Cellular Protein HuR Regulates the Switching of Genomic RNA Templates for Differential Functions during the Coxsackievirus B3 Life Cycle.

Coxsackievirus B3 (CVB3) is an enterovirus belonging to the family Picornaviridae. Its 5' untranslated region (UTR) contains a cloverleaf structure followed by an internal ribosome entry site (IRES). The cloverleaf forms an RNA-protein complex known to regulate virus replication, translation, and stability of the genome, and the IRES regulates virus RNA translation. For positive-strand RNA-containing viruses, such as members of the flaviviruses or enteroviruses, the genomic RNA is used for translation, replication, and encapsidation. Only a few regulatory mechanisms which govern the accessibility of genomic RNA templates for translation or replication have been reported. Here, we report the role of human antigen R (HuR) in regulating the fate of CVB3 positive-strand RNA into the replication cycle or translation cycle. We have observed that synthesis of HuR is induced during CVB3 infection, and it suppresses viral replication by displacing PCBP-2 (a positive regulator of virus replication) at the cloverleaf RNA. Silencing of HuR increases viral RNA replication and consequently reduces viral RNA translation in a replication-dependent manner. Furthermore, we have shown that HuR level is upregulated upon CVB3 infection. Moreover, HuR limits virus replication and can coordinate the availability of genomic RNA templates for translation, replication, or encapsidation. Our study highlights the fact that the relative abundance of translation factors and replication factors in the cell decides the outcome of viral infection. IMPORTANCE A positive-strand RNA virus must balance the availability of its genomic template for different viral processes at different stages of its life cycle. A few host proteins are shown to be important to help the virus in switching the usage of a template between these processes. These proteins inhibit translation either by displacing a stimulator of translation or by binding to an alternative site. Both mechanisms lead to ribosome clearance and availability of the genomic strand for replication. We have shown that HuR also helps in maintaining this balance by inhibiting replication and subsequently promoting translation and packaging.

Targeting the HuR Oncogenic Role with a New Class of Cytoplasmic Dimerization Inhibitors.

The development of novel therapeutics that exploit alterations in the activation state of key cellular signaling pathways due to mutations in upstream regulators has generated the field of personalized medicine. These first-generation efforts have focused on actionable mutations identified by deep sequencing of large numbers of tumor samples. We propose that a second-generation opportunity exists by exploiting key downstream "nodes of control" that contribute to oncogenesis and are inappropriately activated due to loss of upstream regulation and microenvironmental influences. The RNA-binding protein HuR represents such a node. Because HuR functionality in cancer cells is dependent on HuR dimerization and its nuclear/cytoplasmic shuttling, we developed a new class of molecules targeting HuR protein dimerization. A structure-activity relationship algorithm enabled development of inhibitors of HuR multimer formation that were soluble, had micromolar activity, and penetrated the blood-brain barrier. These inhibitors were evaluated for activity validation and specificity in a robust cell-based assay of HuR dimerization. SRI-42127, a molecule that met these criteria, inhibited HuR multimer formation across primary patient-derived glioblastoma xenolines (PDGx), leading to arrest of proliferation, induction of apoptosis, and inhibition of colony formation. SRI-42127 had favorable attributes with central nervous system penetration and inhibited tumor growth in mouse models. RNA and protein analysis of SRI-42127-treated PDGx xenolines across glioblastoma molecular subtypes confirmed attenuation of targets upregulated by HuR. These results highlight how focusing on key attributes of HuR that contribute to cancer progression, namely cytoplasmic localization and multimerization, has led to the development of a novel, highly effective inhibitor. SIGNIFICANCE: These findings utilize a cell-based mechanism of action assay with a structure-activity relationship compound development pathway to discover inhibitors that target HuR dimerization, a mechanism required for cancer promotion.

MSC-induced lncRNA AGAP2-AS1 promotes stemness and trastuzumab resistance through regulating CPT1 expression and fatty acid oxidation in breast cancer.

