Leukemia virus long terminal repeat activates NFkappaB pathway by a TLR3-dependent mechanism

The Role of Toll-Like Receptors in Retroviral Infection

Toll-like receptors (TLRs) are key pathogen sensing receptors that respond to diverse microbial ligands, and trigger both innate and adaptive immune responses to infection. Since their discovery, a growing body of evidence has pointed to an important role for TLRs in retroviral infection and pathogenesis. These data suggest that multiple TLRs contribute to the anti-retroviral response, and that TLR engagement by retroviruses can have complex and divergent outcomes for infection. Despite this progress, numerous questions remain about the role of TLRs in retroviral infection. In this review, I summarize existing evidence for TLR-retrovirus interactions and the functional roles these receptors play in immunity and pathogenesis, with particular focus on human immunodeficiency virus (HIV).

Comparative measurement of FeLV load in hemolymphatic tissues of cats with hematologic cytopenias

BACKGROUND

Feline leukemia virus (FeLV) is a serious viral infection in cats. FeLV is found in some tissues, such as spleen, lymph nodes and epithelial tissues. However, there is controversy about the organ in which the virus can be reliably detected in infected cats. The purpose of this study was to determine the level of viral infection in hemolymphatic tissues, including blood, bone marrow and spleen by reverse-transcriptase quantitative polymerase chain reaction (RT-qPCR).

RESULTS

A total of 31 cats with clinical signs of FeLV infection associated with at least a single lineage hematologic cytopenia were included in this study. Peripheral blood, bone marrow and spleen samples were obtained from each cat. Complete blood counts, biochemical tests, and a rapid test to detect FeLV p27 antigen in blood samples of cats were performed. Of 31 cats, 9 had anemia alone, 4 had thrombocytopenia alone, 2 had neutropenia alone, 9 had bicytopenia of anemia and thrombocytopenia, 3 had bicytopenia of anemia and neutropenia, and 4 had pancytopenia. FeLV RNA was then detected by RT-qPCR in the whole blood, bone marrow and spleen. Viral RNA copy numbers were detected in all cats by RT-qPCR whereas 24 out of 31 cats were positive for the serum FeLV antigen. We detected a significantly greater number of viral RNA in the spleen compared with the whole blood and bone marrow.

CONCLUSION

Spleen is a site where FeLV is most frequently detected in cats with hematologic cytopenias.

Methanol extract of Codium fragile inhibits tumor necrosis factor-α-induced matrix metalloproteinase-9 and invasiveness of MDA-MB-231 cells by suppressing nuclear factor-κB activation

OBJECTIVE

To evaluate whether the methanol extract of Codium fragile (MECF) regulates tumor necrosis factor-α (TNF-α)-induced invasion of human breast cancer MDA-MB-231 cells by suppressing matrix metalloproteinase-9 (MMP-9).

METHODS

Reverse transcription-polymerase chain reaction (RT-PCR) and western blot analysis were performed to analyze the expression of MMP-9 and nuclear factor-κB (NF-κB) subunits, p65 and p50, and IκB in MDA-MB-231 cells. 3-(4,5-Dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay was used for cell viability. MMP-9 activity and invasion were measured by gelatin zymography and a matrigel invasion assay, respectively. NF-κB activity was measured by an electrophoretic mobility shift assay and luciferase activity.

RESULTS

MECF had no effect on cell viability up to a concentration of 100 μg/mL in human breast cancer MDA-MB-231 cells regardless of the presence of TNF-α. MDA-MB-231 cells that were stimulated with TNF-α showed a marked increase of invasion compared to the untreated control, whereas pretreatment with MECF downregulated the TNF-α-induced invasion of MDA-MB-231 cells. Additionally, zymography, western blot analysis, and RT-PCR confirmed that MECF decreased TNF-α-induced MMP-9 expression and activity which is a key regulator for cancer invasion. According to an electrophoretic morbidity shift assay, pretreatment with MECF in MDA-MB-231 cells significantly decreased the TNF-α-induced DNA-binding activity of NF-κB, which is an important transcription factor for regulating cancer invasion-related genes such as MMP-9. Furthermore, treatment with MECF sustained the expression of p65 and p50 in response to TNF-α in the cytosolic compartment. The luciferase assay demonstrated that MECF attenuated TNF-α-induced NF-κB luciferase activity.

