Submitted on April 5, 2006
Accepted on August 5, 2006
Interleukin (IL)-1 and IL-6 induce hepatocyte plasminogen activator inhibitor-1
expression through independent signaling pathways converging on
C/EBP
Jie Dong1, Satoshi Fujii1, Shogo Imagawa1, Shuichiro Matsumoto2, Michiaki Matsushita2, Satoru Todo2, Hiroyuki Tsutsui1, and Burton E. Sobel3*
1 Cardiovasc. Med., Hokkaido Univ., Japan
2 Surgery, Hokkaido Univ., Japan
3 Medicine, University of Vermont, Colchester, Vermont, United States
* To whom correspondence should be addressed. E-mail: burt.sobel{at}vtmednet.org.
To elucidate signaling pathways activated by IL-1 and IL-6 that contribute to increased expression of PAI-1 we studied human hepatoma (HepG2) cells and primary mouse hepatocytes. HepG2 cell PAI-1mRNA increased in response to IL-1
, IL-6 and IL-1+IL-6 as shown by real-time PCR. Activity of the transiently transfected PAI-1 promoter (-829 bp to +36 bp) increased as well. Systematic promoter deletion assays showed that the region from -239 bp to -210 bp containing a putative CCAAT-enhancer binding protein (C/EBP) binding site was critical. Point mutations in this region abolished the IL-1 and IL-6 responses. Antibody interference electrophoretic mobility-shift assays showed that C/EBP
(but not C/EBP
or C/EBP) binding and protein were increased by IL-1, IL-6 and IL-1+IL-6 in HepG2 cells. IL-1 and IL-6 increased expression of both PAI-1 mRNA and C/EBP mRNA in mouse primary hepatocytes as well. Down-regulation of C/EBP induced with small interfering RNA (siRNA) decreased secretion of PAI-1. As judged from results obtained with inhibitors, signal transduction in all three of the MAPK pathways was involved in IL-1 inducible PAI-1 expression. By contrast, JAK signaling was responsible for the IL-6 induced inducible expression. Thus, IL-1 and IL-6 exert directionally similar effects on PAI-1 expression, but the induction involves distinct signaling pathways with a final common mediator, C/EBP.