Trastuzumab resistance has been becoming a major obstacle for treatment of HER-2-positive breast cancer patients. Increasing evidence suggests that mesenchymal stem cells (MSCs) play critical roles during the formation of drug resistance, however, the underlying mechanism is not well known. In this study, mass spectrometry, RNA pulldown and RNA immunoprecipitation assays were performed to verify the direct interactions among AGAP2-AS1 and other associated targets, such as human antigen R (HuR), miR-15a-5p, and carnitine palmitoyl transferase 1 (CPT1). In vitro and in vivo experimental assays were done to clarify the functional role of AGAP2-AS1 in trastuzumab resistance, stemness, and fatty acid oxidation (FAO). The results showed that MSC co-culture induced trastuzumab resistance. AGAP2-AS1 was upregulated in MSC-cultured cells, and knockdown of AGAP2-AS1 reversed the MSC-mediated trastuzumab resistance. Furthermore, MSC culture-induced AGAP2-AS1 regulates stemness and trastuzumab resistance via activating FAO. Mechanistically, AGAP2-AS1 is associated with HuR, and the AGAP2-AS1-HuR complex could directly bind to the CPT1, increasing its expression via improving RNA stability. In addition, AGAP2-AS1 could serve as ceRNA via sponging miR-15a-5p and releasing CPT1 mRNA. Clinically, increased expression of serum AGAP2-AS1 predicts poor response to trastuzumab treatment in breast cancer patients. In conclusion, MSC culture-induced AGAP2-AS1 caused stemness and trastuzumab resistance via promoting CPT1 expression and inducing FAO. Our results provide new insight of the role of MSCs in trastuzumab resistance and AGAP2-AS1 could be promising predictive biomarker and therapeutic target for HER-2+ breast cancer patients.

HuR promotes miRNA-mediated upregulation of NFI-A protein expression in MDSCs during murine sepsis.

Myeloid-derived suppressor cells (MDSCs) contribute to high mortality rates during sepsis, but how sepsis induces MDSCs is unclear. Previously we reported that microRNA (miR)-21 and miR-181b reprogram MDSCs in septic mice by increasing levels of DNA binding transcription factor, nuclear factor 1 (NFI-A). Here, we provide evidence that miR-21 and miR-181b stabilize NFI-A mRNA and increase NFI-A protein levels by recruiting RNA-binding proteins HuR and Ago1 to its 3' untranslated region (3'UTR). We also find that the NFI-A GU-rich element (GRE)-binding protein CUGBP1 counters miR-21 and miR-181b dependent NFI-A mRNA stabilization and decreases protein production by replacing 3'UTR bound Ago1 with Ago2. We confirmed the miR-21 and miR-181b dependent reprogramming pathway in MDSCs transfected with a luciferase reporter construct containing an NFI-A 3'UTR fragment with point mutations in the miRNA binding sites. These results suggest that targeting NFI-A in MDSCs during sepsis may enhance resistance to uncontrolled infection.

Human antigen R-regulated mRNA metabolism promotes the cell motility of migrating mouse neurons.

Neocortex development during embryonic stages requires the precise control of mRNA metabolism. Human antigen R (HuR) is a well-studied mRNA-binding protein that regulates mRNA metabolism, and it is highly expressed in the neocortex during developmental stages. Deletion of HuR does not impair neural progenitor cell proliferation or differentiation, but it disturbs the laminar structure of the neocortex. We report that HuR is expressed in postmitotic projection neurons during mouse brain development. Specifically, depletion of HuR in these neurons led to a mislocalization of CDP+ neurons in deeper layers of the cortex. Time-lapse microscopy showed that HuR was required for the promotion of cell motility in migrating neurons. PCR array identified profilin 1 (Pfn1) mRNA as a major binding partner of HuR in neurons. HuR positively mediated the stability of Pfn1 mRNA and influenced actin polymerization. Overexpression of Pfn1 successfully rescued the migration defects of HuR-deleted neurons. Our data reveal a post-transcriptional mechanism that maintains actin dynamics during neuronal migration.

