Lipopolysaccharide-inducible Macrophage Early Genes Are Induced in Balb/c 3T3 Cells by Platelet-derived Growth Factor

PDGF synergistically enhances IFN-gamma-induced expression of CXCL10 in blood-derived macrophages: implications for HIV dementia

There is increasing cumulative evidence that activated mononuclear phagocytes (macrophages/microglia) releasing inflammatory mediators in the CNS are a better correlate of HIV-associated dementia (HAD) than the actual viral load in the brain. Earlier studies on simian HIV/rhesus macaque model of NeuroAIDS confirmed that pathological changes in brains of macaques with encephalitis were associated with up-regulation of platelet-derived growth factor (PDGF) and the chemokine, CXCL10. Because the complex interplay of inflammatory mediators released by macrophages often leads to the induction of neurotoxins in HAD, we hypothesized that PDGF could interact with IFN-gamma to modulate the expression of CXCL10 in these primary virus target cells. Although PDGF alone had no effect on the induction of CXCL10 in human macrophages, in conjunction with IFN-gamma, it significantly augmented the expression of CXCL10 RNA & protein through transcriptional and posttranscriptional mechanisms. Signaling molecules, such as JAK and STATs, PI3K, MAPK, and NF-kappaB were found to play a role in the synergistic induction of CXCL10. Furthermore, PDGF via its activation of p38 MAPK was able to increase the stability of IFN-gamma-induced CXCL10 mRNA. Understanding the mechanisms involved in the synergistic up-regulation of CXCL10 could aid in the development of therapeutic modalities for HAD.

Role of the Interferon-Inducible Gene IFI16 in the Etiopathogenesis of Systemic Autoimmune Disorders

Interferons (IFNs) are now known to exert a multitude of immunological functions on both the innate and adaptive immunity. Given their pleiotropic effects on the immune system, it is conceivable that excess type I IFN or aberrant regulation of its signaling could contribute to autoimmunity. Several lines of evidence link IFNs to autoimmune disorders, in particular to systemic lupus erythematosus (SLE) and systemic sclerosis (SSc). Expression of a spectrum of genes that constitutes an "IFN signature" is the most significant observation indicating that IFNs may be dominant among the pathogenic mediators involved in some autoimmune diseases. A family of IFN-inducible genes, designated HIN-200 in the human and IFI-200 in the murine species, encodes evolutionary related human (IFI16, MNDA, AIM2, IFIX) and murine proteins (Ifi202 a, Ifi202b, Ifi203, Ifi204, Ifi205/D3). Physiological IFI16 expression was found in cells of the immune system, in endothelial cells, and in stratified squamous epithelia, such as skin. The presence of anti-IFI16 antibodies was reported in SLE and primary/secondary Sjögren's syndrome. More recently, we reported that anti-IFI16 autoantibodies differentiate limited cutaneous systemic sclerosis (lcSSc) from diffuse systemic sclerosis (dcSSc). Molecular studies performed in primary endothelial cells overexpressing IFI16 demonstrated that it may be involved in the early steps of inflammation by modulating endothelial cell function, such as expression of adhesion molecules and chemokine production, cell growth, and apoptosis. Moreover, here we report that IFI16 expression is induced by proinflammatory cytokines. In this article the role of the IFI16 protein and its corresponding autoantibodies in the etiopathogenesis of systemic autoimmune diseases, in which chronic inflammation is involved, are discussed.

Effector ExoU from the type III secretion system is an important modulator of gene expression in lung epithelial cells in response to Pseudomonas aeruginosa infection

Pseudomonas aeruginosa is an important pathogen in immunocompromised patients and secretes a diverse set of virulence factors that aid colonization and influence host cell defenses. An important early step in the establishment of infection is the production of type III-secreted effectors translocated into host cells by the bacteria. We used cDNA microarrays to compare the transcriptomic response of lung epithelial cells to P. aeruginosa mutants defective in type IV pili, the type III secretion apparatus, or in the production of specific type III-secreted effectors. Of the 18,000 cDNA clones analyzed, 55 were induced or repressed after 4 h of infection and could be classified into four different expression patterns. These include (i) host genes that are induced or repressed in a type III secretion-independent manner (32 clones), (ii) host genes induced specifically by ExoU (20 clones), and (iii) host genes induced in an ExoU-independent but type III secretion dependent manner (3 clones). In particular, ExoU was essential for the expression of immediate-early response genes, including the transcription factor c-Fos. ExoU-dependent gene expression was mediated in part by early and transient activation of the AP1 transcription factor complex. In conclusion, the present study provides a detailed insight into the response of epithelial cells to infection and indicates the significant role played by the type III virulence mechanism in the initial host response.

