Characterization of a spliced variant of human IRF-3 promoter and its regulation by the transcription factor Sp1.

Interferon regulatory factor 3 (IRF-3), an essential transcriptional regulator of the interferon genes, plays an important role in host defense against viral and microbial infection as well as in cell growth regulation. Promoter plays a crucial role in gene transcription. We have reported the characterization of the wide type of human IRF-3 promoter, but the characterization of the spliced variant of human IRF-3 Int2V1 promoter has not been systematically analyzed. To observe the spliced variant of human IRF-3 promoter, we have cloned the human IRF-3 gene promoter region containing 300 nucleotides upstream the transcription start site (TSS). Transient transfection of 5' deleted promoter-reporter constructs and luciferase assay illustrated the region -159/-100 relative to the TSS is sufficient for full promoter activity. This region contains GATA1 and specific protein-1 (Sp1) transcription factor binding sites. Interestingly, mutation of this Sp1 site reduced the promoter activity by 50%. However, overexpression of Sp1 increased the transcription activity by 2.4-fold. These results indicated that the spliced variant of human IRF-3 gene core promoter was located within the region -159/-100 relative to the TSS. Sp1 transcription factor upregulates the spliced variant of human IRF-3 gene promoter.