Down-regulation of high mobility group-I(Y) protein contributes to the inhibition of nitric-oxide synthase 2 by transforming growth factor-beta1

Correction of immunosuppression in aged septic rats by human ghrelin and growth hormone through the vagus nerve-dependent inhibition of TGF-β production

BACKGROUND

Co-administration of human ghrelin and growth hormone (GH) reverse immunosuppression in septic aged animals, but the mechanism remains elusive. Here, we hypothesize that ghrelin and GH co-treatment restores the immune response in aged septic rats by inhibiting the production of transforming growth factor-β (TGF-β), an immunoregulatory cytokine, through the vagus nerve.

METHODS

Male aged Fischer rats (22-23-month-old) were made septic by cecal ligation and puncture (CLP) with or without dissecting the vagus nerve (vagotomy). Human ghrelin and GH or vehicle (PBS) were administrated subcutaneously at 5 h post CLP. After 20 h of CLP, serum and spleens were harvested.

RESULTS

Serum TGF-β levels were increased in septic aged rats, while ghrelin and GH treatment significantly reduced its levels. Expression of TGF-β in the spleen was upregulated after sepsis, while ghrelin and GH treatment significantly inhibited its expression. TNF-α and IL-6 levels were significantly reduced after ex vivo LPS stimulation of splenocytes from rats that underwent CLP compared to sham rats; while these levels were significantly higher in splenocytes from ghrelin and GH-treated CLP rats compared to vehicle-treated CLP rats. Ghrelin and GH treatment reduced program death receptor-1 (PD-1) expression, increased human leukocyte antigen-DR (HLA-DR) expression, attenuated lymphopenia, and cleaved caspase-3 levels in the spleen of septic aged rats. Vagotomy diminished the beneficial effects of ghrelin and GH treatment in septic rats. In vitro, the addition of ghrelin, GH, or ghrelin and GH together had no effect on restoring immune response in splenocytes from CLP rats following LPS stimulation, indicating the requirement of the vagus nerve for ghrelin and GH's effect.

CONCLUSIONS

Ghrelin and GH attenuate immunosuppression in aged septic rats through the vagus nerve-dependent inhibition of TGF-β production.

Frontline Science: Targeted expression of a dominant-negative high mobility group A1 transgene improves outcome in sepsis

High mobility group (HMG) proteins are a family of architectural transcription factors, with HMGA1 playing a role in the regulation of genes involved in promoting systemic inflammatory responses. We speculated that blocking HMGA1-mediated pathways might improve outcomes from sepsis. To investigate HMGA1 further, we developed genetically modified mice expressing a dominant negative (dn) form of HMGA1 targeted to the vasculature. In dnHMGA1 transgenic (Tg) mice, endogenous HMGA1 is present, but its function is decreased due to the mutant transgene. These mice allowed us to specifically study the importance of HMGA1 not only during a purely pro-inflammatory insult of endotoxemia, but also during microbial sepsis induced by implantation of a bacterial-laden fibrin clot into the peritoneum. We found that the dnHMGA1 transgene was only present in Tg and not wild-type (WT) littermate mice, and the mutant transgene was able to interact with transcription factors (such as NF-κB), but was not able to bind DNA. Tg mice exhibited a blunted hypotensive response to endotoxemia, and less mortality in microbial sepsis. Moreover, Tg mice had a reduced inflammatory response during sepsis, with decreased macrophage and neutrophil infiltration into tissues, which was associated with reduced expression of monocyte chemotactic protein-1 and macrophage inflammatory protein-2. Collectively, these data suggest that targeted expression of a dnHMGA1 transgene is able to improve outcomes in models of endotoxin exposure and microbial sepsis, in part by modulating the immune response and suggest a novel modifiable pathway to target therapeutics in sepsis.

Curcumin inhibits lipopolysaccharide (LPS)-induced endotoxemia and airway inflammation through modulation of sequential release of inflammatory mediators (TNF-α and TGF-β1) in murine model

OBJECTIVE

Curcumin (diferuloylmethane), a major component of turmeric is well known for its anti-inflammatory potential. Present study investigates sequential release of inflammatory mediators post LPS challenge (10 mg/kg,i.p.) causing lung inflammation and its modulation by curcumin through different routes (20 mg/kg, i.p and 10 mg/kg, i.n.) in murine model. Dexamethasone (1 mg/kg, i.p) was used as standard drug.

