Stabilization of Snail by HuR in the process of hydrogen peroxide induced cell migration

RNA-binding proteins in breast cancer: Biological implications and therapeutic opportunities

RNA-binding proteins (RBPs) refer to a class of proteins that participate in alternative splicing, RNA stability, polyadenylation, localization and translation of RNAs, thus regulating gene expression in post-transcriptional manner. Dysregulation of RNA-RBP interaction contributes to various diseases, including cancer. In breast cancer, disorders in RBP expression and function influence the biological characteristics of tumor cells. Targeting RBPs has fostered the development of innovative therapies for breast cancer. However, the RBP-related mechanisms in breast cancer are not completely clear. In this review, we summarize the regulatory mechanisms of RBPs and their signaling crosstalk in breast cancer. Specifically, we emphasize the potential of certain RBPs as prognostic factors due to their effects on proliferation, invasion, apoptosis, and therapy resistance of breast cancer cells. Most importantly, we present a comprehensive overview of the latest RBP-related therapeutic strategies and novel therapeutic targets that have proven to be useful in the treatment of breast cancer.

Redox-Mediated Rewiring of Signalling Pathways: The Role of a Cellular Clock in Brain Health and Disease

Metazoan signalling pathways can be rewired to dampen or amplify the rate of events, such as those that occur in development and aging. Given that a linear network topology restricts the capacity to rewire signalling pathways, such scalability of the pace of biological events suggests the existence of programmable non-linear elements in the underlying signalling pathways. Here, we review the network topology of key signalling pathways with a focus on redox-sensitive proteins, including PTEN and Ras GTPase, that reshape the connectivity profile of signalling pathways in response to an altered redox state. While this network-level impact of redox is achieved by the modulation of individual redox-sensitive proteins, it is the population by these proteins of critical nodes in a network topology of signal transduction pathways that amplifies the impact of redox-mediated reprogramming. We propose that redox-mediated rewiring is essential to regulate the rate of transmission of biological signals, giving rise to a programmable cellular clock that orchestrates the pace of biological phenomena such as development and aging. We further review the evidence that an aberrant redox-mediated modulation of output of the cellular clock contributes to the emergence of pathological conditions affecting the human brain.

Cooperation and competition by RNA-binding proteins in cancer

Post-transcriptional regulation of gene expression plays a major role in determining the cellular proteome in health and disease. Post-transcriptional control mechanisms are disrupted in many cancers, contributing to multiple processes of tumorigenesis. RNA-binding proteins (RBPs), the main post-transcriptional regulators, often show altered expression and activity in cancer cells. Dysregulation of RBPs contributes to many cancer phenotypes, functioning in complex regulatory networks with other cellular players such as non-coding RNAs, signaling mediators and transcription factors to alter the expression of oncogenes and tumor suppressor genes. RBPs often function combinatorially, based on their binding to target sequences/structures on shared mRNA targets, to regulate the expression of cancer-related genes. This gives rise to cooperativity and competition between RBPs in mRNA binding and resultant functional outcomes in post-transcriptional processes such as mRNA splicing, stability, export and translation. Cooperation and competition is also observed in the case of interaction of RBPs and microRNAs with mRNA targets. RNA structural change is a common mechanism mediating the cooperative/competitive interplay between RBPs and between RBPs and microRNAs. RNA modifications, leading to changes in RNA structure, add a new dimension to cooperative/competitive binding of RBPs to mRNAs, further expanding the RBP regulatory landscape. Therefore, cooperative/competitive interplay between RBPs is a major determinant of the RBP interactome and post-transcriptional regulation of gene expression in cancer cells.

Study on the prognosis, immune and drug resistance of m6A-related genes in lung cancer

Background

Few studies have demonstrated that the relationship between m6A-related genes and the prognosis, tumor microenvironment and drug resistance of LC.

Methods

The main results were analyzed with bioinformatics methods.

Results

Hence, we found 10 m6A-related genes expressed less in tumor samples in comparison with normal ones. Using consensus clustering, all LC patients were grouped into 2 subgroups according to the overall expression of 10 differential expressed m6A-related genes. In two clusters, the OS and immune characteristics were different. We analyzed the predictive potential of 10 m6A-related genes in the prognosis of LC, and obtained a risk prognosis model on the strength of ZC3H13, CBLL1, ELAVL1 and YTHDF1 as the hub candidate genes through LASSO cox. The expression of 4 hub m6A-related genes was validated by IHC in the HPA database. The infiltration level of dendritic cell, CD4+ T cell and neutrophil that were affected by CNV level of m6A-related genes in LUAD and LUSC patients. Moreover, based on GSCALite database, we found that LUSC patients with hypermethylation tended to have a better overall survival. In terms of drug sensitivity, etoposide correlated negatively with ELAVL1, HNRNPC, RBM15B, YTHDF2 and CBLL1. ZC3H13 had positively association with afatinib, while HNRNPC was positively associated with dasatinib, erlotinib, lapatinib and TGX221. Crizotinib had a negative correlation with ELAVL1, CBLL1, HNRNPC and RBM15B.

Conclusion

In conclusion, m6A-related genes are important participants in LC and the expression levels of ZC3H13, CBLL1, ELAVL1 and YTHDF1 are significant for prediction and treatment of LC. Researches of drug resistance based on m6A-related genes need to pay more attention for producing new therapeutic strategies of LC and CBLL1 may contribute to target treatment for further research.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12859-022-04984-5.

RNA-binding protein Elavl1/HuR is required for maintenance of cranial neural crest specification

While neural crest development is known to be transcriptionally controlled via sequential activation of gene regulatory networks (GRNs), recent evidence increasingly implicates a role for post-transcriptional regulation in modulating the output of these regulatory circuits. Using available single-cell RNA-sequencing datasets from avian embryos to identify potential post-transcriptional regulators, we found that Elavl1, which encodes for an RNA-binding protein with roles in transcript stability, was enriched in the premigratory cranial neural crest. Perturbation of Elavl1 resulted in premature neural crest delamination from the neural tube as well as significant reduction in transcripts associated with the neural crest specification GRN, phenotypes that are also observed with downregulation of the canonical Wnt inhibitor Draxin. That Draxin is the primary target for stabilization by Elavl1 during cranial neural crest specification was shown by RNA-sequencing, RNA immunoprecipitation, RNA decay measurement, and proximity ligation assays, further supporting the idea that the downregulation of neural crest specifier expression upon Elavl1 knockdown was largely due to loss of Draxin. Importantly, exogenous Draxin rescued cranial neural crest specification defects observed with Elavl1 knockdown. Thus, Elavl1 plays a critical a role in the maintenance of cranial neural crest specification via Draxin mRNA stabilization. Together, these data highlight an important intersection of post-transcriptional regulation with modulation of the neural crest specification GRN.

