circSNTB2 and CUL4A Induces Dysfunction of Nucleus Pulposus Cells by Competitively Binding miR-665

Circular RNA (circRNA) plays important roles in lumbar degenerative diseases. This study aimed to investigate the role of circSNTB2 in regulating the development of lumbar disc herniation (LDH) in vitro and in vivo. The abnormally expressed circSNTB2 in intervertebral disc degeneration (IDD) through bioinformatics analysis was identified, and verified in nucleus pulposus (NP) tissues of patients with LDH. NP cells were treated with TNF-α to mimic the LDH microenvironment. RT-qPCR was applied to determine levels of mRNA and microRNA (miRNA) in clinical samples and cells. We performed CCK-8, EdU, TUNEL and flow cytometric apoptosis assays to evaluate the proliferation and apoptosis of NP cells. The predicted the miRNAs and downstream target genes were verified with the help of luciferase reporter gene and RNA pull-down experiments. Finally, we established an LDH rat model to further verify the role of circSNTB2 in vivo. circSNTB2 was significantly up-regulated in the NP tissues of LDH group and TNF-α -treated NP cells. miR-665 binds to circSNTB2 and cullin 4A (CUL4A) is the downstream target gene of miR-665. Knockdown of circSNTB2 promoted NP cells proliferation and inhibited apoptosis, which was reversed by down-regulation of miR-665. In addition, up-regulated CUL4A reversed the effects of over-expressed miR-665 on proliferation and apoptosis of NP cells. Meanwhile, results of in vivo experiments demonstrated that knocking down circSNTB2 alleviated LDH-induced thermo-mechanical pain and NP injury. In summary, circSNTB2 regulates the proliferation and apoptosis of NP by mediating miR-665 regulation of CUL4A, which provides a reliable idea for targeted therapy of LDH.

CUL4A Ubiquitin Ligase Is an Independent Predictor of Overall Survival in Pancreatic Adenocarcinoma

BACKGROUND/AIM

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive malignancy with dismal prognosis. Genomic instability due to defects in cell-cycle regulation/mitosis or deficient DNA-damage repair is a major driver of PDAC progression with clinical relevance. Deregulation of licensing of DNA replication leads to DNA damage and genomic instability, predisposing cells to malignant transformation. While overexpression of DNA replication-licensing factors has been reported in several human cancer types, their role in PDAC remains largely unknown. We aimed here to examine the expression and prognostic significance of the DNA replication-licensing factors chromatin licensing and DNA replication factor 1 (CDT1), cell-division cycle 6 (CDC6), minichromosome maintenance complex component 7 (MCM7) and also of the ubiquitin ligase regulator of CDT1, cullin 4A (CUL4A), in PDAC.

MATERIALS AND METHODS

Expression levels of CUL4, CDT1, CDC6 and MCM7 were evaluated by immunohistochemistry in 76 formalin-fixed paraffin-embedded specimens of PDAC patients in relation to DNA-damage response marker H2AX, clinicopathological parameters and survival. We also conducted bioinformatics analysis of data from online available databases to corroborate our findings.

RESULTS

CUL4A and DNA replication-licensing factors were overexpressed in patients with PDAC and expression of CDT1 positively correlated with H2AX. Expression of CUL4A and CDT1 positively correlated with lymph node metastasis. Importantly, elevated CUL4A expression was associated with reduced overall survival and was an independent indicator of poor prognosis on multivariate analysis.

CONCLUSION

Our findings implicate CUL4A, CDT1, CDC6 and MCM7 in PDAC progression and identify CUL4A as an independent prognostic factor for this disease.

Targeted Protein Degradation through Recruitment of the CUL4A Complex Adaptor Protein DDB1

Targeted protein degradation has arisen as a powerful therapeutic modality for eliminating proteins. Thus far, most heterobifunctional Proteolysis Targeting Chimeras (PROTACs) have utilized recruiters against substrate receptors of Cullin RING E3 ubiquitin ligases, such as cereblon and VHL. However, previous studies have surprisingly uncovered molecular glue degraders that exploit a CUL4A adaptor protein DDB1 to degrade neosubstrate proteins. Here, we sought to investigate whether DDB1 recruiters can be discovered that can be exploited for PROTAC applications. We utilized activity-based protein profiling and cysteine chemoproteomic screening to identify a covalent recruiter that targets C173 on DDB1 and exploited this recruiter to develop PROTACs against BRD4 and androgen receptor (AR). We demonstrated that the BRD4 PROTAC results in selective degradation of the short BRD4 isoform over the long isoform in a proteasome, NEDDylation, and DDB1-dependent manner. We also demonstrated degradation of AR with the AR PROTAC in prostate cancer cells. Our study demonstrated that covalent chemoproteomic approaches can be used to discover recruiters against Cullin RING adapter proteins and that these recruiters can be used for PROTAC applications to degrade neo-substrates.

CUL4A-mediated ZEB1/microRNA-340-5p/HMGB1 axis promotes the development of osteoporosis

Understanding the molecular mechanisms underlying osteoclast differentiation provides insights into bone loss and even osteoporosis. The specific mechanistic actions of cullin 4A (CUL4A) in osteoclast differentiation and resultant osteoporosis is poorly explored. We developed a mouse model of osteoporosis using bilateral ovariectomy (OVX) and examined CUL4A expression. It was noted that CUL4A expression was increased in the bone marrow of OVX mice. Overexpression of CUL4A promoted osteoclast differentiation, and knockdown of CUL4A alleviated osteoporosis symptoms of OVX mice. Bioinformatic analyses were applied to identify the downstream target genes of microRNA-340-5p (miR-340-5p), followed by interaction analysis. The bone marrow macrophages (BMMs) were isolated from femur of OVX mice, which were transfected with different plasmids to alter the expression of CUL4A, Zinc finer E-box binding homeobox 1 (ZEB1), miR-340-5p, and Toll-like receptor 4 (TLR4). ChIP assay was performed to detect enrichment of ZEB1 promoter by H3K4me3 antibody in BMMs. ZEB1 was overexpressed in the bone marrow of OVX mice. Overexpression of CUL4A mediated H3K4me3 methylation to increase ZEB1 expression, thus promoting osteoclast differentiation. Meanwhile, ZEB1 could inhibit miR-340-5p expression and upregulate HMGB1 to induce osteoclast differentiation. Overexpressed ZEB1 activated the TLR4 pathway by regulating the miR-340-5p/HMGB1 axis to induce osteoclast differentiation, thus promoting the development of osteoporosis. Overall, E3 ubiquitin ligase CUL4A can upregulate ZEB1 to repress miR-340-5p expression, leading to HMGB1 upregulation and the TLR4 pathway activation, which promotes osteoclast differentiation and the development of osteoporosis.

