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

The regulatory roles of RNA-binding proteins in the tumour immune microenvironment of gastrointestinal malignancies

The crosstalk between the tumour immune microenvironment (TIME) and tumour cells promote immune evasion and resistance to immunotherapy in gastrointestinal (GI) tumours. Post-transcriptional regulation of genes is pivotal to GI tumours progression, and RNA-binding proteins (RBPs) serve as key regulators via their RNA-binding domains. RBPs may exhibit either anti-tumour or pro-tumour functions by influencing the TIME through the modulation of mRNAs and non-coding RNAs expression, as well as post-transcriptional modifications, primarily N6-methyladenosine (m6A). Aberrant regulation of RBPs, such as HuR and YBX1, typically enhances tumour immune escape and impacts prognosis of GI tumour patients. Further, while targeting RBPs offers a promising strategy for improving immunotherapy in GI cancers, the mechanisms by which RBPs regulate the TIME in these tumours remain poorly understood, and the therapeutic application is still in its early stages. This review summarizes current advances in exploring the roles of RBPs in regulating genes expression and their effect on the TIME of GI tumours, then providing theoretical insights for RBP-targeted cancer therapies.

Modulating versatile pathways using a cleavable PEG shell and EGFR-targeted nanoparticles to deliver CRISPR-Cas9 and docetaxel for triple-negative breast cancer inhibition

Human antigen R (HuR), an RNA-binding protein, is implicated in regulating mRNA stability and translation in cancer, especially in triple-negative breast cancer (TNBC), a highly aggressive form. CRISPR/Cas9-mediated HuR knockout (HuR CRISPR) presents a promising genetic therapeutic approach, but it encounters transfection limitations. Docetaxel (DTX), an effective cytotoxic agent against metastatic breast cancer (BC), faces challenges related to vehicle-associated adverse events in DTX formulations. Therefore, we designed multifunctional nanoparticles with pH-sensitive PEG derivatives and targeting peptides to enable efficient HuR CRISPR and DTX delivery to human TNBC MDA-MB-231 cells and tumor-bearing mice. Our findings indicated that these nanoparticles displayed pH-responsive cytotoxicity, precise EGFR targeting, efficient tumor penetration, successful endosomal escape, and accurate nuclear and cytoplasmic localization. They also demonstrated the ability to spare normal cells and prevent hemolysis. Our study concurrently modulated multiple pathways, including EGFR, Wnt/β-catenin, MDR, and EMT, through the regulation of EGFR/PI3K/AKT, HuR/galectin-3/GSK-3β/β-catenin, and P-gp/MRPs/BCRP, as well as YAP1/TGF-β/ZEB1/Slug/MMPs. The combined treatment arrested the cell cycle at the G2 phase and inhibited EMT, effectively impeding tumor progression. Tissue distribution, biochemical assays, and histological staining revealed the enhanced safety profile of pH-responsive PEG- and peptide-modified nanoformulations in TNBC mice. The DTX-embedded and peptide-modified nanoparticles mitigated the side effects of DTX, enhanced cytotoxicity in TNBC MDA-MB-231 cells, and exhibited remarkable antitumor efficacy and safety in TNBC-bearing mice with HuR CRISPR deletion. Collectively, the combination therapy of DTX and CRISPR/Cas9 offers an effective platform for delivering antineoplastic agents and gene-editing systems to combat tumor resistance and progression in TNBC.

Strategies to enhance the response of liver cancer to pharmacological treatments

In contrast to other types of cancers, there is no available efficient pharmacological treatment to improve the outcomes of patients suffering from major primary liver cancers, i.e., hepatocellular carcinoma and cholangiocarcinoma. This dismal situation is partly due to the existence in these tumors of many different and synergistic mechanisms of resistance, accounting for the lack of response of these patients, not only to classical chemotherapy but also to more modern pharmacological agents based on the inhibition of tyrosine kinase receptors (TKIs) and the stimulation of the immune response against the tumor using immune checkpoint inhibitors (ICIs). This review summarizes the efforts to develop strategies to overcome this severe limitation, including searching for novel drugs derived from synthetic, semisynthetic, or natural products with vectorial properties against therapeutic targets to increase drug uptake or reduce drug export from cancer cells. Besides, immunotherapy is a promising line of research that is already starting to be implemented in clinical practice. Although less successful than in other cancers, the foreseen future for this strategy in treating liver cancers is considerable. Similarly, the pharmacological inhibition of epigenetic targets is highly promising. Many novel "epidrugs," able to act on "writer," "reader," and "eraser" epigenetic players, are currently being evaluated in preclinical and clinical studies. Finally, gene therapy is a broad field of research in the fight against liver cancer chemoresistance, based on the impressive advances recently achieved in gene manipulation. In sum, although the present is still dismal, there is reason for hope in the non-too-distant future.

Targeting the "tumor microenvironment": RNA-binding proteins in the spotlight in colorectal cancer therapy

Colorectal cancer (CRC) is the third most common cancer and has the second highest mortality rate among cancers. The development of CRC involves both genetic and epigenetic abnormalities, and recent research has focused on exploring the ex-transcriptome, particularly post-transcriptional modifications. RNA-binding proteins (RBPs) are emerging epigenetic regulators that play crucial roles in post-transcriptional events. Dysregulation of RBPs can result in aberrant expression of downstream target genes, thereby affecting the progression of colorectal tumors and the prognosis of patients. Recent studies have shown that RBPs can influence CRC pathogenesis and progression by regulating various components of the tumor microenvironment (TME). Although previous research on RBPs has primarily focused on their direct regulation of colorectal tumor development, their involvement in the remodeling of the TME has not been systematically reported. This review aims to highlight the significant role of RBPs in the intricate interactions within the CRC tumor microenvironment, including tumor immune microenvironment, inflammatory microenvironment, extracellular matrix, tumor vasculature, and CRC cancer stem cells. We also highlight several compounds under investigation for RBP-TME-based treatment of CRC, including small molecule inhibitors such as antisense oligonucleotides (ASOs), siRNAs, agonists, gene manipulation, and tumor vaccines. The insights gained from this review may lead to the development of RBP-based targeted novel therapeutic strategies aimed at modulating the TME, potentially inhibiting the progression and metastasis of CRC.

