Adaptive and maladaptive expression of the mRNA regulatory protein HuR

mRNA metabolism regulator human antigen R (HuR) regulates age-related hearing loss in aged mice

Age-related hearing loss (ARHL) is among the most prevalent and complex disorders in older adults. However, the pathogenesis of ARHL remains poorly understood. Using a single-cell transcriptomic landscape of mouse cochlea at five time points (1, 2, 5, 12 and 15 months), we found that the levels of human antigen R (HuR)-a classical RNA-binding protein-increase with age. Here we show that HuR is specifically transported from the nucleus to the cytoplasm in hair cells in both aging mice and nonhuman primates. HuR overexpression in cochlea could successfully alleviate ARHL in aged mice. Meanwhile, HuR deficiency led to premature hearing dysfunction characterized by degeneration of stereocilia and the subsequent loss of hair cells. RNA immunoprecipitation sequencing analysis revealed that HuR can bind to messenger RNAs that enable stereocilia maintenance, including Gnai3. Adeno-associated virus-mediated Gnai3 overexpression partially rescues the hearing defects in HuR-deficient mice. Taken together, these findings indicate that HuR is a potential therapeutic target for ARHL.

Human antigen R: Exploring its inflammatory response impact and significance in cardiometabolic disorders

RNA-binding proteins (RBPs) play a crucial role in the regulation of posttranscriptional RNA networks, which can undergo dysregulation in many pathological conditions. Human antigen R (HuR) is a highly researched RBP that plays a crucial role as a posttranscriptional regulator. HuR plays a crucial role in the amplification of inflammatory signals by stabilizing the messenger RNA of diverse inflammatory mediators and key molecular players. The noteworthy correlations between HuR and its target molecules, coupled with the remarkable impacts reported on the pathogenesis and advancement of multiple diseases, position HuR as a promising candidate for therapeutic intervention in diverse inflammatory conditions. This review article examines the significance of HuR as a member of the RBP family, its regulatory mechanisms, and its implications in the pathophysiology of inflammation and cardiometabolic illnesses. Our objective is to illuminate potential directions for future research and drug development by conducting a comprehensive analysis of the existing body of research on HuR.

Heat shock response during the resolution of inflammation and its progressive suppression in chronic-degenerative inflammatory diseases

The heat shock response (HSR) is a crucial biochemical pathway that orchestrates the resolution of inflammation, primarily under proteotoxic stress conditions. This process hinges on the upregulation of heat shock proteins (HSPs) and other chaperones, notably the 70 kDa family of heat shock proteins, under the command of the heat shock transcription factor-1. However, in the context of chronic degenerative disorders characterized by persistent low-grade inflammation (such as insulin resistance, obesity, type 2 diabetes, nonalcoholic fatty liver disease, and cardiovascular diseases) a gradual suppression of the HSR does occur. This work delves into the mechanisms behind this phenomenon. It explores how the Western diet and sedentary lifestyle, culminating in the endoplasmic reticulum stress within adipose tissue cells, trigger a cascade of events. This cascade includes the unfolded protein response and activation of the NOD-like receptor pyrin domain-containing protein-3 inflammasome, leading to the emergence of the senescence-associated secretory phenotype and the propagation of inflammation throughout the body. Notably, the activation of the NOD-like receptor pyrin domain-containing protein-3 inflammasome not only fuels inflammation but also sabotages the HSR by degrading human antigen R, a crucial mRNA-binding protein responsible for maintaining heat shock transcription factor-1 mRNA expression and stability on heat shock gene promoters. This paper underscores the imperative need to comprehend how chronic inflammation stifles the HSR and the clinical significance of evaluating the HSR using cost-effective and accessible tools. Such understanding is pivotal in the development of innovative strategies aimed at the prevention and treatment of these chronic inflammatory ailments, which continue to take a heavy toll on global health and well-being.

Liposome-polyethylenimine complexes for the effective delivery of HuR siRNA in the treatment of diabetic retinopathy

Diabetic retinopathy (DR) is a vision-impairing complication of diabetes, damaging the retinal microcirculatory system. Overexpression of VEGF (vascular endothelial growth factor) is implicated in the pathogenesis of DR. Human antigen R (HuR) is an RNA-binding protein that favorably regulates VEGF protein expression by binding to VEGF-encoding mRNA. Downregulating HuR via RNA interference strategies using small interfering RNAs (siRNAs) may constitute a novel therapeutic method for preventing VEGF protein overexpression in DR. Delivery of siRNAs to the cellular cytoplasm can be facilitated by cationic peptides or polymers and lipids. In this study, a cationic polymer (polyethylenimine (PEI)) and lipid nanoparticles (liposomes) were co-formulated with siRNA to form lipopolyplexes (LPPs) for the delivery of HuR siRNA. LPPs-siRNA were analyzed for size, zeta potential, serum stability, RNase stability, heparin stability, toxicity, and siRNA encapsulation efficiency. Cellular uptake, downregulation of the target HuR (mRNA and protein), and associated VEGF protein were used to demonstrate the biological efficacy of the LPPs-HuR siRNA, in vitro (human ARPE-19 cells), and in vivo (Wistar rats). In vivo efficacy study was performed by injecting LPPs-HuR siRNA formulations into the eye of streptozotocin (STZ)-induced diabetic rats after the development of retinopathy. Our findings demonstrated that high retinal HuR and VEGF levels observed in the eyes of untreated STZ rats were lowered after LPPs-HuR siRNA administration. Our observations indicate that intravitreal treatment with HuR siRNA is a promising option for DR using LPPs as delivery agents.

