HuR is a post-transcriptional regulator of core metabolic enzymes in pancreatic cancer

PIM1 kinase and its diverse substrate in solid tumors

The PIM kinase family, consisting of PIM1, PIM2, and PIM3, is a group of serine/threonine protein kinases crucial for cellular growth, immunoregulation, and oncogenesis. PIM1 kinase is often overexpressed in solid and hematopoietic malignancies, promoting cell survival, proliferation, migration, and senescence by activating key genes. In vitro and in vivo studies have established the oncogenic potential of PIM1 kinases. These kinases have been implicated in tumor progression, metastasis, and resistance to chemotherapy, underscoring their potential as a therapeutic target for cancer therapy. This review delves into the intricate molecular mechanisms through which PIM1 interacts with specific substrates in different tumor tissues, leading to diverse outcomes in various human cancers. Over the past decade, the inhibition of PIM1 in cancers has garnered significant attention as a potential standalone treatment. Various in vitro, in vivo, and early clinical trial data have provided support for this approach to varying extents. Novel compounds that inhibit PIM1 kinase have shown effectiveness and a favorable toxicity profile in preclinical studies. Several of these substances are now being studied in clinical trials due to their promising outcomes. This article provides a thorough examination of the PIM1 kinase pathways and the recent advancements in producing PIM1 kinase inhibitors for the treatment of cancer.

A novel NR4A2-HuR axis promotes pancreatic cancer growth and tumorigenesis that is inhibited by NR4A2 antagonists

Pancreatic ductal adenocarcinoma (PDAC) patients' express higher levels of the orphan Nuclear Receptor 4A2 (NR4A2, NURR1) compared to normal pancreas and NR4A2 is a prognostic factor for patient survival. Knockdown of NR4A2 by RNA interference (RNAi) inhibited cell proliferation, invasion, and migration. RNA sequencing performed in NR4A2(+/+) and NR4A2(-/-) MiaPaCa2 cells demonstrated that NR4A2 played a significant role in cellular metabolism. Human antigen R (HuR) and isocitrate dehydrogenase 1 (IDH1) were identified as NR4A2 target genes. HuR is a pro-oncogenic RNA binding protein and silencing of HuR by RNAi significantly downregulated expression of NR4A2. Expression of HuR and IDH1 were significantly downregulated after treatment with NR4A2 inverse agonist, 1,1-bis(3'-indolyl)-1-(p-chlorophenyl)methane resulting in significant inhibition of tumor growth in an athymic nude mouse xenograft model. This study demonstrates that NR4A2 and HuR regulate genes and signaling pathways that enhance tumorigenesis and targeting NR4A2 and HuR expression with an NR4A2 inverse agonist represents a novel regimen for treating PDAC.

LncRNAs as nodes for the cross-talk between autophagy and Wnt signaling in pancreatic cancer drug resistance

Pancreatic cancer is a malignancy with high mortality. In addition to the few symptoms until the disease reaches an advanced stage, the high fatality rate is attributed to its rapid development, drug resistance and lack of appropriate treatment. In the selection and research of therapeutic drugs, gemcitabine is the first-line drug for pancreatic cancer. Solving the problem of gemcitabine resistance in pancreatic cancer will contribute to the progress of pancreatic cancer treatment. Long non coding RNAs (lncRNAs), which are RNA transcripts longer than 200 nucleotides, play vital roles in cellular physiological metabolic activities. Currently, our group and others have found that some lncRNAs are aberrantly expressed in pancreatic cancer cells, which can regulate the process of cancer through autophagy and Wnt/β-catenin pathways simultaneously and affect the sensitivity of cancer cells to therapeutic drugs. This review presents an overview of the recent evidence concerning the node of lncRNA for the cross-talk between autophagy and Wnt/β-catenin signaling in pancreatic cancer, together with the practicability of lncRNAs and the core regulatory factors as targets in therapeutic resistance.

Distinct hypoxia-induced translational profiles of embryonic and adult-derived macrophages

Tissue resident macrophages are largely of embryonic (fetal liver) origin and long-lived, while bone marrow-derived macrophages (BMDM) are recruited following an acute perturbation, such as hypoxia in the setting of myocardial ischemia. Prior transcriptome analyses identified BMDM and fetal liver-derived macrophage (FLDM) differences at the RNA expression level. Posttranscriptional regulation determining mRNA stability and translation rate may override transcriptional signals in response to hypoxia. We profiled differentially regulated BMDM and FLDM transcripts in response to hypoxia at the level of mRNA translation. Using a translating ribosome affinity purification (TRAP) assay and RNA-seq, we identified non-overlapping transcripts with increased translation rate in BMDM (Ly6e, vimentin, PF4) and FLDM (Ccl7, Ccl2) after hypoxia. We further identified hypoxia-induced transcripts within these subsets that are regulated by the RNA-binding protein HuR. These findings define translational differences in macrophage subset gene expression programs, highlighting potential therapeutic targets in ischemic myocardium.

Deletion of the mRNA stability factor ELAVL1 (HuR) in pancreatic cancer cells disrupts the tumor microenvironment integrity

Stromal cells promote extensive fibrosis in pancreatic ductal adenocarcinoma (PDAC), which is associated with poor prognosis and therapeutic resistance. We report here for the first time that loss of the RNA-binding protein human antigen R (HuR, ELAVL1) in PDAC cells leads to reprogramming of the tumor microenvironment. In multiple in vivo models, CRISPR deletion of ELAVL1 in PDAC cells resulted in a decrease of collagen deposition, accompanied by a decrease of stromal markers (i.e. podoplanin, α-smooth muscle actin, desmin). RNA-sequencing data showed that HuR plays a role in cell-cell communication. Accordingly, cytokine arrays identified that HuR regulates the secretion of signaling molecules involved in stromal activation and extracellular matrix organization [i.e. platelet-derived growth factor AA (PDGFAA) and pentraxin 3]. Ribonucleoprotein immunoprecipitation analysis and transcription inhibition studies validated PDGFA mRNA as a novel HuR target. These data suggest that tumor-intrinsic HuR supports extrinsic activation of the stroma to produce collagen and desmoplasia through regulating signaling molecules (e.g. PDGFAA). HuR-deficient PDAC in vivo tumors with an altered tumor microenvironment are more sensitive to the standard of care gemcitabine, as compared to HuR-proficient tumors. Taken together, we identified a novel role of tumor-intrinsic HuR in its ability to modify the surrounding tumor microenvironment and regulate PDGFAA.

Pyrvinium Pamoate: Past, Present, and Future as an Anti-Cancer Drug

Pyrvinium, a lipophilic cation belonging to the cyanine dye family, has been used in the clinic as a safe and effective anthelminthic for over 70 years. Its structure, similar to some polyaminopyrimidines and mitochondrial-targeting peptoids, has been linked with mitochondrial localization and targeting. Over the past two decades, increasing evidence has emerged showing pyrvinium to be a strong anti-cancer molecule in various human cancers in vitro and in vivo. This efficacy against cancers has been attributed to diverse mechanisms of action, with the weight of evidence supporting the inhibition of mitochondrial function, the WNT pathway, and cancer stem cell renewal. Despite the overwhelming evidence demonstrating the efficacy of pyrvinium for the treatment of human cancers, pyrvinium has not yet been repurposed for the treatment of cancers. This review provides an in-depth analysis of the history of pyrvinium as a therapeutic, the rationale and data supporting its use as an anticancer agent, and the challenges associated with repurposing pyrvinium as an anti-cancer agent.

