Initiation of Apaf-1 translation by internal ribosome entry

The apoptotic protease activating factor (Apaf-1) plays a central role in apoptosis: interaction of this protein with procaspase-9 leads to cleavage and activation of this initiator caspase. In common with other mRNAs whose protein products have a major regulatory function, the 5' untranslated region (UTR) of Apaf-1 is long, G-C rich and has the potential to form secondary structure. We have shown that the 5' UTR of Apaf-1 contains an internal ribosome entry segment, located in a 233 nucleotide region towards the 3' end of the leader, and that the translation initiation of this mRNA occurs only by internal ribosome entry. The Apaf-1 IRES is active in almost all human cell types tested, including Human cervical carcinoma (HeLa), Human liver carcinoma (HepG2), Human breast carcinoma (MCF7), Human embryonic kidney (HK293), African Green Monkey kidney (COS7) and Human lung (MRC5). The Apaf-1 IRES initiates translation as efficiently as the HRV IRES, but is less active than the c-myc IRES. We propose that the Apaf-1 IRES ensures that a constant cellular level of Apaf-1 protein is maintained even under conditions where cap-dependent translation is compromised. Oncogene (2000) 19, 899 - 905.     

The chicken c-Jun 5' untranslated region directs translation by internal initiation

The 5' untranslated region (UTR) of the chicken c-jun message is exceptionally GC rich and has the potential to form a complex and extremely stable secondary structure. Because stable RNA secondary structures can serve as obstacles to scanning ribosomes, their presence suggests inefficient translation or initiation through alternate mechanisms. We have examined the role of the c-jun 5' UTR with respect to its ability to influence translation both in vitro and in vivo. We find, using rabbit reticulocyte lysates, that the presence of the c-jun 5' UTR severely inhibits translation of both homologous and heterologous genes in vitro. Furthermore, translational inhibition correlates with the degree of secondary structure exhibited by the 5' UTR. Thus, in the rabbit reticulocyte lysate system, the c-jun 5' UTR likely impedes ribosome scanning resulting in inefficient translation. In contrast to our results in vitro, the c-jun 5' UTR does not inhibit translation in a variety of different cell lines suggesting that it may direct an alternate mechanism of translational initiation in vivo. To distinguish among the alternate mechanisms, we generated a series of bicistronic expression plasmids. Our results demonstrate that the downstream cistron, in the bicistronic gene, is expressed to a much higher level when directly preceded by the c-jun 5' UTR. In addition, inhibition of ribosome scanning on the bicistronic message, through insertion of a synthetic stable hairpin, inhibits translation of the first cistron but does not inhibit translation of the cistron downstream of the c-jun 5' UTR. These results are consistent with a model by which the c-jun message is translated through cap independent internal initiation. Oncogene (2000) 19, 2836 - 2845     

替莫唑胺通过调控miR-216a/PRKCA抑制胶质瘤细胞U251增殖和侵袭作用的研究

目的:探讨替莫唑胺抑制胶质瘤细胞U251增殖和侵袭的作用,推测其作用机制是通过微小RNA-216a（microRNA-216a,miR-216a）/蛋白激酶Cα(protein kinase C-alpha,PRKCA)进行调控。方法:体外培养胶质瘤细胞U251,用不同剂量替莫唑胺染毒48 h后,构建野生型PRKCA 3' UTR-荧光素酶报告载体及检测荧光素酶活性,检测替莫唑胺对胶质瘤细胞U251增殖和侵袭的影响及miR-216a和PRKCA表达的影响。结果:miR-216a mimics使野生型PRKCA 3' UTR-荧光素酶报告载体的活性下降了47.52%,差异具有统计学意义（P＜0.05）;miR-216a mimics使突变型PRKCA 3' UTR-荧光素酶报告载体的活性下降不显著,差异无统计学意义（P＞0.05）。与空白对照组比较,低、中、高剂量组胶质瘤细胞U251增殖率、侵袭细胞数、PRKCA mRNA相对表达量和PRKCA蛋白表达量均降低,miR-216a mRNA相对表达量均增高,差异具有统计学意义（P＜0.05）;随着替莫唑胺剂量的增加,胶质瘤细胞U251增殖率、侵袭细胞数、PRKCA mRNA相对表达量和PRKCA蛋白表达量随之降低,miR-216a mRNA相对表达量随之增高,差异具有统计学意义（P＜0.05）。结论:替莫唑胺可以通过促进miR-216a的表达而抑制PRKCA的表达,降低胶质瘤细胞U251增殖和侵袭。     