RNA-binding proteins and cancer metastasis

RNA-binding proteins (RBPs) can regulate gene expression through post-transcriptionally influencing all manner of RNA biology, including alternative splicing (AS), polyadenylation, stability, and translation of mRNAs, as well as microRNAs (miRNAs) and circular RNAs (circRNAs) processing. There is accumulating evidence reinforcing the perception that dysregulation or dysfunction of RBPs can lead to various human diseases, including cancers. RBPs influence diverse cancer-associated cellular phenotypes, such as proliferation, apoptosis, senescence, migration, invasion, and angiogenesis, contributing to the initiation and development of tumors, as well as clinical prognosis. Metastasis is the leading cause of cancer-related recurrence and death. Therefore, it is necessary to elucidate the molecular mechanisms behind tumor metastasis. In fact, a growing body of published research has proved that RBPs play pivotal roles in cancer metastasis. In this review, we will summarize the recent advances for helping us understand the role of RBPs in tumor metastasis, and discuss dysfunctions and dysregulations of RBPs affecting metastasis-associated processes including epithelial-mesenchymal transition (EMT), migration, and invasion of cancer cells. Furthermore, we will discuss emerging RBP-based strategy for the treatment of cancer metastasis.

RNA Interference and Nanotechnology: A Promising Alliance for Next Generation Cancer Therapeutics

Cancer is a significant health hazard of the 21st century, and GLOBOCAN predicts increasing cancer incidence in the coming decades. Though several conventional treatment modalities exist, most of them end up causing off-target and debilitating effects, and drug resistance acquisition. Advances in our understanding of tumor molecular biology offer alternative strategies for precise, robust, and potentially less toxic treatment paradigms for circumventing the disease at the cellular and molecular level. Several deregulated molecules associated with tumorigenesis have been developed as targets in RNA interference (RNAi) based cancer therapeutics. RNAi, a post-transcriptional gene regulation mechanism, has significantly gained attention because of its precise multi-targeted gene silencing. Although the RNAi approach is favorable, the direct administration of small oligonucleotides has not been fruitful because of their inherent lower half-lives and instability in the biological systems. Moreover, the lack of an appropriate delivery system to the primary site of the tumor that helps determine the potency of the drug and its reach, has limited the effective medical utilization of these bio-drugs. Nanotechnology, with its unique characteristics of enhanced permeation and better tumor-targeting efficiency, offers promising solutions owing to the various possibilities and amenability for modifications of the nanoparticles to augment cancer therapeutics. Nanoparticles could be made multimodal, by designing and synthesizing multiple desired functionalities, often resulting in unique and potentially applicable biological structures. A small number of Phase I clinical trials with systemically administered siRNA molecules conjugated with nanoparticles have been completed and the results are promising, indicating that, these new combinatorial therapies can successfully and safely be used to inhibit target genes in cancer patients to alleviate some of the disease burden. In this review, we highlight different types of nano-based delivery strategies for engineering Nano-RNAi-based bio drugs. Furthermore, we have highlighted the insights gained from current research that are entering the preclinical evaluation and information about initial clinical developments, shaping the future for next generation cancer therapeutics.

RNA-Binding Proteins Hold Key Roles in Function, Dysfunction, and Disease

RNA-binding proteins (RBPs) are multi-faceted proteins in the regulation of RNA or its RNA splicing, localisation, stability, and translation. Amassing proof from many recent and dedicated studies reinforces the perception of RBPs exerting control through differing expression levels, cellular localization and post-transcriptional alterations. However, since the regulation of RBPs is reliant on the micro-environment and events like stress response and metabolism, their binding affinities and the resulting RNA-RBP networks may be affected. Therefore, any misregulation and disruption in the features of RNA and its related homeostasis can lead to a number of diseases that include diabetes, cardiovascular disease, and other disorders such as cancer and neurodegenerative diseases. As such, correct regulation of RNA and RBPs is crucial to good health as the effect RBPs exert through loss of function can cause pathogenesis. In this review, we will discuss the significance of RBPs and their typical function and how this can be disrupted in disease.