HuR (Human Antigen R) Regulates the Contraction of Vascular Smooth Muscle and Maintains Blood Pressure.

OBJECTIVE: HuR (human antigen R)-an RNA-binding protein-is involved in regulating mRNA stability by binding adenylate-uridylate-rich elements. This study explores the role of HuR in the regulation of smooth muscle contraction and blood pressure. Approach and Results: Vascular HuRSMKO (smooth muscle-specific HuR knockout) mice were generated by crossbreeding HuRflox/flox mice with α-SMA (α-smooth muscle actin)-Cre mice. As compared with CTR (control) mice, HuRSMKO mice showed hypertension and cardiac hypertrophy. HuR levels were decreased in aortas from hypertensive patients and SHRs (spontaneously hypertensive rats), and overexpression of HuR could lower the blood pressure of SHRs. Contractile response to vasoconstrictors was increased in mesenteric artery segments isolated from HuRSMKO mice. The functional abnormalities in HuRSMKO mice were attributed to decreased mRNA and protein levels of RGS (regulator of G-protein signaling) protein(s) RGS2, RGS4, and RGS5, which resulted in increased intracellular calcium increase. Consistently, the degree of intracellular calcium ion increase in HuR-deficient smooth muscle cells was reduced by overexpression of RGS2, RGS4, or RGS5. Finally, administration of RGS2 and RGS5 reversed the elevated blood pressure in HuRSMKO mice. CONCLUSIONS: Our findings indicate that HuR regulates vascular smooth muscle contraction and maintains blood pressure by modulating RGS expression.

The RNA-Binding Protein ELAVL1 Regulates GnRH Receptor Expression and the Response to GnRH.

Gonadotropin secretion, which is elicited by GnRH stimulation of the anterior pituitary gonadotropes, is a critical feature of reproductive control and the maintenance of fertility. In addition, activation of the GnRH receptor (GnRHR) regulates transcription and translation of multiple factors that regulate the signaling response and synthesis of gonadotropins. GnRH stimulation results in a broad redistribution of mRNA between active and inactive polyribosomes within the cell, but the mechanism of redistribution is not known. The RNA-binding protein embryonic lethal, abnormal vision, Drosophila-like 1 (ELAVL1) binds to AU-rich elements in mRNA and is one of the most abundant mRNA-binding proteins in eukaryotic cells. It is known to serve as a core component of RNA-binding complexes that direct the fate of mRNA. In LßT2 gonadotropes, we showed that ELAVL1 binds to multiple mRNAs encoding factors that are crucial for gonadotropin synthesis and release. Association with some mRNAs is GnRH sensitive but does not correlate with abundance of binding. We also showed MAPK-dependent changes in intracellular localization of ELAVL1 in response to GnRH stimulation. Knockdown of ELAVL1 gene expression resulted in reduced Lhb and Gnrhr mRNA levels, reduced cell surface expression of GnRHR, and reduced LH secretion in response to GnRH stimulation. Overall, these observations not only support the role of ELAVL1 in GnRHR-mediated regulation of gene expression and LH secretion but also indicate that other factors may contribute to the precise fate of mRNA in response to GnRH stimulation of gonadotropes.

Multiple functions of HuR in urinary tumors.

