Adenovirus infection inhibits the phosphorylation of major histocompatibility complex class I proteins

Human adenovirus DNA polymerase is evolutionarily and functionally associated with human telomerase reverse transcriptase based on in silico molecular characterization that implicate abacavir and zidovudine

Human adenoviruses (HAdVs) are non-enveloped, small double stranded DNA (dsDNA) viruses that cause asymptomatic infections, clinical syndromes and significant susceptibility to infections in immunocompromised people. The aim of the present study was to identify critical host proteins and HAdV hypothetical proteins that could be developed as potential host-viral targets for antiHAdV therapy. Here, the function of selected hypothetical proteins of HAdV based on phylogenetic relationship with the therapeutic targets of antiretroviral drugs of human immunodeficiency virus (HIV) was predicted computationally, and characterized the molecular dynamics and binding affinity of DNA polymerase of HAdV. Thirty-eight hypothetical proteins (HPs) of human adenovirus (HAdV) were used in this study. The results showed that HAdV DNA polymerase (P03261) is related to Human TERT (O14746) and HLA-B (P01889) genes. The protein-protein interaction of human five molecular targets (PNP, TERT, CCR5, HLA-B, and NR1I2) of ARVDs are well-coordinated/networked with CD4, AHR, FKBP4, NR3C1, HSP90AA1, and STUB1 proteins in the anti-HIV infection mechanism. The results showed that the free energy score of abacavir and zidovudine binding to HAdV DNA polymerase are -5.8 and -5.4 kcal mol^-1 respectively. Also, the control drug, cidofovir and ganciclovir have less binding affinity for DNA polymerase of HAdV when compare to that of abacavir and zidovudine. Similarity was observed in the binding of abacavir and zidovudine to HAdV DNA polymerase (ASP742, ALA743, LEU772, ARG773 and VAL776). In conclusion, combination of abacavir and zidovudine was predicted to be potential therapy for controlling HAdV infection targeting HAdV DNA polymerase.

The hemochromatosis protein HFE 20 years later: An emerging role in antigen presentation and in the immune system

Introduction

Since its discovery, the hemochromatosis protein HFE has been primarily defined by its role in iron metabolism and homeostasis, and its involvement in the genetic disease termed hereditary hemochromatosis (HH). While HH patients are typically afflicted by dysregulated iron levels, many are also affected by several immune defects and increased incidence of autoimmune diseases that have thereby implicated HFE in the immune response. Growing evidence has supported an immunological role for HFE with recent studies describing HFE specifically as it relates to MHC I antigen presentation.

Methods/Results

Here, we present a comprehensive overview of the relationship between iron metabolism, HFE, and the immune system to better understand the origin and cause of immune defects in HH patients. We further describe the role of HFE in MHC I antigen presentation and its potential to impair autoimmune responses in homeostatic conditions, a mechanism which may be exploited by tumors to evade immune surveillance.

Conclusion

Overall, this increased understanding of the role of HFE in the immune response sets the stage for better treatment and management of HH and other iron‐related diseases, as well as of the immune defects related to this condition.

Downregulation of class I major histocompatibility complex surface expression by varicella-zoster virus involves open reading frame 66 protein kinase-dependent and -independent mechanisms

We show here that the varicella-zoster virus (VZV) open reading frame 66 (ORF66) protein kinase is one mechanism employed to reduce class I major histocompatibility complex (MHC-I) surface expression in VZV-infected cells. Cells expressing enhanced green fluorescent protein-tagged functional and inactivated ORF66 (GFP-66 and GFP-66kd) from replication-defective adenovirus vectors revealed that ORF66 reduced MHC-I surface levels in a manner dependent on kinase activity. Cells infected with recombinant VZV expressing GFP-66 exhibited a significantly greater reduction in MHC-I surface expression than that observed in cells infected with VZV disrupted in GFP-66 expression. MHC-I maturation was delayed in its transport from the endoplasmic reticulum through the Golgi in both adenovirus-transduced cells expressing only GFP-66 and in VZV-infected cells expressing high levels of GFP-66, and this was predominantly kinase dependent. MHC-I levels were reduced in VZV-infected cells, and analyses of intracellular MHC-I revealed accumulation of folded MHC-I in the Golgi region, irrespective of ORF66 expression. Thus, the ORF66 kinase is important for VZV-mediated MHC-I downregulation, but additional mechanisms also may be involved. Analyses of the VZV ORF9a protein, the ortholog of the bovine herpesvirus 1 transporter associated with antigen processing inhibitor UL49.5 revealed no effects on MHC-I. These results establish a new role for viral protein kinases in immune evasion and suggest that VZV utilizes unique mechanisms to inhibit antigen presentation.

