| Interleukin-6 has a wide range of biological effects, and is particularly relevant in hematopoeisis and lineage commitment of progenitor cells in blood. It has been previously demonstrated that IL-6 reduces steady-state gamma globin mRNA levels in K562 cells. Several cis-acting elements have been identified in the promoters of the various globin genes however; the precise mechanism for cytokine-mediated globin gene regulation has not yet been fully characterized. Detailed molecular analyses have yielded novel information about the regulation of the gamma globin gene. Specific inhibitors of the Janus Kinase/Signal Transducer and Activator of Transcription (JAK/STAT) signaling pathway abrogated the IL-6 mediated inhibition of gamma globin mRNA production in erythroid cells. DNA-protein binding studies established Stat3 binding in the 5' untranslated region of the gamma globin promoter region. Co-transfection experiments with Stat3beta demonstrate gamma promoter inhibition in a concentration-dependant manner. This effect is dependant on a cognate Stat3 binding site in the 5' untranslated region. Increased levels of Stat3beta enhanced the repressive effect of IL-6 on the gamma globin promoter. Lastly, truncation experiments of the gamma promoter confirmed the area of activity through which IL-6 mediates its repression of gamma globin to be in the proximal promoter region, containing the AgammaStat3 site. In conclusion, this study has identified a Stat3 site (AgammaStat3) acting as a silencing element in the gamma globin gene. |
