Elevated A20 promotes TNF-induced and RIPK1-dependent intestinal epithelial cell death

Abstract

Intestinal epithelial cell (IEC) death is a common feature of inflammatory bowel disease (IBD) that triggers inflammation by compromising barrier integrity. In many patients with IBD, epithelial damage and inflammation are TNF-dependent. Elevated TNF production in IBD is accompanied by increased expression of the gene, which encodes A20, a negative feedback regulator of NF-κB. A20 in intestinal epithelium from patients with IBD coincided with the presence of cleaved caspase-3, and A20 transgenic (Tg) mice, in which A20 is expressed from an IEC-specific promoter, were highly susceptible to TNF-induced IEC death, intestinal damage, and shock. A20-expressing intestinal organoids were also susceptible to TNF-induced death, demonstrating that enhanced TNF-induced apoptosis was a cell-autonomous property of A20. This effect was dependent on Receptor Interacting Protein Kinase 1 (RIPK1) activity, and A20 was found to associate with the Ripoptosome complex, potentiating its ability to activate caspase-8. A20-potentiated RIPK1-dependent apoptosis did not require the A20 deubiquitinase (DUB) domain and zinc finger 4 (ZnF4), which mediate NF-κB inhibition in fibroblasts, but was strictly dependent on ZnF7 and A20 dimerization. We suggest that A20 dimers bind linear ubiquitin to stabilize the Ripoptosome and potentiate its apoptosis-inducing activity.

Tight junctions in the development of asthma, chronic rhinosinusitis, atopic dermatitis, eosinophilic esophagitis, and inflammatory bowel diseases

“…In patients with Crohn's disease, epithelial damage and inflammation also depend on TNF. Elevated TNF‐α production is accompanied by increased expression of the TNFAIP3 gene, which encodes A20 200 . In a mouse model of TNF‐driven Crohn's‐like ileitis, CCR7 is critical for orchestrating immune cell trafficking and regulates the intestinal Th1/Th17/Treg balance 201 .…”

Regulatory interplay between deubiquitinating enzymes and cytokines

“…In intestinal epithelial cells (IEC), A20 dimer interacted with the Ripoptosome (also known as complex IIa), which allowed ubiquitins on RIPK1 to sustain, increasing caspase-8 activation to promote TNF-induced apoptosis [67]. However, this effect was not DUB activity dependent [67].…”

RIPK1 Mediates TNF-Induced Intestinal Crypt Apoptosis During Chronic NF-κB Activation

“…[19][20][21] Adding to the complexities of TNF-mediated cell death and its dependence on NF-kB inhibition or RIPK1 kinase activation, we found that elevated A20 expression facilitates ripoptosome formation and RIPK1 activation. 13 Here we describe the role of RIPK1 in TNF-mediated IEC killing and mucosal erosion in Ikkb(EE) IEC mice.…”

“…Elevated expression of A20, a protein thought to be a negative regulator of NF-kB, also sensitizes IEC to TNF-mediated killing but this effect is not due to NF-kB inhibition. 13 Indeed, IKK or NF-kB deficiencies have not been described in IBD.…”

“…We conducted immunohistochemistry (IHC) analysis of human tissue specimens from healthy individuals and patients suffering with either ileal or colonic CD or UC to determine the correlation between NF-kB activation and cell death. As previously described, 13 we examined 10 normal colon specimens, 10 samples with active UC, and 10 samples with colonic CD, as well as 4 active ileitis samples and 5 inactive ileal CD samples, all of which were stained for p65/ RelA and cleaved caspase-3 (cC-3). In general, normal colonic or ileal specimens contained hardly any IEC that were positive for cC-3 or nuclear p65 ( Figure 1A).…”