Replacement of 198MQMDII203 of mouse IRF-1 by 197IPVEVV202 of human IRF-1 abrogates induction of IFN-β, iNOS, and COX-2 gene expression by IRF-1

Porcine Alveolar Macrophages' Nitric Oxide Synthase-Mediated Generation of Nitric Oxide Exerts Important Defensive Effects against Glaesserella parasuis Infection

Glaesserella parasuis is a habitual bacterium of pigs' upper respiratory tracts. Its infection initiates with the invasion and colonization of the lower respiratory tracts of pigs, and develops as the bacteria survive host pulmonary defenses and clearance by alveolar macrophages. Alveolar macrophage-derived nitric oxide (NO) is recognized as an important mediator that exerts antimicrobial activity as well as immunomodulatory effects. In this study, we investigated the effects and the signaling pathway of NO generation in porcine alveolar macrophages 3D4/21 during G. parasuis infection. We demonstrated a time and dose-dependent generation of NO in 3D4/21 cells by G. parasuis, and showed that NO production required bacterial viability and nitric oxide synthase 2 upregulation, which was largely contributed by G. parasuis-induced nuclear factor-κB signaling's activation. Moreover, the porcine alveolar macrophage-derived NO exhibited prominent bacteriostatic effects against G. parasuis and positive host immunomodulation effects by inducing the production of cytokines and chemokines during infection. G. parasuis in turn, selectively upregulated several nitrate reductase genes to better survive this NO stress, revealing a battle of wits during the bacteria-host interactions. To our knowledge, this is the first direct demonstration of NO production and its anti-infection effects in alveolar macrophages with G. parasuis infection.

Application of Genetically Encoded Fluorescent Nitric Oxide (NO•) Probes, the geNOps, for Real-time Imaging of NO• Signals in Single Cells

Nitric Oxide (NO•) is a small radical, which mediates multiple important cellular functions in mammals, bacteria and plants. Despite the existence of a large number of methods for detecting NO• in vivo and in vitro, the real-time monitoring of NO• at the single-cell level is very challenging. The physiological or pathological effects of NO• are determined by the actual concentration and dwell time of this radical. Accordingly, methods that allow the single-cell detection of NO• are highly desirable. Recently, we expanded the pallet of NO• indicators by introducing single fluorescent protein-based genetically encoded nitric oxide (NO•) probes (geNOps) that directly respond to cellular NO• fluctuations and, hence, addresses this need. Here we demonstrate the usage of geNOps to assess intracellular NO• signals in response to two different chemical NO•-liberating molecules. Our results also confirm that freshly prepared 3-(2-hydroxy-1-methyl-2-nitrosohydrazino)-N-methyl-1-propanamine (NOC-7) has a much higher potential to evoke change in intracellular NO• levels as compared with the inorganic NO• donor sodium nitroprusside (SNP). Furthermore, dual-color live-cell imaging using the green geNOps (G-geNOp) and the chemical Ca2+ indicator fura-2 was performed to visualize the tight regulation of Ca2+-dependent NO• formation in single endothelial cells. These representative experiments demonstrate that geNOps are suitable tools to investigate the real-time generation and degradation of single-cell NO• signals in diverse experimental setups.

Replacement of the C-terminal tetrapeptide (314 PAPV 317 to 314 SSSM 317) in interferon regulatory factor-2 alters its N-terminal DNA-binding activity

Interferon regulatory factor-2 (IRF-2) is an important transcription factor involved in cell growth regulation, immune response and cancer. IRF-2 can function as a transcriptional repressor and activator depending on its DNA-binding activity and protein-protein interactions. We compared the amino acid sequences of IRF-2 and found a C-terminal tetrapeptide (314PAPV317) of mouse IRF-2 to be different (314SSSM317) from human IRF-2. Recombinant GST-IRF-2 with 314PAPV317 (wild type) and 314SSSM317 (mutant) expressed in Escherichia coli were assessed for DNA-binding activity with 32P-(GAAAGT) 4 by electrophoretic mobility shift assay (EMSA). Wild type- and mutant GST-IRF-2 showed similar expression patterns and immunoreactivities but different DNA-binding activities. Mutant (mt) IRF-2 formed higher-molecular-mass, more and stronger DNA-protein complexes in comparison to wild type (wt) IRF-2. Anti-IRF-2 antibody stabilized the DNA-protein complexes formed by both wt IRF-2 and mt IRF-2, resolving the differences. This suggests that PAPV and SSSM sequences at 314-317 in the C-terminal region of mouse and human IRF-2 contribute to conformation of IRF-2 and influence DNA-binding activity of the N-terminal region, indicating intramolecular interactions. Thus, evolution of IRF-2 from murine to human genome has resulted in subtle differences in C-terminal amino acid motifs, which may contribute to qualitative changes in IRF-2-dependent DNA-binding activity and gene expression.

The effects of cardamonin on lipopolysaccharide-induced inflammatory protein production and MAP kinase and NFkappaB signalling pathways in monocytes/macrophages

BACKGROUND AND PURPOSE

In this study we examined the effect of the natural product cardamonin, upon lipopolysaccharide (LPS)-induced inflammatory gene expression in order to attempt to pinpoint the mechanism of action.

