A transgenic model to study the pathogenesis of somatic mtDNA mutation accumulation in beta-cells

Low levels of somatic mutations accumulate in mitochondrial DNA (mtDNA) as we age; however, the pathogenic nature of these mutations is unknown. In contrast, mutational loads of >30% of mtDNA are associated with electron transport chain defects that result in mitochondrial diseases such as mitochondrial encephalopathy lactic acidosis and stroke-like episodes. Pancreatic beta-cells may be extremely sensitive to the accumulation of mtDNA mutations, as insulin secretion requires the mitochondrial oxidation of glucose to CO(2). Type 2 diabetes arises when beta-cells fail to compensate for the increased demand for insulin, and many type 2 diabetics progress to insulin dependence because of a loss of beta-cell function or beta-cell death. This loss of beta-cell function/beta-cell death has been attributed to the toxic effects of elevated levels of lipids and glucose resulting in the enhanced production of free radicals in beta-cells. mtDNA, localized in close proximity to one of the major cellular sites of free radical production, comprises more than 95% coding sequences such that mutations result in changes in the coding sequence. It has long been known that mtDNA mutations accumulate with age; however, only recently have studies examined the influence of somatic mtDNA mutation accumulation on disease pathogenesis. This article will focus on the effects of low-level somatic mtDNA mutation accumulation on ageing, cardiovascular disease and diabetes.

Zinc induces ERK-dependent cell death through a specific Ras isoform

The effect of Zn on p53-independent cell death was examined in IIC9 embryonic fibroblasts. Despite the fact that these cells are p53-minus, Zn-mediated death occurs via an apoptotic mechanism. Death is facilitated by the presence of the Zn ionophore, pyrithione, indicating that intracellular Zn initiates the death response. Our investigations of the mechanism of Zn action demonstrate that Zn induces the death of IIC9 cells in a manner that is ERK-dependent. Expression of dn-(dominant negative)Ras attenuates ERK1/2 activation by Zn, and correspondingly reduces its cytotoxic effects. Raf-RBD pull-down experiments confirm that Zn treatment activates Ras and identified H-Ras as the specific isoform activated. This contrasts the activation of N-Ras that occurs when IIC9 cells are stimulated with thrombin. Thus, although the prolonged activation of the Ras/ERK pathway by Zn is similar to that seen when induced by mitogen, the distinguishing feature appears to be the isoform specificity of Ras activation.

The success of orthodontic satellite practices

OBJECTIVE

To evaluate the financial success and personal satisfaction of orthodontists operating satellite practices.

MATERIALS AND METHODS

A questionnaire was e-mailed to 4426 members of the American Association of Orthodontists (AAO), and 817 completed surveys were returned, yielding an 18% response rate. Only replies from solo practitioner orthodontists were analyzed to limit variability among respondents.

RESULTS

Solo practitioner orthodontists with satellite practices reported an increase in net profit and started significantly more cases than orthodontists with one office. Yet, only 27% of respondents with one satellite and 48% of practitioners operating multiple satellites recommend opening a satellite practice. Ninety-two percent of orthodontists stated they were satisfied with the clinical aspects of their practice, and 99% of orthodontists described themselves as happy and satisfied individuals.

CONCLUSION

Despite the ability of a satellite office to expand a patient base and increase net income, most practitioners would not encourage young orthodontists to establish a satellite office.