RNA-Binding Proteins: Emerging Therapeutics for Vascular Dysfunction

Vascular diseases account for a significant number of deaths worldwide, with cardiovascular diseases remaining the leading cause of mortality. This ongoing, ever-increasing burden has made the need for an effective treatment strategy a global priority. Recent advances in regenerative medicine, largely the derivation and use of induced pluripotent stem cell (iPSC) technologies as disease models, have provided powerful tools to study the different cell types that comprise the vascular system, allowing for a greater understanding of the molecular mechanisms behind vascular health. iPSC disease models consequently offer an exciting strategy to deepen our understanding of disease as well as develop new therapeutic avenues with clinical translation. Both transcriptional and post-transcriptional mechanisms are widely accepted to have fundamental roles in orchestrating responses to vascular damage. Recently, iPSC technologies have increased our understanding of RNA-binding proteins (RBPs) in controlling gene expression and cellular functions, providing an insight into the onset and progression of vascular dysfunction. Revelations of such roles within vascular disease states have therefore allowed for a greater clarification of disease mechanisms, aiding the development of novel therapeutic interventions. Here, we discuss newly discovered roles of RBPs within the cardio-vasculature aided by iPSC technologies, as well as examine their therapeutic potential, with a particular focus on the Quaking family of isoforms.

HuR Affects the Radiosensitivity of Esophageal Cancer by Regulating the EMT-Related Protein Snail

Purpose

We previously found that Hu antigen R (HuR) can regulate the proliferation and metastasis of esophageal cancer cells. This study aims to explore the effects of HuR on the radiosensitivity of esophageal cancer.

Materials and Method

Analyses of CCK-8, colony formation assay, Western blot, immunofluorescence, flow cytometry, reactive oxygen species (ROS), and mitochondrial membrane potential were conducted to characterize the esophageal cancer cells. Nude mouse models were used to detect the effects of HuR in a combination of X-ray treatment on the subcutaneous xenografts of esophageal cancer. In addition, a luciferase assay was used to detect the direct interaction of HuR with Snail mRNA 3’-UTR.

Results

The down-regulation of HuR combined with X-ray can significantly inhibit the proliferation and colony formation of esophageal cancer cells. Flow cytometry data showed that the down-regulation of HuR could induce a G1 phase cell cycle block in esophageal cancer cells, and aggravate X-ray-induced apoptosis, indicated by the increases of apoptosis-related proteins Bax, caspase-3 and caspase-9. Moreover, the down-regulation of HuR could significantly impair the mitochondrial membrane potential and increase the ROS production and DNA double-strand break marker γH2AX expression in esophageal cancer cells that were exposed to X-rays. In vivo data showed that the down-regulation of HuR combined with radiation significantly decreased the growth of subcutaneous xenograft tumors. Furthermore, HuR could interact with Snail. Up-regulation of Snail can reverse the EMT inhibitory effects caused by HuR down-regulation, and attenuate the tumor-inhibiting and radiosensitizing effects caused by HuR down-regulation.

Conclusion

In summary, our data demonstrate that HuR effectively regulates the radiosensitivity of esophageal cancer, which may be achieved by stabilizing Snail. Thus, HuR/Snail axis is a potentially therapeutic target for the treatment of esophageal cancer.

Hu Antigen R (HuR) Protein Structure, Function and Regulation in Hepatobiliary Tumors

Simple Summary

Hepatobiliary tumors are a group of primary malignancies encompassing the liver, the intra- and extra-hepatic biliary tracts, and the gall bladder. Within the liver, hepatocellular carcinoma (HCC) is the most common type of primary cancer, which is, also, representing the third-most recurrent cause of cancer-associated death and the sixth-most prevalent type of tumor worldwide, nowadays. Although less frequent, cholangiocarcinoma (CCA) is, currently, a fatal cancer with limited therapeutic options. Here, we review the regulatory role of Hu antigen R (HuR), a ubiquitous member of the ELAV/Hu family of RNA-binding proteins (RBPs), in the pathogenesis, progression, and treatment of HCC and CCA. Overall, HuR is proposed as a valuable diagnostic and prognostic marker, as well as a therapeutic target in hepatobiliary cancers. Therefore, novel therapeutic approaches that can selectively modulate HuR function appear to be highly attractive for the clinical management of these types of tumors.

Abstract

Hu antigen R (HuR) is a 36-kDa ubiquitous member of the ELAV/Hu family of RNA-binding proteins (RBPs), which plays an important role as a post-transcriptional regulator of specific RNAs under physiological and pathological conditions, including cancer. Herein, we review HuR protein structure, function, and its regulation, as well as its implications in the pathogenesis, progression, and treatment of hepatobiliary cancers. In particular, we focus on hepatocellular carcinoma (HCC) and cholangiocarcinoma (CCA), tumors where the increased cytoplasmic localization of HuR and activity are proposed, as valuable diagnostic and prognostic markers. An overview of the main regulatory axes involving HuR, which are associated with cell proliferation, invasion, metastasis, apoptosis, and autophagy in HCC, is provided. These include the transcriptional, post-transcriptional, and post-translational modulators of HuR function, in addition to HuR target transcripts. Finally, whereas studies addressing the relevance of targeting HuR in CCA are limited, in the past few years, HuR has emerged as a potential therapeutic target in HCC. In fact, the therapeutic efficacy of some pharmacological inhibitors of HuR has been evaluated, in early experimental models of HCC. We, further, discuss the major findings and future perspectives of therapeutic approaches that specifically block HuR interactions, either with post-translational modifiers or cognate transcripts in hepatobiliary cancers.

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).

