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Mol. Cell. Biol., 04 1996, 1584-1594, Vol 16, No. 4
A Ray and BK Ray
Serum amyloid A (SAA) is a plasma protein which has been associated with
several diseases, including amyloidosis, arthritis, and atherosclerosis,
and its abnormal expression, particularly in nonhepatic cells, is
implicated in the pathogenesis of these diseases. Transfection and
DNA-binding studies were performed to investigate the mechanism controlling
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-chloramphenicol
acetyltransferase reporter gene in both nonhepatic and hepatic cells. DNase
I protection assays revealed, within this region, three homologous highly
pyrimidine rich octanucleotide sequence motifs, termed SAA-activating
sequences (SAS). Specific mutations within these three SAS motifs severely
reduced IL-6- mediated induction of the reporter gene in transfected
nonhepatic cells but not in liver cells. A nuclear factor activated by IL-6
in both hepatic and nonhepatic cells efficiently interacts with the SAS.
The induction kinetics and cycloheximide sensitivity of this SAS-binding
factor (SAF) suggested that de novo synthesis of this factor itself or an
activator protein is essential. Loss of DNA-binding ability as a result of
in vitro dephosphorylation, induction of SAA-chloramphenicol
acetyltransferase reporter gene activity in the presence of genistein, a
protein kinase inhibitor, further indicate that a phosphorylation step is
necessary for the activation of SAF. Our results suggest that SAF is a key
regulator of cytokine-mediated SAA gene expression in some nonhepatic
cells.
Copyright © 1996, American Society for Microbiology
A novel cis-acting element is essential for cytokine-mediated transcriptional induction of the serum amyloid A gene in nonhepatic cells
Department of Veterinary Pathobiology, University of Missouri, Columbia, 65211, USA.
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