Regulation of macrophage IFNγ-stimulated gene expression by the transcriptional coregulator CITED1

Abstract

Macrophages serve as a first line of defense against microbial pathogens. Exposure to interferon-γ (IFNγ) increases interferon-stimulated gene (ISG) expression in these cells, resulting in enhanced antimicrobial and proinflammatory activity. Although this response must be sufficiently vigorous to ensure the successful clearance of pathogens, it must also be carefully regulated to prevent tissue damage. This is controlled in part by CBP/p300-interacting transactivator with glutamic acid/aspartic acid-rich carboxyl-terminal domain 2 (CITED2), a transcriptional coregulator that limits ISG expression by inhibiting STAT1 and IRF1. Here, we show that the closely related Cited1 is an ISG, which is expressed in a STAT1-dependent manner, and that IFNγ stimulates the nuclear accumulation of CITED1 protein. In contrast to CITED2, ectopic 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 maintains proinflammatory gene expression during periods of prolonged IFNγ exposure and suggest that there is an antagonistic relationship between CITED proteins in the regulation of macrophage inflammatory function. This article has an associated First Person interview with the first author of the paper.

Exploring the role of CITED transcriptional regulators in the control of macrophage polarization

“…The differences between CITED1 and 2 go beyond the regulation of their expression and localization and extends to their function with the two transcriptional regulators exerting opposing effects on macrophage pro-inflammatory gene expression. This was shown by Subramani et al using a complementary loss-and gain-of-function approach, where it was found that CITED1 enhances STAT1-and IRF1-regulated gene expression in IFNg-stimulated macrophages, increasing transcript levels of Ccl, Isg, and Ifit family members amongst many others (113). These data suggest that CITED1 is functioning as a transcriptional co-enhancer (Figure 2C), versus the largely coinhibitory effects of CITED2 in the same context.…”

“…While Cited2 expression is ubiquitous, Cited1 is largely restricted to a small number of tissues (113), and was thought to be absent in macrophages (85). This perception was changed in 2020 when Cited1 transcripts were detected in M1-polarized RAW264.7 murine macrophage-like cells infected with the fungal pathogen, Cryptococcus neoformans (114).…”

“…It was subsequently determined that exposure of these cells to IFNg for periods greater than 24 hours stimulated expression of CITED1 proteins, regulated by both STAT1 and IRF1 at the transcriptional level. Cited1 expression was unaffected by other M1 polarizing stimuli (i.e., LPS), indicating that it operates as an interferon-stimulated gene (ISG) (113). This pattern of regulation is in stark contrast to Cited2, which is transiently downregulated following short periods of exposure (6 hours) to M1 polarizing stimuli (LPS or IFNg) and upregulated by M2 stimuli (IL-4 or IL-13) (85), indicating that the circumstances under which CITED1 and 2 operate may be minimal or non-overlapping.…”

“…A further regulatory difference between CITED1 and 2 is their subcellular localization under varying polarizing conditions. While CITED2 has been shown to be constitutively nuclear (97), CITED1 is predominantly cytoplasmic in unstimulated cells but becomes enriched in the nucleus following IFNg stimulation (113). Quite how this shift in subcellular distribution is controlled is presently unclear, but it may be connected to the increased phosphorylation of the protein observed in IFNg-stimulated macrophages as CITED1 phosphorylation at Ser79 following parathyroidhormone-stimulation in murine osteoblastic cells is known to be associated with its nuclear translocation (115,116).…”

Roles and signaling pathways of CITED1 in tumors: overview and novel insights

“… 62 Studies indicated that prolonged exposure of adipose tissue macrophages to interferon-γ can increase the expression of interferon-stimulated genes such as CITED1, resulting in adipose tissue “browning” and enhanced pro-inflammatory activity. 63 , 64 However, it has not been confirmed whether excess lactate released during adjacent adipose tissue “browning” can promote tumor progression. 65 It is believed that with further research, the relationships of CITED1 with tumor development and progression through beige fat will be elucidated.…”