A high-efficiency translational control element with potential for cancer gene therapy

An active internal ribosome entry sequence (IRES) that efficiently mediates cap (m7pppGN)-independent translation in human carcinoma cells could be an effective device for gene co-transduction in cancer gene therapy. In this study using the cytomegalovirus (CMV) promoter, a remarkable internal translation activity was observed and mediated by the sequence localized to the 183-653 region of 5' NF-kappaB repressor mRNA (NFR183IRES). To test the potential of such sequence for therapeutic application, we carried out in vitro functional assays using the dicistronic constructs that internally expressed human PTEN tumor suppressor. The PTEN expression mediated by NFR183IRES was found to result in growth inhibition of carcinoma cells more effectively than the expression by NFR1IRES that contained the 1-653 region. When compared to the internal translation driven by the picornaviral IRES element of the encephalomyocarditis virus (EMCV) or the foot-and-mouth disease virus (FMDV), NFR183IRES consistently exhibited a higher activity in the human carcinoma cells, HeLa, LNCaP and MCF7. Such high-efficiency translational control element may prove useful for cancer gene therapy.     

N-myc translation is initiated via an internal ribosome entry segment that displays enhanced activity in neuronal cells.

Eukaryotic translation can be initiated either by a cap-dependent mechanism or by internal ribosome entry, a process by which ribosomes are directly recruited to structured regions of mRNA upstream of the initiation codon. We analysed the 5' untranslated region (UTR) of the proto-oncogene N-myc, and demonstrated by transfections in a dicistronic vector system that it contains a potent internal ribosome entry segment (IRES). The IRES is similar in length to the c-myc IRES and the activities of these IRESs are comparable in non-neuronal cells. Transfections were also carried out in cell lines derived from neuroblastomas, in which N-myc is expressed, and in a neuronal precursor cell line. In these cells the N-myc IRES is up to seven times more active than that of c-myc, suggesting that neuronal-specific non-canonical trans-acting factors are used by the N-myc but not the c-myc IRES. N-myc expression is increased by gene amplification in many neuroblastomas, but this is the first example of a translational mechanism by which N-myc expression could be further increased. The discovery of an IRES that displays enhanced activity in neuronal cell lines has important potential as a tool for protein expression in neural tissue.     

miR-194通过靶定DNMT3A基因调控肝癌细胞的生长

目的:探讨miR-194对肝癌细胞增殖和细胞周期的影响及其潜在的作用机制。方法:实时定量聚合酶链式反应检测肝癌细胞系HepG2和正常肝细胞系L-O2中miR-194的表达水平。构建miR-194过表达质粒,采用MTT法检测细胞增殖活力,流式细胞术检测细胞周期;双荧光素酶报告基因分析法预测和验证miR-194可能的靶基因。结果:实时定量PCR结果显示,miR-194在肝癌细胞中的表达明显低于肝脏正常细胞。在肝癌细胞中过表达miR-194抑制细胞生长。而流式细胞术检测发现细胞周期进程减慢,G1期比例增加,S期比例相应的减少。靶基因筛选得到DNMT3A为miR-194的候选靶基因。荧光报告载体实验证实,miR-194能够通过作用于靶基因3' 非翻译区的特定位点,对其表达在转录后进行负性调节。而在miR-194表达增加的肝癌细胞中,靶基因的mRNA表达水平和蛋白表达水平都有明显降低。在肝癌细胞HepG2中,敲除靶基因DNMT3A后,细胞的增殖能力减弱,相反,当把DNMT3A过表达后,细胞的增殖能力增强,可以挽救miR-194对细胞的表型影响。结论:miR-194可通过靶定DNMT3A基因抑制肝癌细胞的生长。     

