UBR5 promotes cell proliferation and inhibits apoptosis in colon cancer by destablizing P21

Research advancements on the involvement of E3 ubiquitin ligase UBR5 in gastrointestinal cancers

E3 ubiquitin ligases comprise a family of ubiquitination-catalyzing enzymes that have been extensively researched and are considered crucial components of the ubiquitin-proteasome system involved in various diseases. The ubiquitin-protein ligase E3 component n-recognition 5 (UBR5) is an E3 ubiquitin-protein ligase that has garnered considerable interest of late. Recent studies demonstrate that UBR5 undergoes high-frequency mutations, chromosomal amplification, and/or abnormalities during expression of various malignant tumors. These alterations correlate with the biological behaviors and prognoses of malignancies, such as tumor invasion, metastasis, and resistance to chemotherapeutic agents. This study aimed to comprehensively elucidate the biological functions of UBR5, and its role and relevance in the context of gastrointestinal cancers. Furthermore, this article expounds a scientific basis to explore the molecular mechanisms underlying gastrointestinal cancers and developing targeted therapeutic strategies for their remediation.

Roles of transducin-like enhancer of split (TLE) family proteins in tumorigenesis and immune regulation

Mammalian transducin-like enhancer of split family proteins (TLEs) are homologous to Drosophila Groucho (Gro) and are essential transcriptional repressors. Seven TLE family members, TLE1-7, have been identified to date. These proteins do not bind DNA directly; instead, they bind a set of transcription factors and thereby inhibit target gene expression. Loss of TLEs in mice usually leads to defective early development; however, TLE functions in developmentally mature cells are unclear. Recent studies have revealed that TLEs are dysregulated in certain human cancer types and may function as oncogenes or tumor suppressors in different contexts. TLE levels also affect the efficacy of cancer treatments and the development of drug resistance. In addition, TLEs play critical roles in the development and function of immune cells, including macrophages and lymphocytes. In this review, we provide updates on the expression, function, and mechanism of TLEs; discuss the roles played by TLEs in tumorigenesis and the inflammatory response; and elaborate on several TLE-associated signaling pathways, including the Notch, Wnt, and MAPK pathways. Finally, we discuss potential strategies for targeting TLEs in cancer therapy.

UBR5 promotes tumor immune evasion through enhancing IFN-γ-induced PDL1 transcription in triple negative breast cancer

Background: The up-regulation of PD-L1 is recognized as an adaption of cancer cells to evade immune surveillance and attack. However, the intrinsic mechanisms of the induction of PD-L1 by interferon-γ (IFN-γ) in tumor microenvironment remain incompletely characterized. Ubiquitin ligase E3 component N-recognition protein 5 (UBR5) has a critical role in tumorigenesis of triple negative breast cancer (TNBC) by triggering specific immune responses to the tumor. Dual targeting of UBR5 and PD-L1 exhibited superior therapeutic benefits in a preclinical TNBC model in short term. Methods: The regulation of UBR5 to PD-L1 upon IFN-γ stimulation was evaluated through in UBR5 deficiency, reconstitution or overexpression cell line models by quantitative PCR, immunohistochemistry and RNA-seq. The effects of PD-L1 regulation by UBR5 and double blockade of both genes were evaluated in mouse TNBC model. Luciferase reporter assay, chromatin immunoprecipitation-qPCR and bioinformatics analysis were performed to explore the transcription factors involved in the regulation of UBR5 to PD-L1. Results: E3 ubiquitin ligase UBR5 plays a key role in IFN-γ-induced PDL1 transcription in TNBC in an E3 ubiquitination activity-independent manner. RNA-seq-based transcriptomic analyses reveal that UBR5 globally affects the genes in the IFN-γ-induced signaling pathway. Through its poly adenylate binding (PABC) domain, UBR5 enhances the transactivation of PDL1 by upregulating protein kinase RNA-activated (PKR), and PKR's downstream factors including signal transducers and activators of transcription 1 (STAT1) and interferon regulatory factor 1 (IRF1). Restoration of PD-L1 expression in UBR5-deficient tumor cells recoups their malignancy in vivo, whereas CRISPR/Cas9-mediated simultaneous abrogation of UBR5 and PD-L1 expression yields synergistic therapeutic benefits than either blockade alone, with a strong impact on the tumor microenvironment. Conclusions: This study identifies a novel regulator of PDL1 transcription, elucidates the underlying molecular mechanisms and provides a strong rationale for combination cancer immunotherapies targeting UBR5 and PD-L1.

