CUL4B activates Wnt/β-catenin signalling in hepatocellular carcinoma by repressing Wnt antagonists

Unraveling the relationship between histone methylation and nonalcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) poses a significant health challenge in modern societies due to shifts in lifestyle and dietary habits. Its complexity stems from genetic predisposition, environmental influences, and metabolic factors. Epigenetic processes govern various cellular functions such as transcription, chromatin structure, and cell division. In NAFLD, these epigenetic tendencies, especially the process of histone methylation, are intricately intertwined with fat accumulation in the liver. Histone methylation is regulated by different enzymes like methyltransferases and demethylases and influences the expression of genes related to adipogenesis. While early-stage NAFLD is reversible, its progression to severe stages becomes almost irreversible. Therefore, early detection and intervention in NAFLD are crucial, and understanding the precise role of histone methylation in the early stages of NAFLD could be vital in halting or potentially reversing the progression of this disease.

CUL4B mutations impair human cortical neurogenesis through PP2A-dependent inhibition of AKT and ERK

Mutation in CUL4B gene is one of the most common causes for X-linked intellectual disability (XLID). CUL4B is the scaffold protein in CUL4B-RING ubiquitin ligase (CRL4B) complex. While the roles of CUL4B in cancer progression and some developmental processes like adipogenesis, osteogenesis, and spermatogenesis have been studied, the mechanisms underlying the neurological disorders in patients with CUL4B mutations are poorly understood. Here, using 2D neuronal culture and cerebral organoids generated from the patient-derived induced pluripotent stem cells and their isogenic controls, we demonstrate that CUL4B is required to prevent premature cell cycle exit and precocious neuronal differentiation of neural progenitor cells. Moreover, loss-of-function mutations of CUL4B lead to increased synapse formation and enhanced neuronal excitability. Mechanistically, CRL4B complex represses transcription of PPP2R2B and PPP2R2C genes, which encode two isoforms of the regulatory subunit of protein phosphatase 2 A (PP2A) complex, through catalyzing monoubiquitination of H2AK119 in their promoter regions. CUL4B mutations result in upregulated PP2A activity, which causes inhibition of AKT and ERK, leading to premature cell cycle exit. Activation of AKT and ERK or inhibition of PP2A activity in CUL4B mutant organoids rescues the neurogenesis defect. Our work unveils an essential role of CUL4B in human cortical development.

CUL4B enhances the malignant phenotype of esophageal squamous cell carcinoma by suppressing TGFBR3 expression

Cullin 4B (CUL4B), which acts as a scaffold protein in CUL4B-RING ubiquitin ligase complexes (CRL4B), is frequently overexpressed in cancer and represses tumor suppressors through epigenetic mechanisms. However, the expression and function of CUL4B in esophageal squamous cell carcinoma (ESCC) have not been well illustrated. In this study, we show that upregulation of CUL4B in ESCC cells enhances proliferation, invasion and cisplatin (CDDP)-resistance, while knockdown of CUL4B significantly represses the malignant activities. Mechanistically, we demonstrate that CUL4B promotes proliferation and migration of ESCC cells through inhibiting expression of transforming growth factor beta receptor III (TGFBR3). CRL4B complex binds to the promoter of TGFBR3, and represses its transcription by catalyzing monoubiquitination at H2AK119 and coordinating with PRC2 and HDAC complexes. Taken together, our findings establish a critical role for the CUL4B/TGFBR3 axis in the regulation of ESCC malignancy.

CUL4B functions as a tumor suppressor in KRAS-driven lung tumors by inhibiting the recruitment of myeloid-derived suppressor cells

Lung cancer is the leading cause of cancer-related death worldwide. KRAS mutations are the most common oncogenic alterations found in lung cancer. Unfortunately, treating KRAS-mutant lung adenocarcinoma (ADC) remains a major oncotherapeutic challenge. Here, we used both autochthonous and transplantable KRAS-mutant tumor models to investigate the role of tumor-derived CUL4B in KRAS-driven lung cancers. We showed that knockout or knockdown of CUL4B promotes lung ADC growth and progression in both models. Mechanistically, CUL4B directly binds to the promoter of Cxcl2 and epigenetically represses its transcription. CUL4B deletion increases the expression of CXCL2, which binds to CXCR2 on myeloid-derived suppressor cells (MDSCs) and promotes their migration to the tumor microenvironment. Targeting of MDSCs significantly delayed the growth of CUL4B knockdown KRAS-mutant tumors. Collectively, our study provides mechanistic insights into the novel tumor suppressor-like functions of CUL4B in regulating KRAS-driven lung tumor development.

A comprehensive insight into the correlation between ncRNAs and the Wnt/β-catenin signalling pathway in gastric cancer pathogenesis

During the past decades, gastric cancer (GC) has emerged as one of the most frequent malignancies with a growing rate of prevalence around the world. Despite considerable advances in therapeutic methods, the prognosis and management of patients with gastric cancer (GC) continue to be poor. As one of the candidate molecular targets in the treatment of many types of cancer, the Wnt/β-catenin pathway includes a family of proteins that have important functions in adult tissue homeostasis and embryonic development. The aberrant regulation of Wnt/β-catenin signaling is strongly correlated with the initiation and development of numerous cancers, including GC. Therefore, Wnt/β-catenin signaling has been identified as one of the main targets for extending therapeutic approaches for GC patients. Non-coding RNAs (ncRNAs), including microRNAs and long ncRNAs, are important components of epigenetic mechanisms in gene regulation. They play vital roles in various molecular and cellular processes and regulate many signaling pathways, such as Wnt/β-catenin pathways. Insights into these regulatory molecules involved in GC development may lead to the identification of potential targets for overcoming the limitations of current therapeutic approaches. Consequently, this review aimed to provide a comprehensive overview of ncRNAs interactions involved in Wnt/β-catenin pathway function in GC with diagnostic and therapeutic perspectives. Video Abstract.

CRL4B complex-mediated H2AK119 monoubiquitination restrains Th1 and Th2 cell differentiation

CD4+ T helper (Th) cell differentiation is regulated by lineage-specific expression of transcription factors, which is tightly associated with epigenetic modifications, including histone acetylation and methylation. However, the factors regulating histone modifications involved in Th cell differentiation remain largely unknown. We herein demonstrated a critical role of Cullin 4B (CUL4B) in restricting Th1 and Th2 cell differentiation. CUL4B, which is assembled into the CUL4B-RING E3 ligase (CRL4B) complex, participates in various physiological and developmental processes through epigenetic repression of transcription. Depletion of Cul4b in CD4+ T cells enhanced Th1 and Th2 cell differentiation. In vivo, an aggravated Th2 response caused by the absence of CUL4B was observed in a murine asthma model. Mechanistically, the CRL4B complex promoted monoubiquitination at H2AK119 (H2AK119ub1) and polycomb repressive complex 2 (PRC2)-mediated trimethylation at H3K27 (H3K27me3) at Tbx21 and Maf and consequently repressed their expression during Th cell differentiation. Our study suggests that CRL4B complex-mediated H2AK119ub1 deposition functions to prevent the aberrant expression of Th1 and Th2 lineage-specific genes.

SMEK1 promotes lung adenocarcinoma proliferation and invasion by activating Wnt/β-catenin signaling pathway

PURPOSE

SMEK1, also known as PP4R3α, the regulatory subunit 3α of serine and threonine phosphatase PP4, participates in diversely critical biological processes such as the integration of centromere, deacetylation of histones, asymmetric divisions of neuroblast, and other crucial cellular activities. SMEK1 was formerly reported to play a part in carcinogenesis. This study aims to reveal the role of SMEK1 in lung adenocarcinoma and the underlying molecular mechanism.

METHODS

Using immunohistochemical (IHC) staining, the protein level of SMEK1 in lung adenocarcinoma and adjacent non-tumor tissue was detected. The functional role of SMEK1 in cell proliferation and invasion was explored using cell counting kit-8 and Transwell assay, respectively. Xenograft tumor experiment was used to investigate the effect of SMEK1 on tumor growth in vivo. The alteration of Wnt/β-catenin signaling pathway was detected by Western blotting, quantitative PCR, and dual-luciferase reporter assays.