PGJ2-stimulated beta-cell apoptosis is associated with prolonged UPR activation

Peroxisome proliferator-activated receptor-gamma (PPARgamma) ligands have been shown to possess anti-inflammatory properties that include the inhibition of transcription factor activation and the expression of inflammatory genes. Using pancreatic beta-cells, we have shown that PPARgamma ligands such as 15-deoxy-Delta(12,14)-prostaglandin J(2) (PGJ(2)) attenuate interferon-gamma-induced signal transducer and activator of transcription 1 activation and interleukin (IL)-1beta-induced nuclear factor-kappaB activation by a pathway that correlates with endoplasmic reticulum stress and the induction of the unfolded protein response (UPR). The UPR is a conserved cellular response activated by a number of cell stressors and is believed to alleviate the stress and promote cell survival. However, prolonged activation of the UPR results in cellular death by apoptosis. In this report, we have examined the effects of PGJ(2) on UPR activation and the consequences of this activation on cell survival. Consistent with induction of a cell death pathway, treatment of rat islets and RINm5F cells for 24 h with PGJ(2) results in caspase-3 activation and caspase-dependent beta-cell death. The actions of these ligands do not appear to be selective for beta-cells, because PGJ(2) stimulates macrophage apoptosis in a similar fashion. Associated with cell death is the enhanced phosphorylation of eukaryotic initiation factor 2alpha (eIF2alpha), and in cells expressing a mutant of eIF2alpha that cannot be phosphorylated, the stimulatory actions of PGJ(2) on caspase-3 activation are augmented. These findings suggest that, whereas PGJ(2)-induced UPR activation is associated with an inhibition of cytokine signaling, prolonged UPR activation results in cell death, and that eIF2alpha phosphorylation may function in a protective manner to attenuate cell death.

Induction of natural killer cell responses by ectromelia virus controls infection

Natural killer (NK) cells play a pivotal role in the innate immune response to viral infections, particularly murine cytomegalovirus (MCMV) and human herpesviruses. In poxvirus infections, the role of NK cells is less clear. We examined disease progression in C57BL/6 mice after the removal of NK cells by both antibody depletion and genetic means. We found that NK cells were crucial for survival and the early control of virus replication in spleen and to a lesser extent in liver in C57BL/6 mice. Studies of various knockout mice suggested that gammadelta T cells and NKT cells are not important in the C57BL/6 mousepox model and CD4+ and CD8+ T cells do not exhibit antiviral activity at 6 days postinfection, when the absence of NK cells has a profound effect on virus titers in spleen and liver. NK cell cytotoxicity and/or gamma interferon (IFN-gamma) secretion likely mediated the antiviral effect needed to control virus infectivity in target organs. Studies of the effects of ectromelia virus (ECTV) infection on NK cells demonstrated that NK cells proliferate within target tissues (spleen and liver) and become activated following a low-dose footpad infection, although the mechanism of activation appears distinct from the ligand-dependent activation observed with MCMV. NK cell IFN-gamma secretion was detected by intracellular cytokine staining transiently at 32 to 72 h postinfection in the lymph node, suggesting a role in establishing a Th1 response. These results confirm a crucial role for NK cells in controlling an ECTV infection.

Chemically chaperoning the actions of insulin

The role of inflammation as a mediator of insulin resistance in type 2 diabetes and obesity has been a major focus of studies over the past ten years. In mouse models of obesity and type 2 diabetes, the development of insulin resistance correlates with elevated levels of endoplasmic reticulum stress and induction of the unfolded protein response. Activation of N-terminal C-Jun kinase is known to be associated with unfolded protein response activation, and has been shown to participate in the inhibition of insulin action by stimulating serine phosphorylation of the insulin receptor substrate 1, an event that attenuates insulin signaling. 'Chemical chaperones' are small molecules that have been shown to attenuate unfolded protein response activation. The exciting new findings of Ozcan et al. indicate that chemical chaperones improve glucose tolerance and insulin action in a mouse model of type 2 diabetes. These findings offer a potential new target for therapeutic strategies designed to improve insulin action and glucose tolerance in diabetic individuals.

Role of MAPK in the regulation of double-stranded RNA- and encephalomyocarditis virus-induced cyclooxygenase-2 expression by macrophages