Utilizing non-coding RNA-mediated regulation of ATP binding cassette (ABC) transporters to overcome multidrug resistance to cancer chemotherapy

Multidrug resistance (MDR) is one of the primary factors that produces treatment failure in patients receiving cancer chemotherapy. MDR is a complex multifactorial phenomenon, characterized by a decrease or abrogation of the efficacy of a wide spectrum of anticancer drugs that are structurally and mechanistically distinct. The overexpression of the ATP-binding cassette (ABC) transporters, notably ABCG2 and ABCB1, are one of the primary mediators of MDR in cancer cells, which promotes the efflux of certain chemotherapeutic drugs from cancer cells, thereby decreasing or abolishing their therapeutic efficacy. A number of studies have suggested that non-coding RNAs (ncRNAs), particularly microRNAs (miRNAs), long non-coding RNAs (lncRNAs) and circular RNAs (circRNAs), play a pivotal role in mediating the upregulation of ABC transporters in certain MDR cancer cells. This review will provide updated information about the induction of ABC transporters due to the aberrant regulation of ncRNAs in cancer cells. We will also discuss the measurement and biological profile of circulating ncRNAs in various body fluids as potential biomarkers for predicting the response of cancer patients to chemotherapy. Sequence variations, such as alternative polyadenylation of mRNA and single nucleotide polymorphism (SNPs) at miRNA target sites, which may indicate the interaction of miRNA-mediated gene regulation with genetic variations to modulate the MDR phenotype, will be reviewed. Finally, we will highlight novel strategies that could be used to modulate ncRNAs and circumvent ABC transporter-mediated MDR.

RNA binding proteins in cancer chemotherapeutic drug resistance

Drug resistance has been a major obstacle in the quest for a cancer cure. Many chemotherapeutic treatments fail to overcome chemoresistance, resulting in tumor remission. The exact process that leads to drug resistance in many cancers has not been fully explored or understood. However, the discovery of RNA binding proteins (RBPs) has provided insight into various pathways and post-transcriptional gene modifications involved in drug tolerance. RBPs are evolutionarily conserved proteins, and their abnormal gene expression has been associated with cancer progression. Additionally, RBPs are aberrantly expressed in numerous neoplasms. RBPs have also been implicated in maintaining cancer stemness, epithelial-to-mesenchymal transition, and other processes. In this review, we aim to provide an overview of RBP-mediated mechanisms of drug resistance and their implications in cancer malignancy. We discuss in detail the role of major RBPs and their correlation with noncoding RNAs (ncRNAs) that are associated with the inhibition of chemosensitivity. Understanding and exploring the pathways of RBP-mediated chemoresistance will contribute to the development of improved cancer diagnosis and treatment strategies.

The multifaceted role of Fragile X-Related Protein 1 (FXR1) in cellular processes: an updated review on cancer and clinical applications

RNA-binding proteins (RBPs) modulate the expression level of several target RNAs (such as mRNAs) post-transcriptionally through interactions with unique binding sites in the 3'-untranslated region. There is mounting information that suggests RBP dysregulation plays a significant role in carcinogenesis. However, the function of FMR1 autosomal homolog 1(FXR1) in malignancies is just beginning to be unveiled. Due to the diversity of their RNA-binding domains and functional adaptability, FXR1 can regulate diverse transcript processing. Changes in FXR1 interaction with RNA networks have been linked to the emergence of cancer, although the theoretical framework defining these alterations in interaction is insufficient. Alteration in FXR1 expression or localization has been linked to the mRNAs of cancer suppressor genes, cancer-causing genes, and genes involved in genomic expression stability. In particular, FXR1-mediated gene regulation involves in several cellular phenomena related to cancer growth, metastasis, epithelial-mesenchymal transition, senescence, apoptosis, and angiogenesis. FXR1 dysregulation has been implicated in diverse cancer types, suggesting its diagnostic and therapeutic potential. However, the molecular mechanisms and biological effects of FXR1 regulation in cancer have yet to be understood. This review highlights the current knowledge of FXR1 expression and function in various cancer situations, emphasizing its functional variety and complexity. We further address the challenges and opportunities of targeting FXR1 for cancer diagnosis and treatment and propose future directions for FXR1 research in oncology. This work intends to provide an in-depth review of FXR1 as an emerging oncotarget with multiple roles and implications in cancer biology and therapy.

