Regulation of Macrophage IFNγ-Stimulated Gene Expression by the Transcriptional Coregulator CITED1

Abstract

AbstractMacrophages are highly dynamic innate immune cells that adopt temporary phenotypes, known as polarization states, in response to changing environmental signals to combat microbial infection and contribute to the maintenance of tissue homeostasis. During the early stages of an infection, exposure to interferon-gamma (IFNγ) and microbial ligands induce M1 polarization, a heightened proinflammatory anti-microbial state, by regulating the expression of interferon stimulated genes (ISGs). While this response must be sufficiently vigorous to ensure the successful clearance of invading pathogens, it must also be spatially and temporally restricted to prevent uncontrolled inflammation that could result in tissue damage and disease. This is controlled by a variety of cell-extrinsic and -intrinsic mechanisms, including the expression of CBP/p300-interacting transactivator with glutamic acid/aspartic acid-rich carboxyl-terminal domain 2 (CITED2), a transcriptional coregulator that limits IFNγ-stimulated proinflammatory gene expression by inhibiting STAT1- and IRF1-regulated ISGs. In this study, we show that CITED1, another member of the CITED family of proteins, is itself an ISG and is expressed in a STAT1-dependent manner, and that IFNγ stimulates the nuclear accumulation of fluorescently tagged CITED1 proteins. In contrast to CITED2, ectopic expression of CITED1 enhanced the expression of a subset of ISGs, including Ccl2, Ifit3b, Isg15, and Oas2. This effect was reversed in a Cited1 null cell line produced by CRISPR-based genomic editing. Collectively, these data show that CITED1 helps to maintain proinflammatory gene expression during periods of prolonged IFNγ exposure and suggests a distinct and antagonistic relationship between CITED proteins in the regulation of macrophage inflammatory function.