HuR-targeted agents: An insight into medicinal chemistry, biophysical, computational studies and pharmacological effects on cancer models

The Human antigen R (HuR) protein is an RNA-binding protein, ubiquitously expressed in human tissues, that orchestrates target RNA maturation and processing both in the nucleus and in the cytoplasm. A survey of known modulators of the RNA-HuR interactions is followed by a description of its structure and molecular mechanism of action - RRM domains, interactions with RNA, dimerization, binding modes with naturally occurring and synthetic HuR inhibitors. Then, the review focuses on HuR as a validated molecular target in oncology and briefly describes its role in inflammation. Namely, we show ample evidence for the involvement of HuR in the hallmarks and enabling characteristics of cancer, reporting findings from in vitro and in vivo studies; and we provide abundant experimental proofs of a beneficial role for the inhibition of HuR-mRNA interactions through silencing (CRISPR, siRNA) or pharmacological inhibition (small molecule HuR inhibitors).

Glucose deprivation enhances resistance to paclitaxel via ELAVL2/4-mediated modification of glycolysis in ovarian cancer cells

The dysregulation of glycolysis regardless of oxygen availability is one of the major characteristics of cancer cells. While the drug resistance of ovarian cancer cells has been extensively studied, the molecular mechanism of anticancer drug resistance under low-glucose conditions remains unknown. In this study, we investigated the pathway mediating drug resistance under low-glucose conditions by examining the relationship between embryonic lethal abnormal vision Drosophila homolog-like (ELAVL) protein and glycolysis-related enzymes. Ovarian cancer cells resistant to 2.5 nM paclitaxel were exposed to low-glucose media for 2 weeks, and the expression levels of ELAVL2, ELAVL4, glycolytic enzymes, and drug resistance-related proteins were elevated to levels comparable to those in cells resistant to 100 nM paclitaxel. Gene silencing of ELAVL2/4 using small interfering RNA prevented the upregulation of glycolysis-related enzymes, reduced lactate production, and sensitized 2.5 nM paclitaxel-resistant ovarian cancer cells to anticancer agents under hypoglycemic conditions. Furthermore, pharmacological inhibition of glycolytic enzymes with 2-deoxyglucose, a specific inhibitor of glycolysis, triggered caspase-dependent apoptosis, reduced lactate generation, and blocked the expression of drug resistance-related proteins under low-glucose conditions. These results suggest that the level of ELAVL2/4 is responsible for the development of chemoresistance through activation of the glycolysis pathway under glucose deprivation conditions.

Clinical development of IDH1 inhibitors for cancer therapy

Isocitrate dehydrogenase 1 (IDH1) has been investigated as a promising therapeutic target in select cancers with a mutated version of the enzyme (mtIDH1). With only one phase III trial published to date and two indications approved for routine clinical use by the FDA, we reviewed the entire clinical trial portfolio to broadly understand mtIDH1 inhibitor activity in patients. We queried PubMed.gov and ClinicalTrials.gov to identify published and ongoing clinical trials related to IDH1 and cancer. Progression-free survival (PFS), overall survival (OS), 2-hydroxyglutarate levels, and adverse events were summarized. To date, ten clinical trials investigating mtIDH1 inhibitors among patients with diverse malignancies (cholangiocarcinoma, acute myeloid leukemia, chondrosarcoma, glioma) have been published. Almost every trial (80%) has investigated ivosidenib. In multiple phase I trials, ivosidenib treatment resulted in promising radiographic and biochemical responses with improved survival outcomes (relative to historic data) among patients with both solid and hematologic mtIDH1 malignancies. Among patients enrolled in a phase III trial with advanced cholangiocarcinoma, ivosidenib resulted in a PFS rate of 32% at 6 months, as compared to 0% with placebo. There was a 5.2 month increase in OS with ivosidenib relative to placebo, after considering crossover. The treatment-specific grade ≥3 adverse event rate of ivosidenib was 2%-26% among all patients, and was just 3.6% among 284 patients who had a solid tumor across four trials. Although <1% of malignancies harbor IDH1 mutations, small molecule mtIDH1 inhibitors, namely ivosidenib, appear to be biologically active and well tolerated in patients with solid and hematologic mtIDH1 malignancies.

Divulging the Critical Role of HuR in Pancreatic Cancer as a Therapeutic Target and a Means to Overcome Chemoresistance

Simple Summary

With pancreatic cancer incidence constantly rising, constituting one of the most lethal type of cancers worldwide, the need for discovering novel therapeutic targets and approaches becomes of the utmost importance. Meanwhile, modern eating habits, hyperadiposity, mutational burden affecting core signaling pathways and the unique tumor microenvironment of pancreatic cancer tissues intermingle and form a disease that is lethal and hard to treat. The importance of HuR in pancreatic cancer has repeatedly been observed and represents a key molecule in pancreatic carcinogenesis and chemoresistance. Therefore, creating and obtaining new therapeutic skills against HuR protein could prove to be the answer to pancreatic cancer therapy.

Abstract

Pancreatic cancer is set to become the most lethal and common type of cancer worldwide. This is partly attributed to the mutational burden that affects core signaling pathways and the crosstalk of tumor cells with their surrounding microenvironment, but it is also due to modern eating habits. Hyperadiposity along with the constant rise in metabolic syndrome’s incidence contribute to a state of metaflammation that impacts immune cells and causes them to shift towards an immunosuppressive phenotype that, ultimately, allows tumor cells to evade immune control. Unfortunately, among the conventional therapeutic modalities and the novel therapeutic agents introduced, pancreatic cancer still holds one of the lowest response rates to therapy. Human antigen R (HuR), an RNA binding protein (RBP), has been repeatedly found to be implicated in pancreatic carcinogenesis and chemotherapy resistance through the posttranscriptional binding and regulation of mRNA target genes. Additionally, its overexpression has been linked to adverse clinical outcomes, in terms of tumor grade, stage, lymph node status and metastasis. These properties suggest the prospective role that HuR’s therapeutic targeting can play in facilitating pancreatic neoplasia and could provide the means to overcome chemoresistance.

Quercetin Impairs HuR-Driven Progression and Migration of Triple Negative Breast Cancer (TNBC) Cells

In the present study, we have explored the prognostic value of HuR gene as well as protein in breast cancers. Furthermore, we have also investigated the HuR therapeutic relevance in TNBCs, which is an aggressive breast cancer subtype. Using an online meta-analysis tool, we found that HuR protein overexpression positively correlates with reduced overall survival of TNBC patients (p = 0.028). Furthermore, we demonstrated that the TNBC breast cancer cell lines i.e., MDA-MB-231 and MDA-MB-468 are good model systems to study HuR protein, as they both exhibit a significant amount of cytoplasmic HuR (active form). Quercetin treatment significantly inhibited the cytoplasmic HuR in both TNBC cell lines. By using specific HuR siRNA, we established that quercetin-mediated inhibition of adhesion and migration of TNBC cells is dependent on HuR. Upon analyzing adhesion proteins i.e., β-catenin and CD44, we found that quercetin mediated effect on TNBC adhesion and migration was through the HuR-β-catenin axis and CD44, independently. Overall, the present results demonstrate that elevated HuR levels are associated with TNBC progression and relapse, and the ability of quercetin to inhibit cytoplasmic HuR protein provides a rationale for using it as an anticancer agent for the treatment of aggressive TNBCs.Supplemental data for this article is available online at at 10.1080/01635581.2021.1952628.