CONCLUSION

MECF exhibited its anti-invasive capability by downregulating TNF-α-induced MMP-9 expression, resulting from the suppression of NF-κB activity in the human breast cancer cell line MDA-MB-231.

Texosome-based drug delivery system for cancer therapy: from past to present

Rising worldwide cancer incidence and resistance to current anti-cancer drugs necessitate the need for new pharmaceutical compounds and drug delivery system. Malfunction of the immune system, particularly in the tumor microenvironment, causes tumor growth and enhances tumor progression. Thus, cancer immunotherapy can be an appropriate approach to provoke the systemic immune system to combat tumor expansion. Texosomes, which are endogenous nanovesicles released by all tumor cells, contribute to cell-cell communication and modify the phenotypic features of recipient cells due to the texosomes' ability to transport biological components. For this reason, texosome-based delivery system can be a valuable strategy for therapeutic purposes. To improve the pharmaceutical behavior of this system and to facilitate its use in medical applications, biotechnology approaches and mimetic techniques have been utilized. In this review, we present the development history of texosome-based delivery systems and discuss the advantages and disadvantages of each system.

Porcine epidemic diarrhea virus infection induces NF-κB activation through the TLR2, TLR3 and TLR9 pathways in porcine intestinal epithelial cells

Porcine epidemic diarrhea virus (PEDV) is a coronavirus that induces persistent diarrhoea in swine, resulting in severe economic losses in swine-producing countries. Insights into the interplay between PEDV infection and the innate immune system are necessary for understanding the associated mechanism of pathogenesis. The transcription factor NF-κB plays an important role in regulating host immune responses. Here, we elucidated for the first time to our knowledge the potential mechanism of PEDV-mediated NF-κB activation in porcine small intestinal epithelial cells (IECs). During PEDV infection, NF-κB p65 was found to translocate from the cytoplasm to the nucleus, and PEDV-dependent NF-κB activity was associated with viral dose and active replication. Using small interfering RNAs to screen different mRNA components of the Toll-like receptor (TLR) or RIG-I-like receptor signalling pathways, we demonstrated that TLR2, TLR3 and TLR9 contribute to NF-κB activation in response to PEDV infection, but not RIG-I. By screening PEDV structural proteins for their ability to induce NF-κB activities, we found that PEDV nucleocapsid protein (N) could activate NF-κB and that the central region of N was essential for NF-κB activation. Furthermore, TLR2 was involved in PEDV N-induced NF-κB activation in IECs. Collectively, these findings provide new avenues of investigation into the molecular mechanisms of NF-κB activation induced by PEDV infection.

The immunopathology of sepsis: pathogen recognition, systemic inflammation, the compensatory anti-inflammatory response, and regulatory T cells

Sepsis, the systemic inflammatory response to infection, represents the major cause of death in critically ill veterinary patients. Whereas important advances in our understanding of the pathophysiology of this syndrome have been made, much remains to be elucidated. There is general agreement on the key interaction between pathogen‐associated molecular patterns and cells of the innate immune system, and the amplification of the host response generated by pro‐inflammatory cytokines. More recently, the concept of immunoparalysis in sepsis has also been advanced, together with an increasing recognition of the interplay between regulatory T cells and the innate immune response. However, the heterogeneous nature of this syndrome and the difficulty of modeling it in vitro or in vivo has both frustrated the advancement of new therapies and emphasized the continuing importance of patient‐based clinical research in this area of human and veterinary medicine.

