A20 Inhibits Cytokine-Induced Apoptosis and Nuclear Factor κB–Dependent Gene Activation in Islets

Abstract

Insulin-dependent diabetes mellitus (IDDM) is an autoimmune disease resulting from apoptotic destruction of β cells in the islets of Langerhans. Low expression of antioxidants and a predilection to produce nitric oxide (NO) have been shown to underscore β cell apoptosis. With this perspective in mind, we questioned whether β cells could mount an induced protective response to inflammation. Here we show that human and rat islets can be induced to rapidly express the antiapoptotic gene A20 after interleukin (IL)-1β activation. Overexpression of A20 by means of adenovirus-mediated gene transfer protects islets from IL-1β and interferon γ–induced apoptosis. The cytoprotective effect of A20 against apoptosis correlates with and is dependent on the abrogation of cytokine-induced NO production. The inhibitory effect of A20 on cytokine-stimulated NO production is due to transcriptional blockade of inducible NO synthase (iNOS) induction; A20 inhibits the activation of the transcription factor nuclear factor κB at a level upstream of IκBα degradation. These data demonstrate a dual antiapoptotic and antiinflammatory function for A20 in β cells. This qualifies A20 as part of the physiological cytoprotective response of islets. We propose that A20 may have therapeutic potential as a gene therapy candidate to achieve successful islet transplantation and the cure of IDDM.

A20 protects mice from lethal radical hepatectomy by promoting hepatocyte proliferation via a p21waf1-dependent mechanism

“…These results are consistent with the known anti-inflammatory function of A20 via blockade of NF-B. [7][8][9] To assess the effect of A20 on hepatocyte apoptosis, we treated NI, rAd.␤-gal-and rAd.A20-infected NMuli hepatocytes with 333 nmol of Actinomycin D to block transcription, followed by 100 U/mL of TNF and measured apoptosis 7 hours later by FACS analysis of DNA content. A20 overexpression significantly protected hepatocytes from TNF-mediated apoptosis.…”

“…A20 is a cytoplasmic seven zinc finger protein that is upregulated by the proinflammatory transcription factor NF-B in most cell types, including hepatocytes. [6][7][8][9] In endothelial cells, A20 has a dual cytoprotective function. It is anti-inflammatory through inhibition of NF-B in a negative feedback loop and is antiapoptotic through inhibition of the caspase cascade at the level of initiator caspase 8.…”

Inhibition of IFN-γ-induced STAT1 activation by 15- deoxy-Δ12,14-prostaglandin J2

“…In contrast, a 30-min preincubation of islets or RINm5F cells with either agonist does not stimulate HSP70 expression and also does not inhibit the ability of IL-1 to stimulate JNK phosphorylation or NF-B activation (26). Importantly, NF-B activation is required for ␤-cell expression of iNOS in response to IL-1 treatment (16,17,25). Although previous studies have shown that PGJ 2 attenuates NF-B activation by directly inhibiting I B kinase (IKK) as well as inhibiting NF-B DNA binding activity (30,31,38), this direct inhibition of IKK or NF-B DNA binding activity does not appear to account for the inhibitory actions of PGJ 2 on NF-B activation in RINm5F cells or rat islets, as a 30-min pretreatment with PGJ 2 does not affect the ability of IL-1 to stimulate the activation of NF-B (26).…”

A20 zinc finger protein inhibits TNF-induced apoptosis and stress response early in the signaling cascades and independently of binding to TRAF2 or 14-3-3 proteins

“…in tissue transplantation and diabetes mellitus. 25 This study was undertaken to gain insight into the poorly understood mechanism of action of A20. The ability of A20 to inhibit all three TNF-induced signaling pathways diverging at the level of TRADD together with its inability to inhibit signaling from Fas suggests that it may function upstream of or at the level of TRADD.…”