RESULTS

SMEK1 was highly expressed at the protein level in lung adenocarcinoma compared to the adjacent non-tumor tissue. In vitro, suppression of SMEK1 significantly decreased the proliferation, migration, and invasion of lung adenocarcinoma cell lines, while overexpression of SMEK1 enhanced above abilities. The xenograft model demonstrated that down-regulation of SMEK1 significantly inhibited tumor growth in vivo. In addition, we found that SMEK1 could positively regulate Wnt/β-catenin signaling in lung adenocarcinoma cell lines.

CONCLUSIONS

SMEK1 exerts a cancer-promoting effect in lung adenocarcinoma by activating Wnt/β-catenin signaling.

Aberrant ROS Served as an Acquired Vulnerability of Cisplatin-Resistant Lung Cancer

Lung cancer has become a global health issue in recent decades. Approximately 80-85% of cases are non-small-cell lung cancer (NSCLC). Despite the high rate of resistance, cisplatin-base chemotherapy is still the main treatment for NSCLC patients. Thus, overcoming cisplatin resistance is urgently needed in NSCLC therapy. In this study, we identify NADPH metabolism and reactive oxygen species (ROS) levels as the main causes accounting for cisplatin resistance. Based on a small panel consisting of common chemotherapy drugs or compounds, APR-246 is proved to be an effective compound targeting cisplatin-resistant NSCLC cells. APR-246 specially inhibits proliferation and colony formation of cisplatin-resistant cells. In details, APR-246 can significantly cause G0/G1 accumulation and S phase arrest of cisplatin resistant cells and gives rise to severe mitochondria dysfunction as well as elevated apoptosis. Further study proves that it is the aberrant ROS levels as well as NRF2/SLC7A11/GSH axis dysfunction accounting for the specific antitumor effects of APR-246. Scavenging ROS with N-acetylcysteine (NAC) disrupts the inhibitory effect of APR-246 on cisplatin-resistant cells. Mechanistically, NRF2 is specifically degraded by the proteasome following its own ubiquitylation in APR-246-treated cisplatin-resistant cells, which in turn decreases NRF2/SLC7A11/GSH axis activity. Our study provides new insights into the biology driving cisplatin resistance of lung cancer and highlights APR-246 as a potential therapeutic reagent for overcoming cisplatin resistance.

Role of IQ Motif-Containing GTPase-Activating Proteins in Hepatocellular Carcinoma

IQ motif-containing GTPase-activating proteins (IQGAPs) are a class of scaffolding proteins, including IQGAP1, IQGAP2, and IQGAP3, which govern multiple cellular activities by facilitating cytoskeletal remodeling and cellular signal transduction. The role of IQGAPs in cancer initiation and progression has received increasing attention in recent years, especially in hepatocellular carcinoma (HCC), where the aberrant expression of IQGAPs is closely related to patient prognosis. IQGAP1 and 3 are upregulated and are considered oncogenes in HCC, while IQGAP2 is downregulated and functions as a tumor suppressor. This review details the three IQGAP isoforms and their respective structures. The expression and role of each protein in different liver diseases and mainly in HCC, as well as the underlying mechanisms, are also presented. This review also provides a reference for further studies on IQGAPs in HCC.

CUL4B Upregulates RUNX2 to Promote the Osteogenic Differentiation of Human Periodontal Ligament Stem Cells by Epigenetically Repressing the Expression of miR-320c and miR-372/373-3p

Mesenchymal stem cells (MSCs) within the periodontal ligament (PDL), termed periodontal ligament stem cells (PDLSCs), have a self-renewing capability and a multidirectional differentiation potential. The molecular mechanisms that regulate multidirectional differentiation, such as the osteogenic differentiation of PDLSCs, remain to be elucidated. Cullin 4B (CUL4B), which assembles the CUL4B-RING ubiquitin ligase (CRL4B) complex, is involved in regulating a variety of developmental and physiological processes including the skeletal development and stemness of cancer stem cells. However, nothing is known about the possible role of CUL4B in the osteogenic differentiation of PDLSCs. Here, we found that knockdown of CUL4B decreased the proliferation, migration, stemness and osteogenic differentiation ability of PDLSCs. Mechanistically, we demonstrate that CUL4B cooperates with the PRC2 complex to repress the expression of miR-320c and miR-372/373-3p, which results in the upregulation of RUNX2, a master transcription factor (TF) that regulates osteogenic differentiation. In brief, the present study reveals the role of CUL4B as a new regulator of osteogenic differentiation in PDLSCs.

Targeting Cullin-RING E3 Ubiquitin Ligase 4 by Small Molecule Modulators

Cullin-RING E3 ubiquitin ligase 4 (CRL4) plays an essential role in cell cycle progression. Recent efforts using high throughput screening and follow up hit-to-lead studies have led to identification of small molecules 33-11 and KH-4-43 that inhibit E3 CRL4's core ligase complex and exhibit anticancer potential. This review provides: 1) an updated perspective of E3 CRL4, including structural organization, major substrate targets and role in cancer; 2) a discussion of the challenges and strategies for finding the CRL inhibitor; and 3) a summary of the properties of the identified CRL4 inhibitors as well as a perspective on their potential utility to probe CRL4 biology and act as therapeutic agents.

Cullin-4B promotes cell proliferation and invasion through inactivation of p53 signaling pathway in colorectal cancer

Cullin 4B (CUL4B) is a member of the Cullin RING E3 ligase family, which is found to be overexpressed in multiple cancers, thus facilitating tumorigenesis and progression. However, the correlation between CUL4B and p53 in colorectal cancer cells (CRC) remains to be further elucidated. In this study, we newly identified that CUL4B functions as a negative regulator of p53, thereby facilitating CRC tumorigenesis and progression. Our data has demonstrated that CUL4B was frequently overexpressed in CRC tissues, and its upregulation was closely correlated with disease progression and poor prognosis. Moreover, CUL4B knockdown suppressed cell proliferation, invasion and epithelial-mesenchymal transition (EMT) of CRC cells. Mechanistically, CUL4B depletion increased the expression of p53 protein and its downstream targets p21, PUMA and MDM2. Furthermore, CUL4B depletion prolonged the half-life of p53 protein, and CUL4B is a binding partner of MDM2. In conclusion, our study shed new lights on the complex regulatory network between CUL4B and p53, and clarifies this CUL4B-p53 axis contributes greatly to CRC tumorigenesis and progression.

CUL4B Promotes Breast Carcinogenesis by Coordinating with Transcriptional Repressor Complexes in Response to Hypoxia Signaling Pathway

Cullin4B (CUL4B) is a scaffold protein of the CUL4B-Ring E3 ligase (CRL4B) complex. However, the role of CUL4B in the development of breast cancer remains poorly understood. Here it is shown that CRL4B interacts with multiple histone deacetylase (HDAC)-containing corepressor complexes, including MTA1/NuRD, SIN3A, CoREST, and NcoR/SMRT complexes. It is demonstrated that CRL4B/NuRD(MTA1) complexes cooccupy the E-cadherin and AXIN2 promoters, and could be recruited by transcription factors including Snail and ZEB2 to promote cell invasion and tumorigenesis both in vitro and in vivo. Remarkably, CUL4B responded to transformation and migration/invasion stimuli and is essential for multiple epithelial-mesenchymal transition (EMT) signaling pathways such as hypoxia. Furthermore, the transcription of CUL4B is directedly activated by hypoxia-inducible factor 1α (HIF1α) and repressed by the ERα-GATA3 axis. Overexpressing of CUL4B successfully induced CSC-like properties. Strikingly, CUL4B expression is markedly upregulated during breast cancer progression and correlated with poor prognosis. The results suggest that CUL4B lies at a critical crossroads between EMT and stem cell properties, supporting CUL4B as a potential novel target for the development of anti-breast cancer therapy.