Human immunodeficiency virus type 1 Nef: adapting to intracellular trafficking pathways

The Nef protein of primate lentiviruses is a unique protein that has evolved in several ways to manipulate the biology of an infected cell to support viral replication, immune evasion, pathogenesis, and viral spread. Nef is a small (25- to 34-kDa), myristoylated protein that binds to a collection of cellular factors and acts as an adaptor to generate novel protein interactions to accomplish specific functions. Of the many biological activities attributed to Nef, the reduction of surface levels of the viral receptor (CD4) and antigen-presenting molecules (major histocompatibility complex class I) has been intensely examined; recent evidence demonstrates that Nef utilizes multiple, distinct pathways to affect these proteins. To accomplish this, Nef promotes the formation of multiprotein complexes, recruiting host adaptor proteins to commandeer intracellular vesicular trafficking routes. The altered trafficking of several other host molecules has also been reported, and an emerging theory suggests that Nef generates pleiotrophic effects in the secretory and endocytic pathways that reprogram intracellular protein trafficking and may ultimately provide an efficient platform for viral assembly. This review critically discusses some of the major findings regarding the impact of human immunodeficiency virus type 1 Nef on host protein transport and addresses some emerging directions in this area of human immunodeficiency virus biology.

HIV-1 Nef disrupts antigen presentation early in the secretory pathway

Human immunodeficiency virus, type 1 Nef disrupts viral antigen presentation and promotes viral immune evasion from cytotoxic T lymphocytes. There is evidence that Nef acts early in the secretory pathway to redirect major histocompatibility complex class I (MHC-I) from the trans-Golgi network to the endolysosomal pathway. However, a competing model suggests that Nef acts much later by accelerating MHC-I turnover at the cell surface. Here we demonstrate that Nef targets early forms of MHC-I molecules in the endoplasmic reticulum by preferentially binding hypophosphorylated cytoplasmic tails. The Nef-MHC-I complex migrates normally into the Golgi apparatus but subsequently fails to arrive at the cell surface and become phosphorylated. Cell type-specific differences in the rate of MHC-I transport through the secretory pathway correlate with responsiveness to Nef and co-precipitation of adaptor protein 1 with the Nef.MHC-I complex. We propose that the assembly of a Nef.MHC-I.adaptor protein 1 complex early in the secretory pathway is important for Nef activity.

The ER-Lumenal Domain of the HHV-7 Immunoevasin U21 Directs Class I MHC Molecules to Lysosomes

Like all members of the herpesvirus family, human herpesvirus-7 has evolved mechanisms to evade immune detection. The human herpesvirus-7 gene product U21 encodes an immunoevasin that binds to class I major histocompatibility complex molecules and diverts them to a lysosomal compartment. Here we show that the cytoplasmic tail of U21, although sufficient to sequester a heterologous membrane protein (CD4 chimera), has no effect on U21's ability to redirect class I major histocompatibility complex molecules to lysosomes. Instead, the ER-lumenal domain of U21 is sufficient to redirect class I major histocompatibility complex molecules to the lysosomal compartment. These observations demonstrate a novel viral immunoevasive mechanism for U21, and implicate the ER-lumenal domain of a type I transmembrane protein in lysosomal sorting.

Natural pathogens of laboratory mice, rats, and rabbits and their effects on research

Laboratory mice, rats, and rabbits may harbor a variety of viral, bacterial, parasitic, and fungal agents. Frequently, these organisms cause no overt signs of disease. However, many of the natural pathogens of these laboratory animals may alter host physiology, rendering the host unsuitable for many experimental uses. While the number and prevalence of these pathogens have declined considerably, many still turn up in laboratory animals and represent unwanted variables in research. Investigators using mice, rats, and rabbits in biomedical experimentation should be aware of the profound effects that many of these agents can have on research.

Detection of restricted isoform expression and tyrosine phosphatase activity of CD45 in murine dendritic cells

CD45 is a cell surface transmembrane tyrosine phosphatase. It is expressed as distinct protein isoforms via alternative splicing of exons 4, 5 and 6. In T and B lymphocytes, CD45 is thought to play a critical role in antigen-dependent signaling through their respective antigen receptor complexes. However, the isoform expression and enzymatic activity of CD45 in other leukocytes remains largely unknown. Here, we examine the isoform expression and phosphatase activity of CD45 in murine dendritic cells (DC). Flow cytometric double-labeling analysis and biochemical analysis of purified splenic DC CD45 demonstrate that DC express both the CD45RB and CD45R0 isoforms. Flow cytometric analyses of freshly isolated splenic DC and thymic DC also indicate the expression of CD45RB and CD45R0 on these DC populations. In addition, we find that purified splenic DC CD45 possesses a high level of intrinsic tyrosine phosphatase activity. These data therefore establish the restricted isoform expression pattern of CD45 in murine DC and demonstrate that cells lacking specific antigen receptor complexes have active tyrosine phosphatase activity associated with CD45.

