In this task, you're given a paragraph from the research paper and your task is to generate a suitable title for the research paper based on the given paper. Under 100 words is a good title length.
--------
Question: Murine norovirus-1 (MNV-1) is known to subvert host cell division inducing an accumulation of cells in the G 0 /G 1 phase, creating conditions where viral replication is favored. This study identified that NS5 (VPg), is capable of inducing cell cycle arrest in the absence of viral replication or other viral proteins in an analogous manner to MNV-1 infection. NS5 expression induced an accumulation of cells in the G 0 /G 1 phase in an asynchronous population by inhibiting progression at the G 1 /S restriction point. Furthermore, NS5 expression resulted in a down-regulation of cyclin A expression in asynchronous cells and inhibited cyclin A expression in cells progressing from G 1 to S phase. The activity of NS5 on the host cell cycle occurs through an uncharacterized function. Amino acid substitutions of NS5(Y26A) and NS5(F123A) that inhibit the ability for NS5 to attach to RNA and recruit host eukaryotic translation initiation factors, respectively, retained the ability to induce an accumulation of cells in the G 0 /G 1 phase as identified for wild-type NS5. To the best of our knowledge, this is the first report of a VPg protein manipulating the host cell cycle.

Answer: Expression of the NS5 (VPg) Protein of Murine Norovirus Induces a G1/S Phase Arrest


Question: Among RNA viruses, the order Nidovirales stands out for including viruses with the largest RNA genomes currently known. Nidoviruses employ a complex RNAsynthesizing machinery comprising a variety of non-structural proteins (nsps). One of the postulated drivers of the expansion of nidovirus genomes is the presence of a proofreading 3 -to-5 exoribonuclease (ExoN) belonging to the DEDDh family. ExoN may enhance the fidelity of RNA synthesis by correcting nucleotide incorporation errors made by the RNA-dependent RNA polymerase. Here, we review our current understanding of ExoN evolution, structure, and function. Most experimental data are derived from studies of the ExoN domain of coronaviruses (CoVs), which were triggered by the bioinformatics-based identification of ExoN in the genome of severe acute respiratory syndrome coronavirus (SARS-CoV) and its relatives in 2003. Although convincing data supporting the proofreading hypothesis have been obtained, from biochemical assays and studies with CoV mutants lacking ExoN functionality, the features of ExoN from most other nidovirus families remain to be characterized. Remarkably, viable ExoN knockout mutants were obtained only for two CoVs, mouse hepatitis virus (MHV) and SARS-CoV, whose RNA synthesis and replication kinetics were mildly affected by the lack of ExoN function. In several other CoV species, ExoN inactivation was not tolerated, and knockout mutants could not be rescued when launched using a reverse genetics system. This suggests that ExoN is also critical for primary viral RNA synthesis, a property that poorly matches the profile of an enzyme that would merely boost longterm replication fidelity. In CoVs, ExoN resides in a bifunctional replicase subunit (nsp14) whose C-terminal part has (N7-guanine)-methyltransferase activity. The crystal structure of SARS-CoV nsp14 has shed light on the interplay between these two domains, and on nsp14's interactions with nsp10, a co-factor that strongly enhances ExoN activity in vitro assays. Further elucidation of the structure-function relationships of ExoN and its interactions with other (viral and/or host) members of the CoV replication machinery will be key to understanding the enzyme's role in viral RNA synthesis and pathogenesis, and may contribute to the design of new approaches to combat emerging nidoviruses.

Answer: The Curious Case of the Nidovirus Exoribonuclease: Its Role in RNA Synthesis and Replication Fidelity