CUL4A silencing attenuates cervical carcinogenesis and improves Cisplatin sensitivity

CUL4A is an ubiquitin ligase deregulated in numerous pathologies including cancer and even hijacked by viruses for facilitating their survival and propagation. However, its role in Human papilloma virus (HPV)-mediated cervical carcinogenesis remains elusive. The UALCAN and GEPIA datasets were analyzed to ascertain the transcript levels of CUL4A in cervical squamous cell carcinoma and endocervical adenocarcinoma (CESC) patients. Subsequently, various biochemical assays were employed to explore the functional contribution of CUL4A in cervical carcinogenesis and to shed some light on its involvement in Cisplatin resistance in cervical cancer. Our UALCAN and GEPIA datasets analyses reveal elevated CUL4A transcript levels in cervical squamous cell carcinoma and endocervical adenocarcinoma (CESC) patients that correlate with adverse clinicopathological parameters such as tumor stage and lymph node metastasis. Kaplan-Meier plot and GEPIA assessment depict poor prognosis of CESC patients having high CUL4A expression. Varied biochemical assays illustrate that CUL4A inhibition severely curtails hallmark malignant properties such as cellular proliferation, migration, and invasion of cervical cancer cells. We also show that CUL4A knockdown in HeLa cells causes increased susceptibility and better apoptotic induction toward Cisplatin, a mainstay drug used in cervical cancer treatment. More interestingly, we find reversion of Cisplatin-resistant phenotype of HeLa cells and an augmented cytotoxicity towards the platinum compound upon CUL4A downregulation. Taken together, our study underscores CUL4A as a cervical cancer oncogene and illustrates its potential as a prognosis indicator. Our investigation provides a novel avenue in improving current anti-cervical cancer therapy and overcoming the bottle-neck of Cisplatin resistance.

How cells recognize and remove the perforated lysosome

Macroautophagy (hereafter autophagy) is a highly conserved intracellular degradation system to maintain cellular homeostasis by degrading cellular components such as misfolded proteins, nonfunctional organelles, pathogens, and cytosol. Conversely, selective autophagy targets and degrades specific cargo, such as organelles, bacteria, etc. We previously reported that damaged lysosomes are autophagy targets, via a process called lysophagy. However, how cells target damaged lysosomes through autophagy is not known. We performed proteomics analysis followed by siRNA screening to identify genes involved in targeting damaged lysosomes and identified a new E3 ligase complex, involving CUL4A (cullin 4A), as a regulatory complex in lysophagy. We also found that this complex mediates K48-linked poly-ubiquitination on lysosome protein LAMP2 during lysosomal damage; particularly, the lumenal side of LAMP2 is important to recruit the complex to damaged lysosomes. This protein modification is thus critical to initiate the clearance of damaged lysosomes.

[Retracted] Suppression of CUL4A attenuates TGF‑β1‑induced epithelial‑to‑mesenchymal transition in breast cancer cells

Subsequently to the publication of the above article, and a Corrigendum that was published with the intention of rectifying the issue of overlapping data panels showing cell migration and invasion assay data in Fig. 8 (DOI: 10.3892/mmr.2018.9415; published online on September 24, 2017), it was drawn to the Editors' attention by a concerned reader that certain of the data shown for the epithelial‑mesenchymal transition experiments in Fig. 2B, western blotting data in Fig. 6 and scratch‑wound assay data shown in Fig. 7A were strikingly similar to data appearing in different form in other articles by different authors at different research institutes, which had already been published elsewhere prior to this paper's submission to International Journal of Molecular Medicine. In addition, several other instances of overlapping data panels were identified in Fig. 8. Owing to the fact that a substantial number of contentious data included in this paper had already been published elsewhere prior to its submission to International Journal of Molecular Medicine, the Editor has decided that this paper should be retracted from the Journal. The authors were asked for an explanation to account for these concerns, but the Editorial Office did not receive a reply. The Editor apologizes to the readership for any inconvenience caused. [International Journal of Molecular Medicine 40: 1114‑1124, 2017; DOI: 10.3892/ijmm.2017.3118].

Identification of CUL4A-DDB1-WDFY1 as an E3 ubiquitin ligase complex involved in initiation of lysophagy

Macroautophagy is a bulk degradation system in which double membrane-bound structures called autophagosomes to deliver cytosolic materials to lysosomes. Autophagy promotes cellular homeostasis by selectively recognizing and sequestering specific targets, such as damaged organelles, protein aggregates, and invading bacteria, termed selective autophagy. We previously reported a type of selective autophagy, lysophagy, which helps clear damaged lysosomes. Damaged lysosomes become ubiquitinated and recruit autophagic machinery. Proteomic studies using transfection reagent-coated beads and further evaluations reveal that a CUL4A-DDB1-WDFY1 E3 ubiquitin ligase complex is essential to initiate lysophagy and clear damaged lysosomes. Moreover, we show that LAMP2 is ubiquitinated by the CUL4A E3 ligase complex as a substrate on damaged lysosomes. These results reveal how cells selectively tag damaged lysosomes to initiate autophagy for the clearance of lysosomes.

LncRNA AIRN influences the proliferation and apoptosis of hepatocellular carcinoma cells by regulating STAT1 ubiquitination

Long non-coding RNAs (LncRNAs) have been implicated in the pathogenesis of various human diseases. In this study, we probed into the role and potential mechanisms of the antisense of IGF2R non-protein coding RNA (LncRNA AIRN) in the progression of hepatocellular carcinoma (HCC). Using a quantitative real-time polymerase chain reaction, we corroborated that LncRNA AIRN expression was raised in the HCC tissues and cells. The bioinformatic analysis revealed that a potential interaction between LncRNA AIRN and STAT1, which was verified by the RNA pull-down and RNA immunoprecipitation. In the cycloheximide-chase assay, the knockdown of LncRNA AIRN enhanced the stability of STAT1 protein. In the immunoprecipitation assay, the knockdown of LncRNA AIRN restrained the cullin 4A (CUL4A)-mediated ubiquitination of STAT1 protein. The cell transfection, MTT and flow cytometry assays expounded that the LncRNA AIRN/STAT1 axis was bound up with the regulation of the proliferation and apoptosis of HCC cells. The in vivo experiments corroborated that the knockdown of LncRNA AIRN restrained the tumor growth of HCC. Our data expounded that the knockdown of LncRNA AIRN restrained HCC cell proliferation and boosted cell apoptosis by restraining the CUL4A-mediated ubiquitination of STAT1 protein.

Autophagy Plays a Role in the CUL4A-Related Poor Prognosis of Intrahepatic Cholangiocarcinoma

CUL4A regulate the termination of autophagy in a physical process. However, the relationship between CUL4A and autophagy in cancer is unclear. We retrospectively investigated 99 intrahepatic cholangiocarcinoma (iCCA) cases. Whole sections were used for immunohistochemical analysis for p62, and LC3B expression. Q-score was defined as the sum of the labeling intensity and proportion. The cut-off point for immunoreactivity was set. CUL4A was overexpressed in cell lines and autophagy reflux was compared after manipulation. The iCCA cases with CUL4A overexpression had significantly higher prevalence of intact activated autophagy (42.4 vs. 15.2%; p = 0.003), which was significantly associated with advance tumor stage (34.1% vs. 15.4%; p = 0.032), less extensive necrosis (8.3 vs. 49.3%; p < 0.001), and shortened disease-free survival (mean, 19.6 vs. 65.5 months, p = 0.015). In vitro, iCCA cells with CUL4A overexpression significantly increased LC3II level as compared to the cells under basal condition. Although both cell types showed intact autophagy with increased LC3II expression after bafilomycin A1 treatment, the accumulation of LC3II was higher in CUL4A-overexpressing cells. CUL4A overexpression increased the proliferation of cells as compared with control cells. After treatment with bafilomycin A1, proliferation was inhibited in both cell types, but the effects were more prominent in the cells overexpressing CUL4A. CUL4A promotes autophagy, and exhibits significantly higher autophagic flux which affects the proliferation of iCCA cells; these effects correlated with advance tumor stage and poor prognosis. Thus, targeting autophagy may be potentially therapeutic in iCCA.

