Cell-specific expression of artificial microRNAs targeting essential genes exhibit potent antitumor effect on hepatocellular carcinoma cells

Translational Regulation by eIFs and RNA Modifications in Cancer

Translation is a fundamental process in all living organisms that involves the decoding of genetic information in mRNA by ribosomes and translation factors. The dysregulation of mRNA translation is a common feature of tumorigenesis. Protein expression reflects the total outcome of multiple regulatory mechanisms that change the metabolism of mRNA pathways from synthesis to degradation. Accumulated evidence has clarified the role of an increasing amount of mRNA modifications at each phase of the pathway, resulting in translational output. Translation machinery is directly affected by mRNA modifications, influencing translation initiation, elongation, and termination or altering mRNA abundance and subcellular localization. In this review, we focus on the translation initiation factors associated with cancer as well as several important RNA modifications, for which we describe their association with cancer.

Artificial miRNAs as therapeutic tools: Challenges and opportunities

RNA interference (RNAi) technology has been used for almost two decades to study gene functions and in therapeutic approaches. It uses cellular machinery and small, designed RNAs in the form of synthetic small interfering RNAs (siRNAs) or vector-based short hairpin RNAs (shRNAs), and artificial miRNAs (amiRNAs) to inhibit a gene of interest. Artificial miRNAs, known also as miRNA mimics, shRNA-miRs, or pri-miRNA-like shRNAs have the most complex structures and undergo two-step processing in cells to form mature siRNAs, which are RNAi effectors. AmiRNAs are composed of a target-specific siRNA insert and scaffold based on a natural primary miRNA (pri-miRNA). siRNAs serve as a guide to search for complementary sequences in transcripts, whereas pri-miRNA scaffolds ensure proper processing and transport. The dynamics of siRNA maturation and siRNA levels in the cell resemble those of endogenous miRNAs; therefore amiRNAs are safer than other RNAi triggers. Delivered as viral vectors and expressed under tissue-specific polymerase II (Pol II) promoters, amiRNAs provide long-lasting silencing and expression in selected tissues. Therefore, amiRNAs are useful therapeutic tools for a broad spectrum of human diseases, including neurodegenerative diseases, cancers and viral infections. Recent reports on the role of sequence and structure in pri-miRNA processing may contribute to the improvement of the amiRNA tools. In addition, the success of a recently initiated clinical trial for Huntington's disease could pave the way for other amiRNA-based therapies, if proven effective and safe. This article is categorized under: RNA Processing > Processing of Small RNAs Regulatory RNAs/RNAi/Riboswitches > RNAi: Mechanisms of Action RNA in Disease and Development > RNA in Disease.

An ultrasonic nanobubble-mediated PNP/fludarabine suicide gene system: A new approach for the treatment of hepatocellular carcinoma

OBJECTIVE

The purpose of this study is to generate an ultrasonic nanobubble (NB)-mediated purine nucleoside phosphorylase (PNP)/fludarabine suicide gene system for the treatment of human hepatocellular carcinoma (HCC).

METHODS

NBs were prepared from a mixture the phospholipids 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphate (DPPA), perfluoropropane gas and other materials using the high shear dispersion method. NBs treated with ultrasound irradiation functioned as a gene-transfer system, and a self-constructed suicide gene expression plasmid, pcDNA3.1(+)/PNP, treated with fludarabine functioned as a therapeutic gene. This system was used to determine the cytotoxic effects of PNP/fludarabine on HepG2 cells and SMMC7721 cells.

RESULTS

1. NBs with a small diameter (208-416 nm) and at a high concentration and fine homogeneity were prepared under the optimal method. 2. The pcDNA3.1(+)/PNP plasmid was efficiently transfected into HCC cells using ultrasonic NBs. 3. At 0.75μg/ml fludarabine, PNP/fludarabine showed marked cytotoxic effects toward HepG2 and SMMC7721 cells. PNP/fludarabine achieved the same effect against both SMMC7721 and HepG2 cells but at a lower concentration of fludarabine for the latter. 4. Bystander effects: a 10-20% decrease in the cell survival rate was observed when only 5-10% of transfected cells were PNP positive.

CONCLUSIONS

NBs constitute a non-toxic, stable and effective gene-delivery platform. The PNP/fludarabine suicide gene system inhibited the growth of HCC cells, induced HCC cell apoptosis, and caused a notable bystander effect at a low fludarabine concentration. This study establishes an important new method for miniaturizing microbubbles and improving a new NB-mediated approach for gene therapy of HCC.

