Isoforms of RNF128 Regulate the Stability of Mutant P53 in Barrett's Esophageal Cells

Downregulation of RNF128 Inhibits the Proliferation, Migration, Invasion and EMT of Colorectal Cancer Cells

Colorectal cancer has the third highest incidence and second highest mortality rate among all cancer types. Exploring the molecular mechanisms driving malignant proliferation and metastasis of colorectal cancer will benefit the treatment and management of cancer patients. Recent studies have reported diametrically opposed roles of Ring finger protein 128 (RNF128) in different types of cancer. However, the role of RNF128 in colorectal cancer is still completely unknown, which this study attempts to analyze. The differential expression of RNF128 mRNA and protein in 30 pairs of colorectal cancer and corresponding peritumoral tissues was detected using RT-qPCR, western blot and immunohistochemical staining. siRNA specifically targeting RNF128 was transfected into colorectal cancer cell lines (SW1116 and SW480) cultured in vitro. Proliferation, growth, migration, invasion and epithelial-mesenchymal transition (EMT) of colorectal cancer cells were examined by CCK-8, clone formation, wound-healing, transwell, western blot and immunofluorescence assays. Both RNF128 mRNA and protein levels were significantly increased in colorectal cancer tissues compared to pericarcinoma tissues. Knockdown of RNF128 significantly inhibited the proliferation, growth, migration, invasion and EMT of SW480 and SW1116 cells. Targeting RNF128 may benefit the treatment and management of colorectal cancer.

ISG15/GRAIL1/CD3 axis influences survival of patients with esophageal adenocarcinoma

Immunosuppression is a common feature of esophageal adenocarcinoma (EAC) and has been linked to poor overall survival (OS). We hypothesized that upstream factors might negatively influence CD3 levels and T cell activity, thus promoting immunosuppression and worse survival. We used clinical data and patient samples of those who progressed from Barrett's to dysplasia to EAC, investigated gene (RNA-Seq) and protein (tissue microarray) expression, and performed cell biology studies to delineate a pathway impacting CD3 protein stability that might influence EAC outcome. We showed that the loss of both CD3-ε expression and CD3+ T cell number correlated with worse OS in EAC. The gene related to anergy in lymphocytes isoform 1 (GRAIL1), which is the prominent isoform in EACs, degraded (ε, γ, δ) CD3s and inactivated T cells. In contrast, isoform 2 (GRAIL2), which is reduced in EACs, stabilized CD3s. Further, GRAIL1-mediated CD3 degradation was facilitated by interferon-stimulated gene 15 (ISG15), a ubiquitin-like protein. Consequently, the overexpression of a ligase-dead GRAIL1, ISG15 knockdown, or the overexpression of a conjugation-defective ISG15-leucine-arginine-glycine-glycine mutant could increase CD3 levels. Together, we identified an ISG15/GRAIL1/mutant p53 amplification loop negatively influencing CD3 levels and T cell activity, thus promoting immunosuppression in EAC.

Isoform alterations in the ubiquitination machinery impacting gastrointestinal malignancies

The advancement of RNAseq and isoform-specific expression platforms has led to the understanding that isoform changes can alter molecular signaling to promote tumorigenesis. An active area in cancer research is uncovering the roles of ubiquitination on spliceosome assembly contributing to transcript diversity and expression of alternative isoforms. However, the effects of isoform changes on functionality of ubiquitination machineries (E1, E2, E3, E4, and deubiquitinating (DUB) enzymes) influencing onco- and tumor suppressor protein stabilities is currently understudied. Characterizing these changes could be instrumental in improving cancer outcomes via the identification of novel biomarkers and targetable signaling pathways. In this review, we focus on highlighting reported examples of direct, protein-coded isoform variation of ubiquitination enzymes influencing cancer development and progression in gastrointestinal (GI) malignancies. We have used a semi-automated system for identifying relevant literature and applied established systems for isoform categorization and functional classification to help structure literature findings. The results are a comprehensive snapshot of known isoform changes that are significant to GI cancers, and a framework for readers to use to address isoform variation in their own research. One of the key findings is the potential influence that isoforms of the ubiquitination machinery have on oncoprotein stability.

