinoma (PDAC): roles, regulatory networks, and therapeutic potential

INTRODUCTION

Glycometabolic rearrangements (aerobic glycolysis) is a hallmark of pancreatic ductal adenocarcinoma (PDAC) and contributes to tumorigenesis and progression through numerous mechanisms. The targeting of aerobic glycolysis is recognized as a potential therapeutic strategy which offers the possibility of improving treatment outcomes for PDAC patients.

AREAS COVERED

In this review, the role of aerobic glycolysis and its regulatory networks in PDAC are discussed. The targeting of aerobic glycolysis in PDAC is examined, and its therapeutic potential is evaluated. The relevant literature published from 2001 to 2021 was searched in databases including PubMed, Scopus, and Embase.

EXPERT OPINION

Regulatory networks of aerobic glycolysis in PDAC are based on key factors such as c-Myc, hypoxia-inducible factor 1α, the mammalian target of rapamycin pathway, and non-coding RNAs. Experimental evidence suggests that modulators or inhibitors of aerobic glycolysis promote therapeutic effects in preclinical tumor models. Nevertheless, successful clinical translation of drugs that target aerobic glycolysis in PDAC is an obstacle. Moreover, it is necessary to identify the potential targets for future interventions from regulatory networks to design efficacious and safer agents.

Suppressive role of E3 ubiquitin ligase FBW7 in type I diabetes in non-obese diabetic mice through mediation of ubiquitination of EZH2

The current study tried to uncover the molecular mechanism of E3 ubiquitin ligase F-box and WD repeat domain-containing 7 (FBW7) in a heritable autoimmune disease, type I diabetes (T1D). After streptozotocin-induced T1D model establishment in non-obese diabetic (NOD) mouse, the protein expression of FBW7, enhancer of zeste homolog 2 (EZH2), and Zinc finger and BTB domain containing 16 (ZBTB16) was quantified. Next, splenocytes and pancreatic beta cells were isolated to measure the production of pro-inflammatory cytokines in splenocytes, as well as islet beta-cell apoptosis. Additionally, the stability of EZH2 induced by FBW7 was analyzed by cycloheximide chase assay. The binding affinity of FBW7 and EZH2 and the consequence of ubiquitination were monitored by co-immunoprecipitation assay. Last, a chromatin immunoprecipitation assay was employed to analyze the accumulation of EZH2 and H3K27me3 at the ZBTB16 promoter region. Our study demonstrated downregulated FBW7 and ZBTB16 and upregulated EZH2 in diabetic NOD mice. Overexpression of FBW7 in the NOD mice inhibited pro-inflammatory cytokine release in the splenocytes and the apoptosis of islets beta cells. FBW7 destabilized EZH2 and accelerated ubiquitin-dependent degradation. EZH2 and H3K27me3 downregulated the ZBTB16 expression by accumulating in the ZBTB16 promoter and methylation. FBW7 upregulates the expression of ZBTB16 by targeting histone methyltransferase EZH2 thus reducing the occurrence of T1D.

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

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

Mutations in key driver genes of pancreatic cancer: molecularly targeted therapies and other clinical implications

Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal cancers, with a minimal difference between its incidence rate and mortality rate. Advances in oncology over the past several decades have dramatically improved the overall survival of patients with multiple cancers due to the implementation of new techniques in early diagnosis, therapeutic drugs, and personalized therapy. However, pancreatic cancers remain recalcitrant, with a 5-year relative survival rate of <9%. The lack of measures for early diagnosis, strong resistance to chemotherapy, ineffective adjuvant chemotherapy and the unavailability of molecularly targeted therapy are responsible for the high mortality rate of this notorious disease. Genetically, PDAC progresses as a complex result of the activation of oncogenes and inactivation of tumor suppressors. Although next-generation sequencing has identified numerous new genetic alterations, their clinical implications remain unknown. Classically, oncogenic mutations in genes such as KRAS and loss-of-function mutations in tumor suppressors, such as TP53, CDNK2A, DPC4/SMAD4, and BRCA2, are frequently observed in PDAC. Currently, research on these key driver genes is still the main focus. Therefore, studies assessing the functions of these genes and their potential clinical implications are of paramount importance. In this review, we summarize the biological function of key driver genes and pharmaceutical targets in PDAC. In addition, we conclude the results of molecularly targeted therapies in clinical trials and discuss how to utilize these genetic alterations in further clinical practice.