METHODS

Lung Inflammation was evaluated by histopathological analysis, myeloperoxidase (MPO) activity followed by inflammatory cell count and total protein content measurements in bronchoalveolar fluid (BALF). Reactive oxygen species (ROS), nitrite and TNF-α levels were measured as markers of endotoxin shock at different time points (1-72 h). The mRNA expression of transforming growth factors-β1 (TGF-β1), iNOS and Toll-like receptor-4 (TLR-4) were measured followed by Masson's trichrome staining and hydroxyproline levels as collagen deposition marker leading to fibrotic changes in lungs.

RESULTS

We found that LPS-induced lung inflammation and injury was maximum 24-h post LPS challenge shown by MPO and histological analysis which was further supported by elevated nitrite and ROS levels whereas TNF-α level was highest after 1 h. Endotoxin-induced mortality was significantly reduced in curcumin (i.p) pretreatment groups up to 72-h post LPS challenge. Significant inhibition in mRNA expression of iNOS, TGF-β1 and TNF-α level was noted after curcumin treatment along with lowered MPO activity, inflammatory cell count, ROS, nitrite levels and collagen deposition in lungs.

CONCLUSION

Our results suggest that higher endotoxin dose causes inflammatory mediator release in chronological order which tend to increase with time and reached maximum after 24-h post-endotoxin (LPS) exposure. Intraperitoneal route of curcumin administration was better in modulating inflammatory mediator release in early phase as compared to intranasal route of administration. It can be used as supplementary therapeutic intervention at early stage of endotoxemia, having fewer side effects.

The High Mobility Group A1 (HMGA1) Transcriptome in Cancer and Development

BACKGROUND & OBJECTIVES

Chromatin structure is the single most important feature that distinguishes a cancer cell from a normal cell histologically. Chromatin remodeling proteins regulate chromatin structure and high mobility group A (HMGA1) proteins are among the most abundant, nonhistone chromatin remodeling proteins found in cancer cells. These proteins include HMGA1a/HMGA1b isoforms, which result from alternatively spliced mRNA. The HMGA1 gene is overexpressed in cancer and high levels portend a poor prognosis in diverse tumors. HMGA1 is also highly expressed during embryogenesis and postnatally in adult stem cells. Overexpression of HMGA1 drives neoplastic transformation in cultured cells, while inhibiting HMGA1 blocks oncogenic and cancer stem cell properties. Hmga1 transgenic mice succumb to aggressive tumors, demonstrating that dysregulated expression of HMGA1 causes cancer in vivo. HMGA1 is also required for reprogramming somatic cells into induced pluripotent stem cells. HMGA1 proteins function as ancillary transcription factors that bend chromatin and recruit other transcription factors to DNA. They induce oncogenic transformation by activating or repressing specific genes involved in this process and an HMGA1 "transcriptome" is emerging. Although prior studies reveal potent oncogenic properties of HMGA1, we are only beginning to understand the molecular mechanisms through which HMGA1 functions. In this review, we summarize the list of putative downstream transcriptional targets regulated by HMGA1. We also briefly discuss studies linking HMGA1 to Alzheimer's disease and type-2 diabetes.

CONCLUSION

Further elucidation of HMGA1 function should lead to novel therapeutic strategies for cancer and possibly for other diseases associated with aberrant HMGA1 expression.

Neonatal sepsis and inflammatory mediators

Neonatal sepsis is a major cause of morbidity and mortality and its signs and symptoms are nonspecific, which makes the diagnosis difficult. The routinely used laboratory tests are not effective methods of analysis, as they are extremely nonspecific and often cause inappropriate use of antibiotics. Sepsis is the result of an infection associated with a systemic inflammatory response with production and release of a wide range of inflammatory mediators. Cytokines are potent inflammatory mediators and their serum levels are increased during infections, so changes from other inflammatory effector molecules may occur. Although proinflammatory and anti-inflammatory cytokines have been identified as probable markers of neonatal infection, in order to characterize the inflammatory response during sepsis, it is necessary to analyze a panel of cytokines and not only the measurement of individual cytokines. Measurements of inflammatory mediators bring new options for diagnosing and following up neonatal sepsis, thus enabling early treatment and, as a result, increased neonatal survival. By taking into account the magnitude of neonatal sepsis, the aim of this review is to address the role of cytokines in the pathogenesis of neonatal sepsis and its value as a diagnostic criterion.

