RNAi在研究EGF生理效应机制中的应用

目的RNA干扰(RNA interference,RNAi)是发生在mRNA水平上的一种基因沉寂现象,即在外源性双链RNA导入细胞后可以引起细胞内与其同源的mRNA特异性降解,使该基因在RNA水平上被关闭而导致其不表达,即转录后基因沉寂。小干扰RNA(small interferring RNA,siRNA)已经发展成为研究基因功能的有效工具,具有相当高的特异性;可以高效、特异地阻断体内同源基因的表达,促进同源mRNA降解。而表皮生长因子能诱导成纤维细胞的移动,促进EGF受体激活与推动力产生的分子链接,构成完整的信号传递链,从而使EGF信号完成传递,最终引发一系列的细胞生化反应。     

RNA干扰技术在哺乳动物中的应用

RNA干扰技术已被广泛应用于线虫、植物和果蝇的基因功能分析中.随着Dicer酶和siRNAs的发现,人们已经能够利用人工合成的siRNAs,或转染siRNAs的表达载体来诱发哺乳动物细胞特定基因的抑制以及将上述方法应用于整体实验中,证明整体哺乳动物也存在RNA干扰现象.     

Systemic Delivery of DNA or siRNA Mediated by Linear Polyethylenimine (L-PEI) Does Not Induce an Inflammatory Response

Purpose  The success of nucleic acid therapies depends upon delivery vehicle’s ability to selectively and efficiently deliver therapeutic nucleic acids to target organ with minimal toxicity. The cationic polymer polyethylenimine (PEI) has been widely used for nucleic acid delivery due to its versatility and efficiency. In particular, the last generation of linear PEI (L-PEI) is being more efficient in vivo than the first generation of branched PEI. This led to several clinical trials including phase II bladder cancer therapy and human immunodeficiency virus immunotherapy. When moving towards to the clinic, it is crucial to identify potential side-effects induced by the delivery vehicle. Materials and Methods  For this purpose we have analyzed the production of pro-inflammatory cytokines [tumor necrosis factor-α, interferon (IFN)-γ, interleukin (IL)-6, IL-12/IL-23, IFN-β and IL-1β] and hepatic enzyme levels (alanine aminotransferase, aspartate aminotransferase, lactate dehydrogenase and alkaline phosphatase) in the blood serum of mice after systemic injection of DNA or siRNAs delivered with L-PEI. Results  Our data show no major production of pro-inflammatory cytokines or hepatic enzymes after injection of DNA or oligonucleotides active for RNA interference (siRNAs or sticky siRNAs) complexed with L-PEI. Only a slight induction of IFN-γ was measured after DNA delivery, which is probably induced by the CpG mediated response. Conclusion  Taken together our data highlight that linear polyethylenimine is a delivery reagent of choice for nucleic acid therapeutics.

MEK1-ERKs signal cascade is required for the replication of Enterovirus 71 (EV71)

The role of the MEK1-ERK signaling cascade in the replication cycle of Enterovirus 71 (EV71), the primary cause of hand, foot and mouth disease (HFMD), has been analyzed. In vitro infection with EV71 induced a biphasic activation of ERK. The two phases of activation appeared to be triggered by different mechanisms, with the first phase being activated by the binding of viral particles to the membrane receptor of host cells and the second probably being in response to the production of new virus particles. Inhibition of ERK activation by U0126 was found to severely impair virus production. A similar reduction in EV71 replication was also observed when MEK1 expression was subject to knockdown using specific siRNAs. By contrast knockdown of MEK2 expression showed that it was dispensable for virus replication cycle, despite both MEK isoforms being activated and translocated to the nucleus equally well in response to virus infection. Overall, this study suggests distinct functions of the two isoforms of MEK in EV71 replication cycle, with an essential role for MEK1 in stimulating the ERK signaling cascade to promote virus replication. Taken together with our previous work on herpes simplex virus type 2 (HSV2) this study highlights MEK1 as a potential broad antiviral molecular target.     