GnRHa protects the ovarian reserve by reducing endoplasmic reticulum stress during cyclophosphamide-based chemotherapy

Chemotherapy-induced ovarian dysfunction is a serious adverse effect in premenopausal patients with cancer. Gonadotrophin-releasing hormone analogs (GnRHa) protect ovarian function, but its molecular mechanisms have not yet been determined. In this study, we attempted to determine the previously unknown molecular mechanism by which such protection occurs. Serum anti-Müllerian hormone (AMH) levels were tested in tumor-bearing nude mice, a series of exploratory experiments were conducted. We discovered that GnRHa protects granulosa cells from chemotherapeutic toxicity in vivo and in vitro. We also showed that CTX-induced endoplasmic reticulum stress inhibits the secretion of AMH, and treatment with GnRHa relieves ER stress and the subsequent unfolded-protein response by modulating mTOR signaling to induce autophagy. The results of mechanistic studies indicated that GnRHa-modulated mTOR signaling to induce autophagy, which alleviated CTX-induced ER stress and promoted the secretion of AMH.

Implications of FBXW7 in Neurodevelopment and Neurodegeneration: Molecular Mechanisms and Therapeutic Potential

The ubiquitin-proteasome system (UPS) mediated protein degradation is crucial to maintain quantitive and functional homeostasis of diverse proteins. Balanced cellular protein homeostasis controlled by UPS is fundamental to normal neurological functions while impairment of UPS can also lead to some neurodevelopmental and neurodegenerative disorders. Functioning as the substrate recognition component of the SCF-type E3 ubiquitin ligase, FBXW7 is essential to multiple aspects of cellular processes via targeting a wide range of substrates for proteasome-mediated degradation. Accumulated evidence shows that FBXW7 is fundamental to neurological functions and especially implicated in neurodevelopment and the nosogenesis of neurodegeneration. In this review, we describe general features of FBXW7 gene and proteins, and mainly present recent findings that highlight the vital roles and molecular mechanisms of FBXW7 in neurodevelopment such as neurogenesis, myelination and cerebral vasculogenesis and in the pathogenesis of some typical neurodegenerative disorders such as Alzheimer’s disease, Parkinson’s disease and Huntington’s disease. Additionally, we also provide a prospect on focusing FBXW7 as a potential therapeutic target to rescue neurodevelopmental and neurodegenerative impairment.

MTAP deficiency-induced metabolic reprogramming creates a vulnerability to co-targeting de novo purine synthesis and glycolysis in pancreatic cancer

Methylthioadenosine phosphorylase (MTAP) is a key enzyme associated with the salvage of methionine and adenine that is deficient in 20%-30% of pancreatic cancer. Our previous study revealed that MTAP-deficiency indicates a poor prognosis for pancreatic ductal adenocarcinoma (PDAC) patients. In this study, bioinformatics analysis of The Cancer Genome Atlas (TCGA) data indicated that PDACs with MTAP deficiency display a signature of elevated glycolysis. Metabolomics studies showed that that MTAP deletion-mediated metabolic reprogramming enhanced glycolysis and de novo purine synthesis in pancreatic cancer cells. Western blot analysis revealed that MTAP knockout stabilized hypoxia-inducible factor 1α (HIF-1α) protein via posttranslational phosphorylation. RIO kinase 1 (RIOK1), a downstream kinase upregulated in MTAP-deficient cells, interacted with and phosphorylated HIF-1α to regulate its stability. In vitro experiments demonstrated that the glycolysis inhibitor 2-deoxy-D-glucose (2-DG) and the de novo purine synthesis inhibitor L-alanosine synergized to kill MTAP-deficient pancreatic cancer cells. Collectively, these results reveal that MTAP deficiency drives pancreatic cancer progression by inducing metabolic reprogramming, providing a novel target and therapeutic strategy for treating MTAP-deficient disease.

