针对点突变癌基因T24—ras转录物的核酶性质研究

通过改变核酶体外反应的各种条件,对针对点突变癌基因Ｔ２４－ｒａｓ转录物的核酶Ｒ８的性质进行了系统研究,结果表明：Ｒ８切割底物反应的最适ｐＨ值约为８．２,最适温度为５０℃,反应必须有镁离子参加,生理环境中常见的阴离子对反应没有影响,一些变性剂能够促进反应的进行,Ｒ８切割底物的反应为二级反应。     

针对点突变癌基因T24－ras转录物的核酶性质研究

通过改变核酶体外反应的各种条件,对针对点突变癌基因Ｔ２４－ｒａｓ转录物的核酶Ｒ８的性质进行了系统研究,结果表明：Ｒ８切割底物反应的最适ｐＨ值约为８．２,最适温度为５０℃,反应必须有镁离子参加,生理环境中常见的阴离子对反应没有影响,一些变性剂能够促进反应的进行,Ｒ８切割底物的反应为二级反应。     

反义RNA抑制活化癌基因表达的研究

本文将构建的活化癌基因Ｔ２４－ｒａｓｃＤＮＡ的正、反义真核表达重组体,按先正义后反义和先反义后正义的不同转染顺序,转染ＮＩＨ３Ｔ３细胞,经药物筛选,建立细胞系。通过细胞形态及生物学特性观察、Ｓｏｕｔｈｅｒｎ杂交实验、软琼脂集落形成实验和Ｐ２１蛋白表达量的检测等实验对转化细胞进行了研究。结果表明：本室构建的正义重组体能诱导ＮＩＨ３Ｔ３细胞转化,而反义重组体可有效抑制这一转化,并且抑制效果与正、反义质粒转染的先后顺序有关。     

反义RNA对人胃癌细胞生长抑制及恶性表型的阻断作用

ｒａｓ原癌基因的点突变是人胃癌发生发展的重要机理之一。利用能表达ｃ－Ｈ－ｒａｓ癌基因反义ＲＮＡ的质粒,导入人胃癌细胞系ＢＧＣ－８２３,研究了ｒａｓ癌基因反义ＲＮＡ对人胃癌细胞生长及恶性表型的作用,结果表明,ｃ－Ｈ－ｒａｓ反义ＲＮＡ可引起ＢＧＣ－８２３生长速率及形态的变化,在半固体培养基中细胞集落形成能力减弱,部分也抑制了ＢＧＣ－８２３在裸鼠体内的致瘤性。ｃ－Ｈ－ｒａｓ反义ＲＮＡ对其ＲＮＡ的过量表达     

反义RNA对人胃癌细胞生长抑制及恶性表型的阻断作用

ｒａｓ原癌基因的点突变是人胃癌发生发展的重要机理之一。利用能表达ｃ－Ｈ－ｒａｓ癌基因反义ＲＮＡ的质粒,导入人胃癌细胞系ＢＧＣ－８２３,研究了ｒａｓ癌基因反义ＲＮＡ对人胃癌细胞生长及恶性表型的作用,结果表明,ｃ－Ｈ－ｒａｓ反义ＲＮＡ可引起ＢＧＣ－８２３生长速率及形态的变化,在半固体培养基中细胞集落形成能力减弱,部分地抑制了ＢＧＣ－８２３在裸鼠体内的致瘤性。ｃ－Ｈ－ｒａｓ反义ＲＮＡ对其ＲＮＡ的过量表达呈特异性抑制作用。     

Forskolin对放射性转化细胞TGF基因及部分癌基因表达的影响

＾３Ｈ－ＴｄＲ放射性转化细胞经１×１０＾－５ｍｏｌ／Ｌ Ｆｏｓｋｏｌｉｎ处理２４ｈ后,ＴＧＦａ,ｃ－ｍｙｃ,ｃ－Ｋ－ｒａｓ基因的ｍＲＮＡ表达下降;ＴＧＦβ,ｃ－ｆｏｓ基因表达无明显变化。非转化细胞经相同条件处理,ＴＧＦａ,ＴＧＦβ,ｃ－ｍｙｃ及ｃ－Ｋ－ｒａｓ基因表达无显著改变。提示：Ｆｏｒｓｋｏｌｉｎ介导的转化细胞的生长抑制作用与ＴＧＦａ,ｃ－ｍｙｃ,ｃ－Ｋ－ｒａｓ基因的转录表达下降有关。     

