The cytokines interleukin-1 beta (IL-1β) and tumor necrosis factor-alpha (TNF-α) induced interleukin-6 (IL-6) gene expression in astrocytes. The molecular mechanism(s) by which these cytokines activate IL-6 expression was examined by transient transfection of the human IL-6 promoter linked to the reporter gene CAT (IL-6-CAT) in primary rat astrocytes. We show that both IL-1β and TNF-α exert their effects through the IL-6 promoter to increase CAT activity, indicating that the cytokines act at the transcriptional level. Use of deletion mutants revealed that the NF-κ B-like binding site is required for cytokine induction of IL-6 promoter activity. The correlary effects of IL-1β and TNF-α on DNA-binding proteins specific for this elements were examined. Treatments of astrocytes with cytokine leads to a rapid activation (15 min) of a nuclear protein which specifically complexes with the NF-κ B-like binding region in the IL-6 promoter. These results suggest that TNF-α and IL-1β activate IL-6 gene expression in astrocytes by a mechanism(s) involving activation of an NF-κ B-like protein. © 1992.