Effects of microRNA-26b on proliferation and invasion of glioma cells and related mechanisms

Neuroglioma is the most common primary malignant tumor in neurosurgery. Due to its short survival period and high patient mortality rate, neuroglioma is a major challenge in clinics. Elucidating the pathogenic mechanisms and associated molecular targets of neuroglioma can therefore benefit diagnosis and treatment of glioma. Previous studies have established the role of microRNA (miR)‑26b in various tumors, including breast cancer, lymphoma and glioma. Its function and mechanism in neuroglioma, however, remains to be elucidated. In the present study, in vitro cultured U87 glioma cells were randomly divided into miR‑26b mimic, miR‑26b inhibitor and respective control (NC) groups. MTT assay was performed to detect the effect of miR‑26b on cell proliferation, while a cell invasion assay detected its effects on cell invasion. Caspase‑3 activity was also quantified to test cell apoptosis, followed by reverse transcription-quantitative polymerase chain reaction and western blotting to detect the variation of Bcl‑2 expression under the effect of miR‑26b. miR‑26b mimics transfection upregulated its expression in U87 cells, which had significantly reduced Bcl‑2 mRNA and protein expression levels and higher casapse3 activity, and inhibited cell proliferation and invasion compared with the control group. The transfection of miR‑26b inhibitor, in contrast, facilitated U87 cell proliferation and invasion, inhibited caspase‑3 activity and elevated Bcl‑2 mRNA/protein expression. In conclusion, miR‑26 could facilitate apoptosis and inhibit proliferation/invasion of neuroglioma cells via downregulating Bcl‑2 expression and potentiating caspase-3 activity.

Eukaryotic translation initiation factors and cancer

Recent technological advancements have shown tremendous mechanistic accomplishments in our understanding of the mechanism of messenger RNA translation in eukaryotic cells. Eukaryotic messenger RNA translation is very complex process that includes four phases (initiation, elongation, termination, and ribosome recycling) and diverse mechanisms involving protein and non-protein molecules. Translation regulation is principally achieved during initiation step of translation, which is organized by multiple eukaryotic translation initiation factors. Eukaryotic translation initiation factor proteins help in stabilizing the formation of the functional ribosome around the start codon and provide regulatory mechanisms in translation initiation. Dysregulated messenger RNA translation is a common feature of tumorigenesis. Various oncogenic and tumor suppressive genes affect/are affected by the translation machinery, making the components of the translation apparatus promising therapeutic targets for the novel anticancer drug. This review provides details on the role of eukaryotic translation initiation factors in messenger RNA translation initiation, their contribution to onset and progression of tumor, and how dysregulated eukaryotic translation initiation factors can be used as a target to treat carcinogenesis.

MicroRNA-15b promotes proliferation and invasion of non‑small cell lung carcinoma cells by directly targeting TIMP2

MicroRNA-15b (miR-15b) plays an important role in tumor development and progression. miR-15b functions differently in various types of malignant tumors. However, the expression pattern and role of miR-15b in non-small cell lung cancer (NSCLC) have not been elucidated. In the present study, we investigated the effect of miR-15b on the occurrence and development of lung cancer and the underlying mechanism. Lung cancer cell lines A549 and LTEP-a-2 were transfected with miR-15b inhibitor or mimic, respectively. Real-time PCR revealed that the expression level of miR-15b was significantly higher in human NSCLC tissues and NSCLC cells, than that of normal tissues and cells, respectively (P<0.05). Moreover, the effect of miR-15b on A549 and LTEP-a-2 cell viability, cell cycle, migration and invasion was further evaluated. Experiments indicated that miR‑15b knockdown inhibited the viability, cell cycle, migration and invasion in A549 cells, while upregulation of miR-15b exhibited the opposite effect. Tissue inhibitor of metallopeptidases 2 (TIMP2) protein and mRNA levels were downregulated after miR-15b overexpression in A549 and LTEP-a-2 cells, respectively. The dual-luciferase reporter gene assay implied that TIMP2 is a direct target gene of miR-15b. Our results indicate that high expression of miR-15b is associated with NSCLC and suggest that miR-15b expression may be a novel biomarker for predicting clinical outcomes in NSCLC patients. The inhibition of miR-15b may even provide helpful therapeutic strategies for the treatment of NSCLC.

MiR-15b mediates liver cancer cells proliferation through targeting BCL-2

The incidence and mortality of liver cancer increased year by year. Our country presents high incidence of liver cancer. MicroRNAs have tissue sensitivity as tumor biomarkers that play a role by promoting tumor growth as oncogenes or inhibit malignant cell growth as tumor suppressor genes. Studies showed that miR-15b abnormal expression in the tumor and can be treated as one of the tumor molecular markers. However, miR-15b expression and role in the liver cancer cells have not been elucidated. This study intended to explore the mechanism of miR-15b effect on liver cancer occurrence and development. Liver cancer cell line HepG2 was transfected with miR-15b mimic or inhibitor. Real-time PCR was applied to detect miR-15b expression. MTT was used to test cell proliferation. Transwell assay was performed to determine cell invasive ability. Real-time PCR and Western blot were used to detect BCL2 expression. MiR-15b mimic transfection promoted miR-15b overexpression and inhibited HepG2 cell proliferation significantly (P < 0.05). MiR-15b overexpression downregulated BCL2 mRNA and protein expression obviously (P < 0.05). On the contrary, miR-15b inhibitor transfection markedly reduced miR-15b expression in liver cancer cells (P < 0.05), promoted tumor cell proliferation, and increased BCL2 mRNA and protein expression. MiR-15b expression changes did not affect cell invasion (P > 0.05). MiR-15b can inhibit HepG2 cell proliferation and down-regulate BCL2 mRNA and protein expression.