Abstracts (complete list) - Wissenschaft Online

Malte Bachmann, Jens Paulukat, Josef Pfeilschifter, Heiko Mühl
MOLECULAR MECHANISMS OF IFNγ-INDUCED IL-18 BINDING
PROTEIN PROMOTER ACTIVATION AS DETECTED IN HUMAN
DLD-1 COLON CARCINOMA CELLS
Due to its prominent activity as IFNγ inducing factor, IL-18 has been introduced as a
pivotal mediator of inflammation. Accordingly, IL-18 bioactivity is strongly associated
with the pathogenesis of acute and chronic inflammatory diseases, among others,
sepsis, rheumatoid arthritis, and Crohn`s disease. IL-18 Binding Protein (IL-18BP) is a
naturally occurring inhibitor that counteracts IL-18 bioactivity. We and others could
previously demonstrate that IL-18BP is strongly induced by IFNγ, resulting in a negative
feedback mechanism that has been recognized in cell culture and in vivo. Here we
sought to investigate in DLD-1 colon carcinoma cells molecular mechanisms that direct
IL-18BP expression under the influence of IFNγ. The capability of IFNγ to induce IL-18BP
was confirmed on the promoter level by performing luciferase reporter studies. Those
experiments revealed that a proximal GAS element (gamma-activated sequence;-24bp
to -32bp) plays a pivotal role in IL-18BP expression by IFNγ activated DLD-1 cells. IL-
18BP was dependent on STAT1 activation as shown by siRNA technology. Indeed, EMSA
and ChIP analysis proved STAT1 binding to the GAS element at the proximal IL-18BP
promoter position. Full induction of IL-18BP by IFNγ was in part dependent on de novo
protein synthesis. In fact, induction of IRF-1 by IFNγ and the presence of an IRF-1
binding site close to the GAS element under investigation suggests a role for IRF-1 in
IFNγ induced IL-18BP. Altogether, data on DLD-1 colon carcinoma cells presented herein
indicate that direct action of STAT1 on the proximal GAS element of the IL-18BP
promoter is key to IFNγ induction of this most relevant immunoregulatory cytokine
antagonist.