PURPOSE: Human embryonic lethal abnormal visual-like protein, HuR, belongs to a member of the Hu family of RNA-binding protein and plays a critical role in urinary tumors. The purpose of this review is to summarize the current literature to demonstrate the importance of HuR in urinary tract tumors' biology and explore the potential role in therapeutic strategies aimed at targeting this molecule in cancer cells. METHODS: The relevant literature from PubMed and Medline databases is reviewed in this article. RESULTS: Increasing evidence supports that HuR plays a critical role in urinary tumors' biology because it regulates the expression of many urinary tumors-associated molecules through post-transcriptional regulatory mechanisms (including mRNA trafficking, mRNA decay and protein translation). Recent studies have demonstrated that HuR is associated with chemoresistance of urinary tumors, suggesting that HuR might be a novel therapeutic target and a marker for therapeutic response and prognosis assessment. CONCLUSION: HuR is associated with various urinary tumors biological characteristics. Targeted therapy of HuR may become an attractive treatment strategy. What's more, more preclinical and clinical trials of this targeted strategy are necessary for the treatment of urinary tumors.

Phosphorylation of ELAVL1 (Ser219/Ser316) mediated by PKC is required for erythropoiesis.

Elavl1 (also known as HuR), an RNA binding protein highly conserved between zebrafish and human, regulates gene expression by stabilizing target mRNA. Our previous studies have uncovered that the predominant isoform elavl1a is required for zebrafish embryonic erythropoiesis. However, the exact mechanism of how elav11 spatiotemporally stabilizes target mRNAs to regulate specific erythropoiesis is not yet understood. Here we show that phosphorylation of elavl1a at Ser219 and Ser316 by PKC is necessarily required for cytosolic shuttling from the nucleus to stabilize gata1 mRNA and thus promotes erythropoiesis. Knockdown of elavl1a resulted in the hindrance of erythropoiesis and Hemin-induced erythroid differentiation of human myeloid leukemia K562 cells. Interestingly, inhibition of PKC reproduced the phenotype seen during zebrafish embryogenesis and erythroid differentiation of myeloid leukemia. Mechanistically, Hemin induced elavl1a export from nuclear to cytoplasmic space in K562 cells in a manner dependent on phosphorylation on Ser219 and Ser316, as overexpression of elavl1a with mutations on Ser219 and Ser316 resulted in erythropoiesis failure. Additionally, co-administration of low doses of elavl1a morpholino (MO) and three PKC inhibitors showed a combined effect in zebrafish embryonic erythropoiesis dysplasia. In conclusion, our study reveals that PKC-mediated phosphorylation of elavl1a at Ser219 and Ser316 sites controls its nucleo-cytoplasmic translocation in zebrafish, thereby regulating embryonic erythropoiesis.

Activation of ferritinophagy is required for the RNA-binding protein ELAVL1/HuR to regulate ferroptosis in hepatic stellate cells.