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

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

Targeting the RNA-Binding Protein HuR in Cancer

The RNA-binding protein human antigen R (HuR) is a well-established regulator of gene expression at the posttranscriptional level. Its dysregulation has been implicated in various human diseases, particularly cancer. In cancer, HuR is considered "active" when it shows increased subcellular localization in the cytoplasm, in addition to its normal nuclear localization. Cytoplasmic HuR plays a crucial role in stabilizing and enhancing the translation of prosurvival mRNAs that are involved in stress responses relevant to cancer progression, such as hypoxia, radiotherapy, and chemotherapy. In general, due to HuR's abundance and function in cancer cells compared with normal cells, it is an appealing target for oncology research. Exploiting the principles underlying HuR's role in tumorigenesis and resistance to stressors, targeting HuR has the potential for synergy with existing and novel oncologic therapies. This review aims to explore HuR's role in homeostasis and cancer pathophysiology, as well as current targeting strategies, which include silencing HuR expression, preventing its translocation and dimerization from the nucleus to the cytoplasm, and inhibiting mRNA binding. Furthermore, this review will discuss recent studies investigating the potential synergy between HuR inhibition and traditional chemotherapeutics.

Development of multi-drug resistance to anticancer drugs in HepG2 cells due to MRP2 upregulation on exposure to menthol

BACKGROUND

Menthol exerts relaxing, antibacterial, and anti-inflammatory activities, and is marketed as a functional food and therapeutic drug.

AIM

In the present study, the effects of menthol on the expression of multidrug resistance associated protein 2 (MRP2) and its association with the cytotoxicity of epirubicin (EPI) and cisplatin (CIS) were examined using HepG2 cells.

METHODS

The expression levels of target genes were examined by real-time PCR. The intracellular concentration of incorporated EPI was measured by high-performance liquid chromatography. Cell viability was evaluated by MTT analysis.

RESULTS

The expression of MRP2 mRNA was increased by exposing HepG2 cells to menthol for 24 hr. Consistent with a previous report suggesting an inverse correlation between MRP2 and Akt behavior, increased expression of MRP2 was also observed on suppression of the Akt function. Intracellular accumulation of EPI was significantly decreased by exposure of HepG2 cells to menthol, and a significant decrease in the intracellular concentration of EPI remaining was observed in HepG2 cells exposed to menthol. The decreased intracellular accumulation of EPI was significantly suppressed by treatment with MK-571, but not verapamil. Both EPI and CIS exerted cytocidal effects on HepG2 cells, but the decrease in cell viability was significantly attenuated by 24-hr menthol pre-exposure.

CONCLUSION

These results demonstrate that menthol causes hepatocellular carcinoma to acquire resistance to anticancer drugs such as EPI and CIS by MRP2 induction.

RBM38 Reverses Sorafenib Resistance in Hepatocellular Carcinoma Cells by Combining and Promoting lncRNA-GAS5

BACKGROUND

Hepatocellular carcinoma (HCC) is a life-threatening human malignancy and the fourth leading cause of cancer-related deaths worldwide. Patients with HCC are often diagnosed at an advanced stage with a poor prognosis. Sorafenib is a multikinase inhibitor used as the first-line treatment for patients with advanced HCC. However, acquired resistance to sorafenib in HCC leads to tumor aggression and limits the drug's survival benefits; the underlying molecular mechanisms for this resistance remain unclear.

METHODS

This study aimed to examine the role of the tumor suppressor RBM38 in HCC, and its potential to reverse sorafenib resistance. In addition, the molecular mechanisms underlying the binding of RBM38 and the lncRNA GAS5 were examined. The potential involvement of RBM38 in sorafenib resistance was examined using both in vitro and in vivo models. Functional assays were performed to assess whether RBM38: binds to and promotes the stability of the lncRNA GAS5; reverses the resistance of HCC to sorafenib in vitro; and suppresses the tumorigenicity of sorafenib-resistant HCC cells in vivo.

RESULTS

RBM38 expression was lower in HCC cells. The IC₅₀ value of sorafenib was significantly lower in cells with RBM38 overexpression than in control cells. RBM38 overexpression improved sorafenib sensitivity in ectopic transplanted tumors and suppressed the growth rate of tumor cells. RBM38 could bind to and stabilize GAS5 in sorafenib-resistant HCC cells. In addition, functional assays revealed that RBM38 reversed sorafenib resistance both in vivo and in vitro in a GAS5-dependent manner.

CONCLUSIONS

RBM38 is a novel therapeutic target that can reverse sorafenib resistance in HCC by combining and promoting the lncRNA GAS5.

Relationship between HuR and tumor drug resistance

Human resistance protein R (HuR), also known as embryonic lethal abnormal visual-like protein (ELAVL1), is an RNA-binding protein widely expressed in vivo that affects the mRNA stability of targeted and is involved in post-transcriptional regulation. Recent studies have shown that HuR is aberrantly expressed in different human cancers and is an essential factor in poor clinical prognosis. The role of HuR in numerous tumors suggests that it could be a new target for tumor therapy and as a marker for efficacy and prognostic assessment. This review focuses on the relationship between HuR and drug resistance in different tumors and briefly describes the structure, function, and inhibitors of HuR. We summarize the mechanisms by which HuR causes tumor resistance and the molecular targets affected.

iASPP suppression mediates terminal UPR and improves BRAF-inhibitor sensitivity of colon cancers

Unfolded protein response (UPR) signaling is activated under endoplasmic reticulum (ER) stress, an emerging cancer hallmark, leading to either adaptive survival or cell death, while the mechanisms underlying adaptation-death switch remain poorly understood. Here, we examined whether oncogene iASPP regulates the switch and how the mechanisms can be used in colon cancer treatment. iASPP is downregulated when cells undergo transition from adaptation to death during therapy-induced ER stress. Blocking iASPP's downregulation attenuates stress-induced cell death. Mechanistically, Hu-antigen R (HuR)-mediated stabilization of iASPP mRNA and subsequent iASPP protein production is significantly impaired with prolonged ER stress, which facilitates the degradation of GRP78, a key regulator of the UPR, in the cytosol. Because iASPP competes with GRP78 in binding the ER-resident E3 ligase RNF185, and tips the balance in favor of cell death. Positive correlation between the levels of HuR, iASPP, and GRP78 are detectable in colon cancer tissues in vivo. Genetic inhibition of iASPP/GRP78 or chemical inhibition of HuR not only inhibits tumor growth, but also sensitizes colon cancer cells' responses to BRAF inhibitor-induced ER stress and cell death. This study provides mechanistic insights into the switch between adaptation and death during ER stress, and also identifies a potential strategy to improve BRAF-inhibitor efficiency in colon cancers.

