RNA Binding Protein CUGBP1 Inhibits Liver Cancer in a Phosphorylation-Dependent Manner

Summary of biological research on hepatoblastoma: a scoping review

Background

Hepatoblastoma is the most prevalent primary hepatic malignancy in children, comprising 80% of pediatric hepatic malignancies and 1% of all pediatric malignancies. However, traditional treatments have proven inadequate in effectively curing hepatoblastoma, leading to a poor prognosis.

Methods

A literature search was conducted on multiple electronic databases (PubMed and Google Scholar). A total of 86 articles were eligible for inclusion in this review.

Result

This review aims to consolidate recent developments in hepatoblastoma research, focusing on the latest advances in cancer-associated genomics, epigenetic studies, transcriptional programs and molecular subtypes. We also discuss the current treatment approaches and forthcoming strategies to address cancer-associated biological challenges.

Conclusion

To provide a comprehensive summary of the molecular mechanisms associated with hepatoblastoma occurrence, this review highlights three key aspects: genomics, epigenetics, and transcriptomics. Our review aims to facilitate the exploration of novel molecular mechanisms and the development of innovative clinical treatment strategies for hepatoblastoma.

Therapeutic Targeting of the GSK3β-CUGBP1 Pathway in Myotonic Dystrophy

Myotonic Dystrophy type 1 (DM1) is a neuromuscular disease associated with toxic RNA containing expanded CUG repeats. The developing therapeutic approaches to DM1 target mutant RNA or correct early toxic events downstream of the mutant RNA. We have previously described the benefits of the correction of the GSK3β-CUGBP1 pathway in DM1 mice (HSALR model) expressing 250 CUG repeats using the GSK3 inhibitor tideglusib (TG). Here, we show that TG treatments corrected the expression of ~17% of genes misregulated in DM1 mice, including genes involved in cell transport, development and differentiation. The expression of chloride channel 1 (Clcn1), the key trigger of myotonia in DM1, was also corrected by TG. We found that correction of the GSK3β-CUGBP1 pathway in mice expressing long CUG repeats (DMSXL model) is beneficial not only at the prenatal and postnatal stages, but also during adulthood. Using a mouse model with dysregulated CUGBP1, which mimics alterations in DM1, we showed that the dysregulated CUGBP1 contributes to the toxicity of expanded CUG repeats by changing gene expression and causing CNS abnormalities. These data show the critical role of the GSK3β-CUGBP1 pathway in DM1 muscle and in CNS pathologies, suggesting the benefits of GSK3 inhibitors in patients with different forms of DM1.

RNA-binding protein CELF1 promotes cardiac hypertrophy via interaction with PEBP1 in cardiomyocytes

Cardiac hypertrophy is considered as a common pathophysiological process in various cardiovascular diseases. CUG triplet repeat-binding protein 1 (CELF1) is an RNA-binding protein that has been shown to be an important post-transcription regulator and involved in several types of cancer, whereas its role in cardiac remodeling remains unclear. Herein, we found that the expression of CELF1 was significantly increased in pressure overload-induced hypertrophic hearts and angiotensin II (Ang II)-induced neonatal cardiomyocytes. Based on transverse aortic constriction-induced cardiac hypertrophy model, CELF1 deficiency markedly ameliorated cardiac hypertrophy, cardiac fibrosis, oxidative stress, and apoptosis. Accordingly, CELF1 deficiency alleviated the production of reactive oxygen species (ROS) and apoptosis of neonatal cardiomyocytes via inhibition of Raf1, TAK1, ERK1/2, and p38 phosphorylation. Mechanistically, depletion or overexpression of CELF1 negatively regulated the protein expression of phosphatidylethanolamine-binding protein 1 (PEBP1), while the mRNA expression of PEBP1 remained unchanged. RNA immunoprecipitation revealed that CELF1 directly interacted with PEBP1 mRNA. Biotin pull-down analysis and dual-luciferase assay showed that CELF1 directly bound to the fragment 1 within 3'UTR of PEBP1. Moreover, knockdown of PEBP1 partially enhanced the production of ROS and apoptosis of neonatal cardiomyocytes inhibited by CELF1 deficiency. In conclusion, CELF1 binds to the 3'UTR of PEBP1 and acts as an endogenous activator of MAPK signaling pathway. Inhibition of CELF1 attenuates pathological cardiac hypertrophy, oxidative stress, and apoptosis, thus could be a potential therapeutic strategy of pathological cardiac hypertrophy.