Importance of Cullin4 Ubiquitin Ligase in Malignant Pleural Mesothelioma

Neurofibromatosis type 2 (NF2), the tumor suppressor frequently lost in malignant pleural mesothelioma (MPM), suppresses tumorigenesis in part by inhibiting the Cullin4 ubiquitin ligase (CUL4) complex in the nucleus. Here, we evaluated the importance of CUL4 in MPM progression and tested the efficacy of cullin inhibition by pevonedistat, a small molecule inhibiting cullin neddylation. CUL4 paralogs (CUL4A and CUL4B) were upregulated in MPM tumor specimens compared to nonmalignant pleural tissues. High gene and protein expressions of CUL4B was associated with a worse progression-free survival of MPM patients. Among 13 MPM cell lines tested, five (38%) were highly sensitive to pevonedistat (half maximal inhibitory concentration of cell survival IC₅₀ < 0.5 µM). This remained true in a 3D spheroid culture. Pevonedistat treatment caused the accumulation of CDT1 and p21 in both sensitive and resistant cell lines. However, the treatment induced S/G2 cell cycle arrest and DNA rereplication predominantly in the sensitive cell lines. In an in vivo mouse model, the pevonedistat treatment significantly prolonged the survival of mice bearing both sensitive and resistant MPM tumors. Pevonedistat treatment reduced growth in sensitive tumors but increased apoptosis in resistant tumors. The mechanism in the resistant tumor model may be mediated by reduced macrophage infiltration, resulting from the suppression of macrophage chemotactic cytokines, C-C motif chemokine ligand 2 (CCL2), expression in tumor cells.

lncRNA SNHG11 Promotes Gastric Cancer Progression by Activating the Wnt/β-Catenin Pathway and Oncogenic Autophagy

Long non-coding RNAs (lncRNAs) are under active investigation in the development of cancers, including gastric cancer (GC). Oncogenic autophagy is required for cancer cell survival. The present study aimed to investigate the regulatory role of lncRNA small nucleolar host gene 11 (SNHG11) in GC. We show that SNHG11 is upregulated in GC, and that its upregulation correlated with dismal patient outcomes. Functionally, SNHG11 aggravated oncogenic autophagy to facilitate cell proliferation, stemness, migration, invasion, and epithelial-to-mesenchymal transition (EMT) in GC. Mechanistically, SNHG11 post-transcriptionally upregulated catenin beta 1 (CTNNB1) and autophagy related 12 (ATG12) through miR-483-3p/miR-1276, while the processing of precursor (pre-)miR-483/pre-miR-1276 was hindered by SNHG11. SNHG11 induced GSK-3β ubiquitination through interacting with Cullin 4A (CUL4A) to further activate the Wnt/β-catenin pathway. Intriguingly, SNHG11 regulated autophagy in a manner dependent on ATG12 rather than the Wnt/β-catenin pathway, whereas SNHG11 contributed to the malignant behaviors of GC cells via both pathways. Finally, SNHG11 upregulation in GC cells was shown to be transcriptionally induced by TCF7L2. In conclusion, we reveal that SNHG11 is an onco-lncRNA in GC and might be a promising prognostic and therapeutic target for GC.

The small molecule PSSM0332 disassociates the CRL4ADCAF8 E3 ligase complex to decrease the ubiquitination of NcoR1 and inhibit the inflammatory response in a mouse sepsis-induced myocardial dysfunction model

Sepsis-induced myocardial dysfunction (SIMD) is a life-threatening complication caused by inflammation, but how it is initiated is still unclear. Several studies have shown that extracellular high mobility group box 1 (HMGB1), an important cytokine triggering inflammation, is overexpressed during the pathogenesis of SIMD, but the underlying mechanism regarding its overexpression is still unknown. Herein, we discovered that CUL4A (cullin 4A) assembled an E3 ligase complex with RBX1 (ring-box 1), DDB1 (DNA damage-binding protein 1), and DCAF8 (DDB1 and CUL4 associated factor 8), termed CRL4A^DCAF8, which ubiquitinated and degraded NcoR1 (nuclear receptor corepressor 1) in an LPS-induced SIMD mouse model. The degradation of NcoR1 failed to form a complex with the SP1 transcription factor, leading to the upregulation of HMGB1. Mature HMGB1 functioned as an effector to induce the expression of proinflammatory cytokines, causing inflammation and resulting in SIMD pathology. Using an in vitro AlphaScreen technology, we identified three small molecules that could inhibit the CUL4A-RBX1 interaction. Of them, PSSM0332 showed the strongest ability to inhibit the ubiquitination of NcoR1, and its administration in SIMD mice exhibited promising effects on decreasing the inflammatory response. Collectively, our results reveal that the CRL4A^DCAF8 E3 ligase is critical for the initiation of SIMD by regulating the expression of HMGB1 and proinflammatory cytokines. Our results suggest that PSSM0332 is a promising candidate to inhibit the inflammatory response in the pathogenesis of SIMD, which will provide a new option for the therapy of SIMD.

CUL4A, ERCC5, and ERCC1 as Predictive Factors for Trabectedin Efficacy in Advanced Soft Tissue Sarcomas (STS): A Spanish Group for Sarcoma Research (GEIS) Study

A translational study was designed to analyze the expression of nucleotide excision repair (NER) and homologous recombination (HR) genes as potential predictive biomarkers for trabectedin in soft-tissue sarcoma (STS). This study is part of a randomized phase II trial comparing trabectedin plus doxorubicin versus doxorubicin in advanced STS. Gene expression levels were evaluated by qRT-PCR, while CUL4A protein levels were quantified by immunohistochemistry. Expression levels were correlated with patients’ progression-free survival (PFS) and overall survival (OS). Gene expression was also evaluated in cell lines and correlated with trabectedin sensitivity. In doxorubicin arm and in the whole series, which includes samples from both arms, no significant differences in terms of PFS were observed amongst the analyzed genes. In the group treated with trabectedin plus doxorubicin, the median of PFS was significantly longer in cases with CUL4A, ERCC1, or ERCC5 overexpression, while BRCA1 expression did not correlated with PFS. Gene expression had no prognostic influence in OS. CUL4A protein levels correlated with worse PFS in doxorubicin arm and in the whole series. In cell lines, only overexpression of ERCC1 was significantly correlated with trabectedin sensitivity. In conclusion, CUL4A, ERCC5, and mainly ERCC1 acted as predictive factors for trabectedin efficacy in advanced STS.

