Transcriptional Regulation of Mouse Mast Cell Protease-2 by Interleukin-15

Abstract

Mast cells (MCs) play a critical role in innate and adaptive immunity through the release of cytokines, chemokines, lipid mediators, biogenic amines, and proteases. We recently showed that the activities of MC proteases are transcriptionally regulated by intracellularly retained interleukin-15 (IL-15), and we provided evidence that this cytokine acts as a specific regulator of mouse mast cell protease-2 (mMCP-2). Here, we show that in wild-type bone marrow-derived mast cells (BMMCs) IL-15 inhibits mMCP-2 transcription indirectly by inducing differential expression and mMCP-2 promoter binding of the bifunctional transcription factors C/EBP␤ and YY1. In wild-type BMMCs, C/EBP␤ expression predominates over YY1 expression, and thus C/EBP␤ preferentially binds to the mMCP-2 promoter. In IL-15-deficient BMMCs, the opposite is found: YY1 expression predominates and binds to the mMCP-2 promoter at the expense of C/EBP␤. Hypertranscription of the mMCP-2 gene in IL-15-deficient BMMCs is associated with histone acetylation and, intriguingly, with methylation of non-CpG dinucleotides within the MCP-2 promoter. This suggests a novel model of cytokine-controlled protease transcription: non-CpG methylation maintains a chromosomal domain in an "open" configuration that is permissive for gene expression. Mast cells (MCs)3 are key cellular mediators of host innate defense (1). Upon activation, MC secretory granules release a number of preformed inflammatory molecules that include cytokines, histamine, serglycin proteoglycans, and several MC-specific proteases (chymases, tryptases, and carboxypeptidase A) (2, 3). Upon release into the extracellular space, these mediators regulate a broad variety of responses ranging from acute phase immediate reactions over recruitment of specific cell populations to sites of infection to long term tissue-remodeling reactions (1).In the mouse, several mast cell proteases (mMCPs) have been identified and partially characterized, including the chymases mMCP-1, -2, -4, -5, and -9 and the tryptases mMCP-6 and -7 (4). Proteases play an important role in extracellular matrix remodeling, extravascular coagulation, and fibrinolysis as well as angiogenesis. Our recent investigation of the mechanisms that regulate mMCP gene expression has shown that intracellular cytokines can regulate mMCP activities (5). Murine MCs express constitutive and lipopolysaccharide-inducible IL-15 and store IL-15 intracellularly, where it colocalizes with tumor necrosis factor-␣ and proteases in MC granula. IL-15 Ϫ/Ϫ MCs exhibit markedly elevated chymase activity, leading to increased bactericidal activity and processing of neutrophil-recruiting chemokines. In particular, intracellular IL-15 operates as a specific negative transcriptional regulator of mMCP-2 (5).In this report, we show that transcriptional repression of mMCP-2 by intracellular IL-15 is indirect. IL-15-mediated repression is effected by changing the expression levels of the transcription factors (TFs) C/EBP␤ and YY1 and thus the amount of each TF bound to the mMC...

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“…These players prominently include the following; CTLA‐4, an important T‐cell immunoinhibitory surface molecule, CTLA4 ligands CD80 and CD86, 297‐299 and IL‐15, 42,106,300 a key immunostimulatory cytokine that drives NK/NKT cell development and survival. IL‐15 is also is a key mast cell regulator and effector 301‐304 …”

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“…Protease activity is tightly regulated at a minimum of four levels, which include transcriptional regulation, post-translational modification, physical compartmentalization and functional inhibition (Chow et al 1995; Gorogh et al 2006; Lopez-Otin and Matrisian 2007; Mirghomizadeh et al 2009; Muzio et al 1997). The multiple levels of protease regulation provide for tight tissue, temporal and environmentally responsive control of activity.…”