scholarly journals Replication of Alphaviruses: A Review on the Entry Process of Alphaviruses into Cells

2011 ◽  
Vol 2011 ◽  
pp. 1-9 ◽  
Author(s):  
Jason Yat-Sing Leung ◽  
Mary Mah-Lee Ng ◽  
Justin Jang Hann Chu
Keyword(s):  
Viral Entry ◽  
Sindbis Virus ◽  
Chikungunya Virus ◽  
Semliki Forest Virus ◽  
Genetic Material ◽  
Endocytic Pathway ◽  
Human Pathogens ◽  
Potential Threat ◽  
Equine Encephalitis Virus ◽  
Alphavirus Entry

Alphaviruses are small, enveloped viruses, ~70 nm in diameter, containing a single-stranded, positive-sense, RNA genome. Viruses belonging to this genus are predominantly arthropod-borne viruses, known to cause disease in humans. Their potential threat to human health was most recently exemplified by the 2005 Chikungunya virus outbreak in La Reunion, highlighting the necessity to understand events in the life-cycle of these medically important human pathogens. The replication and propagation of viruses is dependent on entry into permissive cells. Viral entry is initiated by attachment of virions to cells, leading to internalization, and uncoating to release genetic material for replication and propagation. Studies on alphaviruses have revealed entry via a receptor-mediated, endocytic pathway. In this paper, the different stages of alphavirus entry are examined, with examples from Semliki Forest virus, Sindbis virus, Chikungunya virus, and Venezuelan equine encephalitis virus described.

scholarly journals Role of TSPAN9 in Alphavirus Entry and Early Endosomes

2016 ◽  
Vol 90 (9) ◽  
pp. 4289-4297 ◽  
Author(s):  
Katie M. Stiles ◽  
Margaret Kielian
Keyword(s):  
Membrane Fusion ◽  
Sindbis Virus ◽  
Semliki Forest Virus ◽  
Early Endosome ◽  
Late Endosome ◽  
Host Cells ◽  
Human Pathogens ◽  
Early Endosomes ◽  
Alphavirus Entry

ABSTRACTAlphaviruses are small enveloped RNA viruses that infect cells via clathrin-mediated endocytosis and low-pH-triggered fusion in the early endosome. Using a small interfering RNA (siRNA) screen in human cells, we previously identified TSPAN9 as a host factor that promotes infection by the alphaviruses Sindbis virus (SINV), Semliki Forest virus (SFV), and chikungunya virus (CHIKV). Depletion of TSPAN9 specifically decreases SFV membrane fusion in endosomes. TSPAN9 is a member of the tetraspanin family of multipass membrane proteins, but its cellular function is currently unknown. Here we used U-2 OS cells stably overexpressing TSPAN9 to show that TSPAN9 is localized at the plasma membrane and in early and late endosomes. Internalized SFV particles colocalized with TSPAN9 in vesicles early during infection. Depletion of TSPAN9 led to reductions in the amounts of the late endosomal proteins LAMP1 and CD63 and an increase in the amount of LAMP2. However, TSPAN9 depletion did not alter the delivery of SFV to early endosomes or change their pH or protease activity. Comparative studies showed that TSPAN9 depletion strongly inhibited infection by several viruses that fuse in early endosomes (SFV, SINV, CHIKV, and vesicular stomatitis virus [VSV]), while viruses that fuse in the late endosome (recombinant VSV-Lassa and VSV-Junin), including an SFV point mutant with a lower pH threshold for fusion (SFV E2 T12I), were relatively resistant. Our data suggest that TSPAN9 modulates the early endosome compartment to make it more permissive for membrane fusion of early-penetrating viruses.IMPORTANCEAlphaviruses are spread by mosquitoes and can cause serious human diseases such as arthritis and encephalitis. Recent outbreaks of CHIKV infection are responsible for millions of cases of acute illness and long-term complications. There are no vaccines or antiviral treatments for these important human pathogens. Alphaviruses infect host cells by utilizing the endocytic machinery of the cell and fusing their membrane with that of the endosome. Although the mechanism of virus-membrane fusion is well studied, we still know relatively little about the host cell proteins that are involved in alphavirus entry. Here we characterized the role of the host membrane protein TSPAN9 in alphavirus infection. TSPAN9 was localized to early endosomes containing internalized alphavirus, and depletion of TSPAN9 inhibited virus fusion with the early endosome membrane. In contrast, infection of viruses that enter through the late endosome was relatively resistant to TSPAN9 depletion, suggesting an important role for TSPAN9 in the early endosome.