In response to virus infection or treatment with dsRNA, macrophages express the inducible form of cyclooxygenase-2 (COX-2) and produce proinflammatory prostaglandins. Recently, we have shown that NF-kappaB is required for encephalomyocarditis virus (EMCV)- and dsRNA-stimulated COX-2 expression in mouse macrophages. The dsRNA-dependent protein kinase R is not required for EMCV-stimulated COX-2 expression, suggesting the presence of protein kinase R-independent pathways in the regulation of this antiviral gene. In this study, the role of MAPK in the regulation of macrophage expression of cyclooxygenase-2 (COX)-2 in response to EMCV infection was examined. Treatment of mouse macrophages or RAW-264.7 cells with dsRNA or infection with EMCV stimulates the rapid activation of the MAPKs p38, JNK, and ERK. Inhibition of p38 and JNK activity results in attenuation while ERK inhibition does not modulate dsRNA- and EMCV-induced COX-2 expression and PGE2 production by macrophages. JNK and p38 appear to selectively regulate COX-2 expression, as inhibition of either kinase fails to prevent dsRNA- or EMCV-stimulated inducible NO synthase expression by macrophages. Using macrophages isolated from TLR3-deficient mice, we show that p38 and JNK activation and COX-2 expression in response to EMCV or poly(IC) does not require the presence the dsRNA receptor TLR3. These findings support a role for p38 and JNK in the selective regulation of COX-2 expression by macrophages in response to virus infection.

Insulin biosynthesis: the IREny of it all

Recent studies have shown that the unfolded protein response (UPR) is essential for the survival of insulin-producing beta cells. Work in this issue of Cell Metabolism (Lipson et al., 2006) identifies a novel role for UPR activation in beta cell function by demonstrating that the UPR effector IRE1 is a positive regulator of glucose-stimulated proinsulin biosynthesis.

Posttranslational, translational, and transcriptional responses to nitric oxide stress in Cryptococcus neoformans: implications for virulence

The ability of the fungal pathogen Cryptococcus neoformans to evade the mammalian innate immune response and cause disease is partially due to its ability to respond to and survive nitrosative stress. In this study, we use proteomic and genomic approaches to elucidate the response of C. neoformans to nitric oxide stress. This nitrosative stress response involves both transcriptional, translational, and posttranslational regulation. Proteomic and genomic analyses reveal changes in expression of stress response genes. In addition, genes involved in cell wall organization, respiration, signal transduction, transport, transcriptional control, and metabolism show altered expression under nitrosative conditions. Posttranslational modifications of transaldolase (Tal1), aconitase (Aco1), and the thiol peroxidase, Tsa1, are regulated during nitrosative stress. One stress-related protein up-regulated in the presence of nitric oxide stress is glutathione reductase (Glr1). To further investigate its functional role during nitrosative stress, a deletion mutant was generated. We show that this glr1Delta mutant is sensitive to nitrosative stress and macrophage killing in addition to being avirulent in mice. These studies define the response to nitrosative stress in this important fungal pathogen.

Interleukin-1 stimulates beta-cell necrosis and release of the immunological adjuvant HMGB1

BACKGROUND

There are at least two phases of beta-cell death during the development of autoimmune diabetes: an initiation event that results in the release of beta-cell-specific antigens, and a second, antigen-driven event in which beta-cell death is mediated by the actions of T lymphocytes. In this report, the mechanisms by which the macrophage-derived cytokine interleukin (IL)-1 induces beta-cell death are examined. IL-1, known to inhibit glucose-induced insulin secretion by stimulating inducible nitric oxide synthase expression and increased production of nitric oxide by beta-cells, also induces beta-cell death.

METHODS AND FINDINGS

To ascertain the mechanisms of cell death, the effects of IL-1 and known activators of apoptosis on beta-cell viability were examined. While IL-1 stimulates beta-cell DNA damage, this cytokine fails to activate caspase-3 or to induce phosphatidylserine (PS) externalization; however, apoptosis inducers activate caspase-3 and the externalization of PS on beta-cells. In contrast, IL-1 stimulates the release of the immunological adjuvant high mobility group box 1 protein (HMGB1; a biochemical maker of necrosis) in a nitric oxide-dependent manner, while apoptosis inducers fail to stimulate HMGB1 release. The release of HMGB1 by beta-cells treated with IL-1 is not sensitive to caspase-3 inhibition, while inhibition of this caspase attenuates beta-cell death in response to known inducers of apoptosis.

CONCLUSIONS

These findings indicate that IL-1 induces beta-cell necrosis and support the hypothesis that macrophage-derived cytokines may participate in the initial stages of diabetes development by inducing beta-cell death by a mechanism that promotes antigen release (necrosis) and islet inflammation (HMGB1 release).

