Down syndrome (DS) is a genetic disorder caused by the presence of an extra partial or whole copy of chromosome 21. In addition to musculoskeletal and neurodevelopmental abnormalities, children with DS exhibit various hematologic disorders and have an increased risk of developing acute lymphoblastic leukemia and acute megakaryocytic leukemia. Using the Ts65Dn mouse model, we investigated bone marrow defects caused by trisomy for 132 orthologs of the genes on human chromosome 21. The results showed that, although the total bone marrow cellularity as well as the frequency of hematopoietic progenitor cells (HPCs) was comparable between Ts65Dn mice and their age-matched euploid wild-type (WT) control littermates, human chromosome 21 trisomy led to a significant reduction in hematopoietic stem cell (HSC) numbers and clonogenic function in Ts65Dn mice. We also found that spontaneous DNA double-strand breaks (DSBs) were significantly increased in HSCs from the Ts65Dn mice, which was correlated with the significant reduction in HSC clonogenic activity compared to those from WT controls. Moreover, analysis of the repair kinetics of radiation-induced DSBs revealed that HSCs from Ts65Dn mice were less proficient in DSB repair than the cells from WT controls. This deficiency was associated with a higher sensitivity of Ts65Dn HSCs to radiation-induced suppression of HSC clonogenic activity than that of euploid HSCs. These findings suggest that an additional copy of genes on human chromosome 21 may selectively impair the ability of HSCs to repair DSBs, which may contribute to DS-associated hematological abnormalities and malignancies.

ABSTRACT During cell entry, native poliovirus (160S) converts to a cell-entry intermediate (135S) particle, resulting in the externalization of capsid proteins VP4 and the amino terminus of VP1 (residues 1 to 53). Externalization of these entities is followed by release of the RNA genome (uncoating), leaving an empty (80S) particle. The antigen-binding fragment (Fab) of a monospecific peptide 1 (P1) antibody, which was raised against a peptide corresponding to amino-terminal residues 24 to 40 of VP1, was utilized to track the location of the amino terminus of VP1 in the 135S and 80S states of poliovirus particles via cryogenic electron microscopy (cryo-EM) and three-dimensional image reconstruction. On 135S, P1 Fabs bind to a prominent feature on the external surface known as the “propeller tip.” In contrast, our initial 80S-P1 reconstruction showed P1 Fabs also binding to a second site, at least 50 Å distant, at the icosahedral 2-fold axes. Further analysis showed that the overall population of 80S-P1 particles consisted of three kinds of capsids: those with P1 Fabs bound only at the propeller tips, P1 Fabs bound only at the 2-fold axes, or P1 Fabs simultaneously bound at both positions. Our results indicate that, in 80S particles, a significant fraction of VP1 can deviate from icosahedral symmetry. Hence, this portion of VP1 does not change conformation synchronously when switching from the 135S state. These conclusions are compatible with previous observations of multiple conformations of the 80S state and suggest that movement of the amino terminus of VP1 has a role in uncoating. Similar deviations from icosahedral symmetry may be biologically significant during other viral transitions.

Disparities in breast cancer survival rates suggest that biological processes contribute. Translational research addressing health disparities would benefit from using a community-based participatory approach (CBPR) to examine biological processes commonly seen as the proximal causes of illness as well as behavioral and social-ecological “causes of the causes” within an integrated conceptual framework. This paper describes a CBPR study that explored perceptions regarding breast cancer relevant behaviors, and the application of the study’s results to develop translational research. Data from eight focus groups of African American ( n = 29) and Caucasian women ( n = 27) were analyzed, using the framework of the social-ecological model. Nutrition and physical activity were valued over screening and research participation. Treatment of illness was emphasized over prevention. Women’s perspectives are presented within a framework that facilitated the collaborative development of translational research to examine associations among biological, behavioral, and societal processes contributing to disparities.

