Detection of a novel transcription factor for the A alpha fibrinogen gene in response to interleukin-6

The three fibrinogen genes belong to the class II hepatic acute phase proteins that are regulated in part by members of the interleukin-6 (IL-6) family of cytokines and glucocorticoids. The common DNA sequence that characterizes this group of proteins is a hexanucleotide CTGGGA residing in the promoter regions of these genes. Investigations of IL-6 control of the A alpha fibrinogen gene by electrophoretic mobility shift assays using a 30-base pair DNA probe containing the CTGGGA element revealed that a novel protein is associated with this site during non-IL-6-stimulated conditions. Sensitive time-course studies of IL-6 stimulation using primary hepatocyte cultures, high resolution polyacrylamide gel electrophoresis, and site-directed mutagenesis show that upon IL-6 stimulation of hepatocytes, this DNA binding protein transiently leaves the CTGGGA site and binds 12 base pairs down-stream but then begins to re-associate with the original DNA site at 1 h and is completed by 2 h. A recently characterized and cloned IL-6-activated transcription factor, Stat-3, which has been reported to bind a CT-GGGAA site in the alpha-2 macroglobulin gene, another member of the class II acute phase proteins, does not bind to the CTGGGA sequence in the A alpha fibrinogen gene. These findings reveal the presence of a previously undefined IL-6-regulated event, which involves a new DNA binding protein and demonstrates for the first time additional details of the kinetics of IL-6 control of fibrinogen gene expression.