Requirements for RNA Replication of a Poliovirus Replicon by Coxsackievirus B3 RNA Polymerase

A chimeric poliovirus type 1 (PV1) genome was constructed in which the 3D RNA polymerase (3D(pol)) coding sequences were replaced with those from coxsackievirus B3 (CVB3). No infectious virus was produced from HeLa cells transfected with the chimeric RNA. Processing of the PV1 capsid protein precursor was incomplete, presumably due to inefficient recognition of the P1 protein substrate by the chimeric 3CD proteinase containing CVB3 3D sequences. The ability of the chimeric RNA to replicate in the absence of capsid formation was measured after replacement of the P1 region with a luciferase reporter gene. No RNA synthesis was detected, despite efficient production of enzymatically active 3D(pol) from the 3D portion of the chimeric 3CD. The chimeric 3CD protein was unable to efficiently bind to the cloverleaf-like structure (CL) at the 5' end of PV1 RNA, which has been demonstrated previously to be required for viral RNA synthesis. The CVB3 3CD protein bound the PV1 CL as well as PV1 3CD. An additional chimeric PV1 RNA that contained CVB3 3CD sequences also failed to produce virus after transfection. Since processing of PV1 capsid protein precursors by the CVB3 3CD was again incomplete, a luciferase-containing replicon was also analyzed for RNA replication. The 3CD chimera replicated at 33 degrees C, but not at 37 degrees C. Replacement of the PV1 5'-terminal CL with that of CVB3 did not rescue the temperature-sensitive phenotype. Thus, there is an essential interaction(s) between 3CD and other viral P2 or P3 protein products required for efficient RNA replication which is not fully achieved between proteins from the two different members of the same virus genus.     

针对2B区域的短双链RNA抑制柯萨奇B3病毒感染HeLa细胞的特性研究

为了研究短双链RNA(Small interfering RNA,siRNA)对柯萨奇B组3型病毒(CVB3)复制的影响及其作用特性,合成针对CVB3基因组2B区的siRNA-2B,脂质体法转染HeLa细胞后感染CVB3病毒,观测转染效率及存留时间、毒性作用、病毒致细胞病变效应、病毒滴度、病毒RNA含量、siRNA-2B对重组基因的特异性降解及培养上清有限稀释后再感染情况.结果发现siRNA-2B能高效转染入HeLa细胞并存留长达48h,高剂量的siRNA-2B对培养细胞无明显毒性,siRNA-2B能特异性针对2B区有效地降解病毒RNA,能明显抑制病毒RNA的复制.随着转染浓度的增加,siRNA-2B的抗病毒作用逐渐增强.siRNA-2B还能明显降低CVB3的再感染能力.这些结果提示,针对基因组2B区的siRNA-2B可以明显抑制CVB3基因复制,有效控制病毒再感染,并具有高效性、特异性和量效关系等特点.为siRNA可能成为预防和治疗CVB3感染的新途径奠定基础.     

Elution and uncoating of Coxsackievirus B3 by isolated HeLa cell plasma membranes.

Plasma membranes isolated from HeLa cells on discontinuous sucrose gradients were assayed for their capacity to elute and uncoat coxsackievirus B3 at 37 C. Because the viral receptors are limited to the surface of HeLa cells, the addition of radioactively labeled virus to the cells prior to cell homogenization provided a useful marker for locating the plasma membranes during the fractionation procedure. Four bands were formed on the discontinuous sucrose gradients with approximately 70% or more of the membrane-associated viral label being recovered in the most dense bands, designated as bands 3 and 4. Bands 3 and 4 also possessed the plasma membrane marker enzymes, Na+, K+ adenosine triphosphatase and 5'-nucleotidase and revealed typical structures characteristic of plasma membranes as revealed by electron microscopy. Pelleted and washed membranes from band 3 both eluted and uncoated B3 32P-labeled virus, whereas membranes from band 4 eluted virus but failed to uncoat it. The membranes from band 4 were shown to inhibit the viral uncoating activity when mixed with membranes of band 3. Characteristically, unfractionated homogenates of cell membranes eluted but did not uncoat virus. The finding of a naturally occurring inhibitor of virus uncoating provides for the first time a way to distinguish between the membrane activities of virus elution and virus uncoating. The inhibitor remains to be characterized.     