EXPERIMENTAL APPROACHES

Cardamonin was isolated from the Greek plant A. absinthium L. Its effects were assessed on LPS-induced nitrite release and iNOS and COX-2 protein expression in two macrophage cell lines. Western blotting was used to investigate its effects on phosphorylation of the mitogen activated protein (MAP) kinases, ERK, JNK and p38 MAP kinase, and activation of the NFkappaB pathway, at the level of IkappaBalpha degradation and phosphorylation of NFkappaB. Also its effects on NFkappaB and GAS/GAF-DNA binding were assessed by EMSA.

KEY RESULTS

Cardamonin concentration-dependently inhibited both NO release and iNOS expression but had no effect on COX-2 expression. It did not affect phosphorylation of the MAP kinases, degradation of IkappaBalpha or phosphorylation of NFkappaB. However, it inhibited NFkappaB DNA-binding in both LPS-stimulated cells and nuclear extracts of the cells (in vitro). It also inhibited IFNgamma-stimulated iNOS induction and GAS/GAF-DNA binding.

CONCLUSIONS AND IMPLICATIONS

These results show that the inhibitory effect of cardamonin on LPS-induced iNOS induction is not mediated via effects on the initial activation of the NFkappaB or MAP kinase pathways but is due to a direct effect on transcription factor binding to DNA. However, although some selectivity in cardamonin's action is implicated by its inability to affect COX-2 expression, its exact mechanism(s) of action has yet to be identified.

Aberrant alternative splicing of interferon regulatory factor-1 (IRF-1) in myelodysplastic hematopoietic progenitor cells

Interferon regulatory factor-1 (IRF-1) mRNA expression was examined in specific cell populations (BMMC, CD34+ and CD71+) derived from 45 MDS patients and 20 controls. All the MDS cell populations, presented an identical IRF-1 mRNA expression pattern, characterized by the absence of full-length IRF-1 mRNA and presence of multiple alternative transcripts. The most common deletions involved exons 2 and 3. Two novel truncated IRF-1 protein forms were detected in MDS BMMC. IRF-1-induced iNOS mRNA expression was exclusively detected in BMMC having full-length transcript. The expression of IRF-1 truncated mRNA and protein forms might be a critical event in the development of MDS.

Expression and DNA binding activity of the recombinant interferon regulatory factor-1 (IRF-1) of mouse

Interferon regulatory factor-1 (IRF-1) is a positive transcription factor for genes involved in immune response, cell growth regulation and apoptosis in mammalian cells. Many agents like virus, interferon (IFN), double-stranded RNA (dsRNA), proinflammatory cytokines, prolactin etc. induce IRF-1 at transcriptional level. IRF-1 transcriptionally activates many IRF-1-regulated genes during normal physiological and pathological conditions. We have expressed recombinant mouse IRF-1 (329 amino acids) as a GST(glutathione-S-transferase)-IRF-1 fusion protein from a 1029 bp IRF-1 cDNA in pGEX-2TK expression vector in Escherichia coli XL-1 blue cells. Recombinant GST-IRF-1 was highly expressed as a approximately 66 kDa soluble protein by IPTG-induction, and was biologically active in terms of its DNA binding activity with a 24 bp specific oligonucleotide, i.e. 32P(GAAAGT)4 but not with a similar but nonspecific oligonucleotide i.e. 32P(GAAA)6. GST-alone expressed from the vector did not bind 32P(GAAAGT)4. We observed multiple (1-4) GST-IRF-1-(GAAAGT)4 protein-DNA complexes which were competed out by 25x- to 100x-fold molar excess of (GAAAGT)4 showing that the complexes 1-4 were specific for IRF-1. Such GAAANN (N = any nucleotide) hexanucleotides occur in the promoters of many virus- and interferon-inducible mammalian genes. Multimeric GAAAGT/C sequences are inducible by virus, IFN, dsRNA and IRF-1. Specificity of DNA binding by IRF-1 lies in the 5th and 6th nucleotides in the GAAAGT sequence. Multiple IRF-1-DNA complexes should stimulate transcription by IRF-1.

Regulation of the expression of inducible nitric oxide synthase

The role of nitric oxide (NO) generated by the inducible isoform of nitric oxide synthase (iNOS) is very complex. Induction of iNOS expression and hence NO production has been described to have beneficial antiviral, antiparasital, microbicidal, immunomodulatory, and antitumoral effects. However, induced at the wrong place or at the wrong time, iNOS has detrimental consequences and seems to be involved in the pathophysiology of different human diseases. The pathways regulating iNOS expression seem to vary in different cells or different species. In general, activation of the transcription factors nuclear factor (NF)-kappaB and signal transducer and activator of transcription (STAT)-1alpha and thereby activation of the iNOS promoter seems to be an essential step in the regulation of iNOS expression in most cells. Also, post-transcriptional mechanisms are critically involved in the regulation of iNOS expression.