Differential regulation of interferon synthesis in lymphoblastoid cells

A novel PRD I and TG binding activity involved in virus-induced transcription of IFN-A genes

Comparative analysis of the inducible elements of the mouse interferon A4 and A11 gene promoters (IE-A4 and IE-A11) by transient transfection experiments, DNase 1 footprinting and electrophoretic mobility shift assays resulted in identification of a virus-induced binding activity suggested to be involved in NDV-induced activation of transcription of these genes. The virus-induced factor, termed VIF, is activated early by contact of virions with cells. It specifically recognizes the PRD I-like domain shared by both inducible elements, as well as the TG-like domain of IE-A4. This factor, distinct from the IRF-1, IRF-2 and the alpha F1 binding proteins and presenting a different affinity pattern from that of the TG protein, is proposed as a candidate for IFN-type I gene regulation.

Stimulation of interferon and cytokine gene expression by imiquimod and stimulation by Sendai virus utilize similar signal transduction pathways

The imidazoquinolineamine derivative 1-(2-methyl propyl)-1H-imidazole [4,5-c]quinoline-4-amine (imiquimod) has been shown to induce alpha interferon (IFN-alpha) synthesis both in vivo and in peripheral blood mononuclear cells in vitro. In this study, we show that, in these cells, imiquimod induces expression of several IFNA genes (IFNA1, IFNA2, IFNA5, IFNA6, and IFNA8) as well as the IFNB gene. Imiquimod also induced the expression of interleukin (IL)-6, IL-8, and tumor necrosis factor alpha genes. Expression of all these genes was transient, independent of cellular protein synthesis, and inhibited in the presence of tyrosine kinase and protein kinase C inhibitors. Infection with Sendai virus led to expression of a similar set of cytokine genes and several of the IFNA genes. Imiquimod stimulates binding of several induction-specific nuclear complexes: (i) the NF-kappa B-specific complexes binding to the kappa B enhancer present in the promoters of all cytokine genes, but not in IFNA genes, and (ii) the complex(es) binding to the A4F1 site, 5'-GTAAAGAAAGT-3', conserved in the inducible element of IFNA genes. These results indicate that imiquimod, similar to viral infection, stimulates expression of a large number of cytokine genes, including IFN-alpha/beta, and that the signal transduction pathway induced by both of these stimuli requires tyrosine kinase and protein kinase activity.

Constitutive interferon expression from retroviral vector

A genomic fragment with the human beta-interferon gene was cloned into a pL3-4, a defective Moloney murine leukemia virus (M-MuLV) vector. Here we show that clones selected after viral infection of mouse NIH 3T3 cells constitutively produced 128 IU/ml of human beta-interferon. Constitutive synthesis of retroviral RNA was confirmed by dot blot hybridization of RNA isolated from two of the selected clones. Poly(I) x poly(C) and cycloheximide induction resulted in an increased RNA level, but this was not reflected in an increased production of biologically active interferon.

Priming of human monocytes for enhanced lipopolysaccharide responses: expression of alpha interferon, interferon regulatory factors, and tumor necrosis factor

Culture of human monocytes with either granulocyte-macrophage colony-stimulating factor or gamma interferon (IFN-gamma) results in a primed state, during which these cells express heightened responses to bacterial lipopolysaccharide (LPS). The production of IFN-alpha in response to LPS by human monocytes has an absolute requirement for priming. Tumor necrosis factor (TNF) expression is also greatly enhanced in primed monocytes after LPS stimulation, but unlike IFN-alpha, TNF is readily expressed in unprimed monocytes as well. In an effort to determine the molecular events associated with IFN-alpha induction in this system, freshly isolated human monocytes were primed by culture with either IFN-gamma or granulocyte-macrophage colony-stimulating factor and then treated with LPS; expression of IFN-alpha subtype 2 (IFN-alpha 2), IFN regulatory factors (IRFs), and TNF was assessed by Northern (RNA blot) analysis. IRF-1 mRNA is expressed at high levels in monocytes and is regulated by both LPS and priming cytokines, but its expression alone does not correlate with the induction of IFN-alpha 2 expression. IRF-2 mRNA is expressed in a more gradual manner following LPS stimulation, implying a possible feedback mechanism for inhibiting IFN-alpha expression. However, nuclear run-on analysis indicates that IFN-alpha 2 is not transcriptionally modulated in this system, in striking contrast to TNF, which is clearly regulated at the transcriptional level. In addition, IFN-alpha 2 mRNA accumulation is superinduced when primed monocytes are treated with LPS plus cycloheximide, while TNF mRNA is relatively unaffected. The results demonstrate that priming can affect subsequent LPS-induced gene expression at different levels in human monocytes.

Retrovirus vector-targeted inducible expression of human beta-interferon gene to B-cells

We have introduced the human beta-interferon gene with its promoter region into murine B-cell and fibroblast cell lines via a Moloney murine leukemia virus (M-MuLV) vector and have studied the inducible expression of the beta-interferon gene as a function of the various retroviral vector designs. By deleting the enhancer within the 3' viral long terminal repeat (LTR), inserting the human beta-interferon gene, and varying placement of the immunoglobulin heavy chain enhancer, we were able to construct vectors which yielded proviruses with various cell type-specific regulation. One of the vectors (pT154) led to a greater than 21-fold increase in beta-interferon protein synthesis after viral infection in the two B-cell lines analyzed, while no inducibility was seen in the fibroblast cells. The data show that inducible beta-interferon expression within a MuLV vector was highly dependent on the absence of the viral enhancer region in the long terminal repeat and the orientation of the beta-interferon gene within the proviral transcriptional unit; the insertion of the immunoglobulin enhancer elevated both constitutive and (or) inducible expression of beta-interferon in B-cells but inhibited constitutive expression of this gene in fibroblasts.