Characterizing isoform switching events in esophageal adenocarcinoma

Isoform switching events with predicted functional consequences are common in many cancers, but characterization of switching events in esophageal adenocarcinoma (EAC) is lacking. Next-generation sequencing was used to detect levels of RNA transcripts and identify specific isoforms in treatment-naïve esophageal tissues ranging from premalignant Barrett’s esophagus (BE), BE with low- or high-grade dysplasia (BE.LGD, BE.HGD), and EAC. Samples were stratified by histopathology and TP53 mutation status, identifying significant isoform switching events with predicted functional consequences. Comparing BE.LGD with BE.HGD, a histopathology linked to cancer progression, isoform switching events were identified in 75 genes including KRAS, RNF128, and WRAP53. Stratification based on TP53 status increased the number of significant isoform switches to 135, suggesting switching events affect cellular functions based on TP53 mutation and tissue histopathology. Analysis of isoforms agnostic, exclusive, and shared with mutant TP53 revealed unique signatures including demethylation, lipid and retinoic acid metabolism, and glucuronidation, respectively. Nearly half of isoform switching events were identified without significant gene-level expression changes. Importantly, two TP53-interacting isoforms, RNF128 and WRAP53, were significantly linked to patient survival. Thus, analysis of isoform switching events may provide new insight for the identification of prognostic markers and inform new potential therapeutic targets for EAC.

The emerging roles of HDACs and their therapeutic implications in cancer

Deregulation of protein post-translational modifications is intensively involved in the etiology of diseases, including degenerative diseases, inflammatory injuries, and cancers. Acetylation is one of the most common post-translational modifications of proteins, and the acetylation levels are controlled by two mutually antagonistic enzyme families, histone acetyl transferases (HATs) and histone deacetylases (HDACs). HATs loosen the chromatin structure by neutralizing the positive charge of lysine residues of histones; whereas HDACs deacetylate certain histones, thus inhibiting gene transcription. Compared with HATs, HDACs have been more intensively studied, particularly regarding their clinical significance. HDACs extensively participate in the regulation of proliferation, migration, angiogenesis, immune escape, and therapeutic resistance of cancer cells, thus emerging as critical targets for clinical cancer therapy. Compared to HATs, inhibitors of HDAC have been clinically used for cancer treatment. Here, we enumerate and integratethe mechanisms of HDAC family members in tumorigenesis and cancer progression, and address the new and exciting therapeutic implications of single or combined HDAC inhibitor (HDACi) treatment.

RING finger protein 128 (RNF128) regulates malignant biological behaviors of colorectal cancer cells via PI3K/AKT signaling pathway

This study was designed and conducted to clarify the impact of RNF128 expression on malignant biological behaviors of colorectal cancer (CRC) cells and the underlying mechanism. The expression of RNF128 in CRC tissues was analyzed using mRNA sequencing data of TCGA database and was validated by Western blot assay. The experimental studies on biological functions of RNF128 in vitro were conducted to assess its impact on the proliferation, apoptosis, and metastasis of CRC cells. Furthermore, tumor xenograft models in nude mice were established to investigate the relationship between RNF128 expression and tumor growth in vivo. The expression levels of both RNF128 mRNA and protein were significantly increased in CRC tissues (p < .001). The knockdown of RNF128 markedly suppressed the malignant phenotype of HCT116 and SW480 cells in vitro, including cell growth, antiapoptosis, migration, and invasion (p < .001). On the other hand, knockdown of RNF128 exerted a remarkable effect on the growth inhibition of tumor xenografts in vivo (p < .001). Further investigation revealed that RNF128 knockdown lead to a significant decrease in the expression of p-AKT and p-PI3K protein. More importantly, the proliferative, antiapoptotic, metastatic abilities of RNF128-knockdown cells were markedly increased by 740 Y-P treatment (p < .001). These findings further suggested that PI3K/AKT signaling pathway played a key role in RNF128-mediated aggressive phenotype of CRC cells. RNF128 functions as a tumor promoter in the pathogenesis of CRC via regulating PI3K/AKT pathway, and it could be a valuable target for CRC treatment.

