TRANSFORMING GROWTH-FACTOR-BETA-1 (TGF-BETA-1) POTENTIATES IL-1-ALPHA-INDUCED IL6 MESSENGER-RNA AND CYTOKINE PROTEIN-PRODUCTION IN A HUMAN ASTROCYTOMA CELL-LINE

We analyzed the response of human astrocytoma cell line U373-MG to var ious cytokines by measuring the production of interleukin-6 (IL6) mRNA and cytokine protein. Interferon gamma (IFN I), transforming growth f actor beta 1 (TGF-beta 1), granulocyte-macrophage colony-stimulating f actor (GM-CSF) and granulocyte-colony-stimulating factor (G-CSF) did n ot induce IL6 mRNA production; however, IL6 mRNA expression and protei n production was strongly induced by IL1 alpha and to a lesser extent by IFN alpha. The IL6 mRNA expression induced by IL1 alpha was potenti ated by TGF-beta 1 and IFN alpha and slightly decreased by IFN gamma. The potentiation of cytokine mRNA accumulation by TGF-beta 1 was both time- and concentration-dependent. Induction of IL6 mRNA by IL1 alpha was optimally potentiated either if U373-MG cells were pretreated with TGF-beta 1 or if TGF-beta 1 was added within 30 min after stimulation with IL1 alpha. The potentiation of IL6 mRNA by TGF-beta 1 required d e novo synthesis of an intermediate protein since treatment with cyclo heximide abrogated the amount of mRNA enhanced by TGF-beta 1 without a ffecting IL1 alpha-driven mRNA production. Nuclear run-on analyses dem onstrated increased transcriptional activity of the IL6 gene when stim ulated with IL1 alpha in the presence of TGF-beta 1. However, actinomy cin-D pulse chase experiments showed that TGF-beta 1 did not increase the stability of IL6 mRNA. Thus, in concert, the results demonstrate t hat TGF-beta 1 potentiates IL6 production in astrocytoma cells by prom oting the transcriptional activity of the IL6 gene and requires coexpr ession of new proteins. Since cytokines can provide potent mitogenic s ignals to tumor cells, the results presented here further suggest that the antitumor effect of combination cytokine therapy might partly dep end on heterotypic interactions between tumor cells and cytokines.