Altered kinetics of Tap-1 gene expression in macrophages following stimulation with both IFN-gamma and LPS

IFN-γ-Dependent Recruitment of CD4(+) T Cells and Macrophages Contributes to Pathogenesis During Leishmania amazonensis Infection

Interferon gamma (IFN-γ) is a key factor in the protection of hosts against intracellular parasites. This cytokine induces parasite killing through nitric oxide and reactive oxygen species production by phagocytes. Surprisingly, during Leishmania amazonensis infection, IFN-γ plays controversial roles. During in vitro infections, IFN-γ induces the proliferation of the amastigote forms of L. amazonensis. However, this cytokine is not essential at the beginning of an in vivo infection. It is not clear why IFN-γ does not mediate protection during the early stages of infection. Thus, the aim of our study was to investigate the role of IFN-γ during L. amazonensis infection. We infected IFN-γ(-/-) mice in the footpad and followed the development of leishmaniasis in these mice compared with that in WT mice. CD4(+) T lymphocytes and macrophages migrated earlier to the site of infection in the WT mice, and the earlier migration of these 2 cell types was associated with lesion development and parasite growth, respectively. These differences in the infiltrate populations were explained by the increased expression of chemokines in the lesions of the WT mice. Thus, we propose that IFN-γ plays a dual role during L. amazonensis infection; it is an important inducer of effector mechanisms, particularly through inducible nitric oxide synthase expression, and conversely, it is a mediator of inflammation and pathogenesis through the induction of the expression of chemokines. Our data provided evidence for a pathogenic effect of IFN-γ production during leishmaniasis that was previously unknown.

A combined omics study on activated macrophages--enhanced role of STATs in apoptosis, immunity and lipid metabolism

BACKGROUND

Macrophage activation by lipopolysaccharide and adenosine triphosphate (ATP) has been studied extensively because this model system mimics the physiological context of bacterial infection and subsequent inflammatory responses. Previous studies on macrophages elucidated the biological roles of caspase-1 in post-translational activation of interleukin-1β and interleukin-18 in inflammation and apoptosis. However, the results from these studies focused only on a small number of factors. To better understand the host response, we have performed a high-throughput study of Kdo2-lipid A (KLA)-primed macrophages stimulated with ATP.

RESULTS

The study suggests that treating mouse bone marrow-derived macrophages with KLA and ATP produces 'synergistic' effects that are not seen with treatment of KLA or ATP alone. The synergistic regulation of genes related to immunity, apoptosis and lipid metabolism is observed in a time-dependent manner. The synergistic effects are produced by nuclear factor kappa-light-chain-enhancer of activated B cells (NF-kB) and activator protein (AP)-1 through regulation of their target cytokines. The synergistically regulated cytokines then activate signal transducer and activator of transcription (STAT) factors that result in enhanced immunity, apoptosis and lipid metabolism; STAT1 enhances immunity by promoting anti-microbial factors; and STAT3 contributes to downregulation of cell cycle and upregulation of apoptosis. STAT1 and STAT3 also regulate glycerolipid and eicosanoid metabolism, respectively. Further, western blot analysis for STAT1 and STAT3 showed that the changes in transcriptomic levels were consistent with their proteomic levels. In summary, this study shows the synergistic interaction between the toll-like receptor and purinergic receptor signaling during macrophage activation on bacterial infection.

AVAILABILITY

Time-course data of transcriptomics and lipidomics can be queried or downloaded from http://www.lipidmaps.org.

CONTACT

shankar@ucsd.edu.

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

Localization, expression change in PRRSV infection and association analysis of the porcine TAP1 gene

The transporter associated with antigen processing (TAP) translocates antigenic peptides from the cytosol into the lumen of the endoplasmic reticular and plays a critical role in the major histocompatibility complex (MHC) class I molecule-mediated antigenic presentation pathway. In this study, the porcine TAP1 gene was mapped to the pig chromosome 7 (SSC7) and was closely linked to the marker SSC2B02 (retention fraction=43%, LOD=15.18). Subcellular localization of TAP1 by transient transfection of PK15 cells indicated that the TAP1 protein might be located in the endoplasmic reticulum (ER) in pig kidney epithelial cells (PK-15). Gene expression analysis by semi-quantitative RT-PCR revealed that TAP1 was selectively expressed in some immune and immune-related tissues. Quantitative real-time PCR (qRT-PCR) analysis revealed that this gene was up-regulated after treatments that mimic viral and bacterial infection (polyriboinosinic-polyribocytidylic acid (poly(I:C)) and lipopolysaccharide (LPS), respectively). In addition, elevated TAP1 expression was detected after porcine reproductive and respiratory syndrome virus (PRRSV) infection in porcine white blood cells (WBCs). One single nucleotide polymorphism (SNP) in exon 3 of TAP1 was detected in a Landrace pig population by Bsp143I restriction enzyme digestion. Different genotypes of this SNP had significant associations (P<0.05) with the red blood cell distribution width (RDW) of 1-day-old (1 d) pigs (P=0.0168), the PRRSV antibody level (PRRSV Ab) (P=0.0445) and the absolute lymphocyte count (LYM#) (P=0.024) of 17 d pigs. Our results showed that the TAP1 gene might have important roles in swine immune responses, and these results provide useful information for further functional studies.