CUL4B renders breast cancer cells tamoxifen-resistant via miR-32-5p/ER-α36 axis

Tamoxifen (TAM) resistance is a significant clinical challenge in endocrine therapies for estrogen receptor (ER)-positive breast cancer patients. Cullin 4B (CUL4B), which acts as a scaffold protein in CUL4B-RING ubiquitin ligase complexes (CRL4B), is frequently overexpressed in cancer and represses tumor suppressors through diverse epigenetic mechanisms. However, the role and the underlying mechanisms of CUL4B in regulating drug resistance remain unknown. Here, we showed that CUL4B promotes TAM resistance in breast cancer cells through a miR-32-5p/ER-α36 axis. We found that upregulation of CUL4B correlated with decreased TAM sensitivity of breast cancer cells, and knockdown of CUL4B or expression of a dominant-negative CUL4B mutant restored the response to TAM in TAM-resistant MCF7-TAM^R and T47D-TAM^R cells. Mechanistically, we demonstrated that CUL4B renders breast cancer cells TAM-resistant by upregulating ER-α36 expression, which was mediated by downregulation of miR-32-5p. We further showed that CRL4B epigenetically represses the transcription of miR-32-5p by catalyzing monoubiquitination at H2AK119 and coordinating with PRC2 and HDAC complexes to promote trimethylation at H3K27 at the promoter of miR-32-5p. Pharmacologic or genetic inhibition of CRL4B/PRC2/HDAC complexes significantly increased TAM sensitivity in breast cancer cells in vitro and in vivo. Taken together, our findings thus establish a critical role for the CUL4B-miR-32-5p-ER-α36 axis in the regulation of TAM resistance and have important therapeutic implications for combined application of TAM and the inhibitors of CRL4B/PRC2/HDAC complex in breast cancer treatment. © 2021 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

CUL4B Promotes Temozolomide Resistance in Gliomas by Epigenetically Repressing CDNK1A Transcription

Resistance to temozolomide (TMZ), the first-line chemotherapeutic drug for glioblastoma (GBM) and anaplastic gliomas, is one of the most significant obstacles in clinical treatment. TMZ resistance is regulated by complex genetic and epigenetic networks. Understanding the mechanisms of TMZ resistance can help to identify novel drug targets and more effective therapies. CUL4B has been shown to be upregulated and promotes progression and chemoresistance in several cancer types. However, its regulatory effect and mechanisms on TMZ resistance have not been elucidated. The aim of this study was to decipher the role and mechanism of CUL4B in TMZ resistance. Western blot and public datasets analysis showed that CUL4B was upregulated in glioma specimens. CUL4B elevation positively correlated with advanced pathological stage, tumor recurrence, malignant molecular subtype and poor survival in glioma patients receiving TMZ treatment. CUL4B expression was correlated with TMZ resistance in GBM cell lines. Knocking down CUL4B restored TMZ sensitivity, while upregulation of CUL4B promoted TMZ resistance in GBM cells. By employing senescence β-galactosidase staining, quantitative reverse transcription PCR and Chromatin immunoprecipitation experiments, we found that CUL4B coordinated histone deacetylase (HDAC) to co-occupy the CDKN1A promoter and epigenetically silenced CDKN1A transcription, leading to attenuation of TMZ-induced senescence and rendering the GBM cells TMZ resistance. Collectively, our findings identify a novel mechanism by which GBM cells develop resistance to TMZ and suggest that CUL4B inhibition may be beneficial for overcoming resistance.

HDAC8-dependent deacetylation of PKM2 directs nuclear localization and glycolysis to promote proliferation in hepatocellular carcinoma

Pyruvate kinase M2 (PKM2) is not only a key rate-limiting enzyme that guides glycolysis, but also acts as a non-metabolic protein in regulating gene transcription. In recent years, a series of studies have confirmed that post-translational modification has become an important mechanism for regulating the function of PKM2, which in turn affects tumorigenesis. In this study, we found that K62 residues were deacetylated, which is related to the prognosis of HCC. Further studies indicate that HDAC8 binds and deacetylates the K62 residue of PKM2. Mechanistically, K62 deacetylation facilitate PKM2 transport into the nucleus and bind β-catenin, thereby promoting CCND1 gene transcription and cell cycle progression. In addition, the deacetylation of K62 affects the enzyme activity of PKM2 and the flux of glucose metabolism. Therefore, these results suggest that HDAC8 / PKM2 signaling may become a new target for the treatment of HCC.

EPB41 suppresses the Wnt/β-catenin signaling in non-small cell lung cancer by sponging ALDOC

Despite advancements in therapeutic options, the overall prognosis for non-small-cell lung cancer (NSCLC) remains poor. Further exploration of the etiology and targets for novel treatments is crucial for managing NSCLC. In this study, we revealed the significant potential of EPB41 for inhibiting NSCLC proliferation, invasion and metastasis in vitro and in vivo. Consistent with its tumor suppressor role in NSCLC, the expression of EPB41 in NSCLC specimens evidently decreased compared to that in normal tissues, and low EPB41 expression was associated with poor prognoses for NSCLC patients. We further demonstrated the importance of EPB41 protein as a novel inhibitor of the Wnt signaling, which regulates β-Catenin stability, and elucidated the crucial role of the EPB41/ALDOC/GSK3β/β-Catenin axis in NSCLC. Suppression of EPB41 expression in cancer cells elevated the levels of free ALDOC protein released from the EPB41-ALDOC complex, leading to disassembly of the β-catenin destruction complex, reduced proteolytic degradation of β-catenin, elevated cytoplasmic accumulation and nuclear translocation of β-catenin, thereby activating the expression of multiple oncogenes and, thus, NSCLC pathogenesis. Our study highlights the potential of EPB41 as a future therapeutic target for lung cancer.

CUL4B promotes aggressive phenotypes of renal cell carcinoma via upregulating c-Met expression

Cullin 4B (CUL4B), encoding a scaffold protein in Cullin RING ubiquitin-ligase complexes (CRL4B), is overexpressed and serves as an oncogene in various solid tumors. However, the roles and the underlying mechanisms of CUL4B in renal cell carcinoma (RCC) are still unknown. In this study, we demonstrated that CUL4B was significantly upregulated in RCC cells and clinical specimens, and its overexpression was correlated with poor survival of RCC patients. Knockdown of CUL4B resulted in the inhibition of proliferation, migration and invasion of RCC cells. Furthermore, we found that the expression of CUL4B is positively correlated with c-Met expression in RCC cells and tissues. Konckdown of c-Met or treatment with c-Met inhibitor, SU11274, could block the increase in cell proliferation, migration and invasion induced by CUL4B-overexpression. We also showed that CUL4B overexpression significantly accelerated xenograft tumor growth, and administration of SU11274 could also abrogate the accelerated tumor growth induced by CUL4B overexpression in vivo. These findings shed light on the contribution of CUL4B to tumorigenesis in RCC via activating c-Met signaling and its therapeutic implications in RCC patients.

LncRNA SLC26A4-AS1 suppresses the MRN complex-mediated DNA repair signaling and thyroid cancer metastasis by destabilizing DDX5

Lymph node metastasis is the major adverse feature for recurrence and death of thyroid cancer patients. To identify lncRNAs involved in thyroid cancer metastasis, we systemically screened differentially expressed lncRNAs in lymph node metastasis, thyroid cancer, and normal tissues via RNAseq. We found that lncRNA SLC26A4-AS1 was continuously, significantly down-regulated in normal tissues, thyroid cancer, and lymph node metastasis specimens. Low SLC26A4-AS1 levels in tissues were significantly associated with poor prognosis of thyroid cancer patients. LncRNA SLC26A4-AS1 markedly inhibited migration, invasion, and metastasis capability of cancer cells in vitro and in vivo. Intriguingly, SLC26A4-AS1 could simultaneously interact with DDX5 and the E3 ligase TRIM25, which promoting DDX5 degradation through the ubiquitin-proteasome pathway. In particular, SLC26A4-AS1 inhibited expression of multiple DNA double-strand breaks (DSBs) repair genes, especially genes coding proteins in the MRE11/RAS50/NBS1 (MRN) complex. Enhanced interaction between DDX5 and transcriptional factor E2F1 due to silencing of SLC26A4-AS1 promoted binding of the DDX5-E2F1 complex at promoters of the MRN genes and, thus, stimulate the MRN/ATM dependent DSB signaling and thyroid cancer metastasis. Our study uncovered new insights into the biology driving thyroid cancer metastasis and highlights potentials of lncRNAs as future therapeutic targets again cancer metastasis.

Cul4B promotes the progression of ovarian cancer by upregulating the expression of CDK2 and CyclinD1

Background

Ovarian cancer is one of the most common malignant tumors in the female reproductive system with the highest mortality rate. Cul4B participates in the oncogenesis and progression of several malignant tumors. However, the role of Cul4B in ovarian cancer has not been studied.

