Regulated expression of the Shiga toxin B gene induces apoptosis in mammalian fibroblastic cells

Shiga toxins (Stxs) produced by enterohaemorrhagic Escherichia coli may induce colonic ulceration, bloody diarrhoea and acute renal failure. The A subunit (StxA) is known to inhibit protein synthesis, whereas the B subunits (StxB) bind to Gb3 on the cell surface. However, the mechanisms by which Stxs kill target cells remain unclear. Stx1A or Stx1B genes were introduced into pcDNA3.1 vectors and transfected into NIH3T3 and HeLa cells. The Stx1B gene-transfected cells became apoptotic with accompanying DNA fragmentation, whereas the Stx1A gene-transfected cells were found to be necrotic and no DNA fragmentation occurred. The HeLa/C4 cells integrated with the Stx1B gene with a tetracycline-inducible promoter eventually produced cytoplasmic Stx1B, leading to DNA fragmentation on the addition of doxycycline. These apoptotic changes were abrogated by pretreatment with Z-VAD-fmk. These results suggest that the transfected Stx1B gene induces apoptosis by activating the caspase cascade after Stx1B expression in the cytoplasm.     

Herpesvirus saimiri U RNAs are expressed and assembled into ribonucleoprotein particles in the absence of other viral genes.

Marmoset T lymphocytes transformed by herpesvirus saimiri contain a set of five virally encoded U RNAs called HSUR1 through HSUR5. HSUR genes have been individually transfected into a nonlymphoid, nonsimian cell line (HeLa cells) in the absence of any other coding regions of the herpesvirus saimiri genome. The levels of HSUR1 through HSUR4 in HeLa transient-expression systems are comparable to those found in virally transformed T cells (23 to 91%). In contrast, HSUR5 is expressed at ninefold-higher levels in transfected HeLa cells. Immunoprecipitation experiments show that HSURs expressed in transfected cells bind proteins with Sm determinants and acquire a 5' trimethylguanosine cap structure, as they do in transformed T cells. HSUR1 or HSUR4 particles from transfected HeLa cells migrate between 10S and 15S in velocity gradients, identical to the sedimentation of "monoparticles" produced in virally transformed lymphocytes. We conclude from these transfection experiments that no other herpesvirus saimiri or host-cell-specific gene products appear to be required for efficient expression of the HSUR genes or for subsequent assembly of the viral U RNAs into small nuclear ribonucleoprotein particles. In lymphocytes transformed by herpesvirus saimiri, HSUR small nuclear ribonucleoprotein particles are involved in higher-order complexes that sediment between 20S and 25S. HSUR1, HSUR2, and HSUR5 dissociate from such complexes upon incubation at 30 degrees C, whereas the complex containing HSUR4 is stable to incubation.     

Cyclic AMP-Response Element Regulated Cell Cycle Arrests in Cancer Cells

Recently, we have demonstrated that trichosanthin (TCS), a promising agent for the treatment of cervical adenocarcinoma, inhibited HeLa cell proliferation through the PKC/MAPK/CREB signal pathway. Furthermore, TCS down-regulated Bcl-2 expression was abrogated by a decoy oligonucleotide (OGN) to the cyclic AMP-responsive element (CRE). The decoy OGN blocked the binding of CRE-binding protein (CREB) to Bcl-2. These results suggested that CRE-mediated gene expression may play a pivotal role in HeLa cell proliferation. However, little is known about the effect of TCS on cell cycle arrests, particularly, whether the genes involved in cell cycle were regulated by CRE. Our present study shows that the arrests of S, G1 and G2/M phases were accompanied by the significant down-regulation of cyclin A, D1 and CDK 2, 4 in HeLa cells, cyclin D1, E and CDK 2, 4 in Caski and C33a cells, and cyclin A, B1, E and CDK 2 in SW1990 cells. However, the cell cycle arrests were reversed via the significant up-regulation of cyclin A and D1, by the combined treatment of TCS and CRE. In conclusion, these data demonstrate for the first time that specific cell cycle arrests in cancer cells can be induced by TCS by inhibiting the binding of CREB to CRE on genes related to cell proliferation.     

干扰素膜蛋白Tet-on系统稳定细胞系的建立及对CA16病毒的抑制作用

通过Tet-on调控系统,构建受多西环素诱导表达干扰素诱导的跨膜蛋白(interferon-induced transmembrane proteins 1/2/3,IFITM1/2/3)基因的HeLa细胞系,并初步探索了IFITM蛋白对柯萨奇病毒A16(CA16)的抑制作用.首先将调控质粒pTet-on转染进入HeLa细胞,通过G418筛选出阳性克隆细胞系,在此细胞系基础上共同转染反应质粒pTRE2-IFITM1/2/3和伴侣质粒pTK-Hyg,通过潮霉素筛选出单克隆细胞系,加入多西环素后利用Western印迹筛选出可诱导表达IFITM1/2/3蛋白的单克隆细胞系.使用实时荧光定量PCR(RT-qPCR)检测发现,多西环素诱导表达的IFITM蛋白对不同感染复数(multiplicity of infection,MOI)的CA16具有明显的抑制作用,其中IFITM 3对CA16的抑制效果最为明显.Tet调控IFITM1/2/3基因表达HeLa细胞系的成功建立,为进一步研究IFITM基因的功能及其抗病毒机理提供了一个理想的细胞模型.     