RNF128 suppresses the malignancy of colorectal cancer cells via inhibition of Wnt/β-catenin signaling

PURPOSE

Colorectal cancer (CRC) is one of the most frequent tumors and causes of mortality worldwide. Ubiquitin ligase was reported to regulate multiple cellular processes, including tumorigenesis. As ubiquitin E3 ligases, RING-finger proteins play a key role in physiological and pathophysiological processes.

METHODS

We compared the expression levels of RNF128 in CRC tissues by western-blotting and qRT-PCR. Knockdown and overexpression of RNF128 were performed to examine its effect on proliferation and metastasis of CRC cells. Using western blot and co-immunoprecipitation assays, we explored the possible mechanisms underlying the effect of RNF128 in CRC cells.

RESULTS

We found that the expression level of RNF128 was correlated with the CRC tumorigenicity. Overexpression or knockdown of RNF128 suppressed or elevated CRC cell proliferation, migration and invasion, respectively. We further determined that RNF128 regulated β-catenin ubiquitination and thus inhibited Wnt/β-catenin signaling in CRC cells.

CONCLUSION

Our research demonstrated that RNF128 inhibited cell proliferation and metastasis of CRC cells via Wnt/β-catenin signaling-mediated deubiquitination.

UBCH5 Family Members Differentially Impact Stabilization of Mutant p53 via RNF128 Iso1 During Barrett's Progression to Esophageal Adenocarcinoma

BACKGROUND & AIMS

TP53 mutations underlie Barrett's esophagus (BE) progression to dysplasia and cancer. During BE progression, the ubiquitin ligase (E3) RNF128/GRAIL switches expression from isoform 2 (Iso2) to Iso1, stabilizing mutant p53. However, the ubiquitin-conjugating enzyme (E2) that partners with Iso1 to stabilize mutant p53 is unknown.

METHODS

Single-cell RNA sequencing of paired normal esophagus and BE tissues identified candidate E2s, further investigated in expression data from BE to esophageal adenocarcinoma (EAC) progression samples. Biochemical and cellular studies helped clarify the role of RNF128-E2 on mutant p53 stability.

RESULTS

The UBE2D family member 2D3 (UBCH5C) is the most abundant E2 in normal esophagus. However, during BE to EAC progression, loss of UBE2D3 copy number and reduced expression of RNF128 Iso2 were noted, 2 known p53 degraders. In contrast, expression of UBE2D1 (UBCH5A) and RNF128 Iso1 in dysplastic BE and EAC forms an inactive E2-E3 complex, stabilizing mutant p53. To destabilize mutant p53, we targeted RNF128 Iso1 either by mutating asparagine (N48, 59, and 101) residues to block glycosylation to facilitate β-TrCP1-mediated degradation or by mutating proline (P54 and 105) residues to restore p53 polyubiquitinating ability. In addition, either loss of UBCH5A catalytic activity, or disruption of the Iso1-UBCH5A interaction promoted Iso1 loss. Consequently, overexpression of either catalytically dead or Iso1-binding-deficient UBCH5A mutants destabilized Iso1 to degrade mutant p53, thus compromising the clonogenic survival of mutant p53-dependent BE cells.

CONCLUSIONS

Loss of RNF128 Iso2-UBCH5C and persistence of the Iso1-UBCH5A complex favors mutant p53 stability to promote BE cell survival. Therefore, targeting of Iso1-UBCH5A may provide a novel therapeutic strategy to prevent BE progression.

