Characterization of a second transcription initiation element (STIE) in the human interleukin-1 beta (IL-1beta) gene

Interleukin-1-beta (IL-1beta) is a significant mediator in the inflammation process. Although the human IL-1beta genomic sequence has been known for several years, our understanding of its molecular regulation of transcription remains incomplete. We are reporting a new transcription initiation element that is located within intron 1 and exon 2 of the human IL-1beta gene. Different lengths of the human IL-1beta gene fragment (-685 to +550) were cloned upstream from a chloramphenical acetyltransferase (CAT) gene to make the IL-1beta promoter/CAT reporter constructs. Transient CAT expression with these constructs in the human monocytic leukemia cell line THP1 illustrates an important positive regulatory element exists within the region from +387 to +550. Using electromobility shift assays and by DNase I footprinting analysis, we identified three nuclear factor binding sites (+448 to +502, +513 to +531, and +539 to +548). Functional studies show that CAT production is undetectable when the 19 bp region (+513 to +531) is removed, and CAT production is diminished when the 10-bp region (+539 to +548) is deleted. The region containing these sites is likely to initiate a new transcript starting at +559 of exon 2. This second transcript of the IL-1beta gene shares the same reading frame with the previously recognized cDNA transcript.