A NOVEL CIS-ACTING ELEMENT IS ESSENTIAL FOR CYTOKINE-MEDIATED TRANSCRIPTIONAL INDUCTION OF THE SERUM AMYLOID-A GENE IN NONHEPATIC CELLS

Serum amyloid A (SAA) is a plasma protein which has been associated wi th several diseases, including amyloidosis, arthritis, and atheroscler osis, and its abnormal expression, particularly in nonhepatic cells, i s implicated in the pathogenesis of these diseases, Transfection and D NA-binding studies were performed to investigate the mechanism control ling cytokine-induced, nonhepatic expression of the SAA gene. We have identified a novel promoter, located between positions -280 and -224, that confers interleukin-6 (IL-6) inducibility to an SAA-chloramphenic ol acetyltransferase reporter gene in both nonhepatic and hepatic cell s, DNase I protection assays revealed, within this region, three homol ogous highly pyrimidine rich octanucleotide sequence motifs, termed SA A-activating sequences (SAS), Specific mutations within these three SA S motifs severely reduced IL-6-mediated induction of the reporter gene in transfected nonhepatic cells but not in liver cells, A nuclear fac tor activated by IL-6 in both hepatic and nonhepatic cells efficiently interacts with the SAS, The induction kinetics and cycloheximide sens itivity of this SAS-binding factor (SAF) suggested that de novo synthe sis of this factor itself or an activator protein is essential, Loss o f DNA-binding ability as a result of in vitro dephosphorylation, induc tion of SAA-chloramphenicol acetyltransferase reporter gene activity i n the presence of a protein phosphatase inhibitor, and loss of IL-6-me diated inducible DNA-binding activity and reporter gene activation in the presence of genistein, a protein kinase inhibitor, further indicat e that a phosphorylation step is necessary for the activation of SAF. Our results suggest that SAF is a key regulator of cytokine-mediated S AA gene expression in some nonhepatic cells.