IP-10 gene transcription by virus in astrocytes requires cooperation of ISRE with adjacent kappaB site but not IRF-1 or viral transcription

Transcription of the IP-10 gene requires interferon (IFN)-stimulated response element (ISRE) and kappaB sites to be induced by lipopolysaccharide (LPS), IFN-gamma, virus, and poly(I:C). A requirement for Stat1 binding to ISRE for IFN-gamma and IFN regulatory factor-1 (IRF-1) binding to ISRE for LPS, poly(I:C), and virus has been reported. We investigated whether viral transcription is required for IP-10 induction and how ISRE interacts with IRF-1 and with two kappaB sites. IP-10 mRNA was induced by Newcastle disease virus and Sendai virus in rat astrocytes and the human astrocytoma U251 cell line. IP-10 was also induced by UV-irradiated virus, which is unable to carry out viral transcription. The minimal IP-10 virus response element (VRE) consists of an ISRE and adjacent kappaB site between -236 and -153, to which p50/p65 NF-kappaB proteins and IRF-like proteins bind. Virus induced NF-kappaB binding to an isolated kappaB sequence adjacent to ISRE. However, no protein binding to isolated ISRE was induced by virus. Virus also induced IP-10 in cells expressing a defective IRF-1 gene. Therefore, effective ISRE activity of IP-10 VRE may require an IRF-like protein binding, which is enhanced by an NF-kappaB heterodimer binding to an adjacent KB site. IRF-1 is not required for virus-induced IP-10 gene expression.

Expression and regulation of interferon-gamma-inducible protein 10 gene in rat Leydig cells

In the present study, we report the cloning of a gene that is differentially expressed in normal adult rat Leydig cells and whose expression is inhibited by hCG but is induced by interferon-gamma (IFNgamma). DNA sequence analysis identified this gene as rat IFNgamma-inducible protein 10 (IP-10), a member of the -C-X-C- chemokine superfamily of proinflammatory cytokines. High levels of IP-10 messenger RNA (mRNA) were constitutively expressed in freshly isolated and primary cultured Leydig cells. hCG inhibited this expression in a dose-dependent manner. The addition of 1 ng/ml hCG inhibited IP-10 mRNA levels more than 80%. Conversely, IP-10 mRNA levels were markedly increased in response to murine interleukin-1alpha, murine tumor necrosis factor-alpha, and murine IFNgamma by 3.3-, 10-, and 26-fold, respectively. Concomitant addition of murine interleukin-1alpha, murine tumor necrosis factor-alpha, and murine IFNgamma synergistically increased IP-10 mRNA levels by 58-fold. Furthermore, in addition to one previously described rat IP-10 mRNA transcript (1.5 kb), another larger transcript (2.7 kb) was identified by Northern blot in rat Leydig cells. After screening a rat testis complementary DNA library, we obtained a partial structural gene and an intron sequence, which possibly originated from the larger transcript of rat IP-10 mRNA. Histochemical and immunocytochemical staining revealed that purified cells were positive for 3beta-hydroxysteroid dehydrogenase and IP-10, confirming that IP-10 is indeed present in Leydig cells. IP-10 antisense oligonucleotides enhanced basal and hCG-induced testosterone formation. This suggests that endogenous IP-10 has an inhibitory effect on Leydig cell steroidogenesis. In conclusion, IP-10 is expressed in rat Leydig cells and may have paracrine and autocrine effects on testicular function.