Drug delivery approaches for HuR-targeted therapy for lung cancer

Lung cancer (LC) is often diagnosed at an advanced stage and conventional treatments for disease management have limitations associated with them. Novel therapeutic targets are thus avidly sought for the effective management of LC. RNA binding proteins (RBPs) have been convincingly established as key players in tumorigenesis, and their dysregulation is linked to multiple cancers, including LC. In this context, we review the role of Human antigen R (HuR), an RBP that is overexpressed in LC, and further associated with various aspects of LC tumor growth and response to therapy. Herein, we describe the role of HuR in LC progression and outline the evidences supporting various pharmacologic and biologic approaches for inhibiting HuR expression and function. These approaches, including use of small molecule inhibitors, siRNAs and shRNAs, have demonstrated favorable results in reducing tumor cell growth, invasion and migration, angiogenesis and metastasis. Hence, HuR has significant potential as a key therapeutic target in LC. Use of siRNA-based approaches, however, have certain limitations that prevent their maximal exploitation as cancer therapies. To address this, in the conclusion of this review, we provide a list of nanomedicine-based HuR targeting approaches currently being employed for siRNA and shRNA delivery, and provide a rationale for the immense potential therapeutic benefits offered by nanocarrier-based HuR targeting and its promise for treating patients with LC.

An RNA-Binding Protein, Hu-antigen R, in Pancreatic Cancer Epithelial to Mesenchymal Transition, Metastasis, and Cancer Stem Cells

Pancreatic cancer has poor prognosis and treatment outcomes due to its highly metastatic nature and resistance to current treatments. The RNA-binding protein (RBP) Hu-antigen R (HuR) is a central player in posttranscriptional regulation of cancer-related gene expression, and contributes to tumorigenesis, tumor growth, metastasis, and drug resistance. HuR has been suggested to regulate pancreatic cancer epithelial-to-mesenchymal transition (EMT), but the mechanism was not well understood. Here, we further elucidated the role HuR plays in pancreatic cancer cell EMT, and developed a novel inhibitor specifically interrupting HuR-RNA binding. The data showed that HuR binds to the 3'-UTR of the mRNA of the transcription factor Snail, resulting in stabilization of Snail mRNA and enhanced Snail protein expression, thus promoted EMT, metastasis, and formation of stem-like cancer cells (CSC) in pancreatic cancer cells. siRNA silencing or CRISPR/Cas9 gene deletion of HuR inhibited pancreatic cancer cell EMT, migration, invasion, and inhibited CSCs. HuR knockout cells had dampened tumorigenicity in immunocompromised mice. A novel compound KH-3 interrupted HuR-RNA binding, and KH-3 inhibited pancreatic cancer cell viability, EMT, migration/invasion in vitro KH-3 showed HuR-dependent activity and inhibited HuR-positive tumor growth and metastasis in vivo.

The RNA Binding Protein HuR: A Promising Drug Target for Anticancer Therapy

The stability of mRNA is one of the key factors governing the regulation of eukaryotic gene expression and function. Human antigen R (HuR) is an RNA-binding protein that regulates the stability, translation, and nucleus-to-cytoplasm shuttling of its target mRNAs. While HuR is normally localized within the nucleus, it has been shown that HuR binds mRNAs in the nucleus and then escorts the mRNAs to the cytoplasm where HuR protects them from degradation. It contains several RNA recognition motifs, which specifically bind to adenylate and uridylate-rich regions within the 3'-untranslated region of the target mRNA to mediate its effect. Many of the HuR target mRNAs encode proteins important for cell growth, tumorigenesis, angiogenesis, tumor inflammation, invasion and metastasis. HuR overexpression is known to correlate well with high-grade malignancy and poor prognosis in many tumor types. Thus, HuR has emerged as an attractive drug target for cancer therapy. Novel small molecule HuR inhibitors have been identified by high throughput screening and new formulations for targeted delivery of HuR siRNA to tumor cells have been developed with promising anticancer activity. This review summarizes the significant role of HuR in cancer development, progression, and poor treatment response. We will discuss the potential and challenges of targeting HuR therapeutically.

AUF1 promotes stemness in human mammary epithelial cells through stabilization of the EMT transcription factors TWIST1 and SNAIL1

The AU-rich element RNA-binding protein 1 (AUF1) is an RNA-binding protein, which can both stabilize and destabilize the transcripts of several cancer-related genes. Since epithelial-to-mesenchymal transition (EMT) and the acquisition of cancer stem cell traits are important for cancer onset and progression, we sought to determine the role of AUF1 in these two important processes. We have shown that AUF1 induces EMT and stemness in breast epithelial cells via stabilization of the SNAIL1 and TWIST1 mRNAs, and their consequent upregulation. Indeed, AUF1 binds the transcripts of these two genes at their 3′UTR and reduces their turnover. Ectopic expression of AUF1 also promoted stemness in mammary epithelial cells, and thereby increased the proportion of cancer stem cells. Importantly, breast cancer cells that ectopically express AUF1 were more efficient in forming orthotopic tumor xenografts in nude mice than their corresponding controls with limiting cell inocula. On the other hand, AUF1 downregulation with specific siRNA inhibited EMT and reduced the stemness features in breast cancer cells. Moreover, AUF1 knockdown sensitized breast cancer cells to the killing effect of cisplatin. Together, these findings provide clear evidence that AUF1 is an important inducer of the EMT process through stabilization of SNAIL1 and TWIST1 and the consequent promotion of breast cancer stem cells. Thereby, AUF1 targeted molecules could constitute efficient therapeutics for breast cancer patients.

Targeting the interaction between RNA-binding protein HuR and FOXQ1 suppresses breast cancer invasion and metastasis

Patients diagnosed with metastatic breast cancer have a dismal 5-year survival rate of only 24%. The RNA-binding protein Hu antigen R (HuR) is upregulated in breast cancer, and elevated cytoplasmic HuR correlates with high-grade tumors and poor clinical outcome of breast cancer. HuR promotes tumorigenesis by regulating numerous proto-oncogenes, growth factors, and cytokines that support major tumor hallmarks including invasion and metastasis. Here, we report a HuR inhibitor KH-3, which potently suppresses breast cancer cell growth and invasion. Furthermore, KH-3 inhibits breast cancer experimental lung metastasis, improves mouse survival, and reduces orthotopic tumor growth. Mechanistically, we identify FOXQ1 as a direct target of HuR. KH-3 disrupts HuR–FOXQ1 mRNA interaction, leading to inhibition of breast cancer invasion. Our study suggests that inhibiting HuR is a promising therapeutic strategy for lethal metastatic breast cancer.

Wu et al. identify an inhibitor to the RNA-binding protein HuR, KH-3, that disrupts the interaction between HuR and target RNAs and inhibits human cancer growth and metastasis in mouse xenograft assays. This study suggests the therapeutic potential of targeting HuR in breast cancer with HuR overexpression.