Inhibition of human immunodeficiency virus (HIV) replication by HIV-trans-activated alpha 2-interferon

We have prepared stable cell lines, derived from Vero cells and A3.01 cells, that express a hybrid human alpha 2-interferon gene under control of the human immunodeficiency virus (HIV) long terminal repeat. These cells constitutively produced low levels (50-150 units/ml) of alpha 2-interferon. However, high levels of interferon (10(3) units/ml) could be induced upon trans-activation by the product of the tat gene (pIIIextatIII), and de novo infection by HIV resulted in a moderate increase (400 units/ml) in alpha 2-interferon synthesis. In contrast to the fully permissive HIV replication, in transfected Vero cells or infected A3.01 cells, the transcription and replication of HIV in Vero or A3.01 cells containing the HIV long terminal repeat--alpha 2-interferon hybrid gene (VN89 and A3N89 cells, respectively) was completely inhibited. These data suggest that virus-trans-activated alpha 2-interferon synthesis can be used as a selective inhibitor of HIV replication.

Differential and cell type specific expression of murine alpha-interferon genes is regulated on the transcriptional level

In mouse cells induced with virus infection or dsRNA, the relative levels of alpha-4 interferon mRNA were higher than the levels of alpha-1 and alpha-6 mRNAs; the ratio between relative levels of alpha-4 and alpha-1 or alpha-6 mRNA was, however, dependent on the cell type. Recombinant plasmids, in which the expression of chloramphenicol acetyltransferase (CAT) gene was directed by the promoter regions of alpha-1, alpha-4 or alpha-6 interferon genes were constructed and their inducible expression was studied either in transient assay or in permanently transfected mouse cells. The highest levels of CAT activity and CAT mRNA were observed with alpha-4 CAT plasmid, while the expression of alpha-1 CAT was consistently higher than that coded by alpha-6 CAT plasmid; the ratio between CAT activities coded by alpha-4 CAT and alpha-1 CAT was dependent on cell type. However, in heterologous Vero cells, the transfected alpha-1 and alpha-4 genes were expressed constitutively, and the levels of mRNAs were comparable. These results show that the difference in the relative levels of individual alpha-1 and alpha-4 mRNAs reflects the transcriptional inducibility of the respective promoter regions.

Human fibroblast but not lymphoid cells have unusually long polyadenylated interferon-beta 1 mRNAs

The transcription unit of human interferon-beta 1 (IFN-beta 1) mRNA was examined by chain elongation of nascent RNA in isolated nuclei of human fibroblasts and lymphoid cells induced to produce IFN. In fibroblasts, transcription proceeds beyond 2,400 nucleotides downstream from the poly(A) site of mature mRNA and appears to terminate in the region rich in Alu sequences. Northern hybridization showed the presence of a minor polyadenylated RNA species, about 3,200 nucleotides long, that hybridized to the probes derived from 3'-flanking regions of IFN-beta 1 mRNA. S1 nuclease analysis established that this long polyadenylated transcript represents a mixture of three RNA molecules with defined 3' termini. In all three mRNAs, as in mature IFN-beta 1 mRNA, the polyadenylation site was located within a few nucleotides downstream from the AAUAAA hexanucleotide consensus sequence. Surprisingly, in Namalva lymphoblastoid cells no transcription beyond the polyadenylation site of mature IFN-beta 1 mRNA could be detected either in isolated nuclei or total RNA.

Differential effect of poly rI.rC and Newcastle disease virus on the expression of interferon and cellular genes in mouse cells

The expression of type I murine interferon (MuIFN) genes and several other cellular genes was examined in poly rI.rC induced and Newcastle disease virus (NDV) infected mouse cells. Northern analysis of RNA from induced L cells revealed that the MuIFN-alpha s are expressed efficiently in NDV infected cells but only at low levels in poly rI.rC induced cells. MuIFN-beta 1, however, is expressed equally well in cells treated with poly rI.rC or infected with NDV. As shown by the use of a probe specific for poly rI.rC, interferon induction correlates with the cellular uptake of poly rI.rC into the cells. The relative levels of alpha and beta 1 mRNAs in the cells reached a maximum at 10 hr after the induction which indicates coordinate expression of alpha and beta 1 interferon genes. The effect of viral infection on the expression of two murine genes coinduced with interferon (pMIF20/11 and pMIF3/10) and several cellular genes was also examined. While pMIF20/11 is an inducible gene, the pMIF3/10 gene is expressed constitutively in mouse L cells. Viral infection, but not poly rI.rC treatment, enhanced the expression of the pMIF3/10 gene, as well as two other cellular genes; H-2 and c-myc, however, the expression of beta-actin gene was unaltered. These data indicate that enhancement of gene expression in virus infected cells in not limited to the interferon system.