Cytokines in sepsis: potent immunoregulators and potential therapeutic targets--an updated view

Sepsis and septic shock are among the leading causes of death in intensive care units worldwide. Numerous studies on their pathophysiology have revealed an imbalance in the inflammatory network leading to tissue damage, organ failure, and ultimately, death. Cytokines are important pleiotropic regulators of the immune response, which have a crucial role in the complex pathophysiology underlying sepsis. They have both pro- and anti-inflammatory functions and are capable of coordinating effective defense mechanisms against invading pathogens. On the other hand, cytokines may dysregulate the immune response and promote tissue-damaging inflammation. In this review, we address the current knowledge of the actions of pro- and anti-inflammatory cytokines in sepsis pathophysiology as well as how these cytokines and other important immunomodulating agents may be therapeutically targeted to improve the clinical outcome of sepsis.

Maternal smoking and the retinoid pathway in the developing lung

BACKGROUND

Maternal smoking is a risk factor for pediatric lung disease, including asthma. Animal models suggest that maternal smoking causes defective alveolarization in the offspring. Retinoic acid signaling modulates both lung development and postnatal immune function. Thus, abnormalities in this pathway could mediate maternal smoking effects. We tested whether maternal smoking disrupts retinoic acid pathway expression and functioning in a murine model.

METHODS

Female C57Bl/6 mice with/without mainstream cigarette smoke exposure (3 research cigarettes a day, 5 days a week) were mated to nonsmoking males. Cigarette smoke exposure continued throughout the pregnancy and after parturition. Lung tissue from the offspring was examined by mean linear intercept analysis and by quantitative PCR. Cell culture experiments using the type II cell-like cell line, A549, tested whether lipid-soluble cigarette smoke components affected binding and activation of retinoic acid response elements in vitro.

RESULTS

Compared to tobacco-naïve mice, juvenile mice with tobacco toxin exposure had significantly (P < 0.05) increased mean linear intercepts, consistent with an alveolarization defect. Tobacco toxin exposure significantly (P < 0.05) decreased mRNA and protein expression of retinoic acid signaling pathway elements, including retinoic acid receptor alpha and retinoic acid receptor beta, with the greatest number of changes observed between postnatal days 3-5. Lipid-soluble cigarette smoke components significantly (P < 0.05) decreased retinoic acid-induced binding and activation of the retinoic acid receptor response element in A549 cells.

CONCLUSIONS

A murine model of maternal cigarette smoking causes abnormal alveolarization in association with altered retinoic acid pathway element expression in the offspring. An in vitro cell culture model shows that lipid-soluble components of cigarette smoke decrease retinoic acid response element activation. It is feasible that disruption of retinoic acid signaling contributes to the pediatric lung dysfunction caused by maternal smoking.

Distamycin A inhibits HMGA1-binding to the P-selectin promoter and attenuates lung and liver inflammation during murine endotoxemia

BACKGROUND

The architectural transcription factor High Mobility Group-A1 (HMGA1) binds to the minor groove of AT-rich DNA and forms transcription factor complexes ("enhanceosomes") that upregulate expression of select genes within the inflammatory cascade during critical illness syndromes such as acute lung injury (ALI). AT-rich regions of DNA surround transcription factor binding sites in genes critical for the inflammatory response. Minor groove binding drugs (MGBs), such as Distamycin A (Dist A), interfere with AT-rich region DNA binding in a sequence and conformation-specific manner, and HMGA1 is one of the few transcription factors whose binding is inhibited by MGBs.

OBJECTIVES

To determine whether MGBs exert beneficial effects during endotoxemia through attenuating tissue inflammation via interfering with HMGA1-DNA binding and modulating expression of adhesion molecules.

