Transcription of the human immunodeficiency virus (HIV)-1 is controlled by the cooperation of virally encoded and host regulatory proteins. The Tat protein is essential for viral replication, however, expression of Tat after virus entry requires HIV-1 promoter activation. A sequence in the 5′ HIV-1 LTR, containing a binding site for transcription factors of the interferon regulatory factors (IRF) family has been suggested to be critical for HIV-1 transcription and replication. Here we show that IRF-1 activates HIV-1 LTR transcription in a dose-dependent fashion and in the absence of Tat. This has biological significance since IRF-1 is produced early upon virus entry, both in cell lines and in primary CD4+ T cells, and before expression of Tat. IRF-1 also cooperates with Tat in amplifying virus gene transcription and replication. This cooperation depends upon a physical interaction that is blocked by overexpression of IRF-8, the natural repressor of IRF-1, and, in turn is released by overexpression of IRF-1. These data suggest a key role of IRF-1 in the early phase of viral replication and/or during viral reactivation from latency, when viral transactivators are absent or present at very low levels, and suggest that the interplay between IRF-1 and IRF-8 may play a key role in virus latency.

Human immunodeficiency virus type 1 (HIV-1) gene expression is controlled by a complex interplay between viral and host factors. We have previously shown that interferon-regulatory factor 1 (IRF-1) is stimulated early after HIV-1 infection and regulates promoter transcriptional activity even in the absence of the viral transactivator Tat.In this work we demonstrate that IRF-1 is also required for full NF-B transcriptional activity. We provide evidence that IRF-1 and NF-B form a functional complex at the long terminal repeat (LTR) B sites, which is abolished by specific mutations in the two adjacent B sites in the enhancer region. Silencing IRF-1 with small interfering RNA resulted in impaired NF-B-mediated transcriptional activity and in repressed HIV-1 transcription early in de novoinfected T cells. These data indicate that in early phases of HIV-1 infection or during virus reactivation from latency, when the viral transactivator is absent or present at very low levels, IRF-1 is an additional component of the p50/p65 heterodimer binding the LTR enhancer, absolutely required for efficient HIV-1 replication.

The Tat protein is the transcriptional activator of HIV-1 gene expression, which is not only essential for viral replication, but also important in the complex HIV-induced pathogenesis of AIDS, as both an intracellular and an extracellular released protein. Accordingly, Tat is able to profoundly affect cellular gene expression, regulating several cellular functions, also in non-infected cells. We showed recently that Tat induces modification of immunoproteasomes in that it up-regulates LMP7 (low-molecular-mass polypeptide 7) and MECL1 (multicatalytic endopeptidase complex-like 1) subunits and down-modulates the LMP2 subunit, resulting in a change in the generation and presentation of epitopes in the context of MHC class I. In particular, Tat increases presentation of subdominant and cryptic epitopes. In the present study, we investigated the molecular mechanism responsible for the Tat-induced LMP2 down-regulation and show that intracellular Tat represses transcription of the LMP2 gene by competing with STAT1 (signal transducer and activator of transcription 1) for binding to IRF-1 (interferon-regulatory factor-1) on the overlapping ICS-2 (interferon consensus sequence-2)-GAS (gamma-interferon-activated sequence) present in the LMP2 promoter. This element is constitutively occupied in vivo by the unphosphorylated STAT1-IRF-1 complex, which is responsible for the basal transcription of the gene. Sequestration of IRF-1 by intracellular Tat impairs the formation of the complex resulting in lower LMP2 gene transcription and LMP2 protein expression, which is associated with increased proteolytic activity. On the other hand, extracellular Tat induces the expression of LMP2. These effects of Tat provide another effective mechanism by which HIV-1 affects antigen presentation in the context of the MHC class I complex and may have important implications in the use of Tat for vaccination strategies.

The RNA purification is the gold standard for the detection of SARS-CoV-2 in swab samples, but it is dependent on the availability of chemical reagents. In this study, we evaluated the heat treatment method without RNA extraction as a reliable option to nucleic acid purification.

Hepatitis C virus (HCV) proteins are known to interfere at several levels with both innate and adaptive responses of the host. A key target in these effects is the interferon (IFN) signaling pathway. While the effects of nonstructural proteins are well established, the role of structural proteins remains controversial. We investigated the effect of HCV structural proteins on the expression of interferon regulatory factor 1 (IRF-1), a secondary transcription factor of the IFN system responsible for inducing several key antiviral and immunomodulatory genes. We found substantial inhibition of IRF-1 expression in cells expressing the entire HCV replicon. Suppression of IRF-1 synthesis was mainly mediated by the core structural protein and occurred at the transcriptional level. The core protein in turn exerted a transcriptional repression of several interferonstimulated genes, targets of IRF-1, including interleukin-15 (IL-15), IL-12, and low-molecular-mass polypeptide 2. These data recapitulate in a unifying mechanism, i.e., repression of IRF-1 expression, many previously described pathogenetic effects of HCV core protein and suggest that HCV core-induced IRF-1 repression may play a pivotal role in establishing persistent infection by dampening an effective immune response.Infection with hepatitis C virus (HCV) represents the major cause of liver disease, affecting more than 170 million individuals worldwide (26). After a subclinical phase, more than 80% of patients progress to persistent HCV infection, which is the leading cause of chronic liver disease associated with cirrhosis and hepatocellular carcinoma (13). The persistence of the virus in the majority of infected individuals is linked to the ability of HCV to evade and/or antagonize the host immune response at both the local and systemic levels. Accordingly, although hepatocytes are a major target of HCV infection, the virus can also replicate in immune cells, including effector cells (1,11). In this respect, resistance to interferon (IFN) therapy is a hallmark of evolution in persistence, indicating that knocking down the antiviral and immunomodulating effects of IFN is a successful strategy for evading the host immune surveillance (21). The production and secretion of IFN type I is pivotal in inducing a global antiviral state through paracrine IFN production and the subsequent activation of interferon-stimulated genes (ISGs) within the infected cells and in the surrounding tissues (70). The role of IFN in HCV infection is thus crucial (21). Functional genomic analyses from cohorts of human subjects with chronic infection have shown that infection is associated with a gene expression profile marked by ISGs whose level of expression is related to different degrees of liver fibrosis and cirrhosis (67). Similarly, gene expression profiling has demonstrated that acute resolving infections in chimpanzees are associated with high levels of hepatic ISG expression (4).The single-stranded RNA genome of HCV is translated into a polypeptide precursor of 3,010 amino aci...