CELF Family Proteins in Cancer: Highlights on the RNA-Binding Protein/Noncoding RNA Regulatory Axis

Post-transcriptional modifications to coding and non-coding RNAs are unquestionably a pivotal way in which human mRNA and protein diversity can influence the different phases of a transcript's life cycle. CELF (CUGBP Elav-like family) proteins are RBPs (RNA-binding proteins) with pleiotropic capabilities in RNA processing. Their responsibilities extend from alternative splicing and transcript editing in the nucleus to mRNA stability, and translation into the cytoplasm. In this way, CELF family members have been connected to global alterations in cancer proliferation and invasion, leading to their identification as potential tumor suppressors or even oncogenes. Notably, genetic variants, alternative splicing, phosphorylation, acetylation, subcellular distribution, competition with other RBPs, and ultimately lncRNAs, miRNAs, and circRNAs all impact CELF regulation. Discoveries have emerged about the control of CELF functions, particularly via noncoding RNAs, and CELF proteins have been identified as competing, antagonizing, and regulating agents of noncoding RNA biogenesis. On the other hand, CELFs are an intriguing example through which to broaden our understanding of the RBP/noncoding RNA regulatory axis. Balancing these complex pathways in cancer is undeniably pivotal and deserves further research. This review outlines some mechanisms of CELF protein regulation and their functional consequences in cancer physiology.

Olaparib Inhibits Tumor Growth of Hepatoblastoma in Patient-Derived Xenograft Models

BACKGROUND AND AIMS

Hepatoblastoma (HBL) is a devastating pediatric liver cancer with multiple treatment options, but it ultimately requires surgery for a cure. The most malicious form of HBL is a chemo-resistant aggressive tumor that is characterized by rapid growth, metastases, and poor response to treatment. Very little is known of the mechanisms of aggressive HBL, and recent focuses have been on developing alternative treatment strategies. In this study, we examined the role of human chromosomal regions, called aggressive liver cancer domains (ALCDs), in liver cancer and evaluated the mechanisms that activate ALCDs in aggressive HBL.

RESULTS

We found that ALCDs are critical regions of the human genome that are located on all human chromosomes, preferentially in intronic regions of the oncogenes and other cancer-associated genes. In aggressive HBL and in patients with Hepatocellular (HCC), JNK1/2 phosphorylates p53 at Ser6, which leads to the ph-S6-p53 interacting with and delivering the poly(adenosine diphosphate ribose) polymerase 1 (PARP1)/Ku70 complexes on the oncogenes containing ALCDs. The ph-S6-p53-PARP1 complexes open chromatin around ALCDs and activate multiple oncogenic pathways. We found that the inhibition of PARP1 in patient-derived xenografts (PDXs) from aggressive HBL by the Food and Drug Administration (FDA)-approved inhibitor olaparib (Ola) significantly inhibits tumor growth. Additionally, this is associated with the reduction of the ph-S6-p53/PARP1 complexes and subsequent inhibition of ALCD-dependent oncogenes. Studies in cultured cancer cells confirmed that the Ola-mediated inhibition of the ph-S6-p53-PARP1-ALCD axis inhibits proliferation of cancer cells.

CONCLUSIONS

In this study, we showed that aggressive HBL is moderated by ALCDs, which are activated by the ph-S6-p53/PARP1 pathway. By using the PARP1 inhibitor Ola, we suppressed tumor growth in HBL-PDX models, which demonstrated its utility in future clinical models.