Impact of posttranslational modifications in pancreatic carcinogenesis and treatments

Pancreatic cancer (PC) is a highly aggressive cancer, with a 9% 5-year survival rate and a high risk of recurrence. In part, this is because PC is composed of heterogeneous subgroups with different biological and functional characteristics and personalized anticancer treatments are required. Posttranslational modifications (PTMs) play an important role in modifying protein functions/roles and are required for the maintenance of cell viability and biological processes; thus, their dysregulation can lead to disease. Different types of PTMs increase the functional diversity of the proteome, which subsequently influences most aspects of normal cell biology or pathogenesis. This review primarily focuses on ubiquitination, SUMOylation, and NEDDylation, as well as the current understanding of their roles and molecular mechanisms in pancreatic carcinogenesis. Additionally, we briefly summarize studies and clinical trials on PC treatments to advance our knowledge of drugs available to target the ubiquitination, SUMOylation, and NEDDylation PTM types. Further investigation of PTMs could be a critical field of study in relation to PC, as they have been implicated in the initiation and progression of many other types of cancer.

TIPE2 Suppresses Malignancy of Pancreatic Cancer Through Inhibiting TGFβ1 Mediated Signaling Pathway

Pancreatic cancer is one of the major reasons of cancer-associated deaths due to poor diagnosis, high metastasis and drug resistance. Therefore, it is important to understand the cellular and molecular mechanisms of pancreatic cancer to identify new targets for the treatment. TIPE2 is an essential regulator of tumor apoptosis, inflammation and immune homeostasis. However, the role of TIPE2 is still not fully understood in pancreatic cancer. In this study, we found the expression of TIPE2 was decreased in pancreatic cancer tissues compare to paracancerous tissues, which was negatively correlated with tumor size in patients. Overexpression of TIPE2 significantly decreased cell proliferation, metastasis and increased apoptotic events in pancreatic cancer cell lines. Moreover, the results obtained from real time PCR and western blot revealed that TIPE2 was also involved in inhibiting MMPs and N-Cadherin expression while increasing Bax expression in pancreatic cancer cells. Similarly, TIPE2 could inhibit tumor growth in vivo, decrease the expression of Ki-67 and N-Cadherin, and increase the expression of Bax by IHC analysis in tumor tissues isolated from tumor-bearing mice. Mechanistic studies exhibited that TIPE2 might suppress pancreatic cancer development through inhibiting PI3K/AKT and Raf/MEK/ERK signaling pathways triggered by TGFβ1. Moreover, the tumor-infiltrating lymphocytes from tumor-bearing mice were analyzed by flow cytometry, and showed that TIPE2 could promote T cell activation to exert an anti-tumor effect possibly through activation of DCs in a TGFβ1 dependent manner. In general, we described the multiple regulatory mechanisms of TIPE2 in pancreatic tumorigenesis and tumor microenvironment, which suggested TIPE2 may act as a potential therapeutic target in pancreatic cancer.

Phosphorylation regulates cullin-based ubiquitination in tumorigenesis

Cullin-RING ligases (CRLs) recognize and interact with substrates for ubiquitination and degradation, and can be targeted for disease treatment when the abnormal expression of substrates involves pathologic processes. Phosphorylation, either of substrates or receptors of CRLs, can alter their interaction. Phosphorylation-dependent ubiquitination and proteasome degradation influence various cellular processes and can contribute to the occurrence of various diseases, most often tumorigenesis. These processes have the potential to be used for tumor intervention through the regulation of the activities of related kinases, along with the regulation of the stability of specific oncoproteins and tumor suppressors. This review describes the mechanisms and biological functions of crosstalk between phosphorylation and ubiquitination, and most importantly its influence on tumorigenesis, to provide new directions and strategies for tumor therapy.

