RIG-I Is Required for the Inhibition of Measles Virus by Retinoids

Vitamin A can significantly decrease measles-associated morbidity and mortality. Vitamin A can inhibit the replication of measles virus (MeV) in vitro through an RARα- and type I interferon (IFN)-dependent mechanism. Retinoid-induced gene I (RIG-I) expression is induced by retinoids, activated by MeV RNA and is important for IFN signaling. We hypothesized that RIG-I is central to retinoid-mediated inhibition of MeV in vitro. We demonstrate that RIG-I expression is increased in cells treated with retinoids and infected with MeV. The central role of RIG-I in the retinoid-anti-MeV effect was demonstrated in the Huh-7/7.5 model; the latter cells having non-functional RIG-I. RAR-dependent retinoid signaling was required for the induction of RIG-I by retinoids and MeV. Retinoid signaling was also found to act in combination with IFN to induce high levels of RIG-I expression. RIG-I promoter activation required both retinoids and MeV, as indicated by markers of active chromatin. IRF-1 is known to be regulated by retinoids and MeV, but we found recruitment of IRF-1 to the RIG-I promoter by retinoids alone. Using luciferase expression constructs, we further demonstrated that the IRF-1 response element of RIG-I was required for RIG-I activation by retinoids or IFN. These results reveal that retinoid treatment and MeV infection induces significant RIG-I. RIG-I is required for the retinoid-MeV antiviral response. The induction is dependent on IFN, retinoids and IRF-1

Staurosporine inhibits interferon alpha-induced gene expression in Friend erythroleukemia cells through a PKC independent pathway.

Interferons (IFNs) are able to induce an increased transcription of several genes, which can occur within minutes of the binding of IFNs to their receptors. The specific induced transcription is mediated by the interaction of specific transcription factors with regulatory DNA sequences that lie upstream the promoters of IFN induced genes. Phosphorylation of IFN-specific transcription factors is required for activation of transcription. We have studied the antiviral effect and the induction of gene expression by IFN-alpha in Friend Leukemia cells (FLC) in the presence of a series of inhibitors of known kinases. Protein kinase C (PKC)-specific inhibitors, i.e. calphostin C and bisindolylmaleimide, failed to influence the IFN-induced gene expression and the antiviral state. Likewise, little or no effect was found using inhibitors such as H7 or K252a. Chronic exposure of FLC to phorbol ester, that causes down regulation of PKC (the effectiveness of TPA treatment was proven by PKC enzymatic assay), has no effect on IFN-alpha action. In addition, treatment of FLC with staurosporine prevented the induction of IFN-stimulated genes and the establishment of the antiviral state only when this drug was used at high dosage (500 nM). This result indicates that, also in FLC activation of PKC is not involved in the transcriptional response of the cells to IFN-alpha treatment. The non receptor tyrosine kinases of the JAK family that take part in the IFNs-specific transduction pathways could be the target of the staurosporine specific inhibition of the IFN-alpha action

HMGB1 and cord blood: its role as immuno-adjuvant factor in innate immunity

In newborn the innate immune system provides essential protection during primary infections before the generation of an appropriate adaptive immune response that is initially not fully operative. Innate immune response is evoked and perpetuated by molecules derived from microorganisms or by the damage/death of host cells. These are collectively known as damage-associated molecular-pattern (DAMP) molecules. High-mobility group box 1 protein (HMGB1) or amphoterin, which previously was considered to be only a nuclear factor, has been recently identified as a DAMP molecule. When it is actively secreted by inflammatory cells or passively released from necrotic cells, HMGB1 mediates the response to infection, injury and inflammation, inducing dendritic cells maturation and T helper-1-cell responses. To characterize the role of HMGB1 in the innate and immature defense mechanisms in newborns, human cord blood (CB) mononuclear cells, in comparison to adult peripheral blood (PB) mononuclear cells, have been analyzed for its expression. By flow cytometry and western blot analysis, we observed that in CB and PB cells: i) HMGB1 is expressed on cell surface membranes of myeloid dendritic cell precursors, mostly, and lymphocytes (gamma/delta and CD4(+) T cells) to a lesser extent; ii) different pro-inflammatory stimuli or molecules that mimic infection increased cell surface expression of HMGB1 as well as its secretion into extracellular environment; iii) the treatment with synthetic molecules such as aminobisphosphonates (ABs), identified to be gamma delta T cell antigens, triggered up-regulation of HMGB1 expression on mononuclear cells, as well gamma delta T lymphocytes, inducing its secretion. The modulation of its secretion and the HMGB1-mediated migration of monocytes indicated HMGB1 as regulator of immune response in an immature system, like CB, through engagement of gamma delta T lymphocytes and myeloid dendritic cell precursors, essential components of innate immunity. In addition, the increased HMGB1 expression/secretion triggered by ABs, previously characterized for their immuno-modulating and immune-adjuvant capabilities, indicated that immunomodulation might represent a new therapeutical approach for neonatal and adult pathologies