专一切割苹果锈果类病毒多体自切割核酶的克隆和转录物的体外活性测定

将苹果锈果类病毒的1个14nt的靶序列连接在锤头型核酶的3′末端,构成自切割核酶。经人工合成和PCR扩增,克隆在转录载体pGEM7zf（＋）的XhoⅠ-Hind Ⅲ位点。利用限制酶Xho I与SalI的连接,消失其识别位点序列,将自切割核酶片段插入到重组质粒中,经连续5次亚克隆,分别获得2、4、6、8、10和12拷贝的多体自切割核酶。在T7RNA聚合酶作用下,线性化重组质粒转录的多体自切割核酶通过内部的顺式切割释放出较多数量的核酶分子,提示在转录水平能够提高核酶转录物的浓度。用相同摩尔浓度的单体和12体自切割核酶分别对32P标记的靶ASSVd进行反式切割,核酶与靶RNA摩尔浓度比为1：1。放射自显影结果表明：多体自切割核酶对靶ASSVd的切割效率明显高于单体自切割核酶。我们推测多体自切割核酶在体内系统中可能具有更好的应用价值。     

癌基因EJ－ras在小鼠胚胎干细胞（ES－5）中的表达及其对ES－5细胞一些特征的影响

转基因动物在研究基因的功能、医药、畜牧业等方面有重要的应用。利用胚胎干细胞（ＥＳ）制作转基因动物,比传统的显微注射法有无可比拟的优点。但是,目前、只在小鼠中建立起了ＥＳ细胞系,在其它哺乳动物（包括家畜）中尚未建成。近来,人们开始探索：改变胚胎细胞的遗传物质（如：把外源基因导入胚胎细胞）是否有利于获得ＥＳ细胞系．在各种外源基因中,癌基因是值得尝试的基因。因为：（１）ＥＳ细胞的建系是使胚胎的ＩＣＭ细胞永生化的过程;（２）在体外利用癌基因转染可使许多原代培养细胞永生化;（３）ＥＳ细胞高表达一些原癌基因。我们用癌基因ＥＪ－ｒａｓ转染小鼠ＥＳ细胞,观察其对ＥＳ－５细胞一些特性（增殖、嵌合能力）的影响,以便选择合适的癌基因用于家畜ＥＳ细胞的建系。ＥＳ－５细胞通常培养在丝裂霉素处理的小鼠胚胎成纤维细胞（ＭＥＦ）上（Ｆｉｇ．Ａ）。转染用ＥＳ－５细胞培养在无饲养层细胞的、含有大鼠肝细胞（ＢＲＬ）的条件培养液ＤＭＥＭ中。ＥＪ－ｒａｓ基因克隆在真核表达载体ＰＳＶ２ｎｅｏ的ＢａｍＨＩ位点上、使用磷酸钙法转染ＥＳ－５细胞,Ｇ－４１８法筛选阳性克隆,得到的抗性克隆仍以集落形式生长（Ｆｉｇ．Ｂ）,选取５个较好的克隆（ＥＳ－ｒａｓ１,２,     

逆转录病毒介导的TNFa基因在胶质瘤细胞系（C6）中的表达及对肿瘤细胞恶性生长的影响

利用逆转录病毒载体ＬＸＳＮ构建了含有完整编码ＴＮＦｃＤＮＡ的重组逆转录病毒质粒ｐＬＸＳＮ－ｔｎｆ,用Ｌｉｐｏｆｅｃｔａｍｉｎｅ将重组质粒导入病毒包装细胞ｐＡ３１７,经Ｇ４１８筛选培养获得抗性克隆,用ＮＩＨ３Ｔ３细胞测定病毒滴度,获得滴度为５×１０５ＣＦＵ／ｍｌ的细胞克隆。利用病毒上清液感染大鼠胶质瘤细胞系Ｃ６,得到Ｇ４１８抗性克隆细胞Ｃ６ｐＬＸＳＮ－ｔｎｆ,经ＰＣＲ检测,ＴＮＦｃＤＮＡ完整地整合在细胞基因组中。测定Ｃ６ｐＬＸＳＮ－ｔｎｆ细胞上清中ＴＮＦ的生物活性,结果显示ＴＮＦ有相对稳定的表达（４８～１８０Ｕ／ｍｌ１０６ｃｅｌｌｓ／２４ｈ）。实验还显示经ＴＮＦ基因转导的Ｃ６ｐＬＸＳＮ－ｔｎｆ细胞生长速度较之亲本肿瘤细胞Ｃ６明显下降,基因修饰后的肿瘤细胞在Ｗｉｓｔａｒ大鼠体内形成肿瘤的能力明显受到抑制。进一步用超离心法浓缩病毒对胶质瘤移植模型进行了体内治疗研究。     