Essential role of Stat3 in PI3K-induced oncogenic transformation

Cells transformed by the p110α-H1047R mutant of PI3K show increased tyrosine phosphorylation of Stat3. This activation of Stat3 is important for the transformation process, because a dominant-negative mutant of Stat3 interferes with PI3K-induced oncogenesis. GDC-0941, a specific inhibitor of PI3K reduces the level of Stat3 phosphorylation. The effect of PI3K on Stat3 appears to be mediated by a member of the Tec kinase family. The Tec kinase inhibitor LFM-A13 blocks Stat3 phosphorylation in H1047R-transformed cells. The Janus kinase inhibitor AG490 and the Src kinase inhibitor Src-1, as well as rapamycin, have no effect on Stat3 phosphorylation in H1047R-transformed cells. The H1047R-transformed cells also release a factor that induces Stat3 phosphorylation in normal cells with possible effects on the cellular microenvironment. In some human tumor cell lines, the enhanced phosphorylation of Stat3 is inhibited by both PI3K and by Tec kinase inhibitors, suggesting that the link between PI3K and Stat3 is significant in human cancer.

The use of chromatin insulators to improve the expression and safety of integrating gene transfer vectors

The therapeutic application of recombinant retroviruses and other integrating gene transfer vectors has been limited by problems of vector expression and vector-mediated genotoxicity. These problems arise in large part from the interactions between vector sequences and the genomic environment surrounding sites of integration. Strides have been made in overcoming both of these problems through the modification of deleterious vector sequences, the inclusion of better enhancers and promoters, and the use of alternative virus systems. However, these modifications often add other restrictions on vector design, which in turn can further limit therapeutic applications. As an alternative, several groups have been investigating a class of DNA regulatory elements known as chromatin insulators. These elements provide a means of blocking the interaction between an integrating vector and the target cell genome in a manner that is independent of the vector transgene, regulatory elements, or virus of origin. This review outlines the background, rationale, and evidence for using chromatin insulators to improve the expression and safety of gene transfer vectors. Also reviewed are topological factors that constrain the use of insulators in integrating gene transfer vectors, alternative sources of insulators, and the role of chromatin insulators as one of several components for optimal vector design.

Prevalence of feline leukaemia provirus DNA in feline lymphomas

A significant drop in the prevalence of feline leukaemia virus (FeLV) antigenaemic cats and antigen-associated lymphomas has been observed after the introduction of FeLV vaccination and antigen-testing with removal of persistently antigenaemic cats. However, recent reports have indicated that regressively infected cats may contain FeLV provirus DNA and that lymphoma development may be associated with the presence of provirus alone. In the present study, we investigated the presence of FeLV antigen and provirus DNA in 50 lymphomas by immunohistochemistry and semi-nested polymerase chain reaction, respectively. Interestingly, almost 80% of T-cell lymphomas and 60% of B-cell lymphomas contained provirus DNA while only 21% of T-cell lymphomas and 11% of B-cell lymphomas expressed FeLV antigen. In conclusion, our results support previous hypotheses that vaccination and removal of persistently antigenaemic cats have led to a drop in FeLV antigen-expressing lymphomas. However, FeLV provirus DNA is still present in a high percentage of feline lymphomas.

Identification of LTR-specific small non-coding RNA in FeLV infected cells

The U3-LTR region of leukemia viruses transactivates cancer-related signaling pathways through the production of a non-coding RNA transcript although the role of this transcript in virus infection remains unknown. In this study we demonstrate for the first time that an long terminal repeat (LTR)-specific small non-coding RNA is produced from a feline leukemia virus (FeLV)-infected feline cell line. RNA cloning identified this as a 104 base transcript that originates from the U3-LTR region. We also demonstrate that in in vitro assays this LTR-RNA transcript activates NF kappaB signaling. Taken together, our findings suggest a possible role for this LTR transcript in FeLV pathogenesis.

Sensing of viral infection and activation of innate immunity by toll-like receptor 3

Toll-like receptors (TLRs) form a major group of transmembrane receptors that are involved in the detection of invading pathogens. Double-stranded RNA is a marker for viral infection that is recognized by TLR3. TLR3 triggering activates specific signaling pathways that culminate in the activation of NF-kappaB and IRF3 transcription factors, as well as apoptosis, enabling the host to mount an effective innate immune response through the induction of cytokines, chemokines, and other proinflammatory mediators. In this review, we describe the paradoxical role of TLR3 in innate immunity against different viruses and in viral pathogenesis but also the evidence for TLR3 as a "danger" receptor in nonviral diseases. We also discuss the structure and cellular localization of TLR3, as well as the complex signaling and regulatory events that contribute to TLR3-mediated immune responses.