Regulation of p53 by E3s

More than 40 years of research on p53 have given us tremendous knowledge about this protein. Today we know that p53 plays a role in different biological processes such as proliferation, invasion, pluripotency, metabolism, cell cycle control, ROS (reactive oxygen species) production, apoptosis, inflammation and autophagy. In the nucleus, p53 functions as a bona-fide transcription factor which activates and represses transcription of a number of target genes. In the cytoplasm, p53 can interact with proteins of the apoptotic machinery and by this also induces cell death. Despite being so important for the fate of the cell, expression levels of p53 are kept low in unstressed cells and the protein is largely inactive. The reason for the low expression level is that p53 is efficiently degraded by the ubiquitin-proteasome system and the vast inactivity of the tumor suppressor protein under normal growth conditions is due to the absence of activating and the presence of inactivating posttranslational modifications. E3s are important enzymes for these processes as they decorate p53 with ubiquitin and small ubiquitin-like proteins and by this control p53 degradation, stability and its subcellular localization. In this review, we provide an overview about E3s that target p53 and discuss the connection between p53, E3s and tumorigenesis.

Immune determinants of Barrett's progression to esophageal adenocarcinoma

Esophageal adenocarcinoma (EAC) develops from Barrett’s esophagus (BE), a chronic inflammatory state that can progress through a series of transformative dysplastic states before tumor development. While molecular and genetic changes of EAC tumors have been studied, immune microenvironment changes during Barrett’s progression to EAC remain poorly understood. In this study, we identify potential immunologic changes that can occur during BE-to-EAC progression. RNA sequencing (RNA-Seq) analysis on tissue samples from EAC patients undergoing surgical resection demonstrated that a subset of chemokines and cytokines, most notably IL6 and CXCL8, increased during BE progression to EAC. xCell deconvolution analysis investigating immune cell population changes demonstrated that the largest changes in expression during BE progression occurred in M2 macrophages, pro–B cells, and eosinophils. Multiplex immunohistochemical staining of tissue microarrays showed increased immune cell populations during Barrett’s progression to high-grade dysplasia. In contrast, EAC tumor sections were relatively immune poor, with a rise in PD-L1 expression and loss of CD8⁺ T cells. These data demonstrate that the EAC microenvironment is characterized by poor cytotoxic effector cell infiltration and increased immune inhibitory signaling. These findings suggest an immunosuppressive microenvironment, highlighting the need for further studies to explore immune modulatory therapy in EAC.

Chaperones and Ubiquitin Ligases Balance Mutant p53 Protein Stability in Esophageal and Other Digestive Cancers

The incidence of esophageal adenocarcinoma (EAC) and other gastrointestinal (GI) cancers have risen dramatically, thus defining the oncogenic drivers to develop effective therapies are necessary. Patients with Barrett's Esophagus (BE), have an elevated risk of developing EAC. Around 70%-80% of BE cases that progress to dysplasia and cancer have detectable TP53 mutations. Similarly, in other GI cancers higher rates of TP53 mutation are reported, which provide a significant survival advantage to dysplastic/cancer cells. Targeting molecular chaperones that mediate mutant p53 stability may effectively induce mutant p53 degradation and improve cancer outcomes. Statins can achieve this via disrupting the interaction between mutant p53 and the chaperone DNAJA1, promoting CHIP-mediated degradation of mutant p53, and statins are reported to significantly reduce the risk of BE progression to EAC. However, statins demonstrated sub-optimal efficacy depending on cancer types and TP53 mutation specificity. Besides the well-established role of MDM2 in p53 stability, we reported that individual isoforms of the E3 ubiquitin ligase GRAIL (RNF128) are critical, tissue-specific regulators of mutant p53 stability in BE progression to EAC, and targeting the interaction of mutant p53 with these isoforms may help mitigate EAC development. In this review, we discuss the critical ubiquitin-proteasome and chaperone regulation of mutant p53 stability in EAC and other GI cancers with future insights as to how to affect mutant p53 stability, further noting how the precise p53 mutation may influence the efficacy of treatment strategies and identifying necessary directions for further research in this field.