HuR Protein in Hepatocellular Carcinoma: Implications in Development, Prognosis and Treatment

Hu-antigen R (HuR) is a post-transcriptional regulator that belongs to the embryonic lethal abnormal vision Drosophila-like family (ELAV). HuR regulates the stability, translation, subcellular localization, and degradation of several target mRNAs, which are implicated in carcinogenesis and could affect therapeutic options. HuR protein is consistently highly expressed in hepatocellular carcinoma (HCC) compared to the adjacent normal liver tissue and is involved in the post-transcriptional regulation of various genes implicated in liver malignant transformation. Additionally, HuR protein seems to be a putative prognosticator in HCC, predicting worse survival. This review summarizes the recent evidence regarding the role of HuR in primary liver tumors, as presented in clinical studies, in vitro experiments and in vivo animal models. In conclusion, our review supports the consistent role of HuR protein in the development, prognosis, and treatment of HCC. Additional studies are expected to expand current information and exploit its putative employment as a future candidate for more personalized treatment in these tumors.

Alternative splicing in endothelial cells: novel therapeutic opportunities in cancer angiogenesis

Alternative splicing (AS) is a pervasive molecular process generating multiple protein isoforms, from a single gene. It plays fundamental roles during development, differentiation and maintenance of tissue homeostasis, while aberrant AS is considered a hallmark of multiple diseases, including cancer. Cancer-restricted AS isoforms represent either predictive biomarkers for diagnosis/prognosis or targets for anti-cancer therapies. Here, we discuss the contribution of AS regulation in cancer angiogenesis, a complex process supporting disease development and progression. We consider AS programs acting in a specific and non-redundant manner to influence morphological and functional changes involved in cancer angiogenesis. In particular, we describe relevant AS variants or splicing regulators controlling either secreted or membrane-bound angiogenic factors, which may represent attractive targets for therapeutic interventions in human cancer.

HuR Promotes Ovarian Cancer Cell Proliferation by Regulating TIMM44 mRNA Stability

The human antigen R (HuR) could play an essential role in stabilizing the mRNAs of many tumor-associated genes. Little research is performed to investigate the relevant mechanism mediated by HuR to promote the progress of ovarian cancer. The Cancer Genome Atlas (TCGA) dataset was retrieved to calculate the correlation between HuR and translocase of inner mitochondrial membrane 44 (TIMM44) expression. HuR expression plasmid, TIMM44 expression plasmid, siRNA HuR, and TIMM44 siRNAs were further transfected into A2780 and SKOV3 cells. The 3'UTR of TIMM44 fragment was cloned into the back of Renilla luciferase in the pSicheck2 dual fluorescent reporter to indicate the interaction between HuR and TIMM44. Cell count and MTT assay were performed to assay the proliferation ability of A2780 and SKOV3 cells. High-level HuR expression in 56 ovarian cancer patients recruited in Zibo Central Hospital was positively correlated with metastasis status and poor prognosis revealed by Kaplan-Meier analysis. Both HuR and TIMM44 can promote the proliferation of SKOV3 and A2780 cells. A high correlation of HuR and TIMM44 expression was testified in the TCGA data. Luciferase reporter assay confirmed that HuR could bind to TIMM44 to maintain the mRNA stability. TIMM44 siRNA administration inhibited the proliferation of SKOV3 cells, which could not be rescued. All of these indicate that the main function of HuR on ovarian cancer proliferation is mediated by TIMM44 through mRNA stability regulation, and HuR/TIMM44 complex can be used as a target to inhibit the proliferation of ovarian cancer cells.

HuR Affects Proliferation and Apoptosis of Chronic Lymphocytic Leukemia Cells via NF-κB Pathway

OBJECTIVE

To investigate the effects of HuR protein on the treatment of chronic lymphocytic leukemia (CLL).

METHODS

LCL lymphoblast cells and B lymphocytes were subjected to HuR overexpression (OV) or interference (IV). Western blot was used to observe the protein expression of human tumor necrosis factor-associated factor 1 (TRAF1), human inhibitor of nuclear factor kappa-B kinase α (IKK-α), NF-κB-inducing kinase (NIK), and p52. Flow cytometry was performed to evaluate apoptosis, and the mRNA expression of TRAF1 was examined by quantitative reverse transcription polymerase chain reaction. Immunofluorescence was carried out to visualize the expression of HuR, and the relationship between HuR and TRAF1 was observed by pull-down test. Cell sensitivity to chlorambucil (CLB) and fludarabine (Flu) was assessed by Cell Counting Kit-8.

RESULTS

The expression of HuR and TRAF1 in LCLs was significantly increased compared to that in B lymphocytes. Compared with the control, HuR OV significantly increased the expression of TRAF1 (P < 0.05), whereas it was significantly decreased in the IV group (P < 0.05). HuR can bind to TRAF1 directly, and the binding rate is positively correlated with HuR expression. After inhibiting HuR, the expression of TRAF1, IKK-α, NIK, p52, pro-Caspase 3, and PARP was significantly upregulated in LCLs and B lymphocytes (P < 0.05), while Caspase 3 was downregulated (P < 0.05). Compared with the control, the proliferation of LCLs and B lymphocytes treated by CLB and Flu decreased significantly after HuR blockade (P < 0.05).

