Requirement for endocytosis of poly(rI).poly(rC) to generate toxicity on interferon-treated LM cells

Involvement of toll-like receptor 3 in the immune response of lung epithelial cells to double-stranded RNA and influenza A virus

Influenza A is a highly contagious single-stranded RNA virus that infects both the upper and lower respiratory tracts of humans. The host innate immune Toll-like receptor (TLR) 3 was shown previously in cells of myeloid origin to recognize the viral replicative, intermediate double-stranded RNA (dsRNA). Thus, dsRNA may be critical for the outcome of the infection. Here we first compared the activation triggered by either influenza A virus or dsRNA in pulmonary epithelial cells. We established that TLR3 is constitutively expressed in human alveolar and bronchial epithelial cells, and we describe its intracellular localization. Expression of TLR3 was positively regulated by the influenza A virus and by dsRNA but not by other inflammatory mediators, including bacterial lipopolysaccharide, the cytokines tumor necrosis factor-alpha and interleukin (IL)-1beta, and the protein kinase C activator phorbol 12-myristate 13-acetate. We also demonstrated that TLR3 contributes directly to the immune response of respiratory epithelial cells to influenza A virus and dsRNA, and we propose a molecular mechanism by which these stimuli induce epithelial cell activation. This model involves mitogen-activated protein kinases, phosphatidylinositol 3-kinase/Akt signaling, and the TLR3-associated adaptor molecule TRIF but not MyD88-dependent activation of the transcription factors NF-kappaB or interferon regulatory factor/interferon-sensitive response-element pathways. Ultimately, this signal transduction elicits an epithelial response that includes the secretion of the cytokines IL-8, IL-6, RANTES (regulated on activation normal T cell expressed and secreted), and interferon-beta and the up-regulation of the major adhesion molecule ICAM-1.

An antiviral state induced in Chinook salmon embryo cells (CHSE-214) by transfection with the double-stranded RNA poly I:C

Type I interferons (IFN alpha and beta) convert vertebrate cells into an antiviral state by inducing expression of proteins that inhibit virus replication. In humans and mice, Mx proteins constitute one family of interferon-induced antiviral proteins. Mx genes have recently been cloned from Atlantic salmon and rainbow trout. Moreover, double-stranded RNA (dsRNA) and type I IFN-like activity have been shown to induce Mx protein in salmonid cells. Chinook salmon embryo cells (CHSE-214 cells) have been suggested to have a defect in the IFN-system because the dsRNA polyinosinic polycytidylic acid (poly I:C) failed to induce an antiviral state in the cells. We have studied this phenomenon more closely in the present work. CHSE-214 cells were either transfected with poly I:C or incubated with poly I:C without transfection reagent. The cells were then studied for Mx protein expression and protection against infectious pancreatic necrosis virus (IPNV) infection. The results showed that cells transfected with poly I:C were protected from IPNV infection, whilst cells incubated with poly I:C were not protected. Cells transfected with the double-stranded DNA poly dI:dC were also not protected against IPNV. Mx protein was expressed in CHSE-214 cells upon transfection with poly I:C, but not after incubation with poly I:C alone. Stimulation of CHSE-214 cells with supernatants from cells transfected with poly I:C, induced protection against IPNV, indicating production of type I IFN-like activity. These results suggest that CHSE-214 cells in fact are able to produce type I IFN, but may have defects in the mechanisms mediating uptake of poly I:C or may degrade unprotected poly I:C.

Viral double-stranded RNA, cytokines, and the flu

The symptoms of the flu, such as fever, drowsiness, and malaise, are the sole means by which this common clinical syndrome is defined. The syndrome is usually the first clinical manifestation of both acute bacterial and viral infections. In the case of acute bacterial infections, several proinflammatory cytokines induced by bacterial products have been implicated as the causative agents of the flu syndrome. Viruses induce similar cytokines to bacteria, plus substantial amounts of interferon-alpha (IFN-alpha), although the direct association of these cytokines with the viral flu syndrome is less clear. Furthermore, the viral inducer(s) of cytokines has not been defined. The best candidate cytokine inducer associated with a majority of viral infections is virus-associated double-stranded RNA (dsRNA). This review examines the essential physical properties of toxic dsRNA, the cytokines induced by it, its viral and cellular sources, evidence for its presence in infected cells, its quantities in normal and infected cells, its cytotoxic mechanisms, and its cell-penetration properties. Toxic effects of viruses and dsRNA are compared. Energetics and extraction artifact issues are also discussed. Whereas most research on dsRNA toxicity has employed synthetic dsRNA, studies with virus-associated dsRNA are featured when available. Finally, a model for how viral dsRNA might initiate systemic disease is presented.