The immunobiology of interferon-gamma inducible protein 10 kD (IP-10): a novel, pleiotropic member of the C-X-C chemokine superfamily

Interferon-gamma inducible protein 10 kD (IP-10) is a highly inducible, primary response gene that belongs to the C-X-C chemokine superfamily. Despite the original cloning of IP-10 in 1985, its biological functions are still unclear although accumulating reports indicate that it is a pleiotropic molecule capable of eliciting potent biological effects, including stimulation of monocytes, natural killer and T-cell migration, regulation of T-cell and bone marrow progenitor maturation, modulation of adhesion molecule expression as well as inhibition of angiogenesis. More interest is now likely to be focused on IP-10 due to the recent cloning of an IP-10 receptor. This paper aims to highlight our current knowledge of IP-10 and its homologues as well as defining its likely involvement in regulating fibroproliferation following inflammatory lung injury.

Induction of IP-10 chemokine promoter by measles virus: comparison with interferon-gamma shows the use of the same response element but with differential DNA-protein binding profiles

Measles virus (MV) and interferon (IFN)-gamma induced IP-10 chemokine mRNA in U373 glioblastoma cells. The minimal response element for both MV and IFN-gamma was localized between nucleotide -231 and -153 of muIP-10 promoter, which contains an IFN-stimulated response element (ISRE) and the distal NF-kappa Bd site. Mutation of individual elements showed that ISRE and NF-kappa Bd were required to function together. DNA-protein binding profiles with the minimal response element showed that IFN-gamma induced a complex consisting of STAT1 while MV induced a complex consisting of p50 and p65 in the absence of new protein synthesis. IFN-gamma and MV also induced IRF-1 DNA binding activity which persisted for longer time periods with IFN-gamma stimulation. Despite the functional requirement of both ISRE and NF-kappa Bd elements, different combinations of DNA binding factors are used in the induction of IP-10 by MV or IFN-gamma.

Do chemokines mediate inflammatory cell invasion of the central nervous system parenchyma?

Inflammatory cell recruitment into the central nervous system (CNS) is a critical step in the response to diverse insults, including infection, trauma and infarction, as well as immune-mediated disorders such as multiple sclerosis (MS). Despite considerable advances in understanding immune surveillance and antigen recognition in the CNS, the signals resulting in parenchymal inflammation are incompletely understood. Members of a novel family of chemo-attractant cytokines, the chemokines, are made in the CNS and are emerging as likely mediators of inflammatory cell migration into the CNS.

Dissociation of lipopolysaccharide (LPS)-inducible gene expression in murine macrophages pretreated with smooth LPS versus monophosphoryl lipid A

Lipopolysaccharide (LPS) and the nontoxic derivative of lipid A, monophosphoryl lipid A (MPL), were employed to assess the relationship between expression of LPS-inducible inflammatory genes and the induction of tolerance to LPS in murine macrophages. Both LPS and MPL induced expression (as assessed by increased steady-state mRNA levels) of a panel of seven "early" inflammatory genes including the tumor necrosis factor alpha (TNF-alpha), interleukin-1 beta, type 2 TNF receptor (TNFR-2), IP-10, D3, D8, and D2 genes (the last four represent LPS-inducible early genes whose functions remain unknown). In addition, LPS and MPL were both capable of inducing tolerance to LPS. The two stimuli differed in the relative concentration required to induce various outcome measures, with LPS being 100- to 1,000-fold more potent on a mass concentration basis. Characterization of the tolerant state identified three distinct categories of responsiveness. Two genes (IP-10 and D8) exhibited strong desensitization in macrophages pretreated with tolerance-inducing concentrations of either LPS or MPL. In macrophages rendered tolerant by pretreatment with LPS or MPL, a second group of inducible mRNAs (TNF-alpha, interleukin-1 beta, and D3) showed moderate suppression of response to secondary stimulation by LPS. The third category of inducible genes (TNFR-2 and D2) showed increased expression in macrophages pretreated with tolerance-inducing concentrations of either LPS or MPL. All of the LPS-inducible genes examined exhibited modest superinduction with less than tolerance-inducing concentrations of either stimulus, suggesting a priming effect of these adjuvants at low concentration. The differential behavior of the members of this panel of endotoxin-responsive genes thus offers insight into molecular events associated with acquisition of transient tolerance to LPS.