We have used multiplexed high-throughput sequencing to characterize changes in small RNA populations that occur during viral infection in animal cells. Small RNA-based mechanisms such as RNA interference (RNAi) have been shown in plant and invertebrate systems to play a key role in host responses to viral infection. Although homologs of the key RNAi effector pathways are present in mammalian cells, and can launch an RNAi-mediated degradation of experimentally targeted mRNAs, any role for such responses in mammalian host-virus interactions remains to be characterized. Six different viruses were examined in 41 experimentally susceptible and resistant host systems. We identified virus-derived small RNAs (vsRNAs) from all six viruses, with total abundance varying from "vanishingly rare" (less than 0.1% of cellular small RNA) to highly abundant (comparable to abundant micro-RNAs "miRNAs"). In addition to the appearance of vsRNAs during infection, we saw a number of specific changes in host miRNA profiles. For several infection models investigated in more detail, the RNAi and Interferon pathways modulated the abundance of vsRNAs. We also found evidence for populations of vsRNAs that exist as duplexed siRNAs with zero to three nucleotide 3' overhangs. Using populations of cells carrying a Hepatitis C replicon, we observed strand-selective loading of siRNAs onto Argonaute complexes. These experiments define vsRNAs as one possible component of the interplay between animal viruses and their hosts.

The majority of pathogen vaccines are used within the prophylactic setting as opposed to the therapeutic setting proposed for cancer vaccines. Due to the intricate role of the immune system in tumorigenesis, tumor immunotherapy may have to borrow approaches from autoimmunity. The size of the malignant population that has to be eliminated, the associated immunosuppressive effects of the tumor, the diversion of inflammatory and immune processes by the organized stroma surrounding the tumor, the antigenic diversity of the tumor cell population leading to immune escape, all present barriers that predestine the failure of most attempts for active immunotherapy. Tumor immune suppression necessitates adhering to the adjuvant mode of immunotherapy, i.e. after the removal of large tumor masses. Understanding immune tolerance as active, threshold dependent and redundant processes helps to rationalize the reshaping and repair, rather than breaking, of tolerance as a tumor immunotherapy objective. Instead of true vaccines, the emerging concept is rather of immunomodulators that target the interface of innate and adaptive immunity.

The induction of high affinity antibodies capable of broad neutralization and protection against infection and/or disease is a major goal in the development of a vaccine for human immunodeficiency virus (HIV). Insights into the structure and function of the envelope (Env) protein of HIV-1 suggest that the virus is under strong selection pressure by the immune response leading to constant mutations in the Env protein including the N-glycosylation sites. Initially considered a shield against the immune system, the heavily glycosylated outer surface of the HIV Env protein has drawn attention lately as a legitimate target. The dense cluster of high mannose glycans and the great variety of complex glycans present epitopes that might impact on disease progression. Indeed a number of mannose binding proteins and at least one human anti-mannose antibody - 2G12, are broadly neutralizing. Due to the low immunogenicity of carbohydrates, these targets on HIV are of limited value unless new powerful immunogens are found. One approach would be the molecular design of peptide carbohydrate mimotopes that can elicit neutralizing antibodies by recruiting optimal T cell help. Here we review existing data on carbohydrate interactions and HIV immunogenicity that serves as a basis for structural concepts and approaches used for vaccine design targeting HIV associated carbohydrate antigens. In particular, the value and the limitations of chemical (peptide libraries), structural and immunological information is illustrated.

The task of rationally designing vaccines that can effectively impact on the survival of cancer patients remains challenging. Monoclonal antibodies and T cell receptors have proven to be viable templates for the application of pharmacophore design principles to develop antigens and immunogens as these immune system molecules recognize a variety of sequentially and structurally unrelated ligands. This structural information combined with immunological assessment has contributed to the development of strategies to elicit effective humoral and cellular responses to cancer cells. Understanding the structural requirements for antibody and T cell recognition provides a basis for identifying potentially new sets of immunogens that may have both fundamental immunological and clinical value. Here we review the structural concepts and approaches used in vaccine design applications that illustrate the value and limitations of using chemical (peptide libraries) and immunological information to define novel peptide immunogens that function as mimotopes to generate immune responses targeting tumor associated carbohydrate antigens.