利用报道基因检测鼻咽癌细胞的RNA干扰作用

背景与目的:RNA干扰(RNAinterference,RNAi)具有高效特异阻断基因表达的特点,在基因功能研究、信号转导通路的研究以及基因治疗中得到很广泛的应用。本实验通过体外转录合成siRNA和构建表达shRNA的质粒载体两种方法,检测鼻咽癌细胞系的RNAi作用,建立一个较完善的RNAi技术平台。方法:体外转录合成或通过pSUPER.retro构建表达针对GFP和荧光素酶的siRNAs或shRNAs,将它们和报道基因一起瞬时转染HeLa、CNE1、CNE2和5-8F细胞,用荧光显微镜和Westernblot检测GFP表达情况;用荧光素酶检测系统分析荧光素酶的活性。结果:3'末端带UU突出的siGFP2和psGFP能特异性地抑制细胞中GFP的表达,而单链反义RNA和3'末端不带UU突出的siGFP1无此作用。定量荧光素酶活性分析发现,siLuc能抑制HeLa、CNE1、CNE2和5-8F细胞中荧光素酶的表达,其抑制率分别达到91.43%,78.01%,90.30%和62.85%。HeLa细胞瞬时转染psLuc后,荧光素酶的表达抑制率可达到78.22%。结论:体外转录合成的siRNA和表达shRNA的质粒均能诱发RNAi效应。3'UU突出末端在siRNA诱发的RNAi中起作用。鼻咽癌细胞与HeLa细胞一样存在RNAi效应。     

Analysis of the activation of the myc family oncogene and of its stability over time in xenografted human lung carcinomas

In order to validate the use of the nude mouse as a model for studying lung cancers, 21 different lung cancers were xenografted onto nude mice and the tumoral DNA and RNA were analyzed for abnormality in the myc family genes (c-myc, L-myc, and N-myc). Six of 14 small cell lung cancers (SCLC) showed a 4-35-fold amplification for L-myc, 5 of 7 non-SCLC a 3-5-fold amplification for c-myc, and 1 of 14 SCLC an 80-fold amplification for N-myc. Of the 7 SCLC with amplified L- or N-myc oncogenes, 4 were of the small and large histological type, while only 5 of the 21 cases studied were of the small and large type. All xenografted tumors with amplification of one of the myc genes showed overexpression of the related mRNA. Overexpression without amplification of the myc genes was observed for 3 SCLC and 2 non-SCLC. These results indicate that the L-myc gene seems to be associated with the small and large phenotype in SCLC, whereas c-myc seems to be implicated in non-SCLC. Of the 21 lung cancers studied 14 were analyzed for myc family gene activation for serial passages into nude mice. No variation of DNA amplification was observed during long-term growth in nude mice for any of the myc oncogenes. Changes in the level of mRNA expression were observed only for c-myc; a beginning of expression in one SCLC and an increase in expression in one non-SCLC were noted in late passages when compared with early ones. The nude mouse is therefore a valuable model for the study of lung cancers "over a 4-year period at least."     

Synthesis and evaluation of fluoromycin: a novel fluorescence-labeled derivative of talisomycin S10b.