MBNL1 regulates resistance of HeLa cells to cisplatin via Nrf2

Chemotherapy is an important method in the treatment of cervical cancer, but some patients will face drug resistance, which often indicates a poor prognosis. Moreover, there is no complete solution at present. Therefore, it is urgent to study the drug resistance mechanism of cervical cancer. Based on sequencing data mining, we predicted that MBNL1 might be involved in the occurrence and poor prognosis of cervical cancer, and verifed that MBNL1 could regulate the resistance of HeLa cells to cisplatin via Nrf2. In addition, we demonstrated that MBNL1 up regulated the degradation of Nrf2 protein by increasing the mRNA stability of Cul3. These results can provide theoretical basis for clinical development of new diagnosis and treatment targets for cisplatin resistance.

UDP-glucose accelerates SNAI1 mRNA decay and impairs lung cancer metastasis

Cancer metastasis is the primary cause of morbidity and mortality, and accounts for up to 95% of cancer-related deaths1. Cancer cells often reprogram their metabolism to efficiently support cell proliferation and survival2,3. However, whether and how those metabolic alterations contribute to the migration of tumour cells remain largely unknown. UDP-glucose 6-dehydrogenase (UGDH) is a key enzyme in the uronic acid pathway, and converts UDP-glucose to UDP-glucuronic acid4. Here we show that, after activation of EGFR, UGDH is phosphorylated at tyrosine 473 in human lung cancer cells. Phosphorylated UGDH interacts with Hu antigen R (HuR) and converts UDP-glucose to UDP-glucuronic acid, which attenuates the UDP-glucose-mediated inhibition of the association of HuR with SNAI1 mRNA and therefore enhances the stability of SNAI1 mRNA. Increased production of SNAIL initiates the epithelial-mesenchymal transition, thus promoting the migration of tumour cells and lung cancer metastasis. In addition, phosphorylation of UGDH at tyrosine 473 correlates with metastatic recurrence and poor prognosis of patients with lung cancer. Our findings reveal a tumour-suppressive role of UDP-glucose in lung cancer metastasis and uncover a mechanism by which UGDH promotes tumour metastasis by increasing the stability of SNAI1 mRNA.

The RNA-binding protein ESRP1 promotes human colorectal cancer progression

Epithelial splicing regulatory protein 1 (ESRP1) is an epithelial cell-specific RNA binding protein that controls several key cellular processes, like alternative splicing and translation. Previous studies have demonstrated a tumor suppressor role for this protein. Recently, however, a pro-metastatic function of ESRP1 has been reported. We thus aimed at clarifying the role of ESRP1 in Colorectal Cancer (CRC) by performing loss- and gain-of-function studies, and evaluating tumorigenesis and malignancy with in vitro and in vivo approaches. We found that ESRP1 plays a role in anchorage-independent growth of CRC cells. ESRP1-overexpressing cells grown in suspension showed enhanced fibroblast growth factor receptor (FGFR1/2) signalling, Akt activation, and Snail upregulation. Moreover, ESRP1 promoted the ability of CRC cells to generate macrometastases in mice livers. High ESRP1 expression may thus stimulate growth of cancer epithelial cells and promote colorectal cancer progression. Our findings provide mechanistic insights into a previously unreported, pro-oncogenic role for ESRP1 in CRC, and suggest that fine-tuning the level of this RNA-binding protein could be relevant in modulating tumor growth in a subset of CRC patients.

Posttranscriptional control of airway inflammation

Acute inflammation in the lungs is a vital protective response, efficiently and swiftly eliminating inciters of tissue injury. However, in respiratory diseases characterized by chronic inflammation, such as chronic obstructive pulmonary disease and asthma, enhanced expression of inflammatory mediators leads to tissue damage and impaired lung function. Although transcription is an essential first step in the induction of proinflammatory genes, tight regulation of inflammation requires more rapid, flexible responses. Increasing evidence shows that such responses are achieved by posttranscriptional mechanisms directly affecting mRNA stability and translation initiation. RNA-binding proteins, microRNAs, and long noncoding RNAs interact with messenger RNA and each other to impact the stability and/or translation of mRNAs implicated in lung inflammation. Recent research has shown that these biological processes play a central role in the pathogenesis of several important pulmonary conditions. This review will highlight several posttranscriptional control mechanisms that influence lung inflammation and the known associations of derangements in these mechanisms with common respiratory diseases. WIREs RNA 2018, 9:e1455. doi: 10.1002/wrna.1455 This article is categorized under: RNA in Disease and Development > RNA in Disease RNA Structure and Dynamics > Influence of RNA Structure in Biological Systems RNA Interactions with Proteins and Other Molecules > Protein-RNA Interactions: Functional Implications RNA Turnover and Surveillance > Regulation of RNA Stability.

Extracellular Vesicles Secreted by Atherogenic Macrophages Transfer MicroRNA to Inhibit Cell Migration

OBJECTIVE

During inflammation, macrophages secrete vesicles carrying RNA, protein, and lipids as a form of extracellular communication. In the vessel wall, extracellular vesicles (EVs) have been shown to be transferred between vascular cells during atherosclerosis; however, the role of macrophage-derived EVs in atherogenesis is not known. Here, we hypothesize that atherogenic macrophages secrete microRNAs (miRNAs) in EVs to mediate cell-cell communication and promote proinflammatory and proatherogenic phenotypes in recipient cells.

APPROACH AND RESULTS

We isolated EVs from mouse and human macrophages treated with an atherogenic stimulus (oxidized low-density lipoprotein) and characterized the EV miRNA expression profile. We confirmed the enrichment of miR-146a, miR-128, miR-185, miR-365, and miR-503 in atherogenic EVs compared with controls and demonstrate that these EVs are taken up and transfer exogenous miRNA to naive recipient macrophages. Bioinformatic pathway analysis suggests that atherogenic EV miRNAs are predicted to target genes involved in cell migration and adhesion pathways, and indeed delivery of EVs to naive macrophages reduced macrophage migration both in vitro and in vivo. Inhibition of miR-146a, the most enriched miRNA in atherogenic EVs, reduced the inhibitory effect of EVs on macrophage migratory capacity. EV-mediated delivery of miR-146a repressed the expression of target genes IGF2BP1 (insulin-like growth factor 2 mRNA-binding protein 1) and HuR (human antigen R or ELAV-like RNA-binding protein 1) in recipient cells, and knockdown of IGF2BP1 and HuR using short interfering RNA greatly reduced macrophage migration, highlighting the importance of these EV-miRNA targets in regulating macrophage motility.