Small molecule NSC1892 targets the CUL4A/4B-DDB1 interactions and causes impairment of CRL4DCAF4 E3 ligases to inhibit colorectal cancer cell growth

Cullin 4A and 4B (CUL4A and 4B) function as oncogenes in colorectal cancer (CRC) cells. Both of them conservatively associate with DNA damage-binding protein 1 (DDB1) and DDB1-CUL4-associated factor 4 (DCAF4) to form Cullin-RING E3 ligases known as CRL4^DCAF4, which specifically ubiquitinate and degrade tumor suppressor ST7 (suppression of tumorigenicity 7). Knockdown either CUL4A/4B or DDB1 significantly inhibits tumor cell growth in vitro and in vivo. Thus, targeting these CRL4^DCAF4 components and their interactions may be an effective strategy for the therapy of CRC. In this study, we developed an in vitro AlphaScreen assay to identify small molecules targeting the CUL4A-DDB1 interaction. We obtained a compound NSC1892, which strongly disrupted the CUL4A-DDB1 interaction (IC₅₀ = 1.8 μM). Oncogenic phenotype analyses indicated that NSC1892 showed significant cytotoxicity to decrease cell proliferation, colony formation and invasion in CRC cells. Biochemical analyses demonstrated that NSC1892 treatment did not change CUL4A and CUL4B protein levels, but caused the degradation of DDB1, thereby leading to the impaired assembly of CRL4^DCAF4 E3 ligases and resulting in the accumulation of ST7. The administration of NSC1892 in mice also significantly inhibited tumor growth through degrading DDB1 and accumulating ST7. Interestingly, NSC1892 also showed promising cytotoxicity to decrease the growth of other CUL4A- or CUL4B-overexpressing tumor cells such as SKOV3 ovarian cells and Saos2 osteosarcoma cells. Our results provide a new avenue for the development of a therapeutic compound targeting tumors through disrupting the CUL4-DDB1 interaction.

The CARM1-p300-c-Myc-Max (CPCM) transcriptional complex regulates the expression of CUL4A/4B and affects the stability of CRL4 E3 ligases in colorectal cancer

The transcription factor c-Myc and two cullin family members CUL4A/4B function as oncogenes in colorectal cancer. Our recent publication reveals that c-Myc specifically activates the expression of CUL4A/4B through binding to their promoters. However, the underlying mechanism of how c-Myc actions in this process is still unknown. Using mass spectrometry and immunoprecipitation assays, we identified c-Myc formed a transcriptional complex with its partner Max (Myc-associated factor X), a histone acetyltransferase p300 and a coactivator associated arginine methyltransferase 1 (CARM1) in the present study. Knockdown or overexpression of the components of CARM1-p300-c-Myc-Max (CPCM) complex resulted in a decrease or increase of CUL4A/4B levels, respectively. Individual knockdown or inhibition of CPCM components decreased cell proliferation, colony formation, and cell invasion. Biochemically, knockdown or inhibition of CPCM components decreased their occupancies on the promoters of CUL4A/4B and resulted in their downregulation. Importantly, inhibition of CPCM components also caused a decrease of CRL4 E3 ligase activities and eventually led to an accumulation of ST7 (suppression of tumorigenicity 7), the specific substrate of CRL4 E3 ligases in colorectal cancer. Moreover, the in vivo tumor formation results indicated that knockdown or inhibition of CPCM components significantly decreased the tumor volumes. Together, our results suggest that the CPCM complex mediates explicitly the expression of CUL4A/4B, and thus affects the stability of CRL4 E3 ligases and the ubiquitination of ST7. These results provide more options by targeting the CPCM components to inhibit tumor growth in the therapy of colorectal cancer.

Development of a Novel Oncolytic Adenovirus Expressing a Short-hairpin RNA Against Cullin 4A

BACKGROUND

Arming of an oncolytic adenovirus (OAd) by inserting expression cassettes of therapeutic transgenes into the OAd genome is a promising approach to enhance the therapeutic effects of an OAd. Ideally, this approach would simultaneously promote the replication of an OAd in tumor cells and transgene product-mediated antitumor effects by expressing therapeutic transgenes. We previously demonstrated that knockdown of cullin 4A (CUL4A), which is an E3 ubiquitin ligase, significantly promoted adenovirus replication by increasing the c-JUN protein level. In addition, previous studies reported that CUL4A was highly expressed in various types of tumor, and was involved in tumor growth and metastasis.

MATERIALS AND METHODS

In this study, we developed a novel OAd expressing a short-hairpin RNA (shRNA) against CUL4A (OAd-shCUL4A).

RESULTS

OAd-shCUL4 mediated higher levels of cytotoxic effects on various types of human tumor cell than a conventional OAd. Higher levels of OAd genome copy numbers were found in the tumor cells for OAd-shCUL4A, compared with a conventional OAd.

CONCLUSION

OAd-shCUL4A showed efficient antitumor effects by both enhancing OAd replication and inhibiting tumor cell growth.

DTL promotes cancer progression by PDCD4 ubiquitin-dependent degradation

Background

Ubiquitin E3 ligase CUL4A plays important oncogenic roles in the development of cancers. DTL, one of the CUL4-DDB1 associated factors (DCAFs), may involve in the process of cancer development. Programmed cell death 4 (PDCD4) is a tumor suppressor gene involved in cell apoptosis, transformation, invasion and tumor progression.

Methods

Affinity-purification mass spectrometry was used to identify potential DTL interaction proteins. Co-immunoprecipitation (Co-IP) was performed to verify protein interaction between DTL and PDCD4. mRNA levels in cancer cells and tissues were detected by Quantitative real-time PCR. Lentivirus was used to establish stable overexpression and knocking down cell lines for DTL and PDCD4. Transwell and wound healing assays were used to determine migration ability of cancer cells. Matrigel assay was used to determine invasion ability of cancer cells. MTT and colony formation assays were used to evaluate proliferation of cancer cells.

Results

In this study, programmed cell death 4 (PDCD4) was identified as a potential substrate of DTL. Co-IP and immunofluorescence assays further confirmed the interaction between DTL and PDCD4. Moreover, DTL overexpression decreased the protein level and accelerated the degradation rate of PDCD4. Through in vitro ubiquitination experiment, we proved that PDCD4 was degraded by DTL through ubiquitination. Clinically DTL was significantly up-regulated in cancer tissues than that in normal tissues. The survival curves showed that cancer patients with higher DTL expression owned lower survival rate. Functional experiments showed that DTL not only enhanced the proliferation and migration abilities of cancer cells, but also promoted the tumorigenesis in nude mice. Rescued experiment results demonstrated that silencing PDCD4 simultaneous with DTL recovered the phenotypes defect caused by DTL knocking down.

Conclusions

Our results elucidated that DTL enhanced the motility and proliferation of cancer cells through degrading PDCD4 to promote the development of cancers.

Electronic supplementary material

The online version of this article (10.1186/s13046-019-1358-x) contains supplementary material, which is available to authorized users.