CONCLUSION

HuR may be a key protein regulating CLL resistance. After inhibiting HuR, inflammatory response and apoptosis were significantly increased, and the cell sensitivity to CLB and Flu increased, suggesting that inhibiting HuR activity may be a potential strategy to solve the problem of drug resistance in CLL cells.

The RNA-Binding Protein HuR in Digestive System Tumors

Human antigen R (HuR) is a member of the Hu family of RNA-binding proteins. This molecule, which was first described in tumors nearly two decades ago, has recently received much attention in tumor-related research because it regulates the expression of many tumor-associated molecules through posttranscriptional regulatory mechanisms, thereby affecting biological characteristics. It is suggested that HuR might be a novel therapeutic target and a marker for therapeutic response and prognostic assessment. Increasing evidence supports that HuR also plays critical roles in the development, therapy, and prognosis of digestive system tumors. Herein, we review the relationships between HuR and digestive system tumors, demonstrating the importance of HuR in digestive system tumor diagnosis.

The HuR CMLD-2 inhibitor exhibits antitumor effects via MAD2 downregulation in thyroid cancer cells

Hu antigen R (HuR) is indeed one of the most studied RNA-binding protein (RBP) since its fundamental role both in tumorigenesis and cancer progression. For this reason, downregulation in HuR protein levels or inhibition of HuR biological function are, nowadays, attractive goals in cancer research. Here, we examined the antitumor effects of CMLD-2 in four thyroid cancer cell lines (SW1736, 8505 C, BCPAP and K1). Indeed, CMLD-2 competitively binds HuR protein disrupting its interaction with RNA-targets. 35 μM CLMD-2 produced a significant downregulation in thyroid cancer cell viability, coupled to an increase in apoptosis. Moreover, CMLD-2 treatment hindered both migration and colony formation ability. MAD2 is a microtubules-associated protein known to be greatly overexpressed in cancer and correlating with tumor aggressiveness. Furthermore, MAD2 is known to be a HuR target. CMLD-2 treatment induced a strong MAD2 downregulation and rescue experiments depicted it as a key effector in HuR-mediated in cancer. Altogether, these data contributed to foster HuR inhibition as valid antineoplastic treatment in thyroid cancer, highlighting MAD2 as a novel therapeutic target.

Regulation of Kv11.1 potassium channel C-terminal isoform expression by the RNA-binding proteins HuR and HuD

The potassium voltage-gated channel subfamily H member 2 (KCNH2) gene encodes the Kv11.1 potassium channel, which conducts the rapidly activating delayed rectifier current in the heart. KCNH2 pre-mRNA undergoes alternative polyadenylation and forms a functional, full-length Kv11.1a isoform if exon 15 is polyadenylated or a nonfunctional, C-terminally truncated Kv11.1a-USO isoform if intron 9 is polyadenylated. The molecular mechanisms that regulate Kv11.1 isoform expression are poorly understood. In this study, using HEK293 cells and reporter gene expression, pulldown assays, and RNase protection assays, we identified the RNA-binding proteins Hu antigen R (HuR) and Hu antigen D (HuD) as regulators of Kv11.1 isoform expression. We show that HuR and HuD inhibit activity at the intron 9 polyadenylation site. When co-expressed with the KCNH2 gene, HuR and HuD increased levels of the Kv11.1a isoform and decreased the Kv11.1a-USO isoform in the RNase protection assays and immunoblot analyses. In patch clamp experiments, HuR and HuD significantly increased the Kv11.1 current. siRNA-mediated knockdown of HuR protein decreased levels of the Kv11.1a isoform and increased those of the Kv11.1a-USO isoform. Our findings suggest that the relative expression levels of Kv11.1 C-terminal isoforms are regulated by the RNA-binding HuR and HuD proteins.

RBPs Play Important Roles in Vascular Endothelial Dysfunction Under Diabetic Conditions

Diabetes is one of the major health care problems worldwide leading to huge suffering and burden to patients and society. Diabetes is also considered as a cardiovascular disorder because of the correlation between diabetes and an increased incidence of cardiovascular disease. Vascular endothelial cell dysfunction is a major mediator of diabetic vascular complications. It has been established that diabetes contributes to significant alteration of the gene expression profile of vascular endothelial cells. Post-transcriptional regulation by RNA binding proteins (RBPs) plays an important role in the alteration of gene expression profile under diabetic conditions. The review focuses on the roles and mechanisms of critical RBPs toward diabetic vascular endothelial dysfunction. Deeper understanding of the post- transcriptional regulation by RBPs could lead to new therapeutic strategies against diabetic manifestation in the future.

