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/β-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., β-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, β-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/β-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.

Cytoplasmic overexpression of RNA-binding protein HuR is a marker of poor prognosis in meningioma, and HuR knockdown decreases meningioma cell growth and resistance to hypoxia

HuR regulates cytoplasmic mRNA stability and translatability, and the HuR expression level has been shown to correlate with poor disease outcome in several cancer types; however, the prognostic value and potential pro-oncogenic properties of HuR in meningioma remain unclear. Thus, in the present study, we analysed 85 meningioma tissue samples to establish the relationship between HuR expression, tumour cell proliferation, and/or patient survival. In addition, we examined the anti-proliferative effects of HuR knockdown in two meningioma cell lines (IOMM-Lee and Ben-Men-1) and conducted transcriptome-wide analyses (IOMM-Lee cells) to elucidate the molecular consequences of HuR knockdown. The results of the present study showed HuR cytoplasmic expression to correlate positively with tumour grade (p = 1.2 × 10^-8 ) and negatively with progression-free and overall survival (p = 0.01) time in human meningioma tissues. In vitro, siHuR-induced HuR knockdown was shown to reduce the growth of both Ben-Men-1 (p = 2 × 10^-8 ) and IOMM-Lee (p = 4 × 10^-9 ) cells. Transcriptome analyses revealed HuR knockdown in IOMM-Lee cells to deregulate the HIF1A signalling pathway (p = 1.5 × 10^-6 ) and to up-regulate the expression of genes essential for the assembly of the cytoplasmic mRNA processing body, global genome nucleotide-excision repair, poly(A)-specific ribonuclease activity, the positive regulation of apoptosis and of cell cycle arrest, and the negative regulation of RNA splicing [p(FDR) < 0.001]. Interestingly, HuR knockdown under hypoxic culture conditions further potentiated the effects of HuR knockdown on cell growth, apoptosis, and HIF1A expression. We thus conclude that cytoplasmic HuR expression is a marker of poor prognosis in meningioma and that HuR is a promising potential therapeutic target for use in tumours refractory to standard therapies. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Biomarkers of Osteosarcoma, Chondrosarcoma, and Ewing Sarcoma

Osteosarcoma is the most frequent malignant bone neoplasm, followed by chondrosarcoma and Ewing sarcoma. The diagnosis of bone neoplasms is generally made through histological evaluation of a biopsy. Clinical and radiological features are also important in aiding diagnosis and to complete the staging of bone cancer. In addition to these, there are several non-specific serological or specific molecular markers for bone neoplasms. In bone tumors, molecular markers increase the accuracy of the diagnosis and assist in subtyping bone tumors. Here, we review these markers and discuss their role in the diagnosis and prognosis of the three most frequent malignant bone neoplasms, namely osteosarcoma, chondrosarcoma, and Ewing sarcoma.

Repression of caspase-3 and RNA-binding protein HuR cleavage by cyclooxygenase-2 promotes drug resistance in oral squamous cell carcinoma

A well-studied RNA-binding protein Hu Antigen-R (HuR), controls post-transcriptional gene regulation and undergoes stress-activated caspase-3 dependent cleavage in cancer cells. The cleavage products of HuR are known to promote cell death however, the underlying molecular mechanisms facilitating caspase-3 activation and HuR cleavage remains unknown. Here, we show that HuR cleavage associated with active caspase-3 in oral cancer cells treated with ionizing radiation and chemotherapeutic drug, paclitaxel. We determined that oral cancer cells overexpressing cyclooxygenase-2 (COX-2) limited the cleavage of caspase-3 and HuR, which reduced the rate of cell death in paclitaxel resistant oral cancer cells. Specific inhibition of COX-2 by celecoxib, promoted apoptosis through activation of caspase-3 and cleavage of HuR in paclitaxel-resistant oral cancer cells, both in vitro and in vivo. In addition, oral cancer cells overexpressing cellular HuR increased the half-life of COX-2 mRNA, promoted COX-2 protein expression and exhibited enhanced tumor growth in vivo in comparison with cells expressing a cleavable form of HuR. Finally, our ribonucleoprotein immunoprecipitation and sequencing (RIP-seq) analyses of HuR in oral cancer cells treated with ionizing radiation (IR), determined that HuR cleavage product-1 (HuR-CP1) bound and promoted the expression of mRNAs encoding proteins involved in apoptosis. Our results indicated that, cellular non-cleavable HuR controls COX-2 mRNA expression and enzymatic activity. In addition, overexpressed COX-2 protein repressed the cleavage of caspase-3 and HuR to promote drug resistance and tumor growth. Altogether, our observations support the use of the COX-2 inhibitor celecoxib, in combination with paclitaxel, for the management of paclitaxel resistant oral cancer cells.