Ferroptosis is a recently recognized form of regulated cell death that is characterized by lipid peroxidation. However, the molecular mechanisms regulating ferroptosis are largely unknown. In this study, we report that the RNA-binding protein ELAVL1/HuR plays a crucial role in regulating ferroptosis in liver fibrosis. Upon exposure to ferroptosis-inducing compounds, ELAVL1 protein expression was remarkably increased through the inhibition of the ubiquitin-proteasome pathway. ELAVL1 siRNA led to ferroptosis resistance, whereas ELAVL1 plasmid contributed to classical ferroptotic events. Interestingly, upregulated ELAVL1 expression also appeared to increase autophagosome generation and macroautophagic/autophagic flux, which was the underlying mechanism for ELAVL1-enhanced ferroptosis. Autophagy depletion completely impaired ELAVL1-mediated ferroptotic events, whereas autophagy induction showed a synergistic effect with ELAVL1. Importantly, ELAVL1 promoted autophagy activation via binding to the AU-rich elements within the F3 of the 3'-untranslated region of BECN1/Beclin1 mRNA. The internal deletion of the F3 region abrogated the ELAVL1-mediated BECN1 mRNA stability, and, in turn, prevented ELAVL1-enhanced ferroptosis. In mice, treatment with sorafenib alleviated murine liver fibrosis by inducing hepatic stellate cell (HSC) ferroptosis. HSC-specific knockdown of ELAVL1 impaired sorafenib-induced HSC ferroptosis in murine liver fibrosis. Noteworthy, we retrospectively analyzed the effect of sorafenib on HSC ferroptosis in advanced fibrotic patients with hepatocellular carcinoma receiving sorafenib monotherapy. Attractively, ELAVL1 upregulation, ferritinophagy activation, and ferroptosis induction occurred in primary human HSCs from the collected human liver tissue. Overall, these results reveal novel molecular mechanisms and signaling pathways of ferroptosis, and also identify ELAVL1-autophagy-dependent ferroptosis as a potential target for the treatment of liver fibrosis. Abbreviations: ACTA2/alpha-SMA: actin, alpha 2, smooth muscle, aorta; ACTB/beta-actin: actin beta; ARE: AU-rich element; ATG: autophagy related; BDL: bile duct ligation; BECN1: beclin 1; BSO: buthionine sulfoximine; COL1A1: collagen type I alpha 1 chain; ELAVL1/HuR: ELAV like RNA binding protein 1; FDA: fluorescein diacetate; FTH1: ferritin heavy chain 1; GOT1/AST: glutamic-oxaloacetic transaminase 1; GPT/ALT: glutamic-pyruvic transaminase; GPX4: glutathione peroxidase 4; GSH: glutathione; HCC: hepatocellular carcinoma; HSC: hepatic stellate cell; LCM: laser capture microdissection; MAP1LC3B: microtubule associated protein 1 light chain 3 beta; MDA: malondialdehydep; NCOA4: nuclear receptor coactivator 4; PTGS2: prostaglandin-endoperoxide synthase 2; ROS: reactive oxygen species; SQSTM1/p62: sequestosome 1; TBIL: total bilirubin; TEM: transmission electron microscopy; TGFB1: trasforming growth factor beta 1; UTR: untranslated region; VA-Lip-ELAVL1-siRNA: vitamin A-coupled liposomes carrying ELAVL1-siRNA.

Modulation of the mRNA-binding protein HuR as a novel reversal mechanism of epirubicin-triggered multidrug resistance in colorectal cancer cells.

HuR (ELAVL1), a RNA-binding protein, plays a key role in posttranscriptional regulation of multidrug resistance (MDR)-related genes. Among various HuR-regulated oncogenic transcripts, the activation of galectin-3/ß-catenin survival pathway is critical to induce transcription of cyclin D1, P-glycoprotein (P-gp) and/or multidrug resistance-associated proteins (MRPs). In this study, we aim to elucidate the HuR-regulating pathways related to epirubicin-mediated resistance in human colorectal carcinoma cells. The effects and mechanisms of epirubicin treatment on the expressions of upstream survival signals (e.g., ß-catenin) and downstream MDR transporters (e.g., P-gp) and anti-apoptotic pathways (e.g., Bcl-2) were assessed with or without HuR knockdown (siHuR) or overexpression (overHuR; ectopic HuR or pcDNA3/HA-HuR). Our results showed that siHuR decreased transcriptional expressions of galectin-3, ß-catenin, cyclin D1, Bcl-2, P-gp, MRP1, and MRP2 in epirubicin-treated colon cancer cells. Consistently, the co-treatment of epirubicin and siHuR diminished the expressions of galectin-3, ß-catenin, c-Myc, P-gp and MRP1. HuR silencing enhanced the intracellular accumulation of epirubicin in colon cancer cells. On the other hand, overHuR abolished such effects. Furthermore, siHuR significantly intensified epirubicin-mediated apoptosis via increasing reactive oxygen species and thus promoted the cytotoxic effect of epirubicin. The combined treatments of siHuR and epirubicin significantly reduced the expression of Bcl-2, but increased the expression of Bax, as well as activity and expression levels of caspase-3 and -9. In contrast, overHuR abrogated these effects. Our findings provide insight into the mechanisms by which siHuR potentiated epirubicin-induced cytotoxicity via inhibiting galectin-3/ß-catenin signaling, suppressing MDR transporters and provoking apoptosis. To our best knowledge, this is an innovative investigation linking the post-transcriptional control by HuR silencing to survival signaling repression, efflux transporter reversal and apoptosis induction. Our study thus provides a powerful regimen for circumventing MDR in colon cancer cells.