Dendritic cell subsets and toll-like receptors

Toll-like receptors exist as highly conserved pathogen sensors throughout the animal kingdom and they represent a key family of molecules bridging the ancient innate and adaptive immune systems. The first molecules of adaptive immunity appeared in the cartilaginous fishes and, with these, major histocompatibility proteins and cells expressing these molecules, and thus, by definition, the advent of antigen-presenting cells and the "professional" antigen-presenting cells, the dendritic cells. Dendritic cells themselves are highly specialized subsets of cells with the major roles of antigen presentation and stimulation of lymphocytes. The dendritic cell functions of inducing immunity are regulated by their own activation status, which is governed by their encounter with pathogen-associated molecular patterns that signal through pattern recognition receptors, including Toll-like receptors, expressed at the surface and within the cytoplasm and endosomal membranes of dendritic cells. Thus although dendritic cells play a crucial role in the induction of adaptive immunity, the adaptive response is itself initiated at the level of ancient receptors of the innate immune system. A further degree in the complexity of dendritic cell activation is established by the fact that not all dendritic cells are equal. Dendritic cells exist as multiple subsets that vary in location, function, and phenotype. Distinct dendritic cell subsets display great variation in the type of Toll-like receptors expressed and consequently variation in the type of pathogens sensed and the subsequent type of immune responses initiated.

Friend retrovirus infection of myeloid dendritic cells impairs maturation, prolongs contact to naïve T cells, and favors expansion of regulatory T cells

Retroviruses have developed immunmodulatory mechanisms to avoid being attacked by the immune system. The mechanisms of this retrovirus-associated immune suppression are far from clarified. Dendritic cells (DCs) have been attributed a decisive role in these pathogenic processes. We have used the Friend retrovirus (FV) mouse model in order to acquire further knowledge about the role of infection of DCs in virus-induced immunosuppression. About 20% of the myeloid DCs that were generated from the bone marrow of FV-infected mice carried FV proteins. The infection was productive, and infected DCs transmitted the virus in cell culture and in vivo. FV infection of DCs led to a defect in DC maturation, as infected cells expressed very little costimulatory molecules. Live imaging analysis of the cell contact between DCs and T cells revealed prolonged contacts of T cells with infected DCs compared with uninfected DCs. Although naive T cells were still activated by FV-infected DCs, this activation did not result in antigen-specific T-cell proliferation. Interestingly, infected DCs expanded a population of Foxp3+ regulatory T cells with immunosuppressive potential, suggesting that the contact between naive T cells and retrovirus-infected DCs results in tolerance rather than immunity. Thus, retroviral infection of DCs leads to an expansion of regulatory T cells, which might serve as an immune escape mechanism of the virus.

Pattern recognition receptors in companion and farm animals - the key to unlocking the door to animal disease?

The innate immune system is essential for host defence and is responsible for early detection of potentially pathogenic microorganisms. Upon recognition of microbes by innate immune cells, such as macrophages and dendritic cells, diverse signalling pathways are activated that combine to define inflammatory responses that direct sterilisation of the threat and/or orchestrate development of the adaptive immune response. Innate immune signalling must be carefully controlled and regulation comes in part from interactions between activating and inhibiting signalling receptors. In recent years, an increasing number of pattern recognition receptors (PRRs), including C-type lectin receptors and Toll-like receptors (TLRs), has been described that participate in innate recognition of microbes, especially through the so called pathogen-associated molecular patterns (PAMPs). Recent studies demonstrate strong interactions between signalling through these receptors. Whereas useful models to study these receptors in great detail in the murine and human system are now emerging, relatively little is known regarding these receptors in companion and farm animals. In this review, current knowledge regarding these receptors in species of veterinary relevance is summarised.