Results

High expression of intratumor Cul4B was associated with poor patient survival. Cul4B expression was associated with FIGO stage and Cul4B was independent risk factor of ovarian cancer disease-free survival and overall survival. In vitro studies revealed that overexpression of Cul4B promoted tumor proliferation while knockdown of Cul4B significantly inhibited the proliferation capacity of ovarian cancer cells. Mechanistically, Cul4B was found to promotes cell entering S phase from G0/G1 phase by regulating the expression of CDK2 and CyclinD1. Cul4B regulates the expression of CDK2 and CyclinD1 by repressing miR-372.

Conclusions

The results revealed that high expression of Cul4B is associated with poor ovarian cancer prognosis and Cul4B may serve as a potential treating target for an adjuvant therapy.

The CUL4B-miR-372/373-PIK3CA-AKT axis regulates metastasis in bladder cancer

CUL4B, which acts as a scaffold protein in CUL4B-RING ubiquitin ligase (CRL4B) complexes, participates in a variety of biological processes. Previous studies have shown that CUL4B is often overexpressed and exhibits oncogenic activities in a variety of solid tumors. However, the roles and the underlying mechanisms of CUL4B in bladder cancer (BC) were poorly understood. Here, we showed that CUL4B levels were overexpressed and positively correlated with the malignancy of BC, and CUL4B could confer BC cells increased motility, invasiveness, stemness, and chemoresistance. The PIK3CA/AKT pathway was identified as a critical downstream mediator of CUL4B-driven oncogenicity in BC cells. Furthermore, we demonstrated that CRL4B epigenetically repressed the transcription of miR-372/373, via catalyzing monoubiquitination of H2AK119 at the gene cluster encoding miR-372/373, leading to upregulation of PIK3CA and activation of AKT. Our findings thus establish a critical role for the CUL4B-miR-372/373-PIK3CA/AKT axis in the pathogenesis of BC and have important prognostic and therapeutic implications in BC.

CUL4B contributes to cancer stemness by repressing tumor suppressor miR34a in colorectal cancer

Given that colorectal cancer stem cells (CCSCs) play key roles in the tumor dormancy, metastasis, and relapse, targeting CCSCs is a promising strategy in cancer therapy. Here, we aimed to identify the new regulators of CCSCs and found that Cullin 4B (CUL4B), which possesses oncogenic properties in multiple solid tumors, drives the development and metastasis of colon cancer by sustaining cancer stem-like features. Elevated expression of CUL4B was confirmed in colon tumors and was associated with poor overall survival. Inhibition of CUL4B in cancer cell lines and patient-derived tumor organoids led to reduced sphere formation, proliferation and metastasis capacity. Mechanistically, CUL4B coordinates with PRC2 complex to repress miR34a expression, thus upregulates oncogenes including MYCN and NOTCH1, which are targeted by miR34a. Furthermore, we found that elevated CUL4B expression is associated with miR34a downregulation and upregulation of miR34a target genes in colon cancer specimens. Collectively, our findings demonstrate that CUL4B functions to repress miR34a in maintaining cancer stemness in CRC and provides a potential therapeutic target.

Upregulation of Cullin 4B Promotes Gastric Cancer and Predicts Poor Prognosis

Aim

Cullin 4B (CUL4B) is a member of the cullin ubiquitin-ligase family, which participates in proteolysis. Aberrant CUL4B expression has been shown in many malignancies. This study aimed to elucidate oncogenic role of CUL4B in gastric cancer (GC).

Methods

CUL4B expression in GC tissues was examined by RT-PCR and immunohistochemistry. The proliferation, invasion and tumorigenicity of GC cells with CUL4B overexpression or knockdown were evaluated.

Results

CUL4B expression significantly increased in GC tissues, and was correlated to UICC stage and differentiation of GC, as well as poor overall survival and disease-free survival. Both univariate and multivariate analysis identified CUL4B as an independent predictor for GC patient prognosis. In addition, CUL4B promoted GC cell proliferation and invasion in vitro and tumor formation in vivo.

Conclusion

CUL4B is overexpressed to promote GC development and progression. CUL4B is a promising prognostic marker and therapeutic target for GC.

Cullin 4-DCAF Proteins in Tumorigenesis

Cullin-RING ligase 4 (CRL4), a member of the cullin-RING ligase family, orchestrates a variety of critical cellular processes and pathophysiological events. Recent results from mouse genetics, clinical analyses, and biochemical studies have revealed the impact of CRL4 in development and cancer etiology and elucidated its in-depth mechanism on catalysis of ubiquitination as a ubiquitin E3 ligase. Here, we summarize the versatile roles of the CRL4 E3 ligase complexes in tumorigenesis dependent on the evidence obtained from knockout and transgenic mouse models as well as biochemical and pathological studies.

CUL4B negatively regulates Toll-like receptor-triggered proinflammatory responses by repressing Pten transcription

Toll-like receptors (TLRs) play critical roles in innate immunity and inflammation. The molecular mechanisms by which TLR signaling is fine-tuned remain to be completely elucidated. Cullin 4B (CUL4B), which assembles the CUL4B-RING E3 ligase complex (CRL4B), has been shown to regulate diverse developmental and physiological processes by catalyzing monoubiquitination for histone modification or polyubiquitination for proteasomal degradation. Here, we identified the role of CUL4B as an intrinsic negative regulator of the TLR-triggered inflammatory response. Deletion of CUL4B in macrophages increased the production of proinflammatory cytokines and decreased anti-inflammatory cytokine IL-10 production in response to pathogens that activate TLR3, TLR4, or TLR2. Myeloid cell-specific Cul4b knockout mice were more susceptible to septic shock when challenged with lipopolysaccharide, polyinosinic-polycytidylic acid or Salmonella typhimurium infection. We further demonstrated that enhanced TLR-induced inflammatory responses in the absence of CUL4B were mediated by increased GSK3β activity. Suppression of GSK3β activity efficiently blocked the TLR-triggered increase in proinflammatory cytokine production and attenuated TLR-triggered death in Cul4b mutant mice. Mechanistically, CUL4B was found to negatively regulate TLR-triggered signaling by epigenetically repressing the transcription of Pten, thus maintaining the anti-inflammatory PI3K-AKT-GSK3β pathway. The upregulation of PTEN caused by CUL4B deletion led to uncontrolled GSK3β activity and excessive inflammatory immune responses. Thus, our findings indicate that CUL4B functions to restrict TLR-triggered inflammatory responses through regulating the AKT-GSK3β pathway.

Insight into the relationship between aryl-hydrocarbon receptor and β-catenin in human colon cancer cells

β-Catenin is a multi-functional protein involved in cell adhesion and signal transduction and has a critical role in colorectal cancer development. β-Catenin positively regulates the aryl-hydrocarbon receptor (AhR) mediated signal by both induction of AhR expression and enhancement of AhR-dependent gene induction. Conversely, it was reported that AhR negatively regulates the β-catenin signal via ubiquitination and subsequent degradation in a ligand dependent manner. However, there have been conflicting data among previous studies regarding the relationship between these two proteins. In this report, we conducted confirmatory studies dissecting the relationship between AhR and β-catenin. We did not observe β-catenin degradation by AhR ligands in several colon cancer cell lines. Reporter assays revealed that the AhR ligand did not alter TcF/β-catenin dependent transcription. Yeast and mammalian two-hybrid assays failed to reconstruct the interaction of β-catenin and AhR even when other factors, Arnt, CUL4B, and DDB1, were co-expressed additionally. Independently to induction of AhR expression, β-catenin enhanced AhR-dependent transcriptional activation via the xenobiotic response element (XRE). Coimmunoprecipitation detected the formation of a β-catenin and ligand-activated AhR complex, which was thought to reflect the β-catenin mediated enhancement of the AhR signaling. Overall, we could only confirm unidirectional interaction, which is positive regulation of the AhR signal by β-catenin. These results suggested that data from previous reports on the degradation of β-catenin via liganded AhR warrants further investigation to yield clarity in the field.

CUL4B regulates cancer stem-like traits of prostate cancer cells by targeting BMI1 via miR200b/c

BACKGROUND

Cancer stem-like traits contribute to prostate cancer (PCa) progression and metastasis. Cullin 4B (CUL4B) is a member of the ubiquitin E3 ligase family and overexpressed in several solid malignancies including PCa. CUL4B has been suggested to be an oncogene through epigenetic repression of tumor suppressors. However, the link between CUL4B expression and cancer stem-like phenotype remains unclear.