CONCLUSIONS

EV-derived miRNAs from atherogenic macrophages, in particular miR-146a, may accelerate the development of atherosclerosis by decreasing cell migration and promoting macrophage entrapment in the vessel wall.

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.

RNA-Binding Proteins in Cancer: Old Players and New Actors

RNA-binding proteins (RBPs) are key players in post-transcriptional events. The combination of versatility of their RNA-binding domains with structural flexibility enables RBPs to control the metabolism of a large array of transcripts. Perturbations in RBP-RNA networks activity have been causally associated with cancer development, but the rational framework describing these contributions remains fragmented. We review here the evidence that RBPs modulate multiple cancer traits, emphasize their functional diversity, and assess future trends in the study of RBPs in cancer.

The Role of Reactive Oxygen and Nitrogen Species in the Expression and Splicing of Nitric Oxide Receptor

SIGNIFICANCE

Nitric oxide (NO)-dependent signaling is critical to many cellular functions and physiological processes. Soluble guanylyl cyclase (sGC) acts as an NO receptor and mediates the majority of NO functions. The signaling between NO and sGC is strongly altered by reactive oxygen and nitrogen species. Recent Advances: Besides NO scavenging, sGC is affected by oxidation/loss of sGC heme, oxidation, or nitrosation of cysteine residues and phosphorylation. Apo-sGC or sGC containing oxidized heme is targeted for degradation. sGC transcription and the stability of sGC mRNA are also affected by oxidative stress.

CRITICAL ISSUES

Studies cited in this review suggest the existence of compensatory processes that adapt cellular processes to diminished sGC function under conditions of short-term or moderate oxidative stress. Alternative splicing of sGC transcripts is discussed as a mechanism with the potential to both enhance and reduce sGC function. The expression of α1 isoform B, a functional and stable splice variant of human α1 sGC subunit, is proposed as one of such compensatory mechanisms. The expression of dysfunctional splice isoforms is discussed as a contributor to decreased sGC function in vascular disease.

FUTURE DIRECTIONS

Targeting the process of sGC splicing may be an important approach to maintain the composition of sGC transcripts that are expressed in healthy tissues under normal conditions. Emerging new strategies that allow for targeted manipulations of RNA splicing offer opportunities to use this approach as a preventive measure and to control the composition of sGC splice isoforms. Rational management of expressed sGC splice forms may be a valuable complementary treatment strategy for existing sGC-directed therapies. Antioxid. Redox Signal. 26, 122-136.

Loss of Scribble Promotes Snail Translation through Translocation of HuR and Enhances Cancer Drug Resistance

Drug resistance of cancer cells to various therapeutic agents and molecular targets is a major problem facing current cancer research. The tumor suppressor gene Scribble encodes a polarity protein that is conserved between Drosophila and mammals; loss of the locus disrupts cell polarity, inhibits apoptosis, and mediates cancer process. However, the role of Scribble in drug resistance remains unknown. We show here that knockdown of Scribble enhances drug resistance by permitting accumulation of Snail, which functions as a transcription factor during the epithelial-mesenchymal transition. Then, loss of Scribble activates the mRNA-binding protein human antigen R (HuR) by facilitating translocation of HuR from the nucleus to the cytoplasm. Furthermore, we demonstrate HuR can recognize AU-rich elements of the Snail-encoding mRNA, thereby regulating Snail translation. Moreover, loss of Scribble-induced HuR translocation mediates the accumulation of Snail via activation of the p38 MAPK pathway. Thus, this work clarifies the role of polarity protein Scribble, which is directly implicated in the regulation of developmental transcription factor Snail, and suggesting a mechanism for Scribble mediating cancer drug resistance.

Identification of Small-Molecule Inhibitors of the HuR/RNA Interaction Using a Fluorescence Polarization Screening Assay Followed by NMR Validation

The human antigen R (HuR) stabilizes many mRNAs of proto-oncogene, transcription factors, cytokines and growth factors by recognizing AU-rich elements (AREs) presented in their 3’ or 5’ untranslated region (UTR). Multiple lines of experimental evidence suggest that this process plays a key role in cancer development. Thus, destabilizing HuR/RNA interaction by small molecules presents an opportunity for cancer treatment/prevention. Here we present an integrated approach to identify inhibitors of HuR/RNA interaction using a combination of fluorescence-based and NMR-based high throughput screening (HTS). The HTS assay with fluorescence polarization readout and Z’-score of 0.8 was used to perform a screen of the NCI diversity set V library in a 384 well plate format. An NMR-based assay with saturation transfer difference (STD) detection was used for hits validation. Protein NMR spectroscopy was used to demonstrate that some hit compounds disrupt formation of HuR oligomer, whereas others block RNA binding. Thus, our integrated high throughput approach provides a new avenue for identification of small molecules targeting HuR/RNA interaction.

Human antigen R mediated post-transcriptional regulation of epithelial-mesenchymal transition related genes in diabetic nephropathy

BACKGROUND

Human antigen R (HuR) is a ubiquitously expressed RNA-binding protein that modulates gene expression at the post-transcriptional level. While cytoplasmic HuR expression was identified as a marker in epithelial-mesenchymal transition (EMT) process of several types of cancer, its role in diabetic nephropathy (DN) remains unclear.

METHODS

Renal biopsies from Type 2 diabetic patients and STZ-induced DN rats were stained for HuR and EMT markers. Redistribution of HuR was detected by immunostaining and western blot in high glucose stimulated cells. RNAi was used to supress HuR expression. The binding affinity for EMT-related genes was evaluated by immunoprecipitation.

RESULTS

Cytoplasmic HuR expression was elevated in human and rat DN specimens along with EMT changes compared to normal controls. HuR shuttling between nucleus and cytoplasm facilitated epithelial to mesenchymal transition in renal epithelial cells. The suppression of HuR partially inhibited EMT of high glucose stimulated HK-2 cells. Furthermore, HuR bound to 3'-UTRs of critical cytokines or transcription factors mRNA involved in EMT process.

CONCLUSION

Acquired phenotypic traits of EMT were partially through the enhanced HuR-binding proteins and its post-transcriptional regulation role in DN.