Impaired phospholipases A₂production by stimulated macrophages from patients with acute respiratory distress syndrome

The aim of this study was to investigate whether early phase of acute respiratory distress syndrome (ARDS) is associated with changes in immune response, either systemic or localized to the lung. ARDS and control mechanically ventilated patients, as well as healthy volunteers were studied. Alveolar macrophages (AMΦ) and blood monocytes (BM) were treated ex vivo with lipopolysaccharide (LPS), interferon-γ (IFNγ), and surfactant. Phospholipase A₂ (PLA₂) activity and TLR4 expression were evaluated as markers of cell response. AMΦ from ARDS patients did not respond upon treatment with either LPS or IFN-γ by inducing PLA₂ production. On the contrary, upon stimulation, in control patients the intracellular PLA₂, (mainly cPLA₂) levels were increased, but secretion of PLA₂ (mainly sPLA₂-IIA) was observed only after treatment with LPS. Surfactant suppressed PLA₂ production in cells from both groups of patients. Increased relative changes of total PLA₂ activity and an upregulation of TLR4 expression upon stimulation was observed in BM from primary ARDS, control patients and healthy volunteers. In BM from secondary ARDS patients, however, no PLA₂ induction was observed, with a concomitant down-regulation of TLR4 expression. Cytosolic PLA₂, its activated form, p-cPLA₂, and sPLA₂-IIA were the predominant PLA₂ types within the cells, while extracellularly only sPLA₂-IIA was identified. These results support the concept of down-regulated innate immunity in early ARDS that is compartmentalized in primary and systemic in secondary ARDS. PLA₂ isoforms could serve as markers of the immunity status in ARDS. Finally, our data highlight the role of surfactant in controlling inflammation.

Regulation of murine Tap1 and Lmp2 genes in macrophages by interferon gamma is mediated by STAT1 and IRF-1

The genes of the transporter associated with antigen processing (Tap)-1, and the low molecular weight peptide (Lmp)-2, are crucial for class I major histocompatibility complex function and share a common bidirectional promoter. In murine bone marrow-derived macrophages, interferon gamma (IFN-gamma) induced Tap-1 and upregulated Lmp-2, which is constitutively expressed at low levels. The IFN-gamma-induction was independent of early gene synthesis. The mRNA induced by IFN-gamma was very stable. In macrophages from STAT1 knockout mice, IFN-gamma did not induce the expression of Tap-1 or Lmp-2. Several areas in the promoter can be controlled by IFN-gamma, such as proximal and distal GAS boxes in the direction of the Tap-1 gene, NFgammaB and IRF-1 boxes. By making deletions of the promoter, we found that only the proximal GAS and IRF-1 boxes are required for IFN-gamma induction of Tap-1 and Lmp-2. Experiments using nuclear extracts from macrophages treated for 30 min with IFN-gamma and gel shift analysis indicated that STAT1 binds to the GAS box. The nuclear extracts from macrophages treated for at least 2 h with IFN-gamma bound to the IRF-1 box. These results indicate that both STAT1 and IRF-1 are required for the IFN-gamma induction of Tap-1 and Lmp-2 genes.

STAT1 regulates lipopolysaccharide- and TNF-alpha-dependent expression of transporter associated with antigen processing 1 and low molecular mass polypeptide 2 genes in macrophages by distinct mechanisms

Transporter associated with Ag processing 1 and low molecular mass polypeptide 2 (LMP2) are essential for class I MHC function and share a common bidirectional promoter. In murine bone marrow-derived macrophages, LPS and TNF-alpha induced Tap1 and up-regulated Lmp2, which is constitutively expressed at low levels. These two genes are induced by LPS and TNF-alpha with distinct kinetics, at 6 and 12-24 h, respectively. Using macrophages derived from the TNF-alpha receptors of knockout mice, we found that induction by LPS is not due to the autocrine production of TNF-alpha. In macrophages from STAT-1 knockout mice, neither LPS nor TNF-alpha induced the expression of Tap1 or Lmp2. The shared promoter contains several areas that can be controlled by STAT-1, such as the proximal and distal IFN-gamma activation site (GAS) boxes in the direction of the Tap1 gene. By making deletions of the promoter, we determined that only the proximal GAS box is required for LPS induction of Tap1 and Lmp2. In contrast, TNF-alpha induction of these two genes is dependent on the IFN regulatory factor-1 and NF-kappaB boxes, and not on the GAS box. Our experiments using gel shift analysis and Abs indicated that STAT1 binds to the GAS box in nuclear extracts from LPS-treated macrophages. The nuclear extracts obtained from macrophages treated with TNF-alpha bound to the IFN regulatory factor-1 and NF-kappaB boxes. These results show that LPS and TNF-alpha regulate the induction of Tap1 and Lmp2 through STAT1, but use distinct areas of the promoter.