MicroRNA-361-5p slows down gliomas development through regulating UBR5 to elevate ATMIN protein expression

MicroRNA (miR)-361-5p has been studied to suppress gliomas development. Based on that, an insight into the regulatory mechanism of miR-361-5p in gliomas was supplemented from ubiquitin protein ligase E3 component N-recognin 5 (UBR5)-mediated ubiquitination of ataxia-telangiectasia mutated interactor (ATMIN). miR-361-5p, ATMIN, and UBR5 levels were clinically analyzed in gliomas tissues, which were further validated in gliomas cell lines. Loss/gain-of-function method was applied to determine the roles of miR-361-5p and UBR5 in gliomas, as to cell viability, migration, invasion, colony formation ability, and apoptosis in vitro and tumorigenesis in vivo. The relationship between miR-361-5p and UBR5 was verified and the interaction between UBR5 and ATMIN was explored. It was detected that reduced miR-361-5p and ATMIN and enhanced UBR5 levels showed in gliomas. Elevating miR-361-5p was repressive in gliomas progression. UBR5 was directly targeted by miR-361-5p. UBR5 can ubiquitinate ATMIN. miR-361-5p suppressed gliomas by regulating UBR5-mediated ubiquitination of ATMIN. Downregulating UBR5 impeded gliomas tumor growth in vivo. Upregulating miR-361-5p targets UBR5 to promote ATMIN protein expression, thus to recline the malignant phenotype of gliomas cells.

Combining UBR5 and CD163+ tumor-associated macrophages better predicts prognosis of clear cell renal cell carcinoma patients

PURPOSE

Identification of reliable postoperative indicators for accurately evaluating prognosis of clear cell renal cell carcinoma (ccRCC) patients remains an important clinical issue. This study determined the prognostic value of UBR5 expression in ccRCC patients by combining with CD163⁺ tumor-associated macrophages (TAMs) and the established clinical parameters.

METHODS

The expression of UBR5 was analyzed in ccRCC patients from TCGA databases. A total of 310 ccRCC patients were randomly divided into the training and validation cohorts at a 3:2 or 1:1 ratio, and immunohistochemistry (IHC) and statistical analyses were performed to examine the prognostic value of UBR5 and CD163⁺ TAMs.

RESULTS

UBR5 expression was commonly downregulated in human ccRCC specimens, which was associated with TNM stage, SSIGN, WHO/ISUP Grading and poor prognosis of ccRCC patients. In addition, UBR5 expression was negatively correlated with CD163 expression (a TAM marker) in ccRCC tissues, and combining expressions of UBR5 and CD163 better predicted worse overall survival and progression-free survival of ccRCC patients. Even after multivariable adjustment, UBR5, CD163, TNM stage and SSIGN appeared to be independent risk factors. By time-dependent c-index analysis, the integration of intratumoral UBR5 and CD163 achieved higher c-index value than UBR5, CD163, TNM stage or SSIGN alone in predicting ccRCC patients' prognosis. Moreover, the incorporation of both UBR5 and CD163 into the clinical indicators TNM stage or SSIGN exhibited highest c-index value.

CONCLUSIONS

Integrating intratumoral UBR5 and CD163⁺ TAMs with the current clinical parameters achieves better accuracy in predicting ccRCC patients' postoperative prognosis.

The E3 ubiquitin ligase UBR5 interacts with TTC7A and may be associated with very early onset inflammatory bowel disease

Very early onset inflammatory bowel disease (VEOIBD) denotes children with onset of IBD before six years of age. A number of monogenic disorders are associated with VEOIBD including tetratricopeptide repeat domain 7A (TTC7A) deficiency. TTC7A-deficiency is characterized by apoptotic colitis in milder cases with severe intestinal atresia and immunodeficiency in cases with complete loss of protein. We used whole exome sequencing in a VEOIBD patient presenting with colitis characterized by colonic apoptosis and no identified known VEOIBD variants, to identify compound heterozygous deleterious variants in the Ubiquitin protein ligase E3 component N-recognin 5 (UBR5) gene. Functional studies demonstrated that UBR5 co-immunoprecipitates with the TTC7A and the UBR5 variants had reduced interaction between UBR5 and TTC7A. Together this implicates UBR5 in regulating TTC7A signaling in VEOIBD patients with apoptotic colitis.