METHODS

Western blot analysis, sphere formation, and colony formation assays were used to examine the effect of CUL4B on cancer stem-like traits in PCa cells. Mechanically, bioinformatic analysis was utilized to evaluate whether BMI1 was a target of CUL4B. Moreover, real-time polymerase chain reaction, chromatin immunoprecipitation, and luciferase reporter assays were performed to identify microRNAs regulated by CUL4B. Finally, Western blot assay was used to validate the regulation of CUL4B, miR200b, and miR200c (miR200b/c) on the stem-like characteristics of PCa cells.

RESULTS

CUL4B promotes PCa pluripotency-associated markers expression, sphere formation, and anchorage-independent growth ability in vitro. Mechanically, CUL4B upregulates BMI1 expression via epigenetically repressing miR200b/c expression. In addition, miR200b/c could partially reverse CUL4B-induced BMI1 and pluripotency-associated marker expression.

CONCLUSIONS

Our study revealed that CUL4B regulates cancer stem-like traits of prostate cancer cells by targeting BMI1 via miR200b/c, which might give novel insight into how CUL4B promotes PCa progression through regulating cancer stem-like traits.

Embryonic Cul4b is important for epiblast growth and location of primitive streak layer cells

Cul4b-null (Cul4bΔ/Y) mice undergo growth arrest and degeneration during the early embryonic stages and die at E9.5. The pathogenic causes of this lethality remain incompletely characterized. However, it has been hypothesized that the loss of Cul4b function in extraembryonic tissues plays a key role. In this study, we investigated possible causes of death for Cul4b-null embryos, particularly in regard to the role of embryonic Cul4b. First, we show that the loss of embryonic Cul4b affects the growth of the inner cell mass in vitro and delays epiblast development during the gastrulation period at E6.5~E7.5 in vivo, as highlighted by the absence of the epiblastic transcription factor Brachyury from E6.5~E7.5. Additionally, at E7.5, strong and laterally expanded expression of Eomes and Fgf8 signaling was detected. Sectioning of these embryos showed disorganized primitive streak layer cells. Second, we observed that Mash2-expressing cells were present in the extraembryonic tissues of Cul4b-deficient embryos at E6.5 but were absent at E7.5. In addition, the loss of Cul4b resulted in decreased expression of cyclin proteins, which are required for the cell cycle transition from G1 to S. Taken together, these observations suggest that the embryonic expression of Cul4b is important for epiblast growth during E6.5~E7.5, and the loss of Cul4b results in either delayed growth of the epiblast or defective localization of primitive streak layer cells. As a result, the signaling activity mediated by the epiblast for subsequent ectoplacental cone development is affected, with the potential to induce growth retardation and lethality in Cul4bΔ/Y embryos.

Upregulation of IL-6 in CUL4B-deficient myeloid-derived suppressive cells increases the aggressiveness of cancer cells

Cancer progression depends on a tumor-supportive microenvironment. Myeloid-derived suppressor cells (MDSCs) represent key cellular components in tumor microenvironment and have been demonstrated to facilitate tumor progression by restricting host immune responses and by sustaining the malignancy of cancer cells. CUL4B, which assembles the CUL4B-RING E3 ligase complex (CRL4B), possesses a potent oncogenic property in cancer cells by epigenetically inactivating many tumor suppressors. However, CUL4B in hematopoietic cells exerts tumor-suppressive effect by restricting the accumulation and function of MDSCs. How CUL4B regulates the function of MDSCs is not fully characterized. In the present study, we demonstrate that the enhanced growth and metastasis of transplanted tumor cells in hematopoietic or myeloid cell-specific Cul4b knockout recipient mice is mediated by increased production of IL-6 in MDSCs. CUL4B complex epigenetically represses IL-6 transcription in myeloid cells. The IL-6 produced by MDSCs renders cancer cells stem cell-like properties by activating IL-6/STAT3 signaling. This crosstalk was effectively blocked either by blocking IL-6 in MDSCs or by inhibition of STAT3 activation in tumor cells. These findings provide a new mechanistic insight into the cancer-promoting property of MDSCs.

ID3 Promotes Stem Cell Features and Predicts Chemotherapeutic Response of Intrahepatic Cholangiocarcinoma

Cancer stem cells contribute to a high rate of recurrence and chemotherapeutic resistance in many types of cancer, including intrahepatic cholangiocarcinoma (ICC). Inhibitor of differentiation 3 (ID3) has been reported to promote cancer stem cells, but its role in ICC is obscure. In this study, we identified that ID3 is highly expressed in human ICC tissues compared with matched normal tissues and correlates with poor prognosis. Functional studies demonstrate that ID3 is required for stemness maintenance in cholangiocarcinoma both in vitro and in vivo. Consistent with the regulation of cancer stem cell features by ID3, transgenic expression of ID3 enhances chemoresistance of cholangiocarcinoma cells. Moreover, we found that ICC patients with low ID3 levels benefited from postoperative transarterial chemoembolization, whereas patients with high ID3 levels did not, indicating the significance of ID3 in individualized ICC therapy. Mechanistically, ID3 could interact with E47 and block E47 recruitment to the promoter of β-catenin, which leads to activation of Wnt/β-catenin signaling. Conclusion: Our results show that ID3 could promote the stemness of ICC by increasing the transcriptional activity of β-catenin and could serve as a biomarker in predicting ICC patients' response to adjuvant chemotherapeutics.

CUL4B promotes aggressive phenotypes of HNSCC via the activation of the Wnt/β-catenin signaling pathway

Previous studies have revealed that CUL4B is overexpressed in various types of cancer and that its overexpression is related to the progression and metastasis of tumors. However, the biological functions of CUL4B in the progression of head and neck squamous cell carcinoma (HNSCC) are still not well understood. In the current study, we aimed to determine the changes in biological functions and molecular events that are related to CUL4B overexpression. Interestingly, our results showed that CUL4B is upregulated in HNSCC and that its upregulation is associated with poor survival and worse histological grade. Overexpression of CUL4B promoted cancer cell growth, invasion, and migration, as well as epithelial-mesenchymal transition, whereas the loss of CUL4B abrogated these malignant phenotypes. Moreover, our mechanistic investigations suggest that the Wnt/β-catenin signaling pathway was activated by CUL4B overexpression. Treatment with a Wnt/β-catenin inhibitor decreased CUL4B-induced migration and invasion, establishing a key role of Wnt/β-catenin signaling in mediating the effects of CUL4B expression. Together, these results demonstrate a key contribution of CUL4B overexpression in the malignant behavior of HNSCC cells, at least in part through the stimulation of angiogenesis and the activation of the Wnt/β-catenin signaling pathway.

CUL4B/miR-33b/C-MYC axis promotes prostate cancer progression

BACKGROUND

Cullin 4B (CUL4B), a scaffold protein that assembles CRL4B ubiquitin ligase complexes, is overexpressed in many types of solid tumors and contributes to epigenetic silencing of tumor suppressors. However, its clinical significance and underlying molecular mechanisms in prostate cancer (PCa) remain unknown.

METHODS

The clinical significance of CUL4B in PCa was characterized by in silico method. RT-qPCR and Western blot were used to study the transcript and protein expression levels of CUL4B and C-MYC. Bioinformatics tools, chromatin immunoprecipitation (ChIP) and luciferase reporter assay were utilized to identify and characterize the microRNAs (miRNAs) regulated by CUL4B. The biological function of CUL4B and miR-33b-5p was evaluated by MTS, transwell, and wound healing assays, accordingly.

RESULTS

CUL4B is significantly overexpressed in PCa tissues compared with benign prostatic tissues and its overexpression is correlated with poor prognosis. CUL4B promotes proliferation and aggressiveness of PCa cells in vitro. Mechanistically, we demonstrate that CUL4B upregulates the expression of C-MYC at post-transcriptional level through epigenetic silencing of miR-33b-5p. Importantly, CUL4B-induced oncogenic activity in PCa by targeting C-MYC is repressed by miR-33b-5p.

CONCLUSIONS

Our results suggested a novel CUL4B/miR-33b/C-MYC axis implicated in PCa cell growth and progression. This might provide novel insight into how CUL4B contributed to PCa aggressiveness and progression.