Super model for viruses The nematode Caenorhabditis elegans is an ideal model for the study of many aspects of cell biology, including the hot topic of RNA interference (RNAi). But there was a problem in using the worm to study antiviral RNAi responses: C. elegans seemed not to support viral replication. But now the insect pathogen Flock house virus and the mammalian pathogen vesicular stomatitis virus are both shown to infect the worm, and to provoke a strong RNAi-based antiviral defence. So this important genetic model is now available for the study of host–virus interactions, and the antiviral effect of RNAi.

ABSTRACTExpression of the poliovirus receptor (PVR) on cells is a major host determinant of infection by poliovirus. Previously, the only immune cell type known to express PVR was the blood-derived monocyte, which is susceptible to infection at very low frequency. We demonstrate that professional antigen-presenting cells—macrophages and dendritic cells, generated upon differentiation of monocytes—retain expression of PVR and are highly susceptible to infection by type 1 Mahoney strain of poliovirus. Maximal cell-associated titers of virus are obtained within 6 to 8 h postinfection, and cell death and lysis occurs within 24 h postinfection. Similar kinetics are observed in cells infected with the Sabin 1 vaccine strain. Although protein synthesis and receptor-mediated endocytosis are inhibited upon poliovirus infection of these critical antigen-presenting cells, we demonstrate for the first time that functional presentation of antigen occurs in these infected cells via the HLA class II pathway.

Poliovirus (PV) infection starts with binding to its receptor (PVR), followed by a receptor-aided, temperature-sensitive conformational change of the infectious particle (sedimenting at 160S) to a particle which sediments at 135S. Reported in this communication is the successful incorporation into lipid bilayers of two forms of the receptor: the full-length human receptor and a modified clone in which the extracellular domains of the receptor were fused to a glycosylphosphatidylinositol tail. Addition of virus (160S) to receptor-containing bilayers leads to channel formation, whereas no channels were observed when the receptor-modified viral particle (135S) was added. Increasing the temperature from 21 to 31 degreesC led to a 10-fold increase in the magnitude of the single channel conductance, which can be interpreted as a conformational change in the channel structure. A mutant PV with an amino acid change in VP4 (one of the coat proteins) which is defective in genome uncoating failed to produce channels, suggesting that VP4 might be involved in the channel architecture. These studies provide the first electrophysiological characterization of the interactions between poliovirus and its receptor incorporated into a lipid bilayer membrane. Furthermore, they form the foundation for future studies aiming at defining the molecular architecture of the virus-receptor complex.

During entry into host cells, poliovirus undergoes a receptor-mediated conformational transition to form 135S particles with irreversible exposure of VP4 capsid sequences and VP1 N termini. To understand the role of VP4 during virus entry, the fate of VP4 during infection by site-specific mutants at threonine-28 of VP4 (4028T) was compared with that of the parental Mahoney type 1 virus. Three virus mutants were studied: the entry-defective, nonviable mutant 4028T.G and the viable mutants 4028T.S and 4028T.V, in which residue threonine-28 was changed to glycine, serine, and valine, respectively. We show that mutant and wild-type (WT) VP4 proteins are localized to cellular membranes after the 135S conformational transition. Both WT and viable 4028T mutant particles interact with lipid bilayers to form ion channels, whereas the entry-defective 4028T.G particles do not. In addition, the electrical properties of the channels induced by the mutant viruses are different from each other and from those of WT Mahoney and Sabin type 3 viruses. Finally, uncoating and/or cytoplasmic delivery of the viral genome is altered in the 4028T mutants: the 4028T.G lethal mutant does not release its genome into the cytoplasm, and genome delivery is slower during infection by mutant 4028T.V 135S particles than by mutant 4028T.S or WT 135S particles. The distinctive electrical characteristics of the different 4028T mutant channels indicate that VP4 sequences might form part of the channel structure. The different entry phenotypes of these VP4 mutants suggest that the ion channels may be related to VP4's role during genome uncoating and/or delivery.