Effective prediction of potential ferroptosis critical genes in clinical colorectal cancer

Background

Colon cancer is common worldwide, with high morbidity and poor prognosis. Ferroptosis is a novel form of cell death driven by the accumulation of iron-dependent lipid peroxides, which differs from other programmed cell death mechanisms. Programmed cell death is a cancer hallmark, and ferroptosis is known to participate in various cancers, including colon cancer. Novel ferroptosis markers and targeted colon cancer therapies are urgently needed. To this end, we performed a preliminary exploration of ferroptosis-related genes in colon cancer to enable new treatment strategies.

Methods

Ferroptosis-related genes in colon cancer were obtained by data mining and screening for differentially expressed genes (DEGs) using bioinformatics analysis tools. We normalized the data across four independent datasets and a ferroptosis-specific database. Identified genes were validated by immunohistochemical analysis of pathological and healthy clinical samples.

Results

We identified DEGs in colon cancer that are involved in ferroptosis. Among these, five core genes were found: ELAVL1, GPX2, EPAS1, SLC7A5, and HMGB1. Bioinformatics analyses revealed that the expression of all five genes, except for EPAS1, was higher in tumor tissues than in healthy tissues.

Conclusions

The preliminary exploration of the five core genes revealed that they are differentially expressed in colon cancer, playing an essential role in ferroptosis. This study provides a foundation for subsequent research on ferroptosis in colon cancer.

HuR affects chemoresistance of small cell lung cancer by regulating FGFRL1 expression

Human antigen R (HuR), an RNA-binding protein, has been demonstrated to serve an oncogenic role in various types of cancer. Fibroblast growth factor receptor-like 1 (FGFRL1) has been shown to regulate small cell lung cancer (SCLC) chemoresistance. In the present study, the role of HuR in chemoresistance of SCLC, as well as its possible molecular mechanism involving FGFRL1, was explored by reverse transcription-quantitative PCR, western blotting, Cell Counting Kit-8 assay, flow cytometry and RNA immunoprecipitation. The results revealed that HuR expression levels were markedly upregulated in drug-resistant SCLC cell lines (H69AR and H446DDP) compared with in the parental cell lines (H69 and H446). Knockdown of HuR in drug-resistant SCLC cells enhanced drug sensitivity, cell apoptosis and cell cycle arrest. Furthermore, molecular mechanism studies indicated that HuR could bind and regulate FGFRL1 expression levels to increase FGFRL1 mRNA stability. Taken together, the present study suggested that HuR may mediate chemoresistance of SCLC by regulating FGFRL1 expression. HuR may represent a prognostic predictor and a potential target for overcoming chemoresistance in SCLC.

Circ_0014130 is involved in the drug sensitivity of colorectal cancer through miR-197-3p/PFKFB3 axis

BACKGROUND AND AIM

Colorectal cancer (CRC) is one of the most deadly cancers in the world, with few treatments and a poor prognosis. In recent years, many circular RNAs have been studied in CRC, but the role of circ_0014130 in CRC has not been investigated. Therefore, this research is designed to investigate the impact of circ_0014130 on the resistance of 5-fluorouracil (5-FU) in CRC.

METHODS

Quantitative real-time polymerase chain reaction was conducted to assess the expression of circ_0014130, microRNA-197-3p (miR-197-3p), and 6-phosphofructo-2-kinase/fructose-2, 6-bisphosphatase 3 (PFKFB3). The expression of PFKFB3 protein was detected by Western blot. The effect of cric_0014130 on drug resistance in CRC was verified by Cell Counting Kit-8 assay, clone formation assay, Transwell, and flow cytometry. The effect of circ_0014130 on tumor growth was evaluated by xenograft tumor model in vivo.

RESULTS

Circ_0014130 and PFKFB3 were increased, while miR-197-3p was reversed in CRC tissues and cells. Knocking down circ_0014130 can promote cell apoptosis, inhibit the proliferation of CRC cells, and reduced the IC50 of 5-FU. In addition, miR-197-3p inhibitors reversed the effect of si-circ_0014130 on CRC cells. Similarly, overexpression of PFKFB3 can regulate CRC cell behavior and 5-FU resistance caused by miR-197-3p. Finally, decrease of circ_0014130 was demonstrated to enhance the resistance of 5-FU in CRC tissues in vivo.

CONCLUSION

Circ_0014130 modulates 5-FU resistance in CRC by modulating the miR-197-3p/PFKFB3 axis, which is helpful for drug chemotherapy in CRC.

