Publications

Emerging evidence indicates that ionizing radiation (IR) and chemotherapy activate Type I interferon (IFN) signaling in tumor and host cells. However, the mechanism of induction is poorly understood. We identified a novel radioprotective role for the DEXH box RNA helicase LGP2 (DHX58) through its suppression of IR-induced cytotoxic IFN-beta [1]. LGP2 inhibits activation of the RIG-I-like receptor (RLR) pathway upon binding of viral RNA to the cytoplasmic sensors RIG-I (DDX58) and MDA5 (IFIH1) and subsequent IFN signaling via the mitochondrial adaptor protein MAVS (IPS1). Here we show that MAVS is necessary for IFN-beta induction and interferon-stimulated gene expression in the response to IR. Suppression of MAVS conferred radioresistance in normal and cancer cells. Germline deletion of RIG-I, but not MDA5, protected mice from death following total body irradiation, while deletion of LGP2 accelerated the death of irradiated animals. In human tumors depletion of RIG-I conferred resistance to IR and different classes of chemotherapy drugs. Mechanistically, IR stimulated the binding of cytoplasmic RIG-I with small endogenous non-coding RNAs (sncRNAs), which triggered IFN-beta activity. We demonstrate that the small nuclear RNAs U1 and U2 translocate to the cytoplasm after IR treatment, thus stimulating the formation of RIG-I: RNA complexes and initiating downstream signaling events. Taken together, these findings suggest that the physiologic responses to radio-/chemo-therapy converge on an antiviral program in recruitment of the RLR pathway by a sncRNA-dependent activation of RIG-I which commences cytotoxic IFN signaling. Importantly, activation of interferon genes by radiation or chemotherapy is associated with a favorable outcome in patients undergoing treatment for cancer. To our knowledge, this is the first demonstration of a cell-intrinsic response to clinically relevant genotoxic treatments mediated by an RNA-dependent mechanism.

Although the NLRP3 inflammasome plays a pivotal role in host defense, its uncontrolled activation is associated with inflammatory disorders, suggesting that regulation of the inflammasome is important to prevent detrimental effects. Type I IFNs and long-term LPS stimulation were shown to negatively regulate NLRP3 activation. In this study, we found that endogenous NO is involved in the regulation of NLRP3 inflammasome activation by either IFN-β pretreatment or long-term LPS stimulation. Furthermore, S-nitroso-N-acetylpenicillamine (SNAP), an NO donor, markedly inhibited NLRP3 inflammasome activation, whereas the AIM2 and NLRC4 inflammasomes were only partially inhibited by SNAP. An increase in mitochondrial reactive oxygen species induced by ATP was only modestly affected by SNAP treatment. Interestingly, S-nitrosylation of NLRP3 was detected in macrophages treated with SNAP, and this modification may account for the NO-mediated mechanism controlling inflammasome activation. Taken together, these results revealed a novel role for NO in regulating the NLRP3 inflammasome.

Accumulating evidence has shown the importance of Stat6-mediated signaling in allergic diseases. In this study, we show a novel regulatory mechanism of Stat6-mediated signaling in mast cells. When Stat6 is activated by interleukin (IL)-4 and translocated to the nucleus, Stat6 is cleaved by a nucleus-associated protease in mast cells. The cleaved 65-kD Stat6 lacks the COOH-terminal transactivation domain and functions as a dominant-negative molecule to Stat6-mediated transcription. The retrovirus-mediated expression of cleavage-resistant Stat6 mutants prolongs the nuclear accumulation of Stat6 upon IL-4 stimulation and enhances IL-4–induced gene expression and growth inhibition in mast cells. These results indicate that the proteolytic processing of Stat6 functions as a lineage-specific negative regulator of Stat6-dependent signaling in mast cells, and thus suggest that it may account for the limited role of Stat6 in IL-4 signaling in mast cells.