Lipopolysaccharide induces competence genes JE and KC in Balb/C 3T3 cells

The expression of the early genes JE and KC has been examined in Balb/C 3T3 cells treated with bacterial lipopolysaccharide (LPS). Previous studies showed that JE and KC mRNAs are induced in murine peritoneal macrophages treated with LPS, suggesting a role for these genes in inflammatory responses. Consistent with this possibility are recently published cDNA sequences which document that both genes are members of a superfamily of inflammation- and/or growth-related cytokines. In the present study, we provide evidence that the mRNAs for JE and KC are specifically induced by LPS treatment of Balb/c 3T3 cells. The LPS-stimulated expression of JE and KC was dose dependent, and exhibited a transient time course; message levels were maximal between 2 and 4 hr and declined by 8 hr. The LPS-augmented accumulation of JE and KC occurred even in the presence of cyclohexamide, which additionally had a superinducing effect on the expression of both genes. Cyclohexamide alone, in the absence of LPS, also induced JE and KC mRNA accumulation. LPS-stimulated JE and KC mRNA expression was dependent upon the stimulation of transcription as determined by nuclear "run-on" studies. Comparative analyses indicated that, under the conditions employed, LPS was a somewhat less effective stimulant of JE expression than PDGF or EGF, and was more effective than PDGF and equivalent to EGF in its ability to augment KC accumulation. Unlike PDGF and EGF, LPS did not stimulate DNA synthesis by Balb/c 3T3 cells at any time over the 72 hr period examined. The ability of the inflammatory, non-mitogenic stimulus LPS to selectively induce JE and KC mRNA expression by fibroblasts may reflect their participation in inflammation and wound healing as secretory cells.

A macrophage LPS-inducible early gene encodes the murine homologue of IP-10

Recently, we have isolated and characterized a set of cDNA clones which encode lipopolysaccharide-inducible proteins in murine peritoneal macrophages. Here, we report the sequence and identification of one of these cDNAs previously termed C7. Nucleotide sequence analysis revealed an open reading frame encoding a predicted polypeptide composed of 98 amino acids, which contained a 21 amino acid residue signal peptide, indicating approximately 9 kDa of mature protein. The deduced protein sequence showed homology (67% identity, 77% considering conservative amino acid changes) with the human INF gamma-inducible gene IP-10, a member of the recently described superfamily of chemotactic and mitogenic proteins which includes platelet factor 4, monocyte-derived neutrophil chemotactic factor (NAF, NAP-1, IL-8), and MGSA/gro/KC. Thus C7 would appear to represent the murine homologue of the human IP-10 gene or a very closely related gene.

Dexamethasone selectively regulates LPS-inducible gene expression in murine peritoneal macrophages

Our laboratory has recently described the characterization of three distinct cDNAs (designated C7, D3 and D8) encoding genes whose expression is induced in murine peritoneal macrophages by treatment with inflammatory stimuli such as IFNs and lipopolysaccharide (LPS). Sequence analysis of full-length cDNA for C7 suggests that this encodes the murine homologue of the human IFN gamma-inducible protein IP-10. Partial sequence analysis of D3 and D8 cDNAs has revealed no significant homology with known sequences. Treatment of macrophages with the corticosteroid hormone dexamethasone (Dex) suppressed LPS-induced gene expression in a selective manner, having little or no effect on induced D3 mRNA levels, but markedly inhibiting the accumulation of both C7 and D8 mRNAs. The suppression of LPS-induced C7 and D8 mRNAs was dose-dependent in the range 0.01-10 microM Dex. Furthermore, the inhibitory effect was corticosteroid-specific because testosterone, beta-estradiol and progesterone had no effect on gene expression when used at comparable doses. Inhibition of protein synthesis did not abolish the suppressive activity of Dex, indicating that no intermediate Dex-inducible protein was necessary to suppress the expression of LPS-inducible genes. When macrophages were treated with Dex after initiation of LPS treatment, the suppressive effects were diminished in a time-dependent fashion. However, even when the hormone was added as much as 2 h after LPS, sensitive gene expression was still markedly inhibited. Finally, Dex inhibited the transcription of genes encoding C7 and D8 mRNAs when administered 15 min before LPS but had little effect when added 1 h after LPS.(ABSTRACT TRUNCATED AT 250 WORDS)