Structure-function based molecular relationships in Ewing's sarcoma

Ewing's Sarcoma Oncogene (ews) on chromosome 22q12 is encoding a ubiquitously expressed RNA-binding protein (EWS) with unknown function that is target of tumor-specific chromosomal translocations in Ewing's sarcoma family of tumors. A model of transcription complex was proposed in which the heterodimer Rpb4/7 binds to EAD, connecting it to Core RNA Pol II. The DNA-binding domain, provided by EFP, is bound to the promoter. Rpb4/7 binds RNA, stabilizing the transcription complex. The complex Rpb4/7 can stabilize the preinitiation complexes by converting the conformation of RNA Pol II. EWS may change its conformation, so that NTD becomes accessible. Two different mechanisms of interaction between EWS and RNA Pol II are proposed: (I) an intermolecular EWS-EWS interaction between two molecules, pushing conformation from “closed” to “open” state, or (II) an intramolecular interaction inside the molecule of EWS, pushing conformation of the molecule from “closed” to “open” state. The modified forms of EWS may interact with Pol II subunits hsRpb5 and hsRpb7. The EWS and EFPs binding partners are described schematically in a model, an attempt to link the transcription with the splicing. The proposed model helps to understand the functional molecular interactions in cancer, to find new partners and ways to treat cancer.

Expression of HuR and Cyclooxygenase-2 in Nodular Fasciitis and Low-Grade Sarcoma: An Immunohistochemical Study

BACKGROUND

Nodular fasciitis is the most common reactive mesenchymal lesion to be misidentified as a type of sarcoma. HuR is an mRNA-binding protein that can stabilize cyclooxygenase-2 (COX-2) mRNA leading to COX-2 overexpression. The aim of this study is a comparison of the expressions of COX-2 and HuR and the relationships between their expressions and the clinicopathological parameters in nodular fasciitis and low-grade sarcoma.

METHODS

We measured the expression of HuR and COX-2 in 21 cases of nodular fasciitis and 37 cases of low-grade sarcoma using immunohistochemistry.

RESULTS

The frequency of cytoplasmic immunoreactivity for HuR was 5 of 21 cases of nodular fasciitis (23.8%) and 23 of 37 cases of low-grade sarcoma (62.1%) (p=.013). COX-2 expression was moderate or strong in nodular fasciitis (12/21, 57.1%) and in low-grade sarcoma (29/37, 78.4%) (p=.034). In addition, a significant difference existed between these two entities in terms of the relationship between moderate or strong COX-2 expression and HuR cytoplasmic immunoreactivity (p=.009). Moderate or strong COX-2 immunoreactivity correlated with nuclear (p=.016) or cytoplasmic HuR (p=.024) expression in low-grade sarcoma but not in nodular fasciitis.

CONCLUSIONS

This study suggests that HuR and COX-2 expression may be useful to differentiate nodular fasciitis from low-grade sarcoma.

MicroRNA-519a demonstrates significant tumour suppressive activity in laryngeal squamous cells by targeting anti-carcinoma HuR gene

Objective:

This study investigated the expression and functional effects, and related molecular mechanisms, of microRNA-519a in laryngeal squamous cell carcinoma.

Methods:

MicroRNA-519a and HuR messenger RNA in laryngeal squamous cell carcinoma were measured using reverse transcription polymerase chain reaction. MicroRNA-519a effects on the growth of human epithelial type 2 cells were tested using an MTT assay. The influence of microRNA-519a on the expression levels of HuR and other related genes in protein was tested by Western blotting. Cell cycle analyses were performed using flow cytometry. Associations between expression levels and patients' clinical parameters were analysed with Pearson correlation analysis.

Results:

Expression of microRNA-519a in laryngeal squamous cell carcinoma tissues was significantly lower than in adjacent non-cancerous tissues. The expression of microRNA-519a was negatively associated with histological differentiation, tumour–node–metastasis stage, lymphatic metastasis and disease-free survival time. After increasing the level of microRNA-519a in laryngeal squamous cell carcinoma human epithelial type 2 cells, cell growth was inhibited and cell cycle was arrested in the G2/M phase. MicroRNA-519a down-regulated HuR gene expression in protein levels without affecting messenger RNA levels.

Conclusion:

MicroRNA-519a may function as a tumour suppressor by inhibiting HuR expression, and may serve as a therapeutic target for laryngeal squamous cell carcinoma.

Inhibitory effect of HuR gene small interfering RNA segment on laryngeal carcinoma Hep-2 cell growth

OBJECTIVES

To investigate the effect of the HuR gene on laryngeal carcinoma Hep-2 cell growth, and to analyse correlations between the HuR, cyclooxygenase-2 and survivin genes.

STUDY DESIGN

Experiment study.

SETTING

Department of Otolaryngology-Head and Neck Surgery, Lihuili Hospital of Ningbo University, Ningbo, a tertiary care centre in China.

METHODS

Copies of a small interfering RNA segment directed against the HuR gene were transfected into Hep-2 cells using Lipofectamine™ 2000. The effect of the small interfering RNA segment on Hep-2 cell proliferation was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Changes in the expression of the HuR, cyclooxygenase-2 and survivin genes were detected by semi-quantitative reverse transcription polymerase chain reaction analysis. Concentrations of the HuR, cyclooxygenase-2 and survivin proteins were evaluated using Western blotting.

RESULTS

Expression of the HuR, cyclooxygenase-2 and survivin genes, as indicated by messenger RNA and protein levels, was suppressed by the HuR gene small interfering RNA segment in a dose-dependent manner. The proliferation indices of all treated groups were significantly lower than those of control groups (p < 0.05).

CONCLUSIONS

Impairment of HuR gene expression, using interfering RNA technology, can significantly suppress Hep-2 cell proliferation and induce apoptosis. The HuR gene may be an effective target for gene therapy in patients with laryngeal carcinoma.