The homeodomain protein, Pit-1/GHF-1, is capable of binding to and activating cell-specific elements of both the growth hormone and prolactin gene promoters

Studies were conducted to determine whether the trans-acting protein Pit-1/GHF-1 can bind to and activate promoter elements in both the GH and PRL genes that are necessary for cell-specific expression. Four pituitary cell lines that differentially express the endogenous GH and PRL genes were examined for their ability to activate GH and PRL promoter constructs containing sequences necessary for cell-specific expression (CSEs). Plasmids containing one CSE, -96 PRL and -104 GH, were similarly expressed in each of the four cell lines. Of the plasmids containing two CSEs, -173 PRL was always activated to a greater extent than -145 GH, with this relative activation being stronger in GC and GH1 cells than in 235-1 and GH4C1 cells. Protein-DNA binding assays were used to show that the GH and PRL CSEs specifically bound two highly abundant nuclear proteins (31 and 33 kDa). The two proteins were present at similar levels in all four pituitary cell lines and were recognized by a Pit-1/GHF-1 antibody. In contrast, HeLa and Rat2 cells did not activate transfected GH or PRL plasmids and did not contain nuclear proteins that specifically bound to the GH and PRL CSEs. However, cotransfection of these cells with the expression vector RSV-Pit-1/GHF-1 resulted in the activation of -173 PRL and -145 GH (PRL greater than GH). HeLa cells transfected with RSV-Pit-1/GHF-1 also contained 31- and 33-kDa nuclear proteins that bound to the GH and PRL CSEs. These results show that Pit-1/GHF-1 is present at levels in pituitary cell lines that are sufficient to activate the minimal elements in both the GH and PRL promoters necessary for cell-specific expression of these genes.     

利用线粒体膜电位测定筛选参与细胞凋亡的人类新基因

细胞凋亡(apoptosis)属于细胞程序化死亡(programmed cell death),是细胞内涉及到许多生化反应的复杂过程.建立了基于细胞水平的凋亡筛选模型,用于筛选人类基因组中功能未知的序列,以发现与细胞凋亡相关的新基因.通过构建人类未知基因的表达文库,并将未知基因表达载体瞬时转染HeLa细胞,用阳离子染料JC-1标记HeLa细胞线粒体内膜并检测线粒体跨膜电位,用流式细胞术进行阳性结果的验证.经过对未知基因表达文库内600个新基因的筛选,得到7个线粒体跨膜电位下降相关新基因(CHMP6、CGI-38、hCAP-H2、NUDT16L1、ARMC1、PHF17和FLJ21103),经实验验证,其中3个基因(CHMP6、CGI-38和hCAP-H2)与细胞凋亡相关.结果表明,所建立的基于细胞的凋亡筛选模型稳定高效,3个细胞凋亡相关基因将被进行深入研究.     

CD4-independent human immunodeficiency virus infection involves participation of endocytosis and cathepsin B

During a comparison of the infectivity of mNDK, a CD4-independent human immunodeficiency virus type 1 (HIV-1) strain, to various cell lines, we found that HeLa cells were much less susceptible than 293T and TE671 cells. Hybridoma cells between HeLa and 293T cells were as susceptible as 293T cells, suggesting that cellular factors enhance the mNDK infection in 293T cells. By screening a cDNA expression library in HeLa cells, cystatin C was isolated as an enhancer of the mNDK infection. Because cathepsin B protease, a natural ligand of cystatin C, was upregulated in HeLa cells, we speculated that the high levels of cathepsin B activities were inhibitory to the CD4-independent infection and that cystatin C enhanced the infection by impairing the excessive cathepsin B activity. Consistent with this idea, pretreatment of HeLa cells with 125 μM of CA-074Me, a cathepsin B inhibitor, resulted in an 8-fold enhancement of the mNDK infectivity. Because cathepsin B is activated by low pH in acidic endosomes, we further examined the potential roles of endosomes in the CD4-independent infection. Suppression of endosome acidification or endocytosis by inhibitors or by an Eps15 dominant negative mutant reduced the infectivity of mNDK in which CD4-dependent infections were not significantly impaired. Taken together, these results suggest that endocytosis, endosomal acidification, and cathepsin B activity are involved in the CD4-independent entry of HIV-1.     