Encephalomyocarditis virus induces PKR-independent mitogen-activated protein kinase activation in macrophages

In this study, we provide evidence that the double-stranded RNA-dependent protein kinase (PKR) is not required for virus-induced expression of inducible nitric oxide synthase (iNOS) or the activation of specific signaling pathways in macrophages. The infection of RAW264.7 cells with encephalomyocarditis virus (EMCV) induces iNOS expression and nitric oxide production, which are unaffected by a dominant-negative mutant of PKR. EMCV infection also activates the mitogen-activated protein kinase, cyclic AMP response element binding protein, and nuclear factor kappaB (NF-kappaB) signaling cascades at 15 to 30 min postinfection in PKR+/+ and PKR-/- macrophages. Activation of these signaling cascades does not temporally correlate with PKR activity or the accumulation of EMCV RNA, suggesting that an interaction between a structural component of the virion and the cell surface may activate macrophages. Consistent with this hypothesis, empty EMCV capsids induced comparable levels of iNOS expression, nitrite production, and activation of these signaling cascades to those induced by intact virions. These findings support the hypothesis that virion-host cell interactions are primary mediators of the PKR-independent activation of signaling pathways that participate in the macrophage antiviral response of inflammatory gene expression.

Genetic and pharmacologic evidence that calcium-independent phospholipase A2beta regulates virus-induced inducible nitric-oxide synthase expression by macrophages

Recent evidence supports a regulatory role for the calcium-independent phospholipase A2 (iPLA2) in the antiviral response of inducible nitric-oxide synthase (iNOS) expression by macrophages. Because two mammalian isoforms of iPLA2 (iPLA2beta and iPLA2gamma) have been cloned and characterized, the aim of this study was to identify the specific isoform(s) in macrophages that regulates the expression of iNOS in response to virus infection. Bromoenol lactone (BEL), a suicide substrate inhibitor of iPLA2, inhibits the activity of both isoforms at low micromolar concentrations. However, the R- and S-enantiomers of BEL display approximately 10-fold greater potency for inhibition of the enzymatic activity of iPLA2gamma and iPLA2beta, respectively. In this study, we show that the iPLA2beta-selective (S)-BEL inhibits encephalomyocarditis virus (EMCV)-induced iNOS expression, nitric oxide production, and iPLA2 enzymatic activity in macrophages in a concentration-related manner that closely resembles the inhibitory properties of racemic BEL. cAMP response element-binding protein (CREB) is one downstream target of iPLA2 that is required for the transcriptional activation of iNOS in response to virus infection, and consistent with the effects of BEL enantiomers on iNOS expression, (S)-BEL more effectively inhibits EMCV-induced CREB phosphorylation than (R)-BEL in macrophages. Using macrophages isolated from iPLA2beta-null mice, virus infection fails to stimulate iNOS mRNA accumulation and protein expression, thus providing genetic evidence that iPLA2beta is required for EMCV-induced iNOS expression. These findings provide evidence for a signaling role for iPLA2beta in virus-induced iNOS expression by macrophages.

Distinct stress responses of two functional laccases in Cryptococcus neoformans are revealed in the absence of the thiol-specific antioxidant Tsa1

Laccases are thought to be important to the virulence of many fungal pathogens by producing melanin, a presumed oxygen radical scavenger. A laccase in Cryptococcus neoformans has been shown to synthesize melanin and contributes to the virulence and the survival in macrophages of this fungal pathogen. One C. neoformans laccase gene, LAC1, previously called CNLAC1, has been extensively studied, and we describe a homologous gene, LAC2, that is found 8 kb away from LAC1 in the genome. In this study we report a role for both laccases, in addition to the thiol peroxidase, Tsa1, in oxidative and nitrosative stress resistance mechanisms of C. neoformans. With use of real-time PCR, similar changes in expression of the two laccase genes occur in response to oxidative and nitrosative stresses, but only the regulation of the LAC2 gene during stress is influenced by Tsa1. Both laccases contribute to melanin production using L-dopa as a substrate and are differentially localized in the cell based on green fluorescent protein fusions. A single deletion of either LAC1 or LAC2 alone had no effect on sensitivity to H2O2 or nitric oxide. However, deletion of either LAC1 or LAC2 in combination with a TSA1 deletion resulted in a slight peroxide sensitivity, and a lac2Delta tsa1Delta deletion strain was sensitive to nitric oxide stress. In addition, the deletion of both laccases reduces survival of C. neoformans in primary macrophages. Based on our expression and functional analysis, we propose a novel model for the interaction of these two systems, which are both important for virulence.