Silencing of the RNA-binding protein HuR attenuates hyperalgesia and motor disability in experimental autoimmune encephalomyelitis.

Multiple sclerosis (MS) is an inflammatory demyelinating disease of the central nervous system associated with progressive neuronal loss and axonal degeneration. Neuronal lesions and dysfunction lead often to neuropathic pain, the most prevalent and difficult to treat pain syndrome observed in MS patients. Despite its widespread occurrence, the underlying neural mechanisms for MS pain are not fully understood. For a better clarification of the pathophysiology of MS-associated pain, we investigated the role of HuR, an RNA-binding protein that positively regulates the stability of many target mRNAs, including several cytokines. The influence of HuR in the generation of the hypernociceptive response in a mouse model of relapsing-remitting experimental autoimmune encephalomyelitis (RR-EAE), an experimental model of MS, was investigated. HuR silencing, obtained through the repeated intrathecal administration of an antisense oligonucleotide (aODN) anti-HuR, completely attenuated hindpaw mechanical allodynia and thermal hyperalgesia developed by RR-EAE mice. Anti-HuR aODN also reduced severity of motor deficits as reflected by a reduction of clinical EAE score and improvement of rotarod performance. RR-EAE mice showed demyelination in spinal cord sections that was significantly reduced by HuR silencing. Double-staining immunofluorescence studies showed a neuronal localization of HuR within dorsal horn spinal cord, consistent with a neuronal mechanism of action. Our findings suggest the involvement of HuR in the hypernociceptive behaviour of RR-EAE mice providing the first pharmacological assessment of an antiallodynic and antihyperalgesic effect of HuR silencing. These data may provide support for HuR modulation as a therapeutic perspective for the management of MS-related neuropathic pain.

Regulation of Postoperative Ileus by Lentivirus-Mediated HuR RNA Interference via the p38/MK2 Signaling Pathway.

OBJECTIVES: The objective of the present study is to explore the effect of lentivirus-mediated HuR interference on the development and progression of postoperative ileus and the role of HuR in the regulation of the p38/MAPK-activated protein kinase-2 (MK2) signaling pathway during postoperative ileus. METHODS: To establish a mouse model of lentiviral transduction, we first determined the optimum effective titer of lentiviral vectors for transduction of the murine small intestine via the abdominal cavity by using hematoxylin and eosin (HE) staining, immunohistochemistry, detection of GFP messenger RNA (mRNA) and protein, and Western blotting. To investigate the effect of HuR interference on gene expression during postoperative ileus, we established a mouse model of postoperative ileus and used RT-PCR to measure the expression of proinflammatory genes, ELISA to measure the expression of serum inflammatory cytokines, immunohistochemistry to evaluate inflammatory cell infiltration in the small intestine, HE staining of paraffin sections to examine the pathology of the small intestine, and Western blotting to measure HuR expression and identify its role in the regulation of the p38/MK2 inflammatory pathway. RESULTS: We successfully designed a mouse model of intraperitoneal transduction of HuR-RNAi lentivirus. When HuR gene expression was suppressed in a mouse model of postoperative ileus, the infiltration of inflammatory cells, the expression of proinflammatory genes, and the levels of serum inflammatory cytokines were significantly reduced. This reduction in inflammation correlated with reduced cytoplasmic localization of HuR and reduced activation of MK2. CONCLUSIONS: Within the p38/MK2 signal transduction pathway, HuR may increase the mRNA stability of various inflammatory cytokines, thereby promoting inflammation that causes postoperative ileus. Suppressing the expression of HuR in a postoperative ileus model can effectively suppress the postoperative ileus inflammatory reaction. HuR might serve as a candidate drug target for the prevention and mitigation of postoperative ileus.