scholarly journals Phosphorylation Sites in the Hypervariable Domain in Chikungunya Virus nsP3 Are Crucial for Viral Replication

2021 ◽  
Vol 95 (9) ◽  
Author(s):  
Mona Teppor ◽  
Eva Žusinaite ◽  
Andres Merits
Keyword(s):  
Protein Interactions ◽  
Mammalian Cells ◽  
Sindbis Virus ◽  
Chikungunya Virus ◽  
Semliki Forest Virus ◽  
Virus Infectivity ◽  
Valuable Insight ◽  
Phosphorylation Sites ◽  
Nonstructural Proteins ◽  
Host Proteins

ABSTRACT Chikungunya virus (CHIKV, family Togaviridae) is a mosquito-transmitted alphavirus. The positive-sense RNA genome of CHIKV encodes four nonstructural proteins (nsP1 to nsP4) that are virus-specific subunits of the RNA replicase. Among nsP functions, those of nsP3 are the least understood. The C-terminal hypervariable domain (HVD) in nsP3 is disordered and serves as a platform for interactions with multiple host proteins. For Sindbis virus (SINV) and Semliki Forest virus (SFV), the nsP3 HVD has been shown to be phosphorylated. Deletion of phosphorylated regions has a mild effect on the growth of SFV and SINV in vertebrate cells. Using radiolabeling, we demonstrated that nsP3 in CHIKV and o’nyong-nyong virus is also phosphorylated. We showed that the phosphorylated residues in CHIKV nsP3 are not clustered at the beginning of the HVD. The substitution of 20 Ser/Thr residues located in the N-terminal half of the HVD or 26 Ser/Thr residues located in its C-terminal half with Ala residues reduced the activity of the CHIKV replicase and the infectivity of CHIKV in mammalian cells. Furthermore, the substitution of all 46 potentially phosphorylated residues resulted in the complete loss of viral RNA synthesis and infectivity. The mutations did not affect the interaction of the HVD in nsP3 with the host G3BP1 protein; interactions with CD2AP, BIN1, and FHL1 proteins were significantly reduced but not abolished. Thus, CHIKV differs from SFV and SINV both in the location of the phosphorylated residues in the HVD in nsP3 and, significantly, in their effect on replicase activity and virus infectivity. IMPORTANCE CHIKV outbreaks have affected millions of people, creating a need for the development of antiviral approaches. nsP3 is a component of the CHIKV RNA replicase and is involved in interactions with host proteins and signaling cascades. Phosphorylation of the HVD in nsP3 is important for the virulent alphavirus phenotype. Here, we demonstrate that nsP3 in CHIKV is phosphorylated and that the phosphorylation sites in the HVD are distributed in a unique pattern. Furthermore, the abrogation of some of the phosphorylation sites results in the attenuation of CHIKV, while abolishing all the phosphorylation sites completely blocked its replicase activity. Thus, the phosphorylation of nsP3 and/or the phosphorylation sites in nsP3 have a major impact on CHIKV infectivity. Therefore, they represent promising targets for antiviral compounds and CHIKV attenuation. In addition, this new information offers valuable insight into the vast network of virus-host interactions.

scholarly journals The Cholesterol Requirement for Sindbis Virus Entry and Exit and Characterization of a Spike Protein Region Involved in Cholesterol Dependence

1999 ◽  
Vol 73 (5) ◽  
pp. 4272-4278 ◽  
Author(s):  
Yanping E. Lu ◽  
Todd Cassese ◽  
Margaret Kielian
Keyword(s):  
Sindbis Virus ◽  
Semliki Forest Virus ◽  
Virus Entry ◽  
Single Point ◽  
Endocytic Pathway ◽  
Progeny Virus ◽  
Single Point Mutation ◽  
Entry And Exit ◽  
Wild Type

ABSTRACT Semliki Forest virus (SFV) and Sindbis virus (SIN) are enveloped alphaviruses that enter cells via low-pH-triggered fusion in the endocytic pathway and exit by budding from the plasma membrane. Previous studies with cholesterol-depleted insect cells have shown that SFV requires cholesterol in the cell membrane for both virus fusion and efficient exit of progeny virus. An SFV mutant, srf-3, shows efficient fusion and exit in the absence of cholesterol due to a single point mutation in the E1 spike subunit, proline 226 to serine. We have here characterized the role of cholesterol in the entry and exit of SIN, an alphavirus quite distantly related to SFV. Growth, primary infection, fusion, and exit of SIN were all dramatically inhibited in cholesterol-depleted cells compared to control cells. Based on sequence differences within the E1 226 region between SFV,srf-3, and SIN, we constructed six SIN mutants with alterations within this region and characterized their cholesterol dependence. A SIN mutant, SGM, that had thesrf-3 amino acid sequence from E1 position 224 to 235 showed increases of ∼100-fold in infection and ∼250-fold in fusion with cholesterol-depleted cells compared with infection and fusion of wild-type SIN. Pulse-chase analysis demonstrated that SGMexit from cholesterol-depleted cells was markedly more efficient than that of wild-type SIN. Thus, similar to SFV, SIN was cholesterol dependent for both virus entry and exit, and the cholesterol dependence of both steps could be modulated by sequences within the E1 226 region.