METHODOLOGY/PRINCIPAL FINDINGS

Administration of Dist A significantly decreased lung and liver inflammation during murine endotoxemia. In intravital microscopy studies, Dist A attenuated neutrophil-endothelial interactions in vivo following an inflammatory stimulus. Endotoxin induction of P-selectin expression in lung and liver tissue and promoter activity in endothelial cells was significantly reduced by Dist A, while E-selectin induction was not significantly affected. Moreover, Dist A disrupted formation of an inducible complex containing NF-kappaB that binds an AT-rich region of the P-selectin promoter. Transfection studies demonstrated a critical role for HMGA1 in facilitating cytokine and NF-kappaB induction of P-selectin promoter activity, and Dist A inhibited binding of HMGA1 to this AT-rich region of the P-selectin promoter in vivo.

CONCLUSIONS/SIGNIFICANCE

We describe a novel targeted approach in modulating lung and liver inflammation in vivo during murine endotoxemia through decreasing binding of HMGA1 to a distinct AT-rich region of the P-selectin promoter. These studies highlight the ability of MGBs to function as molecular tools for dissecting transcriptional mechanisms in vivo and suggest alternative treatment approaches for critical illness.

Netropsin improves survival from endotoxaemia by disrupting HMGA1 binding to the NOS2 promoter

The inducible form of nitric oxide synthase (NOS2) plays an important role in sepsis incurred as a result of infection with Gram-negative bacteria that elaborate endotoxin. The HMGA1 (high-mobility group A1) architectural transcription factor facilitates NOS2 induction by binding a specific AT-rich Oct (octamer) sequence in the core NOS2 promoter via AT-hook motifs. The small-molecule MGB (minor-groove binder) netropsin selectively targets AT-rich DNA sequences and can interfere with transcription factor binding. We therefore hypothesized that netropsin would improve survival from murine endotoxaemia by attenuating NOS2 induction through interference with HMGA1 DNA binding to the core NOS2 promoter. Netropsin improved survival from endotoxaemia in wild-type mice, yet not in NOS2-deficient mice, supporting an important role for NOS2 in the beneficial effects of MGB administration. Netropsin significantly attenuated NOS2 promoter activity in macrophage transient transfection studies and the AT-rich HMGA1 DNA-binding site was critical for this effect. EMSAs (electrophoretic mobility-shift assays) demonstrated that netropsin interferes with HMGA1 NOS2 promoter binding and NMR spectroscopy was undertaken to characterize this disruption. Chemical shift perturbation analysis identified that netropsin effectively competes both HMGA1 DNA-binding AT-hooks from the AT-rich NOS2 promoter sequence. Furthermore, NOESY data identified direct molecular interactions between netropsin and A/T base pairs within the NOS2 promoter HMGA1-binding site. Finally, we determined a structure of the netropsin/NOS2 promoter Oct site complex from molecular modelling and dynamics calculations. These findings represent important steps toward refined structure-based ligand design of novel compounds for therapeutic benefit that can selectively target key regulatory regions within genes that are important for the development of critical illness.

Mechanistic exploration of phthalimide neovascular factor 1 using network analysis tools

Neovascularization is essential for the survival and successful integration of most engineering tissues after implantation in vivo. The objective of this study was to elucidate possible mechanisms of phthalimide neovascular factor 1 (PNF1), a new synthetic small molecule proposed for therapeutic induction of angiogenesis. Complementary deoxyribonucleic acid microarray analysis was used to identify 568 transcripts in human microvascular endothelial cells (HMVECs) that were significantly regulated after 24-h stimulation with 30 muM of PNF1, previously known as SC-3-149. Network analysis tools were used to identify genetic networks of the global biological processes involved in PNF1 stimulation and to describe known molecular and cellular functions that the drug regulated most highly. Examination of the most significantly perturbed networks identified gene products associated with transforming growth factor-beta (TGF-beta), which has many known effects on angiogenesis, and related signal transduction pathways. These include molecules integral to the thrombospondin, plasminogen, fibroblast growth factor, epidermal growth factor, ephrin, Rho, and Ras signaling pathways that are essential to endothelial function. Moreover, real-time reverse-transcriptase polymerase chain reaction (RT-PCR) of select genes showed significant increases in TGF-beta-associated receptors endoglin and beta glycan. These experiments provide important insight into the pro-angiogenic mechanism of PNF1, namely, TGF-beta-associated signaling pathways, and may ultimately offer new molecular targets for directed drug discovery.