FAX-RIC enables robust profiling of dynamic RNP complex formation in multicellular organisms in vivo

RNA-protein interaction is central to post-transcriptional gene regulation. Identification of RNA-binding proteins relies mainly on UV-induced crosslinking (UVX) followed by the enrichment of RNA-protein conjugates and LC-MS/MS analysis. However, UVX has limited applicability in tissues of multicellular organisms due to its low penetration depth. Here, we introduce formaldehyde crosslinking (FAX) as an alternative chemical crosslinking for RNA interactome capture (RIC). Mild FAX captures RNA-protein interaction with high specificity and efficiency in cell culture. Unlike UVX-RIC, FAX-RIC robustly detects proteins that bind to structured RNAs or uracil-poor RNAs (e.g. AGO1, STAU1, UPF1, NCBP2, EIF4E, YTHDF proteins and PABP), broadening the coverage. Applied to Xenopus laevis oocytes and embryos, FAX-RIC provided comprehensive and unbiased RNA interactome, revealing dynamic remodeling of RNA-protein complexes. Notably, translation machinery changes during oocyte-to-embryo transition, for instance, from canonical eIF4E to noncanonical eIF4E3. Furthermore, using Mus musculus liver, we demonstrate that FAX-RIC is applicable to mammalian tissue samples. Taken together, we report that FAX can extend the RNA interactome profiling into multicellular organisms.

Small Molecule Cjoc42 Improves Chemo-Sensitivity and Increases Levels of Tumor Suppressor Proteins in Hepatoblastoma Cells and in Mice by Inhibiting Oncogene Gankyrin

Objective: Relapsed hepatoblastoma (HBL) and upfront hepatocellular carcinoma (HCC) are notoriously chemoresistant tumors associated with poor outcomes. Gankyrin (Gank) is a known oncogene that is overexpressed in pediatric liver cancer and implicated in chemo-resistance. The goal of this study was to evaluate if the Gank-tumor suppressor axis is activated in chemoresistant hepatoblastoma patients and examine if an inhibitor of Gank, Cjoc42, might improve the chemosensitivity of cancer cells.

Methods: Expression of Gank and its downstream targets were examined in fresh human HBL samples using immunostaining, QRT-PCR, and Western Blot. Cancer cells, Huh6 (human HBL) and Hepa1c1c7 (mouse HCC) were treated with Cjoc42 and with Cjoc42 in combination with cisplatin or doxorubicin. Cell proliferation, apoptosis, and chemoresistance were examined. To examine activities of Cjoc42 in vivo, mice were treated with different doses of Cjoc42, and biological activities of Gank and cytotoxicity of Cjoc42 were tested.

Results: Elevation of Gank and Gank-mediated elimination of TSPs are observed in patients with minimal necrosis after chemotherapy and relapsed disease. The treatment of Huh6 and Hepa1c1c7 with Cjoc42 was not cytotoxic; however, in combination with cisplatin or doxorubicin, Cjoc42 caused a significant increase in cytotoxicity compared to chemotherapy alone with increased apoptosis. Examination of Cjoc42 in WT mice showed that Cjoc42 is well tolerated without systemic toxicity, and levels of tumor suppressors CUGBP1, Rb, p53, C/EBPα, and HNF4α are increased by blocking their Gank-dependent degradation.

Conclusions: Our work shows that Cjoc42 might be a promising adjunct to chemotherapy for the treatment of severe pediatric liver cancer and presents mechanisms by which Cjoc42 increases chemo-sensitivity.

Molecular signatures of aggressive pediatric liver cancer

Liver masses account for 5 to 6% of pediatric cancer, which includes hepatoblastoma (HBL) along with rare cases of hepatocellular carcinoma (HCC). The most dangerous form of pediatric liver cancer is aggressive HBL, which can be characterized by chemo-resistance and multiple nodules or metastases at diagnosis, all correlating with worse clinical prognosis. Despite intensive studies and a significant improvement in overall outcomes, very little is known about the key molecular pathways which determine the aggressiveness of pediatric liver cancer. Although genetic mutations have been reported in aggressive HBL, they represent a low level (1.9% per case) and are found mainly in two genes CTNNB1 and NRF2. Over the past 5 years, our liver biology and tumor group at Cincinnati Children's Hospital Medical Center has investigated molecular signatures of aggressive HBL by examination of fresh tissue specimens, which were studied immediately after surgery to preserve the integrity of key biochemical pathways. Summarization of these high quality HBL samples discovered several critical pathways that are specific for aggressive pediatric liver cancer. These pathways include three characteristics: Conversion of tumor suppressor proteins (TSPs) by posttranslational modifications into oncogenesActivation of specific chromosomal regions, i.e., Aggressive Liver Cancer Domains (ALCDs) within many oncogenes, resulting in increased expression of oncogenesPotential epigenetic mechanisms that open chromatin structure of oncogenes via ALCDs. This commentary summarizes our key findings and discusses development of potential ALCD-based therapeutic approaches.