Involvement of the cellular prion protein in the migration of brain microvascular endothelial cells

The conversion of cellular prion protein (PrP(C)) to its protease-resistant isoform is involved in the pathogenesis of prion disease. Although PrP(C) is a ubiquitous glycoprotein that is present in various cell types, the physiological role of PrP(C) remains obscure. The present study aimed to determine whether PrP(C) mediates migration of brain microvascular endothelial cells. Small interfering RNAs (siRNAs) targeting PrP(C) were transfected into a mouse brain microvascular endothelial cell line (bEND.3 cells). siPrP1, selected among three siRNAs, reduced mRNA and protein levels of PrP(C) in bEND.3 cells. Cellular migration was evaluated with a scratch-wound assay. siPrP1 suppressed migration without significantly affecting cellular proliferation. This study provides the first evidence that PrP(C) may be necessary for brain microvascular endothelial cells to migrate into damaged regions in the brain. This function of PrP(C) in the brain endothelium may be a mechanism by which the neurovascular unit recovers from an injury such as an ischemic insult.     

PEG grafting of polyethylenimine (PEI) exerts different effects on DNA transfection and siRNA-induced gene targeting efficacy

Background: Gene targeting by RNA interference (RNAi) is mediated through small interfering RNA (siRNA), which, as plasmid DNA molecules, can be delivered into cells by polyethylenimines (PEI). Grafting with poly(ethylene glycol) has been introduced previously to improve PEI biocompatibility; however, data on the effects of PEGylation have been somewhat contradictory and various PEI(-PEG) need to be evaluated independently for DNA transfection and siRNA gene targeting efficacies.

Aim: We directly compare plasmid DNA transfection and siRNA-mediated gene targeting efficacies, employing a larger set of polyethylenimine-graft-poly(ethylene glycol) (PEI-g-PEG; PEI(-PEG)) with different molecular weights and degrees of PEG substitution.

Method: We performed tissue culture-based bioassays on DNA transfection and siRNA-mediated targeting efficacies as well as on toxicity and cellular nucleic acid uptake, and, using sensitive assays based on radioactive labelling, physicochemically characterize the complexes regarding the degree of nucleic acid complexation and complex stabilities under various conditions.

Results: In contrast to the DNA transfection efficacy, siRNA-mediated gene targeting is much less dependent on the PEGylation of PEI or on the N/P (= PEI nitrogen/nucleic acid phosphate) ratio. A more detailed analysis reveals that, in order to define optimal N/P ratios for DNA transfection, complex toxicities and nucleic acid uptake are the most critical parameters. In contrast, at optimal N/P ratios, complex stabilities and complexation efficacies determine PEI(-PEG)/DNA transfection efficacies and the major differences between various PEI(-PEG) are observed. All these parameters are less critical for PEI(-PEG)/siRNA gene targeting efficacy. Thus, our data lead to the distinction between three PEI(-PEG) groups, which relies on the differences in transfection rather than gene targeting efficacies, and which is correlated with the molecular weights and degrees of PEG substitution.

Conclusion: In contrast to PEI(-PEG)/DNA complexes, a broader panel of PEI-PEG are capable of siRNA-mediated gene targeting. Thus, PEG grafting of PEI requires a separate evaluation of siRNA and DNA complexes, which expands the portfolio of available PEI(-PEG) for the preparation of non-toxic, biocompatible siRNA delivery reagents for the induction of RNAi.     

Downregulation of xIAP Expression by Small Interfering RNA Inhibits Cellular Viability and Increases Chemosensitivity to Methotrexate in Human Hepatoma Cell Line HepG2

Abstract

The aim of this study was to investigate whether downregulating the expression of xIAP by RNAi (RNA interference) technology can induce the apoptosis of HepG2 cells, inhibit cellular viability and increase chemosensitivity of cancer cells. HepG2 cells were transfected with U6 promoter plasmids coding for short interfering RNAs (siRNAs) targeting xIAP. RT-PCR and western blot analysis were used to assess the mRNA and protein levels of xIAP expression. The suppression efficiency of xIAP by RNAi was evaluated using the MTT assay for cellular viability and Annexin V-PI binding assay for apoptosis. These results showed that siRNAs reduced cellular viability and increased cellular apoptosis. Moreover, downregulation of xIAP expression enhanced the chemosensitivity of HepG2 cells to methotrexate. These results suggest that the downregulation of xIAP by RNAi could potentially be used as a therapeutic strategy for human hepatocellular carcinoma.