Caspase Activation and Specific Cleavage of Substrates after Coxsackievirus B3-Induced Cytopathic Effect in HeLa Cells

Coxsackievirus B3 (CVB3), an enterovirus in the family Picornaviridae, induces cytopathic changes in cell culture systems and directly injures multiple susceptible organs and tissues in vivo, including the myocardium, early after infection. Biochemical analysis of the cell death pathway in CVB3-infected HeLa cells demonstrated that the 32-kDa proform of caspase 3 is cleaved subsequent to the degenerative morphological changes seen in infected HeLa cells. Caspase activation assays confirm that the cleaved caspase 3 is proteolytically active. The caspase 3 substrates poly(ADP-ribose) polymerase, a DNA repair enzyme, and DNA fragmentation factor, a cytoplasmic inhibitor of an endonuclease responsible for DNA fragmentation, were degraded at 9 h following infection, yielding their characteristic cleavage fragments. Inhibition of caspase activation by benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone (ZVAD.fmk) did not inhibit the virus-induced cytopathic effect, while inhibition of caspase activation by ZVAD.fmk in control apoptotic cells induced by treatment with the porphyrin photosensitizer benzoporphyrin derivative monoacid ring A and visible light inhibited the apoptotic phenotype. Caspase activation and cleavage of substrates may not be responsible for the characteristic cytopathic effect produced by picornavirus infection yet may be related to late-stage alterations of cellular homeostatic processes and structural integrity.     

Infectious cDNA, Cell Receptors and Transgenic Mice in the Study of Sabin's Poliovirus Vaccines

Abstract. The determination of the nucleotide sequence of the poliovirus genome, the isolation of infectious poliovirus cDNAs, and the identification of the cell receptor for poliovirus and establishment of a transgenic mouse model for poliomyelitis have all contributed to our understanding of the live, attenuated Sabin poliovirus vaccines. These highly effective vaccines have been studied extensively by many laboratories to determine the molecular basis for their attenuation phenotype. For this special issue I would like to review how our research has improved the understanding of Sabin's poliovirus vaccines, and highlight Albert's influence on our work.     

柯萨奇病毒B组3型基因组剪切片段的序列分析

柯萨奇病毒B组(Coxsackievirus B,CVB)感染细胞时其基因组RNA存在不稳定现象,但产生机制尚不清楚。本研究将柯萨奇病毒B组3型(CVB3)感染细胞后,利用5′ cDNA末端快速扩增技术(5′ rapid amplification of cDNA ends,5′ RACE)扩增并克隆细胞内CVB3基因组片段,并对每条序列及其5′端的二级结构进行分析。结果获得的20条CVB3基因组片段,长度为 2 067～5 547 bp,片段断端主要分布于2Apro和2C编码区。RNAfold分析显示,这些片段多数在5′断点端形成二级茎-环结构。本研究显示,CVB在宿主细胞感染时可形成大量不完整基因组RNA片段,这些片段可在5′断点端形成局部双链结构,提示片段不是随机产生,可能是RNA酶剪切产物。此发现有助于理解CVB基因组不稳定的机制。     