Molecular mechanism of miR-34b-5p and RNA binding protein HuR binding to lncRNA OIP5-AS1 in colon cancer cells

Colon cancer (CC) is a leading cause of cancer-related death. Long non-coding RNA OIP5-AS1 (lncRNA OIP5-AS1) expression pattern has been studied in many cancers. We aimed to identify the mechanism of lncRNA OIP5-AS1 in CC development. OIP5-AS1 expression pattern in CC tissues and cells was detected and the relation between OIP5-AS1 level and CC prognosis was analyzed. The proliferation, migration and invasion of CC cells were detected after silencing or overexpression of OIP5-AS1. Tumor xenograft in nude mice was established to verify the effect of OIP5-AS1 in vivo. The interaction between HuR protein and OIP5-AS1 and the interaction of miR-34b-5p with HuR and OIP5-AS1 were measured. OIP5-AS1 was highly expressed in CC and associated with poor prognosis. Silencing OIP5-AS1 inhibited CC cell malignant behaviors and inhibited the growth rate and tumor weight. In the mechanism, HuR bound to OIP5-AS1 and stabilized OIP5-AS1 expression. Both miR-34-5p and HuR bind to OIP5 and oppositely affect its expression. miR-34b-5p inhibited the proliferation and invasion of CC cells by inhibiting OIP5-AS1 and PI3K/Akt pathway. miR-34b-5p inhibited CC growth by inhibiting OIP5-AS1. Collectively, miR-34b-5p targets HuR and miR-34b-5p binds to OIP5-AS1 with HuR, thus inhibiting OIP5-AS1 and PI3K/Akt pathway and CC progression.

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.

Gene-editing by CRISPR-Cas9 in combination with anthracycline therapy via tumor microenvironment-switchable, EGFR-targeted, and nucleus-directed nanoparticles for head and neck cancer suppression

Head and neck cancer (HNC) has a high incidence and a poor prognosis. Epirubicin, a topoisomerase inhibitor, is a potential anthracycline chemotherapeutic for HNC treatment. HuR (ELAVL1), an RNA-binding protein, plays a critical role in promoting tumor survival, invasion, and resistance. HuR knockout via CRISPR/Cas9 (HuR CRISPR) is a possible strategy for the simultaneous modulation of the various pathways of tumor progression. Multifunctional nanoparticles modified with pH-sensitive epidermal growth factor receptor (EGFR)-targeting and nucleus-directed peptides were designed for the efficient delivery of HuR CRISPR and epirubicin to human tongue squamous carcinoma SAS cells and SAS tumor-bearing mice. The pH-sensitive nanoparticles responded to the acidic pH value as a switch to expose the targeting peptides. The cellular uptake and transfection efficiency of these nanoparticles in SAS cells increased via EGFR targeting, ligand-mediated endocytosis, and endosomal escape. These nanoparticles showed low cytotoxicity towards normal oral keratinocyte NOK cells. CRISPR/Cas9 was transported into the nucleus via the nuclear directing peptide and successfully knocked out HuR to suppress proliferation, metastasis, and resistance in SAS cells. The multiple inhibition of EGFR/β-catenin/epithelial-mesenchymal transition pathways was mediated through modulating the EGFR/PI3K/mTOR/AKT axis. The co-treatment of epirubicin and HuR CRISPR in SAS cells further facilitated apoptosis/necroptosis/autophagy and caused cancer cell death. In combination with HuR CRISPR nanoparticles, the efficacy and safety of epirubicin nanoparticles against cancer in SAS tumor-bearing mice improved significantly. Collectively, these nanoparticles showed a tumor pH response, active EGFR targeting, and nuclear localization and thus offered a combinatorial spatiotemporal platform for chemotherapy and the CRISPR/Cas gene-editing system.

Ursolic acid reduces Adriamycin resistance of human ovarian cancer cells through promoting the HuR translocation from cytoplasm to nucleus

Ursolic acid (UA) has been shown to suppress various tumor progression, however, its roles in Adriamycin resistance of human ovarian cancer (OC) cells are still unclear. This work aims to investigate the effects of UA on the Adriamycin resistance of human OC cells. Here, we constructed Adriamycin-resistant OC SKOV3-Adr cells and found that UA attenuated Adriamycin resistance in SKOV3-Adr cells. Additionally, UA enhanced Adriamycin sensitivity in the parental SKOV3 and another OC cell line A2780 cells. Mechanistic studies showed that HuR mRNA level was similar between SKOV3 and SKOV3-Adr cells, but the cytoplasmic expression of HuR protein was increased in SKOV3-Adr cells compared with that in SKOV3 cells, and subsequently enhancing the mRNA stability of multidrug resistance gene 1 (MDR1). Moreover, UA had no effects on HuR expression, but promoted the cytoplasm-nucleus translocation of HuR protein, decreased MDR1 mRNA stability and thus reduced MDR1 expression. Furthermore, overexpression of MDR1 rescued the effects of UA on Adriamycin resistance and sensitivity. This work reveals a novel HuR/MDR1 axis responsible for UA-mediated attenuation on Adriamycin resistance in OC cells.

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.