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.

Hexokinase 2 Promotes Cell Growth and Tumor Formation Through the Raf/MEK/ERK Signaling Pathway in Cervical Cancer

Hexokinase 2 (HK2) is a member of the hexokinases (HK) that has been reported to be a key regulator during glucose metabolism linked to malignant growth in many types of cancers. In this study, stimulation of HK2 expression was observed in squamous cervical cancer (SCC) tissues, and HK2 expression promoted the proliferation of cervical cancer cells in vitro and tumor formation in vivo by accelerating cell cycle progression, upregulating cyclin A1, and downregulating p27 expression. Moreover, transcriptome sequencing analysis revealed that MAPK3 (ERK1) was upregulated in HK2-overexpressing HeLa cells. Further experiments found that the protein levels of p-Raf, p-MEK1/2, ERK1/2, and p-ERK1/2 were increased in HK2 over-expressing SiHa and HeLa cells. When ERK1/2 and p-ERK1/2 expression was blocked by an inhibitor (FR180204), reduced cyclin A1 expression was observed in HK2 over-expressing cells, with induced p27 expression and inhibited cell growth. Therefore, our data demonstrated that HK2 promoted the proliferation of cervical cancer cells by upregulating cyclin A1 and down-regulating p27 expression through the Raf/MEK/ERK signaling pathway.

FBW7-NRA41-SCD1 axis synchronously regulates apoptosis and ferroptosis in pancreatic cancer cells

FBW7 functions as a tumor suppressor by targeting oncoproteins for degradation. Our previous study found FBW7 was low expressed in pancreatic cancer due to sustained activation of Ras-Raf-MEK-ERK pathway, which destabilized FBW7 by phosphorylating at Thr205. MicroPET/CT imaging results revealed that FBW7 substantially decreased 18F-fluorodeoxyglucose uptake in xenograft tumors. Mechanistically, FBW7 inhibited glucose metabolism via c-Myc/TXNIP axis. But in these studies, we observed FBW7 down-regulated genes were widely involved in redox reaction and lipid metabolism. Here we reanalyzed previous gene expression profiling and conducted targeted cell metabolites analysis. Results revealed that FBW7 regulated lipid peroxidation and promoted ferroptosis, a non-apoptotic form of cell death. Mechanistically, we found FBW7 inhibited the expression of stearoyl-CoA desaturase (SCD1) via inhibiting nuclear receptor subfamily 4 group A member 1 (NR4A1). SCD1 was reported to inhibit both ferroptosis and apoptosis, which was consistent with the function of FBW7 and NR4A1, another FBW7 down-regulated gene in the gene expression profiling. Moreover, FBW7 potentiated cytotoxic effect of gemcitabine via activating ferroptosis and apoptosis. Combination ferroptosis inducers and apoptosis activators could also significantly potentiated cytotoxic effect of gemcitabine in pancreatic cancer. Therefore, our findings might provide new strategies for the comprehensive treatment of pancreatic cancer.

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Ferroptosis possesses great potential in pancreatic cancer therapy.

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FBW7 synchronously induces apoptosis and ferroptosis.

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Activation of apoptosis and ferroptosis potentiates cytotoxic effect of gemcitabine.

SETD8 potentiates constitutive ERK1/2 activation via epigenetically silencing DUSP10 expression in pancreatic cancer

