Adenosine-induced expression of interleukin-6 in astrocytes through protein kinase A and NF-IL-6

In various neurologic diseases, astrocytes express interleukin-6 (IL-6), wh ich is an endogenous pyrogen, a neuroprotective factor, and a regulator of the blood-brain barrier. The expression of IL-6 in astrocytes is stimulated by extracellular adenosine through A(2B) receptors. To investigate the sig naling cascade that induces IL-6 gene transcription further, we transfected primary mouse astrocytes with a reporter gene construct, in which lucifera se expression is directed by the human IL-6 promoter. Expression of PKI, an inhibitor of protein kinase A (PKA), interfered with IL-6 transcription in dicating that PKA mediates the effect of adenosine. The CAAT box of the IL- 6 promoter is necessary for the stimulation by adenosine as a mutation in t his element reduced the stimulation by adenosine. Indeed, the cAMP agonist forskolin increased the binding of the transcription factors NF-IL-6 and C/ EBP delta to the CAAT box of the IL-6 promoter in nuclear extracts of astro cytes. Inhibition of the de novo synthesis of NF-IL-6 by cycloheximide or a n antisense oligonucleotide reduced the enhancement of NF-IL-6 binding to t he CAAT box and inhibited stimulation of IL-6 transcription by forskolin. I n addition, overexpression of NF-IL-6 induced IL-6 transcription. This sugg ests that adenosine induces the de novo synthesis of NF-IL-6 through activa tion of PKA and thereby stimulates transcription of IL-6 in astrocytes. (C) 2000 Wiley-Liss, Inc.