Platelet-derived growth factor isoforms AA, AB, and BB differentially activate poly r(I):r(C)-induced genes in human fibroblast FS4 cells

Polyribocytidylic-polyriboinosinic acid [poly r(I):r(C)]-inducible genes were isolated by a differential screening procedure from a human fibroblast cell (FS-4) cDNA bank. Among yet unidentified genes (gene 274), one codes for a protein with multiple finger motifs and has previously been detected in endothelial cells after tumor necrosis factor-alpha (TNF-alpha) treatment (A20; Opipari et al., 1990), the second one codes for a variant of the I kappa B family (Haskill et al., 1991), and a third one for the Ca2+ ATPase (isoform 1). Platelet-derived growth factor (PDGF) isoforms (AA, AB, and BB) stimulated the expression of these immediate-early genes. But the extent of the respective induction correlated neither with the number of the two receptors alpha or beta nor with the level of PDGF-stimulated receptor autophosphorylation on tyrosine. Although alpha-receptors were less abundant than beta-receptors (12,500 binding sites were estimated for PDGF-AA, KD 0.03 nM; 20,000 for PDGF-AB, KD 0.03 nM; 35,000 for PDGF-BB KD 0.16 nM) and tyrosine phosphorylation induced by PDGF-AA was significantly less than that evoked by PDGF-BB, some of the investigated genes were more strongly induced by PDGF-AA. We discuss how the differences in the biological potency of the PDGF isoforms may reside in different functions of the two receptors by activation of alternative signaling pathways.

Cyclic AMP mediates the direct antiproliferative action of mismatched double-stranded RNA

Previous experiments have demonstrated that double-stranded RNAs (dsRNAs) can exert an antiproliferative effect on human tumor cells, independent of interferon (IFN) induction. However, the mechanism by which dsRNAs inhibit tumor growth has not been elucidated. As a first step in determining the molecular events responsible for growth arrest, we have explored the role of signal transduction through the cAMP system in the antiproliferative effect of the mismatched dsRNA, r(I)n.r(C12,U)n (Ampligen). These studies utilized the human glioma cell line A1235, which does not produce detectable levels of IFN-alpha, -beta, or -gamma in response to mismatched dsRNA treatment. Treatment of A1235 cells with mismatched dsRNA in combination with either 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H-7), which inhibits cAMP-dependent protein kinase and protein kinase C, or N-(2-guanidinoethyl)-5-isoquinolinesulfonamide (HA1004), which preferentially inhibits the cAMP-dependent protein kinase, yielded an antagonism of the mismatched dsRNA-induced antiproliferative effect. Measurement of adenylate cyclase activation showed a dose-dependent increase in activity at antiproliferative mismatched dsRNA concentrations, but not at lower, nonantiproliferative doses. This increase in activity was rapid, seen as early as 30 sec after initiation of treatment, and it was sustained at peak levels for 1-2 hr. Analysis of the intracellular cAMP concentration gave similar kinetics of induction. Exposure of cells to the stable cAMP analogue dibutyryl cAMP yielded dose-dependent inhibition of cell growth. The cAMP phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine also inhibited proliferation. In contrast, neither H-7 nor HA1004 had an effect on growth inhibition induced by human natural IFN-alpha treatment. In addition, antiproliferative doses of IFN-alpha did not increase cAMP concentrations. These results indicate that the cAMP system is utilized by mismatched dsRNA as an early signal transduction mechanism for growth control. Furthermore, the antiproliferative effects induced by mismatched dsRNA and IFN can occur by different mechanisms of action.

Evidence for a novel signal transduction pathway activated by platelet-derived growth factor and by double-stranded RNA

Platelet-derived growth factor (PDGF) and the synthetic double-stranded RNA poly(I).poly(C) [poly(I.C)] stimulate transcription of the JE gene in BALB/c-3T3 fibroblasts. The response of JE to poly(I.C) does not appear to be channeled through any known component of the PDGF receptor signal transduction apparatus. In addition, JE sequences upstream of the transcription start site are devoid of previously identified poly(I.C)-responsive elements, such as those found in the beta-interferon gene. These data suggest that a novel signal transduction pathway regulates the JE response to PDGF and double-stranded RNA. The c-myc and c-fos proto-oncogenes also respond to this pathway but with poor efficiency. However, this pathway operates very efficiently on other PDGF-inducible genes that encode the secretory proteins KC and M-CSF.

Evidence for a novel signal transduction pathway activated by platelet-derived growth factor and by double-stranded RNA

Platelet-derived growth factor (PDGF) and the synthetic double-stranded RNA poly(I).poly(C) [poly(I.C)] stimulate transcription of the JE gene in BALB/c-3T3 fibroblasts. The response of JE to poly(I.C) does not appear to be channeled through any known component of the PDGF receptor signal transduction apparatus. In addition, JE sequences upstream of the transcription start site are devoid of previously identified poly(I.C)-responsive elements, such as those found in the beta-interferon gene. These data suggest that a novel signal transduction pathway regulates the JE response to PDGF and double-stranded RNA. The c-myc and c-fos proto-oncogenes also respond to this pathway but with poor efficiency. However, this pathway operates very efficiently on other PDGF-inducible genes that encode the secretory proteins KC and M-CSF.