Incretin hormones and insulin sensitivity

Incretin hormones such as glucagon-like peptide-1 (GLP-1) and the longer lasting analog exendin-4 show clinical promise for the treatment of diabetes because of glucoregulatory activities that enhance beta-cell function and growth, and actions in the central nervous system that induce satiety and decrease caloric intake. The actions of these peptides on insulin-responsive tissues is less clear, but recent advances indicate that chronic treatment with exendin-4 increases insulin sensitivity via two distinct mechanisms: one is attributable to changes in food intake and the subsequent improvements in glycemia; the second is largely independent of reductions in blood glucose. In addition, exendin-4 might also have direct effects on beta-cell neogenesis that are independent of insulin demand.

PPARgamma ligands induce ER stress in pancreatic beta-cells: ER stress activation results in attenuation of cytokine signaling

Peroxisome proliferator-activated receptor (PPAR)gamma ligands are known to have anti-inflammatory properties that include the inhibition of cytokine signaling, transcription factor activation, and inflammatory gene expression. We have recently observed that increased expression of heat shock protein (HSP)70 correlates with, but is not required for, the anti-inflammatory actions of PPARgamma ligands on cytokine signaling. In this study, we provide evidence that the inhibitory actions of PPARgamma ligands on cytokine signaling are associated with endoplasmic reticulum (ER) stress or unfolded protein response (UPR) activation in pancreatic beta-cells. 15-Deoxy-Delta(12,14)-prostaglandin J(2), at concentrations that inhibit cytokine signaling, stimulates phosphorylation of eukaryotic initiation factor-2alpha, and this event is followed by a rapid inhibition of protein translation. Under conditions of impaired translation, PPARgamma ligands stimulate the expression of a number of ER stress-responsive genes, such as GADD 153, BiP, and HSP70. Importantly, ER stress activation in response to PPARgamma ligands or known UPR activators results in the attenuation of IL-1 and IFN-gamma signaling. These findings indicate that PPARgamma ligands induce ER stress, that ER stress activation is associated with an attenuation of cytokine signaling in beta-cells, and that the attenuation of responsiveness to extracellular stimuli appears to be a novel protective action of the UPR in cells undergoing ER stress.

Role of cyclooxygenase-2 in cytokine-induced beta-cell dysfunction and damage by isolated rat and human islets

Type I diabetes mellitus is an autoimmune disease characterized by the selective destruction of the insulin-secreting beta-cell found in pancreatic islets of Langerhans. Cytokines such as interleukin-1 (IL-1), interferon-gamma (IFN-gamma), and tumor necrosis factor-alpha (TNF-alpha) mediate beta-cell dysfunction and islet degeneration, in part, through the induction of the inducible isoform of nitric-oxide synthase and the production of nitric oxide by beta-cells. Cytokines also stimulate the expression of the inducible isoform of cyclooxygenase, COX-2, and the production of prostaglandin E(2) (PGE(2)) by rat and human islets; however, the role of increased COX-2 expression and PGE(2) production in mediating cytokine-induced inhibition of islet metabolic function and viability has been incompletely characterized. In this study, we have shown that treatment of rat islets with IL-1beta or human islets with a cytokine mixture containing IL-1beta + IFN-gamma +/- TNF-alpha stimulates COX-2 expression and PGE(2) formation in a time-dependent manner. Co-incubation of rat and human islets with selective COX-2 inhibitors SC-58236 and Celecoxib, respectively, attenuated cytokine-induced PGE(2) formation. However, these inhibitors failed to prevent cytokine-mediated inhibition of insulin secretion or islet degeneration. These findings indicate that selective inhibition of COX-2 activity does not protect rat and human islets from cytokine-induced beta-cell dysfunction and islet degeneration and, furthermore, that islet production of PGE(2) does not mediate these inhibitory and destructive effects.