Fraxinellone: From pesticidal control to cancer treatment

Fraxinellone (FRA) is a degraded limonoid isolated from the root bark of Dictamnus plants. The potent insecticidal activity of FRA has led to the synthesis of numerous derivatives (presented here with the structure-activity relationships) active against the oriental armyworm Mythimna separata Walker. In addition to its pesticidal activity, the natural product displays potent anti-inflammatory and immuno-modulatory effects at the origin of hepatoprotective and anticancer properties. This mini-review provides an update of the mechanism of action of FRA to highlight the recently discovered capacity of the compound to deactivate cancer-associated fibroblasts and thus to limit the immunosuppressive tumor microenvironment. The anticancer mode of action of FRA raises new ideas to better understand its primary insecticidal activity. The relationship between drug-induced cancer cell death and insect cell death is discussed. A drug interaction with the insect cytokine growth-blocking peptide (GBP), a member of the large EGF family, is proposed, supported by preliminary molecular modeling data. Altogether, the review shed light on the pharmacological properties of fraxinellone as an antitumor agent and a natural insecticide.

Optimizing the aryl-triazole of cjoc42 for enhanced gankyrin binding and anti-cancer activity

Gankyrin is an oncoprotein overexpressed in numerous cancer types and appears to play a key role in regulating cell proliferation, cell growth, and cell migration. These roles are largely due to gankyrin's protein-protein interaction with the 26S proteasome. We previously published a study exploring the aryl sulfonate ester of cjoc42 in an effort to enhance gankyrin binding and inhibit cancer cell proliferation. In order to further improve the gankyrin binding ability of the cjoc42 scaffold, an extensive SAR for the aryl-triazole moiety of cjoc42 was developed. Our cjoc42 derivatives exhibited enhanced gankyrin binding, as well as enhanced antiproliferative activity against Hep3B, HepG2, A549, and MDA-MB-231 cancer cell lines.

Correction of Glycogen Synthase Kinase 3β in Myotonic Dystrophy 1 Reduces the Mutant RNA and Improves Postnatal Survival of DMSXL Mice

Myotonic dystrophy type 1 (DM1) is a multisystem neuromuscular disease without cure. One of the possible therapeutic approaches for DM1 is correction of the RNA-binding proteins CUGBP1 and MBNL1, misregulated in DM1. CUGBP1 activity is controlled by glycogen synthase kinase 3β (GSK3β), which is elevated in skeletal muscle of patients with DM1, and inhibitors of GSK3 were suggested as therapeutic molecules to correct CUGBP1 activity in DM1. Here, we describe that correction of GSK3β with a small-molecule inhibitor of GSK3, tideglusib (TG), not only normalizes the GSK3β-CUGBP1 pathway but also reduces the mutant DMPK mRNA in myoblasts from patients with adult DM1 and congenital DM1 (CDM1). Correction of GSK3β in a mouse model of DM1 (HSA^LR mice) with TG also reduces the levels of CUG-containing RNA, normalizing a number of CUGBP1- and MBNL1-regulated mRNA targets. We also found that the GSK3β-CUGBP1 pathway is abnormal in skeletal muscle and brain of DMSXL mice, expressing more than 1,000 CUG repeats, and that the correction of this pathway with TG increases postnatal survival and improves growth and neuromotor activity of DMSXL mice. These findings show that the inhibitors of GSK3, such as TG, may correct pathology in DM1 and CDM1 via several pathways.