Constitutive ERK1/2 activation has been frequently observed in pancreatic adenocarcinoma (PDAC). How ERK1/2 activation status been potentiated and maintained by epigenetic mechanisms has seldom been discussed in PDAC. In this study, we first examined the expression status of p-ERK1/2 in PDAC tissues by immunohistochemical staining and then screened possible epigenetic factors that displayed different expression status between p-ERK1/2 high and low groups by RNA profiling, and found that SETD8 displayed an increased expressional pattern in p-ERK1/2^high patient group. Then the impact of SETD8 on the proliferation of PDAC cells were investigated on the basis of gain or loss-of-function assays. RNA sequencing assays were performed to screen potential SETD8 downstream targets that contribute to ERK1/2 activation. Mass spectrometry and transcriptional analysis, including dual-luciferase assay and chromatin immunoprecipitation assay (ChIP), were used to explore the molecular mechanisms that governing SETD8-mediated ERK1/2 activation. In vitro cell line studies and in vivo xenograft mouse model studies indicated that SETD8 promoted cell proliferation and increased tumor formation capacity of PDAC cell lines. Mechanism explorations uncovered that SETD8 suppressed the expression of DUSP10, which was responsible for dephosphorylation of ERK1/2. Mass spectrometry and transcriptional analysis results demonstrated that STAT3 interacted with SETD8 and recruited SETD8 to the promoter region of DUSP10, leading to epigenetic silencing of DUSP10 and the resultant activation of ERK1/2. In conclusion, SETD8 interacts with STAT3 on DUSP10 promoter region and epigenetically silences DUSP10 expression. Decreased DUSP10 expression in PDAC potentiates activation of ERK1/2 phosphorylation, resulting in unfavorable prognosis of PDAC.

Tumor-associated macrophages promote human hepatoma Huh-7 cell migration and invasion through the Gli2/IGF-II/ERK1/2 axis by secreting TGF-β1

AIM

In this study, we explored the ability of TAMs to affect the malignant phenotype of human hepatoma Huh-7 cells through the Gli2/IGF-II/ERK1/2 pathway.

METHODS

The TAMs were characterized by flow cytometry and ELISA assays. Huh-7 cells were treated with conditioned medium of TAMs (TAMs-CM), and the proliferation, migration and invasion abilities were measured by CCK-8, Transwell and scratch assays. The levels of TGF-β1, Gli2, IGF-II and related proteins in the ERK1/2 pathway and the epithelial-mesenchymal transition (EMT) process were examined by RT-qPCR and western blot. Huh-7 cells were injected subcutaneously into nude mice with TAMs to explore the role of TAMs in tumor growth.

RESULTS

The expression levels of TGF-β1, Gli2 and IGF-II and the cell proliferation, migration and invasion abilities were elevated in Huh-7 cells treated with TAMs-CM. TGF-β1 was upregulated in the conditioned medium and was found to be involved in the promotion of migration, invasion and the EMT of Huh-7 cells. The activation of TGF-β1 signaling increased the expression of Gli2. Knockdown of Gli2 decreased the expression of IGF-II and also reversed the promotional effect of the conditioned medium on migration, invasion and the EMT of Huh-7 cells. TGF-β1/Gli2/IGF-II signaling was shown to promote the malignant phenotype of Huh-7 cells by activating the ERK1/2 signaling pathway. Further, TGF-β1 knockdown attenuated the influence of TAMs on tumor growth in mouse model.

CONCLUSION

The TGF-β1 secreted by TAMs promotes the migration, invasion and EMT of human hepatoma Huh-7 cells through the Gli2/IGF-II/ERK1/2 pathway.

Oncogenic function of TRIM2 in pancreatic cancer by activating ROS-related NRF2/ITGB7/FAK axis

Evidence suggests that tripartite motif-containing 2 (TRIM2) is associated with carcinogenic effects in several malignancies. However, the expression patterns and roles of TRIM2 in pancreatic cancer are rarely studied. Our study demonstrated that TRIM2 was expressed in a high percentage of pancreatic tumors. High TRIM2 expression was negatively correlated with the outcome of pancreatic cancer. TRIM2 silencing significantly inhibited the proliferation, migration, invasion, and in vivo tumorigenicity of pancreatic cancer cells. Regarding the mechanism involved, TRIM2 activated ROS-related E2-related factor 2 (NRF2)/antioxidant response element (ARE) signaling and the integrin/focal adhesion kinase (FAK) pathway. Treatment of pancreatic cancer cells with the antioxidant N-acetyl-L-cysteine decreased ROS activity and expression level of NRF2 and ITGB7. Increased translocation of NRF2 protein into nucleus further rescued the inhibited ITGB7 transcription. Moreover, NRF2 bound to the potential ARE on the promoter region and enhanced the transcriptional activity of ITGB7, indicating the bridging effect of NRF2 between the two signaling pathways. In summary, our study provides evidence that upregulated TRIM2 in pancreatic cancer predicts short survival for pancreatic cancer patients. TRIM2 accelerates pancreatic cancer progression via the ROS-related NRF2/ITGB7/FAK axis.