Glucose Regulation of Insulin Gene Expression Requires the Recruitment of p300 by the β-Cell-Specific Transcription Factor Pdx-1

Regulation of insulin gene expression in response to increases in blood glucose levels is essential for maintaining normal glucose homeostasis; however, the exact mechanisms by which glucose stimulates insulin gene transcription are not known. We have shown previously that glucose stimulates insulin gene expression by causing the hyperacetylation of histone H4 at the insulin promoter. We demonstrate that the histone acetyltransferase p300 is recruited to the insulin promoter only at high concentrations of glucose via its interaction with the beta-cell-specific transcription factor Pdx-1. Disruption of the function of the endogenous Pdx-1 abolishes the recruitment of p300 to the insulin gene promoter at high concentrations of glucose and results in decreased histone H4 acetylation and insulin gene expression. Furthermore, we demonstrate that the glucose-dependent interaction of Pdx-1 with p300 is regulated by a phosphorylation event that changes the localization of Pdx-1. Based on these data, we conclude that hyperacetylation of histone H4 at the insulin gene promoter in response to high concentrations of glucose depends on the beta-cell-specific transcription factor Pdx-1, which is required for the recruitment of the histone acetyltransferase p300 to the insulin gene promoter.

The role and regulation of COX-2 during viral infection

Prostaglandins are lipid mediators, generated by cyclooxygenase (COX), that have been shown to participate in the regulation of virus replication and the modulation of inflammatory responses following infection. A number of studies support a role for PGE2 in the modulation of virus replication and virulence in a cell type and virus selective manner. Virus infection also stimulates the expression of a number of proinflammatory gene products, including COX-2, inducible nitric oxide synthase (iNOS) as well as proinflammatory cytokines. This review will focus on the mechanisms by which proinflammatory prostaglandin production regulates virus replication and virulence. In addition, the signaling pathways that are activated during a virus infection, and that regulate proinflammatory gene expression in macrophages will be reviewed. Specific attention will be placed on the ability of virus infection to activate multiple signaling cascades (such as PKR, MAPK, iPLA2, NF-kappaB) and how these pathways are integrated in the regulation of individual target gene expression.

PPARgamma is not required for the inhibitory actions of PGJ2 on cytokine signaling in pancreatic beta-cells

Peroxisome proliferator-activated receptor (PPAR)gamma agonists, such as 15-deoxy-delta 12,14-prostaglandin J2 (PGJ2) and troglitazone, have been shown to elicit anti-inflammatory effects in pancreatic beta-cells that include inhibition of cytokine-stimulated inducible nitric oxide synthase (iNOS) gene expression and production of nitric oxide. In addition, these ligands impair IL-1-induced NF-kappaB and MAPK as well as IFN-gamma-stimulated signal transducer and activator of transcription (STAT)1 activation in beta-cells. The purpose of this study was to determine if PPARgamma activation participates in the anti-inflammatory actions of PGJ2 in beta-cells. Pretreatment of RINm5F cells for 6 h with PGJ2 results in inhibition of IL-1-stimulated IkappaB degradation and IFN-gamma-stimulated STAT1 phosphorylation. Overexpression of a dominant-negative (dn) PPARgamma mutant or treatment with the PPARgamma antagonist GW-9662 does not modulate the inhibitory actions of PGJ2 on cytokine signaling in RINm5F cells. Although these agents fail to attenuate the inhibitory actions of PGJ2 on cytokine signaling, they do inhibit PGJ2-stimulated PPARgamma response element reporter activity. Consistent with the inability to attenuate the inhibitory actions of PGJ2 on cytokine signaling, neither dnPPARgamma nor GW-9662 prevents the inhibitory actions of PGJ2 on IL-1-stimulated iNOS gene expression or nitric oxide production by RINm5F cells. These findings support a PPARgamma-independent mechanism by which PPARgamma ligands impair cytokine signaling and iNOS expression by islets.