CUL4B promotes prostate cancer progression by forming positive feedback loop with SOX4

How to distinguish indolent from aggressive disease remains a great challenge in prostate cancer (PCa) management. Cullin 4B (CUL4B) is a scaffold protein and exhibits oncogenic activity in a variety of human malignancies. In this study, we utilized PCa tissue specimens, cell lines and xenograft models to determine whether CUL4B contributes to PCa progression and metastasis. Here, we show that CUL4B expression highly correlates with the aggressiveness of PCa. CUL4B expression promotes proliferation, epithelial−mesenchymal transition, and metastatic potential of PCa cells, whereas CUL4B knockdown inhibits. Mechanically, CUL4B positively regulates SOX4, a key regulator in PCa, through epigenetic silencing of miR-204. In turn, SOX4 upregulates CUL4B expression through transcriptional activation, thereby fulfilling a positive feedback loop. Clinically, CUL4B+/SOX4+ defines a subset of PCa patients with poor prognosis. Bioinformatics analysis further reveals that Wnt/ß-catenin activation signature is enriched in CUL4B+/SOX4+ patient subgroup. Intriguingly, Wnt inhibitors significantly attenuates oncogenic capacities of CUL4B in vitro and in vivo. Together, our study identifies CUL4B as a key modulator of aggressive PCa by a positive feedback loop that interacts with SOX4. This regulatory circuit may have a crucial role in PCa progression.

A novel lncRNA MCM3AP-AS1 promotes the growth of hepatocellular carcinoma by targeting miR-194-5p/FOXA1 axis

Background

Hepatocellular carcinoma (HCC) is the most common malignant liver tumor with poor clinical outcomes. Increasing amount of long non-coding RNAs (lncRNAs) have been revealed to be implicated in the carcinogenesis and progression of HCC. However, the expressions, clinical significances, and roles of most lncRNAs in HCC are still unknown.

Methods

The expression of lncRNA MCM3AP antisense RNA 1 (MCM3AP-AS1) in HCC tissues and cell lines was detected by qRT-PCR and fluorescence in situ hybridization. Immunoblotting, CCK-8, EdU, colony formation and flow cytometry were performed to investigate the role of MCM3AP-AS1 in HCC cell proliferation, cell cycle and apoptosis in vitro. A subcutaneous tumor mouse model was constructed to analyze in vivo growth of HCC cells after MCM3AP-AS1 knockdown. The interactions among MCM3AP-AS1, miR-194-5p and FOXA1 were measured by RNA pull-down, RNA immunoprecipitation and luciferase reporter assay.

Results

We revealed a novel oncogenic lncRNA MCM3AP-AS1, which is overexpressed in HCC and positively correlated with large tumor size, high tumor grade, advanced tumor stage and poor prognosis of HCC patients. MCM3AP-AS1 knockdown suppressed HCC cell proliferation, colony formation and cell cycle progression, and induced apoptosis in vitro, and depletion of MCM3AP-AS1 inhibited tumor growth of HCC in vivo. Mechanistically, MCM3AP-AS1 directly bound to miR-194-5p and acted as competing endogenous RNA (ceRNA), and subsequently facilitated miR-194-5p’s target gene forkhead box A1 (FOXA1) expression in HCC cells. Interestingly, FOXA1 restoration rescued MCM3AP-AS1 knockdown induced proliferation inhibition, G1 arrest and apoptosis of HCC cells.

Conclusions

Our results recognized MCM3AP-AS1 as a novel oncogenic lncRNA, which indicated poor clinical outcomes in patients with HCC. MCM3AP-AS1 exerted an oncogenic role in HCC via targeting miR-194-5p and subsequently promoted FOXA1 expression. Our findings suggested that MCM3AP-AS1 could be a potential prognostic biomarker and therapeutic target for HCC.

Electronic supplementary material

The online version of this article (10.1186/s12943-019-0957-7) contains supplementary material, which is available to authorized users.

CUL4B regulates autophagy via JNK signaling in diffuse large B-cell lymphoma

Aberrant expression of CUL4B was identified in various types of solid cancers. Cumulative evidences support the oncogenic role of CUL4B in cancers, including regulation of cell proliferation and signal transduction. However, its clinical value and potential pathogenic mechanism in diffuse large B-cell lymphoma (DLBCL) have not been described previously. Therefore, we hypothesize that overexpressed CUL4B may contribute to the pathogenesis of DLBCL. The aim of this study is to assess the expression and the biological function of CUL4B in DLBCL progression. In our study, CUL4B overexpression was observed in DLBCL tissues, and its upregulation was closely associated with poor prognosis in patients. Furthermore, the functional roles of CUL4B was detected both in vitro and in vivo. We demonstrated that silencing CUL4B could not only induce cell proliferation inhibition, cell cycle arrest, and motility attenuation of DLBCL cells in vitro, but also decrease tumor growth in DLBCL xenografts mice. In addition, we identified that CUL4B may act as a potent inductor of JNK phosphorylation in regulation of autophagy. Our findings demonstrated a significant role of CUL4B in the development and progression of DLBCL. CUL4B may act as a useful biomarker and a novel therapeutic target in DLBCL.

The emerging role for Cullin 4 family of E3 ligases in tumorigenesis

As a member of the Cullin-RING ligase family, Cullin-RING ligase 4 (CRL4) has drawn much attention due to its broad regulatory roles under physiological and pathological conditions, especially in neoplastic events. Based on evidence from knockout and transgenic mouse models, human clinical data, and biochemical interactions, we summarize the distinct roles of the CRL4 E3 ligase complexes in tumorigenesis, which appears to be tissue- and context-dependent. Notably, targeting CRL4 has recently emerged as a noval anti-cancer strategy, including thalidomide and its derivatives that bind to the substrate recognition receptor cereblon (CRBN), and anticancer sulfonamides that target DCAF15 to suppress the neoplastic proliferation of multiple myeloma and colorectal cancers, respectively. To this end, PROTACs have been developed as a group of engineered bi-functional chemical glues that induce the ubiquitination-mediated degradation of substrates via recruiting E3 ligases, such as CRL4 (CRBN) and CRL2 (pVHL). We summarize the recent major advances in the CRL4 research field towards understanding its involvement in tumorigenesis and further discuss its clinical implications. The anti-tumor effects using the PROTAC approach to target the degradation of undruggable targets are also highlighted.

miR‑381 and miR‑489 suppress cell proliferation and invasion by targeting CUL4B via the Wnt/β‑catenin pathway in gastric cancer

Accumulating evidence has highlighted the critical role of cullin 4B (CUL4B) in driving tumourigenesis in several malignancies, including gastric cancer (GC); however, the mechanisms underlying CUL4B upregulation remain unclear. The dysregulation of microRNAs (miRNAs or miRs) is known to be involved in tumourigenesis. In this study, we report that the expression of miR‑381 and miR‑489 is downregulated and is negatively correlated with that of CUL4B in GC tissues and cell lines. Further analysis verified that miR‑381 and miR‑489 directly targeted CUL4B. CUL4B silencing inhibited cell proliferation, migration and invasion by inactivating the Wnt/β‑catenin pathway. miR‑381/miR‑489 overexpression recapitulated the effects of CUL4B silencing, while CUL4B restoration negated the suppressive effects induced by the ectopic expression of miR‑381/miR‑489. Furthermore, miR‑381/miR‑489 exerted tumour suppressive functions by inactivating the Wnt/β‑catenin pathway through the targeting of CUL4B. Taken together, the findings of this study suggest that the miR‑381/miR‑489‑mediated expression of CUL4B modulates the proliferation and invasion of GC cells via the Wnt/β‑catenin pathway, which indicates that the miR‑381/miR‑489‑CUL4B axis is critical in the control of GC tumourigenesis.