The RNA binding protein HuR determines the differential translation of autism-associated FoxP subfamily members in the developing neocortex.

Forkhead-box domain (Fox) containing family members are known to play a role in neocorticogenesis and have also been associated with disorders on the autism spectrum. Here we show that a single RNA-binding protein, Hu antigen R (HuR), dictates translation specificity of bound mRNAs and is sufficient to define distinct Foxp-characterized subpopulations of neocortical projection neurons. Furthermore, distinct phosphorylation states of HuR differentially regulate translation of Foxp mRNAs in vitro. This demonstrates the importance of RNA binding proteins within the framework of the developing brain and further confirms the role of mRNA translation in autism pathogenesis.

Mesenchymal Stromal Cells Prevent Renal Fibrosis in a Rat Model of Unilateral Ureteral Obstruction by Suppressing the Renin-Angiotensin System via HuR.

We studied Mesenchymal Stromal Cells (MSC) effects in experimental Unilateral Ureteral Obstruction (UUO), a fibrogenic renal disease. Rats were divided in 5 groups: sham, UUO, MSC treated-UUO, ACEi treated-UUO, MSC+ACEi treated- UUO. Data were collected at 1, 7, 21 days. UUO induced monocyte renal infiltration, tubular cell apoptosis, tubular atrophy, interstitial fibrosis and overexpression of TGFß, Renin mRNA (RENmRNA), increase of Renin, Angiotensin II (AII) and aldosterone serum levels. Both lisinopril (ACEi) and MSC treatment prevented monocyte infiltration, reduced tubular cell apoptosis, renal fibrosis and TGFß expression. Combined therapy provided a further suppression of monocyte infiltration and tubular injury. Lisinopril alone caused a rebound activation of Renin-Angiotensin System (RAS), while MSC suppressed RENmRNA and Renin synthesis and induced a decrease of AII and aldosterone serum levels. Furthermore, in in-vitro and in-vivo experiments, MSC inhibit Human antigen R (HuR) trascription, an enhancer of RENmRNA stability by IL10 release. In conclusion, we demonstrate that in UUO MSC prevent fibrosis, by decreasing HuR-dependent RENmRNA stability. Our findings give a clue to understand the molecular mechanism through which MSC may prevent fibrosis in a wide and heterogeneous number of diseases that share RAS activation as common upstream pathogenic mechanism.

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

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

MicroRNA-519 enhances HL60 human acute myeloid leukemia cell line proliferation by reducing the expression level of RNA-binding protein human antigen R.

Previous studies have demonstrated that microRNAs (miRs) are involved in cell apoptosis. However, the role of miR-519 in acute myeloid leukemia (AML) has yet to be elucidated. The present study identified the effects of miR­519 on HL60 human acute myeloid leukemia cell growth and apoptosis. The expression levels of miR­519 were examined in AML cells, as well as AML tissue samples. Furthermore, cell viability and apoptosis were examined in HL60 cells transfected with miR­519 mimics, miR­519 inhibitors or a negative control. In addition, the effects of human antigen R (HuR) on cell apoptosis were investigated using specific small interfering RNA targeting HuR. The results demonstrated that the expression levels of miR­519 were significantly increased in the AML cells and the tissue samples, suggesting that miR­519 may contribute to abnormal HL60 cell proliferation. Upregulation of miR­519 expression decreased HL60 cell viability and induced cell apoptosis. Furthermore, knockdown of HuR reduced cell migration and enhanced cell apoptosis. The results of the present study indicate that miR­519 may contribute to HL60 cell apoptosis by regulating the expression of HuR.

Suppression of miR-199a maturation by HuR is crucial for hypoxia-induced glycolytic switch in hepatocellular carcinoma.