Identification and Functional Characterization of Long Non-coding RNA MIR22HG as a Tumor Suppressor for Hepatocellular Carcinoma

Long non-coding RNAs (lncRNAs) have recently been identified as critical regulators in tumor initiation and development. However, the function of lncRNAs in human hepatocellular carcinoma (HCC) remains largely unknown. Our study was designed to explore the biological function and clinical implication of lncRNA MIR22HG in HCC. Methods: We evaluated MIR22HG expression in 52-patient, 145-patient, TCGA, and GSE14520 HCC cohorts. The effects of MIR22HG on HCC were analyzed in terms of proliferation, invasion, and metastasis, both in vitro and in vivo. The mechanism of MIR22HG action was explored through bioinformatics, luciferase reporter, and RNA immunoprecipitation analyses. Results:MIR22HG expression was significantly down-regulated in 4 independent HCC cohorts compared to that in controls. Its low expression was associated with tumor progression and poor prognosis of patients with HCC. Forced expression of MIR22HG in HCC cells significantly suppressed proliferation, invasion, and metastasis in vitro and in vivo. Mechanistically, MIR22HG derived miR-22-3p to target high mobility group box 1 (HMGB1), thereby inactivating HMGB1 downstream pathways. Additionally, MIR22HG directly interacted with HuR and regulated its subcellular localization. MIR22HG competitively bound to human antigen R (HuR), resulting in weakened expression of HuR-stabilized oncogenes, such as β-catenin. Furthermore, miR-22-3p suppression, HuR or HMGB1 overexpression rescued the inhibitory effects caused by MIR22HG overexpression. Conclusion: Our findings revealed that MIR22HG plays a key role in tumor progression by suppressing the proliferation, invasion, and metastasis of tumor cells, suggesting its potential role as a tumor suppressor and prognostic biomarker in HCC.

Identification of tumorigenesis-related mRNAs associated with RNA-binding protein HuR in thyroid cancer cells

RNA binding proteins (RBPs) play a central role in cell physiology and pathology. Among them, HuR is a nuclear RBP, which shuttles to the cytoplasm to allow its RNA targets processing. HuR over-expression and delocalization are often associated to cell transformation. Numerous cancers display increased HuR protein levels and its high cytoplasmic levels has been associated with a worse prognosis.

In our study, we first evaluated HuR expression in normal and cancer thyroid tissues and then evaluated its function in thyroid cell lines. HuR is over-expressed in all thyroid tumor tissues; high cytoplasmic levels are detected in all thyroid carcinomas. HuR silencing decreased cell viability and determined apoptotic cell death, in a non-tumorigenic (Nthy-ori-3.1) and a tumorigenic (BCPAP) thyroid cell line. Global transcriptome analysis indicated that HuR silencing, though having similar biological effects, induces distinct gene expression modifications in the two cell lines. By using the RIP-seq approach, the HuR-bound RNA profiles of different thyroid cell lines were evaluated. We show that in distinct cell lines HuR-bound RNA profiles are different. A set of 114 HuR-bound RNAs distinguishing tumorigenic cell lines from the non-tumorigenic one was identified.

Altogether, our data indicate that HuR plays a role in thyroid tumorigenesis. Moreover, our findings are a proof of concept that RBP targets differ between cells with the same origin but with distinct biological behavior.

HuR-mediated SCN5A messenger RNA stability reduces arrhythmic risk in heart failure

BACKGROUND

Downregulated sodium currents in heart failure (HF) have been linked to increased arrhythmic risk. Reduced expression of the messenger RNA (mRNA)-stabilizing protein HuR (also known as ELAVL1) may be responsible for the downregulation of sodium channel gene SCN5A mRNA.

OBJECTIVE

The purpose of this article was to investigate whether HuR regulates SCN5A mRNA expression and whether manipulation of HuR benefits arrhythmia control in HF.

METHODS

Quantitative real-time reverse-transcriptase polymerase chain reaction was used to investigate the expression of SCN5A. Optical mapping of the intact heart was adopted to study the effects of HuR on the conduction velocity and action potential upstroke in mice with myocardial infarct and HF after injection of AAV9 viral particles carrying HuR.

RESULTS

HuR was associated with SCN5A mRNA in cardiomyocytes, and expression of HuR was downregulated in failing hearts. The association of HuR and SCN5A mRNA protected SCN5A mRNA from decay. Injection of AAV9 viral particles carrying HuR increased SCN5A expression in mouse heart tissues after MI. Optical mapping of the intact heart demonstrated that overexpression of HuR improved action potential upstroke and conduction velocity in the infarct border zone, which reduced the risk of reentrant arrhythmia after MI.

CONCLUSION

Our data indicate that HuR is an important RNA-binding protein in maintaining SCN5A mRNA abundance in cardiomyocytes. Reduced expression of HuR may be at least partially responsible for the downregulation of SCN5A mRNA expression in ischemic HF. Overexpression of HuR may rescue decreased SCN5A expression and reduce arrhythmic risk in HF. Increasing mRNA stability to increase ion channel currents may correct a fundamental defect in HF and represent a new paradigm in antiarrhythmic therapy.

Clinical Significance and Biological Role of HuR in Head and Neck Carcinomas

Background

Hu-antigen R (HuR) is a posttranscriptional regulator of several target mRNAs, implicated in carcinogenesis. This review aims to present the current evidence regarding the biological role and potential clinical significance of HuR in head and neck carcinomas.

Methods

The existing literature concerning HuR expression and function in head and neck carcinomas is critically presented and summarised.

