• Open Access

Molecular mechanisms of IL-18BP regulation in DLD-1 cells: pivotal direct action of the STAT1/GAS axis on the promoter level

Authors


Current address: InfectoPharm Arzneimittel GmbH, 64646 Heppenheim, Germany.

Correspondence to: Heiko MÜHL, Ph.D.,
Pharmazentrum Frankfurt/ZAFES,
University Hospital Goethe-University Frankfurt, Theodor-Stern-Kai 7, Haus 74, 60590 Frankfurt am Main, Germany.
Tel.: +49 69 6301 6962
Fax: +49 69 6301 7942
E-mail: H.Muehl@em.uni-frankfurt.de

Abstract

Interleukin (IL)-18, formerly known as interferon (IFN)-γ-inducing factor, is a crucial mediator of host defence and inflammation. Control of IL-18 bioactivity by its endogenous antagonist IL-18 binding protein (IL-18BP) is a major objective of immunoregulation. IL-18BP is strongly up-regulated by IFN-γ, thereby establishing a negative feedback mechanism detectable in cell culture and in vivo. Here we sought to investigate in D.L. Dexter (DLD) colon carcinoma cells molecular mechanisms of IL-18BP induction under the influence of IFN-γ. Mutational analysis revealed that a proximal γ-activated sequence (GAS) at the IL-18BP promoter is of pivotal importance for expression by IFN-γ-activated cells. Use of siRNA underscored the essential role of the signal transducer and activator of transcription (STAT)-1 in this process. Indeed, electrophoretic mobility shift assay and chromatin immunoprecipitation analysis proved STAT1 binding to this particular GAS site. Maximal expression of IL-18BP was dependent on de novo protein synthesis but unaffected by silencing of interferon regulatory factor-1. Altogether, data presented herein indicate that direct action of STAT1 on the IL-18BP promoter at the proximal GAS element is key to IL-18BP expression by IFN-γ-stimulated DLD-1 colon carcinoma cells.

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