UBR-box containing protein, UBR5, is over-expressed in human lung adenocarcinoma and is a potential therapeutic target

Background

N-end rule ubiquitination pathway is known to be disrupted in many diseases, including cancer. UBR5, an E3 ubiquitin ligase, is mutated and/or overexpressed in human lung cancer cells suggesting its pathological role in cancer.

Methods

We determined expression of UBR5 protein in multiple lung cancer cell lines and human patient samples. Using immunoprecipitation followed by mass spectrometry we determined the UBR5 interacting proteins. The impact of loss of UBR5 for lung adenocarcinoma cell lines was analyzed using cell viability, clonogenic assays and in vivo xenograft models in nude mice. Additional Western blot analysis was performed to assess the loss of UBR5 on downstream signaling. Statistical analysis was done by one-way ANOVA for in vitro studies and Wilcoxon paired t-test for in vivo tumor volumes.

Results

We show variability of UBR5 expression levels in lung adenocarcinoma cell lines and in primary human patient samples. To gain better insight into the role that UBR5 may play in lung cancer progression we performed unbiased interactome analyses for UBR5. Data indicate that UBR5 has a wide range of interacting protein partners that are known to be involved in critical cellular processes such as DNA damage, proliferation and cell cycle regulation. We have demonstrated that shRNA-mediated loss of UBR5 decreases cell viability and clonogenic potential of lung adenocarcinoma cell lines. In addition, we found decreased levels of activated AKT signaling after the loss of UBR5 in lung adenocarcinoma cell lines using multiple means of UBR5 knockdown/knockout. Furthermore, we demonstrated that loss of UBR5 in lung adenocarcinoma cells results in significant reduction of tumor volume in nude mice.

Conclusions

These findings demonstrate that deregulation of the N-end rule ubiquitination pathway plays a crucial role in the etiology of some human cancers, and blocking this pathway via UBR5-specific inhibitors, may represent a unique therapeutic target for human cancers.

Acetyl-11-keto-β-boswellic acid enhances the cisplatin sensitivity of non-small cell lung cancer cells through cell cycle arrest, apoptosis induction, and autophagy suppression via p21-dependent signaling pathway

Cisplatin-based therapy is a widely used chemotherapeutic regimen for non-small cell lung cancer (NSCLC); however, drug resistance limits its efficacy. Acetyl-11-keto-β-boswellic acid (AKBA), a bioactive compound from frankincense, has been shown to exert anti-cancer effects. The aim of this study is to explore the potential of AKBA in combination with cisplatin as a new regimen for NSCLC. CCK8 assay and clone formation assay were used to determine the effects of AKBA in combination with cisplatin on cell viability of NSCLC cell lines. A three-dimensional spherification assay was used to simulate in vivo tumor formation. Flow cytometry was performed to examine cell cycle distribution and the percentages of apoptotic cells. The associated proteins and mRNA of cell cycle, apoptosis, and autophagy were measured by western blotting and real-time fluorescence quantitative PCR. Immunofluorescence assay was used to test apoptotic nuclei and autolysosome. Small interfering RNA experiments were used to silence the expression of p21. Combination treatment of AKBA and cisplatin inhibited cell viability, clone formation, and three-dimensional spherification, enhanced G₀/G₁ phase arrest, increased the percentages of apoptotic cells, and decreased the ratio of positive autolysosomes, compared with cisplatin alone. AKBA in combination with cisplatin suppressed the protein expressions of cyclin A2, cyclin E1, p-cdc2, CDK4, Bcl-xl, Atg5, and LC3A/B, and upregulated p27 and p21 mRNA levels in A549 cells. Downregulation of p21 decreased G₀/G₁ phase arrest and the percentages of apoptotic cells, and promoted autophagy in NSCLC A549 cells. Our study demonstrates that AKBA enhances the cisplatin sensitivity of NSCLC cells and that the mechanisms involve G₀/G₁ phase arrest, apoptosis induction, and autophagy suppression via targeting p21-dependent signaling pathway.

p21 in Cancer Research

p21 functions as a cell cycle inhibitor and anti-proliferative effector in normal cells, and is dysregulated in some cancers. Earlier observations on p21 knockout models emphasized the role of this protein in cell cycle arrest under the p53 transcription factor activity. Although tumor-suppressor function of p21 is the most studied aspect of this protein in cancer, the role of p21 in phenotypic plasticity and its oncogenic/anti-apoptotic function, depending on p21 subcellular localization and p53 status, have been under scrutiny recently. Basic science and translational studies use precision gene editing to manipulate p21 itself, and proteins that interact with it; these studies have led to regulatory/functional/drug sensitivity discoveries as well as therapeutic approaches in cancer field. In this review, we will focus on targeting p21 in cancer research and its potential in providing novel therapies.