The cullin4A is up-regulated in chronic obstructive pulmonary disease patient and contributes to epithelial-mesenchymal transition in small airway epithelium

Background

Chronic obstructive pulmonary disease (COPD) is a common respiratory disease with high morbidity and mortality. The most important pathophysiological change of COPD is airway obstruction. Airway obstruction can cause airflow restriction and obstructive ventilation dysfunction. Currently, many studies have shown that there is EMT phenomenon in the process of airway remodeling of COPD. Cullin4A (CUL4A) is an E3 ubiquitin ligase that interacts with other factors to form the E3 complex. Studies have shown that CLU4A is associated with EMT in non-small cell lung cancer and other cancers. However, its relationship with EMT in COPD has not been reported systematically. In this study, we detected the expression of CUL4A in lung epithelium of COPD patients. In addition, the regulatory effect and mechanism of CUL4A on EMT in COPD were clarified in small airway epithelial cells.

Methods

The expression of CUL4A was assessed by immunohistochemistry in lung epithelium specimens from smokers, non-smokers and patients with chronic obstructive pulmonary disease. The role of CUL4A on cigarette smoke extract (CSE)-induced epithelial-mesenchymal transition (EMT) in human small airway epithelial cells (HSAEpiCs) was assessed by silencing or overexpression CUL4A in vitro. Cigarette smoke is recognized as a high-risk factor in the induction of COPD, and its damage to the airway involves airway damage, airway inflammation and airway remodeling.

Results

The results shown that CUL4A expression in small airway epithelium was significantly increased in patients with COPD. We also observed a significant negative association between CUL4A and FEV₁%, a useful clinical marker for the diagnosis and evaluation of COPD severity, in small airway epithelial cells. In vitro, CSE-induced EMT is associated with high expression of CUL4A, and targeted silencing of CUL4A with shRNA inhibits CSE-induced EMT in human small airway epithelial cells.

Conclusions

Our results showed that CUL4A was overexpressed in lung epithelium of COPD patients, and CUL4A could regulate EMT of human small airway epithelium, which revealed a new mechanism of remodeling of small airway epithelium of COPD patients.

Electronic supplementary material

The online version of this article (10.1186/s12931-019-1048-4) contains supplementary material, which is available to authorized users.

Inflammation-dependent overexpression of c-Myc enhances CRL4DCAF4 E3 ligase activity and promotes ubiquitination of ST7 in colitis-associated cancer

Inflammation is well known as an important driver of the initiation of colitis-associated cancer (CAC). Some cytokines, such as IL-6 and TNF-α can activate expression of the oncogene c-Myc (MYC) and regulate its downstream effects. Cullin-RING E3 Ligases (CRLs) are emerging as master regulators controlling tumorigenesis. Here, we demonstrate that two cullin genes, CUL4A and CUL4B, but not other members, are specifically overexpressed in CAC tumour samples and positively correlate with levels of the proinflammatory cytokines IL-1β and IL-6. In vitro experiments revealed that the transcription factor c-Myc can specifically activate the expression of CUL4A and CUL4B by binding to a conserved site (CACGTG) located in their promoters. Additionally, we found that both CUL4A and CUL4B can form an E3 complex with DNA damage-binding protein 1 (DDB1) and DDB1-CUL4-associated factor 4 (DCAF4). In vitro and in vivo ubiquitination analyses indicate that CRL4^DCAF4 E3 ligase specifically directs degradation of ST7 (suppression of tumorigenicity 7). Overexpression of c-Myc in human colon epithelial cells resulted in the accumulation of CUL4A, CUL4B and DCAF4, but degradation of ST7. In contrast, knockdown of c-Myc, CUL4A or CUL4B in the colon adenocarcinoma cell line HT29 caused accumulation of ST7 and inhibition of cell proliferation, colony formation ability and in vivo tumour growth. Collectively, our results provide in vitro and in vivo evidence that c-Myc regulates CRL4^DCAF4 E3 ligase activity to mediate ubiquitination of ST7, whose presence is physiologically essential for CAC tumorigenesis. © 2019 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

A feedback regulation of CREB activation through the CUL4A and ERK signaling

CUL4A; an E3 ubiquitin ligase is involved in the degradation of negative regulators of cell cycle such as p21, p27, p53, etc., through polyubiquitination-mediated protein degradation. The functional role(s) of CUL4A proteins on their targets are well characterized; however, the transcriptional regulation of CUL4A, particularly at its promoter level is not yet studied. Therefore, in this study, using computational tools, we found cAMP responsive elements (CRE) at the locations of - 926 and - 764 with respect to transcription state site + 1 of CUL4A promoter. Hence, we investigated the role of CREB on the regulation of CUL4A transcription. Our chromatin immunoprecipitation (ChIP) data clearly showed increased levels of promoter occupancy of both CREB and pCREB on both CREs of CUL4A promoter. As expected, the expression of CUL4A increases and decreases upon the overexpression of and knocking down of CREB, respectively. Moreover, the inhibition of ERK pathway by U0126 not only reduces the CREB activation but also the CUL4A levels suggesting that CREB is the upstream activator of CUL4A transcription. The reduction of CUL4A levels upon the knocking down of CREB or by U0126 treatment increases the protein levels of CUL4A substrates such as p21 and p27. It is reported that CUL4A activates the ERK1/2 transcription and ERK1/2 pathway activates the CREB by phosphorylation. Based on our data and earlier findings, we report that CREB regulates the CUL4A levels positively which in turn activates the CREB through ERK1/2 pathway in the form of auto-regulatory looped mechanism.This suggests that CUL4A might be involved in proliferation of cancer cells by regulating the ERK1/2 and CREB signaling.

A Novel lncRNA, LINC00460, Affects Cell Proliferation and Apoptosis by Regulating KLF2 and CUL4A Expression in Colorectal Cancer

Emerging evidence has proven that long noncoding RNAs (lncRNAs) play important roles in human colorectal cancer (CRC) biology, although few lncRNAs have been characterized in CRC. Therefore, the functional significance of lncRNAs in the malignant progression of CRC still needs to be further explored. In this study, through analyzing TCGA RNA sequencing data and other publicly available microarray data, we found a novel lncRNA, LINC00460, whose expression was significantly upregulated in CRC tissues compared to adjacent normal tissues. Consistently, real-time qPCR results also verified that LINC00460 was overexpressed in CRC tissues and cells. Furthermore, high LINC00460 expression levels in CRC specimens were correlated with larger tumor size, advanced tumor stage, lymph node metastasis and shorter overall survival. In vitro and in vivo assays of LINC00460 alterations revealed a complex integrated phenotype affecting cell growth and apoptosis. Mechanistically, LINC00460 repressed Krüppel-like factor 2 (KLF2) transcription by binding to enhancer of zeste homolog 2 (EZH2). LINC00460 also functioned as a molecular sponge for miR-149-5p, antagonizing its ability to repress cullin 4A (CUL4A) protein translation. Taken together, our findings support a model in which the LINC00460/EZH2/KLF2 and LINC00460/miR-149-5p/CUL4A crosstalk serve as critical effectors in CRC tumorigenesis and progression, suggesting new therapeutic directions in CRC.

