REGULATION OF TNF-ALPHA, IL-1 AND IL-6 SYNTHESIS IN DIFFERENTIATING HUMAN MONOBLASTOID LEUKEMIC U937 CELLS

The human monoblastoid tumor cell line U937 was induced to differentiate along the monocyte/macrophage lineage by treatment with 5 x 10(-9) M 12-O-tetradecanoyl phorbol-13-acetate (TPA). Between 2 h and 4 h following TPA-treatment U937 cells started to release significant amounts of TNF-alpha which remained detectable until 8-10 days. A significant IL-1-beta release was measured 24 h-48 h post stimulation and increased levels of IL-1-beta persisted until 20-22 days of culture. In contrast no release of either IL-1-alpha or IL-6 could be detected with 5 x 10(-9) M TPA during the whole time course of the experiments. The sequential induction of TNF-alpha and IL-1-beta appeared to be independently regulated since TNF-alpha release was not required for the onset of IL-1-beta production. Northern-blot analysis confirmed the sequential induction and the long term expression of TNF-alpha and IL-1-beta mRNAs. Western-blot analysis predominantly showed a high molecular weight IL-1-beta protein of about 35 kD. Further investigations on the regulation of cytokine production and release by TPA-differentiated U937 cells revealed that TNF-alpha and IL-1-beta synthesis was not influenced by exogenously added rhTNF-alpha or PGE2, whereas rh-gamma-IFN specifically enhanced the IL-1-beta production. Thus, the regulation and intracellular processing of cytokines generated by differentiating U937 cells shows some differences when compared to mature monocytes/macrophages which may be related to the tumorigenic orign of U937 cells or to an incomplete differentiation.