The stress phenotype makes cancer cells addicted to CDT2, a substrate receptor of the CRL4 ubiquitin ligase

Identification of DTL as Related Biomarker and Immune Infiltration Characteristics of Nasopharyngeal Carcinoma via Comprehensive Strategies

Purpose

Although considerable progress has been made in basic and clinical research on nasopharyngeal carcinoma (NPC), the biomarkers of the progression of NPC have not been fully studied and described. This study was designed to identify potential novel biomarkers for NPC using integrated analyses and explore the immune cell infiltration in this pathological process.

Methods

Five GEO data sets were downloaded from gene expression omnibus database (GEO) and analysed to identify differentially expressed genes (DEGs), followed by Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses. The four algorithms were adopted for screening of novel and key biomarkers for NPC, including random forest (RF) machine learning algorithm, least absolute shrinkage and selection operator (LASSO) logistic regression, support vector machine-recursive feature elimination (SVM-RFE), and weighted gene co-expression network analysis (WGCNA). Lastly, CIBERSORT was used to assess the infiltration of immune cells in NPC, and the correlation between diagnostic markers and infiltrating immune cells was analyzed.

Results

Herein, we identified 46 DEGs, and enrichment analysis results showed that DEGs and several kinds of signaling pathways might be closely associated with the occurrence and progression of NPC. DTL was recognized as NPC-related biomarker. DTL, also known as retinoic acid-regulated nuclear matrix-associated protein (RAMP), or DNA replication factor 2 (CDT2), is reported to be correlated with the cell proliferation, cell cycle arrest and cell invasion in hepatocellular carcinoma, breast cancer and gastric cancer. Immune infiltration analysis demonstrated that macrophages M0, macrophages M1 and T cells CD4 memory activated were linked to pathogenesis of NPC.

Conclusion

In summary, we adopted a comprehensive strategy to screen DTL as biomarkers related to NPC and explore the critical role of immune cell infiltration in NPC.

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.

DDB2 regulates DNA replication through PCNA-independent degradation of CDT2

Background

Targeting ubiquitin-dependent proteolysis is one of the strategies in cancer therapy. CRL^CDT2 and CRL^DDB2 are two key E3 ubiquitin ligases involved in DNA replication and DNA damage repair. But CDT2 and DDB2 are opposite prognostic factors in kinds of cancers, and the underlining mechanism needs to be elucidated.

Methods

Small interfering RNAs were used to determine the function of target genes. Co-immunoprecipitation (Co-IP) was performed to detect the interaction between DDB2 and CDT2. Immunofluorescence assays and fluorescence activating cell sorting (FACS) were used to measure the change of DNA content. In vivo ubiquitination assay was carried out to clarify the ubiquitination of CDT2 mediated by DDB2. Cell synchronization was performed to arrest cells at G1/S and S phase. The mechanism involved in DDB2-mediated CDT2 degradation was investigated by constructing plasmids with mutant variants and measured by Western blot. Immunohistochemistry was performed to determine the relationship between DDB2 and CDT2. Paired two-side Student’s t-test was used to measure the significance of the difference between control group and experimental group.

Results

Knockdown of DDB2 stabilized CDT2, while over-expression of DDB2 enhanced ubiquitination of CDT2, and subsequentially degradation of CDT2. Although both DDB2 and CDT2 contain PIP (PCNA-interacting protein) box, PIP box is dispensable for DDB2-mediated CDT2 degradation. Knockdown of PCNA had negligible effects on the stability of CDT2, but promoted accumulation of CDT1, p21 and SET8. Silencing of DDB2 arrested cell cycle in G1 phase, destabilized CDT1 and reduced the chromatin loading of MCMs, thereby blocked the formation of polyploidy induced by ablation of CDT2. In breast cancer and ovarian teratoma tissues, high level of DDB2 was along with lower level of CDT2.

Conclusions

We found that CRL4^DDB2 is the novel E3 ubiquitin ligases of CDT2, and DDB2 regulates DNA replication through indirectly regulates CDT1 protein stability by degrading CDT2 and promotes the assembly of pre-replication complex. Our results broaden the horizon for understanding the opposite function of CDT2 and DDB2 in tumorigenesis, and may provide clues for drug discovery in cancer therapy.