LncRNA KCNQ1OT1 is a key factor in the reversal effect of curcumin on cisplatin resistance in the colorectal cancer cells

The development of cisplatin resistance is a common cause of cancer recurrence in colorectal cancer (CRC). Though many studies have reported the oncogenic function of long non-coding RNA (LncRNA) KCNQ1OT1 in multiple cancers, few studies explored its role in cisplatin resistance of CRC. Curcumin is a natural phenolic compound extracted from turmeric, which can effectively suppress cisplatin resistance in CRC. This study aims to expound the role of KCNQ1OT1 in cisplatin resistance in CRC cells and whether KCNQ1OT1 participates in the reversal effect of curcumin on cisplatin resistance in CRC. The interplay between KCNQ1OT1 and miR-497 was determined using RNA pull-down assay and dual-luciferase reporter gene assay. The combination of B-cell lymphoma 2 (Bcl-2) and miR-497 was confirmed using dual-luciferase reporter gene assay. Compared with CRC cell line HCT8, the cisplatin-resistant CRC cell line HCT8/DDP exhibited a higher expression level of KCNQ1OT1. Functionally, the silence of KCNQ1OT1 suppressed proliferation and boosted apoptosis in HCT8/DDP cells. Subsequently, we found that KCNQ1OT1 could act as a sponge of miR-497 and remove the suppressive effect of miR-497 on Bcl-2 expression. Curcumin treatment restrained proliferation and facilitated apoptosis in HCT8/DDP cells. While KCNQ1OT1 overexpression removed the effect of curcumin on HCT8/DDP cells via miR-497/ Bcl-2 axis. Finally, the in vivo experiments showed that the inhibitory effect of curcumin on the growth of cisplatin-resistant CRC cells was reserved by the ectopic expression of KCNQ1OT1. In conclusion, KCNQ1OT1 aggravated cisplatin resistance in CRC cells via the miR-497/Bcl-2 axis. Administration of curcumin could effectively downregulate KCNQ1OT1 expression, thus reversing cisplatin resistance in CRC cells.

The RNA-Binding Protein HuR in Digestive System Tumors

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

Long non-coding RNAs: Key regulators in oxaliplatin resistance of colorectal cancer

Colorectal cancer (CRC) is one of the most commonly diagnosed malignancies in the world with high relapse and mortality rates. Although oxaliplatin (OXA), a platinum-based anticancer drug, is widely used in CRC treatment, the resulting chemoresistance dramatically attenuates the drug efficacy and increases the failure rate of this therapy. Thus, the study on OXA-induced chemoresistance is extremely urgent. In recent years, emerging evidence has shown that lncRNAs play irreplaceable roles in drug resistance. However, we only have a limited knowledge of the lncRNAs that are closely related to oxaliplatin resistance in CRC. In present study, we identify and characterize these lncRNAs, including their functions, underlying mechanisms and possible applications.

PEG-coated nanoparticles detachable in acidic microenvironments for the tumor-directed delivery of chemo- and gene therapies for head and neck cancer

Background: Head and neck cancer (HNC) is a major cause of morbidity and mortality and has a poor treatment outcome. Irinotecan, a topoisomerase-I inhibitor, induces cell death by decreasing the religation of double-strand DNA. However, epithelial-mesenchymal transition (EMT), therapy resistance, and systemic toxicity caused by available antineoplastic agents hinder the efficacy and safety of HNC treatment. Chemotherapy combined with gene therapy shows potential application in circumventing therapy resistance and EMT. miR-200 exerts a remarkable suppressing effect on EMT-associated genes. Herein, liposomes and solid lipid nanoparticles (SLNs) modified with a pH-sensitive, self-destructive polyethylene glycol (PEG) shell and different peptides were designed as irinotecan and miR-200 nanovectors to enhance tumor-specific accumulation. These peptides included one ligand targeting the angiogenic tumor neovasculature, one mitochondrion-directed apoptosis-inducing peptide, and one cell-penetrating peptide (CPP) with high potency and selectivity toward cancer cells. Methods: Physicochemical characterization, cytotoxicity analysis, cellular uptake, regulation mechanisms, and in vivo studies on miR-200- and irinotecan-incorporated nanoparticles were performed to identify the potential antitumor efficacy and biosafety issues involved in HNC treatment and to elucidate the underlying signaling pathways. Results: We found that the cleavable PEG layer responded to low extracellular pH, and that the CPP and targeting peptides were exposed to improve the uptake and release of miR-200 and irinotecan into HNC human tongue squamous carcinoma (SAS) cells. The apoptosis of SAS cells treated with the combinatorial therapy was significantly induced by regulating various pathways, such as the Wnt/β-catenin, MDR, and EMT pathways. The therapeutic efficacy and safety of the proposed co-treatment outperformed the commercially available Onivyde and other formulations used in a SAS tumor-bearing mouse model in this study. Conclusion: Chemotherapy and gene therapy co-treatment involving pH-sensitive and targeting peptide-modified nanoparticles may be an innovative strategy for HNC treatment.

Understanding and targeting the disease-related RNA binding protein human antigen R (HuR)

Altered gene expression is a characteristic feature of many disease states such as tumorigenesis, and in most cancers, it facilitates cancer cell survival and adaptation. Alterations in global gene expression are strongly impacted by post-transcriptional gene regulation. The RNA binding protein (RBP) HuR (ELAVL1) is an established regulator of post-transcriptional gene regulation and is overexpressed in most human cancers. In many cancerous settings, HuR is not only overexpressed, but it is "overactive" as denoted by increased subcellular localization within the cytoplasm. This dysregulation of HuR expression and cytoplasmic localization allows HuR to stabilize and increase the translation of various prosurvival messenger RNA (mRNAs) involved in the pathogenesis of numerous cancers and various diseases. Based on almost 20 years of work, HuR is now recognized as a therapeutic target. Herein, we will review the role HuR plays in the pathophysiology of different diseases and ongoing therapeutic strategies to target HuR. We will focus on three ongoing-targeted strategies: (1) inhibiting HuR's translocation from the nucleus to the cytoplasm; (2) inhibiting the ability of HuR to bind target RNA; and (3) silencing HuR expression levels. In an oncologic setting, HuR has been demonstrated to be critical for a cancer cell's ability to survive a variety of cancer relevant stressors (including drugs and elements of the tumor microenvironment) and targeting this protein has been shown to sensitize cancer cells further to insult. We strongly believe that targeting HuR could be a powerful therapeutic target to treat different diseases, particularly cancer, in the near future. This article is categorized under: RNA in Disease and Development > RNA in Disease NRA Turnover and Surveillance > Regulation of RNA Stability Translation > Translation Regulation.