Liver Proliferation Is an Essential Driver of Fibrosis in Mouse Models of Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) involves development of hepatic steatosis, fibrosis, and steatohepatitis. Because hepatic steatosis appears first in NAFLD animal models, the current therapy development focuses on inhibition of hepatic steatosis, suggesting that further steps of NAFLD will be also inhibited. In this report, we show that the first event of NAFLD is liver proliferation, which drives fibrosis in NAFLD. We have deleted a strong driver of liver proliferation, gankyrin (Gank), and examined development of NAFLD in this animal model under conditions of a high‐fat diet (HFD). We found that proliferating livers of wild‐type mice develop fibrosis; however, livers of Gank liver‐specific knockout (GLKO) mice with reduced proliferation show no fibrosis. Interestingly, an HFD causes the development of strong macrovesicular steatosis in GLKO mice and is surprisingly associated with improvements in animal health. We observed that key regulators of liver biology CCAAT/enhancer binding protein α (C/EBPα), hepatocyte nuclear factor 4α (HNF4α), p53, and CUG repeat binding protein 1 (CUGBP1) are elevated due to the deletion of Gank and that these proteins support liver functions leading to healthy conditions in GLKO mice under an HFD. To examine the role of one of these proteins in the protection of liver from fibrosis, we used CUGBP1‐S302A knockin mice, which have a reduction of CUGBP1 due to increased degradation of this mutant by Gank. These studies show that reduction of CUGBP1 inhibits steatosis and facilitates liver proliferation, leading to fibrosis and the development of liver tumors. Conclusion: Liver proliferation drives fibrosis, while steatosis might play a protective role. Therapy for NAFLD should include inhibition of proliferation rather than inhibition of steatosis.

The Oncoprotein Gankyrin/PSMD10 as a Target of Cancer Therapy

Gankyrin (also called PSMD10, p28, or p28^GANK) is a crucial oncoprotein that is upregulated in various cancers and assumed to play pivotal roles in the initiation and progression of tumors. Although the in vitro function of gankyrin is relatively well characterized, its role in vivo remains to be elucidated. We have investigated the function of gankyrin in vivo by producing mice with liver parenchymal cell-specific gankyrin ablation (Alb-Cre;gankyrin^f/f) and gankyrin deletion both in liver parenchymal and in non-parenchymal cells (Mx1-Cre;gankyrin^f/f). Gankyrin deficiency both in non-parenchymal cells and parenchymal cells, but not in parenchymal cells alone, reduced STAT3 activity, interleukin-6 production, and cancer stem cell marker expression, leading to attenuated tumorigenic potential in the diethylnitrosamine hepatocarcinogenesis model. Essentially similar results were obtained by analyzing mice with intestinal epithelial cell-specific gankyrin ablation (Villin-Cre;Gankyrin^f/f) and gankyrin deletion both in myeloid and epithelial cells (Mx1-Cre;Gankyrin^f/f) in the colitis-associated cancer model. Clinically, gankyrin expression in the tumor microenvironment was negatively correlated with progression-free survival in patients undergoing treatment with Sorafenib for hepatocellular carcinomas. These findings indicate important roles played by gankyrin in non-parenchymal cells as well as parenchymal cells in the pathogenesis of liver cancers and colorectal cancers, and suggest that by acting both on cancer cells and on the tumor microenvironment, anti-gankyrin agents would be promising as therapeutic and preventive strategies against various cancers, and that an in vitro cell culture models that incorporate the effects of non-parenchymal cells and gankyrin would be useful for the study of human cell transformation.

PARP1 activation increases expression of modified tumor suppressors and pathways underlying development of aggressive hepatoblastoma

Hepatoblastoma (HBL) is a pediatric liver cancer that affects children under the age of three. Reduction of tumor suppressor proteins (TSPs) is commonly seen in liver cancer. However, in our studies we find that aggressive, chemo-resistant HBLs exhibit an elevation of TSPs. HBL patients with a classic phenotype have reduced TSP levels, but patients with aggressive HBL express elevated TSPs that undergo posttranslational modifications, eliminating their tumor suppression activities. Here we identify unique aggressive liver cancer domains (ALCDs) that are activated in aggressive HBL by PARP1-mediated chromatin remodeling leading to elevation of modified TSPs and activation of additional cancer pathways: WNT signaling and β-catenin. Inhibition of PARP1 blocks activation of ALCDs and normalizes expression of corresponding genes, therefore reducing cell proliferation. Our studies reveal PARP1 activation as a mechanism for the development of aggressive HBL, further suggesting FDA-approved PARP1 inhibitors might be used for treatment of patients with aggressive HBL.