Results

HuR is expressed in the majority of the examined samples, showing higher cytoplasmic levels in malignant or premalignant cases. Moreover, HuR modulates several genes implicated in biological processes important for malignant transformation, growth, and invasiveness. HuR seems to be an adverse prognosticator in patients with OSCCs, whereas a correlation with a more aggressive phenotype is reported in several types of carcinomas.

Conclusions

A consistent role of HuR in the carcinogenesis and progression of head and neck carcinomas is suggested; nevertheless, further studies are warranted to expand the present information.

Emerging roles of RNA-binding proteins in diabetes and their therapeutic potential in diabetic complications

Diabetes is a debilitating health care problem affecting 422 million people around the world. Diabetic patients suffer from multisystemic complications that can cause mortality and morbidity. Recent advancements in high-throughput next-generation RNA-sequencing and computational algorithms led to the discovery of aberrant posttranscriptional gene regulatory programs in diabetes. However, very little is known about how these regulatory programs are mis-regulated in diabetes. RNA-binding proteins (RBPs) are important regulators of posttranscriptional RNA networks, which are also dysregulated in diabetes. Human genetic studies provide new evidence that polymorphisms and mutations in RBPs are linked to diabetes. Therefore, we will discuss the emerging roles of RBPs in abnormal posttranscriptional gene expression in diabetes. Questions that will be addressed are: Which posttranscriptional mechanisms are disrupted in diabetes? Which RBPs are responsible for such changes under diabetic conditions? How are RBPs altered in diabetes? How does dysregulation of RBPs contribute to diabetes? Can we target RBPs using RNA-based methods to restore gene expression profiles in diabetic patients? Studying the evolving roles of RBPs in diabetes is critical not only for a comprehensive understanding of diabetes pathogenesis but also to design RNA-based therapeutic approaches for diabetic complications. WIREs RNA 2018, 9:e1459. doi: 10.1002/wrna.1459 This article is categorized under: RNA in Disease and Development > RNA in Disease RNA Processing > Splicing Regulation/Alternative Splicing Translation > Translation Regulation.

Effects of HuR downregulation on anaplastic thyroid cancer cells

Anaplastic thyroid cancer (ATC) constitutes one of the most aggressive types of human solid cancer, and is characterized by the absence of thyroid differentiation features and a marked degree of invasiveness. We have previously demonstrated that the RNA-binding protein Hu antigen R (HuR) is overexpressed in thyroid carcinoma; thus, the biological role of this RNA-binding protein was investigated in the present study using the ATC cell lines SW1736 and 8505C. In both cell lines, HuR protein levels were higher compared with in the non-tumorigenic thyroid cell line Nthy-ori-3.1. HuR silencing by RNA interference in both ATC cell lines decreased cell viability, increased apoptosis rates and reduced the capability to form colonies in soft agar. Thus, HuR plays an important role in the proliferation and aggressiveness of ATC cells. The histone deacetylase inhibitor suberoylanilide hydroxamic acid (SAHA) was able to reduce the viability of ATC cells. The results demonstrated that SAHA was able to decrease HuR expression in SW1736 and 8505C cells. Furthermore, since it is known that the transcription factor nuclear factor (NF)-κB modulates HuR expression, whether SAHA affects the nuclear (active) fraction of NF-κB in ATC cells was investigated. The data suggested that SAHA decreases ATC cell viability by reducing the active form of NF-κB, which, in turn, modulates HuR expression.

Overexpression of the human antigen R suppresses the immediate paradoxical proliferation of melanoma cell subpopulations in response to suboptimal BRAF inhibition

Tumor plasticity and the heterogeneous response of melanoma cells to targeted therapies are major limits for the long‐term efficacy of this line of therapy. Targeting tumor plasticity is theoretically possible through the modulation of the expression of RNA‐binding proteins which can affect many different compensatory mechanisms of the adaptive response of malignant cells to targeted therapies. Human antigen R (HuR) is a modulator of gene expression and a transacting factor in the mRNA‐processing machinery used in the cell stress response, and is a potential target for reducing tumor plasticity. In this experiment, we exploit the inherent heterogeneous response of the A375 melanoma line to suboptimal BRAF inhibition as a model of immediate adaptive response. We first observe that HuR overexpression can prevent the heterogeneous response and thus the immediate paradoxical proliferation induced by low‐doses vemurafenib treatment. We then use single‐cell mass cytometry to characterize subpopulations, including those that paradoxically proliferate, based on their proliferation rate and the expression patterns of markers involved in the reversible adaptive resistance to BRAF inhibition and/or recognized as HuR targets involved in cell cycle regulation. Under suboptimal BRAF inhibition, HuR overexpression affects these subpopulations and their expression pattern with contrasting responses depending on their proliferation rate: faster‐proliferating vemurafenib‐sensitive or ‐resistant subpopulations showed higher death tendency and reduced size, and slower‐proliferating subpopulations showed an attenuated resistant expression response and their paradoxical proliferation was inhibited. These observations pave the way to new therapeutic strategies for preventing the heterogeneous response of tumors to targeted therapies.