scholarly journals An Alphavirus Replicon Particle Chimera Derived from Venezuelan Equine Encephalitis and Sindbis Viruses Is a Potent Gene-Based Vaccine Delivery Vector

2003 ◽  
Vol 77 (19) ◽  
pp. 10394-10403 ◽  
Author(s):  
Silvia Perri ◽  
Catherine E. Greer ◽  
Kent Thudium ◽  
Barbara Doe ◽  
Harold Legg ◽  
...  
Keyword(s):  
Sindbis Virus ◽  
Semliki Forest Virus ◽  
Cultured Cells ◽  
Heterologous Gene Expression ◽  
Envelope Glycoproteins ◽  
Venezuelan Equine Encephalitis ◽  
Vaccine Vectors ◽  
Equine Encephalitis Virus ◽  
Replicon Particle

ABSTRACT Alphavirus replicon particle-based vaccine vectors derived from Sindbis virus (SIN), Semliki Forest virus, and Venezuelan equine encephalitis virus (VEE) have been shown to induce robust antigen-specific cellular, humoral, and mucosal immune responses in many animal models of infectious disease and cancer. However, since little is known about the relative potencies among these different vectors, we compared the immunogenicity of replicon particle vectors derived from two very different parental alphaviruses, VEE and SIN, expressing a human immunodeficiency virus type 1 p55Gag antigen. Moreover, to explore the potential benefits of combining elements from different alphaviruses, we generated replicon particle chimeras of SIN and VEE. Two distinct strategies were used to produce particles with VEE-p55 gag replicon RNA packaged within SIN envelope glycoproteins and SIN-p55 gag replicon RNA within VEE envelope glycoproteins. Each replicon particle configuration induced Gag-specific CD8+ T-cell responses in murine models when administered alone or after priming with DNA. However, Gag-specific responses varied dramatically, with the strongest responses to this particular antigen correlating with the VEE replicon RNA, irrespective of the source of envelope glycoproteins. Comparing the replicons with respect to heterologous gene expression levels and sensitivity to alpha/beta interferon in cultured cells indicated that each might contribute to potency differences. This work shows that combining desirable elements from VEE and SIN into a replicon particle chimera may be a valuable approach toward the goal of developing vaccine vectors with optimal in vivo potency, ease of production, and safety.

scholarly journals Semliki Forest virus chimeras with functional replicase modules from related alphaviruses survive by adaptive mutations in functionally important hotspots

2021 ◽  
Author(s):  
Mona Teppor ◽  
Eva Zusinaite ◽  
Liis Karo-Astover ◽  
Ailar Omler ◽  
Kai Rausalu ◽  
...  
Keyword(s):  
Sindbis Virus ◽  
Semliki Forest Virus ◽  
Vaccine Development ◽  
Rapid Development ◽  
Antiviral Drug ◽  
Survival Strategies ◽  
Functional Modules ◽  
Human Pathogens ◽  
Adaptive Mutations ◽  
Positive Strand Rna