LncRNA H19 is a major mediator of doxorubicin chemoresistance in breast cancer cells through a cullin4A-MDR1 pathway

Development of chemoresistance is a persistent problem during cancer treatment. Long non-coding RNAs (LncRNAs) are currently emerging as an integral functional component of the human genome and as critical regulators of cancer development and progression. In the present study, we investigated the role and molecular mechanism of H19 lncRNA in chemoresistance development by using doxorubicin (Dox) resistance in breast cancer cells as a model system. H19 lncRNA expression was significantly increased in anthracycline-treated and Dox-resistant MCF-7 breast cancer cells. This H19 overexpression was contributed to cancer cell resistance to anthracyclines and paclitaxel as knockdown of H19 lncRNA by a specific H19 shRNA in Dox-resistant cells significantly improved the cell sensitivity to anthracyclines and paclitaxel. Furthermore, gene expression profiling analysis revealed that a total of 192 genes were associated with H19-mediated Dox resistance. These genes were enriched in multiple KEGG pathways that are related to chemoresistance. Using genetic and pharmacological approaches, we demonstrated that MDR1 and MRP4 were major effectors of H19-regulated Dox resistance in breast cancer cells as MDR1 and MRP4 expression was markedly elevated in Dox-resistant cells while dramatically reduced when H19 was knocked down. Moreover, we found that CUL4A, an ubiquitin ligase component, was a critical factor bridging H19 lncRNA to MDR1 expression, and a high tumor CUL4A expression was associated with low survival in breast cancer patients treated with chemotherapy. These data suggest that H19 lncRNA plays a leading role in breast cancer chemoresistance, mediated mainly through a H19-CUL4A-ABCB1/MDR1 pathway.

miR-181a-2 downregulates the E3 ubiquitin ligase CUL4A transcript and promotes cell proliferation

MiR-181a-2 plays a major role in cell proliferation both positively and negatively depending on tissue type by targeting several regulators 3'UTR regions. We have predicted several targets for miR-181a-2 through computational approaches and characterized one its interesting target, CUL4A, an E3 ubiquitin ligase. CUL4A regulates diverse functions in the cells including DNA repair, DNA replication, cell cycle, genomic stability through polyubiquitination of target proteins. Deregulation of both miR-181a-2 and CUL4A are reported in many cancerous cells, but the functional link between them is unknown. We show that miR-181a-5p binds to 3'UTR of CUL4A and regulates its transcripts levels in HEK293 cells through overexpression studies. In addition, by using MTT and Neutral red assays, we showed that miR-181a-2 overexpression increased the proliferation in HEK293 cells. Moreover, cell cycle analysis using flow cytometer revealed that an increase in S-phase cells upon the overexpression of miR-181a-2. Though several miRNAs are known to downregulate the CUL4A levels, here we show that miR-181a-2 also participates in the downregulation of CUL4A. Taken together, our data demonstrated that miR-181a-2 increases the cell proliferation in HEK293 cells possibly through the downregulation of CUL4A.

CUL4A overexpression as an independent adverse prognosticator in intrahepatic cholangiocarcinoma

BACKGROUND

CUL4A has been known for its oncogenic properties in various human cancers. However, its role in intrahepatic cholangiocarcinoma (iCCA) has not been explored.

METHODS

We retrospectively investigated 105 iCCA cases from a single medical institution. Tissue microarrays were used for immunohistochemical analysis of CUL4A expression. CUL4A expression vectors were introduced in cell lines. Cell migration and invasion assays were used to compare the mobility potential of iCCA cells under basal conditions and after manipulation. Then we evaluated the effects of CUL4A on the cell growth by proliferation assay, and further checked the susceptibility to cisplatin in iCCA cells with or without CUL4A overexpression.

RESULTS

CUL4A overexpression was detected in 34 cases (32.4%). Patients with CUL4A-overexpressing tumors exhibited shortened disease-free survival (mean, 27.7 versus 90.4 months; P = 0.011). In the multivariate analysis model, CUL4A overexpression was shown to be an independent unfavorable predictor for disease-free survival (P = 0.045). Moreover, stably transfected CUL4A-overexpressing iCCA cell lines displayed an increased mobility potential and enhanced cell growth without impact on susceptibility to cisplatin.

CONCLUSIONS

Our data demonstrate that overexpression of CUL4A plays an oncogenic role in iCCA and adversely affects disease-free survival. Thus, it may prove to be a powerful prognostic factor and a potential therapeutic target.

A novel lncRNA uc.134 represses hepatocellular carcinoma progression by inhibiting CUL4A-mediated ubiquitination of LATS1

BACKGROUND

Hepatocellular carcinoma (HCC) is one of the most common malignancies worldwide, and tumor recurrence and metastasis are major factors that contribute to the poor outcome of patients with HCC. Long noncoding RNAs (lncRNAs) are known to regulate different tumorigenic processes, and a growing body of evidence indicates that Hippo kinase signaling is inactivated in many cancers. However, the upstream lncRNA regulators of Hippo kinase signaling in HCC are poorly understood.

METHODS

Using a lncRNA microarray, we identified a novel lncRNA, uc.134, whose expression was significantly decreased in the highly aggressive HCC cell line HCCLM3 compared with MHCC97L cells. Furthermore, we evaluated uc.134 expression in clinical samples using in situ hybridization (ISH) and quantitative real-time polymerase chain reaction (qRT-PCR) analysis. The full-length transcript of uc.134 was confirmed using rapid amplification of cDNA ends (RACE) analyses. To investigate the biological function of uc.134, we performed gain-of-function and loss-of-function studies both in vitro and in vivo. The underlying mechanisms of uc.134 in HCC were investigated using RNA pulldown, RNA immunoprecipitation, ubiquitination assays, Western blotting, mRNA microarray analyses, and qRT-PCR analyses.

RESULTS

The ISH assay revealed that uc.134 expression was significantly decreased in 170 paraffin-embedded samples from patients with HCC compared with adjacent tissues and uc.134 expression directly correlated with patient prognosis. Furthermore, we defined a 1867-bp full-length transcript of uc.134 using 5'- and 3'-RACE analysis. The overexpression of uc.134 inhibited HCC cell proliferation, invasion, and metastasis in vitro and in vivo, whereas the knockdown of uc.134 produced the opposite results. Furthermore, we confirmed that uc.134 (1408-1867 nt) binds to CUL4A (592-759 aa region) and inhibits its nuclear export. Moreover, we demonstrated that uc.134 inhibits the CUL4A-mediated ubiquitination of LATS1 and increases YAP^S127 phosphorylation to silence the target genes of YAP. Finally, a positive correlation between uc.134, LATS1, and pYAP^S127 was confirmed in 90 paraffin-embedded samples by ISH and immunohistochemical staining.

CONCLUSIONS

Our study identifies that a novel lncRNA, uc.134, represses hepatocellular carcinoma progression by inhibiting the CUL4A-mediated ubiquitination of LATS1 and increasing YAP^S127 phosphorylation. The use of this lncRNA may offer a promising treatment approach by inhibiting YAP and activating Hippo kinase signaling.

