The suppression of hypoxia-induced erythropoietin (EPO) expression by inflammatory cytokines like interleukin-1 (IL-1) contributes to the development of the anemia of chronic disease (ACD). However, the precise mechanism of this suppression is unclear. The 3'-EPO enhancer mediates the transcriptional response to hypoxia by binding several transcription factors, including hypoxia-inducible factor, hepatocyte nuclear factor-4alpha (HNF-4alpha) and chicken ovalbumin upstream promoter transcription factor. We investigated whether IL-1beta inhibits the activity of the 3'-EPO enhancer via HNF-4alpha. IL-1beta inhibited HNF-4alpha mRNA expression and caused proteasome-dependent degradation of HNF-4alpha protein, which resulted in a strongly reduced DNA-binding activity of HNF-4alpha. Reporter gene assays revealed that IL-1beta caused a complete suppression of the hypoxic inducibility of the 3' enhancer via inhibition of HNF-4alpha. We conclude that IL-1beta, at least partially, reduces hypoxia-induced EPO expression by down-regulation of HNF-4alpha.

Erythropoietin (Epo) mRNA expression is suppressed by interleukin 1 (IL-1). Cyclic adenosine monophosphate (cAMP) can increase Epo mRNA and Epo protein levels in IL-1 treated HepG2 cells to some extent. To identify molecular mechanisms of this reaction we investigated three transcription factors (NF-jB, GATA-2 and HIF-1) that control the Epo gene. Western blot analyses and electrophoretic mobility shift assays (EMSAs) revealed that IL-1 strongly activated NF-jB, which is a likely suppressor of the Epo promoter. Treatment of the cells with dibutyryl-cAMP (Bt 2 -cAMP) inhibited the activation of NF-jB by IL-1. Bt 2 -cAMP increased GATA-2 DNA binding. Since GATA-2 is a suppressor of the Epo promoter, GATA-2 activation was unlikely to cause the increase of Epo mRNA expression in IL-1 treated cells. Furthermore, Western blots, EMSAs and reporter gene studies showed that Bt 2 -cAMP was without effect on the hypoxia-inducible transcription factor HIF-1. Thus, NF-jB is probably the primary transcription factor by which cAMP counteracts the inhibition of Epo gene expression by IL-1.