Vpr-induced cell cycle arrest is conserved among primate lentiviruses.

We previously reported that expression of human immunodeficiency virus type 1 strain NL4-3 (HIV-1(NL4-3))vpr causes cells to arrest in the G2 phase of the cell cycle. We examined the induction of cell cycle arrest by other HIV-1 isolates and by primary lentiviruses other than HIV-1. We demonstrate that the vpr genes from tissue culture-adapted or primary isolates of HIV-1 are capable of inducing G2 arrest. In addition, we demonstrate that induction of cell cycle arrest is a conserved function of members of two other groups of primate lentiviruses, HIV-2/simian immunodeficiency virus strain sm (SIVsm)/SIVmac and SIVagm. vpr from HIV-1, HIV-2, and SIVmac induced cell cycle arrest when transfected in human (HeLa) and monkey (CV-1) cells. vpx from HIV-2 and SIVmac did not induce detectable cell cycle arrest in either cell type, and SIVagm vpx was capable of inducing arrest in CV-1 but not HeLa cells. These results indicate that induction of cell cycle perturbation is a general property of lentiviruses that infect primates. The conservation of this viral function throughout evolution suggests that it plays a key role in virus-host relationships, and elucidation of its mechanism may reveal important clues about pathology induced by primary lentiviruses.     

Cell-surface streptavidin fusion protein for rapid selection of transfected mammalian cells

We developed a series of eight mammalian cell surface marker fusion genes by using the streptavidin gene from Streptomyces avidinii. These fusion genes are useful and non-growth-toxic selection markers for rapid-harvest transfected mammalian cells. Two streptavidin constructs were used; the longer fragment contains the native bacterial signal sequence, which the shorter fragment lacks. For expression of the streptavidin antigen on the surface of mammalian cells, streptavidin was flanked by a mammalian signal sequence and a transmembrane domain (from mouse H2-K or Kit); some constructs also contained the gene for enhanced green fluorescent protein (EGFP). We transfected a series of plasmids encoding the fusion proteins into HeLa cells and determined that the transfected cells produced the fusion protein on their cell surfaces. To separate transfected cells from nontransfected cells, we incubated cells with a polyclonal antibody against streptavidin, and antibody-bound cells were harvested by the use of paramagnetic beads coupled with the corresponding secondary antibody. We obtained highly pure populations of transfected cells; this result also confirmed the production of the fusion protein on the cell surface. Cell growth assays revealed that none of the transfected fusion genes or their products adversely affected the proliferation of HeLa cells. Our results indicate that the fusion constructs we developed and the immunomagnetic separation protocol we used are valuable tools for various transfection applications. In particular, the constructs containing EGFP are advantageous because transfection efficiency can be assessed without additional treatment of cells.     

PLK1基因沉默抑制HeLa细胞凋亡

以高表达Polo样激酶1（Polo-like kinase 1,PLK1）的宫颈癌细胞系HeLa细胞为模型,观察针对PLK1基因的短发夹状RNA（short hairpin RNA,shRNA）对其凋亡和增殖的影响.设计并合成了针对PLK1的shRNA,将其导入构建的携带增强型绿色荧光蛋白（EGFP）的RNAi（RNA interference）表达载体中.通过 RT-PCR和Western 印迹分别检测HeLa细胞PLK1基因和蛋白水平的表达,以流式细胞仪和PI-Hochest双染法测细胞凋亡,MTT法检测细胞的增殖水平.成功构建了携带EGFP的RNAi表达载体pEGFP-H1.转染shRNA后,HeLa细胞PLK1的表达降低至30%.与对照组和空载体转染组相比,shRNA转染组的HeLa细胞凋亡率明显增加,其增殖活性则明显降低.本课题构建的RNAi表达载体便于观察靶基因的转染情况,且不影响H1启动子的体内转录.PLK1的基因沉默能明显增加HeLa细胞的凋亡,抑制该细胞的增殖,有可能为未来肿瘤的治疗找到新的靶点和有效途径.     

Inhibition of IFN-gamma receptor signaling by hepatitis C virus non-structural protein NS4B]

The function of NS4B is incompletely understood. The aim of the study is to understand the influence of NS4B on anti-viral response. After cell line stably expressing NS4B established, the influence of IFN-alpha of different concentration on VSV was studied using plaque assay; cell expression profiling caused by NS4B was studied using DNA microarray, and the IFNGR1 fluorescence intensity was analyzed. Our data showed that HCV-NS4B could suppress immuno-associated gene expression, in particular, IFN-gamma receptor signal transduction-related genes. Taken together, NS4B could play some roles in HCV resistance to IFN therapy.     