Transforming growth factor-beta1 blocks in vitro cardiac myocyte depression induced by tumor necrosis factor-alpha, interleukin-1beta, and human septic shock serum

OBJECTIVE

Serum from patients with septic shock induces depression of myocyte contractility in vitro that is proportional the reduction of ejection fraction in vivo. This effect is mediated, in part, by tumor necrosis factor (TNF)-alpha and interleukin (IL)-1beta. Transforming growth factor (TGF)-beta is an immunomodulatory cytokine with a broad range of anti-inflammatory effects. Using an in vitro assay, this study sought to determine the effect of TGF-beta1 on myocyte depression induced by TNF-alpha, IL-1beta, and serum with known depressant activity from patients with septic shock.

DESIGN

The maximum extent of shortening of electrically paced rat cardiac myocytes in tissue culture was quantified by a closed-loop video tracking system. Myocytes were exposed to different combinations of TNF-alpha, IL-1beta, septic serum, and TGF-beta1.

SETTING

Basic research laboratory.

MEASUREMENTS AND MAIN RESULTS

Increasing concentrations of TNF-alpha and IL-1beta each caused significant depression of maximum extent of myocyte shortening in vitro over 30 mins (p<.0001). Similarly, a synergistic combination of TNF-alpha and IL-1beta as well as serum with known depressant activity from five patients with acute septic shock induced significant depression of cardiac myocyte contraction (p<.01). Increasing concentrations of TGF-beta1 alone had no effect on maximum extent of cardiac myocyte contraction. However, myocytes that were co-incubated with increasing concentrations of TGF-beta1 demonstrated dose-dependent reversal of depression induced by TNF-alpha or IL-1beta (p<.0001). Similarly, depressant effects caused by synergistic concentrations of TNF-alpha and IL-1beta and serum from all five patients with septic shock were prevented by co-incubation with TGF-beta1.

CONCLUSIONS

These data demonstrate that depression of in vitro cardiac myocyte contraction induced by proinflammatory cytokines and septic serum can be blocked by TGF-beta1. TGF-beta1 may have potential as therapy for sepsis-associated myocardial depression in humans.

Multiple inhibitory pathways for lipopolysaccharide- and pro-inflammatory cytokine-induced nitric oxide production in cultured astrocytes

We previously showed that lipopolysaccharide (LPS) and pro-inflammatory cytokines utilized different mechanisms for the production of nitric oxide (NO) by inducible nitric oxide synthase (iNOS) in cultured rat astrocytes. To further characterize these regulatory pathways, we tested the effects of inhibitory factors (anti-inflammatory cytokines, cellular cAMP, and glucocorticoid) on aspects of iNOS expression (from transcription to enzyme activity) during LPS- and cytokine-induced astrocyte NO production. Anti-inflammatory cytokines (transforming growth factor-beta and interleukin-4) suppressed both LPS- and cytokine-induced NO production by reducing iNOS protein expression without affecting mRNA levels. Increased cellular cAMP levels, induced by noradrenaline or forskolin, suppressed LPS-induced, but not cytokine-induced, NO production without affecting iNOS protein expression. The glucocorticoid analog, dexamethasone, suppressed LPS-induced, but not cytokine-induced, NO production by reducing iNOS promoter activity. These different mechanisms would allow the fine control of NO concentration in the brain, as well as accounting for the multiple roles of NO in brain physiology and pathology. Moreover, these mechanisms provide useful therapeutic targets for the treatment of neurodegenerative diseases.

