Erythropoietin production: Molecular mechanisms of the antagonistic actions of cyclic adenosine monophosphate and interleukin-1

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-κB, 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-κB, which is a likely suppressor of the Epo promoter. Treatment of the cells with dibutyryl-cAMP (Bt₂-cAMP) inhibited the activation of NF-κB by IL-1. Bt₂-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 Bt₂-cAMP was without effect on the hypoxia-inducible transcription factor HIF-1. Thus, NF-κB is probably the primary transcription factor by which cAMP counteracts the inhibition of Epo gene expression by IL-1.