Translational remodeling by RNA-binding proteins and noncoding RNAs

Responsible for generating the proteome that controls phenotype, translation is the ultimate convergence point for myriad upstream signals that influence gene expression. System-wide adaptive translational reprogramming has recently emerged as a pillar of cellular adaptation. As classic regulators of mRNA stability and translation efficiency, foundational studies established the concept of collaboration and competition between RNA-binding proteins (RBPs) and noncoding RNAs (ncRNAs) on individual mRNAs. Fresh conceptual innovations now highlight stress-activated, evolutionarily conserved RBP networks and ncRNAs that increase the translation efficiency of populations of transcripts encoding proteins that participate in a common cellular process. The discovery of post-transcriptional functions for long noncoding RNAs (lncRNAs) was particularly intriguing given their cell-type-specificity and historical definition as nuclear-functioning epigenetic regulators. The convergence of RBPs, lncRNAs, and microRNAs on functionally related mRNAs to enable adaptive protein synthesis is a newer biological paradigm that highlights their role as "translatome (protein output) remodelers" and reinvigorates the paradigm of "RNA operons." Together, these concepts modernize our understanding of cellular stress adaptation and strategies for therapeutic development. This article is categorized under: RNA Interactions with Proteins and Other Molecules > Protein-RNA Interactions: Functional Implications Translation > Translation Regulation Regulatory RNAs/RNAi/Riboswitches > Regulatory RNAs.

Hepatic HuR protects against the pathogenesis of non-alcoholic fatty liver disease by targeting PTEN

The liver plays an important role in lipid and glucose metabolism. Here, we show the role of human antigen R (HuR), an RNA regulator protein, in hepatocyte steatosis and glucose metabolism. We investigated the level of HuR in the liver of mice fed a normal chow diet (NCD) and a high-fat diet (HFD). HuR was downregulated in the livers of HFD-fed mice. Liver-specific HuR knockout (HuRLKO) mice showed exacerbated HFD-induced hepatic steatosis along with enhanced glucose tolerance as compared with control mice. Mechanistically, HuR could bind to the adenylate uridylate-rich elements of phosphatase and tensin homolog deleted on the chromosome 10 (PTEN) mRNA 3' untranslated region, resulting in the increased stability of Pten mRNA; genetic knockdown of HuR decreased the expression of PTEN. Finally, lentiviral overexpression of PTEN alleviated the development of hepatic steatosis in HuRLKO mice in vivo. Overall, HuR regulates lipid and glucose metabolism by targeting PTEN.

Role of PRPS2 as a prognostic and therapeutic target in osteosarcoma

AIMS

Osteosarcoma (OS) is the most common primary malignant tumour of the bone. However, further improvement in survival has not been achieved due to a lack of well-validated prognostic markers and more effective therapeutic agents. Recently, the c-Myc-phosphoribosyl pyrophosphate synthetase 2 (PRPS2) pathway has been shown to promote nucleic acid metabolism and cancer cell proliferation in malignant melanoma; phosphorylated mammalian target of rapamycin (p-mTOR) has been upregulated and an effective therapeutic target in OS. However, the p-mTOR-PRPS2 pathway has not been evaluated in OS.

METHODS

In this study, the expression level of PRPS2, p-mTOR and marker of proliferation (MKI-67) was observed in a cohort of specimens (including 236 OS cases and 56 control samples) using immunohistochemistry, and the association between expression level and clinicopathological characteristics of patients with OS was analysed.

RESULTS

PRPS2 protein level, which is related to tumour proliferation, was higher in OS cells (p=0.003) than in fibrous dysplasia, and the higher PRPS2 protein level was associated with a higher tumour recurrence (p=0.001). In addition, our statistical analysis confirmed that PRPS2 is a novel, independent prognostic indicator of OS. Finally, we found that the expression of p-mTOR was associated with the poor prognosis of patients with OS (p<0.05).

CONCLUSIONS

PRPS2 is an independent prognostic marker and a potential therapeutic target for OS.

A network of RNA-binding proteins controls translation efficiency to activate anaerobic metabolism

Protein expression evolves under greater evolutionary constraint than mRNA levels, and translation efficiency represents a primary determinant of protein levels during stimuli adaptation. This raises the question as to the translatome remodelers that titrate protein output from mRNA populations. Here, we uncover a network of RNA-binding proteins (RBPs) that enhances the translation efficiency of glycolytic proteins in cells responding to oxygen deprivation. A system-wide proteomic survey of translational engagement identifies a family of oxygen-regulated RBPs that functions as a switch of glycolytic intensity. Tandem mass tag-pulse SILAC (TMT-pSILAC) and RNA sequencing reveals that each RBP controls a unique but overlapping portfolio of hypoxic responsive proteins. These RBPs collaborate with the hypoxic protein synthesis apparatus, operating as a translation efficiency checkpoint that integrates upstream mRNA signals to activate anaerobic metabolism. This system allows anoxia-resistant animals and mammalian cells to initiate anaerobic glycolysis and survive hypoxia. We suggest that an oxygen-sensitive RBP cluster controls anaerobic metabolism to confer hypoxia tolerance.

mRNA translation efficiency is regulated in response to stimuli. Here the authors employ mass spectrometry analysis of ribosome fractions and show that under hypoxia, oxygen-sensitive RNA binding proteins enhance the translation efficiency of glycolysis pathway transcripts.

Human antigen R: A potential therapeutic target for liver diseases

Human antigen R (HuR), also known as HuA and embryonic lethal abnormal vision-like 1 (ELAVL1), is a ubiquitously expressed RNA binding protein and functions as an RNA regulator and mediates the expression of various proteins by diverse post-transcriptional mechanisms. HuR has been well characterized in the inflammatory responses and in the development of various cancers. The importance of HuR-mediated roles in cell signaling, inflammation, fibrogenesis and cancer development in the liver has attracted a great deal of attention. However, there is still a substantial gap between the current understanding of the potential roles of HuR in the progression of liver disease and whether HuR can be targeted for the treatment of liver diseases. In this review, we introduce the function and mechanistic characterization of HuR, and then focus on the physiopathological roles of HuR in the development of different liver diseases, including hepatic inflammation, alcoholic liver diseases, non-alcoholic fatty liver diseases, viral hepatitis, liver fibrosis and liver cancers. We also summarize existing approaches targeting HuR function. In conclusion, although characterizing the liver-specific HuR function and demonstrating the multi-level regulative networks of HuR in the liver are still required, emerging evidence supports the notion that HuR represents a potential therapeutic target for the treatment of chronic liver diseases.

RNA binding protein HuR regulates extracellular matrix gene expression and pH homeostasis independent of controlling HIF-1α signaling in nucleus pulposus cells

Nucleus pulposus (NP) cells reside in the hypoxic niche of the intervertebral disc. Studies have demonstrated that RNA-binding protein HuR modulates hypoxic signaling in several cancers, however, its function in the disc is unknown. HuR did not show cytoplasmic translocation in hypoxia and its silencing did not alter levels of Hif-1α or HIF-targets in NP cells. RNA-Sequencing data revealed that important extracellular matrix-related genes including several collagens, MMPs, aggrecan, Tgf-β3 and Sdc4 were regulated by HuR. Further analysis of HuR-silenced NP cells confirmed that HuR maintained expression of these matrix genes. We confirmed decreased levels of secreted collagen I and Sdc4 and increased pro-MMP13 in HuR-knockdown cells. In addition, messenger ribonucleoprotein immunoprecipitation demonstrated HuR binding to Tgf-β3 and Sdc4 mRNAs. Interestingly, while HuR bound to Hif-1α and Vegf mRNAs, it was clear that compensatory mechanisms sustained their expression when HuR was silenced. Noteworthy, despite the presence of multiple HuR-binding sites and reported interaction in other cell types, HuR showed no binding to Pgk1, Eno1, Pdk1 and Pfkfb3 in NP cells. Metabolic studies showed a significant decrease in the extracellular acidification rate (ECAR) and mitochondrial oxygen consumption rate (OCR) and acidic pH in HuR-silenced NP cells, without appreciable change in total OCR. These changes were likely due to decreased Ca12 expression in HuR silenced cells. Taken together, our study demonstrates for the first time that HuR regulates extracellular matrix (ECM) and pH homeostasis of NP cells and has important implications in the maintenance of intervertebral disc health.