Calcium-independent phospholipase A2 mediates CREB phosphorylation in double-stranded RNA-stimulated endothelial cells

One of the products of a calcium-independent phospholipase A2 (iPLA2) attack of plasmenylcholine, lysoplasmenylcholine, has previously been shown to activate cAMP-dependent protein kinase (PKA). Because endothelial cells respond to some agonists in part by the activation of iPLA2, the present study was designed to determine whether double-stranded RNA (dsRNA), the primary activator of the antiviral response in endothelial cells, elicits cAMP response element binding protein (CREB) phosphorylation through a mechanism mediated by iPLA2. dsRNA stimulated CREB phosphorylation in bovine pulmonary artery endothelial cells that was inhibited by the iPLA2 inhibitor, bromoenol lactone, and the PKA inhibitor, H-89. Additionally, the product of iPLA2 hydrolysis of plasmenylcholine and lysoplasmenylcholine elicited CREB phosphorylation in bovine pulmonary endothelial cells. Taken together, the present studies suggest that dsRNA as well as other agonists of endothelial cells elicit signaling mechanisms that include in part CREB phosphorylation mediated by iPLA2.

Role for c-Jun N-terminal kinase in beta-cell recovery from nitric oxide-mediated damage

Treatment of rat islets with the cytokine IL-1 results in the inhibition of mitochondrial function and insulin secretion, events that are mediated by beta-cell expression of iNOS [inducible nitric oxide (NO) synthase] and production of NO. beta-Cells recover from the inhibitory actions of NO, produced following 24 h incubation with IL-1, on islet oxidative metabolism and insulin secretion if iNOS enzymatic activity is inhibited and the islets are cultured (in the presence of IL-1 and iNOS inhibitors) for a brief period of 8 h. Islet recovery from cytokine- and NO-mediated damage is an active process that requires new gene expression, and NO itself is one activator of this recovery process. In this study, the mechanism by which NO stimulates islet recovery has been examined. Incubation of rat islets or RINm5F cells with the NO donor compound, sodium (Z)-1(N,N-diethylamino) diazen-1-ium-1,2-diolate (DEA-NO) for 1 h results in a 60% inhibition of mitochondrial aconitase activity. beta-Cells completely recover aconitase activity if the cells are washed to remove the NO donor compound and incubated for an additional 5 h in the absence of DEA-NO. The recovery of mitochondrial aconitase activity correlates with a 4-fold increase in cyclic GMP accumulation and is prevented by the inhibition of guanylate cyclase. The recovery of aconitase activity also correlates with the activation of members of the MAPKs, p38, c-Jun N-terminal kinase (JNK) and ERK, and the activation p38 and JNK is attenuated by inhibition of guanylate cyclase. ERK and p38 do not appear to participate in the recovery process as selective inhibition of these kinases fails to prevent recovery of aconitase activity; however, transduction of beta-cells with a dominant negative mutant JNK prevents beta-cell recovery from NO-mediated damage. These findings support a role for guanylate cyclase and JNK in the recovery of beta-cells from NO-mediated damage.

ERK activation is required for double-stranded RNA- and virus-induced interleukin-1 expression by macrophages

Double-stranded (ds) RNA, which accumulates during viral replication, activates the antiviral response of infected cells. In this study, we have identified a requirement for extracellular signal-regulated kinase (ERK) in the regulation of interleukin 1 (IL-1) expression by macrophages in response to dsRNA and viral infection. Treatment of RAW 264.7 cells or mouse macrophages with dsRNA stimulates ERK phosphorylation that is first apparent following a 15-min incubation and persists for up to 60 min, the accumulation of iNOS and IL-1 mRNA following a 6-h incubation, and the expression of iNOS and IL-1 at the protein level following a 24-h incubation. Inhibitors of ERK activation prevent dsRNA-induced ERK phosphorylation and IL-1 expression by macrophages. The regulation of macrophage activation by ERK appears to be selective for IL-1, as ERK inhibition does not attenuate dsRNA-induced iNOS expression by macrophages. dsRNA stimulates both ERK activation and IL-1 expression by macrophages isolated from dsRNA-dependent protein kinase (PKR)-deficient mice, indicating that PKR does not participate in this antiviral response. These findings support a novel PKR-independent role for ERK in the regulation of the antiviral response of IL-1 expression and release by macrophages.