The chemical synthesis of human interleukin‐2 (IL‐2) , having a core 1 sugar, by a ligation method is reported. Although IL‐2 is a globular glycoprotein, its C‐terminal region, in particular (99‐133), is extremely insoluble when synthesized by solid‐phase method. To overcome this problem, the side‐chain carboxylic acid of the Glu residues was protected by a picolyl ester, thus reversing its polarity from negative to positive. This reverse polarity protection significantly increased the isoelectric point of the peptide segment and made it positive under acidic conditions and facilitated the purification. An efficient method to prepare the prolyl peptide thioester required for the synthesis of the (28‐65) segment was also developed. These efforts resulted in the total synthesis of the glycosylated IL‐2 having full biological activity.

The DEAD box helicase DDX3 assembles IPS-1 (also called Cardif, MAVS, or VISA) in non-infected human cells where minimal amounts of the RIG-I-like receptor (RLR) protein are expressed. DDX3 C-terminal regions directly bind the IPS-1 CARD-like domain as well as the N-terminal hepatitis C virus (HCV) core protein. DDX3 physically binds viral RNA to form IPS-1-containing spots, that are visible by confocal microscopy. HCV polyU/UC induced IPS-1-mediated interferon (IFN)-beta promoter activation, which was augmented by co-transfected DDX3. DDX3 spots localized near the lipid droplets (LDs) where HCV particles were generated. Here, we report that HCV core protein interferes with DDX3-enhanced IPS-1 signaling in HEK293 cells and in hepatocyte Oc cells. Unlike the DEAD box helicases RIG-I and MDA5, DDX3 was constitutively expressed and colocalized with IPS-1 around mitochondria. In hepatocytes (O cells) with the HCV replicon, however, DDX3/IPS-1-enhanced IFN-beta-induction was largely abrogated even when DDX3 was co-expressed. DDX3 spots barely merged with IPS-1, and partly assembled in the HCV core protein located near the LD in O cells, though in some O cells IPS-1 was diminished or disseminated apart from mitochondria. Expression of DDX3 in replicon-negative or core-less replicon-positive cells failed to cause complex formation or LD association. HCV core protein and DDX3 partially colocalized only in replicon-expressing cells. Since the HCV core protein has been reported to promote HCV replication through binding to DDX3, the core protein appears to switch DDX3 from an IFN-inducing mode to an HCV-replication mode. The results enable us to conclude that HCV infection is promoted by modulating the dual function of DDX3.

No abstract is provided for this article.

Advanced fibrosis and portal hypertension influence short-term mortality. Lipocalin 2 (LCN2) regulates infection response and increases in liver injury. We explored the role of intrahepatic LCN2 in human alcoholic hepatitis (AH) with advanced fibrosis and portal hypertension and in experimental mouse fibrosis. We found hepatic LCN2 expression and serum LCN2 level markedly increased and correlated with disease severity and portal hypertension in patients with AH. In control human livers, LCN2 expressed exclusively in mononuclear cells, while its expression was markedly induced in AH livers, not only in mononuclear cells but also notably in hepatocytes. Lcn2 −/− mice were protected from liver fibrosis caused by either ethanol or CCl 4 exposure. Microarray analysis revealed downregulation of matrisome, cell cycle and immune related gene sets in Lcn2 −/− mice exposed to CCl 4 , along with decrease in Timp1 and Edn1 expression. Hepatic expression of COL1A1 , TIMP1 and key EDN1 system components were elevated in AH patients and correlated with hepatic LCN2 expressio n. In vitro , recombinant LCN2 induced COL1A1 expression. Overexpression of LCN2 increased HIF1A that in turn mediated EDN1 upregulation. LCN2 contributes to liver fibrosis and portal hypertension in AH and could represent a new therapeutic target.

No abstract is provided for this article.