p38 activation through Toll-like receptors modulates IFN-gamma-induced expression of the Tap-1 gene only in macrophages

Although interferon-gamma (IFN-gamma) induces the transporter associated with antigen processing (Tap)-1 expression in macrophages, cooperation with lipopolysaccharide signaling through Toll-like receptor 4 (TLR4) accelerates the kinetics and increases the overall levels of this gene. In this report, we show that peptidoglycan signaling through TLR2 and bacterial CpG DNA signaling through TLR9 are functionally equivalent at synergizing with IFN-gamma in regulating Tap-1 expression in macrophages. Activation of the p38 mitogen-activated protein kinase is necessary for this response, which correlates with increased phosphorylation of signal transducer and activator of transcription-1 on serine 727. Activation of p38, however, is not sufficient, as this signaling event does not affect the response to IFN-gamma in HeLa cells. The cooperation between these different signaling pathways also requires membrane fluidity. These data suggest that macrophages possess an ability to coordinate the signaling between the IFN-gamma and TLR receptors.

IFN-alpha beta promote priming of antigen-specific CD8+ and CD4+ T lymphocytes by immunostimulatory DNA-based vaccines

Immunostimulatory sequence (ISS) DNA containing unmethylated CpG dinucleotides stimulate NK and APC to secrete proinflammatory cytokines, including IFN-alphabeta and -gamma, TNF-alpha, and IL-6 and -12, and to express costimulatory surface molecules such as CD40, B7-1, and B7-2. Although ISS DNA has little direct effect on T cells by these criteria, immunization of wild-type mice with ISS DNA and OVA results in Ag-specific CTL and Th1-type T helper activity. This investigation examines the mechanisms by which ISS DNA primes CD8(+) and CD4(+) lymphocyte activities. In this report we demonstrate that ISS DNA regulates the expression of costimulatory molecules and TAP via a novel autocrine or paracrine IFN-alphabeta pathway. Coordinated regulation of B7 costimulation and TAP-dependent cross-presentation results in priming of Ag-specific CD8(+) CTL, whereas CD40, B7, and IL-12 costimulation is required for priming of CD4(+) Th cells by ISS-based vaccines.

Loss of PU.1 expression following inhibition of histone deacetylases

Altering chromatin structure by blocking histone deacetylase activity with specific inhibitors such as trichostatin A can result in an up-regulation of gene expression. In this report, however, we show that expression of the ETS domain transcription factor PU.1 is down-regulated in cells following the addition of trichostatin A. The loss of PU.1 is seen at both the mRNA and protein levels in multiple cell lines and is reversible following removal of the drug. More importantly, we show that the loss of PU.1 results in a loss of PU.1 target gene expression, including CD11b, c-fms, Toll-like receptor 4, and scavenger receptor. Chromatin immunoprecipitation analysis of cells treated with trichostatin A showed a significant increase in the acetylation of histone H4, but not histone H3, across approximately 650 bp of the PU.1 promoter region. Our data suggest that the consequences of using drugs that inhibit histone deacetylase activity may be a loss of blood cell development and/or function due to a block in PU.1 gene expression.

Synergistic induction of the Tap-1 gene by IFN-gamma and lipopolysaccharide in macrophages is regulated by STAT1

Proper regulation of the Tap-1 gene is critical for the initiation and continuation of a cellular immune response. Analysis of the Tap-1/low molecular mass polypeptide 2 bidirectional promoter showed that the IFN-gamma activation site element is critical for the rapid induction of the promoter by IFN-gamma following transfection into the human macrophage cell line THP-1. Furthermore, activation of STAT1 binding to this site was important for the synergistic response seen following the stimulation with both IFN-gamma and LPS. Mutation of an IFN-stimulated regulatory element that binds IFN regulatory factor 1 appeared to enhance the response to IFN-gamma and LPS. These data show that STAT1 is necessary for the activation of Tap-1 gene expression in APCs and initiation of cellular immune responses. Furthermore, our data suggest that bacterial products such as LPS may enhance cellular immune responses through augmenting the ability of STAT1 to regulate IFN-gamma-inducible genes.