Chromatin regulates IL-33 release and extracellular cytokine activity

Abstract

IL-33 is an epithelium-derived, pro-inflammatory alarmin with enigmatic nuclear localization and chromatin binding. Here we report the functional properties of nuclear IL-33. Overexpression of IL-33 does not alter global gene expression in transduced epithelial cells. Fluorescence recovery after photobleaching data show that the intranuclear mobility of IL-33 is ~10-fold slower than IL-1α, whereas truncated IL-33 lacking chromatin-binding activity is more mobile. WT IL-33 is more resistant to necrosis-induced release than truncated IL-33 and has a relatively slow, linear release over time after membrane dissolution as compared to truncated IL-33 or IL-1α. Lastly, IL-33 and histones are released as a high-molecular weight complex and synergistically activate receptor-mediated signaling. We thus propose that chromatin binding is a post-translational mechanism that regulates the releasability and ST2-mediated bioactivity of IL-33 and provide a paradigm to further understand the enigmatic functions of nuclear cytokines.

Epithelial cell–derived cytokines: more than just signaling the alarm

“…IL-33 contains an N-terminal chromatin-binding motif and a predicted nuclear localization sequence. Although some studies suggest a role for IL-33 in transcriptional regulation (82), the intranuclear localization of IL-33 in most cell types is thought to be important in sequestering this cytokine to prevent inappropriate release (83). Transgenic mice that expressed a form of IL-33 that lacked the nuclear localization signal died of systemic inflammation (84).…”

Interleukin‐33 in the developing lung—Roles in asthma and infection

“…Thus, IL‐33 is only released during necrosis, cytolysis, and release of the nuclear contents . The strong binding of IL‐33 to chromatin appears to be a mechanism to slow its release from necrotic cells, thus extending its effective half‐life of release . It was initially hypothesized that nuclear IL‐33 could be acting as a transcription factor; however, recent studies indicate that nuclear IL‐33 does not affect gene expression within the IL‐33–expressing cell .…”

“…The strong binding of IL‐33 to chromatin appears to be a mechanism to slow its release from necrotic cells, thus extending its effective half‐life of release . It was initially hypothesized that nuclear IL‐33 could be acting as a transcription factor; however, recent studies indicate that nuclear IL‐33 does not affect gene expression within the IL‐33–expressing cell . Conversely, deletion of the IL‐33 chromatin‐binding domain leads to uncontrolled IL‐33 release and lethal multi‐organ inflammation .…”

“…Conversely, deletion of the IL‐33 chromatin‐binding domain leads to uncontrolled IL‐33 release and lethal multi‐organ inflammation . Recently, it was shown that full‐length IL‐33 can be released from necrotic cells in complex with histones, and that IL‐33‐histone complexes have increased activity compared to full‐length IL‐33 alone . The activity of IL‐33 can be further increased by protease cleavage between the chromatin‐binding and receptor‐binding domains .…”

Doxorubicin induces large-scale and differential H2A and H2B redistribution in live cells

“…H2B cytoplasmic accumulation was detected using two different (monoclonal vs. polyclonal) anti-H2B antibodies. Both commercially available antibodies are extensively used to visualize H2B with high specificity and sensitivity [28][29][30]. Nonspecific binding of the secondary antibody was ruled out by incubating the cells with the secondary antibody only (see Fig 2).…”