PU.1 regulates cathepsin S expression in professional APCs

Cathepsin S (CTSS) is a cysteine protease that is constitutively expressed in APCs and mediates processing of MHC class II-associated invariant chain. CTSS and the Ets family transcription factor PU.1 are highly expressed in cells of both myeloid (macrophages and dendritic cells) and lymphoid (B lymphocytes) lineages. Therefore, we hypothesized that PU.1 participates in the transcriptional regulation of CTSS in these cells. In A549 cells (a human epithelial cell line that does not express either CTSS or PU.1), the expression of PU.1 enhances CTSS promoter activity approximately 5- to 10-fold. In RAW cells (a murine macrophage-like cell line that constitutively expresses both CTSS and PU.1), the expression of a dominant-negative PU.1 protein and a short-interfering RNA PU.1 construct attenuates basal CTSS promoter activity, mRNA levels, and protein expression. EMSAs show binding of PU.1 to oligonucleotides derived from the CTSS promoter at two different Ets consensus binding elements. Mutation of these sites decreases the baseline CTSS activity in RAW cells that constitutively express PU.1. Chromatin immunoprecipitation experiments show binding of PU.1 with the CTSS promoter in this same region. Finally, the expression of PU.1, in concert with several members of the IFN regulatory factor family, enhances CTSS promoter activity beyond that achieved by PU.1 alone. These data indicate that PU.1 participates in the regulation of CTSS transcription in APCs. Thus, manipulation of PU.1 expression may directly alter the endosomal proteolytic environment in these cells.

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.

A critical role for the Sp1-binding sites in the transforming growth factor-beta-mediated inhibition of lipoprotein lipase gene expression in macrophages

Increasing evidence suggests that the cytokine transforming growth factor-β (TGF-β) inhibits the development of atherosclerosis. The lipoprotein lipase (LPL) enzyme expressed by macrophages has been implicated in the pathogenesis of atherosclerosis by stimulating the uptake of lipoprotein particles. Unfortunately, the action of TGF-β on the expression of LPL in macrophages remains largely unclear. We show that TGF-β inhibits LPL gene expression at the transcriptional level. Transient transfection assays reveal that the −31/+187 sequence contains the minimal TGF-β-responsive elements. Electrophoretic mobility shift assays show that Sp1 and Sp3 interact with two regions in the −31/+187 sequence. Mutations of these Sp1/Sp3 sites abolish the TGF-β-mediated suppression whereas multimers of the sequence impart the response to a heterologous promoter. TGF-β has no effect on the binding or steady-state polypeptide levels of Sp1 and Sp3. These results, therefore, suggest a novel mechanism for the TGF-β-mediated repression of LPL gene transcription that involves regulation of the action of Sp1 and Sp3.

Reduction of nitric oxide synthase 2 expression by distamycin A improves survival from endotoxemia

NO synthase 2 (NOS2) plays an important role in endotoxemia through overproduction of NO. Distamycin A (Dist A) belongs to a class of drugs termed minor-groove DNA binders, which can inhibit transcription factor binding to AT-rich regions of DNA. We and others have previously shown that AT-rich regions of DNA surrounding transcription factor binding sites in the NOS2 promoter are critical for NOS2 induction by inflammatory stimuli in vitro. Therefore, we hypothesized that Dist A would attenuate NOS2 up-regulation in vivo during endotoxemia and improve animal survival. C57BL/6 wild-type (WT) mice treated with Dist A and LPS (endotoxin) showed significantly improved survival compared with animals treated with LPS alone. In contrast, LPS-treated C57BL/6 NOS2-deficient (NOS2-/-) mice did not benefit from the protective effect of Dist A on mortality from endotoxemia. Treatment with Dist A resulted in protection from hypotension in LPS-treated WT mice, but not in NOS2-/- mice. Furthermore, LPS-induced NOS2 expression was attenuated in vivo (WT murine tissues) and in vitro (primary peritoneal and RAW 264.7 murine macrophages) with addition of Dist A. Dist A selectively decreased IFN regulatory factor-1 DNA binding in the enhancer region of the NOS2 promoter, and this IFN regulatory factor-1 site is critical for the effect of Dist A in attenuating LPS induction of NOS2. Our data point to a novel approach in modulating NOS2 expression in vivo during endotoxemia and suggest the potential for alternative treatment approaches for critical illness.