The novel gene LRP15 is regulated by DNA methylation and confers increased efficiency of DNA repair of ultraviolet-induced DNA damage

LRP15 is a novel gene cloned from lymphocytic cells, and its function is still unknown. Bioinformatic data showed that LRP15 might be regulated by DNA methylation and had an important role in DNA repair. In this study, we investigate whether the expression of LRP15 is regulated by DNA methylation, and whether overexpression of LRP15 increases efficiency of DNA repair of UV-induced DNA damage in HeLa cells. The results showed (1) the promoter of LRP15 was hypermethylated in HeLa cells, resulting a silence of its expression. Gene expression was restored by a demethylating agent, 5-aza-2'-deoxycytidine, but not by a histone deacetylase inhibitor, trichostatin A; (2) overexpression of LRP15 inhibited HeLa cell proliferation, and the numbers of cells in the G2/M phase of the cell cycle in cells transfected with LRP15 increased about 10% compared with controls; (3) cyclin B1 level was much lower in cells overexpressing LRP15 than in control cells; and (4) after exposure to UV radiation, the LRP15-positive cells showed shorter comet tails compared with the LRP15-negative cells. From these results we conclude that the expression of LRP15 is controlled by methylation in its promoter in HeLa cells, and LRP15 confers resistance to UV damage and accelerates the DNA repair rate.     

Ubiquitin B在HSP90抑制剂17-AAG诱导人宫颈癌HeLa细胞周期阻滞中的作用

目的 研究Ubiquitin B（Ubb）在热休克蛋白90（HSP90）抑制剂17-AAG诱导人宫颈癌HeLa细胞周期阻滞中的作用及机制.方法 不同浓度17-AAG处理HeLa细胞后,流式细胞术检测细胞周期分布,荧光分光光度法检测细胞蛋白酶体活性变化;Ubb siRNA 转染HeLa细胞后,Real Time PCR法检测Ubb干扰效应,Western 印迹检测细胞周期相关蛋白的表达改变.结果 17-AAG可以诱导HeLa细胞阻滞于G2/M期,同时显著增强细胞内糜蛋白酶样蛋白酶体活性,并且两者的变化均呈现剂量依赖性;干扰HeLa细胞内Ubb后,可以逆转17-AAG引起的G2/M期阻滞;17-AAG可明显下调HeLa细胞周期相关蛋白Cdk1和Hec1的表达,并且这一变化也是Ubb依赖的.结论 Ubb在17-AAG诱导的HeLa细胞周期阻滞中发挥重要作用,Ubb和HSP90抑制剂17-AAG在功能上相互关联,可能成为宫颈癌治疗的新靶点.     

Cyclin B1 Expression in HeLa S3 Cells Studied by Flow Cytometry

Using a procedure to stain cells simultaneously for cyclin B1 protein and DNA, we have examined cyclin B1 expression by flow cytometry in human cells under a variety of perturbing and nonperturbing conditions. The method described is useful for measuring relative differences in cyclin B level (immunochemically detectable epitope) as a function of cell cycle position on an individual cell basis and thus to examine cell cycle-related changes in cyclin B expression without prior cell synchronization. We show that in HeLa S3 cells, cyclin B1 accumulates in cells only after they become 4C and have resided in G2 for a short period of time. During colcemid-induced mitotic arrest cyclin B1 continues to accumulate in HeLa S3 cells, and under specific conditions of aphidicolin-induced unbalanced cell growth induced, cyclin B accumulates to supranormal levels prior to mitosis. Flow cytometric analysis of cyclin B expression and DNA content permits detailed examination of the effects of cell cycle perturbations on cyclin B expression under a variety of conditions.     

Curcumin inhibits ultraviolet light induced human immunodeficiency virus gene expression

Recently, we reported that the herbal drug St. John's Wort is a potent inhibitor of UV-induced HIV-LTR activation in stably transfected HIVcat/HeLa cells [35]. Our previous studies have demonstrated that the activation of p38 MAP kinase (stress-activated protein kinase-2) and NF-B are both required for a full UV-induced HIV gene expression response. In this study we have investigated the mechanism by which curcumin inhibits UV-activated HIV-LTR gene expression. We found that treatment of HIVcat/HeLa cells with micromolar concentrations of curcumin completely abolished UV activation of HIV gene expression. Curcumin treatment at similar doses as those used to inhibit HIV gene expression also effectively blocked UV activation of NF-B, as demonstrated by electrophoretic mobility shift assay. In contrast, curcumin did not inhibit UV-induced phosphorylation of p38 MAP kinase. This observation was also supported by findings that curcumin did not inhibit UV-induced phosphorylation of CREB/ATF-1 and ATF-2. Although curcumin was ineffective in preventing UV-induced p44/42 MAP kinase phosphorylation, the JNK (1 and 2) and AP-1 activation were efficiently blocked by curcumin in HeLa cells. We conclude that the mechanism by which curcumin modulates UV activation of HIV-LTR gene expression mainly involves the inhibition of NF-B activation.