Glucose metabolic reprogramming is a hallmark of cancer. Cancer cells rapidly adjust their energy source from oxidative phosphorylation to glycolytic metabolism in order to efficiently proliferate in a hypoxic environment, but the mechanism underlying this switch is still incompletely understood. Here, we report that hypoxia potently induces the RNA-binding protein HuR to specifically bind primary miR-199a transcript to block miR-199a maturation in hepatocellular carcinoma (HCC) cells. We demonstrate that this hypoxia-suppressed miR-199a plays a decisive role in limiting glycolysis in HCC cells by targeting hexokinase-2 (Hk2) and pyruvate kinase-M2 (Pkm2). Furthermore, systemically delivered cholesterol-modified agomiR-199a inhibits [(18)F]-fluorodeoxyglucose uptake and attenuates tumor growth in HCC tumor-bearing mice. These data reveal a novel mechanism of reprogramming of cancer energy metabolism in which HuR suppresses miR-199a maturation to link hypoxia to the Warburg effect and suggest a promising therapeutic strategy that targets miR-199a to interrupt cancerous aerobic glycolysis.

Pro-inflammatory cytokines reduce human TAFI expression via tristetraprolin-mediated mRNA destabilisation and decreased binding of HuR.

Thrombin activatable fibrinolysis inhibitor (TAFI) is the zymogen form of a basic carboxypeptidase (TAFIa) with both anti-fibrinolytic and anti-inflammatory properties. The role of TAFI in inflammatory disease is multifaceted and involves modulation both of specific inflammatory mediators as well as of the behaviour of inflammatory cells. Moreover, as suggested by in vitro studies, inflammatory mediators are capable of regulating the expression of CPB2, the gene encoding TAFI. In this study we addressed the hypothesis that decreased TAFI levels observed in inflammation are due to post-transcriptional mechanisms. Treatment of human HepG2 cells with pro-inflammatory cytokines TNFα, IL-6 in combination with IL-1ß, or with bacterial lipopolysaccharide (LPS) decreased TAFI protein levels by approximately two-fold over 24 to 48 hours of treatment. Conversely, treatment of HepG2 cells with the anti-inflammatory cytokine IL-10 increased TAFI protein levels by two-fold at both time points. We found that the mechanistic basis for this modulation of TAFI levels involves binding of tristetraprolin (TTP) to the CPB2 3'-UTR, which mediates CPB2 mRNA destabilisation. In this report we also identified that HuR, another ARE-binding protein but one that stabilises transcripts, is capable of binding the CBP2 3'UTR. We found that pro-inflammatory mediators reduce the occupancy of HuR on the CPB2 3'-UTR and that the mutation of the TTP binding site in this context abolishes this effect, although TTP and HuR appear to contact discrete binding sites. Interestingly, all of the mediators tested appear to increase TAFI protein expression in THP-1 macrophages, likewise through effects on CPB2 mRNA stability.

miR-31 Reduces Cell Growth of Papillary Thyroid Carcinoma by RNA-Binding Protein HuR.

BACKGROUND: Increasing evidence suggests that microRNAs are widely involved in cancer progression and metastasis. However, the specific role of miR-31 in papillary thyroid carcinoma (PTC) is still largely unknown. METHODS: The level of miR-31 and HuR was detected in 30 pairedcancerous and noncancerous tissue samples using real time PCR. The impact of miR-31 on PTC cell viability and apoptosis was explored using MTT assay and flow cytometry, respectively. To explore the effect of miR-31 on HuR expression, luciferase reporter assay was used. RESULTS: In papillary thyroid carcinoma patients, miR-31 was significantly down regulated. Furthermore, down regulation of miR-31 increased the proliferation, migration, and invasion of ovarian carcinoma cells. Vice versa, over expression of miR-31 repressed cell invasion and viability. The luciferase reporter assay revealed that HuR was a target for miR-31. Further analysis defined that knockdown of HuR resulted in enhanced cell viability and decreased cell migration rate. CONCLUSIONS: Down regulation of miR-31 contributed to the malignant progression of papillary thyroid carcinoma cells by targeting HuR.