HuR: a promising therapeutic target for angiogenesis

Multiple angiogenic factors and inhibitors are becoming potential therapeutic targets for ischemia diseases and cancer. Posttranscriptional regulation through the untranslated region of mRNA is emerging as a critical regulating level in nearly all the biological processes. As a kind of RNA binding proteins, HuR plays important role in augmenting the hypoxic or inflammatory signal, stabilizing the resultant angiogenic factors and promoting the proliferation and migration of endothelial cells. These implicate HuR in the proangiogenic factors mediated angiogenesis in the hypoxia and inflammatory. We consider hypotheses that a more effective angiogenesis can be acquired through strengthened and prolonged effects of angiogenic factors, and that progresses in therapeutic angiogensis might also shed light on the implication of HuR in blocking tumor angiogensis. These considerations may help us to explain HuR as a promising therapeutic target for angiogenesis related disease. It may be a candidate in hypoxia therapy and cancer management.

Muscadine grape skin extract reverts snail-mediated epithelial mesenchymal transition via superoxide species in human prostate cancer cells

BACKGROUND

Snail transcription factor can induce epithelial-mesenchymal transition (EMT), associated with decreased cell adhesion-associated molecules like E-cadherin, increased mesenchymal markers like vimentin, leading to increased motility, invasion and metastasis. Muscadine grape skin extract (MSKE) has been shown to inhibit prostate cancer cell growth and induce apoptosis without affecting normal prostate epithelial cells. We investigated novel molecular mechanisms by which Snail promotes EMT in prostate cancer cells via Reactive Oxygen Species (ROS) and whether it can be antagonized by MSKE.

METHODS

ARCaP and LNCaP cells overexpressing Snail were utilized to examine levels of reactive oxygen species (ROS), specifically, superoxide, in vitro using Dihydroethidium (DHE) or HydroCy3 dyes. Mitosox staining was performed to determine whether the source of ROS was mitochondrial in origin. We also investigated the effect of Muscadine grape skin extract (MSKE) on EMT marker expression by western blot analysis. Migration and cell viability using MTS proliferation assay was performed following MSKE treatments.

RESULTS

Snail overexpression in ARCaP and LNCaP cells was associated with increased concentration of mitochondrial superoxide, in vitro. Interestingly, MSKE decreased superoxide levels in ARCaP and LNCaP cells. Additionally, MSKE and Superoxide Dismutase (SOD) reverted EMT as evidenced by decreased vimentin levels and re-induction of E-cadherin expression in ARCaP-Snail cells after 3 days, concomitant with reduced cell migration. MSKE also decreased Stat-3 activity in ARCaP-Snail cells.

CONCLUSIONS

This study shows that superoxide species may play a role in Snail transcription factor-mediated EMT. Therefore, therapeutic targeting of Snail with various antioxidants such as MSKE may prove beneficial in abrogating EMT and ROS-mediated tumor progression in human prostate cancer.

Genome-wide activities of RNA binding proteins that regulate cellular changes in the epithelial to mesenchymal transition (EMT)

The epithelial to mesenchymal transition (EMT) and reverse mesenchymal to epithelial transition (MET) are developmentally conserved processes that are essential for patterning of developing embryos and organs. The EMT/MET are further utilized in wound healing, but they can also be hijacked by cancer cells to promote tumor progression and metastasis. The molecular pathways governing these processes have historically focused on the transcriptional regulation and networks that control them. Indeed, global profiling of transcriptional changes has provided a wealth of information into how these networks are regulated, the downstream targets, and functional consequence of alterations to the global transcriptome. However, recent evidence has revealed that the posttranscriptional landscape of the cell is also dramatically altered during the EMT/MET and contributes to changes in cell behavior and phenotypes. While studies of this aspect of EMT biology are still in their infancy, recent progress has been achieved by the identification of several RNA binding proteins (RBPs) that regulate splicing, polyadenylation, mRNA stability, and translational control during EMT. This chapter focuses on the global impact of RBPs that regulate mRNA maturation as well as outlines the functional impact of several key posttranscriptional changes during the EMT. The growing evidence of RBP involvement in the cellular transformation during EMT underscores that a coordinated regulation of both transcriptional and posttranscriptional changes is essential for EMT. Furthermore, new discoveries into these events will paint a more detailed picture of the transcriptome during the EMT/MET and provide novel molecular targets for treatment of human diseases.

Targeting CSCs in tumor microenvironment: the potential role of ROS-associated miRNAs in tumor aggressiveness

Reactive oxygen species (ROS) have been widely considered as critical cellular signaling molecules involving in various biological processes such as cell growth, differentiation, proliferation, apoptosis, and angiogenesis. The homeostasis of ROS is critical to maintain normal biological processes. Increased production of ROS, namely oxidative stress, due to either endogenous or exogenous sources causes irreversible damage of bio-molecules such as DNA, proteins, lipids, and sugars, leading to genomic instability, genetic mutation, and altered gene expression, eventually contributing to tumorigenesis. A great amount of experimental studies in vitro and in vivo have produced solid evidence supporting that oxidative stress is strongly associated with increased tumor cell growth, treatment resistance, and metastasis, and all of which contribute to tumor aggressiveness. More recently, the data have indicated that altered production of ROS is also associated with cancer stem cells (CSCs), epithelial-to-mesenchymal transition (EMT), and hypoxia, the most common features or phenomena in tumorigenesis and tumor progression. However, the exact mechanism by which ROS is involved in the regulation of CSC and EMT characteristics as well as hypoxia- and, especially, HIF-mediated pathways is not well known. Emerging evidence suggests the role of miRNAs in tumorigenesis and progression of human tumors. Recently, the data have indicated that altered productions of ROS are associated with deregulated expression of miRNAs, suggesting their potential roles in the regulation of ROS production. Therefore, targeting ROS mediated through the deregulation of miRNAs by novel approaches or by naturally occurring anti-oxidant agents such as genistein could provide a new therapeutic approach for the prevention and/or treatment of human malignancies. In this article, we will discuss the potential role of miRNAs in the regulation of ROS production during tumorigenesis. Finally, we will discuss the role of genistein, as a potent anti-tumor agent in the regulation of ROS production during tumorigenesis and tumor development.

Regulation of the protein stability of EMT transcription factors

The epithelial to mesenchymal transition (EMT) consists of a rapid change of cell phenotype, characterized by the loss of epithelial characteristics and the acquisition of a more invasive phenotype. Transcription factors regulating EMT (Snail, Twist and Zeb) are extremely labile proteins, rapidly degraded by the proteasome system. In this review we analyze the current mechanisms controlling degradation of EMT transcription factors, focusing on the role of new E3 ubiquitin-ligases involved in EMT. We also summarize the regulation of the stability of these EMT transcription factors, specially observed in different stress conditions, such as hypoxia, chemotherapeutic drugs, oxidative stress or γ-irradiation.