Regulation of metabolic reprogramming by tumor suppressor genes in pancreatic cancer

Background

Pancreatic cancer continues to be one of the most aggressive malignant tumors. Work in recent years in cancer molecular biology has revealed that metabolic reprogramming is an additional hallmark of cancer that is involved in the pathogenesis of cancers, and is intricately linked to gene mutations.

Main text

However, though oncogenes such as KRAS and c-Myc play important roles in the process, and have been extensively studied, no substantial improvements in the prognosis of pancreatic cancer have seen. Therefore, some scientists have tried to explain the mechanisms of abnormal cancer metabolism from the perspective of tumor suppressor genes. In this paper, we reviewed researches about how metabolic reprogramming was regulated by tumor suppressor genes in pancreatic cancer and their clinical implications.

Conclusion

Abnormal metabolism and genetic mutations are mutually causal and complementary in tumor initiation and development. A clear understanding of how metabolic reprogramming is regulated by the mutated genes would provide important insights into the pathogenesis and ultimately treatment of pancreatic cancer.

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.

CSN6 inhibition suppresses pancreatic adenocarcinoma metastasis via destabilizing the c-Fos protein

Deubiquitinase (DUB) can reverse the ubiquitin signal, and participate in virtually all aspects of cancer progression. Thus, DUB represents an attractive target for development of anticancer drugs. However, little is known about DUB which can be used as drug targets. Here, we found that the constitutive photomorphogenic 9 (COP9) signalosome complex subunit 6 (COPS6/CSN6), a DUB belongs to JAMM/MPN domain-associated metallopeptidases(JAMMs) class, was highly expressed in pancreatic adenocarcinoma(PAAD) tissues. High expression of CSN6 was associated with tumor TNM stage and metastasis in PAAD patients. Moreover, we demonstrated that CSN6 promoted invasion and metastasis through regulating forkhead box protein A1 (FOXA1) in PAAD cells. Re-expression of FOXA1 rescued the decreased invasion and metastasis caused by CSN6 knockdown, whereas inhibition of FOXA1 alleviated the pro-metastasis effect induced by CSN6 overexpression. Further, CSN6 regulated the expression of FOXA1 via c-Fos in PAAD cells. Mechanistically, CSN6 stabilized c-Fos protein by binding to it and decreasing its ubiquitination. Our work identified CSN6 as a targeting-permissible deubiquitinase, and CSN6 inhibition maybe a potential treatment strategy for PAAD.

Aberrant methylation of WD-repeat protein 41 contributes to tumour progression in triple-negative breast cancer

WD-repeat proteins are implicated in a variety of biological functions, most recently in oncogenesis. However, the underlying function of WD-repeat protein 41 (WDR41) in tumorigenesis remains elusive. The present study was aimed to explore the role of WDR41 in breast cancer. Combined with Western blotting and immunohistochemistry, the results showed that WDR41 was expressed at low levels in breast cancer, especially in triple-negative breast cancer (TNBC). Using methylation-specific PCR (MSP), we observed that WDR41 presented hypermethylation in MDA-MB-231 cells. Methylation inhibitor 5-aza-2'-deoxycytidine (5-aza-dC) management increased the expression of WDR41 in MDA-MB-231 cells, but not in MCF-10A (normal mammary epithelial cells) or oestrogen receptor-positive MCF-7 breast cancer cells. WDR41-down-regulation promoted, while WDR41-up-regulation inhibited the tumour characteristics of TNBC cells including cell viability, cell cycle and migration. Further, WDR41-up-regulation dramatically suppressed tumour growth in vivo. Mechanistically, WDR41 protein ablation activated, while WDR41-up-regulation repressed the AKT/GSK-3β pathway and the subsequent nuclear activation of β-catenin in MDA-MB-231 cells, and 5-aza-dC treatment enhanced this effect. After treatment with the AKT inhibitor MK-2206, WDR41-down-regulation-mediated activation of the GSK-3β/β-catenin signalling was robustly abolished. Collectively, methylated WDR41 in MDA-MB-231 cells promotes tumorigenesis through positively regulating the AKT/GSK-3β/β-catenin pathway, thus providing an important foundation for treating TNBC.