Leila Valanejad et al. report increased expression of modified tumor suppressor proteins (TSPs) with loss of tumor suppressor activity in aggressive, chemotherapy-resistant hepatoblastoma. They find that TSP upregulation occurs via PARP1-mediated chromatin remodeling, leading to activation of multiple cancer-associated pathways.

Gankyrin Promotes Tumor-Suppressor Protein Degradation to Drive Hepatocyte Proliferation

Background & Aims

Uncontrolled liver proliferation is a key characteristic of liver cancer; however, the mechanisms by which this occurs are not well understood. Elucidation of these mechanisms is necessary for the development of better therapy. The oncogene Gankyrin (Gank) is overexpressed in both hepatocellular carcinoma and hepatoblastoma. The aim of this work was to determine the role of Gank in liver proliferation and elucidate the mechanism by which Gank promotes liver proliferation.

Methods

We generated Gank liver-specific knock-out (GLKO) mice and examined liver biology and proliferation after surgical resection and liver injury.

Results

Global profiling of gene expression in GLKO mice showed significant changes in pathways involved in liver cancer and proliferation. Investigations of liver proliferation after partial hepatectomy and CCl4 treatment showed that GLKO mice have dramatically inhibited proliferation of hepatocytes at early stages after surgery and injury. In control LoxP mice, liver proliferation was characterized by Gank-mediated reduction of tumor-suppressor proteins (TSPs). The failure of GLKO hepatocytes to proliferate is associated with a lack of down-regulation of these proteins. Surprisingly, we found that hepatic progenitor cells of GLKO mice start proliferation at later stages and restore the original size of the liver at 14 days after partial hepatectomy. To examine the proliferative activities of Gank in cancer cells, we used a small molecule, cjoc42, to inhibit interactions of Gank with the 26S proteasome. These studies showed that Gank triggers degradation of TSPs and that cjoc42-mediated inhibition of Gank increases levels of TSPs and inhibits proliferation of cancer cells.

Conclusions

These studies show that Gank promotes hepatocyte proliferation by elimination of TSPs. This work provides background for the development of Gank-mediated therapy for the treatment of liver cancer. RNA sequencing data can be accessed in the NCBI Gene Expression Omnibus: GSE104395.

Probing the role of PPARγ in the regulation of late-onset Alzheimer's disease-associated genes

Peroxisome proliferator-activated receptor-γ (PPARγ), is a transcription factor that governs pathways, such as lipid metabolism and immune response, that have been implicated in the etiology of LOAD. Previously, we established HepG2-derived cell-lines with stable knockdown of PPARγ gene, and showed an increase in mRNA levels of genes mapped in the APOE linkage disequilibrium (LD) region on chromosome 19q13.32, with the greatest effect observed for APOE-mRNA. Here, we extended the analysis using our PPARγ knockdown model system and investigated the broader effect on expression changes of genes implicated in LOAD via genome wide association studies (GWAS). We applied the nCounter gene expression assay (NanoString) using a panel of twenty-four LOAD-associated genes inferred by proximity to the top significantly associated SNPs. Two independent PPARγ knockdown cell-lines showed changes in mRNA levels of a total of seven genes compared to a control HepG2 cell-line; six of which, ABCA7, APOE, CASS4, CELF1, PTK2B, and ZCWPW1, were upregulated and one, DSG2, was downregulated upon PPARγ knockdown. Our results propose that PPARγ may act as a master regulator of the transcription of several genes involved in LOAD pathogenesis. Our study provided the premise for further analyses including a larger set of genes positioned within a wider range of linkage disequilibrium (LD) regions tagged by all LOAD significantly associated SNPs.

RNA Binding Proteins in Intestinal Epithelial Biology and Colorectal Cancer

The intestinal epithelium is highly proliferative and consists of crypt invaginations that house stem cells and villus projections with differentiated cells. There exists a dynamic equilibrium between proliferation, migration, differentiation, and senescence that is regulated by several factors. Among these are RNA binding proteins (RBPs) that bind their targets in a both context dependent and independent manner. RBP-RNA complexes act as rheostats by regulating expression of RNAs both co- and post-transcriptionally. This is important, especially in response to intestinal injury, to fuel regeneration. The manner in which these RBPs function in the intestine and their interactions with other pivotal pathways in colorectal cancer may provide a framework for new insights and potential therapeutic applications.