Question: BACKGROUND-HIV-1-infected mononuclear phagocytes release soluble factors that affect the homeostasis in tissue. HIV-1 can prompt metabolic encephalopathy with the addition of neuronal dysfunction and apoptosis. Recently, we reported that HIV-1 enhances the expression and secretion of bioactive cathepsin B in monocyte-derived macrophages, ultimately contributing to neuronal apoptosis. In this research, we request if microglia respond to HIV infection similarly by modifying the expression, secretion, neurotoxic potential of cathepsin B and the in vivo relevance of these findings. METHODS-HIV-ADA infected human primary microglia and CHME-5 were assessed for expression and activity of cathepsin B, its inhibitors, cystatins B and C, and neurotoxicity associated with these changes. Human primary neurons were exposed to supernatants from HIVinfected and uninfected microglia in the presence of cathepsin B inhibitors and apoptosis was assessed by TUNEL. Microglial expression of cathepsin B was validated in brain tissue from HIVE patients. microglia secreted significantly greater levels of cathepsin B, cystatin B, and cystatin C compared to uninfected cells. Increased apoptosis was observed in neurons exposed to supernatants from HIV-1 infected microglia at days 12 post-infection. The cathepsin B inhibitor CA-074 and cathepsin B antibody prevented neuronal apoptosis. Increased microgliaderived cathepsin B, cystatin B, and cystatin C and caspase-3+ neurons were detected in HIVE brains compared to controls. CONCLUSIONS-Our results suggest that HIV-1-induced cathepsin B production in microglia contributes to neuronal apoptosis and may be an important factor in neuronal death associated with HIVE. Human primary neuron and microglia isolation and culture-Human primary neurons and microglia were provided by Temple University's Comprehensive NeuroAIDS Center. Fetal brain tissue (gestational age 16-18 weeks) was obtained from elective abortion procedures performed in full compliance with National Institutes of Health and Temple University ethical guidelines. The tissue was washed with cold Hanks balanced salt solution (HBSS) and meninges and blood vessels were removed as previously described [Huang et al, 2011; Ghorpade et al, 1998].. For microglia, brain tissue was supplemented with Ca 2+ and Mg 2+ and then digested with 0.25% trypsin (Sigma) for 30 min at 37°C. Trypsin was neutralized with fetal bovine serum (FBS), and the tissue was further dissociated to obtain single-cell suspensions. The cells were cultured in DMEM (Sigma), supplemented with a mixture containing 10% heat-inactivated FBS, 1,000 U of purified recombinant human macrophage colony stimulating factor (MCSF) per ml, penicillin and streptomycin (50 mg/ ml), and 100 mg/ml of neomycin. The mixed culture was maintained under 5% CO 2 for 7 days, and the medium was fully replaced to remove any cell debris. The microglia cells released with further incubation were collected and purified by preferential adhesion. Microglia were seeded as an adherent monolayer at a density of 3 × 10 6 cells/well in a 6well plate and floating cells were removed after 4h. For neurons, tissue in HBSS was digested with papain (Sigma-Aldrich, St. Louis, MO) for 30 min at 37°C. Tissue was then dissociated to obtain single-cell suspensions by repeated pipetting with small bore fire polished glass Pasteur pipettes. Cells were plated in poly-D lysine-coated dishes at a density of ~ 1.8 × 10 6 cells/60mm dish in neurobasal media with B27 supplement, horse serum, and gentamicin (Invitrogen). After 2hr of attachment, media was replaced with fresh complete neurobasal media. Twenty-four hours later, cultures were replaced with neurobasal media without horse serum. Four days later, one fourth of the media was removed and replaced with neurobasal media supplemented with fluorodeoxyuridine (FDU) and uridine. Following FDU treatment, neurons were cultured in neurobasal medium with Glutamax and B27 supplement. One half volume of media was replaced every 48h. Purity of cell type specific cultures was assessed by immunolabeling for cell-type specific markers, including Iba-1 for microglia, GFAP for astrocyte and MAP2, neurofilament, and synaptophysin for neurons. CHME-5 microglia-The microglia cell line CHME-5 was kindly provided by Dr. Randal Davis from Oklahoma State University. It was originally obtained from human fetal microglia (Peudenier et al. 1991) transfected with the T-antigen of SV-40 virus (Janabi et al. 1995). Cells were cultured to 70% confluence in Dulbecco's modified Eagle's medium (DMEM) (Sigma Chemical Company, St. Louis, MO) supplemented with 5% inactivated Zenón et al.

Answer:
HIV-infected microglia mediate cathepsin B induced neurotoxicity