ABSTRACT As an opportunistic bacterial pathogen, Pseudomonas aeruginosa mainly affects immunocompromised individuals as well as patients with cystic fibrosis. In a previous study, we showed that ExoS of P . aeruginosa , when injected into host cells through a type III secretion apparatus, functions as an effector molecule to trigger apoptosis in various tissue culture cells. Here, we show that injection of the ExoS into HeLa cells activates c-Jun NH 2 -terminal kinase (JNK) phosphorylation while shutting down ERK1/2 and p38 phosphorylation. Inhibiting JNK activation by expression of a dominant negative JNK1 or with a specific JNK inhibitor abolishes ExoS-triggered apoptosis, demonstrating the requirement for JNK-mediated signaling. Following JNK phosphorylation, cytochrome c is released into the cytosol, leading to the activation of caspase 9 and eventually caspase 3. Although c-Jun phosphorylation is also observed as a result of JNK activation, ongoing host protein synthesis is not essential for the apoptotic induction, suggesting that c-Jun- or other AP-1-driven activation of gene expression is dispensable in this process. Therefore, ExoS has opposing effects on different cellular pathways that regulate apoptosis: it shuts down host cell survival signal pathways by inhibiting ERK1/2 and p38 activation, and it activates proapoptotic pathways through activation of JNK1/2 leading ultimately to cytochrome c release and activation of caspases. These results highlight the modulation of host cell signaling by the type III secretion system during interaction between P . aeruginosa and host cells.

Pseudomonas aeruginosa is an opportunistic bacterial pathogen that primarily infects immunocompromised individuals and patients with cystic fibrosis. Using a tissue culture system, invasive strains of P. aeruginosa were discovered to induce apoptosis at high frequency in HeLa and other epithelial and fibroblast cell lines. This apoptotic phenotype in the infected cells was determined by several criteria including (i) visual changes in cell morphology, (ii) induction of chromatin condensation and nuclear marginalization, (iii) the presence of a high percentage of cells with subG1 DNA content, and (iv) activation of caspase-3 activity. Induction of the type III secretion machinery, but not invasion of P. aeruginosa is required for induction of apoptosis. The apoptosis phenotype is independent of the cytoskeletal rearrangements that occur in the host cell early after infection. Mutants in P. aeruginosa exoS fail to induce apoptosis and complementation with wild-type exoS restored the apoptosis-inducing capacity, demonstrating that ExoS is the effector molecule. Analysis of exoS activity mutants shows that the ADP-ribosylating capacity of ExoS is essential for inducing the apoptotic pathway.

A combination of structural and genetic studies of poliovirus suggests that the final stages of viral assembly lock the virus in a metastable structure primed to undergo the receptor-catalyted conformational changes required for cell entry. Future studies promise to provide detailed insights into the conformational dynamics of the virion during its life cycle.

Both the prevalence of lipid modifications of proteins and their importance for protein function and cellular localization have been widely observed. The advances made during the past year in defining the enzymology of lipid addition and in understanding the biological consequences of these modifications on protein function are discussed.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTIonically crosslinkable polyphosphazene: a novel polymer for microencapsulationSmadar Cohen, M. Carmen Bano, Karyn B. Visscher, Marie Chow, Harry R. Allcock, and Robert LangerCite this: J. Am. Chem. Soc. 1990, 112, 21, 7832–7833Publication Date (Print):October 1, 1990Publication History Published online1 May 2002Published inissue 1 October 1990https://doi.org/10.1021/ja00177a074RIGHTS & PERMISSIONSArticle Views591Altmetric-Citations115LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts