The Inhibitory Effect of IL-1β on IL-6-Induced α2-Macroglobulin Expression Is Due to Activation of NF-κB

The cross-talk between the signal transduction of simultaneous acting cytokines largely determines the final impact of cytokines on their target genes. Both NF-kappaB and STAT3 are transcription factors well known to be activated by many stimuli and to mediate transcriptional activation by binding to specific enhancer sequences. In this study, it is analyzed how IL-1beta inhibits IL-6-induced transcriptional activation of the alpha(2)-macroglobulin promoter. It is shown that IL-1beta prevents STAT3 binding to the two STAT3-responsive sites within the alpha(2)-macroglobulin promoter by association of IL-1beta-activated NF-kappaB to this region. The observation that inhibition of IL-6-induced transcriptional activation of this promoter by IL-1beta is reversed by cotransfection with I-kappaBalpha provides evidence that NF-kappaB activation by IL-1beta is responsible for inhibition of IL-6-mediated trans activation of the alpha(2)-macroglobulin gene. Accordingly, cotransfection of the NF-kappaB subunits p50 or p65 themselves inhibited activation of the alpha(2)-macroglobulin promoter by IL-6. Introduction of point mutations in each of the two NF-kappaB sites overlapping the two STAT3 binding sites within the alpha(2)-macroglobulin promoter provides evidence that each of these two sites counteracts transcriptional activation via STAT3. Most interestingly, at least one functional NF-kappaB consensus site is essential for the IL-6-induced transcriptional activation of the alpha(2)-macroglobulin promoter. Additional data are provided indicating that the activation of NF-kappaB by IL-1beta is also responsible for the inhibition of other IL-6-inducible genes, such as the alpha(1)-antichymotrypsin gene as well as the suppressor of cytokine signaling 3 gene, suggesting a more general relevance of this mechanism for transcriptional regulation.