Stimulation of Interferon and Cytokine Gene Expression by Imiquimod and Stimulation by Sendai Virus Utilize Similar Signal Transduction Pathways

Abstract

The low-molecular-weight imidazoquinolineamine derivative 1-(2-methyl propyl)-1H-imidazole [4,5-c]quinoline-4-amine (imiquimod) inhibits replication of herpes simplex virus type 2 and cytomegalovirus in infected guinea pigs (6, 24). Imiquimodmediated inhibition of virus replication is related to its ability to induce interferon (IFN). Oral administration of imiquimod induces IFN-␣ in mice, rats, guinea pigs, monkeys, and humans. (New approved nomenclature for IFN genes [9a] is used throughout this paper.) In addition to having antiviral activity, imiquimod was shown to inhibit growth of several transplantable murine tumors, including MC-26 colon carcinoma and Lewis lung carcinoma (71). The induction of IFN-␣ plays a major, but not exclusive, role in this growth inhibition, since an antiserum to mouse IFN-␣ and IFN-␤ significantly reduced the antitumor effect of imiquimod but was not able to abolish it completely.IFN-␣ proteins are represented by a large family of structurally related genes which show about 94% homology at the nucleotide level, while IFN-␤ is encoded by a single gene. IFNA genes are expressed preferentially in cells of lymphoid lineage, and the individual subtypes show cell-type-specific differences in expression (2, 29, 35), while IFNB is expressed in a large variety of cells. The biological significance of the large abundance of IFNA genes is not clear; all IFN-␣ and IFN-␤ subtypes show antiviral and antitumor properties and seem to bind to a common receptor (39); however, some differences between their immunomodulatory effects have been reported (21, 56).Virus-induced expression of IFNA and IFNB genes is mediated by a virus-responsive element (VRE) present in the promoters of IFNA and IFNB genes that, by itself, functions as a virus-specific enhancer and can confer inducibility in infected cells (3,14,19,20,58,65). At least two families of transcriptional factors were shown to play a role in induction of IFN genes that have binding sites within the VRE. One family is the set of IFN-responsive factors IRF-1 and IRF-2, which function as activator and repressor, respectively (22, 23). Overexpression of these two factors can regulate activity of both IFNA and IFNB promoter regions in a transient expression assay; a single nucleotide mutation in the IRF-1 binding site of the murine IFNA4 gene promoter decreased inducibility by about 100-fold (2), and cells expressing IRF-1 antisense mRNA were unable to express IFNB genes (62). However, the role of IRF-1 in induction of the IFN gene has been questioned, since deletion of the IRF-1 gene did not affect virus-mediated inducibility of IFN genes either in mice in vivo or in cultured cells in vitro (53,64). The second family of transcriptional factors are the Bspecific binding proteins that play a role in activation of the IFNB gene (16,19,28,43,77), and recently, a direct role of IFN-induced double-stranded RNA (dsRNA)-dependent kinase in activation of NF-B has been shown (37, 49). Furthermore, it was shown that HMG I(Y) and ATF-2 can bind to the VRE (48...

Premature expression of the latency-related RNA encoded by bovine herpesvirus type 1 correlates with higher levels of beta interferon RNA expression in productively infected cells

“…An initial study was performed to prove that MDBK cells were responsive to stimuli that induce IFN production. To this end, MDBK cells were infected with wt BHV-1 or treated with 10 mg imiquimod (Invitrogen) ml 21 , a compound that stimulates IFN and cytokine production (Megyeri et al, 1995). Following treatment with imiquimod, IFN-b promoter activity increased as a function of time for 24 h and was approximately seven times higher compared with untreated cells (Fig.…”

Virus-induced Heterodimer Formation betweenIRF-5 and IRF-7 Modulates Assembly of theIFNA Enhanceosome in Vivo and Transcriptional Activity of IFNA Genes

“…We have shown previously that NDV-infected 2fTGH/IRF-5 cells preferentially induced the IFNA8 subtype (Table I, values in parentheses, column 3), whereas 2fTGH/IRF-7 cells preferentially expressed the IFNA1 subtype (Table I, amplified the IFNA mRNA and cloned the fragments from NDV-infected cells, as described previously (25,40). We have found that this method yields a more accurate identification of the IFNA subtypes expressed than the previously used RNA protection assay (48).…”

“…Although the promoters of all IFNA genes are highly homologous, differential expression of these genes, as a function of cell type and inducing agent, has been observed (39,40). IFNA1 was identified as the major subtype expressed in human fibroblasts expressing IRF-3 and ectopic IRF-7 (25) but not IRF-5.…”

The Interferon Regulatory Factor, IRF5, Is a Central Mediator of Toll-like Receptor 7 Signaling

“…In addition to single-stranded RNA, the synthetic imidazoquinoline, imiquimod, a low molecular weight immune response modifier, activates TLR7 in both humans and mice, whereas its derivative resiquimod (R-848) activates TLR7 and TLR8 in humans but only TLR7 in mice (10,11). Both imiquimod and R-848 elicit robust anti-viral and anti-tumor immune responses in vivo, which correlate with a strong induction of type I IFNs (12)(13)(14). As a consequence of this activity, imiquimod is used for the treatment of external genital warts caused by human Papillomavirus (15).…”