Alphaviruses (family Togaviridae ) include both human pathogens such as chikungunya virus (CHIKV) and Sindbis virus (SINV) and model viruses such as Semliki Forest virus (SFV). The alphavirus positive-strand RNA genome is translated into nonstructural (ns) polyprotein(s) that are precursors for four nonstructural proteins (nsPs). The three-dimensional structures of nsP2 and the N-terminal 2/3 of nsP3 reveal that these proteins consist of several domains. Cleavage of the ns-polyprotein is performed by the strictly regulated protease activity of the nsP2 region. Processing results in the formation of a replicase complex that can be considered a network of functional modules. These modules work cooperatively and should perform the same task for each alphavirus. To investigate functional interactions between replicase components, we generated chimeras using the SFV genome as a backbone. The functional modules corresponding to different parts of nsP2 and nsP3 were swapped with their counterparts from CHIKV and SINV. Although some chimeras were nonfunctional, viruses harboring the CHIKV N-terminal domain of nsP2 or any domain of nsP3 were viable. Viruses harboring the protease part of nsP2, the full-length nsP2 of CHIKV or the nsP3 macrodomain of SINV required adaptive mutations for functionality. Seven mutations that considerably improved the infectivity of the corresponding chimeric genomes affected functionally important hotspots recurrently highlighted in previous alphavirus studies. These data indicate that alphaviruses utilize a rather limited set of strategies to survive and adapt. Furthermore, functional analysis revealed that the disturbance of processing was the main defect resulting from chimeric alterations within the ns-polyprotein. IMPORTANCE Alphaviruses cause debilitating symptoms and have caused massive outbreaks. There are currently no approved antivirals or vaccines for treating these infections. Understanding the functions of alphavirus replicase proteins (nsPs) provides valuable information for both antiviral drug and vaccine development. The nsPs of all alphaviruses consist of similar functional modules; however, to what extent these are independent in functionality and thus interchangeable among homologous viruses is largely unknown. Homologous domain swapping was used to study the functioning of modules from nsP2 and nsP3 of other alphaviruses in the context of Semliki Forest virus. Most of the introduced substitutions resulted in defects in the processing of replicase precursors that were typically compensated by adaptive mutations that mapped to determinants of polyprotein processing. Understanding the principles of virus survival strategies and identifying hotspot mutations that permit virus adaptation highlight a route to the rapid development of attenuated viruses as potential live vaccine candidates.

Application of Alphaviral Vectors for Immunomodulation in Cancer Therapy

2017 ◽  
Vol 23 (32) ◽  
pp. 4906-4932 ◽  
Author(s):  
Anna Zajakina ◽  
Karina Spunde ◽  
Kenneth Lundstrom
Keyword(s):  
Animal Models ◽  
Protein Delivery ◽  
Sindbis Virus ◽  
Semliki Forest Virus ◽  
Tumor Regression ◽  
Survival Rates ◽  
Expression Vectors ◽  
Cancer Therapies ◽  
Systemic Delivery ◽  
Equine Encephalitis Virus

Background: The lack of specific and efficient cancer therapies has influenced the development of novel approaches, such as immunotherapy, which from its original application of immunogenic protein delivery has developed into the use of more sophisticated recombinant gene delivery methods to achieve better safety and efficacy profiles. This approach involves viral and non-viral delivery systems. Methods: Expression vectors have been engineered for alphaviruses, including Semliki Forest virus, Sindbis virus and Venezuelan equine encephalitis virus. For immunotherapeutic applications, recombinant particles, RNA replicons and layered DNA vectors that express tumor-associated antigens (TAAs) and cytokines have been studied in animal models and in a few clinical trials. Results: Immunization studies with TAAs and cytokines have elicited strong antibody responses and vaccination has provided protection against challenges with tumor cells in mouse models. Furthermore, the combination of TAAs and cytokines, antibodies and growth factors and the co-administration of chemotherapeutics and bacteriabased adjuvants have enhanced immunogenicity. Intratumoral and systemic delivery of recombinant alphavirus particles has demonstrated significant tumor regression and prolonged survival rates in rodent tumor models. Conclusion: Alphavirus-based immunotherapy represents a rapid and efficient method for prophylactic and therapeutic applications in animal models.

scholarly journals Membrane targeting of an alpha-like tetravirus replicase is directed by a region within the RNA-dependent RNA polymerase domain

2012 ◽  
Vol 93 (8) ◽  
pp. 1706-1716 ◽  
Author(s):  
James R. Short ◽  
Rosemary A. Dorrington
Keyword(s):  
Rna Polymerase ◽  
Sindbis Virus ◽  
Semliki Forest Virus ◽  
Strong Association ◽  
Recombinant Baculovirus ◽  
Endocytic Pathway ◽  
Membrane Targeting ◽  
Rna Dependent Rna Polymerase ◽  
Polymerase Domain ◽  
Detergent Resistant Membranes

The members of the family Tetraviridae are small positive-sense insect RNA viruses that exhibit stringent host specificity and a high degree of tissue tropism, suggesting that complex virus–host interactions are likely to occur during infection and viral replication. The alpha-like replicase of Helicoverpa armigera stunt virus (HaSV) (genus Omegatetravirus) has been proposed to associate with membranes of the endocytic pathway, which is similar to Semliki Forest virus, Sindbis virus and rubella virus. Here, we have used replicase–EGFP fusion proteins and recombinant baculovirus expression to demonstrate that the HaSV replicase associates strongly with cellular membranes, including detergent-resistant membranes, and that this association is maintained through a novel membrane targeting domain within the C-terminal region of the RNA-dependent RNA polymerase domain. We show a similar subcellular localization and strong association with detergent-resistant membranes for the carmo-like replicase of another tetravirus, Providence virus, in replicating cells, suggesting a common site of replication for these two tetraviruses.