Transmission and Demographic Dynamics of Coxsackievirus B1

The infectious activity of coxsackievirus B1 (CV-B1) in Taiwan was high from 2008 to 2010, following an alarming increase in severe neonate disease in the United States (US). To examine the relationship between CV-B1 strains isolated in Taiwan and those from other parts of the world, we performed a phylodynamic study using VP1 and partial 3D^pol (414 nt) sequences from 22 strains of CV-B1 isolated in Taiwan (1989–2010) and compared them to sequences from strains isolated worldwide. Phylogenetic trees were constructed by neighbor-joining, maximum likelihood, and Bayesian Monte Carlo Markov Chain methods. Four genotypes (GI–IV) in the VP1 region of CV-B1 and three genotypes (GA–C) in the 3D^pol region of enterovirus B were identified and had high support values. The phylogenetic analysis indicates that the GI and GIII strains in VP1 were geographically distributed in Taiwan (1993–1994) and in India (2007–2009). On the other hand, the GII and GIV strains appear to have a wider spatiotemporal distribution and ladder-like topology A stair-like phylogeny was observed in the VP1 region indicating that the phylogeny of the virus may be affected by different selection pressures in the specified regions. Further, most of the GI and GII strains in the VP1 tree were clustered together in GA in the 3D tree, while the GIV strains diverged into GB and GC. Taken together, these data provide important insights into the population dynamics of CV-B1 and indicate that incongruencies in specific gene regions may contribute to spatiotemporal patterns of epidemicity for this virus.     

An ERK-p38 Subnetwork Coordinates Host Cell Apoptosis and Necrosis during Coxsackievirus B3 Infection

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Highlights? Intracellular signaling predicts the fate of coxsackievirus B3 (CVB3)-infected cells ? p38 and ERK signaling pathways are tightly interconnected during CVB3 infection ? CVB3-induced apoptosis of cardiomyocytes is inhibited by ERK5 and ERK1/2 pathways ? CVB3 induces necrosis of cardiomyocytes via p38 activation     

Time-Lapse Cinemicrographic Studies of X-Irradiated HeLa S3 Cells: I. Cell Progression and Cell Disintegration

Time-lapse cinemicrographs of synchronous HeLa S3 cells irradiated with 220 kv X-rays at various stages of interphase provided data for constructing pedigrees, measuring the duration of both generation cycles and mitoses, and scoring events associated with cell disintegration for up to seven postirradiation generations. The onset of the first mitosis after doses of 500 rads was delayed as expected from previous studies of the age dependence of “mitotic delay.” The interval between this first mitosis and the next was indistinguishable from that for unirradiated control cells, while the subsequent two generations were again prolonged, on the average, though not so severely as was the irradiated generation. The duration of mitosis was increased proportionally more than interphase. Cell disintegration took place by way of two morphologically distinct processes. In three-quarters of the cases the cells were rounded and apparently trapped in metaphase when they disintegrated; the remaining disintegrations occurred in spread, interphase cells. In cells disintegrating from the rounded configuration, the generation preceding disintegration was prolonged relative to that in cells which divided; in cells disintegrating from either configuration, the penultimate generation was also prolonged. The mitotic times were disproportionately increased in both of these generations. It is suggested that in this system X-ray damage is preferentially expressed as derangement of the mitotic process; such damage ultimately brings about permanent mitotic arrest in the majority of cells.     

Probing the Effector and Suppressive Functions of Human T Cell Subsets Using Antigen-Specific Engineered T Cell Receptors

Activation of T cells through the engagement of the T cell receptors (TCRs) with specific peptide-MHC complexes on antigen presenting cells (APCs) is the major determinant for their proliferation, differentiation and display of effector functions. To assess the role of quantity and quality of peptide-MHC presentation in eliciting T cell activation and suppression functions, we genetically engineered human T cells with two TCRs that recognize HLA-A*0201-restricted peptides derived from either HIV or melanoma antigens. The engineered-TCRs are highly functional in both CD8⁺ and CD4⁺ T cells as assessed by the upregulation of activation markers, induction of cytokine secretion and cytotoxicity. We further demonstrated that engineered-TCRs can also be expressed on naïve human T cells, which are stimulated through APCs presenting specific peptides to induce T cell proliferation and acquire effector functions. Furthermore, regulatory T cells (Tregs) ectopically expressing the engineered-TCRs are activated in an antigen-specific fashion and suppress T cell proliferation. In this system, the inhibitory activity of peptide-stimulated Tregs require the presence of dendritic cells (DCs) in the culture, either as presenters or as bystander cells, pointing to a critical role for DCs in suppression by Tregs. In conclusion, the engineered-TCR system reported here advances our ability to understand the differentiation pathways of naïve T cells into antigen-specific effector cells and the role of antigen-specific signaling in Treg-mediated immune suppression.     