We have synthesized fluoromycin (FLM), a novel fluorescein-labeled derivative of talisomycin S10b (TLM S10b), and used it to evaluate cellular drug accumulation and distribution in bleomycin (BLM)-sensitive and -resistant cell lines. The fluorescence intensity of FLM was 300- to 400-fold greater than that of BLM A2, TLM S10b, or the lipophilic BLM analogue, liblomycin. FLM possessed an antiproliferative potency similar to liblomycin in BLM-sensitive human A-253 squamous carcinoma cells but was less potent than BLM A2 or TLM S10b. C-10E cells, a clone of A-253 cells with 40- to 50-fold resistance to BLM A2 and TLM S10b, were 50-fold resistant to FLM. A partially revertant cell population (C-10E ND) regained sensitivity to BLM A2, TLM S10b, and FLM. FLM like BLM cleaved pGEM-3Z plasmid DNA in vitro in a concentration-dependent manner. Flow cytometric analysis of FLM content in C-10E and C-10E ND cell lines showed 4-fold and 2-fold lower fluorescence intensity, respectively, compared with A-253 cells. Similar results were seen by fluorescence spectrophotometry with cell extracts. Fluorescence microscopy indicated heterogeneous distribution among A-253 cells with at least 50% of the cells exhibiting marked nuclear fluorescence localization. In contrast, C-10E cells displayed lower cellular fluorescence and predominantly cytoplasmic localization. C-10E ND cells exhibited a mixed population of nuclear and cytoplasmic vesicular localization with fluorescence levels that were intermediate between A-253 and C-10E cells. Thus, BLM-resistant cells have reduced levels of FLM and appear to have a lower nuclear:cytoplasmic ratio of FLM. FLM may be useful in studying the intracellular fate of BLM-like drugs as well as providing a tool to detect and isolate BLM-resistant cells.     

MicroRNA-1826 directly targets beta-catenin (CTNNB1) and MEK1 (MAP2K1) in VHL-inactivated renal cancer

The aim of this project is to identify new therapeutic microRNAs (miRNAs) for von Hippel-Lindau (VHL)-inactivated renal cancer cells. We initially identified several potential miRNAs targeting CTNNB1 and MEK1 using several targets scan algorithms. Only miR-1826 was found to target CTNNB1 and MEK1. Therefore, we focused on miRNA-1826 and performed 3' untranslated region (UTR) luciferase assay, functional analyses and association study between miR-1826 expression and renal cancer patient outcomes. miR-1826 expression was significantly lower in renal cancer tissues compared with non-neoplastic areas and lower expression was significantly associated with overall shorter survival and earlier recurrence after radical nephrectomy. Following miR-1826 transfection, 3' UTR luciferase activity and protein expression of beta-catenin and MEK1 were significantly downregulated in renal cancer cells. Introduction of miR-1826 also inhibited renal cancer cell proliferation, invasion and migration. Additionally, miR-1826 promoted apoptosis and G(1) arrest in VHL-inactivated renal cancer cells. Knockdowns of CTNNB1 and MEK1 by small interfering RNAs reproduced the tumor-suppressive effect of miR-1826. Our data suggest that the miR-1826 plays an important role as a tumor suppressor by downregulating beta-catenin and MEK1 in VHL-inactivated renal cancers.     

HeLa细胞中Zwint-1选择剪接亚型v7的表达鉴定

目的： 验证在HeLa细胞系中是否存在Zwint-1 v7选择性剪切亚型的mRNA和蛋白产物。方法：在缺失片段两侧设计引物,利用PCR和克隆测序验证HeLa细胞中是否存在缺失片段的mRNA;构建Zwint-1 v7 3′端特异区段(Z7)的GST融合表达载体pGEX-KG-GST-Z7,转化入BL21菌种诱导表达,菌体经超声破碎和2 mol/L尿素洗涤纯化,融合蛋白经SDS-PAGE电泳并切胶回收后作为抗原与佐剂混合乳化并免疫C57BL/6小鼠,收获多克隆抗血清Anti-Z7,采用Dot blot检测多克隆抗体的效价,Western blot检测HeLa细胞全蛋白中的Z7蛋白产物。结果：PCR和测序结果表明存在缺失37 bp的核酸片段;SDS-PAGE电泳显示在30.7 kDa处出现明显的蛋白条带;Dot blot结果表明1∶5 000稀释的多克隆抗体能检出12 ng GST-Z7;Western blot结果表明,1∶200稀释的多克隆抗体可识别HeLa细胞中Zwint-1 v7蛋白。结论：本研究在核酸水平和蛋白水平初步验证了HeLa细胞中存在Zwint-1 v7。