An octamer motif is required for activation of the inducible nitric oxide synthase promoter in pancreatic beta-cells

Nitric oxide, generated by the inducible form of nitric oxide synthase (iNOS), is a potential mediator of cytokine-induced beta-cell dysfunction in type 1 diabetes mellitus. We have previously shown that cytokine-induced iNOS expression is cycloheximide (CHX) sensitive and requires nuclear factor-kappa B (NF-kappa B) activation. In the present study, we show that an octamer motif located 20 bp downstream of the proximal NF-kappa B binding site in the rat iNOS promoter is critical for IL-1 beta and interferon-gamma induction of promoter activity in rat primary beta-cells and insulin-producing RINm5F cells. In gel shift assays, the octamer motif bound constitutively the transcription factor Oct1. Neither Oct1 nor NF-kappa B binding activities were blocked by CHX, suggesting that other factor(s) synthesized in response to IL-1 beta contribute to iNOS promoter induction. The high mobility group (HMG)-I(Y) protein also bound the proximal iNOS promoter region. HMG-I(Y) binding was decreased in cells treated with CHX and HMG-I(Y) silencing by RNA interference reduced IL-1 beta-induced iNOS promoter activity. These results suggest that Oct1, NF-kappa B, and HMG-I(Y) cooperate for transactivation of the iNOS promoter in pancreatic beta-cells.

TGF-β1 increases microbial clearance but worsens lung injury during Escherichia coli pneumonia in rats

We investigated the effects of either intravenous (IV) or intrabronchial (IB) treatment with transforming growth factor beta1 (TGF-beta1) during bacterial pneumonia in rats. Immediately following IB Escherichia coli inoculation (T0), animals (n=270) were randomized to receive a single treatment with human recombinant TGF-beta1 either via IV or IB, or via both IV and IB routes, or to receive placebo (human serum albumin, HSA) only. Blood and lung analysis was done at 6 and 168 h after E. coli inoculation. Other animals (n=40) were administered IV TGF-beta1 or HSA at T0 and 6, 12 and 24 h after E. coli inoculation to investigate the effects of multiple treatments also on survival rates alone. All animals received ceftriaxone daily. Route of administration did not influence TGF-beta1 (p=ns for the effect of TGF-beta1 comparing IV vs IB routes) and we averaged over this variable in analysis. The relative risk of death (mean +/- sem) was not altered by either single treatments administered at T0 (-0.18 +/- 0.25, p=0.47) or multiple treatments (0.40 +/- 0.50, p=0.66) of TGF-beta1. Single treatment with TGF-beta1 first decreased and then increased vascular leukocytes at 6 and 168 h, respectively, but increased alveolar leukocytes at both time points (p=0.02 comparing the differing effects of TGF-beta1 on vascular and alveolar leukocytes at 6 and 168 h). Although TGF-beta1 decreased blood and lung bacteria counts at 6 and 168 h, it also increased serum tumor necrosis factor levels and lung injury scores at these time points (p<0.05 for the effects of TGF-beta1 on each parameter at 6 and 168 h together). Thus, while increases in lung leukocyte recruitment with TGF-beta1 were associated with improved microbial clearance in this rat model of pneumonia, worsened lung injury may have negated these beneficial host defense effects, and overall survival was not significantly improved. Despite these harmful effects, additional studies may be warranted to better define the influence of exogenous TGF-beta1 on host defense during acute bacterial infections.

Elk-3 is a transcriptional repressor of nitric-oxide synthase 2

The inducible isoform of nitric-oxide synthase (NOS2), a key enzyme catalyzing the dramatic increase in nitric oxide by lipopolysaccharide (LPS), plays an important role in the pathophysiology of endotoxemia and sepsis. Recent evidence suggests that Ets transcription factors may contribute to NOS2 induction by inflammatory stimuli. In this study, we investigated the role of Ets transcription factors in the regulation of NOS2 by LPS and transforming growth factor (TGF)-beta 1. Transient transfection assays in macrophages showed that Ets-2 produced an increase in NOS2 promoter activity, whereas the induction by Ets-1 was modest and NERF2 had no effect. Elk-3 (Net/Erp/Sap-2a) markedly repressed NOS2 promoter activity in a dose-dependent fashion, and overexpression of Elk-3 blunted the induction of endogenous NOS2 message. Mutation of the Net inhibitory domain of Elk-3, but not the C-terminal-binding protein interaction domain, partially alleviated this repressive effect. We also found that deletion of the Ets domain of Elk-3 completely abolished its repressive effect on the NOS2 promoter. LPS administration to macrophages led to a dose-dependent decrease in endogenous Elk-3 mRNA levels, and this decrease in Elk-3 preceded the induction of NOS2 mRNA. In a mouse model of endotoxemia, the expression of Elk-3 in kidney, lung, and heart was significantly down-regulated after systemic administration of LPS, and this down-regulation also preceded NOS2 induction. Moreover, TGF-beta 1 significantly increased endogenous Elk-3 mRNA levels that had been down-regulated by LPS in macrophages. This increase in Elk-3 correlated with a TGF-beta 1-induced down-regulation of NOS2. Taken together, our data suggest that Elk-3 is a strong repressor of NOS2 promoter activity and mRNA levels and that endogenous expression of Elk-3 inversely correlates with NOS2. Thus, Elk-3 may serve as an important mediator of NOS2 gene expression.