Human umbilical vein endothelial cells-derived microRNA-203-containing extracellular vesicles alleviate non-small-cell lung cancer progression through modulating the DTL/p21 axis

Non-small cell lung cancer (NSCLC) is the most common type of lung cancer, and is characterized by extensive metastasis and poor prognosis. Extracellular vesicles (EVs) derived from endothelial cells carrying microRNAs (miRNAs/miRs) have diagnostic and therapeutic potential for NSCLC. We herein investigate the potential of EVs derived from human umbilical vein endothelial cells (HUVECs) to transfer miR-203 to affect the progression of NSCLC. miR-203 and p21 were poorly expressed while DTL was highly expressed both in NSCLC tissues and cell lines. We employed CCK-8 proliferation, colony formation, and Transwell migration and invasion assays to evaluate the effects of miR-203 on NSCLC cell behaviors using loss- and gain-function approaches. EVs were isolated from HUVECs and then co-cultured with the A549 cells transfected with mimic-NC or miR-203 inhibitor. miR-203 targeted DTL and downregulated its expression, subsequently leading to increased stability of p21 which is a tumor suppressor. EV-enriched miR-203 from HUVECs suppressed malignant phenotypes of NSCLC cells and delayed tumor growth. In conclusion, miR-203 from HUVEC-derived EVs exerts inhibitory effects on the progression of NSCLC by targeting DTL and promoting p21 protein stability.

The Identification of Potential Therapeutic Targets for Cutaneous Squamous Cell Carcinoma

We performed a small interfering RNA screen to identify targets for cutaneous squamous cell carcinoma (cSCC) therapy in the ubiquitin/ubiquitin-like system. We provide evidence for selective anti-cSCC activity of knockdown of the E3 ubiquitin ligase MARCH4, the ATPase p97/VCP, the deubiquitinating enzyme USP8, the cullin-RING ligase (CRL) 4 substrate receptor CDT2/DTL, and components of the anaphase-promoting complex/cyclosome (APC/C). Specifically attenuating CRL4^CDT2 by CDT2 knockdown can be more potent in killing cSCC cells than targeting CRLs or CRL4s in general by RBX1 or DDB1 depletion. Suppression of the APC/C or forced APC/C activation by targeting its repressor EMI1 are both potential therapeutic approaches. We observed that cSCC cells can be selectively killed by small-molecule inhibitors of USP8 (DUBs-IN-3/compound 22c) and the NEDD8 E1 activating enzyme/CRLs (MLN4924/pevonedistat). A substantial proportion of cSCC cell lines are very highly MLN4924-sensitive. Pathways that respond to defects in proteostasis are involved in the anti-cSCC activity of p97 suppression. Targeting USP8 can reduce the expression of growth factor receptors that participate in cSCC development. EMI1 and CDT2 depletion can selectively cause DNA re-replication and DNA damage in cSCC cells.

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.

Identification of hyper-rewired genomic stress non-oncogene addiction genes across 15 cancer types

Non-oncogene addiction (NOA) genes are essential for supporting the stress-burdened phenotype of tumours and thus vital for their survival. Although NOA genes are acknowledged to be potential drug targets, there has been no large-scale attempt to identify and characterise them as a group across cancer types. Here we provide the first method for the identification of conditional NOA genes and their rewired neighbours using a systems approach. Using copy number data and expression profiles from The Cancer Genome Atlas (TCGA) we performed comparative analyses between high and low genomic stress tumours for 15 cancer types. We identified 101 condition-specific differential coexpression modules, mapped to a high-confidence human interactome, comprising 133 candidate NOA rewiring hub genes. We observe that most modules lose coexpression in the high-stress state and that activated stress modules and hubs take part in homoeostasis maintenance processes such as chromosome segregation, oxireductase activity, mitotic checkpoint (PLK1 signalling), DNA replication initiation and synaptic signalling. We furthermore show that candidate NOA rewiring hubs are unique for each cancer type, but that their respective rewired neighbour genes largely are shared across cancer types.