Inhibition of IFN-gamma -induced STAT1 activation by 15- deoxy-Delta 12,14-prostaglandin J2

The inhibitory actions of 15-deoxy-Delta(12,14)-prostaglandin J(2) (PGJ(2)) on inflammatory gene expression have been attributed to the ability of this prostaglandin to inhibit the activation of NF-kappaB. In this study, we have identified an additional signaling pathway sensitive to inhibition by PGJ(2). We show that PGJ(2) inhibits interferon (IFN)-gamma-stimulated phosphorylation and DNA-binding activity of STAT1. The inhibitory actions on STAT1 phosphorylation are first apparent after a 1- to 2-h incubation and are maximal after a 6-h incubation with PGJ(2), and they correlate with the expression of heat shock protein (HSP)70 in islets. In previous studies, we have correlated the inhibitory actions of PGJ(2) on inducible nitric oxide synthase (iNOS) expression and NF-kappaB activation in response to IL-1 with the increased expression of HSP70. Using overexpression and antisense depletion, we provide evidence that HSP70 does not mediate the inhibitory actions of PGJ(2) on IL-1-induced NF-kappaB or IFN-gamma-induced STAT1 activation or cytokine-stimulated iNOS expression by beta-cells. Last, we show that the inhibitory actions of a short 6-h pulse with PGJ(2) on IL-1 plus IFN-gamma-stimulated iNOS expression and NO production by beta-cells are persistent for extended periods (< or =48 h). These findings suggest that PGJ(2) inhibits multiple cytokine-signaling pathways (IL-1 and IFN-gamma), that the inhibitory actions are persistent for extended periods, and that increased HSP70 expression correlates with, but does not appear to mediate, the inhibitory actions of PGJ(2) on IL-1 and IFN-gamma signaling in beta-cells.

Regulation of cyclooxygenase-2 expression by macrophages in response to double-stranded RNA and viral infection

In this study the regulation of macrophage expression of cyclooxygenase-2 (COX-2) in response to dsRNA and virus infection was examined. Treatment of RAW 264.7 macrophages with dsRNA results in COX-2 mRNA accumulation and protein expression and the production of PGE(2). Similar to dsRNA, encephalomyocarditis virus (EMCV) infection of RAW 264.7 cells stimulates COX-2 expression and PGE(2) accumulation. The dsRNA-dependent protein kinase (PKR), which has been shown to participate in the regulation of gene expression in response to dsRNA and virus infection, does not appear to participate in the regulation of COX-2 expression by macrophages. Expression of dominant negative mutants of PKR in RAW 264.7 cells fails to attenuate dsRNA- and EMCV-induced COX-2 expression or PGE(2) production. Furthermore, dsRNA and EMCV stimulate COX-2 expression and PGE(2) accumulation to similar levels in macrophages isolated from wild-type and PKR-deficient mice. Recently, a novel PKR-independent role for the calcium-independent phospholipase A(2) (iPLA(2)) in the regulation of inducible NO synthase expression by macrophages in response to virus infection has been identified. The selective iPLA(2) suicide substrate inhibitor bromoenol lactone prevents dsRNA- and EMCV-stimulated inducible NO synthase expression; however, bromoenol lactone does not attenuate dsRNA- or EMCV-induced COX-2 expression by macrophages. In contrast, inhibition of NF-kappaB activation prevents dsRNA-stimulated COX-2 expression and PGE(2) accumulation by macrophages. These findings indicate that virus infection and treatment with dsRNA stimulate COX-2 expression by a mechanism that requires the activation of NF-kappaB and that is independent of PKR or iPLA(2) activation.