Evidence for the involvement of the RNA-dependent protein kinase (PKR) in the induction of human cytotoxic T lymphocytes against a synthetic peptide of HIV-1 by regulatory RNA

PKR activation by a non-coding RNA expressed in lymphocytes of mice bearing B16 melanoma

In recent years, non-coding RNAs (ncRNAs) have become an exciting area of research. It has been demonstrated that ncRNAs play an important role in the regulation of gene expression in eukaryotic cells. However, little is known about ncRNAs in lymphocytes. In this study, we investigated the presence of ncRNAs in lymphocytes of C57BL/6 mice bearing B16 melanoma by using the differential display reverse transcription-PCR (DD-RT-PCR). PKR is a serine/threonine kinase containing two RNA-binding domains within the N-terminal region. We took advantage of the ability of RNAs to bind PKR in order to identify ncRNAs of lymphocytes activated during tumor development. Thus, RNAs that co-immunoprecipitated with PKR were reversed transcribed, re-amplified, cloned, sequenced and the secondary structure was determined. The ability of transcripts obtained by in vitro transcription to activate PKR was also examined. We detected a highly structured transcript of 220 nt with no open reading frame (ORF) which is able to activate PKR, and it is only expressed in lymphocytes of C57BL/6 mice bearing B16 melanoma. Therefore, the 220 nt transcript may be included in the class of ncRNAs that act by modifying protein activity and our data suggest that regulation of gene expression in activated lymphocytes by this ncRNA could be mediated by PKR through the activation of the transcription factor NF-kappaB.

The NS2 protein of human respiratory syncytial virus suppresses the cytotoxic T-cell response as a consequence of suppressing the type I interferon response

The NS1 and NS2 proteins of human respiratory syncytial virus (HRSV) have been shown to antagonize the type I interferon (IFN) response, an effect subject to host range constraints. We have now found that the HRSV NS2 protein strongly controls IFN induction in mouse cells in vitro, validating the use of the mouse model to study the consequences of these gene deletions on host immunity. We evaluated the effects of deleting the NS1 and/or NS2 gene on the induction of HRSV-specific pulmonary cytotoxic T lymphocytes (CTL) in BALB/c and 129S6 mice in response to intranasal infection with HRSV lacking the NS1 and/or NS2 gene and subsequent challenge with wild-type (wt) HRSV. In mice infected with HRSV lacking the NS2 gene (DeltaNS2) or lacking the NS2 gene in combination with the NS1 gene (DeltaNS1/2 HRSV), the magnitude of the pulmonary CTL response was substantially elevated compared to that of mice infected with wt HRSV or the DeltaNS1 mutant, whether measured by binding of CD8(+) cells to an HRSV-specific major histocompatibility complex class I tetramer, by measurement of CD8(+) cells secreting gamma interferon (IFN-gamma) in response to specific in vitro stimulation, or by a standard chromium release cell-killing assay. In contrast, in STAT1 knockout mice, which lack responsiveness to type I IFN, the level of IFN-gamma-secreting CD8(+) cells was not significantly different for HRSV lacking the NS2 gene, suggesting that the increase in CTL observed in IFN-responsive mice is type I IFN dependent. Thus, the NS2 protein of HRSV suppresses the CTL component of the adaptive immune response, and this appears to be a consequence of its suppression of type I IFN.

Expression of noncoding mRNA in human blood cells activated with synthetic peptide of HIV

T cells activation includes several steps such as translational events, activation of transcription for different genes, expression of surface molecules, secretion of cytokines, effectors functions. Knowledge has been accumulated on various nontranslatable RNA transcripts that are synthesized. In this context, a member of T cell noncoding transcripts (NTT) has been identified. It has been known that this gene is selectively expressed in activated T cells, as a 17-kb transcript. In this study, we investigate cell activation using RT-PCR to detect NTT. We investigated the expression of IFNgamma mRNA, a cytokine produced by activated blood mononuclear cells treated with HLA-A2 restricted synthetic peptide of HIV (p9) by RT-PCR detecting a fragment of 300 bp. This finding demonstrated that human HLA-A2 blood mononuclear cells have been activated in the presence of synthetic peptide of HIV (p9) and can induce expression of mRNA of NTT and IFNgamma which was confirmed by direct sequencing. For the first time, we have demonstrated an endogenous noncoding human RNA molecule, NTT mRNA, suggesting its implication in the cellular immune response.

Regulatory RNA induces the production of IFN-gamma, but not IL-4 in human lymphocytes: role of RNA-dependent protein kinase (PKR) and NF-kappaB

Previous results with p9-RNA, obtained from lymph nodes of animals immunized with the peptide p9 of HIV-1, suggested that its effects on lymphocytes could be mediated by RNA-dependent protein kinase (PKR). Here we report that p9-RNA activates PKR leading to the degradation of the inhibitor I-kappaB alpha and the concomitant nuclear factor kappa B (NF-kappaB) activation. The fractionation of p9-RNA by affinity chromatography indicates that the poly A(+) p9-RNA is the fraction responsible for PKR activation. We also found that p9-RNA induces the production of interferon-gamma (IFN-gamma), but not interleukin (IL-4) since only IFN-gamma gene promoter contains NF-kappaB binding site. This study provides the first evidence that transcriptional control of gene expression by regulatory RNAs can be mediated by PKR through NF-kappaB activation. A model for the mechanism of action of poly A(+) p9-RNA is proposed.

Antitumor activity induced by regulatory RNA: possible role of RNA-dependent protein kinase and nuclear factor-kappaB

Regulatory RNAs are noncoding RNAs that can regulate gene expression. Our previous results showed that regulatory RNAs can induce the production of interleukin-1, interleukin-2, interleukin-8, tumor necrosis factor-alpha (TNF-alpha), interferon-gamma, and Fas ligand (FasL). These cytokines and FasL are involved in host defense mechanisms against tumors. B16-F10 melanoma cells are highly metastatic to the lungs and we showed that lymphocytes treated with the regulatory B16-RNA reduce significantly the number of metastatic nodules. We also found that B16-RNA activates RNA-dependent protein kinase (PKR) and the active B16-RNA fraction is polyadenylated with a sedimentation coefficient of 18S. Our findings suggest that the antitumor activity of B16-RNA is mediated by PKR through activation of the transcription factor NF-kappaB. Thus, B16-RNA may act as a regulatory RNA and may regulate gene expression at transcriptional level. This study provides the rationale for the use of B16-RNA as an immunomodulator in melanoma.

Activation of RNA-dependent protein kinase and nuclear factor-kB by regulatory RNA from lipopolysaccharide-stimulated macrophages: implications for cytokine production

Our previous results showed that L-RNA, extracted from lipopolysaccharide-stimulated macrophages, induces interleukin-1, interleukin-8 and tumor necrosis factor-alpha (TNF-alpha) in resident macrophages. It was demonstrated the promoter of these cytokine genes contain nuclear factor-kB (NF-kappa B) binding sites. We hypothesized that this effect of L-RNA is mediated by RNA-dependent protein kinase (PKR) through NF-kappa B activation. We found that L-RNA activates PKR and induces NF-kappa B activation through degradation of its inhibitor I-kappa B alpha. These data support the idea that L-RNA acts as a regulatory RNA. A model for the mechanism of action of L-RNA is proposed.