scholarly journals Inhibition of Chikungunya Virus Replication by Harringtonine, a Novel Antiviral That Suppresses Viral Protein Expression

2012 ◽  
Vol 57 (1) ◽  
pp. 155-167 ◽  
Author(s):  
Parveen Kaur ◽  
Meerra Thiruchelvan ◽  
Regina Ching Hua Lee ◽  
Huixin Chen ◽  
Karen Caiyun Chen ◽  
...  
Keyword(s):  
Protein Expression ◽  
Viral Entry ◽  
Viral Protein ◽  
Sindbis Virus ◽  
Chikungunya Virus ◽  
Early Stage ◽  
Antiviral Treatment ◽  
Chikv Infection ◽  
Viral Protein Synthesis ◽  
Viral Protein Expression

ABSTRACTChikungunya virus (CHIKV) is a mosquito-transmitted virus that has reemerged as a significant public health threat in the last decade. Since the 2005-2006 chikungunya fever epidemic in the Indian Ocean island of La Réunion, millions of people in more than 40 countries have been infected. Despite this, there is currently no antiviral treatment for chikungunya infection. In this study, an immunofluorescence-based screening platform was developed to identify potential inhibitors of CHIKV infection. A primary screen was performed using a highly purified natural product compound library, and 44 compounds exhibiting ≥70% inhibition of CHIKV infection were identified as positive hits. Among these, four were selected for dose-dependent inhibition assays to confirm their anti-CHIKV activity. Harringtonine, a cephalotaxine alkaloid, displayed potent inhibition of CHIKV infection (50% effective concentration [EC50] = 0.24 μM) with minimal cytotoxicity and was selected for elucidation of its antiviral mechanism. Time-of-addition studies, cotreatment assays, and direct transfection of viral genomic RNA indicated that harringtonine inhibited an early stage of the CHIKV replication cycle which occurred after viral entry into cells. In addition, quantitative reverse transcription-PCR (qRT-PCR) and Western blot analyses indicated that harringtonine affects CHIKV RNA production as well as viral protein expression. Treatment of harringtonine against Sindbis virus, a related alphavirus, suggested that harringtonine could inhibit other alphaviruses. This study suggests for the first time that harringtonine exerts its antiviral effects by inhibiting CHIKV viral protein synthesis.

scholarly journals BHK-21 Cell Clones Differ in Chikungunya Virus Infection and MXRA8 Receptor Expression

Viruses ◽  
2021 ◽  
Vol 13 (6) ◽  
pp. 949
Author(s):  
Peiqi Yin ◽  
Margaret Kielian
Keyword(s):  
Cell Lines ◽  
Primary Infection ◽  
Sindbis Virus ◽  
Chikungunya Virus ◽  
Mrna Level ◽  
Receptor Expression ◽  
Chikv Infection ◽  
Cell Clones ◽  
Clonal Cell Lines ◽  
Exogenous Expression

Baby hamster kidney-21 (BHK-21) cells are widely used to propagate and study many animal viruses using infection and transfection techniques. Among various BHK-21 cell clones, the fibroblast-like BHK-21/C-13 line and the epithelial-like BHK-21/WI-2 line are commonly used cell clones for alphavirus research. Here we report that BHK-21/WI-2 cells were significantly less susceptible to primary infection by the alphavirus chikungunya virus (CHIKV) than were BHK-21/C-13 cells. The electroporation efficiency of alphavirus RNA into BHK-21/WI-2 was also lower than that of BHK-21/C-13. The growth of CHIKV was decreased in BHK-21/WI-2 compared to BHK-21/C-13, while primary infection and growth of the alphavirus Sindbis virus (SINV) were equivalent in the two cell lines. Our results suggested that CHIKV entry could be compromised in BHK-21/WI-2. Indeed, we found that the mRNA level of the CHIKV receptor MXRA8 in BHK-21/WI-2 cells was much lower than that in BHK-21/C-13 cells, and exogenous expression of either human MXRA8 or hamster MXRA8 rescued CHIKV infection. Our results affirm the importance of the MXRA8 receptor for CHIKV infection, and document differences in its expression in two clonal cell lines derived from the original BHK-21 cell cultures. Our results also indicate that CHIKV propagation and entry studies in BHK-21 cells will be significantly more efficient in BHK-21/C-13 than in BHK-21/WI-2 cells.

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