Histone Deimination As a Response to Inflammatory Stimuli in Neutrophils

Abstract

Posttranslational modifications, such as the deimination of arginine to citrulline by peptidyl arginine deiminase (PAD4), change protein structure and function. For autoantigens, covalent modifications represent a mechanism to sidestep tolerance and stimulate autoimmunity. To examine conditions leading to histone deimination in neutrophils, we used Abs that detect citrullines in the N terminus of histone H3. Deimination was investigated in human neutrophils and HL-60 cells differentiated into granulocytes. We observed rapid and robust H3 deimination in HL-60 cells exposed to LPS, TNF, lipoteichoic acid, f-MLP, or hydrogen peroxide, which are stimuli that activate neutrophils. Importantly, we also observed H3 deimination in human neutrophils exposed to these stimuli. Citrullinated histones were identified as components of extracellular chromatin traps (NETs) produced by degranulating neutrophils. In contrast, apoptosis proceeded without detectable H3 deimination in HL-60 cells exposed to staurosporine or camptothecin. We conclude that histone deimination in neutrophils is induced in response to inflammatory stimuli and not by treatments that induce apoptosis. Our results further suggest that deiminated histone H3, a covalently modified form of a prominent nuclear autoantigen, is released to the extracellular space as part of the neutrophil response to infections. The possible association of a modified autoantigen with microbial components could, in predisposed individuals, increase the risk of autoimmunity.

Regulation of histone modification and chromatin structure by the p53–PADI4 pathway

“…Citrullination of proteins causes a loss of positive charge and results in a significant biochemical effect. Bacterial infection has been indicated to stimulate PADI4-mediated hypercitrullination of histones in neutrophils and subsequently promoted highly decondensed extracellular chromatin structure called NET (neutrophil extracellular trap) that could capture and kill microorganisms 12,13 . On the other hand, citrullinated peptides/proteins are recognized as non-self proteins and subsequently activate immune systems.…”

Neutrophil extracellular trap cell death requires both autophagy and superoxide generation

“…Thus, NETosis should be considered a distinct cell death program. It was recently shown that decondensation of nuclear chromatin preceding NET formation is mediated by histone citrullination [7,10]. The inability of CGD neutrophils to generate NETs in response to PMA indicates that Nox2 activity is essential for the intracellular chromatin decondensation that precedes NET formation [6], but this was not demonstrated directly.…”

“…These vesicles have a double phospholipid bilayer and are believed to originate from the nuclear envelope [6,9], which disintegrates during NET cell death. Finally, but still before plasma membrane permeabilization, nuclear chromatin decondenses and mixes with the contents of the granules; this is essential for formation of functional NETs [7,10]. Permeabilization of the neutrophil plasma membrane releases these chromatin structures, which are loaded with concentrated antimicrobial molecules, such as lactoferrin, BPI, LL-37 and histones [9,11].…”

Histone Arginine Methylation by PRMT7 Controls Germinal Center Formation via Regulating Bcl6 Transcription

“…Previously, NF-kB was also reported to be regulated by other PRMTs (48)(49)(50), suggesting that arginine methylation plays unique roles in NF-kB activation. In addition, it has been reported that histone arginine deimination, which antagonizes arginine methylation, is a response to a wide range of inflammatory stimuli (51,52). Thus, we speculate that PRMT7-mediated arginine methylation may be able to regulate genes involved in mammalian immune and inflammatory responses, and the deletion of PRMT7 in B cells might impair B cells and induce an immune deregulation reminiscent of sterile inflammation.…”