切割Fas mRNA核酶的构建及其体内外切割活性的鉴定

白血病细胞表面可高表达FasL ,诱导表达Fas的T细胞凋亡 ,从而降低其抗白血病的作用 .以高表达Fas的小鼠淋巴瘤细胞系Yac 1作为模型 ,设计并合成了针对FasmRNA 5 96位点的锤头状核酶基因 ,用T7/SP6体外转录系统检测了该核酶对FasmRNA的体外切割效率 ,通过电穿孔转染法将其导入Yac 1细胞 ,通过RT PCR、Western印迹法检测细胞上Fas的表达 .细胞经抗Fas的抗体作用后 ,通过MTT法测细胞的增殖 ,annexin Ⅴ凋亡检测试剂盒测细胞凋亡 .该核酶体外切割活性达6 0 % ,且能有效降低细胞表面Fas的表达 ;细胞经抗Fas的抗体作用后 ,转染核酶的细胞增殖活性较对照增高 ,而凋亡率明显降低 .结果表明 ,构建的切割FasmRNA核酶在体内外均具备良好的切割FasmRNA的活性 ,使细胞免于Fas途径的凋亡 ,为研究抑制T细胞的凋亡从而增强其抗白血病效应提供实验基础 .     

Activity identification of chimeric anti-caspase-3 mRNA hammerhead ribozyme in vitro and in vivo

To study the expression activity of various vectors containing anti-caspase-3 ribozyme cassettes in vivo, and to further study the role of caspas-3 in the apoptotic pathway, we constructed anti-caspase-3 hammerhead ribozyme embedded into the human snRNA U6, and detected the activity of the ribozyme in vitro and in vivo. Meanwhile we compared it with the self-cleaving hammerhead ribozymes that we previously studied, and with the general ribozyme, cloned into RNA polymerase II expression systems. The results showed that the three ribozymes, p1.5RZ107, pRZ107 and pU6RZ107 had the correct structure, and that they could cleave cas-pase-3 mRNA exactly to produce two fragments: 143nt/553nt. p1.5RZ107 has the highest cleavage efficiency in vitro, almost 80%. However, the U6 chimeric ribozyme, pU6RZ107, has the highest cleavage activity in vivo, almost to 65%, though it has lower cleavage activity in vitro. The cleavage results demonstrated that the pU6RZ107, the U6 chimeric ribozyme, could more efficiently expre     

针对乙型肝炎病毒（HBV）前S2基因三靶位串联核酶的实验研究

核酶（Ｒｉｂｏｚｙｍｅ）是一类具有核酸内切酶活性的ＲＮＡ分子,可特异地切割靶ＲＮＡ序列。核酶的催化中心有相对固定的序列,而切割特异性则由催化中心两侧序列与何种靶分子序列互补而决定。根据核酶这一特性,可以人工设计针对某一病毒ＲＮＡ的核酶分子,破坏病毒转...     

特异切割马铃薯卷叶病毒复制酶基因负链的核酶研究

根据锤头状核酶的作用模式,设计、合成并克隆了特异性切割马铃薯地病毒中国分离株（ＰＬＲＶ－Ｃｈ）复制酶基因负链ＲＮＡ的核酶序列,以体外转录的ＰＬＲＶ－Ｃｈ复制酶基因负链ＲＮＡ作为底物,与转录的核酶ＲＮＡ共同保温,以检测核酶对底和的体外切割作用。实验结果表明,核酸疼 ＲＮＡ对ＰＬＲＶ－Ｃｈ复制酶基因负锭ＲＮＡ具有特异切割作用。     

Expression of a chimeric ribozyme gene results in endonucleolytic cleavage of target mRNA and a concomitant reduction of gene expression in vivo.

