N-terminal BET bromodomain inhibitors disrupt a BRD4-p65 interaction and reduce inducible nitric oxide synthase transcription in pancreatic β-cells

Abstract

Chronic inflammation of pancreatic islets is a key driver of β-cell damage that can lead to autoreactivity and the eventual onset of autoimmune diabetes (T1D). In the islet, elevated levels of proinflammatory cytokines induce the transcription of the inducible nitric oxide synthase (iNOS) gene, NOS2, ultimately resulting in increased nitric oxide (NO). Excessive or prolonged exposure to NO causes β-cell dysfunction and failure associated with defects in mitochondrial respiration. Recent studies showed that inhibition of the bromodomain and extraterminal domain (BET) family of proteins, a druggable class of epigenetic reader proteins, prevents the onset and progression of T1D in the non-obese diabetic mouse model. We hypothesized that BET proteins co-activate transcription of cytokine-induced inflammatory gene targets in β-cells and that selective, chemotherapeutic inhibition of BET bromodomains could reduce such transcription. Here, we investigated the ability of BET bromodomain small molecule inhibitors to reduce the β-cell response to the proinflammatory cytokine interleukin 1 beta (IL-1β). BET bromodomain inhibition attenuated IL-1β-induced transcription of the inflammatory mediator NOS2 and consequent iNOS protein and NO production. Reduced NOS2 transcription is consistent with inhibition of NF-κB facilitated by disrupting the interaction of a single BET family member, BRD4, with the NF-κB subunit, p65. Using recently reported selective inhibitors of the first and second BET bromodomains, inhibition of only the first bromodomain was necessary to reduce the interaction of BRD4 with p65 in β-cells. Moreover, inhibition of the first bromodomain was sufficient to mitigate IL-1β-driven decreases in mitochondrial oxygen consumption rates and β-cell viability. By identifying a role for the interaction between BRD4 and p65 in controlling the response of β-cells to proinflammatory cytokines, we provide mechanistic information on how BET bromodomain inhibition can decrease inflammation. These studies also support the potential therapeutic application of more selective BET bromodomain inhibitors in attenuating β-cell inflammation.

Inhibition of HDAC2 sensitises antitumour therapy by promoting NLRP3/GSDMD‐mediated pyroptosis in colorectal cancer

“…The bromodomain‐containing protein BRD4 recognises and directly engages acetylated H3K27, thereby serving as a molecular scaffold that facilitates the recruitment of transcription factors to chromatin 40 . Additionally, multiple studies have shown that BRD4 interacts with NF‐κB p65 to activate transcription 41,42 . Therefore, we hypothesised that the H3K27ac reader BRD4 may scaffold the interaction between the NLRP3 promoter and transcription factor p65 to drive NLRP3 expression.…”

“… 40 Additionally, multiple studies have shown that BRD4 interacts with NF‐κB p65 to activate transcription. 41 , 42 Therefore, we hypothesised that the H3K27ac reader BRD4 may scaffold the interaction between the NLRP3 promoter and transcription factor p65 to drive NLRP3 expression. Our data revealed that H3K27ac forms a complex with phosphorylated P65 in a BRD4‐dependent manner.…”

The impact of vitamin D on the etiopathogenesis and the progression of type 1 and type 2 diabetes in children and adults

“…Vitamin D induces cellular autophagy while inhibiting streptozotocin-induced β-cell apoptosis, increasing insulin secretion and increasing β-cell resistance to cellular stresses encountered in hyperglycemic states ( 55 ). Excessive or prolonged exposure to nitric oxide leads to β-cell dysfunction, whereas vitamin D induces and maintains high levels of the A20 gene protein and reduces nitric oxide levels, thus serving to protect β-cell function ( 56 ).…”

KSHV vIL-6 enhances inflammatory responses by epigenetic reprogramming

“…In the IL-6 Amp disease model, obesity, injury, and infection trigger chronic inflammation and a systemic cytokine storm, which is enhanced by interactions between local non-immune cells and infiltrating immune cells [16]. A prominent example of IL-6 Amp is also seen in Coronavirus disease 2019 (COVID- 19), which is triggered by severe acute respiratory syndrome coronavirus 2 (SARS-CoV2) infection [16]. Consistent with the significance of hIL-6 in disease development, a humanized monoclonal antibody against the hIL-6 receptor, tocilizumab, has proven successful in treating Castleman's disease as well as COVID-19 [17,18].…”

“…The bromodomain and extraterminal domain (BET) family proteins, such as bromodomain containing 4 (BRD4), are transcription regulators that localize to cellular enhancer and promoter loci and control the transcription of a wide range of proinflammatory genes. BRD4 regulates transcription by recognizing acetylated histone tail and interacts with transcription factors such as NF-κB p65 and transcription elongation complex [19]. This mechanism facilitates the phosphorylation of RNA Polymerase II (RNAPII) and promotes transcription initiation and elongation.…”