The characterization of two novel IRF-3 transcripts starting from intron 2 of the wild type of IRF-3.

Interferon regulatory factor 3 (IRF-3) is one of the master transcription factors involved in the stringent regulation of interferon production following virus infection. The aim of our study was to explore new isoforms of IRF-3 and further characterize transcriptional regulation. Two new TSSs of IRF-3 were identified by 5' RACE experiments. The expression profiles of new isoforms were tested using RT-PCR. Additionally, the promoter activity and potential transcription factor binding sites of the promoter regions were analyzed. Here we report two novel spliced variants of IRF-3 starting from intron 2 of the wild type of IRF-3, Int2V1 and Int2V2. We localized the transcription start sites (TSS) in the second intron of IRF-3 in pheochromocytoma tissue and thus identified two distinct transcripts. RT-PCR results showed they were expressed in most of tissues and cell lines tested. The expressions levels of them are varying in different tissues and cells. Furthermore, Int2V2 were expressed higher than Int2V1 in all tissues. Luciferase analysis in Hela and 293T cell line defined the promoter regions of the new transcripts had higher promoter activities. Both of the relative luciferase activities were over 100 times higher than that of pGL3-Basic vector. Bioinformatics analysis demonstrated that it contains Sp1, GATA-1/2, IRF-1/2 and Lyf-1 transcription factor binding sites in the promoter regions. The discovery of new transcripts of IRF-3 provides a further insight into the alternative splicing of IRF-3. The novel isoforms expanded the splice variants numbers of IRF-3.