PFKFB3 Inhibition Attenuates Oxaliplatin-Induced Autophagy and Enhances Its Cytotoxicity in Colon Cancer Cells

6-Phosphofructo-2-kinase/fructose-2,6-bisphosphatase isoform 3 (PFKFB3), a glycolytic enzyme highly expressed in cancer cells, has been reported to participate in regulating metabolism, angiogenesis, and autophagy. Although anti-cancer drug oxaliplatin (Oxa) effectively inhibits cell proliferation and induces apoptosis, the growing resistance and side-effects make it urgent to improve the therapeutic strategy of Oxa. Although Oxa induces the autophagy process, the role of PFKFB3 in this process remains unknown. In addition, whether PFKFB3 affects the cytotoxicity of Oxa has not been investigated. Here, we show that Oxa-inhibited cell proliferation and migration concomitant with the induction of apoptosis and autophagy in SW480 cells. Both inhibition of autophagy by small molecule inhibitors and siRNA modification decreased the cell viability loss and apoptosis induced by Oxa. Utilizing quantitative PCR and immunoblotting, we observed that Oxa increased PFKFB3 expression in a time- and dose-dependent manner. Meanwhile, suppression of PFKFB3 attenuated both the basal and Oxa-induced autophagy, by monitoring the autophagic flux and phosphorylated-Ulk1, which play essential roles in autophagy initiation. Moreover, PFKFB3 inhibition further inhibited the cell proliferation/migration, and cell viability decreased by Oxa. Collectively, the presented data demonstrated that PFKFB3 inhibition attenuated Oxa-induced autophagy and enhanced its cytotoxicity in colorectal cancer cells.

Quantification and Localization of Protein-RNA Interactions in Patient-Derived Archival Tumor Tissue

Abnormal post-transcriptional regulation induced by alterations of mRNA-protein interactions is critical during tumorigenesis and cancer progression and is a hallmark of cancer cells. A more thorough understanding is needed to develop treatments and foresee outcomes. Cellular and mouse tumor models are insufficient for vigorous investigation as they lack consistency and translatability to humans. Moreover, to date, studies in human tumor tissue are predominately limited to expression analysis of proteins and mRNA, which do not necessarily provide information about the frequency of mRNA-protein interactions. Here, we demonstrate novel optimization of a method that is based on FISH and proximity ligation techniques to quantify mRNA interactions with RNA-binding proteins relevant for tumorigenesis and cancer progression in archival patient-derived tumor tissue. This method was validated for multiple mRNA-protein pairs in several cellular models and in multiple types of archival human tumor samples. Furthermore, this approach allowed high-throughput analysis of mRNA-protein interactions across a wide range of tumor types and stages through tumor microarrays. This method is quantitative, specific, and sensitive for detecting interactions and their localization at both the individual cell and whole-tissue scales with single interaction sensitivity. This work presents an important tool in investigating post-transcriptional regulation in cancer on a high-throughput scale, with great potential for translatability into any applications where mRNA-protein interactions are of interest. SIGNIFICANCE: This work presents an approach to sensitively, specifically, and quantitatively detect and localize native mRNA and protein interactions for analysis of abnormal post-transcriptional regulation in patient-derived archival tumor samples.

Post-transcriptional Regulation of Colorectal Cancer: A Focus on RNA-Binding Proteins

Colorectal cancer (CRC) is a major health problem with an estimated 1. 8 million new cases worldwide. To date, most CRC studies have focused on DNA-related aberrations, leaving post-transcriptional processes under-studied. However, post-transcriptional alterations have been shown to play a significant part in the maintenance of cancer features. RNA binding proteins (RBPs) are uprising as critical regulators of every cancer hallmark, yet little is known regarding the underlying mechanisms and key downstream oncogenic targets. Currently, more than a thousand RBPs have been discovered in humans and only a few have been implicated in the carcinogenic process and even much less in CRC. Identification of cancer-related RBPs is of great interest to better understand CRC biology and potentially unveil new targets for cancer therapy and prognostic biomarkers. In this work, we reviewed all RBPs which have a role in CRC, including their control by microRNAs, xenograft studies and their clinical implications.

Abemaciclib Is Effective Against Pancreatic Cancer Cells and Synergizes with HuR and YAP1 Inhibition