Impairment of monocytic function after influenza virus infection

In order to analyze the immunosuppression associated with influenza virus infection, we investigated monocytic function in macrophage hybridoma cell lines 5 weeks after infection with two strains of influenza virus. Clones 30 and 63, chosen for stability in long-term culture, were infected with two strains of influenza virus, X-31 and PR-8. Uniform infection of both cell lines was confirmed by intracytoplasmic staining with the antihemagglutinin strain-specific monoclonal antibodies PY 102 and PY 206. One week after infection, clones 30 and 63 lost their ability to stimulate tetanus toxoid-specific major histocompatibility complex (MHC)-matched responder T cells. Coincident with the inability to stimulate MHC-matched T cells, there was diminished surface expression of class II MHC antigens and LFA-1-alpha and LFA-3 compared with that in uninfected cells: DR, 2.5 versus 10.6% (mean channel 0.3 versus 1.5); DQ, 1.6 versus 15.6% (mean channel 0.3 versus 3.0); DP, 5.0 versus 30.9% (mean channel 0.3 versus 2.0). LFA-1-alpha expression was reduced (13.1 versus 20.0%; mean channel 1.5 versus 2.0) while LFA-3 expression remained the same (22.2 versus 324%; mean channel 3.0 versus 3.3). Class I MHC surface antigen expression was unaltered. Cytokine secretion was also perturbed, as interleukin 1-alpha (IL-1-alpha) and IL-1-beta production was lost 1 week after infection. Production of IL-12 and IL-10 was unchanged, while IL-6 production was increased. The viability of the T cells cocultured with 63Flu was unaltered, demonstrating that the inability of the MHC-restricted T cells to proliferate in response to tetanus toxoid was not due to a toxic effect of 63Flu. Interestingly, other accessory functions, including the ability to support mitogen- and anti-CD3-mediated T-cell proliferation, remained intact. These data suggest that alteration of macrophage function relating to viral infection occurs at multiple levels and may contribute to the immunosuppression observed following influenza virus infection.

Interaction of pseudorabies virus with immortalized porcine B cells: influence on surface class I and II major histocompatibility complex and immunoglobulin M expression

We examined whether the L14 cell line, an immortalized B cell line originating from inbred miniature pigs of the MHC haplotype d/d, could be useful to study T cell responses of pigs to pseudorabies virus (PRV). Compared with porcine kidney cells, the replication of PRV in L14 cells was slower and yielded lower quantities of infectious virus, which agrees with the reported poor replication of PRV in peripheral blood lymphocytes of swine. The virus yield and the number of L14 cells expressing the viral glycoprotein gE were both maximal at 48 h postinfection, when approximately 90% of all viable L14 cells expressed gE. Morphologically detectable effects of PRV replication in L14 cells were not obvious, but the number of viable cells at 72 h postinfection was lower in infected cultures than in uninfected cultures. Major histocompatibility complex (MHC) class I and II antigen expression was significantly higher at different time points postinfection on infected than on uninfected L14 cells. In contrast, expression of IgM appeared very slightly reduced on infected L14 cells, indicating a selective influence of PRV on cellular protein expression. PRV-infected L14 cells were lysed by lymphocytes from PRV-immune minipigs of MHC haplotype d/d, indicating their usefulness in in vitro cytolytic assays.

Increased proliferative activity, loss of beta-adrenergic receptor function and class I major histocompatibility complex antigen surface expression in a modified lymphoma cell line

The molecular interaction of class I major histocompatibility complex (MHC) antigens (Ag) and of beta-adrenergic receptors was previously demonstrated on lymphocytes. By long-term culturing with high concentration of foetal calf serum, the murine S49 lymphoma cell line was modified (S49m) giving phenotypic alterations in beta-adrenergic receptors and class I Ag expression. S49m cells displayed a reduced number of beta-adrenergic sites that were uncoupled to the adenylate cyclase system. These were unable to respond to beta agonist stimulation, despite the fact that direct activation of Gs could be achieved with aluminium tetrafluoride. Although S49m cells showed normal expression of the thy 1.2 Ag, they displayed no expression of class I Ag of the d haplotype. This was assessed by the evident lack of cytotoxic activity of specific monoclonal antibodies (Mo Ab) and of their binding. When performing IFI staining on permeabilized cells, we found positive staining with anti-class d Ab inside the cell. This loss of expression and activity of beta-adrenoceptors and the internalization of class I Ag were accompanied by a higher rate of proliferation in S49m cells. The possibility that the loss of both molecules would modify the biology of the cell is also discussed.