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.

ACSL4 promotes hepatocellular carcinoma progression via c-Myc stability mediated by ERK/FBW7/c-Myc axis

Hepatocellular carcinoma (HCC) is a highly heterogeneous, multigene-driven malignant tumor. Long chain acyl-CoA synthetase 4 (ACSL4), an enzyme has pivotal roles in arachidonic acid (AA) metabolism. However, its function and the underlying molecular mechanisms in HCC are still not fully elucidated. Here, we identified ACSL4 as a novel marker for AFP high subtype HCC through transcriptome profiling. ACSL4 was frequently upregulated in HCC samples and associated with poor prognosis. Functionally, ACSL4 knockdown resulted in decreased cell growth, whereas ectopic ACSL4 expression facilitated tumor formation in vitro and in vivo. Mechanistically, ACSL4 stabilized the oncoprotein c-Myc through ubiquitin–proteasome system in an ERK/FBW7-dependent manner. Cell growth ability mediated by ACSL4 elevation was partly attenuated by c-Myc depletion using siRNA or its inhibitor 10058-F4. In contrast, the effects of ACSL4 silencing were partially reversed by c-Myc overexpression via FBW7 knockdown. Clinically, ACSL4 expression was positively correlated with c-Myc in HCC. In conclusion, ACSL4 is a novel marker for AFP high subtype HCC. Our data uncovered a new mechanism by which ACSL4 promotes HCC progression via c-Myc stability mediated by ERK/FBW7/c-Myc axis and could be a valuable prognostic biomarker and a potential therapeutic target in HCC.

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

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

Targeting p63 Upregulation Abrogates Resistance to MAPK Inhibitors in Melanoma

Targeting the MAPK pathway by combined inhibition of BRAF and MEK has increased overall survival in advanced BRAF-mutant melanoma in both therapeutic and adjuvant clinical settings. However, a significant proportion of tumors develop acquired resistance, leading to treatment failure. We have previously shown p63 to be an important inhibitor of p53-induced apoptosis in melanoma following genotoxic drug exposure. Here, we investigated the role of p63 in acquired resistance to MAPK inhibition and show that p63 isoforms are upregulated in melanoma cell lines chronically exposed to BRAF and MEK inhibition, with consequent increased resistance to apoptosis. This p63 upregulation was the result of its reduced degradation by the E3 ubiquitin ligase FBXW7. FBXW7 was itself regulated by MDM2, and in therapy-resistant melanoma cell lines, nuclear accumulation of MDM2 caused downregulation of FBXW7 and consequent upregulation of p63. Consistent with this, both FBXW7-inactivating mutations and MDM2 upregulation were found in melanoma clinical samples. Treatment of MAPK inhibitor-resistant melanoma cells with MDM2 inhibitor Nutlin-3A restored FBXW7 expression and p63 degradation in a dose-dependent manner and sensitized these cells to apoptosis. Collectively, these data provide a compelling rationale for future investigation of Nutlin-3A as an approach to abrogate acquired resistance of melanoma to MAPK inhibitor targeted therapy. SIGNIFICANCE: Upregulation of p63, an unreported mechanism of MAPK inhibitor resistance in melanoma, can be abrogated by treatment with the MDM2 inhibitor Nutlin-3A, which may serve as a strategy to overcome resistance.