Human antigen R mediated post-transcriptional regulation of inhibitors of apoptosis proteins in pancreatic cancer

AIM

To determine the association of human antigen R (HuR) and inhibitors of apoptosis proteins (IAP1, IAP2) and prognosis in pancreatic cancer.

METHODS

Protein and mRNA expression levels of IAP1, IAP2 and HuR in pancreatic ductal adenocarcinoma (PDAC) were compared with normal pancreatic tissue. The correlations among IAP1/IAP2 and HuR as well as their respective correlations with clinicopathological parameters were analyzed. The Kaplan-Meier method and log-rank tests were used for survival analysis. Immunoprecipitation assay was performed to demonstrate HuR binding to IAP1, IAP2 mRNA. PANC1 cells were transfected with either anti-HuR siRNA or control siRNA for 72 h and quantitative reverse transcription polymerase chain reaction (RT-PCR), western blot analysis was carried out.

RESULTS

RT-PCR analysis revealed that HuR, IAP1, IAP2 mRNA expression were accordingly 3.3-fold, 5.5-fold and 8.4 higher in the PDAC when compared to normal pancreas (P < 0.05). Expression of IAP1 was positively strongly correlated with HuR expression (P < 0.05, r = 0.783). Western blot analysis confirmed RT-PCR results. High IAP1 expression, tumor resection status, T stage, lymph-node metastases, tumor differentiation grade, perineural and lymphatic invasion were identified as significant factors for shorter survival in PDAC patients (P < 0.05). Immunohistological analysis showed that HuR was mainly expressed in the ductal cancer cell's nucleus and less so in cytoplasm. RNA immunoprecipitation analysis confirmed IAP1 and IAP2 post-transcriptional regulation by HuR protein. Following siHuR transfection, IAP1 mRNA and protein levels were decreased, however IAP2 expression levels were increased.

CONCLUSION

HuR mediated overexpression of IAP1 significantly correlates with poor outcomes and early progression of pancreatic cancer. Further studies are needed to assess the underlying mechanisms.

Metabolic Dependencies in Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDA) is a highly lethal cancer with a long-term survival rate under 10%. Available cytotoxic chemotherapies have significant side effects, and only marginal therapeutic efficacy. FDA approved drugs currently used against PDA target DNA metabolism and DNA integrity. However, alternative metabolic targets beyond DNA may prove to be much more effective. PDA cells are forced to live within a particularly severe microenvironment characterized by relative hypovascularity, hypoxia, and nutrient deprivation. Thus, PDA cells must possess biochemical flexibility in order to adapt to austere conditions. A better understanding of the metabolic dependencies required by PDA to survive and thrive within a harsh metabolic milieu could reveal specific metabolic vulnerabilities. These molecular requirements can then be targeted therapeutically, and would likely be associated with a clinically significant therapeutic window since the normal tissue is so well-perfused with an abundant nutrient supply. Recent work has uncovered a number of promising therapeutic targets in the metabolic domain, and clinicians are already translating some of these discoveries to the clinic. In this review, we highlight mitochondria metabolism, non-canonical nutrient acquisition pathways (macropinocytosis and use of pancreatic stellate cell-derived alanine), and redox homeostasis as compelling therapeutic opportunities in the metabolic domain.

RNA-Binding Protein HuR Regulates Both Mutant and Wild-Type IDH1 in IDH1-Mutated Cancer

Isocitrate dehydrogenase 1 (IDH1) is the most commonly mutated metabolic enzyme in human malignancy. A heterozygous genetic alteration, arginine 132, promotes the conversion of α-ketoglutarate to D-2-hydroxyglutarate (2-HG). Although pharmacologic inhibitors of mutant IDH1 are promising, resistance mechanisms to targeted therapy are not understood. Additionally, the role of wild-type IDH1 (WT.IDH1) in cancer requires further study. Recently, it was observed that the regulatory RNA-binding protein, HuR (ELAVL1), protects nutrient-deprived cancer cells without IDH1 mutations, by stabilizing WT.IDH1 transcripts. In the present study, a similar regulatory effect on both mutant (Mut.IDH1) and WT.IDH1 transcripts in heterozygous IDH1-mutant tumors is observed. In ribonucleoprotein immunoprecipitation assays of IDH1-mutant cell lines, wild-type and mutant IDH1 mRNAs each bound to HuR. Both isoforms were profoundly downregulated at the mRNA and protein levels after genetic suppression of HuR (siRNAs or CRISPR deletion) in HT1080 (R132C IDH1 mutation) and BT054 cells (R132H). Proliferation and invasion were adversely affected after HuR suppression and metabolomic studies revealed a reduction in Pentose Phosphate Pathway metabolites, nucleotide precursors, and 2-HG levels. HuR-deficient cells were especially sensitive to stress, including low glucose conditions or a mutant IDH1 inhibitor (AGI-5198). IDH1-mutant cancer cells were rescued by WT.IDH1 overexpression to a greater extent than Mut.IDH1 overexpression under these conditions. This study reveals the importance of HuR's regulation of both mutant and wild-type IDH1 in tumors harboring a heterozygous IDH1 mutation with implications for therapy. IMPLICATIONS: This study highlights the HuR-IDH1 (mutant and wild-type IDH1) regulatory axis as a critical, actionable therapeutic target in IDH1-mutated cancer, and incomplete blockade of the entire HuR-IDH1 survival axis would likely diminish the efficacy of drugs that selectively target only the mutant isoenzyme.

Complex HuR function in pancreatic cancer cells

Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal cancers with dismal patient outcomes. The underlying core genetic drivers of disease have been identified in human tumor specimens and described in genetically engineered mouse models. These genetic drivers of PDAC include KRAS signaling, TP53 mutations, and genetic loss of the SMAD4 tumor suppressor protein. Beyond the known mutational landscape of PDAC genomes, alternative disrupted targets that extend beyond conventional genetic mutations have been elusive and understudied in the context of PDAC cell therapeutic resistance and survival. This last point is important because PDAC tumors have a unique and complex tumor microenvironment that includes hypoxic and nutrient-deprived niches that could select for cell populations that garner therapeutic resistance, explaining tumor heterogeneity in regards to response to different therapies. We and others have embarked in a line of investigation focused on the key molecular mechanism of posttranscriptional gene regulation that is altered in PDAC cells and supports this pro-survival phenotype intrinsic to PDAC cells. Specifically, the key regulator of this mechanism is a RNA-binding protein, HuR (ELAVL1), first described in cancer nearly two decades ago. Herein, we will provide a brief overview of the work demonstrating the importance of this RNA-binding protein in PDAC biology and then provide insight into ongoing work developing therapeutic strategies aimed at targeting this molecule in PDAC cells. This article is categorized under: RNA in Disease and Development > RNA in Disease.

Cytoplasmic HuR Status Predicts Disease-free Survival in Resected Pancreatic Cancer: A Post-hoc Analysis From the International Phase III ESPAC-3 Clinical Trial

OBJECTIVES

We tested cytoplasmic HuR (cHuR) as a predictive marker for response to chemotherapy by examining tumor samples from the international European Study Group of Pancreatic Cancer-3 trial, in which patients with resected pancreatic ductal adenocarcinoma (PDA) received either gemcitabine (GEM) or 5-fluorouracil (5-FU) adjuvant monotherapy.

BACKGROUND

Previous studies have implicated the mRNA-binding protein, HuR (ELAVL1), as a predictive marker for PDA treatment response in the adjuvant setting. These studies were, however, based on small cohorts of patients outside of a clinical trial, or a clinical trial in which patients received multimodality therapy with concomitant radiation.

METHODS

Tissue samples from 379 patients with PDA enrolled in the European Study Group of Pancreatic Cancer-3 trial were immunolabeled with an anti-HuR antibody and scored for cHuR expression. Patients were dichotomized into groups of high versus low cHuR expression.