Regulation of the Expression of Inducible Nitric Oxide Synthase

Nitric oxide (NO), generated by the inducible isoform of nitric oxide synthase (iNOS), has been described to have beneficial microbicidal, antiviral, antiparasital, immunomodulatory, and antitumoral effects. However, aberrant iNOS induction at the wrong place or at the wrong time has detrimental consequences and seems to be involved in the pathophysiology of several human diseases. iNOS is primarily regulated at the expression level by transcriptional and post-transcriptional mechanisms. iNOS expression can be induced in many cell types with suitable agents such as bacterial lipopolysaccharides (LPS), cytokines, and other compounds. Pathways resulting in the induction of iNOS expression may vary in different cells or different species. Activation of the transcription factors NF-kappaB and STAT-1alpha, and thereby activation of the iNOS promoter, seems to be an essential step for iNOS induction in most cells. However, at least in the human system, also post-transcriptional mechanism are critically involved in the regulation of iNOS expression. The induction of iNOS can be inhibited by a wide variety of immunomodulatory compounds acting at the transcriptional levels and/or post-transcriptionally.

The HMG I proteins: dynamic roles in gene activation, development, and tumorigenesis

The high mobility group I, Y, and I-C proteins are low-molecular-weight, nonhistone chromosomal proteins that play a general role modulating gene expression during development and the immune response. Consistent with their role in early development, all three proteins are expressed at high levels during embryogenesis, and their expression is markedly diminished in differentiated cells. Exceptions to the general repression of these genes in adult tissues involve (1) A burst of synthesis of the HMG I protein during the immune response (during lymphocyte activation and preceding cytokine/adhesion molecule gene expression), (2) A constitutive expression of the HMG I and Y proteins in photoreceptor cells, and (3) Derepression of HMG I, Y, and often I-C expression in neoplastic cells. Work from several laboratories has now uncovered how these proteins participate in gene activation: (1) By altering the chromatin structure around an inducible gene-and thus influencing accessibility of the locus to regulatory proteins-(2) By facilitating the loading of transcription factors onto the promoters, and (3) By bridging adjacent transcription factors on a promoter via protein/protein interactions. Despite the similar structures and biochemical properties of the three proteins, the work has also provided clues to a division of labor between these proteins. HMG I and Y have demonstrable roles in enhanceosome formation, whereas HMG I-C has a specific role in adipogenesis. C-terminal truncations of HMG I-C and wild-type HMG Y appear to function in a manner analogous to oncogenes, as assessed by cellular transforation assays and transgenic mice. Future work should clearly define the similarities and differences in the biological roles of the three proteins, and should evolve to include attempts at pharmaceutical intervention in disease, based upon structural information concerning HMG I interactions with DNA and with regulatory proteins.

Nitric oxide and the immune response

During the past two decades, nitric oxide (NO) has been recognized as one of the most versatile players in the immune system. It is involved in the pathogenesis and control of infectious diseases, tumors, autoimmune processes and chronic degenerative diseases. Because of its variety of reaction partners (DNA, proteins, low-molecular weight thiols, prosthetic groups, reactive oxygen intermediates), its widespread production (by three different NO synthases (NOS) and the fact that its activity is strongly influenced by its concentration, NO continues to surprise and perplex immunologists. Today, there is no simple, uniform picture of the function of NO in the immune system. Protective and toxic effects of NO are frequently seen in parallel. Its striking inter- and intracellular signaling capacity makes it extremely difficult to predict the effect of NOS inhibitors and NO donors, which still hampers therapeutic applications.