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Identification and partial characterization of FRAG-6, a novel interferon-stimulated gene that is expressed in an IRF-1-INDEPENDENT manner.

In order to identify new interferon-stimulated genes that could help in the better understanding of the mechanism of action of interferons (IFNs), we decided to compare, by differential display RT-PCR (DDRT-PCR), the pattern of gene expression between IFN-alpha treated and untreated mouse embryonic fibroblasts (MEFs). Here we describe the initial characterization of a new cDNA fragment, named FRAG-6, that is expressed only upon IFN stimulation. The IFN-induced expression of this new gene can be observed in both wild-type and IRF-1-deficient MEF. FRAG-6 cDNA hybridizes with an mRNA of 6-9 kb that is induced by IFNs in a time-dependent manner. Analysis of the cloned nucleotide sequence revealed a 174 amino acid (aa) open reading frame (ORF) contained within the 576 bp. No significant homology with known nucleotide or protein sequences was observed. FRAG-6 is induced in vitro upon treatment of wild type or IRF-1-null cells with IFN-alpha or -gamma, but not with TNF or IL-1. Treatment of mice with imiquimod, a potent inducer of IFN, led to induced expression of FRAG-6 mRNA in various organs from wild type or IRF-1-deficient mice, but not from STAT-1 or type I IFN receptor deficient animals. Our results demonstrate that FRAG-6 mRNA induction by interferons is IRF-1-independent and it is likely to be activated by the JAK/STAT pathway. Further characterization of FRAG-6 will help us in the understanding of the mechanism of action of IFNs.