Sunitinib Stimulates Expression of VEGFC by Tumor Cells and Promotes Lymphangiogenesis in Clear Cell Renal Cell Carcinomas

Sunitinib is an antiangiogenic therapy given as a first-line treatment for renal cell carcinoma (RCC). While treatment improves progression-free survival, most patients relapse. We hypothesized that patient relapse can stem from the development of a lymphatic network driven by the production of the main growth factor for lymphatic endothelial cells, VEGFC. In this study, we found that sunitinib can stimulate vegfc gene transcription and increase VEGFC mRNA half-life. In addition, sunitinib activated p38 MAPK, which resulted in the upregulation/activity of HuR and inactivation of tristetraprolin, two AU-rich element-binding proteins. Sunitinib stimulated a VEGFC-dependent development of lymphatic vessels in experimental tumors. This may explain our findings of increased lymph node invasion and new metastatic sites in 30% of sunitinib-treated patients and increased lymphatic vessels found in 70% of neoadjuvant treated patients. In summary, a therapy dedicated to destroying tumor blood vessels induced the development of lymphatic vessels, which may have contributed to the treatment failure. Cancer Res; 77(5); 1212-26. ©2017 AACR.

Post-transcriptional regulation of cytokine and growth factor signaling in cancer

Cytokines and growth factors regulate cell proliferation, differentiation, migration and apoptosis, and play important roles in coordinating growth signal responses during development. The expression of cytokine genes and the signals transmitted through cytokine receptors are tightly regulated at several levels, including transcriptional and post-transcriptional levels. A majority of cytokine mRNAs, including growth factor transcripts, contain AU-rich elements (AREs) in their 3' untranslated regions that control gene expression by regulating mRNA degradation and changing translational rates. In addition, numerous proteins involved in transmitting signals downstream of cytokine receptors are regulated at the level of mRNA degradation by GU-rich elements (GREs) found in their 3' untranslated regions. Abnormal stabilization and overexpression of ARE or GRE-containing transcripts had been observed in many malignancies, which is a consequence of the malfunction of RNA-binding proteins. In this review, we briefly summarize the role of AREs and GREs in regulating mRNA turnover to coordinate cytokine and growth factor expression, and we describe how dysregulation of mRNA degradation mechanisms contributes to the development and progression of cancer.

Feedback Regulation of Kinase Signaling Pathways by AREs and GREs

In response to environmental signals, kinases phosphorylate numerous proteins, including RNA-binding proteins such as the AU-rich element (ARE) binding proteins, and the GU-rich element (GRE) binding proteins. Posttranslational modifications of these proteins lead to a significant changes in the abundance of target mRNAs, and affect gene expression during cellular activation, proliferation, and stress responses. In this review, we summarize the effect of phosphorylation on the function of ARE-binding proteins ZFP36 and ELAVL1 and the GRE-binding protein CELF1. The networks of target mRNAs that these proteins bind and regulate include transcripts encoding kinases and kinase signaling pathways (KSP) components. Thus, kinase signaling pathways are involved in feedback regulation, whereby kinases regulate RNA-binding proteins that subsequently regulate mRNA stability of ARE- or GRE-containing transcripts that encode components of KSP.

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.

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.

Post-transcriptional up-regulation of PDGF-C by HuR in advanced and stressed breast cancer

Breast cancer is a heterogeneous disease characterized by multiple genetic alterations leading to the activation of growth factor signaling pathways that promote cell proliferation. Platelet-derived growth factor-C (PDGF-C) is overexpressed in various malignancies; however, the involvement of PDGF-C in breast cancers and the mechanisms underlying PDGF-C deregulation remain unclear. Here, we show that PDGF-C is overexpressed in clinical breast cancers and correlates with poor prognosis. PDGF-C up-regulation was mediated by the human embryonic lethal abnormal vision-like protein HuR, which stabilizes the PDGF-C transcript by binding to two predicted AU-rich elements (AREs) in the 3'-untranslated region (3'-UTR). HuR is up-regulated in hydrogen peroxide-treated or ultraviolet-irradiated breast cancer cells. Clinically, HuR levels are correlated with PDGF-C expression and histological grade or pathological tumor-node-metastasis (pTNM) stage. Our findings reveal a novel mechanism underlying HuR-mediated breast cancer progression, and suggest that HuR and PDGF-C are potential molecular candidates for targeted therapy of breast cancers.

MicroRNAs as Mediators of the Ageing Process

Human ageing is a complex and integrated gradual deterioration of cellular processes. There are nine major hallmarks of ageing, that include changes in DNA repair and DNA damage response, telomere shortening, changes in control over the expression and regulation of genes brought about by epigenetic and mRNA processing changes, loss of protein homeostasis, altered nutrient signaling, mitochondrial dysfunction, stem cell exhaustion, premature cellular senescence and altered intracellular communication. Like practically all other cellular processes, genes associated in features of ageing are regulated by miRNAs. In this review, I will outline each of the features of ageing, together with examples of specific miRNAs that have been demonstrated to be involved in each one. This will demonstrate the interconnected nature of the regulation of transcripts involved in human ageing, and the role of miRNAs in this process. Definition of the factors involved in degeneration of organismal, tissue and cellular homeostasis may provide biomarkers for healthy ageing and increase understanding of the processes that underpin the ageing process itself.