An attenuated variant of Coxsackievirus B3 preferentially induces immunoregulatory T cells in vivo.

BALB/c mice infected with the Woodruff variant of coxsackievirus group B type 3 (CVB3W) develop myocarditis mediated by autoimmune cytolytic T lymphocytes. A variant of CVB3W (designated H3-10A1) which infects the myocardium but induces minimal mortality of myocarditis compared to the parental virus was selected. Although H3-10A1 infections stimulate normal CTL responses to CVB3-infected myocytes, the autoimmune response to myocardial antigens is absent. Treatment of H3-10A1-infected mice with 50 mg of cyclophosphamide per kg of body weight, a treatment which preferentially eliminates suppressor cells, allows both the development of the autoimmune cytotoxic T-lymphocyte response and the expression of myocarditis. Similar treatment of CVB3W-infected mice had no effect on the disease. The presence of the immunoregulatory cells was confirmed by adoptive transfer of T lymphocytes from either H3-10A1 or CVB3W-infected donor mice into syngeneic CVB3W-infected recipients. Animals given H3-10A1-immune cells had minimal myocardial inflammation, while animals given CVB3W-immune lymphocytes developed enhanced cardiac disease. Elimination of the T-lymphocyte population from the donor cells prior to transfer abrogated suppression with the H3-10A1-immune population, showing that immunoregulation depended upon T lymphocytes. Both H3-10A1 and CVB3W have cross-reactive epitopes between the adenine translocator protein and the virion which are indicative of antigenic mimicry and may be the basis for the autoimmunity to cardiac antigens. These results suggest that immunoregulatory T cells may be primarily responsible for the nonpathogenicity of the H3-10A1 variant.     

Overexpression of 4EBP1, p70S6K,Akt1 or Akt2 differentially promotes Coxsackievirus B3-induced apoptosis in HeLa cells

Our previous studies have shown that the inhibition of phosphatidylinositol 3-kinase (PI3K) or mTOR complex 1 can obviously promote the Coxsackievirus B3 (CVB3)-induced apoptosis of HeLa cells by regulating the expression of proapoptotic factors. To further illustrate it, Homo sapiens eIF4E-binding protein 1 (4EBP1), p70S6 kinase (p70S6K), Akt1 and Akt2 were transfected to HeLa cells, respectively. And then, we established the stable transfected cell lines. Next, after CVB3 infection, apoptosis in different groups was determined by flow cytometry; the expressions of Bim, Bax, caspase-9 and caspase-3 were examined by real-time fluorescence quantitative PCR and western blot analysis; the expression of CVB3 mRNA and viral capsid protein VP1 were also analyzed by real-time fluorescence quantitative PCR, western blot analysis and immunofluorescence, respectively. At the meantime, CVB3 replication was observed by transmission electron microscope. We found that CVB3-induced cytopathic effect and apoptosis in transfected groups were more obvious than that in controls. Unexpectedly, apoptosis rate in Akt1 group was higher than others at the early stage after viral infection and decreased with the viral-infected time increasing, which was opposite to other groups. Compared with controls, the expression of CVB3 mRNA was increased at 3, 6, 12 and 24 h postinfection (p. i.) in all groups. At the meantime, VP1 expression in 4EBP1 group was higher than control during the process of infection, while the expressions in the other groups were change dynamically. Moreover, overexpression of 4EBP1 did not affect the mRNA expressions of Bim, Bax, caspase-9 and caspase-3; while protein expressions of Bim and Bax were decreased, the self-cleavages of caspase-9 and caspase-3 were stimulated. Meanwhile, overexpression of p70S6K blocked the CVB3-induced Bim, Bax and caspase-9 expressions but promoted the self-cleavage of caspase-9. In the Akt1 group, it is noteworthy that the expressions of Bim protein were higher than controls at 3 and 6 h p. i. but lower at 24 h p. i., and the expression of Bax protein were higher at 6 and 24 h p. i., while their mRNA expressions were all decreased. Furthermore, overexpression of Akt1 stimulated the procaspase-9 and procaspase-3 expression but blocked their self-cleavages. Overexpression of Akt2, however, had little effect on Bim, Bax and caspase-3, while prevented caspase-9 from self-cleavage at the late stage of CVB3 infection. As stated above, our results demonstrated that overexpression of 4EBP1, p70S6K, Akt1 or Akt2 could promote the CVB3-induced apoptosis in diverse degree via different mediating ways in viral replication and proapoptotic factors in BcL-2 and caspase families. As 4EBP1, p70S6K and Akt are the important substrates of PI3K and mammalian target of rapamycin (mTOR), we further illustrated the role of PI3K/Akt/mTOR signaling pathway in the process of CVB3-induced apoptosis.     