Mutation or promoter hypermethylation of CDKN2A is found in over 90% of pancreatic ductal adenocarcinomas (PDAC) and leads to loss of function of cell-cycle inhibitors p16 (INK4A) and p14 (ARF) resulting in unchecked proliferation. The CDK4/6 inhibitor, abemaciclib, has nanomolar IC₅₀s in PDAC cell lines and decreases growth through inhibition of phospho-Rb (pRb), G₁ cell-cycle arrest, apoptosis, and the senescent phenotype detected with β-galactosidase staining and relevant mRNA elevations. Daily abemaciclib treatments in mouse PDAC xenograft studies were safe and demonstrated a 3.2-fold decrease in tumor volume compared with no treatment (P < 0.0001) accompanying a decrease in both pRb and Ki67. We determined that inhibitors of HuR (ELAVL1), a prosurvival mRNA stability factor that regulates cyclin D1, and an inhibitor of Yes-Associated Protein 1 (YAP1), a pro-oncogenic, transcriptional coactivator important for CDK6 and cyclin D1, were both synergistic with abemaciclib. Accordingly, siRNA oligonucleotides targeted against HuR, YAP1, and their common target cyclin D1, validated the synergy studies. In addition, we have seen increased sensitivity to abemaciclib in a PDAC cell line that harbors a loss of the ELAVL1 gene via CRISP-Cas9 technology. As an in vitro model for resistance, we investigated the effects of long-term abemaciclib exposure. PDAC cells chronically cultured with abemaciclib displayed a reduction in cellular growth rates (GR) and coresistance to gemcitabine and 5-fluorouracil (5-FU), but not to HuR or YAP1 inhibitors as compared with no treatment controls. We believe that our data provide compelling preclinical evidence for an abemaciclib combination-based clinical trial in patients with PDAC. IMPLICATIONS: Our data suggest that abemaciclib may be therapeutically relevant for the treatment in PDAC, especially as part of a combination regimen inhibiting YAP1 or HuR.

The RNA-Binding Protein HuR Confers Oxaliplatin Resistance of Colorectal Cancer By Upregulating CDC6

Human antigen R (HuR) is an RNA-binding protein that posttranscriptionally regulates many cancer-trait genes. CDC6, a central regulator of DNA replication, is regulated by HuR. In this study, we investigated the role of HuR in colorectal cancer tumorigenesis and oxaliplatin (L-OHP) resistance, as well as the underlying mechanisms involving CDC6. We detected increased HuR and CDC6 expression, along with a positive correlation between the two in human colorectal cancer tissues. HuR overexpression increased colorectal cancer cell proliferation in vitro and xenograft tumor growth in vivo, and induced resistance to L-OHP. In contrast, HuR knockdown sensitized colorectal cancer cells to L-OHP. CDC6 overexpression increased while CDC6 knockdown decreased colorectal cancer cell malignant behaviors (growth, DNA synthesis, EMT, migration, and invasion) and L-OHP resistance in vitro Moreover, L-OHP resistance induced by HuR overexpression was reversed by CDC6 knockdown. Mechanistically, the results from our luciferase reporter and ribonucleoprotein immunoprecipitation assays indicated that HuR upregulates CDC6 by binding to CDC6 3'-UTR. Taken together, our findings identified HuR's regulation of CDC6 as an essential mechanism driving colorectal cancer tumorigenesis and L-OHP resistance, and this mechanism may represent a potential target for overcoming drug resistance in colorectal cancer.

AU-rich element-binding proteins in colorectal cancer

Trans-acting factors controlling mRNA fate are critical for the post-transcriptional regulation of inflammation-related genes, as well as for oncogene and tumor suppressor expression in human cancers. Among them, a group of RNA-binding proteins called “Adenylate-Uridylate-rich elements binding proteins” (AUBPs) control mRNA stability or translation through their binding to AU-rich elements enriched in the 3’UTRs of inflammation- and cancer-associated mRNA transcripts. AUBPs play a central role in the recruitment of target mRNAs into small cytoplasmic foci called Processing-bodies and stress granules (also known as P-body/SG). Alterations in the expression and activities of AUBPs and P-body/SG assembly have been observed to occur with colorectal cancer (CRC) progression, indicating the significant role AUBP-dependent post-transcriptional regulation plays in controlling gene expression during CRC tumorigenesis. Accordingly, these alterations contribute to the pathological expression of many early-response genes involved in prostaglandin biosynthesis and inflammation, along with key oncogenic pathways. In this review, we summarize the current role of these proteins in CRC development. CRC remains a major cause of cancer mortality worldwide and, therefore, targeting these AUBPs to restore efficient post-transcriptional regulation of gene expression may represent an appealing therapeutic strategy.

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.

Silencing long noncoding RNA PVT1 inhibits tumorigenesis and cisplatin resistance of colorectal cancer

Long noncoding RNA plasmacytoma variant translocation 1 (PVT1) plays pivotal roles in tumorigenesis of many cancers, including colorectal cancer (CRC). However, the clinical significance and the biological functions of PVT1 in CRC remain largely unknown. In this study, we found that PVT1 was highly expressed in CRC tissues and cell lines compared with the corresponding non-cancerous samples and normal colon epithelial cells. Clinically, increased expression of PVT1 was positively correlated with tumor size, advanced histological stages, metastases, poor prognosis, and cisplatin resistance of CRC patients. In vitro studies showed that PVT1 silencing inhibited the proliferation, migration, invasion, and apoptosis escape of CRC cells. Knockdown of PVT1 in cisplatin-resistant CRC cells induced proliferation inhibition and apoptosis, whereas overexpression of PVT1 increased proliferation and decreased apoptosis of CRC cells. Mechanically, the levels of drug resistance-associated molecules, including multidrug resistance 1 and multidrug resistance protein 1, as well as the expression of anti-apoptotic Bcl-2 were significantly downregulated whereas the levels of pro-apoptotic Bax and cleaved caspase-3 were increased in PVT1-silenced cisplatin-resistant CRC cells. However, ectopic expression of PVT1 in CRC cells reversed the expressions of the molecules mentioned above. In addition, PVT1 overexpression in CRC cells significantly promoted cisplatin resistance in vivo. Collectively, these results demonstrated that PVT1 is a significant regulator in tumorigenesis and cisplatin resistance of CRC and provided evidence that PVT1 may be a promising target for CRC therapy.