The Epstein–Barr virus (EBV)-encoded latent membrane protein-1 (LMP1), a functional homologue of the tumor necrosis factor receptor family, substantially contributes to EBV's oncogenic potential by activating nuclear factor-κB (NF-κB). miR-155 is an oncogenic miRNA critical for B-cell maturation and immunoglobulin production in response to antigen. We report that miR-155 expression is much higher in EBV-immortalized B cells than in EBV-negative B cells. LMP1, but not LMP2, up-regulated the expression of miR-155, when transfected in EBV-negative B cells. We analyzed two putative NF-κB binding sites in the miR-155 promoter; both sites recruited NF-κB complex, in nuclear extract from EBV-immortalized cells. The exogenous expression of LMP1, in EBV-negative background, is temporally correlated to induction of p65 with binding on both NF-κB sites and with miR-155 overexpression. The induction of p65 binding together with increased RNA polymerase II binding, confirms that LMP1-mediated activation of miR-155 occurs transcriptionally. In reporter assays, miR-155 promoter lacking NF-κB binding sites was no longer activated by LMP1 expression and an intact AP1 site is needed to attain maximum activation. Finally, we demonstrate that LMP1-mediated activation of miR-155 in an EBV-negative background correlates with reduction of protein PU.1, which is a possible miR target.

Localized mRNAs are thought to be transported in defined particles to their final destination. These particles represent large protein complexes that may be involved in recognizing, transporting, and anchoring localized messages. Few components of these ribonucleoparticles, however, have been identified yet. We chose the strategy to biochemically enrich native RNA–protein complexes involved in RNA transport to identify the associated RNAs and proteins. Because Staufen proteins were implicated in intracellular RNA transport, we chose mammalian Staufen proteins as markers for the purification of RNA transport particles. Here, we present evidence that Staufen proteins exist in two different complexes: ( i ) distinct large, ribosome- and endoplasmic reticulum-containing granules preferentially found in the membrane pellets during differential centrifugation and ( ii ) smaller particles in the S100 from rat brain homogenates. On gel filtration of the S100, we identified soluble 670-kDa Staufen1-containing and 440-kDa Staufen2-containing particles. They do not cofractionate with ribosomes and endoplasmic reticulum but rather coenrich with kinesin heavy chain. Furthermore, the fractions containing the Staufen1 particles show a 15-fold enrichment of mRNAs compared with control fractions. Most importantly, these fractions are highly enriched in BC1, and, to a lesser extent, in the α-subunit of the Ca ²⁺ /calmodulin-dependent kinase II, two dendritically localized RNAs. Finally, both RNAs colocalize with Staufen1–hemagglutinin in particles in dendrites of transfected hippocampal neurons. We therefore propose that these Staufen1-containing particles may represent RNA transport intermediates that are in transit to their final destination within neurons.

Human immunodeficiency virus type 1 (HIV-1) infection is associated with severe psoriasis, B cell lymphoma, and Kaposi's sarcoma. A deregulated production of interleukin-6 (IL6) has been implicated in the pathogenesis of these diseases. The molecular mechanisms underlying the abnormal IL6 secretion of HIV-1-infected cells may include transactivation of the IL6 gene by HIV-1. Here we report the molecular mechanisms of Tat activity on the expression of the IL6 gene. By using 5' deletion mutants of pIL6Pr-CAT and using IL6:HIV-1-LTR hybrid constructs where discrete regions of the IL6 promoter replaced the TAR sequence in HIV-1 LTR, we identified a short sequence of the 5'-untranslated region of the IL6 mRNA that is required for Tat to trans-activate the IL6 promoter. This sequence acquires a stem-loop structure and includes a UCU sequence that binds to Tat and is necessary for full trans-activation. In addition, we provide the evidence that Tat can function by enhancing the CAAT enhancer-binding protein (C/EBP) DNA binding activity and is able to complex with in vitro translated C/EBPbeta, which is a major mediator of IL6 promoter function. By using the yeast two-hybrid system and immunoprecipitation, we observed that the interaction of Tat with C/EBP proteins also occurred in vivo. The data are consistent with the possibility that Tat may function on heterologous genes by interacting with RNA structures possibly present in a large number of cellular and viral genes. In addition, Tat may function by protein-protein interactions, leading to the generation of heterodimers with specific transcription factors.

The review intends to present and recapitulate the current knowledge on the roles and importance of regulatory RNAs, such as microRNAs and small interfering RNAs, RNA binding proteins and enzymes processing RNAs or activated by RNAs, in cells infected by RNA viruses. The review focuses on how non-coding RNAs are involved in RNA virus replication, pathogenesis and host response, especially in retroviruses HIV, with examples of the mechanisms of action, transcriptional regulation, and promotion of increased stability of their targets or their degradation.