RESULTS

There was no association between cHuR expression and prognosis in the overall cohort [disease-free survival (DFS), P = 0.44; overall survival, P = 0.41). Median DFS for patients with high cHuR was significantly greater for patients treated with 5-FU compared to GEM [20.1 months, confidence interval (CI): 8.3-36.4 vs 10.9 months, CI: 7.5-14.2; P = 0.04]. Median DFS was similar between the treatment arms in patients with low cHuR (5-FU, 12.8 months, CI: 10.6-14.6 vs GEM, 12.9 months, CI: 11.2-15.4).

CONCLUSIONS

Patients with high cHuR-expressing tumors may benefit from 5-FU-based adjuvant therapy as compared to GEM, whereas those patients with low cHuR appear to have no survival advantage with GEM compared with 5-FU. Further studies are needed to validate HuR as a biomarker in both future monotherapy and multiagent regimens.

Posttranscriptional Upregulation of IDH1 by HuR Establishes a Powerful Survival Phenotype in Pancreatic Cancer Cells

Cancer aggressiveness may result from the selective pressure of a harsh nutrient-deprived microenvironment. Here we illustrate how such conditions promote chemotherapy resistance in pancreatic ductal adenocarcinoma (PDAC). Glucose or glutamine withdrawal resulted in a 5- to 10-fold protective effect with chemotherapy treatment. PDAC xenografts were less sensitive to gemcitabine in hypoglycemic mice compared with hyperglycemic mice. Consistent with this observation, patients receiving adjuvant gemcitabine (n = 107) with elevated serum glucose levels (HgbA1C > 6.5%) exhibited improved survival. We identified enhanced antioxidant defense as a driver of chemoresistance in this setting. ROS levels were doubled in vitro by either nutrient withdrawal or gemcitabine treatment, but depriving PDAC cells of nutrients before gemcitabine treatment attenuated this effect. Mechanistic investigations based on RNAi or CRISPR approaches implicated the RNA binding protein HuR in preserving survival under nutrient withdrawal, with or without gemcitabine. Notably, RNA deep sequencing and functional analyses in HuR-deficient PDAC cell lines identified isocitrate dehydrogenase 1 (IDH1) as the sole antioxidant enzyme under HuR regulation. HuR-deficient PDAC cells lacked the ability to engraft successfully in immunocompromised mice, but IDH1 overexpression in these cells was sufficient to fully restore chemoresistance under low nutrient conditions. Overall, our findings highlight the HuR-IDH1 regulatory axis as a critical, actionable therapeutic target in pancreatic cancer. Cancer Res; 77(16); 4460-71. ©2017 AACR.

Hu antigen R (HuR) multimerization contributes to glioma disease progression

Among primary brain cancers, gliomas are the most deadly and most refractory to current treatment modalities. Previous reports overwhelmingly support the role of the RNA-binding protein Hu antigen R (HuR) as a positive regulator of glioma disease progression. HuR expression is consistently elevated in tumor tissues, and a cytoplasmic localization appears essential for HuR-dependent oncogenic transformation. Here, we report HuR aggregation (multimerization) in glioma and the analysis of this tumor-specific HuR protein multimerization in clinical brain tumor samples. Using a split luciferase assay, a bioluminescence resonance energy transfer technique, and site-directed mutagenesis, we examined the domains involved in HuR multimerization. Results obtained with the combination of the split HuR luciferase assay with the bioluminescence resonance energy transfer technique suggested that multiple (at least three) HuR molecules come together during HuR multimerization in glioma cells. Using these data, we developed a model of HuR multimerization in glioma cells. We also demonstrate that exposing glioma cells to the HuR inhibitor tanshinone group compound 15,16-dihydrotanshinone-I or to the newly identified compound 5 disrupts HuR multimerization modules and reduces tumor cell survival and proliferation. In summary, our findings provide new insights into HuR multimerization in glioma and highlight possible pharmacological approaches for targeting HuR domains involved in cancer cell-specific multimerization.

CRISPR Knockout of the HuR Gene Causes a Xenograft Lethal Phenotype

Pancreatic ductal adenocarcinoma (PDA) is the third leading cause of cancer-related deaths in the United States, whereas colorectal cancer is the third most common cancer. The RNA-binding protein HuR (ELAVL1) supports a pro-oncogenic network in gastrointestinal (GI) cancer cells through enhanced HuR expression. Using a publically available database, HuR expression levels were determined to be increased in primary PDA and colorectal cancer tumor cohorts as compared with normal pancreas and colon tissues, respectively. CRISPR/Cas9 technology was successfully used to delete the HuR gene in both PDA (MIA PaCa-2 and Hs 766T) and colorectal cancer (HCT116) cell lines. HuR deficiency has a mild phenotype, in vitro, as HuR-deficient MIA PaCa-2 (MIA.HuR-KO(-/-)) cells had increased apoptosis when compared with isogenic wild-type (MIA.HuR-WT(+/+)) cells. Using this isogenic system, mRNAs were identified that specifically bound to HuR and were required for transforming a two-dimensional culture into three dimensional (i.e., organoids). Importantly, HuR-deficient MIA PaCa-2 and Hs 766T cells were unable to engraft tumors in vivo compared with control HuR-proficient cells, demonstrating a unique xenograft lethal phenotype. Although not as a dramatic phenotype, CRISPR knockout HuR HCT116 colon cancer cells (HCT.HuR-KO(-/-)) showed significantly reduced in vivo tumor growth compared with controls (HCT.HuR-WT(+/+)). Finally, HuR deletion affects KRAS activity and controls a subset of pro-oncogenic genes.Implications: The work reported here supports the notion that targeting HuR is a promising therapeutic strategy to treat GI malignancies. Mol Cancer Res; 15(6); 696-707. ©2017 AACR.

In Arabidopsis thaliana distinct alleles encoding mitochondrial RNA PROCESSING FACTOR 4 support the generation of additional 5' termini of ccmB transcripts

In plant mitochondria, the 5' ends of many transcripts are generated post-transcriptionally. We show that the pentatricopeptide repeat (PPR) protein RNA PROCESSING FACTOR 4 (RPF4) supports the generation of extra 5' ends of ccmB transcripts in Landsberg erecta (Ler) and a number of other Arabidopsis thaliana ecotypes. RPF4 was identified in Ler applying a forward genetic approach supported by complementation studies of ecotype Columbia (Col), which generates the Ler-type extra ccmB 5' termini only after the introduction of the RPF4 allele from Ler. Studies with chimeric RPF4 proteins composed of various parts of the RPF4 proteins from Ler and Col identified differences in the N-terminal and central PPR motifs that explain ecotype-specific variations in ccmB processing. These results fit well with binding site predictions in ccmB transcripts based on the known determinants of nucleotide base recognition by PPR motifs.

Pancreatic Cancer: A Review

Pancreatic cancer is now the third leading cause of cancer related deaths in the United States, yet advances in treatment options have been minimal over the past decade. In this review, we summarize the evaluation and treatments for this disease. We highlight molecular advances that hopefully will soon translate into improved outcomes.