Coxsackievirus B Exits the Host Cell in Shed Microvesicles Displaying Autophagosomal Markers

Coxsackievirus B3 (CVB3), a member of the picornavirus family and enterovirus genus, causes viral myocarditis, aseptic meningitis, and pancreatitis in humans. We genetically engineered a unique molecular marker, “fluorescent timer” protein, within our infectious CVB3 clone and isolated a high-titer recombinant viral stock (Timer-CVB3) following transfection in HeLa cells. “Fluorescent timer” protein undergoes slow conversion of fluorescence from green to red over time, and Timer-CVB3 can be utilized to track virus infection and dissemination in real time. Upon infection with Timer-CVB3, HeLa cells, neural progenitor and stem cells (NPSCs), and C2C12 myoblast cells slowly changed fluorescence from green to red over 72 hours as determined by fluorescence microscopy or flow cytometric analysis. The conversion of “fluorescent timer” protein in HeLa cells infected with Timer-CVB3 could be interrupted by fixation, suggesting that the fluorophore was stabilized by formaldehyde cross-linking reactions. Induction of a type I interferon response or ribavirin treatment reduced the progression of cell-to-cell virus spread in HeLa cells or NPSCs infected with Timer-CVB3. Time lapse photography of partially differentiated NPSCs infected with Timer-CVB3 revealed substantial intracellular membrane remodeling and the assembly of discrete virus replication organelles which changed fluorescence color in an asynchronous fashion within the cell. “Fluorescent timer” protein colocalized closely with viral 3A protein within virus replication organelles. Intriguingly, infection of partially differentiated NPSCs or C2C12 myoblast cells induced the release of abundant extracellular microvesicles (EMVs) containing matured “fluorescent timer” protein and infectious virus representing a novel route of virus dissemination. CVB3 virions were readily observed within purified EMVs by transmission electron microscopy, and infectious virus was identified within low-density isopycnic iodixanol gradient fractions consistent with membrane association. The preferential detection of the lipidated form of LC3 protein (LC3 II) in released EMVs harboring infectious virus suggests that the autophagy pathway plays a crucial role in microvesicle shedding and virus release, similar to a process previously described as autophagosome-mediated exit without lysis (AWOL) observed during poliovirus replication. Through the use of this novel recombinant virus which provides more dynamic information from static fluorescent images, we hope to gain a better understanding of CVB3 tropism, intracellular membrane reorganization, and virus-associated microvesicle dissemination within the host.     

