Inhibition of interleukin-6 promoter activity by the 24 kDa isoform of fibroblast growth factor-2 in HeLa cells

The expression of the interleukin (IL-6) gene can be regulated by various a ctivating or inhibitory stimuli. This modulation involves several regulator y binding sites on the IL-6 promoter, and appears to be in general cell-spe cific. We have previously described that the nuclear 24 kDa isoform of fibr oblast growth factor-2 (FGF-2) is able to increase IL-6 gene expression in NIH-3T3 cells. The transduction pathway involved was shown to be distinct f rom the extracellular mode of action of the smallest 18 kDa FGF-2 isoform. In the present study, we show that 24 kDa FGF-2-encoding vectors transfecte d into HeLa cells inhibit various co-transfected constructs incorporating t he promoter element of the IL-6 gene and either the luciferase or the chlor amphenicol acetyltransferase units. This down-regulation occurs dose-depend ently with the 24 kDa FGF-2, is IL-6-promoter-specific, and does not involv e an autocrine loop of the growth factor, since exogenously added FGF-2 fai ls to modulate the IL-6 promoter activity. Furthermore, 24 kDa FGF-2 inhibi ts the activity of both the co-transfected deletion mutants IL-6(-224) and IL-6(-158), and the point-mutated IL-6 promoter constructs in which the act ivating protein-1, nuclear factor (NF)IL-6 and NF-kappa B elements are disr upted. We identify a responsive region to 24 kDa FGF-2 between positions -1 58 and -109 on the IL-6 promoter, which notably contains a retinoblastoma c ontrol element.