CUL4B promotes metastasis and proliferation in pancreatic cancer cells by inducing epithelial-mesenchymal transition via the Wnt/β-catenin signaling pathway

This study determines whether cullin 4B (CUL4B) promotes pancreatic cancer (PC) metastasis by inducing epithelial-mesenchymal transition (EMT) via the Wnt/β-catenin signaling pathway. A total of 64 PC patients were enrolled in this study. Human PC cell lines were distributed into blank, negative control, shCUL4B, PLOC, PLOC-CUL4B, and PLOC-CUL4B + siRNA-β-catenin groups. The expressions of CUL4B, Wnt/β-catenin signaling pathway-related proteins, and EMT-related proteins were determined using RT-qPCR and Western blotting. The positive expressions of CUL4B and β-catenin protein in tissues were detected by immunohistochemistry. MTT assay and flow cytometry was performed for cell proliferation and cell cycle, scratch test, and transwell assay for cell migration and invasion ability. CUL4B and β-catenin were expressed at a higher level in PC tissues than in paracancerous tissues though paracancerous tissues had higher expressions of CUL4B and β-catenin than normal tissues. The PLOC-CUL4B group showed increased CUL4B, Wnt, β-catenin, LEF-1, c-Jun, Cyclin D1, N-cadherin, Vimentin, Snail, and ZEB1 expression; decreased E-cadherin expression; accelerated cell proliferation; increased S-phase cell percentages; increased cell migration ability; more liver metastases; and enlarged tumor than the PLOC and PLOC-CUL4B + siRNA-β-catenin groups. The shCUL4B group showed decreased CUL4B, Wnt, β-catenin, LEF-1, c-Jun, Cyclin D1, N-cadherin, Vimentin, Snail, and ZEB1 expression; increased E-cadherin expression; decelerated cell proliferation; decreased S-phase cell percentages; reduced cell migration ability; less liver metastases; and decreased tumor weight than the blank and negative control groups. We demonstrate that CUL4B promotes PC metastasis by inducing EMT via the Wnt/β-catenin signaling pathway. Therefore, CUL4B might be the clinical target for treating PC.

Effects of cullin 4B on the proliferation and invasion of human gastric cancer cells

The major aim of the present study was to explore the effects of cullin 4B (CUL4B) on the proliferation and invasion of human gastric cancer cells. Gastric tumor tissues and paired adjacent non-tumor tissues were obtained from 21 gastric cancer patients, and gastric cancer cell lines (AGS, MGC-803, KATO-III, MKN-45, SGC-7901, BGC-823 and MKN-74) were cultured. BGC-823 cells were transfected with CUL4B small interfering (si)RNA or control siRNA. Reverse transcription-quantitative polymerase chain reaction analysis was performed to detect the mRNA expression of CUL4B. Western blot analysis was performed to measure the protein levels of Wnt, β-catenin, glutathione synthase kinase (GSK)-3β, caspase-3 and cyclin E. MTT and Transwell assays were performed to examine cell proliferation and invasion following CUL4B knockdown. In addition, the effect of CUL4B knockdown on the cell cycle and apoptosis of BGC-823 cells was evaluated by flow cytometric analysis. The results indicated that compared with the adjacent non-tumor tissues and a normal gastric epithelial cell line, gastric cancer tissues and cell lines exhibited significantly higher expression of CUL4B. Knockdown of CUL4B in gastric cancer cells suppressed cell proliferation, caused G1 arrest and inhibited cell invasion. Silencing of CUL4B also resulted in decreased Wnt and β-catenin expression, but increased expression of GSK-3β, caspase-3 and cyclin E. These results indirectly demonstrate that CUL4B enhances the proliferation and invasion abilities of gastric cancer cells by upregulating the constituent factors Wnt and β-catenin, as well as by negatively regulating the mRNA and protein expression of GSK-3β, caspase-3 and cyclin E. The potential mechanism of CUL4B highlighted in the present study may be helpful for the treatment of patients with gastric cancer.

CUL4B promotes gastric cancer invasion and metastasis-involvement of upregulation of HER2

Cullin 4B (CUL4B) is a scaffold protein overexpressed in several solid malignancies. It is known to silence tumor suppressor through post-transcriptional manner. However, its clinical significance and underlying molecular mechanisms in gastric cancer (GC) remain largely unknown. In this study, we found that CUL4B was significantly overexpressed in GC tissues and its overexpression was correlated with lymph node metastasis and poor prognosis. Through gain- and loss-of-function experiments, we showed that CUL4B promotes GC cell invasion and epithelial-mesenchymal transition (EMT) in vitro, as well as tumor growth and metastasis in vivo. Mechanistically, we identified HER2 as a downstream target gene of CUL4B in GC. CUL4B unregulated HER2 expression via transcriptionally repressing miR-125a. Intriguingly, HER2 inhibitors significantly reversed CUL4B-induced EMT in vitro and partially blocked GC metastasis in tumor xenografts with CUL4B overexpression. Finally, we suggested the involvement of the PI3K/AKT pathway in CUL4B-induced HER2 upregulation in GC. In all, we proposed a model for a CUL4B-miR-125a-HER2 oncoprotein axis, which provided novel insight into how HER2 was activated and contributed to GC progression and metastasis.

CUL4B promotes bladder cancer metastasis and induces epithelial-to-mesenchymal transition by activating the Wnt/β-catenin signaling pathway

Increased expression of cullin 4B (CUL4B) is linked to progression in several cancers. This study aims to explore the effects of CUL4B on bladder cancer (BC) metastasis and epithelial-to-mesenchymal transition (EMT) and potential correlation to the Wnt/β-catenin signaling pathway. We collected BC tissues and adjacent normal tissues from 124 BC patients. Quantitative real-time polymerase chain reaction (qRT-PCR) and western blotting were employed in order to detect the expression of Wnt/β-catenin signaling pathway-related proteins and EMT markers. MTT and Transwell assays were used in order to measure cell proliferation, migration, and invasion. BC 5637 cells were transfected with control, siRNA scramble control (siRNA-NC), si-CUL4B, and CUL4B or Wnt inhibitory factor 1 (WIF-1) overexpression constructs. Levels of CUL4B mRNA and protein were increased in BC tissues in comparison with the adjacent normal tissues. CUL4B expression was negatively correlated with the expression of E-cadherin and positively correlated to the expression of N-cadherin and Vimentin. Compared to the control group, levels of β-catenin, cyclinD1, c-myc, MMP7, and EMT markers were reduced, whereas phosphorylated GSK3β^Ser9 and E-cadherin levels were increased in the si-CUL4B and WIF-1 groups. In addition, cell proliferation, migration, and invasion abilities were also increased. Increasing CUL4B expression had the opposite effect. These findings suggest that CUL4B induces EMT and promotes metastasis of BC by activating the Wnt/β-catenin signaling pathway.

The role of cullin4B in human cancers

Cullin 4B (CUL4B) is a scaffold of the Cullin4B-Ring E3 ligase complex (CRL4B) that plays an important role in proteolysis and is implicated in tumorigenesis. Aberrant expression of CUL4B has been reported in various types of human diseases. Recently, studies have shown that CUL4B was overexpressed in a multitude of solid neoplasms and affect the expression of several tumor suppressor genes. In this review, we aim to summarize the biological function of CUL4B in order to better understand its pathogenesis in human cancers.

Cul4B is a novel prognostic marker in cholangiocarcinoma

Cullin 4B (Cul4B), a scaffold protein that assembles the ubiquitin ligase complex, is involved in a wide variety of physiological and developmental processes, such as cell cycle progression, DNA damage response and gene expression regulation. Cul4B is overexpressed in various solid tumors. However, the prognostic value and role of Cul4B in cholangiocarcinoma (CCA) is largely unknown. The present study demonstrated that Cul4B was overexpressed in 21 (26.6%) of 79 patients with intrahepatic CCA, and in 40 (28.6%) of 140 patients with extrahepatic CCA (EHCC). Kaplan-Meier survival analysis suggested that Cul4B expression is an unfavorable prognostic factor in EHCC patients. Notably, Cul4B and epidermal growth factor receptor expression define a subset of CCA patients with poor prognosis. In vitro data indicated that Cul4B promotes the proliferation, migration and invasion of CCA cells. Furthermore, Cul4B expression promotes the epithelial-mesenchymal transition (EMT) process in CCA cells. Finally, Cul4B repressed the expression of the tumor suppressor genes P16 and phosphatase and tensin homolog. Collectively, the results of the present study revealed an important role of Cul4B in CCA with respect to initiating EMT. Cul4B expression may serve as a prognostic marker for patients with EHCC.

Knockdown of CUL4B Suppresses the Proliferation and Invasion in Non-Small Cell Lung Cancer Cells

Cullin 4B (CUL4B), a scaffold protein that assembles CRL4B ubiquitin ligase complexes, was found to be overexpressed in many types of tumors. However, the expression pattern and role of CUL4B in non-small cell lung cancer (NSCLC) remain largely unknown. Therefore, in the present study, we investigated the role of CUL4B in NSCLC, and the underlying mechanism was also explored. Our results showed that CUL4B was highly expressed in NSCLC cell lines. Silencing CUL4B obviously inhibited proliferation and migration/invasion of NSCLC cells, and it also suppressed the epithelial–mesenchymal transition (EMT) progress in NSCLC cells. Furthermore, knockdown of CUL4B significantly inhibited the expression of β-catenin, cyclin D1, and c-Myc in NSCLC cells. Taken together, these results suggest that knockdown of CUL4B inhibited the proliferation and invasion through suppressing the Wnt/β-catenin signaling pathway in NSCLC cells. Therefore, CUL4B may represent a novel therapeutic target for the treatment of NSCLC.