A DNA-binding domain in the C-terminal region of Cdt2 enhances the DNA synthesis-coupled CRL4Cdt2 ubiquitin ligase activity for Cdt1

The Cullin-RING ubiquitin ligase CRL4Cdt2 maintains genome integrity by mediating the cell cycle- and DNA damage-dependent degradation of proteins such as Cdt1, p21 and Set8. Human Cdt2 has two regions, a conserved N-terminal seven WD40 repeat region and a less conserved C-terminal region. Here, we showed that the N-terminal region is sufficient for complex formation with CRL4, but the C-terminal region is required for the full ubiquitin ligase activity. UV irradiation-induced polyubiquitination and degradation of Cdt1 were impaired in Cdt2 (N-terminus only)-expressing cells. Deletion and mutation analysis identified a domain in the C-terminal region that increased ubiquitination activity and displayed DNA-binding activity. The identified domain mediated binding to double-stranded DNA and showed higher affinity binding to single-stranded DNA. As the ligase activity of CRL4Cdt2 depends on proliferating cell nuclear antigen (PCNA) loading onto DNA, the present results suggest that the DNA-binding domain facilitates the CRL4Cdt2-mediated recognition and ubiquitination of substrates bound to PCNA on chromatin.

Identification of a functional polymorphism within the 3'-untranslated region of denticleless E3 ubiquitin protein ligase homolog associated with survival in acral melanoma

BACKGROUND

High expression of denticleless E3 ubiquitin protein ligase homologue (DTL) correlates with poor disease-free survival and overall survival in cutaneous melanoma, but the molecular features and clinical significance of this gene in acral melanoma (AM) remain unclear.

METHODS

The expression levels of DTL were compared between AM and benign melanocytic nevi using existing Gene Expression Omnibus data and validated in fresh frozen tissues. Two candidate tag single-nucleotide polymorphisms (SNPs) in the 3'-untranslated region (3'UTR) of DTL in patients with AM were sequenced and analysed for their association with survival in a discovery cohort (n = 570), and the significant SNP was subjected to a replication cohort (n = 201). The expression of DTL was evaluated by immunohistochemistry. The microRNA interacting with rs11275300:C > G was predicted using in silico target prediction tools and validated by in vitro analysis.

RESULTS

DTL was overexpressed in AM compared with benign melanocytic nevi. rs11275300:C > G was found to be significantly associated with progression-free survival and overall survival of patients with AM in both cohorts and the combined cohort. Furthermore, the DTL expression level in the patients with the rs11275300:G allele was higher than that in patients with the CC genotype. In vitro analysis demonstrated that DTL was a direct target of hsa-miR-4672, and the rs11275300:G allele interfered with the binding affinity of hsa-miR-4672 with the 3'UTR of DTL and thereby increased DTL expression.

CONCLUSION

The rs11275300:G allele in the 3'UTR of DTL may lead to a poor prognosis and allele-specific increase in the expression of DTL by post-transcriptional regulation in AM.

Correlation of xeroderma pigmentosum complementation group F expression with gastric cancer and prognosis

Correlation of xeroderma pigmentosum complementation group F (XPF) expression with gastric cancer and prognosis was investigated. We randomly selected 76 gastric cancer patients who were admitted to the Second People's Hospital of Dezhou City and received treatment, and detected XPF expression in gastric cancer tissues (observation group) and normal gastric mucosa adjacent to tumor (control group) via immunohistochemistry. Correlation between XPF expression and clinicopathological indicators of gastric cancer was verified via single-factor Chi-square test. Cox's proportional hazard regression model was used in the analysis of influencing factors of patient's prognosis, and Kaplan-Meier was used to analyze the survival rates of XPF-positive and -negative patients. In the observation group, the XPF-positive rate was significantly higher than that in the control group with a statistically significant difference (P<0.05). Single-factor analysis showed that XPF expression was correlated with the family history and Laurén classification (P<0.05). Kaplan-Meier survival analysis revealed that the survival time of XPF-positive patients was shorter than that of XPF-negative patients (P<0.05). Multifactorial analysis using Cox's hazards model suggested that XPF was an independent factor affecting the prognosis of gastric cancer (P<0.05). In conclusion, XPF expression plays an important role in the occurrence and development of gastric cancer, and a high expression of XPF suggests a poor prognosis of gastric cancer patients.