CUL4A promotes cell invasion in gastric cancer by activating the NF-κB signaling pathway

Cullin 4A (CUL4A) overexpression has been reported to be involved in the carcinogenesis and progression of many malignant tumors. However, the role of CUL4A in the progression of gastric cancer (GC) remains unclear. In this study, we explored whether and how CUL4A regulates proinflammatory signaling to promote GC cell invasion. Our results showed that knockdown of CUL4A inhibited GC cell migration and invasion induced by lipopolysaccharide (LPS) stimulation. We also found that both CUL4A and nuclear factor-kappa B (NF-κB) protein expressions were enhanced by LPS stimulation in HGC27 GC cell lines. Furthermore, knockdown of CUL4A decreased the protein expression of NF-κB and mRNA expression of the downstream genes of the NF-κB pathway, such as matrix metalloproteinase (MMP) 2, MMP9, and interleukin-8. Our immunohistochemistry analysis on 50 GC tissue samples also revealed that CUL4A positively correlated with NF-κB expression. Taken together, our findings suggest that CUL4A may promote GC cell invasion by regulating the NF-κB signaling pathway and could be considered as a potential therapeutic target in patients with GC.

Jumonji domain containing 2C promotes cell migration and invasion through modulating CUL4A expression in lung cancer

Jumonji domain containing 2C (JMJD2C), also named as KDM4C, was found to a transcriptional cofactor and enzyme that catalyzes demethylation of histone H3 lysine 9 and 36. Here in this study, we found that the expression of JMJD2C increased in a majority of the human lung cancer tissues examined compared with adjacent tissues. Furthermore, the expression of JMJD2C was found to be higher in metastatic lung cancer tissues than which in non-metastatic lung cancer tissues. Knockdown of JMJD2C inhibited the ability of migration and invasion of lung cancer cells. Moreover, JMJD2C knockdown was proven to inhibit the tumor hepatic metastasis of lung cancer cells in vivo and epithelial-mesenchymal transition (EMT) in vitro. On the contrary, over-expression of JMJD2C was found to promote the ability of migration, invasion and EMT. As to mechanism, knockdown of JMJD2C was found to inhibit the expression of CUL4A while to promote the expression of p53 and p27. Furthermore, we found that JMJD2C regulated the activities of lung cancer cells by directly controlling the expression of CUL4A in JMJD2C over-expression cell line, and interference of CUL4A was found to reverse the ability of migration, invasion and EMT which JMJD2C over-expression bought to. Together, these results of this study not only enriched the JMJD2C biological function of lung cancer, but also illuminated exploring the prevention and treatment of the invasion and metastasis of lung cancer.

CUL4A promotes proliferation and metastasis of colorectal cancer cells by regulating H3K4 trimethylation in epithelial-mesenchymal transition

Increasing evidence suggests that CUL4A, a ubiquitin ligase, is involved in the promotion of cancer malignancy and correlated with worse clinical prognosis in several kinds of human cancers. Although its effect and mechanism on the progression of colorectal cancer (CRC) remain unknown. Our clinical data show that CUL4A protein is overexpressed, positively associated with lymph nodes status, differentiation degree, tumor size, and poor prognosis in 80 CRC patients. CUL4A overexpression promotes cell proliferation and colony formation of CRC cells. Knockdown of CUL4A inhibits cell proliferation and migration. CUL4A can significantly promote the in vitro migration of CRC cells via induction of the epithelial–mesenchymal transition process. And the modulation of CUL4A expression altered the level of H3K4 trimethylation at the E-cadherin, N-cadherin, and vimentin gene promoters, which in turn transcriptionally regulated their expression. Moreover, knockdown of CUL4A also decreased the tumor volume and tumor weight in vivo. Together, our results reveal that CUL4A plays as an oncogene in CRC and may become a potential therapeutic target in the treatment of colorectal cancer.

Identification of a tumor suppressor network in T-cell leukemia

To identify novel cancer-related genes targeted by copy number alterations, we performed genomic profiling of T-cell acute lymphoblastic leukemia (T-ALL) cell lines. In 3/8, we identified a shared deletion at chromosomal position 2p16.3-p21. Within the minimally deleted region, we recognized several candidate tumor suppressor (TS) genes, including FBXO11 and FOXN2. An additional deletion at chromosome 14q23.2-q32.11 included FOXN3, highlighting this class of FOX genes as potential TS. Quantitative expression analyses of FBXO11, FOXN2, and FOXN3 confirmed reduced transcript levels in the identified cell lines. Moreover, reduced expression of these genes was also observed in about 7% of T-ALL patients, showing their clinical relevance in this malignancy. Bioinformatic analyses revealed concurrent reduction of FOXN2 and/or FOXN3 together with homeobox gene ZHX1. Consistently, experiments demonstrated that both FOXN2 and FOXN3 directly activated transcription of ZHX1. Taken together, we identified novel TS genes forming a regulatory network in T-cell development and leukemogenesis.

Cullin 4A (CUL4A), a direct target of miR-9 and miR-137, promotes gastric cancer proliferation and invasion by regulating the Hippo signaling pathway

Although Cullin 4A (CUL4A) is mutated or amplified in several human cancer types, its role in gastric cancer (GC) and the mechanisms underlying its regulation remain largely uncharacterized. In the present study, we report that the expression of CUL4A significantly correlated with the clinical stage of the tumor and lymph node metastasis, and survival rates were lower in GC patients with higher levels of CUL4A than in patients with lower CUL4A levels. The upregulation of CUL4A promoted GC cell proliferation and epithelial-mesenchymal transition (EMT) by downregulating LATS1-Hippo-YAP signaling. Knocking down CUL4A had the opposite effect in vitro and in vivo. Interestingly, CUL4A expression was inhibited by the microRNAs (miRNAs), miR-9 and miR-137, which directly targeted the 3′-UTR of CUL4A. Overexpression of miR-9 and miR-137 downregulated the CUL4A-LATS1-Hippo signaling pathway and suppressed GC cell proliferation and invasion in vitro. Taken together, our findings demonstrate that perturbations to miR-9/137-CUL4A-Hippo signaling contribute to gastric tumorigenesis, and suggest potential therapeutic targets for the future treatment of GC.

CUL4A functions as an oncogene in ovarian cancer and is directly regulated by miR-494

Cullin 4A (CUL4A), as a well-defined oncogene, has been reported to be upregulated in ovarian cancer clinically. However, the biological functions of CUL4A and the molecular mechanism underlying its upregulation in ovarian cancer remains unknown throughly. Here, we show that expression of CUL4A is significantly higher in ovarian cancer tissues compared to corresponding non-cancerous tissues. Moreover, silencing of CUL4A by siRNA markedly inhibits cell proliferation, invasion and epithelial-mesenchymal transition (EMT). We identified CUL4A as a novel target gene of miR-494. Further investigations showed that miR-494 was remarkably downregulated and correlated with poor prognosis in ovarian cancer. Overexpression of miR-494 inhibited proliferation, migration, invasion and EMT of ovarian cancer cells by directly suppressing CUL4A expression. Therefore, our findings indicate that miR-494/CUL4A axis is important in the control of ovarian cancer tumorigenesis.