Dysregulation of the miR-194-CUL4B negative feedback loop drives tumorigenesis in non-small-cell lung carcinoma

Cullin 4B (CUL4B), a scaffold protein that assembles CRL4B ubiquitin ligase complexes, is overexpressed in many types of cancers and represses many tumor suppressors through epigenetic mechanisms. However, the mechanisms by which CUL4B is upregulated remain to be elucidated. Here, we show that CUL4B is upregulated in non‐small‐cell lung carcinoma (NSCLC) tissues and is critically required for cell proliferation and migration in vitro and for xenograft tumor formation in vivo. We found that microRNA‐194 (miR‐194) and CUL4B protein were inversely correlated in cancer specimens and demonstrated that miR‐194 could downregulate CUL4B by directly targeting its 3′‐UTR. We also showed that CUL4B could be negatively regulated by p53 in a miR‐194‐dependent manner. miR‐194 was further shown to attenuate the malignant phenotype of lung cancer cells by downregulating CUL4B. Interestingly, CRL4B also epigenetically represses miR‐194 by catalyzing monoubiquitination at H2AK119 and by coordinating with PRC2 to promote trimethylation at H3K27 at the gene clusters encoding miR‐194. RBX1, another component in CRL4B complex, is also targeted by miR‐194 in NSCLC cells. Our results thus establish a double‐negative feedback loop between miR‐194 and CRL4B, dysregulation of which contributes to tumorigenesis. The function of miR‐194 as a negative regulator of CUL4B has therapeutic implications in lung cancer.

The role and mechanism of CRL4 E3 ubiquitin ligase in cancer and its potential therapy implications

CRLs (Cullin-RING E3 ubiquitin ligases) are the largest E3 ligase family in eukaryotes, which ubiquitinate a wide range of substrates involved in cell cycle regulation, signal transduction, transcriptional regulation, DNA damage response, genomic integrity, tumor suppression and embryonic development. CRL4 E3 ubiquitin ligase, as one member of CRLs family, consists of a RING finger domain protein, cullin4 (CUL4) scaffold protein and DDB1–CUL4 associated substrate receptors. The CUL4 subfamily includes two members, CUL4A and CUL4B, which share extensively sequence identity and functional redundancy. Aberrant expression of CUL4 has been found in a majority of tumors. Given the significance of CUL4 in cancer, understanding its detailed aspects of pathogenesis of human malignancy would have significant value for the treatment of cancer. Here, the work provides an overview to address the role of CRL4 E3 ubiquitin ligase in cancer development and progression, and discuss the possible mechanisms of CRL4 ligase involving in many cellular processes associated with tumor. Finally, we discuss its potential value in cancer therapy.

WNT1 Gene from WNT Signaling Pathway Is a Direct Target of miR-122 in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is an invasive form of hepatic cancer arising from the accumulation of multiple genetic alterations. In this study, the causal role of disturbed canonical Wnt/β-catenin pathway was approved, and some of HCC-driven important gene candidates were determined. MicroRNAs (miRNAs), small non-coding RNAs, are the key regulators of important cancer genes, and their participation in tumorigenesis has been shown. By reviewing literature, WNT1 gene with functional significance was selected to approve miRNAs as new subjects for targeted therapy.For proper and fast miRNA detection and also confirmation of the role of bioinformatics in obtaining practical data, we benefited from different bioinformatics tools such as TargetScan, miRanda, and DIANA. In order to use an HCC model, we used HepG2 cell line. Luciferase assay was applied to assess the ability of the selected miRNAs in targeting WNT1 3'-UTR. To overexpress the selected miRNA in HepG2 cell line, viral construct was prepared. Quantitative real-time PCR was performed to evaluate selected miRNA and target gene expression levels. miR-122 was selected according to data concerning various bioinformatics tools.miR-122 was downregulated and WNT1 gene expression was upregulated in HepG2 cell line. After viral construct transduction, miR-122 expression was elevated and WNT1 expression was notably declined. Finally, we introduced WNT1 gene as one of the important genes in HCC, and also, we showed that miR-122 can regulate WNT1 gene expression.Moreover, our study determines the potential of bioinformatics analyses in providing accurate and reliable data for miRNA: messenger RNA (mRNA) prediction.

Epigenetic Activation of Wnt/β-Catenin Signaling in NAFLD-Associated Hepatocarcinogenesis

Non-alcoholic fatty liver disease (NAFLD), characterized by fat accumulation in liver, is closely associated with central obesity, over-nutrition and other features of metabolic syndrome, which elevate the risk of developing hepatocellular carcinoma (HCC). The Wnt/β-catenin signaling pathway plays a significant role in the physiology and pathology of liver. Up to half of HCC patients have activation of Wnt/β-catenin signaling. However, the mutation frequencies of CTNNB1 (encoding β-catenin protein) or other antagonists targeting Wnt/β-catenin signaling are low in HCC patients, suggesting that genetic mutations are not the major factor driving abnormal β-catenin activities in HCC. Emerging evidence has demonstrated that obesity-induced metabolic pathways can deregulate chromatin modifiers such as histone deacetylase 8 to trigger undesired global epigenetic changes, thereby modifying gene expression program which contributes to oncogenic signaling. This review focuses on the aberrant epigenetic activation of Wnt/β-catenin in the development of NAFLD-associated HCC. A deeper understanding of the molecular mechanisms underlying such deregulation may shed light on the identification of novel druggable epigenetic targets for the prevention and/or treatment of HCC in obese and diabetic patients.

Accelerated hepatocellular carcinoma development in CUL4B transgenic mice

Cullin 4B (CUL4B) is a component of the Cullin 4B-Ring E3 ligase (CRL4B) complex that functions in proteolysis and in epigenetic regulation. CUL4B possesses tumor-promoting properties and is markedly upregulated in many types of human cancers. To determine the role of CUL4B in liver tumorigenesis, we generated transgenic mice that expressed human CUL4B in livers and other tissues and evaluated the development of spontaneous and chemically-induced hepatocellular carcinomas. We observed that CUL4B transgenic mice spontaneously developed liver tumors at a high incidence at old ages and exhibited enhanced DEN-induced hepatocarcinogenesis. There was a high proliferation rate in the livers of CUL4B transgenic mice that was accompanied by increased levels of Cdk1, Cdk4 and cyclin D1 and decreased level of p16. The transgenic mice also exhibited increased compensatory proliferation after DEN-induced liver injury, which was accompanied by activation of Akt, Erk, p38 and NF-κB. We also found that Prdx3 was downregulated and that DEN induced a higher level of reactive oxygen species in the livers of transgenic mice. Together, our results demonstrate a critical role of CUL4B in hepatocarcinogenesis in mice.

miR-522 contributes to cell proliferation of hepatocellular carcinoma by targeting DKK1 and SFRP2

The morbidity and mortality of hepatocellular carcinoma (HCC) is very high, finding new therapeutic targets are critical for HCC treatment. miR-522 has been demonstrated to be upregulated in HCC tissues, but its role in HCC progression remains to be elucidated. In this report, we found miR-522 was upregulated in HCC cells and tissues, miR-522 overexpression promoted cell proliferation, colony formation, and cell cycle progression, whereas knockdown of miR-522 reduced these effects. We also analyzed the expression of several key cell cycle regulatory proteins and found overexpression of miR-522-inhibited cell cycle inhibitors p21 and p27 expression and enhanced cyclin D1 expression and the level of Rb phosphorylation, vice versa. These suggested miR-522-accelerated G1/S transition. DKK1 (dickkopf-1) and SFRP2 (secreted frizzled-related protein 2) were the targets of miR-522, their expression was inversely with miR-522 in HCC tissues. DKK1 and SFRP2 the antagonists of Wnt signaling, suggesting miR-522-promoted HCC progression through activating Wnt signaling. miR-522 might be a valuable target for HCC therapy.