Distinct Human and Mouse Membrane Trafficking Systems for Sweet Taste Receptors T1r2 and T1r3

The sweet taste receptors T1r2 and T1r3 are included in the T1r taste receptor family that belongs to class C of the G protein-coupled receptors. Heterodimerization of T1r2 and T1r3 is required for the perception of sweet substances, but little is known about the mechanisms underlying this heterodimerization, including membrane trafficking. We developed tagged mouse T1r2 and T1r3, and human T1R2 and T1R3 and evaluated membrane trafficking in human embryonic kidney 293 (HEK293) cells. We found that human T1R3 surface expression was only observed when human T1R3 was coexpressed with human T1R2, whereas mouse T1r3 was expressed without mouse T1r2 expression. A domain-swapped chimera and truncated human T1R3 mutant showed that the Venus flytrap module and cysteine-rich domain (CRD) of human T1R3 contain a region related to the inhibition of human T1R3 membrane trafficking and coordinated regulation of human T1R3 membrane trafficking. We also found that the Venus flytrap module of both human T1R2 and T1R3 are needed for membrane trafficking, suggesting that the coexpression of human T1R2 and T1R3 is required for this event. These results suggest that the Venus flytrap module and CRD receive taste substances and play roles in membrane trafficking of human T1R2 and T1R3. These features are different from those of mouse receptors, indicating that human T1R2 and T1R3 are likely to have a novel membrane trafficking system.     

B7-H1 and a Mathematical Model for Cytotoxic T Cell and Tumor Cell Interaction

The surface protein B7-H1, also called PD-L1 and CD274, is found on carcinomas of the lung, ovary, colon, and melanomas but not on most normal tissues. B7-H1 has been experimentally determined to be an antiapoptotic receptor on cancer cells, where B7-H1-positive cancer cells have been shown to be immune resistant, and in vitro experiments and mouse models have shown that B7-H1-negative tumor cells are significantly more susceptible to being repressed by the immune system. We derive a new mathematical model for studying the interaction between cytotoxic T cells and tumor cells as affected by B7-H1. By integrating experimental data into the model, we isolate the parameters that control the dynamics and obtain insights on the mechanisms that control apoptosis.     

Expression and Purification of Recombinant 3C Proteinase of Coxsackievirus B3

We have cloned various lengths of coxsackievirus B3 cDNA encompassing the region encoding the 3C proteinase, which is essential to the viral replication cycle. Such viral cDNAs were fused in frame to the 5′terminal portion of the lacZ’ gene carried on the vector pUCl18 to express mature 3C proteinase in Escherichia coli. In the E. coli cells containing pCXB108 or pCXB117, constructed for this study, a large amount of 23-kDa protein was synthesized in the presence of IPTG. This protein was purified and was shown to be intact 3C proteinase. These data suggest that 3C proteinase, expressed as a part of a fusion protein, was active in E. coli and released itself from the precursor fusion protein by autocatalytic cleavage.     

Time-Lapse Cinemicrographic Studies of X-Irradiated HeLa S3 Cells: II. Cell Fusion

Analysis of time-lapse cinemicrographs of X-irradiated HeLa S3 cells has shown that the incidence of cell fusion was increased from 0.9% (following 1267 divisions) in control cells to an average of 22% (following 655 divisions) in cells irradiated with 500 rad doses of 220 kv X-rays. The incidence depended on the stage of the generation cycle at which the parent cells were irradiated. It was nearly constant in the first three postirradiation generations. Fusion occurred at all stages of the generation cycle, but preferentially during the first 20%. Cells undergoing fusion progressed more slowly through the generation cycle and had a higher probability of disintegrating than did irradiated cells that did not fuse. The occurrence of fusion was clonally distributed in the population. It took place only between sister (or closely related) cells. Protoplasmic bridges were often visible between sister cells prior to fusion. Giant cells arose only as a result of fusion. The incidence of multipolar divisions, though higher than in unirradiated cells, was only 5.5% in cultures irradiated with 500 rads. Fusion occurred following 85% of the multipolar divisions and was often followed by a multipolar division.