Targeting DTL induces cell cycle arrest and senescence and suppresses cell growth and colony formation through TPX2 inhibition in human hepatocellular carcinoma cells

Background

Hepatocellular carcinoma (HCC) has an increasing incidence and high mortality. Surgical operation is not a comprehensive strategy for liver cancer. Moreover, tolerating systemic chemotherapy is difficult for patients with HCC because hepatic function is often impaired due to underlying cirrhosis. Therefore, a comprehensive strategy for cancer treatment should be developed. DTL (Cdc10-dependent transcript 2) is a critical regulator of cell cycle progression and genomic stability. In our previous study, the upregulation of DTL expression in aggressive HCC correlated positively with tumor grade and poor patient survival. We hypothesize that targeting DTL may provide a novel therapeutic strategy for liver cancer. DTL small interference RNAs were used to knock down DTL protein expression.

Methods

A clonogenic assay, immunostaining, double thymidine block, imaging flow cytometry analysis, and a tumor spheroid formation assay were used to analyze the role of DTL in tumor cell growth, cell cycle progression, micronucleation, ploidy, and tumorigenicity.

Results

Our results demonstrated that targeting DTL reduced cell cycle regulators and chromosome segregation genes, resulting in increased cell micronucleation. DTL depletion inhibited liver cancer cell growth, increased senescence, and reduced tumorigenesis. DTL depletion resulted in the disruption of the mitotic proteins cyclin B, CDK1, securin, seprase, Aurora A, and Aurora B as well as the upregulation of the cell cycle arrest gene p21. A rescue assay indicated that DTL should be targeted through TPX2 downregulation for cancer cell growth inhibition. Moreover, DTL silencing inhibited the growth of patient-derived primary cultured HCC cells.

Conclusion

Our study results indicate that DTL is a potential novel target gene for treating liver cancer through liver cancer cell senescence induction. Furthermore, our results provide insights into molecular mechanisms for targeting DTL in liver cancer cells. The results also indicate several other starting points for future preclinical and clinical studies on liver cancer treatment.

MLN4924 suppresses neddylation and induces cell cycle arrest, senescence, and apoptosis in human osteosarcoma

Neddylation is a post-translational protein modification process associated with carcinogenesis and cancer development. MLN4924, a pharmaceutical neddylation inhibitor, induces potent anti-cancer effects in multiple types of cancers. In this study, we investigated the effects of MLN4924 on human osteosarcoma (OS). Levels of both NEDD8 activating enzyme E1 (NAE1) and ubiquitin-conjugating enzyme E2M (Ube2M), two critical components of the neddylation pathway, were much higher in OS tissues and cells than in normal osseous tissues and cells. MLN4924 treatment led to DNA damage, reduced cell viability, senescence and apoptosis in OS cells. Moreover, MLN4924 inhibited OS xenograft tumor growth in mice. Mechanistically, MLN4924 blocked the neddylation of cullins and induced accumulation of several tumor-suppressive substrates of Cullin-RING E3 ubiquitin ligases (CRLs), including CDT1, Wee1, p21, p27, Noxa, and p16. These results suggest clinical studies investigating the utility of MLN4924 for the treatment of OS are warranted.

Integrative analysis of multi-omics data reveals distinct impacts of DDB1-CUL4 associated factors in human lung adenocarcinomas

