Kaposi's sarcoma-associated herpesvirus viral protein kinase phosphorylates extracellular signal-regulated kinase and activates MAPK/ERK signaling pathway.

Open reading frame 36 (ORF36) of Kaposi's sarcoma-associated herpesvirus (KSHV) encodes a serine/threonine-type viral protein kinase (vPK). Previous studies have examined the functions of KSHV vPK; however, its role in the activation of extracellular signal-regulated kinase (ERK1/2) has not yet been described to date. Using HEK 293 cell lines, we performed a human phospho-kinase array analysis to screen for MAPK signaling pathways kinases that are activated by KSHV vPK. In addition, we investigated the regulator protein phosphorylation of up/downstream ERK1/2 pathway; nuclear translocation of phosphorylated ERK1/2; and regulation of transcription factor, inflammatory cytokine, and pro-/anti-apoptotic factor by KSHV vPK transfection. Here, we demonstrated that KSHV vPK activates ERK1/2 signaling pathway and plays an important role in the activation of MAPK/ERK signaling pathway.

Sequence Determinants in Gammaretroviral Env Cytoplasmic Tails Dictate Virus-Specific Pseudotyping Compatibility.

Viruses can incorporate foreign glycoproteins to form infectious particles through a process known as pseudotyping. However, not all glycoproteins are compatible with all viruses. Despite the fact that viral pseudotyping is widely used, what makes a virus/glycoprotein pair compatible is poorly understood. To study this, we chose to analyze a gammaretroviral glycoprotein (Env) whose compatibility with different viruses could be modulated through small changes in its cytoplasmic tail (CT). One form of this glycoprotein is compatible with murine leukemia virus (MLV) particles but incompatible with human immunodeficiency virus type 1 (HIV-1) particles, while the second is compatible with HIV-1 particles but not with MLV particles. To decipher the factors affecting virus-specific Env incompatibility, we characterized Env incorporation, maturation, cell-to-cell fusogenicity, and virus-to-cell fusogenicity of each Env. The HIV-1 particle incompatibility correlated with less efficient cleavage of the R peptide by HIV-1 protease. However, the MLV particle incompatibility was more nuanced. MLV incompatibility appeared to be caused by lack of incorporation into particles, yet incorporation could be restored by further truncating the CT or by using a chimeric MLV Gag protein containing the HIV-1 MA without fully restoring infectivity. The MLV particle incompatibility appeared to be caused in part by fusogenic repression in MLV particles through an unknown mechanism. This study demonstrates that the Env CT can dictate functionality of Env within particles in a virus-specific manner.IMPORTANCE Viruses utilize viral glycoproteins to efficiently enter target cells during infection. How viruses acquire viral glycoproteins has been studied to understand the pathogenesis of viruses and develop safer and more efficient viral vectors for gene therapies. The CTs of viral glycoproteins have been shown to regulate various stages of glycoprotein biogenesis, but a gap still remains in understanding the molecular mechanism of glycoprotein acquisition and functionality regarding the CT. Here, we studied the mechanism of how specific mutations in the CT of a gammaretroviral envelope glycoprotein distinctly affect infectivity of two different viruses. Different mutations caused failure of glycoproteins to function in a virus-specific manner due to distinct fusion defects, suggesting that there are virus-specific characteristics affecting glycoprotein functionality.

Sphingosine 1-Phosphate Lyase Enhances the Activation of IKKε To Promote Type I IFN-Mediated Innate Immune Responses to Influenza A Virus Infection.

Sphingosine 1-phosphate (S1P) lyase (SPL) is an intracellular enzyme that mediates the irreversible degradation of the bioactive lipid S1P. We have previously reported that overexpressed SPL displays anti-influenza viral activity; however, the underlying mechanism is incompletely understood. In this study, we demonstrate that SPL functions as a positive regulator of IKKε to propel type I IFN-mediated innate immune responses against viral infection. Exogenous SPL expression inhibited influenza A virus replication, which correlated with an increase in type I IFN production and IFN-stimulated gene accumulation upon infection. In contrast, the lack of SPL expression led to an elevated cellular susceptibility to influenza A virus infection. In support of this, SPL-deficient cells were defective in mounting an effective IFN response when stimulated by influenza viral RNAs. SPL augmented the activation status of IKKε and enhanced the kinase-induced phosphorylation of IRF3 and the synthesis of type I IFNs. However, the S1P degradation-incompetent form of SPL also enhanced IFN responses, suggesting that SPL's pro-IFN function is independent of S1P. Biochemical analyses revealed that SPL, as well as the mutant form of SPL, interacts with IKKε. Importantly, when endogenous IKKε was downregulated using a small interfering RNA approach, SPL's anti-influenza viral activity was markedly suppressed. This indicates that IKKε is crucial for SPL-mediated inhibition of influenza virus replication. Thus, the results illustrate the functional significance of the SPL-IKKε-IFN axis during host innate immunity against viral infection.