Aberrant Expression of CUL4A Is Associated with IL-6/ STAT3 Activation in Colorectal Cancer Progression

BACKGROUND AND AIMS

Although it has been indicated that the cytokine interleukin-6 (IL-6) promotes colorectal cancer (CRC) tumorigenesis in tumor microenvironment, the mechanisms related to IL-6-induced tumor progression are still not well understood.

METHODS

First, the correlation between pSTAT3, CUL4A and ZEB1 was analyzed using immunocytochemistry. Logistic regression analysis was then used to observe the relationship between levels of pSTAT3, CUL4A and ZEB1 and clinicopathological characteristics. Finally, the mechanism of the effect of the expression level of pSTAT3, CUL4A and ZEB1 on cell invasion ability was verified by cell experiment.

RESULTS

We discovered that the increased expression levels of pSTAT3, CUL4A and ZEB1 had significant relationships in CRC patients. These up-regulated expression levels were also closely associated with CRC aggressiveness. Furthermore, in vitro, we discovered that expression levels of CUL4A and ZEB1 were significantly up-regulated when IL-6 stimulated. However, the CUL4A-knockdown, IL-6, could not induce expression of ZEB1. CHIP assay authenticated that pSTAT3 could bind to CUL4A promoter and worked as their transcription factors. We also demonstrated that IL-6 markedly increased the reporter activity using a luciferase reporter gene containing CUL4A promoter. Finally, silencing CUL4A blocked IL-6-driven invasion in matrigel invasion assay.

CONCLUSION

This study proposed that CUL4A played an oncogene role through ZEB1 in IL-6-induced colorectal carcinoma progression.

Distinct and overlapping functions of the cullin E3 ligase scaffolding proteins CUL4A and CUL4B

The cullin 4 subfamily of genes includes CUL4A and CUL4B, which share a mostly identical amino acid sequence aside from the elongated N-terminal region in CUL4B. Both act as scaffolding proteins for modular cullin RING ligase 4 (CRL4) complexes which promote the ubiquitination of a variety of substrates. CRL4 function is vital to cells as loss of both genes or their shared substrate adaptor protein DDB1 halts proliferation and eventually leads to cell death. Due to their high structural similarity, CUL4A and CUL4B share a substantial overlap in function. However, in some cases, differences in subcellular localization, spatiotemporal expression patterns and stress-inducibility preclude functional compensation. In this review, we highlight the most essential functions of the CUL4 genes in: DNA repair and replication, chromatin-remodeling, cell cycle regulation, embryogenesis, hematopoiesis and spermatogenesis. CUL4 genes are also clinically relevant as dysregulation can contribute to the onset of cancer and CRL4 complexes are often hijacked by certain viruses to promote viral replication and survival. Also, mutations in CUL4B have been implicated in a subset of patients suffering from syndromic X-linked intellectual disability (AKA mental retardation). Interestingly, the antitumor effects of immunomodulatory drugs are caused by their binding to the CRL4CRBN complex and re-directing the E3 ligase towards the Ikaros transcription factors IKZF1 and IKZF3. Because of their influence over key cellular functions and relevance to human disease, CRL4s are considered promising targets for therapeutic intervention.

Knockdown of CUL4A inhibits invasion and induces apoptosis in osteosarcoma cells

Cullin4A (CUL4A) is implicated in many cellular events including cell survival and growth. However, the specific function and underlying mechanisms of CUL4A in cancer invasion have not yet been elucidated. In this work, we were focused on investigating the role of CUL4A in human osteosarcoma (OS). The expression level of CUL4A was evaluated by immunohistochemical (IHC) assay in human OS tissues. Lentivirus-mediated CUL4A shRNA (Lv-shCUL4A) constructed by us was transfected into OS cells for assessing its effects on cell proliferation and invasive potential, respectively detected by MTT and Transwell assays. It was demonstrated that the expression of CUL4A protein was markedly increased in OS tissues compared with the adjacent non-cancerous tissues (ANCT) (57.8% vs. 25.6%, P = 0.019), and was associated with the distant metastases in OS patients (P = 0.016). In vitro, silencing of CUL4A gene inhibited OS cell proliferation and invasion, and induced cell apoptosis, followed by increased expression of p27 and p53 and decreased expression of MMP-2. Therefore, these findings indicate that elevated expression of CUL4A is positively correlated with distant metastases in OS patients, and knockdown of CUL4A suppresses invasion and induces apoptosis in OS cells, suggesting that CUL4A may serve as a potential target for the treatment of OS.

Clinical significance of CUL4A in human prostate cancer

Aberrant expression of the Cullin 4A (CUL4A) is found in many tumor types, but the functions and mechanism of CUL4A in prostate cancer (PCa) development and progression remain largely unknown. The aim of this study was to investigate the possible role of CUL4A in prostate tumorigenesis. Immunohistochemistry was used to examine CUL4A expression in human PCa tissues and BPH tissues. Cell proliferation was assessed by MTT, and migration and invasion were analyzed by Transwell and Matrigel assays after CUL4A knockdown in PCa in vitro. The results showed that CUL4A protein was overexpressed in 86.21 % of PCa tissues. CUL4A knockdown with siRNA in PCa cells decreased cell proliferation, migration, and invasion. Mechanistically, CUL4A could modulate the expression of P53 in PCa cells. Our results indicate that CUL4A overexpression play an oncogenic role in the pathogenesis of PCa, and CUL4A may be a potential therapeutic target for PCa.

CUL4A ubiquitin ligase: a promising drug target for cancer and other human diseases

The ability of cullin 4A (CUL4A), a scaffold protein, to recruit a repertoire of substrate adaptors allows it to assemble into distinct E3 ligase complexes to mediate turnover of key regulatory proteins. In the past decade, a considerable wealth of information has been generated regarding its biology, regulation, assembly, molecular architecture and novel functions. Importantly, unravelling of its association with multiple tumours and modulation by viral proteins establishes it as one of the key proteins that may play an important role in cellular transformation. Considering the role of its substrate in regulating the cell cycle and maintenance of genomic stability, understanding the detailed aspects of these processes will have significant consequences for the treatment of cancer and related diseases. This review is an effort to provide a broad overview of this multifaceted ubiquitin ligase and addresses its critical role in regulation of important biological processes. More importantly, its tremendous potential to be exploited for therapeutic purposes has been discussed.

Pathogenic Role of the CRL4 Ubiquitin Ligase in Human Disease

The cullin 4-RING ubiquitin ligase (CRL4) family employs multiple DDB1–CUL4 associated factors substrate receptors to direct the degradation of proteins involved in a wide spectrum of cellular functions. Aberrant expression of the cullin 4A (CUL4A) gene is found in many tumor types, while mutations of the cullin 4B (CUL4B) gene are causally associated with human X-linked mental retardation. This focused review will summarize our current knowledge of the two CUL4 family members in the pathogenesis of human malignancy and neuronal disease, and discuss their potential as new targets for cancer prevention and therapeutic intervention.