Cellular polarity in aging: role of redox regulation and nutrition

Cellular polarity concerns the spatial asymmetric organization of cellular components and structures. Such organization is important not only for biological behavior at the individual cell level, but also for the 3D organization of tissues and organs in living organisms. Processes like cell migration and motility, asymmetric inheritance, and spatial organization of daughter cells in tissues are all dependent of cell polarity. Many of these processes are compromised during aging and cellular senescence. For example, permeability epithelium barriers are leakier during aging; elderly people have impaired vascular function and increased frequency of cancer, and asymmetrical inheritance is compromised in senescent cells, including stem cells. Here, we review the cellular regulation of polarity, as well as the signaling mechanisms and respective redox regulation of the pathways involved in defining cellular polarity. Emphasis will be put on the role of cytoskeleton and the AMP-activated protein kinase pathway. We also discuss how nutrients can affect polarity-dependent processes, both by direct exposure of the gastrointestinal epithelium to nutrients and by indirect effects elicited by the metabolism of nutrients, such as activation of antioxidant response and phase-II detoxification enzymes through the transcription factor nuclear factor (erythroid-derived 2)-like 2 (Nrf2). In summary, cellular polarity emerges as a key process whose redox deregulation is hypothesized to have a central role in aging and cellular senescence.

Posttranscriptional regulation by RNA-binding proteins during epithelial-to-mesenchymal transition

Epithelial-to-mesenchymal transition (EMT), one of the crucial steps for carcinoma cells to acquire invasive capacity, results from the disruption of cell–cell contacts and the acquisition of a motile mesenchymal phenotype. Although the transcriptional events controlling EMT have been extensively studied, in recent years, several posttranscriptional mechanisms have emerged as critical in the regulation of EMT during tumor progression. In this review, we highlight the regulation of posttranscriptional events in EMT by RNA-binding proteins (RBPs). RBPs are responsible for controlling pre-mRNA splicing, capping, and polyadenylation, as well as mRNA export, turnover, localization, and translation. We discuss the most relevant aspects of RBPs controlling the metabolism of EMT-related mRNAs, and describe the implication of novel posttranscriptional mechanisms regulating EMT in response to different signaling pathways. Novel insight into posttranscriptional regulation of EMT by RBPs is uncovering new therapeutic targets in cancer invasion and metastasis.

Multiple functions of the RNA-binding protein HuR in cancer progression, treatment responses and prognosis

The human embryonic lethal abnormal vision-like protein, HuR, is a member of the Hu family of RNA-binding proteins. Over the past decade, this ubiquitously expressed protein has been extensively investigated in cancer research because it is involved in the regulation of mRNA stability and translation in many cell types. HuR activity and function is associated with its subcellular distribution, transcriptional regulation, translational and post-translational modifications. HuR regulation of target mRNAs is based on the interaction between the three specific domains of HuR protein and one or several U- or AU-rich elements (AREs) in the untranslated region of target mRNAs. A number of cancer-related transcripts containing AREs, including mRNAs for proto-oncogenes, cytokines, growth factors, and invasion factors, have been characterized as HuR targets. It has been proposed that HuR has a central tumorigenic activity by enabling multiple cancer phenotypes. In this review, we comprehensively survey the existing evidence with regard to the diverse functions of HuR in caner development and progression. The current data also suggest that HuR might be a novel and promising therapeutic target and a marker for treatment response and prognostic evaluation.

New insights into the regulation of epithelial-mesenchymal transition and tissue fibrosis

Tissue fibrosis often presents as the final outcome of chronic disease and is a significant cause of morbidity and mortality worldwide. Fibrosis is driven by continuous expansion of fibroblasts and myofibroblasts. Epithelial-mesenchymal transition (EMT) is a form of cell plasticity in which epithelia acquire mesenchymal phenotypes and is increasingly recognized as an integral aspect of tissue fibrogenesis. In this review, we describe recent insight into the molecular and cellular factors that regulate EMT and its underlying signaling pathways. We also consider how mechanical cues from the microenvironment affect the regulation of EMT. Finally, we discuss the role of EMT in fibrotic diseases and propose approaches for detecting and treating fibrogenesis by targeting EMT.

Versatility of RNA-Binding Proteins in Cancer

Posttranscriptional gene regulation is a rapid and efficient process to adjust the proteome of a cell to a changing environment. RNA-binding proteins (RBPs) are the master regulators of mRNA processing and translation and are often aberrantly expressed in cancer. In addition to well-studied transcription factors, RBPs are emerging as fundamental players in tumor development. RBPs and their mRNA targets form a complex network that plays a crucial role in tumorigenesis. This paper describes mechanisms by which RBPs influence the expression of well-known oncogenes, focusing on precise examples that illustrate the versatility of RBPs in posttranscriptional control of cancer development. RBPs appeared very early in evolution, and new RNA-binding domains and combinations of them were generated in more complex organisms. The identification of RBPs, their mRNA targets, and their mechanism of action have provided novel potential targets for cancer therapy.

Altered stability of mRNAs associated with glaucoma progression in human trabecular meshwork cells following oxidative stress

PURPOSE

The goals of this study were to determine if oxidative stress on human trabecular meshwork (HTM) cells influences the stability of key mRNAs containing AU rich elements (AREs) known to be associated with glaucoma progression, and if the presence of topographic cue alters the stability of these mRNAs.

METHODS

HTM cells were treated with 300 μM hydrogen peroxide (H(2)O(2)) for 1 hour in the presence of 5 μg/mL actinomycin D and compared with untreated cells. The selected mRNAs (IL-6, IL-8, myocilin, SPARC [secreted protein, acidic and rich in cysteine], matrix metalloproteinase [MMP]-3, and MMP-9) from the cells were analyzed by using relative quantitative PCR. Immunohistochemistry for Hu antigen R (HuR) was performed in addition to Western blots of HuR. HTM cells were also grown on topographically patterned surfaces, and IL-6 mRNA was analyzed by quantitative PCR.