Targeting the mRNA-binding protein HuR impairs malignant characteristics of pancreatic ductal adenocarcinoma cells

Post-transcriptional regulation is a powerful mediator of gene expression, and can rapidly alter the expression of numerous transcripts involved in tumorigenesis. We have previously shown that the mRNA-binding protein HuR (ELAVL1) is elevated in human pancreatic ductal adenocarcinoma (PDA) specimens compared to normal pancreatic tissues, and its cytoplasmic localization is associated with increased tumor stage. To gain a better insight into HuR’s role in PDA biology and to assess it as a candidate therapeutic target, we altered HuR expression in PDA cell lines and characterized the resulting phenotype in preclinical models. HuR silencing by short hairpin and small interfering RNAs significantly decreased cell proliferation and anchorage-independent growth, as well as impaired migration and invasion. In comparison, HuR overexpression increased migration and invasion, but had no significant effects on cell proliferation and anchorage-independent growth. Importantly, two distinct targeted approaches to HuR silencing showed marked impairment in tumor growth in mouse xenografts. NanoString nCounter^® analyses demonstrated that HuR regulates core biological processes, highlighting that HuR inhibition likely thwarts PDA viability through post-transcriptional regulation of diverse signaling pathways (e.g. cell cycle, apoptosis, DNA repair). Taken together, our study suggests that targeted inhibition of HuR may be a novel, promising approach to the treatment of PDA.

Iron Deprivation Induces Transcriptional Regulation of Mitochondrial Biogenesis

Mitochondria are essential organelles that adapt to stress and environmental changes. Among the nutrient signals that affect mitochondrial form and function is iron, whose depletion initiates a rapid and reversible decrease in mitochondrial biogenesis through unclear means. Here we demonstrate that, unlike the canonical iron-induced alterations to transcript stability, loss of iron dampens the transcription of genes encoding mitochondrial proteins with no change to transcript half-life. Using mass spectrometry, we demonstrate that these transcriptional changes are accompanied by dynamic alterations to histone acetylation and methylation levels that are largely reversible upon readministration of iron. Moreover, histone deacetylase inhibition abrogates the decreased histone acetylation observed upon iron deprivation and restores normal transcript levels at genes encoding mitochondrial proteins. Collectively, we demonstrate that deprivation of an essential nutrient induces transcriptional repression of organellar biogenesis involving epigenetic alterations.

HuR Contributes to TRAIL Resistance by Restricting Death Receptor 4 Expression in Pancreatic Cancer Cells

Pancreatic ductal adenocarcinoma (PDA) is one of the most lethal cancers, in part, due to resistance to both conventional and targeted therapeutics. TRAIL directly induces apoptosis through engagement of cell surface Death Receptors (DR4 and DR5), and has been explored as a molecular target for cancer treatment. Clinical trials with recombinant TRAIL and DR-targeting agents, however, have failed to show overall positive outcomes. Herein, we identify a novel TRAIL resistance mechanism governed by Hu antigen R (HuR, ELAV1), a stress-response protein abundant and functional in PDA cells. Exogenous HuR overexpression in TRAIL-sensitive PDA cell lines increases TRAIL resistance whereas silencing HuR in TRAIL-resistant PDA cells, by siRNA oligo-transfection, decreases TRAIL resistance. PDA cell exposure to soluble TRAIL induces HuR translocation from the nucleus to the cytoplasm. Furthermore, it is demonstrated that HuR interacts with the 3'-untranslated region (UTR) of DR4 mRNA. Pre-treatment of PDA cells with MS-444 (Novartis), an established small molecule inhibitor of HuR, substantially increased DR4 and DR5 cell surface levels and enhanced TRAIL sensitivity, further validating HuR's role in affecting TRAIL apoptotic resistance. NanoString analyses on the transcriptome of TRAIL-exposed PDA cells identified global HuR-mediated increases in antiapoptotic processes. Taken together, these data extend HuR's role as a key regulator of TRAIL-induced apoptosis.

IMPLICATIONS

Discovery of an important new HuR-mediated TRAIL resistance mechanism suggests that tumor-targeted HuR inhibition increases sensitivity to TRAIL-based therapeutics and supports their re-evaluation as an effective treatment for PDA patients. Mol Cancer Res; 14(7); 599-611. ©2016 AACR.

Glucose metabolic phenotype of pancreatic cancer

AIM: To construct a global “metabolic phenotype” of pancreatic ductal adenocarcinoma (PDAC) reflecting tumour-related metabolic enzyme expression.

METHODS: A systematic review of the literature was performed using OvidSP and PubMed databases using keywords “pancreatic cancer” and individual glycolytic and mitochondrial oxidative phosphorylation (MOP) enzymes. Both human and animal studies investigating the oncological effect of enzyme expression changes and inhibitors in both an in vitro and in vivo setting were included in the review. Data reporting changes in enzyme expression and the effects on PDAC cells, such as survival and metastatic potential, were extracted to construct a metabolic phenotype.

RESULTS: Seven hundred and ten papers were initially retrieved, and were screened to meet the review inclusion criteria. 107 unique articles were identified as reporting data involving glycolytic enzymes, and 28 articles involving MOP enzymes in PDAC. Data extraction followed a pre-defined protocol. There is consistent over-expression of glycolytic enzymes and lactate dehydrogenase in keeping with the Warburg effect to facilitate rapid adenosine-triphosphate production from glycolysis. Certain isoforms of these enzymes were over-expressed specifically in PDAC. Altering expression levels of HK, PGI, FBA, enolase, PK-M2 and LDA-A with metabolic inhibitors have shown a favourable effect on PDAC, thus identifying these as potential therapeutic targets. However, the Warburg effect on MOP enzymes is less clear, with different expression levels at different points in the Krebs cycle resulting in a fundamental change of metabolite levels, suggesting that other essential anabolic pathways are being stimulated.

CONCLUSION: Further characterisation of the PDAC metabolic phenotype is necessary as currently there are few clinical studies and no successful clinical trials targeting metabolic enzymes.

Delivery of Therapeutics Targeting the mRNA-Binding Protein HuR Using 3DNA Nanocarriers Suppresses Ovarian Tumor Growth

Growing evidence shows that cancer cells use mRNA-binding proteins and miRNAs to posttranscriptionally regulate signaling pathways to adapt to harsh tumor microenvironments. In ovarian cancer, cytoplasmic accumulation of mRNA-binding protein HuR (ELAVL1) is associated with poor prognosis. In this study, we observed high HuR expression in ovarian cancer cells compared with ovarian primary cells, providing a rationale for targeting HuR. RNAi-mediated silencing of HuR in ovarian cancer cells significantly decreased cell proliferation and anchorage-independent growth, and impaired migration and invasion. In addition, HuR-depleted human ovarian xenografts were smaller than control tumors. A biodistribution study showed effective tumor-targeting by a novel Cy3-labeled folic acid (FA)-derivatized DNA dendrimer nanocarrier (3DNA). We combined siRNAs against HuR with FA-3DNA and found that systemic administration of the resultant FA-3DNA-siHuR conjugates to ovarian tumor-bearing mice suppressed tumor growth and ascites development, significantly prolonging lifespan. NanoString gene expression analysis identified multiple HuR-regulated genes that function in many essential cellular and molecular pathways, an attractive feature of candidate therapeutic targets. Taken together, these results are the first to demonstrate the versatility of the 3DNA nanocarrier for in vivo-targeted delivery of a cancer therapeutic and support further preclinical investigation of this system adapted to siHuR-targeted therapy for ovarian cancer.

HuR mediated post-transcriptional regulation as a new potential adjuvant therapeutic target in chemotherapy for pancreatic cancer

AIM

To investigate the expression of HuR in pancreatic ductal adenocarcinoma (PDA) and to assess the effects of HuR silencing on the expression of cyclooxygenase-2 (COX-2) and heme oxygenase-1 (HO-1) and the in vitro response to gemcitabine (GEM) treatment in pancreatic cell lines.

METHODS

We compared the expression of HuR, COX-2, and HO-1 in PDA and normal pancreatic tissue using quantitative reverse transcription polymerase chain reaction (qRT-PCR) and western blot. In addition, the HuR, COX-2 and HO-1 were analyzed in four types of cancer cell lines (MiaPaca2, Su.86.86, Capan-1, and Capan-2) with and without GEM treatment. Immunocytofluorescence analysis was used to investigate HuR localization in cells. Cell viability and response to GEM after HuR silencing were determined with the 3-(4,5-dimethylthiazol-2-Yl)-2,5-diphenyltetrazolium bromide test and the crystal violet clonogenic assay, respectively. To measure apoptosis, activation of caspases 3/7 was evaluated using immunofluorescence.