Many DDB1-CUL4 associated factors (DCAFs) have been identified and serve as substrate receptors. Although the oncogenic role of CUL4A has been well established, specific DCAFs involved in cancer development remain largely unknown. Here we infer the potential impact of 19 well-defined DCAFs in human lung adenocarcinomas (LuADCs) using integrative omics analyses, and discover that mRNA levels of DTL, DCAF4, 12 and 13 are consistently elevated whereas VBRBP is reduced in LuADCs compared to normal lung tissues. The transcriptional levels of DCAFs are significantly correlated with their gene copy number variations. SKIP2, DTL, DCAF6, 7, 8, 13 and 17 are frequently gained whereas VPRBP, PHIP, DCAF10, 12 and 15 are frequently lost. We find that only transcriptional level of DTL is robustly, significantly and negatively correlated with overall survival across independent datasets. Moreover, DTL-correlated genes are enriched in cell cycle and DNA repair pathways. We also identified that the levels of 25 proteins were significantly associated with DTL overexpression in LuADCs, which include significant decreases in protein level of the tumor supressor genes such as PDCD4, NKX2-1 and PRKAA1. Our results suggest that different CUL4-DCAF axis plays the distinct roles in LuADC development with possible relevance for therapeutic target development.

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.

Inactivation of the CRL4-CDT2-SET8/p21 ubiquitylation and degradation axis underlies the therapeutic efficacy of pevonedistat in melanoma

The cullin-based CRL4-CDT2 ubiquitin ligase is emerging as a master regulator of cell proliferation. CRL4-CDT2 prevents re-initiation of DNA replication during the same cell cycle "rereplication" through targeted degradation of CDT1, SET8 and p21 during S-phase of the cell cycle. We show that CDT2 is overexpressed in cutaneous melanoma and predicts poor overall and disease-free survival. CDT2 ablation inhibited a panel of melanoma cell lines through the induction of SET8- and p21-dependent DNA rereplication and senescence. Pevonedistat (MLN4924), a specific inhibitor of the NEDD8 activating enzyme (NAE), inhibits the activity of cullin E3 ligases, thereby stabilizing a vast number of cullin substrates and resulting in cancer cell inhibition in vitro and tumor suppression in nude mice. We demonstrate that pevonedistat is effective at inhibiting the proliferation of melanoma cell lines in vitro through the induction of rereplication-dependent permanent growth arrest as well as through a transient, non-rereplication-dependent mechanism. CRISPR/Cas9-mediated heterozygous deletion of CDKN1A (encoding p21) or SET8 in melanoma cells demonstrated that the rereplication-mediated cytotoxicity of pevonedistat is mediated through preventing the degradation of p21 and SET8 and is essential for melanoma suppression in nude mice. By contrast, pevonedistat-induced transient growth suppression was independent of p21 or SET8, and insufficient to inhibit tumor growth in vivo. Pevonedistat additionally synergized with the BRAF kinase inhibitor PLX4720 to inhibit BRAF melanoma, and suppressed PLX4720-resistant melanoma cells. These findings demonstrate that the CRL4-CDT2-SET8/p21 degradation axis is the primary target of inhibition by pevonedistat in melanoma and suggest that a broad patient population may benefit from pevonedistat therapy.

RESEARCH IN CONTEXT

The identification of new molecular targets and effective inhibitors is of utmost significance for the clinical management of melanoma. This study identifies CDT2, a substrate receptor for the CRL4 ubiquitin ligase, as a prognostic marker and therapeutic target in melanoma. CDT2 is required for melanoma cell proliferation and inhibition of CRL4(CDT2) by pevonedistat suppresses melanoma in vitro and in vivo through the induction of DNA rereplication and senescence through the stabilization of the CRL4(CDT2) substrates p21 and SET8. Pevonedistat also synergizes with vemurafenib in vivo and suppresses vemurafenib-resistant melanoma cells. These findings show a significant promise for targeting CRL4(CDT2) therapeutically.

The Multifunctions of WD40 Proteins in Genome Integrity and Cell Cycle Progression

Eukaryotic genome encodes numerous WD40 repeat proteins, which generally function as platforms of protein-protein interactions and are involved in numerous biological process, such as signal transduction, gene transcriptional regulation, protein modifications, cytoskeleton assembly, vesicular trafficking, DNA damage and repair, cell death and cell cycle progression. Among these diverse functions, genome integrity maintenance and cell cycle progression are extremely important as deregulation of them is clinically linked to uncontrolled proliferative diseases such as cancer. Thus, we mainly summarize and discuss the recent understanding of WD40 proteins and their molecular mechanisms linked to genome stability and cell cycle progression in this review, thereby demonstrating their pervasiveness and importance in cellular networks.