Synergistic Activation of Interleukin-12 p35 Gene Transcription by Interferon Regulatory Factor-1 and Interferon Consensus Sequence-binding Protein

Jianguo Liu,Xiuqin Guan,Tomohiko Tamura,Keiko Ozato,Xiaojing Ma

doi:10.1074/jbc.m406565200

Abstract

Interferon regulatory factor-1 (IRF-1) and interferon consensus sequence-binding protein (ICSBP or IRF-8) are two members of the IRF family of transcription factors that play critical roles in interferon signaling in a wide range of host responses to infection and malignancy. Interleukin-12 (IL-12) is a key factor in the induction of innate resistance and generation of T helper type 1 cells and cytotoxic T lymphocytes. In this work, we find that ICSBP-deficient macrophages are highly defective in the production of IL-12. The defect is also observed at the level of IL-12 p40 and p35 mRNA expression. Transcriptional analyses revealed that ICSBP is a potent activator of the IL-12 p35 gene. It acts through a site localized to -226 to -219, named ICSBP-response element (ICSBP-RE), in the human IL-12 p35 promoter through physical association with IRF-1 both in vitro and in vivo. Co-expression of ICSBP and IRF-1 synergistically stimulates the IL-12 p35 promoter activity. Mutations at the ICSBP-RE results in the loss of protein binding as well as transcriptional activation by ICSBP alone or together with IRF-1. This study provides novel mechanistic information on how signals initiated during innate and adaptive immune responses synergize to yield greater IL-12 production and sustained cellular immunity.

Highlights

Interferon regulatory factor-1 (IRF-1) and interferon consensus sequence-binding protein (ICSBP or Interferon regulatory factors (IRFs)-8) are two members of the IRF family of transcription factors that play critical roles in interferon signaling in a wide range of host responses to infection and malignancy
The exposure of professional antigen-presenting cells to IFN-␥ activates IRFs including IRF-1 and Interferon consensus sequence-binding protein (ICSBP) that are critical for maximal IL-12 synthesis when coupled with microbial stimuli such as LPS
The critical role of ICSBP in IL-12 production is illustrated in the observation that IL-12 p35 and p40 mRNA expression is impaired in ICSBP-deficient macrophages (Fig. 2) and that IL-12 p40 synthesis is severely reduced (Fig. 1, A and B), whereas IL-12 p70 production is virtually absent (Fig. 1, C and D)

Summary

Introduction

Interferon regulatory factor-1 (IRF-1) and interferon consensus sequence-binding protein (ICSBP or IRF-8) are two members of the IRF family of transcription factors that play critical roles in interferon signaling in a wide range of host responses to infection and malignancy. IRF-1 selectively targets different sets of genes in various cell types in response to diverse cellular stimuli and evokes appropriate innate and adaptive immune responses [1] It has been firmly established as a critical effector molecule in IFN-␥-mediated signaling and in the development and function of NK, NK T cells, and cytotoxic T lymphocytes [2,3,4,5,6,7]. Interferon consensus sequence-binding protein (ICSBP)/IRF-8 is restricted in its expression to myeloid and lymphoid cell lineages It can function both as a transcriptional repressor and an activator depending on the partners with which it interacts, and it plays crucial roles in myeloid differentiation, generation of plasmacytoid dendritic cells [8], macrophage activation, and tumor suppression [1, 9]. This study provides additional mechanistic information regarding how innate and adaptive immune activation jointly lead to greater IL-12 production and persistent inflammatory responses

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Results

Conclusion