A lipid-based partitioning mechanism for selective incorporation of proteins into membranes of HIV particles.

Particles that bud off from the cell surface, including viruses and microvesicles, typically have a unique membrane protein composition distinct from that of the originating plasma membrane. This selective protein composition enables viruses to evade the immune response and infect other cells. But how membrane proteins sort into budding viruses such as human immunodeficiency virus (HIV) remains unclear. Proteins could passively distribute into HIV-assembly-site membranes producing compositions resembling pre-existing plasma-membrane domains. Here, we demonstrate that proteins instead sort actively into HIV-assembly-site membranes, generating compositions enriched in cholesterol and sphingolipids that undergo continuous remodelling. Proteins are recruited into and removed from the HIV assembly site through lipid-based partitioning, initiated by oligomerization of the HIV structural protein Gag. Changes in membrane curvature at the assembly site further amplify this sorting process. Thus, a lipid-based sorting mechanism, aided by increasing membrane curvature, generates the unique membrane composition of the HIV surface.

Author Correction: A lipid-based partitioning mechanism for selective incorporation of proteins into membranes of HIV particles.

In the version of this article originally published, the name of co-author Marc C. Johnson was missing the middle initial. The middle initial 'C.' has been added in the author list as well as in the 'author contributions' section (as M.C.J.). The error has been corrected in the PDF and HTML versions of the paper.

ßTrCP is Required for HIV-1 Vpu Modulation of CD4, GaLV Env, and BST-2/Tetherin.

The Human immunodeficiency virus-1 (HIV-1) accessory protein Vpu modulates numerous proteins, including the host proteins CD4 and BST-2/tetherin. Vpu interacts with the Skp, Cullin, F-Box (SCF) ubiquitin ligase through interactions with the F-Box protein ßTrCP (1 and/or 2). This interaction is dependent on phosphorylation of S52,56 in Vpu. Mutation of S52,56, or inhibition of the SCF, abolishes most Vpu activity against CD4 and partly reduces activity against BST-2/tetherin. Recently, Vpu has also been reported to interact with the clathrin adapter proteins AP-1 and AP-2, and these interactions were also found to be required for BST-2/tetherin antagonism in an S52,56 -dependent manner. In assays where HIV-1 is pseudotyped with gibbon ape leukemia virus (GaLV Env), Vpu has also been found to prevent GaLV Env from being incorporated into viral particles, but the mechanism for this antagonism is not fully understood. To clarify the role of the ßTrCPs in Vpu function we used CRISPR/Cas9 to generate a clonal cell line lacking both ßTrCP-1 and -2. Vpu activity against CD4 and GaLV Env was abolished in this cell line, and activity against BST-2/tetherin reduced significantly. Mutation of the S52,56 residues no longer affected Vpu activity against BST-2/tetherin in this cell line. These data suggest that the primary role of the S52,56 residues in antagonism of CD4, GaLV Env, and BST-2/tetherin is to recruit the SCF/ßTrCP ubiquitin ligase.

Evaluation of food waste disposal options by LCC analysis from the perspective of global warming: Jungnang case, South Korea.

The costs associated with eight food waste disposal options, dry feeding, wet feeding, composting, anaerobic digestion, co-digestion with sewage sludge, food waste disposer, incineration, and landfilling, were evaluated in the perspective of global warming and energy and/or resource recovery. An expanded system boundary was employed to compare by-products. Life cycle cost was analyzed through the entire disposal process, which included discharge, separate collection, transportation, treatment, and final disposal stages, all of which were included in the system boundary. Costs and benefits were estimated by an avoided impact. Environmental benefits of each system per 1 tonne of food waste management were estimated using carbon prices resulting from CO(2) reduction by avoided impact, as well as the prices of by-products such as animal feed, compost, and electricity. We found that the cost of landfilling was the lowest, followed by co-digestion. The benefits of wet feeding systems were the highest and landfilling the lowest.