MicroRNA-570-3p regulates HuR and cytokine expression in airway epithelial cells

Asthma is a chronic lung disease that affects people of all ages and is characterized by high morbidity. The mechanisms of asthma pathogenesis are unclear, and there is a need for development of diagnostic biomarkers and greater understanding of regulation of inflammatory responses in the lung. Post-transcriptional regulation of cytokines, chemokines, and growth factors by the action of microRNAs and RNA-binding proteins on stability or translation of mature transcripts is emerging as a central means of regulating the inflammatory response. In this study, we demonstrate that miR-570-3p expression is increased with TNFα stimuli in normal human bronchial epithelial cells (2.6 ± 0.6, p = 0.01) and the human airway epithelial cell line A549 (4.6 ± 1.4, p = 0.0068), and evaluate the functional effects of its overexpression on predicted mRNA target genes in transfected A549 cells. MiR-570-3p upregulated numerous cytokines and chemokines (CCL4, CCL5, TNFα, and IL-6) and also enhanced their induction by TNFα. For other cytokines (CCL2 and IL-8), the microRNA exhibited an inhibitory effect to repress their upregulation by TNFα. These effects were mediated by a complex pattern of both direct and indirect regulation of downstream targets by miR-570-3p. We also show that the RNA-binding protein HuR is a direct target of miR-570-3p, which has implications for expression of numerous other inflammatory mediators that HuR is known regulate post-transcriptionally. Finally, expression of endogenous miR-570-3p was examined in both serum and exhaled breath condensate (EBC) from asthmatic and healthy patients, and was found to be significantly lower in EBC of asthmatics and inversely correlated to their lung function. These studies implicate miR-570-3p as a potential regulator of asthmatic inflammation with potential as both a diagnostic and therapeutic target in asthma.

Krüppel -like factor 8 is a stress-responsive transcription factor that regulates expression of HuR

BACKGROUND/AIMS

HuR is an RNA-binding protein that regulates the post-transcriptional life of thousands of cellular mRNAs and promotes cell survival. HuR is expressed as two mRNA transcripts that are differentially regulated by cell stress. The goal of this study is to define factors that promote transcription of the longer alternate form.

METHODS

Effects of transcription factors on HuR expression were determined by inhibition or overexpression of these factors followed by competitive RT-PCR, gel mobility shift, and chromatin immunoprecipitation. Transcription factor expression patterns were identified through competitive RT-PCR and Western analysis. Stress responses were assayed in thapsigargin-treated proximal tubule cells and in ischemic rat kidney.

RESULTS

A previously described NF-κB site and a newly identified Sp/KLF factor binding site were shown to be important for transcription of the long HuR mRNA. KLF8, but not Sp1, was shown to bind this site and increase HuR mRNA levels. Cellular stress in cultured or native proximal tubule cells resulted in a rapid decrease of KLF8 levels that paralleled those of the long HuR mRNA variant.

CONCLUSIONS

These results demonstrate that KLF8 can participate in regulating expression of alternate forms of HuR mRNA along with NF-κB and other factors, depending on cellular contexts.

The fat cell senescence hypothesis: a mechanism responsible for abrogating the resolution of inflammation in chronic disease

PURPOSE OF REVIEW

Obesity is a chronic inflammatory disease in which the physiological resolution of inflammation is attenuated, leading to low-grade inflammation throughout the body. However, the heat shock response, which is a key component of the physiological response to resolve inflammation, is seriously hampered in adipose tissue and other metabolic organs (e.g. skeletal muscle, liver, pancreatic β-cells) in metabolic diseases. In this review, we hypothesize that adipocyte metabolic stress triggers the onset of fat cell senescence, and companion senescence-associated secretory phenotype (SASP), and that such a scenario is responsible for attenuating the resolution of inflammation.

RECENT FINDINGS

We shall discuss the role of the heat shock response in the context of the resolution of inflammation and the relevance of heat shock response blockade in chronic inflammatory diseases. Sirtuin-1 is responsible for the induction of heat shock transcription factor-1 mRNA expression and for the stabilization of heat shock transcription factor-1 in a high-profile activity state. However, adipose tissue-emanated SASP depress sirtuin-1 expression, leading adipocytes to a perpetual state of unresolved inflammation, due to a dampening of the heat shock response.

SUMMARY

The advance of inflammasome-mediated SASP from adipose to other tissues promotes cellular senescence in many other cells of the organism, aggravating obesity-dependent chronic inflammation. Inducers of heat shock response (e.g. heat shock itself, physical exercise and calorie restriction) may efficiently interrupt this vicious cycle and are envisaged as the best and also the most economical treatment for obesity-related chronic diseases.