Ubiquitin ligase SMURF2 enhances epidermal growth factor receptor stability and tyrosine-kinase inhibitor resistance

The discovery of activating epidermal growth factor receptor (EGFR) mutations spurred the use of EGFR tyrosine kinase inhibitors (TKIs), such as erlotinib, as the first-line treatment of lung cancers. We previously reported that differential degradation of TKI-sensitive (e.g. L858R) and resistant (T790M) EGFR mutants upon erlotinib treatment correlates with drug sensitivity. We also reported that SMAD ubiquitination regulatory factor 2 (SMURF2) ligase activity is important in stabilizing EGFR. However, the molecular mechanisms involved remain unclear. Here, using in vitro and in vivo ubiquitination assays, MS, and superresolution microscopy, we show SMURF2-EGFR functional interaction is important for EGFR stability and response to TKI. We demonstrate that L858R/T790M EGFR is preferentially stabilized by SMURF2-UBCH5 (an E3-E2)-mediated polyubiquitination. We identified four lysine residues as the sites of ubiquitination and showed that replacement of one of them with acetylation-mimicking glutamine increases the sensitivity of mutant EGFR to erlotinib-induced degradation. We show that SMURF2 extends membrane retention of EGF-bound EGFR, whereas SMURF2 knockdown increases receptor sorting to lysosomes. In lung cancer cell lines, SMURF2 overexpression increased EGFR levels, improving TKI tolerance, whereas SMURF2 knockdown decreased EGFR steady-state levels and sensitized lung cancer cells. Overall, we propose that SMURF2-mediated polyubiquitination of L858R/T790M EGFR competes with acetylation-mediated receptor internalization that correlates with enhanced receptor stability; therefore, disruption of the E3-E2 complex may be an attractive target to overcome TKI resistance.

The Janus Face of p53-Targeting Ubiquitin Ligases

The tumor suppressor p53 prevents tumorigenesis and cancer progression by maintaining genomic stability and inducing cell growth arrest and apoptosis. Because of the extremely detrimental nature of wild-type p53, cancer cells usually mutate the TP53 gene in favor of their survival and propagation. Some of the mutant p53 proteins not only lose the wild-type activity, but also acquire oncogenic function, namely “gain-of-function”, to promote cancer development. Growing evidence has revealed that various E3 ubiquitin ligases are able to target both wild-type and mutant p53 for degradation or inactivation, and thus play divergent roles leading to cancer cell survival or death in the context of different p53 status. In this essay, we reviewed the recent progress in our understanding of the p53-targeting E3 ubiquitin ligases, and discussed the potential clinical implications of these E3 ubiquitin ligases in cancer therapy.

ATM mutations as an independent prognostic factor and potential biomarker for immune checkpoint therapy in endometrial cancer

The morbidity and mortality of endometrial cancer has been increasing over years. Ataxia telangiectasia mutated (ATM) gene, encoding a protein kinase participated in the response to DNA damage, is frequently mutated in endometrial cancer patients. However, the potential relationship between ATM mutations and the progression of endometrial cancer remains unclear. We performed an integrative bioinformatics analysis to investigate the relationship between ATM mutational status with clinical outcomes and tumor microenvironment in endometrial cancer patients. The whole exome sequencing data, RNA sequencing data and clinical information were collected from The Cancer Genome Atlas (TCGA) dataset. We found that mutation in the ATM gene was an independent prognostic factor for endometrial cancer. Antitumor immune pathways were enriched in endometrial tumors with ATM mutations. The tumor-infiltrating T lymphocytes, especially cytotoxic lymphocytes, were generally more abundant in tumors with ATM mutations. Furthermore, patients with ATM mutations exhibited higher tumor mutational burden, higher neoantigen load and increased expression levels of some immune checkpoints. In conclusion, the present study indicated that ATM mutations were linked to longer overall survival of endometrial cancer. Our findings may add better understanding for potential immunotherapy of endometrial cancer.