The subclass of catalytic RNAs termed ribozymes cleave specific target RNA sequences in vitro. Only circumstantial evidence supports the idea that ribozymes may also act in vivo. In this study, ribozymes with a hammerhead motif directed against a target sequence within the mRNA of the neomycin phosphotransferase gene (npt) were embedded into a functional chimeric gene. Two genes, one containing the ribozyme and the other producing the target, were cotransfected into plant protoplasts. Following in vivo expression, a predefined cleavage product of the target mRNA was detected by ribonuclease protection. Expression of both the ribozyme gene and the target gene was driven by the CaMV 35S promoter. Concomitant with the endonucleolytic cleavage of the target mRNA, a complete reduction of NPT activity was observed. An A to G substitution within the ribozyme domain completely inactivates ribozyme-mediated hydrolysis but still shows a reduction in NPT activity, albeit less pronounced. Therefore, the reduction of NPT activity produced by the active ribozyme is best explained by both hydrolytic cleavage and an antisense effect. However, the mutant ribozyme--target complex was more stable than the wildtype ribozyme--target complex. This may result in an overestimation of the antisense effect contributing to the overall reduction of gene expression.     

Target sequence-specific inhibition of HIV-1 replication by ribozymes directed to tat RNA.

The structural motif formed between a hammerhead ribozyme and its substrate consists of three RNA double helices in which the sequence 5' to the XUY is termed helix I and the sequence 3' to the XUY helix III. Two hammerhead ribozymes targeted to the tat gene of HIV-1SF2 were designed to study target specificity and the potential effect of helix I mismatch on ribozyme efficacy both in vitro and in vivo. The first ribozyme (Rz1) targeted to the 5' splicing region of the tat gene was designed to cleave GUC*A. In HIV-1IIIB the A is changed to a G. The second ribozyme (Rz2) was targeted to the translational initiation region of the tat gene which is highly conserved among a variety of HIV-1 isolates, including both HIV-1SF2 and HIV-1IIIB. In vitro cleavage studies demonstrated that Rz1 efficiency cleaved HIV-1SF2 substrate RNA, but not HIV-1IIIB, presumably due to the base change from A to G. In contrast, Rz2 cleaved HIV-1SF2 or HIV-1IIIB substrate with equal efficiency. Both ribozymes were cloned into the 3' untranslated region of the neomycin gene (neo) within the pSV2neo vector and transfected into the SupT1 human CD4+ T cell line. Following selection, stable transfectants were challenged with either HIV-1SF2 or HIV-1IIIB virus. While Rz1-expressing cells were significantly protected from HIV-1SF2 infection, they exhibited no protection when infected with HIV-1IIIB virus. In contrast, Rz2 was effective in inhibiting the replication of both HIV-1SF2 and HIV-1IIIB in SupT1 cells. Expression of both ribozymes in these cells was demonstrated by Northern analysis. RT-PCR sequencing analysis confirmed the respective HIV-1 target sequence integrity. These data demonstrate the importance of the first base pair distal to the XUY within helix I of the hammerhead structure for both in vitro and in vivo ribozyme activities and imply that the effectiveness of the anti-HIV-1 ribozymes against appropriate target sequences is due to their catalytic activities rather than any antisense effect.     

Effective Inhibition of Human Immunodeficiency Virus 1 Replication by Engineered RNase P Ribozyme

Using an in vitro selection procedure, we have previously isolated RNase P ribozyme variants that efficiently cleave an mRNA sequence in vitro. In this study, a variant was used to target the HIV RNA sequence in the tat region. The variant cleaved the tat RNA sequence in vitro about 20 times more efficiently than the wild type ribozyme. Our results provide the first direct evidence that combined mutations at nucleotide 83 and 340 of RNase P catalytic RNA from Escherichia coli (G₈₃ -> U₈₃ and G₃₄₀ -> A₃₄₀) increase the overall efficiency of the ribozyme in cleaving an HIV RNA sequence. Moreover, the variant is more effective in reducing HIV-1 p24 expression and intracellular viral RNA level in cells than the wild type ribozyme. A reduction of about 90% in viral RNA level and a reduction of 150 fold in viral growth were observed in cells that expressed the variant, while a reduction of less than 10% was observed in cells that either did not express the ribozyme or produced a catalytically inactive ribozyme mutant. Thus, engineered ribozyme variants are effective in inhibiting HIV infection. These results also demonstrate the potential of engineering RNase P ribozymes for anti-HIV application.