Involvement Of Cellular Factors Research Articles

Protein-Protein Interactions in RSV Assembly: Potential Targets for Attenuating RSV Strains

Respiratory syncytial virus (RSV) is the major respiratory pathogen of infants and children worldwide, with no effective treatment or vaccine available. Steady progress has been made in understanding the respiratory syncytial virus lifecycle and the consequences of infection, but some areas of RSV still remain poorly understood. Although many of the interactions between virus proteins that are required for efficient RSV assembly have been elucidated, many questions still remain regarding viral assembly, as well as the mechanisms of RSV budding. This review will summarise the current understanding of RSV assembly, including the various interactions between virus proteins and the involvement of cellular factors with a view to identifying possible attenuation and/or drug targets within the assembly pathway.

Diverse Enveloped Viruses Fail to Undergo Complete Fusion with the Cell Plasma Membrane

Recent work from our laboratory (Miyauchi et al. 2009, Cell 137:433-444) provided functional evidence for HIV-1 entry via an endocytic pathway. In contrast, HIV-1 fusion with the plasma membrane (PM) did not proceed beyond the lipid mixing step. We have therefore assessed the ability of other enveloped viruses to fuse with the PM of permissive cells. Imaging of single amphotropic Murine Leukemia Virus particles revealed complete endoplasmic fusion with occasional lipid mixing at the PM. Next, we tested whether low pH-dependent viruses can be forced to fuse with the PM by lowering the external pH. When retroviral cores pseudotyped with the Semliki Forest Virus E1E2 glycoproteins were bound to cells and exposed to acidic pH, lipid mixing, but not viral content transfer was observed. Likewise, Avian Sarcoma and Leukosis Virus (ASLV) that enters target cells via a receptor-mediated endocytosis followed by low pH-induced fusion with endosomes failed to release its content at the PM upon reducing the pH. These results demonstrate a surprisingly strong preference for endosomal fusion among pH-dependent and pH-independent viruses, suggesting the existence of a fusion block at the PM and/or the involvement of an endosomal factor(s) facilitating the viral fusion. Consistent with the latter mechanism, inhibition of the dynamin function blocked endosomal fusion of HIV-1, ASLV and several other viruses. Together, these results are consistent with the involvement of cellular factors in facilitating the viral entry via endosomes. Supported by NIH grants GM054787 and AI053668.

P.065 Involvement of cellular factors during the respiratory vaccinia virus entry in the lung

P.065 Involvement of cellular factors during the respiratory vaccinia virus entry in the lung

The intriguing prion disorders

Prion diseases are among the most intriguing illnesses. Despite their rare incidence, they have captured enormous attention from the scientific community and general public. One of the most hotly debated issues in these diseases is the nature of the infectious material. In recent years increasing evidence has emerged supporting the protein-only hypothesis of prion transmission. In this model PrPSc (the pathological isoform of the prion protein, PrPC) represents the sole component of the infectious particle. However, uncertainties about possible additional factors involved in the conversion of PrPC into PrPSc remain despite extensive attempts to isolate and characterize these elusive components. In this article, we review recent developments concerning the protein-only hypothesis as well as the possible involvement of cellular factors in PrPC to PrPSc conformational change and their influence on the pathogenesis of prion diseases.

Anti-human immunodeficiency virus activity of tau interferon in human macrophages: involvement of cellular factors and beta-chemokines.

Tau interferon (IFN-tau) is a noncytotoxic type I IFN responsible for maternal recognition of the fetus in ruminants. IFN-tau inhibits human immunodeficiency virus (HIV) replication more strongly than human IFN-alpha, particularly in human monocyte-derived macrophages. In this study performed in human macrophages, IFN-tau efficiently inhibited the early steps of the biological cycle of HIV, decreasing intracellular HIV RNA and inhibiting the initiation of the reverse transcription of viral RNA into proviral DNA. Two mechanisms induced by IFN-tau treatment in macrophages may account for this inhibition: (i) the synthesis of the cellular antiviral factors such as 2',5'-oligoadenylate synthetase/RNase L and MxA protein and (ii) an increased production of MIP-1alpha, MIP-1beta, and RANTES, which are natural ligands of CCR5, the principal coreceptor of HIV on macrophages. Our results suggest that IFN-tau induces the same antiviral pathways in macrophages as other type I IFNs but without associated toxicity.

Adenovirus 12-mediated down-regulation of the major histocompatibility complex (MHC) class I promoter: identification of a negative regulatory element responsive to Ad12 E1A.

In highly oncogenic adenovirus (Ad) 12-transformed cells, major histocompatibility complex (MHC) class I gene expression is down-regulated by the products of the viral E1A oncogene at the level of initiation of transcription. However, class I gene expression is unaltered or elevated in non-oncogenic Ad2- or Ad5-transformed cells. These changes in class I expression may permit Ad12-transformed cells to escape host immune surveillance and elicit tumour formation. Here we show that the 2kb of 5' flanking region of the mouse H-2Kb class I gene is sufficient to mediate down-regulation of transcription driven from homologous or heterologous (HSV thymidine kinase) basal promoter elements in cells expressing Ad12 E1A, but not in Ad2 E1A-expressing cells. Deletion analysis of the 2kb region showed that sequences from -1.18 to -1.44kb (relative to the cap site) were a target for Ad12 E1A-mediated transcriptional down-regulation. Deletion of this entire region from the 2kb flanking sequence of the H-2Kb gene abolished Ad12 E1A-mediated down-regulation of transcription. Computer analysis of the -1.18 to -1.44kb sequence identified two 6/7bp matches with the AP-1 transcription factor consensus sequence and two matches with the pig MHC class I PD1 repressor element. Gel retardation analysis using overlapping DNA fragments derived from the -1.18 to -1.44kb sequence revealed several DNA:protein complexes formed using nuclear extract derived from Ad12-, but not from Ad2- or Ad5-transformed cells. Some of these DNA:protein complexes were also present, but at lower levels, in nuclear extracts from untransformed rat cells suggesting the possible involvement of cellular factors in the mechanism of down-regulation mediated by Ad12 E1A. A binding site for the AP-1 factor failed to compete for protein binding to fragments within the -1.18 to -1.44 sequence, while the PD1 site competed for binding only in the -1.15 to -1.23 region. These results indicate that novel factors (as well as a previously identified class I repressor, PD1) may be involved in Ad12 E1A-mediated down-regulation of MHC class I transcription.