RESULTS

H(2)O(2) increased IL-6 mRNA stability 0.145 (0.095-0.27) to 0.345 (0.2-0.48) (normalized ratio, median [interquartile range]) (n = 5), while IL-8 mRNA was increased from 0.565 (0.408-0.6) to 0.775 (0.486-0.873) (n = 5). These differences were statistically significant (P = 0.0313, for both IL-6 and IL-8; Wilcoxon signed-rank test). The mRNAs of myocilin, SPARC, and MMP-3, which do not have AREs, were more stable after actinomycin D treatment and were not altered with oxidation. Western blot and immunohistochemistry demonstrated that H(2)O(2) treatment induces the translocation of HuR from the nucleus to the cytoplasm. Nanopatterned surfaces did not alter IL-6 mRNA stability.

CONCLUSIONS

Oxidative stress stabilizes IL-6 and IL-8 mRNAs significantly. The decay of certain mRNAs associated with glaucoma may be altered in the trabecular meshwork of glaucoma patients.

The oncogenic RNA-binding protein Musashi1 is regulated by HuR via mRNA translation and stability in glioblastoma cells

Musashi1 (Msi1) is an evolutionarily conserved RNA-binding protein (RBP) that has profound implications in cellular processes such as stem cell maintenance, nervous system development, and tumorigenesis. Msi1 is highly expressed in many cancers, including glioblastoma, whereas in normal tissues, its expression is restricted to stem cells. Unfortunately, the factors that modulate Msi1 expression and trigger high levels in tumors are largely unknown. The Msi1 mRNA has a long 3' untranslated region (UTR) containing several AU- and U-rich sequences. This type of sequence motif is often targeted by HuR, another important RBP known to be highly expressed in tumor tissue such as glioblastoma and to regulate a variety of cancer-related genes. In this report, we show an interaction between HuR and the Msi1 3'-UTR, resulting in a positive regulation of Msi1 expression. We show that HuR increased MSI1 mRNA stability and promoted its translation. We also present evidence that expression of HuR and Msi1 correlate positively in clinical glioblastoma samples. Finally, we show that inhibition of cell proliferation, increased apoptosis, and changes in cell-cycle profile as a result of silencing HuR are partially rescued when Msi1 is ectopically expressed. In summary, our results suggest that HuR is an important regulator of Msi1 in glioblastoma and that this regulation has important biological consequences during gliomagenesis.

HuR function in disease

The cytoplasmic events that control mammalian gene expression, primarily mRNA stability and translation, potently influence the cellular response to internal and external signals. The ubiquitous RNA-binding protein (RBP) HuR is one of the best-studied regulators of cytoplasmic mRNA fate. Through its post-transcriptional influence on specific target mRNAs, HuR can alter the cellular response to proliferative, stress, apoptotic, differentiation, senescence, inflammatory and immune stimuli. In light of its central role in important cellular functions, HuR's role in diseases in which these responses are aberrant is increasingly appreciated. Here, we review the mechanisms that control HuR function, its influence on target mRNAs, and how impairment in HuR-governed gene expression programs impact upon different disease processes. We focus on HuR's well-recognized implication in cancer and chronic inflammation, and discuss emerging studies linking HuR to cardiovascular, neurological, and muscular pathologies. We also discuss the progress, potential, and challenges of targeting HuR therapeutically.

Posttranscriptional regulation of cancer traits by HuR

Cancer-related gene expression programs are strongly influenced by posttranscriptional mechanisms. The RNA-binding protein HuR is highly abundant in many cancers. Numerous HuR-regulated mRNAs encode proteins implicated in carcinogenesis. Here, we review the collections of HuR target mRNAs that encode proteins responsible for implementing five major cancer traits. By interacting with specific mRNA subsets, HuR enhances the levels of proteins that (1) promote cell proliferation, (2) increase cell survival, (3) elevate local angiogenesis, (4) help the cancer cell evade immune recognition, and (5) facilitate cancer cell invasion and metastasis. We propose that HuR exerts a tumorigenic function by enabling these cancer phenotypes. We discuss evidence that links HuR to several specific cancers and suggests its potential usefulness in cancer diagnosis, prognosis, and therapy.

Epithelial-mesenchymal transition: from molecular mechanisms, redox regulation to implications in human health and disease

Epithelial to mesenchymal transition (EMT) is a fundamental process, paradigmatic of the concept of cell plasticity, that leads epithelial cells to lose their polarization and specialized junctional structures, to undergo cytoskeleton reorganization, and to acquire morphological and functional features of mesenchymal-like cells. Although EMT has been originally described in embryonic development, where cell migration and tissue remodeling have a primary role in regulating morphogenesis in multicellular organisms, recent literature has provided evidence suggesting that the EMT process is a more general biological process that is also involved in several pathophysiological conditions, including cancer progression and organ fibrosis. This review offers first a comprehensive introduction to describe major relevant features of EMT, followed by sections dedicated on those signaling mechanisms that are known to regulate or affect the process, including the recently proposed role for oxidative stress and reactive oxygen species (ROS). Current literature data involving EMT in both physiological conditions (i.e., embryogenesis) and major human diseases are then critically analyzed, with a special final focus on the emerging role of hypoxia as a relevant independent condition able to trigger EMT.

Role of the RNA-binding protein HuR in human renal cell carcinoma

Human conventional renal cell carcinoma (CRCC) remains resistant to therapy. The RNA-binding protein HuR regulates the stability and/or translation of multiple messenger RNAs involved in malignant transformation. In this study, we aimed to evaluate the potential role of HuR in this pathology. Using seven human CRCC cell lines expressing or not the von Hippel-Lindau (VHL) tumor suppressor gene as well as 15 normal/renal cell carcinoma tumor pairs, we showed that HuR is overexpressed in all tumors independently of the VHL status. Futhermore, HuR cytoplasmic presence appears to be more common in early tumor stages, suggesting a role in tumor promotion. We then assessed the effect of HuR knockdown using small interfering RNA in cultured cell and in tumor-bearing mice. Both in vitro and in vivo, we observed that cell growth was inhibited by 60% and that this effect was obtained through an inhibition of cell proliferation and an induction of cell apoptosis. Finally, we found that expression of vascular endothelium growth factor, tumor growth factor-beta and of the hypoxia-induced transcription factor-2alpha as well as the constitutive activation of the oncogenic phosphoinositide 3-kinase/Akt, nuclear factor-kappaB and mitogen-activated protein kinase pathways were decreased in HuR-depleted cells and tumors. All these results suggest a pivotal role for HuR in human CRCC.