CRlncRC: a machine learning-based method for cancer-related long noncoding RNA identification using integrated features

BACKGROUND

Long noncoding RNAs (lncRNAs) are widely involved in the initiation and development of cancer. Although some computational methods have been proposed to identify cancer-related lncRNAs, there is still a demanding to improve the prediction accuracy and efficiency. In addition, the quick-update data of cancer, as well as the discovery of new mechanism, also underlay the possibility of improvement of cancer-related lncRNA prediction algorithm. In this study, we introduced CRlncRC, a novel Cancer-Related lncRNA Classifier by integrating manifold features with five machine-learning techniques.

RESULTS

CRlncRC was built on the integration of genomic, expression, epigenetic and network, totally in four categories of features. Five learning techniques were exploited to develop the effective classification model including Random Forest (RF), Naïve bayes (NB), Support Vector Machine (SVM), Logistic Regression (LR) and K-Nearest Neighbors (KNN). Using ten-fold cross-validation, we showed that RF is the best model for classifying cancer-related lncRNAs (AUC = 0.82). The feature importance analysis indicated that epigenetic and network features play key roles in the classification. In addition, compared with other existing classifiers, CRlncRC exhibited a better performance both in sensitivity and specificity. We further applied CRlncRC to lncRNAs from the TANRIC (The Atlas of non-coding RNA in Cancer) dataset, and identified 121 cancer-related lncRNA candidates. These potential cancer-related lncRNAs showed a certain kind of cancer-related indications, and many of them could find convincing literature supports.

CONCLUSIONS

Our results indicate that CRlncRC is a powerful method for identifying cancer-related lncRNAs. Machine-learning-based integration of multiple features, especially epigenetic and network features, had a great contribution to the cancer-related lncRNA prediction. RF outperforms other learning techniques on measurement of model sensitivity and specificity. In addition, using CRlncRC method, we predicted a set of cancer-related lncRNAs, all of which displayed a strong relevance to cancer as a valuable conception for the further cancer-related lncRNA function studies.

HJURP promotes hepatocellular carcinoma proliferation by destabilizing p21 via the MAPK/ERK1/2 and AKT/GSK3β signaling pathways

BACKGROUND

Holliday junction recognition protein (HJURP) has been implicated in many cancers including hepatocellular carcinoma (HCC). However, the underlying mechanism by which HJURP promotes HCC cell proliferation remains unclear.

METHODS

RT-qPCR and immunohistochemistry were used to detect HJURP expression in HCC and adjacent tumor tissues and HCC cell lines. The localization of p21 were determined by immunofluorescence and western blot. Co-immunoprecipitation and western blot were used to validate the p21 stability and signaling pathways affected by HJURP. The effects of HJURP on HCC cell proliferation were assessed both in vivo and in vitro. The ERK1/2 pathway inhibitor U0126 and AKT pathway agonist SC-79 were used to treat HCC cell lines for further mechanistic investigations.

RESULTS

HJURP expression was higher in HCC tissues than in para-tumor tissues. Moreover, ectopic HJURP expression facilitated the proliferation of HCC cells, whereas the depletion of HJURP resulted in decreased cell growth in vitro and in vivo. Furthermore, the effects of HJURP silencing were reversed by p21 knockdown. Likewise, p21 overexpression inhibited cell growth ability mediated by HJURP elevation. Mechanistically, HJURP destabilized p21 via the MAPK/ERK1/2 and AKT/GSK3β pathways, which regulated the nucleus-cytoplasm translocation and ubiquitin-mediated degradation of p21. Clinically, high HJURP expression was correlated with unfavorable prognoses in HCC individuals.

CONCLUSIONS

Our data revealed that HJURP is an oncogene that drives cell cycle progression upstream of p21 in HCC. These findings may provide a potential therapeutic and prognostic target for HCC.