RESULTS

In PDA tissue obtained from patients not treated with GEM, HuR mRNA expression was 3.2 times lower (P < 0.05) and COX-2 and HO-1 mRNA expression was 2.3-fold and 7.2-fold higher (P < 0.05), respectively, than normal pancreatic tissue (from organ donor). qRT-PCR analysis showed that HuR, COX-2, and HO-1 mRNA were overexpressed in all cancer cell lines treated with the half maximal inhibitory concentration (IC50) dose of GEM compared with control cells (P < 0.05). Western blot analysis revealed that COX-2 and HO-1 levels were significantly decreased in cancer cells after HuR silencing. Furthermore, HuR silencing increased the response to GEM treatment and decreased cell viability by 11.6%-53.7% compared to control cell lines. Caspases 3 and 7 were activated after HuR silencing and GEM treatment in all pancreatic cancer cell lines. In comparison, treatment with GEM alone did not activate caspases 3 and 7 in the same cell lines.

CONCLUSION

HuR mediated post-transcriptional upregulation of COX-2 and HO-1 expression after GEM treatment in pancreatic cancer cells. HuR silencing significantly increased the effectiveness of GEM treatment in vitro.

The mRNA-binding protein HuR promotes hypoxia-induced chemoresistance through posttranscriptional regulation of the proto-oncogene PIM1 in pancreatic cancer cells

Previously, it has been shown that pancreatic ductal adenocarcinoma (PDA) tumors exhibit high levels of hypoxia, characterized by low oxygen pressure (pO2) and decreased O2 intracellular perfusion. Chronic hypoxia is strongly associated with resistance to cytotoxic chemotherapy and chemoradiation in an understudied phenomenon known as hypoxia-induced chemoresistance. The hypoxia-inducible, pro-oncogenic, serine-threonine kinase PIM1 (Proviral Integration site for Moloney murine leukemia virus 1) has emerged as a key regulator of hypoxia-induced chemoresistance in PDA and other cancers. Although its role in therapeutic resistance has been described previously, the molecular mechanism behind PIM1 overexpression in PDA is unknown. Here, we demonstrate that cis-acting AU-rich elements (ARE) present within a 38-base pair region of the PIM1 mRNA 3'-untranslated region mediate a regulatory interaction with the mRNA stability factor HuR (Hu antigen R) in the context of tumor hypoxia. Predominantly expressed in the nucleus in PDA cells, HuR translocates to the cytoplasm in response to hypoxic stress and stabilizes the PIM1 mRNA transcript, resulting in PIM1 protein overexpression. A reverse-phase protein array revealed that HuR-mediated regulation of PIM1 protects cells from hypoxic stress through phosphorylation and inactivation of the apoptotic effector BAD and activation of MEK1/2. Importantly, pharmacological inhibition of HuR by MS-444 inhibits HuR homodimerization and its cytoplasmic translocation, abrogates hypoxia-induced PIM1 overexpression and markedly enhances PDA cell sensitivity to oxaliplatin and 5-fluorouracil under physiologic low oxygen conditions. Taken together, these results support the notion that HuR has prosurvival properties in PDA cells by enabling them with growth advantages in stressful tumor microenvironment niches. Accordingly, these studies provide evidence that therapeutic disruption of HuR's regulation of PIM1 may be a key strategy in breaking an elusive chemotherapeutic resistance mechanism acquired by PDA cells that reside in hypoxic PDA microenvironments.

Induction of VEGFA mRNA translation by CoCl2 mediated by HuR

Vascular endothelial growth factor (VEGF) A is a master regulator of neovascularization and angiogenesis. VEGFA is potently induced by hypoxia and by pathological conditions including diabetic retinopathy and tumorigenesis. Fine-tuning of VEGFA expression by different stimuli is important for maintaining tissue vascularization and organ homeostasis. Here, we tested the effect of the hypoxia mimetic cobalt chloride (CoCl2) on VEGFA expression in human cervical carcinoma HeLa cells. We found that CoCl2 increased the levels of VEGFA mRNA and VEGFA protein without affecting VEGFA mRNA stability. Biotin pulldown analysis to capture the RNA-binding proteins (RBPs) bound to VEGFA mRNA followed by mass spectrometry analysis revealed that the RBP HuR [human antigen R, a member of the embryonic lethal abnormal vision (ELAV) family of proteins], interacts with VEGFA mRNA. VEGFA mRNA-tagging experiments showed that exposure to CoCl2 increases the interaction of HuR with VEGFA mRNA and promoted the colocalization of HuR and the distal part of the VEGFA 3'-untranslated region (UTR) in the cytoplasm. We propose that under hypoxia-like conditions, HuR enhances VEGFA mRNA translation.

MUC1 Promoter-Driven DTA as a Targeted Therapeutic Strategy against Pancreatic Cancer

Mucin1 (MUC1) is overexpressed in pancreatic ductal adenocarcinoma (PDA) and is associated with tumor aggressiveness, suggesting that MUC1 is a promising therapeutic target for promoter-driven diphtheria toxin A (DTA). Endogenous MUC1 transcript levels were analyzed by quantitative PCR (qPCR) in multiple PDA cells (Capan1, HPAFII, Su.86.86, Capan2, Hs766T, MiaPaCa2, and Panc1). Expression levels were correlated with luciferase activity and cell death after transfection with MUC1 promoter-driven luciferase and DTA constructs. MUC1-positive (+) cells had significantly elevated MUC1 mRNA expression compared with MUC1-negative (-) cells. Luciferase activity was significantly higher in MUC1(+) cells when transfected with MUC1 promoter-driven luciferase and MUC1(+) cells underwent enhanced cell death after transfection with a single dose of MUC1 promoter-driven DTA. IFNγ pretreatment enhanced MUC1 expression in MUC1(-) cells and induced sensitivity to MUC1-DTA therapy. Matched primary and metastatic tumor lesions from clinical specimens revealed similar MUC1 IHC labeling patterns, and a tissue microarray of human PDA biopsies revealed increased immunolabeling with a combination of MUC1 and mesothelin (MSLN) antibodies, compared with either antibody alone. Combining MUC1 with MSLN-targeted DTA enhanced drug efficacy in an in vitro model of heterogeneous PDA. These data demonstrate that MUC1 promoter-driven DTA preferentially kills MUC1-expressing PDA cells and drugs that enhance MUC1 expression sensitize PDA cells with low MUC1 expression.

IMPLICATIONS

MUC1 expression in primary and metastatic lesions provides a rationale for the development of a systemic MUC1 promoter-driven DTA therapy that may be further enhanced by combination with other promoter-driven DTA constructs.

