Histone acetyltransferase activity of p300 enhances the activation of IL-18 promoter

Long Non-Coding RNA NEAT1 Knockdown Alleviates Rheumatoid Arthritis by Reducing IL-18 through p300/CBP Repression

Rheumatoid arthritis (RA) is chronic inflammatory autoimmune disease. The crucial role of long non-coding RNA (lncRNA) in the progression of RA has been highlighted. Hence, this study was designed to explore the specific downstream mechanism of lncRNA nuclear-enriched abundant transcript 1 (NEAT1) in RA. Initially, the expression of NEAT1, p-p65, p300, and IL-18 in clinical tissues and cells was determined. Then, interactions among p65, NEAT1, p300, CBP, and IL-18 were investigated by immunofluorescence staining, dual luciferase reporter gene assay, RT-qPCR assay ChIP assay, and RIP assay followed by the analysis of their effects on RA in vivo and in vitro after expression alteration. The expressions of NEAT1, p-p65, p300, and IL-18 were all upregulated in the synovial tissues from the mice and patients with RA. NEAT1 silencing reduced the infiltration of CD4⁺ T cells and macrophages in synovial tissues, downregulated expression of blood inflammatory factors, relieved RA severity, and lowered incidence of RA in mice. Further, p-p65 could increase the expression of NEAT1 by binding to the NEAT1 promoter region, NEAT1 could co-locate and interact with p300, thus regulating the expression of IL-18 by regulating histone acetylation modification in IL-18 promoter region. NEAT1 aggravated RA via p300/CBP/IL-18 axis, representing a promising therapeutic target in RA.

CREB-induced inflammation is important for malignant mesothelioma growth

Malignant mesothelioma (MM) is an aggressive tumor with no treatment regimen. Previously we have demonstrated that cyclic AMP response element binding protein (CREB) is constitutively activated in MM tumor cells and tissues and plays an important role in MM pathogenesis. To understand the role of CREB in MM tumor growth, we generated CREB-inhibited MM cell lines and performed in vitro and in vivo experiments. In vitro experiments demonstrated that CREB inhibition results in significant attenuation of proliferation and drug resistance of MM cells. CREB-silenced MM cells were then injected into severe combined immunodeficiency mice, and tumor growth in s.c. and i.p. models of MM was followed. We observed significant inhibition in MM tumor growth in both s.c. and i.p. models and the presence of a chemotherapeutic drug, doxorubicin, further inhibited MM tumor growth in the i.p. model. Peritoneal lavage fluids from CREB-inhibited tumor-bearing mice showed a significantly reduced total cell number, differential cell counts, and pro-inflammatory cytokines and chemokines (IL-6, IL-8, regulated on activation normal T cell expressed and secreted, monocyte chemotactic protein-1, and vascular endothelial growth factor). In vitro studies showed that asbestos-induced inflammasome/inflammation activation in mesothelial cells was CREB dependent, further supporting the role of CREB in inflammation-induced MM pathogenesis. In conclusion, our data demonstrate the involvement of CREB in the regulation of MM pathogenesis by regulation of inflammation.

Distinct licensing of IL-18 and IL-1β secretion in response to NLRP3 inflammasome activation

Inflammasome activation permits processing of interleukins (IL)-1β and 18 and elicits cell death (pyroptosis). Whether these responses are independently licensed or are “hard-wired” consequences of caspase-1 (casp1) activity has not been clear. Here, we show that that each of these responses is independently regulated following activation of NLRP3 inflammasomes by a “non-canonical” stimulus, the secreted Listeria monocytogenes (Lm) p60 protein. Primed murine dendritic cells (DCs) responded to p60 stimulation with reactive oxygen species (ROS) production and secretion of IL-1β and IL-18 but not pyroptosis. Inhibitors of ROS production inhibited secretion of IL-1β, but did not impair IL-18 secretion. Furthermore, DCs from caspase-11 (casp11)-deficient 129S6 mice failed to secrete IL-1β in response to p60 but were fully responsive for IL-18 secretion. These findings reveal that there are distinct licensing requirements for processing of IL-18 versus IL-1β by NLRP3 inflammasomes.

Macrophage deletion of p38alpha partially impairs lipopolysaccharide-induced cellular activation

The activation of p38alpha, a MAPK family member, is associated with macrophage activation by microbial pattern molecules, such as LPS. The requirement of p38alpha in inflammatory responses has been shown in a number of studies using chemical inhibitors, though the inhibitors also inhibit p38beta and perhaps some other enzymes. In this study, we used conditional knockout of p38alpha in macrophages to address the role of p38alpha in macrophage activation. We found that p38alpha deficiency causes a significant inhibition in the production of LPS-induced TNF-alpha, IL-12, and IL-18, but it has little or no effect on IL-6 or IFN-beta production. Knockout of p38alpha in macrophages did not affect LPS-induced activation of the other major signaling pathways (NF-kappaB, Jnk, and Erk), nor did it affect the transcriptional activity of NF-kappaB. It had little inhibitory effect on LPS-induced AP-1 activity, but it significantly inhibited LPS-induced C/EBP-beta and CREB activation, indicating that the role of p38alpha in cytokine production in macrophages is at least in part through its regulation of C/EBP-beta and CREB activation. In addition, we also confirmed that p38alpha is important for phagocytosis of bacteria by macrophages. Our in vivo studies with two murine models showed that p38alpha is involved in sepsis. Collectively, our data demonstrate that p38alpha is an important player in inflammatory responses.

Transcription factors Ets2 and Sp1 act synergistically with histone acetyltransferase p300 in activating human interleukin-12 p40 promoter

There has been considerable interest in researching the regulatory mechanisms that control the synthesis of interleukin (IL)-12, which plays a central role in the differentiation of T-helper-1 cells. In this study, we performed a series of transient transfection experiments designed to elucidate the functional relationship between the IL-12 promoter-specific transcription factors (Ets2 and Sp1) and histone acetylation modification in IL-12 regulation mediated by p300 and various histone deacetylases (HDACs). Results presented in this report demonstrated that the transcription factors Ets2 and Sp1 acted synergistically with p300 to activate the human IL-12 promoter. The histone acetyltransferase (HAT) activity of p300 was required for this synergic effect, because the adenovirus E1A protein inhibited the synergy. Conversely, HDACs repressed the synergic effect of transcription factors and histone acetylation on the activation of IL-12, while p300 was able to rectify it. These data indicated that Ets2 and Sp1 worked concertedly and synergistically with p300 in the regulation of human IL-12 expression.