The multifunctional cytokine interleukin-1beta (IL-1beta) plays a central role in the body's immune and inflammatory responses. The mechanism of IL-1beta on thrombocytosis and megakaryocytopoiesis has remained controversial. In previous reports, we have demonstrated the expression of IL-1 receptors (IL-1RI and IL-1RII) and enhancing effects of IL-1beta on primary human megakaryocytic (MK) cells. In this study, we investigated the possible direct effects of IL-1beta on the expression of thrombopoietin (TPO) and transcription factors c-Jun, c-Fos, GATA-1, and p45 nuclear factor-E2 (NF-E2) in MK cell lines CHRF and Meg-01. Our results demonstrated that IL-1beta up-regulated messenger RNA (mRNA) and protein expressions of these transcription factors in a dose- and time-dependent manner. In CHRF cells, mRNA: c-Jun [3.4-fold, peaked at 15 minutes], c-Fos [4.2-fold, 15 minutes], GATA-1 [4.0-fold, 60 minutes], NF-E2 [3.2-fold, 120 minutes] and protein expression: c-Jun [3.0-fold, 30 minutes], c-Fos [1.7-fold, 30 minutes], GATA-1 [11.5-fold, 60 minutes], NF-E2 [12.5-fold, 120 minutes] were evidently enhanced after treatment with IL-1beta. The response to IL-1beta was consistent in the total cell and nuclear extracts and was significantly reduced by pretreatment with actinomycin D or cycloheximide. An IL-1-receptor antagonist (IL-1RA) inhibited the stimulatory effects of IL-1beta on these transcription factors by as much as 78%. TPO expression was increased by more than 9.9-fold on stimulation with IL-1beta. A TPO-neutralizing antibody did not significantly reduce the effects of IL-1beta. We conclude that IL-1beta up-regulates the expression of TPO, c-Jun, c-Fos, GATA-1, and NF-E2 in MK cells. The mechanism might be mediated by IL-1beta receptors and require transcription or protein synthesis. The direct involvement of IL-1beta in the MK lineage may provide an explanation for the phenomenon of thrombocytosis during inflammatory responses.