Hu antigen R (HuR) is a positive regulator of the RNA-binding proteins TDP-43 and FUS/TLS: implications for amyotrophic lateral sclerosis

Posttranscriptional gene regulation is governed by a network of RNA-binding proteins (RBPs) that interact with regulatory elements in the mRNA to modulate multiple molecular processes, including splicing, RNA transport, RNA stability, and translation. Mounting evidence indicates that there is a hierarchy within this network whereby certain RBPs cross-regulate other RBPs to coordinate gene expression. HuR, an RNA-binding protein we linked previously to aberrant VEGF mRNA metabolism in models of SOD1-associated amyotrophic lateral sclerosis, has been identified as being high up in this hierarchy, serving as a regulator of RNA regulators. Here we investigated the role of HuR in regulating two RBPs, TDP-43 and FUS/TLS, that have been linked genetically to amyotrophic lateral sclerosis. We found that HuR promotes the expression of both RBPs in primary astrocytes and U251 cells under normal and stressed (hypoxic) conditions. For TDP-43, we found that HuR binds to the 3' untranslated region (UTR) and regulates its expression through translational efficiency rather than RNA stability. With HuR knockdown, there was a shift of TDP-43 and FUS mRNAs away from polysomes, consistent with translational silencing. The TDP-43 splicing function was attenuated upon HuR knockdown and could be rescued by ectopic TDP-43 lacking the 3' UTR regulatory elements. Finally, conditioned medium from astrocytes in which HuR or TDP-43 was knocked down produced significant motor neuron and cortical neuron toxicity in vitro. These findings indicate that HuR regulates TDP-43 and FUS/TLS expression and that loss of HuR-mediated RNA processing in astrocytes can alter the molecular and cellular landscape to produce a toxic phenotype.

Intestinal epithelial HuR modulates distinct pathways of proliferation and apoptosis and attenuates small intestinal and colonic tumor development

HuR is a ubiquitous nucleocytoplasmic RNA-binding protein that exerts pleiotropic effects on cell growth and tumorigenesis. In this study, we explored the impact of conditional, tissue-specific genetic deletion of HuR on intestinal growth and tumorigenesis in mice. Mice lacking intestinal expression of HuR (Hur (IKO) mice) displayed reduced levels of cell proliferation in the small intestine and increased sensitivity to doxorubicin-induced acute intestinal injury, as evidenced by decreased villus height and a compensatory shift in proliferating cells. In the context of Apc(min/+) mice, a transgenic model of intestinal tumorigenesis, intestinal deletion of the HuR gene caused a three-fold decrease in tumor burden characterized by reduced proliferation, increased apoptosis, and decreased expression of transcripts encoding antiapoptotic HuR target RNAs. Similarly, Hur(IKO) mice subjected to an inflammatory colon carcinogenesis protocol [azoxymethane and dextran sodium sulfate (AOM-DSS) administration] exhibited a two-fold decrease in tumor burden. Hur(IKO) mice showed no change in ileal Asbt expression, fecal bile acid excretion, or enterohepatic pool size that might explain the phenotype. Moreover, none of the HuR targets identified in Apc(min/+)Hur(IKO) were altered in AOM-DSS-treated Hur(IKO) mice, the latter of which exhibited increased apoptosis of colonic epithelial cells, where elevation of a unique set of HuR-targeted proapoptotic factors was documented. Taken together, our results promote the concept of epithelial HuR as a contextual modifier of proapoptotic gene expression in intestinal cancers, acting independently of bile acid metabolism to promote cancer. In the small intestine, epithelial HuR promotes expression of prosurvival transcripts that support Wnt-dependent tumorigenesis, whereas in the large intestine epithelial HuR indirectly downregulates certain proapoptotic RNAs to attenuate colitis-associated cancer. Cancer Res; 74(18); 5322-35. ©2014 AACR.

HuR posttranscriptionally regulates WEE1: implications for the DNA damage response in pancreatic cancer cells

HuR (ELAV1), an RNA-binding protein abundant in cancer cells, primarily resides in the nucleus, but under specific stress (e.g., gemcitabine), HuR translocates to the cytoplasm in which it tightly modulates the expression of mRNA survival cargo. Here, we demonstrate for the first time that stressing pancreatic ductal adenocarcinoma (PDA) cells by treatment with DNA-damaging anticancer agents (mitomycin C, oxaliplatin, cisplatin, carboplatin, and a PARP inhibitor) results in HuR's translocation from the nucleus to the cytoplasm. Importantly, silencing HuR in PDA cells sensitized the cells to these agents, whereas overexpressing HuR caused resistance. HuR's role in the efficacy of DNA-damaging agents in PDA cells was, in part, attributed to the acute upregulation of WEE1 by HuR. WEE1, a mitotic inhibitor kinase, regulates the DNA damage repair pathway, and therapeutic inhibition of WEE1 in combination with chemotherapy is currently in early phase trials for the treatment of cancer. We validate WEE1 as a HuR target in vitro and in vivo by demonstrating (i) direct binding of HuR to WEE1's mRNA (a discrete 56-bp region residing in the 3' untranslated region) and (ii) HuR siRNA silencing and overexpression directly affects the protein levels of WEE1, especially after DNA damage. HuR's positive regulation of WEE1 increases γ-H2AX levels, induces Cdk1 phosphorylation, and promotes cell-cycle arrest at the G2-M transition. We describe a novel mechanism that PDA cells use to protect against DNA damage in which HuR posttranscriptionally regulates the expression and downstream function of WEE1 upon exposure to DNA-damaging agents.

Epidemiological-molecular evidence of metabolic reprogramming on proliferation, autophagy and cell signaling in pancreas cancer

Pancreatic cancer remains one of the deadliest human cancers with little progress made in survival over the past decades, and 5-year survival usually below 5%. Despite this dismal scenario, progresses have been made in understanding of the underlying tumor biology through among other definition of precursor lesions, delineation of molecular pathways, and advances in genome-wide technology. Further, exploring the relationship between epidemiological risk factors involving metabolic features to that of an altered cancer metabolism may provide the foundation for new therapies. Here we explore how nutrients and caloric intake may influence the KRAS-driven ductal carcinogenesis through mediators of metabolic stress, including autophagy in presence of TP53, advanced glycation end products (AGE) and the receptors (RAGE) and ligands (HMGB1), as well as glutamine pathways, among others. Effective understanding the cancer metabolism mechanisms in pancreatic cancer may propose new ways of prevention and treatment.

dCK expression correlates with 5-fluorouracil efficacy and HuR cytoplasmic expression in pancreatic cancer: a dual-institutional follow-up with the RTOG 9704 trial

Deoxycytidine kinase (dCK) and human antigen R (HuR) have been associated with response to gemcitabine in small studies. The present study investigates the prognostic and predictive value of dCK and HuR expression levels for sensitivity to gemcitabine and 5-fluorouracil (5-FU) in a large phase III adjuvant trial with chemoradiation backbone in pancreatic ductal adenocarcinoma (PDA). The dCK and HuR expression levels were determined by immunohistochemistry on a tissue microarray of 165 resected PDAs from the Radiation Therapy Oncology Group (RTOG) 9704 trial. Association with overall survival (OS) and disease-free survival (DFS) status were analyzed using the log-rank test and the Cox proportional hazards model. Experiments with cultured PDA cells were performed to explore mechanisms linking dCK and HuR expression to drug sensitivity. dCK expression levels were associated with improved OS for all patients analyzed from RTOG 9704 (HR: 0.66, 95% CI [0.47-0.93], P = 0.015). In a subset analysis based on treatment arm, the effect was restricted to patients receiving 5-FU (HR: 0.53, 95% CI [0.33-0.85], P = 0.0078). Studies in cultured cells confirmed that dCK expression rendered cells more sensitive to 5-FU. HuR cytoplasmic expression was neither prognostic nor predictive of treatment response. Previous studies along with drug sensitivity and biochemical studies demonstrate that radiation interferes with HuR's regulatory effects on dCK, and could account for the negative findings herein based on the clinical study design (i.e., inclusion of radiation). Finally, we demonstrate that 5-FU can increase HuR function by enhancing HuR translocation from the nucleus to the cytoplasm, similar to the effect of gemcitabine in PDA cells. For the first time, in the pre-treatment tumor samples, dCK and HuR cytoplasmic expression were strongly correlated (chi-square P = 0.015). This dual-institutional follow up study, in a multi-institutional PDA randomized clinical trial, observed that dCK expression levels were prognostic and had predictive value for sensitivity to 5-FU.