We have previously reported that mouse plasmacytoid dendritic cells (DC) produce high levels of IL-12p70, whereas bone marrow-derived myeloid DC and splenic DC produce substantially lower levels of this cytokine when activated with the TLR-9 ligand CpG. We now show that in response to CpG stimulation, high levels of IL-10 are secreted by macrophages, intermediate levels by myeloid DC, but no detectable IL-10 is secreted by plasmacytoid DC. MyD88-dependent TLR signals (TLR4, 7, 9 ligation), Toll/IL-1 receptor domain-containing adaptor-dependent TLR signals (TLR3, 4 ligation) as well as non-TLR signals (CD40 ligation) induced macrophages and myeloid DC to produce IL-10 in addition to proinflammatory cytokines. IL-12p70 expression in response to CpG was suppressed by endogenous IL-10 in macrophages, in myeloid DC, and to an even greater extent in splenic CD8α− and CD8α+ DC. Although plasmacytoid DC did not produce IL-10 upon stimulation, addition of this cytokine exogenously suppressed their production of IL-12, TNF, and IFN-α, showing trans but not autocrine regulation of these cytokines by IL-10 in plasmacytoid DC.

Microsomal prostaglandin E 2 synthase (mPGES)‐1 is an inducible protein recently shown to be an important enzyme in inflammatory prostaglandin E 2 (PGE 2 ) production in some peripheral inflammatory lesions. However, in inflammatory sites in the brain, the induction of mPGES‐1 is poorly understood. In this study, we demonstrated the expression of mPGES‐1 in the brain parenchyma in a lipopolysaccharide (LPS)‐induced inflammation model. A local injection of LPS into the rat substantia nigra led to the induction of mPGES‐1 in activated microglia. In neuron‐glial mixed cultures, mPGES‐1 was co‐induced with cyclooxygenase‐2 (COX‐2) specifically in microglia, but not in astrocytes, oligodendrocytes or neurons. In microglia‐enriched cultures, the induction of mPGES‐1, the activity of PGES and the production of PGE 2 were preceded by the induction of mPGES‐1 mRNA and almost completely inhibited by the synthetic glucocorticoid dexamethasone. The induction of mPGES‐1 and production of PGE 2 were also either attenuated or absent in microglia treated with mPGES‐1 antisense oligonucleotide or microglia from mPGES‐1 knockout (KO) mice, respectively, suggesting the necessity of mPGES‐1 for microglial PGE 2 production. These results suggest that the activation of microglia contributes to PGE 2 production through the concerted de novo synthesis of mPGES‐1 and COX‐2 at sites of inflammation of the brain parenchyma.

Upon viral infection, host cells trigger antiviral immune responses by inducing type I IFN and inflammatory cytokines. dsRNA generated during viral replication is recognized by the cytoplasmic RNA helicases retinoic acid-inducible gene I and melanoma differentiation-associated gene 5, which interact with an adaptor, IFN-beta promoter stimulator-1, to activate the transcription factors NF-kappaB and IFN regulatory factor 3. In this article we demonstrate that caspase-8 and caspase-10 are involved in these pathways. Both caspases were cleaved during dsRNA stimulation, and overexpression of a cleaved form of these caspases activated NF-kappaB. Knockdown of caspase-10 or caspase-8 in a human cell line resulted in the reduction of inflammatory cytokine production. Cells derived from caspase-8-deficient mice also showed reduced expression of inflammatory cytokines as well as NF-kappaB activation. Furthermore, the Fas-associated death domain protein interacted with these two caspases and IFN-beta promoter stimulator 1. These results indicate that caspase-8 and caspase-10 are essential components that mediate NF-kappaB-dependent inflammatory responses in antiviral signaling.

No abstract is provided for this article.

We have generated mice with a cell type-specific disruption of the Stat3 gene in macrophages and neutrophils. The mutant mice are highly susceptible to endotoxin shock with increased production of inflammatory cytokines such as TNFα, IL-1, IFNγ, and IL-6. Endotoxin-induced production of inflammatory cytokines is augmented because the suppressive effects of IL-10 on inflammatory cytokine production from macrophages and neutrophils are completely abolished. The mice show a polarized immune response toward the Th1 type and develop chronic enterocolitis with age. Taken together, Stat3 plays a critical role in deactivation of macrophages and neutrophils mainly exerted by IL-10.

No abstract is provided for this article.