Gene Therapy and Autoimmunity Group, Immunology Program, Garvan Institute of Medical Research, 384 Victoria Street, Darlinghurst, NSW 2010, Australia.
Diabetologia. 2013 Mar;56(3):520-32. doi: 10.1007/s00125-012-2784-x. Epub 2012 Dec 20.
AIMS/HYPOTHESIS: For beta cells, contact with TNF-α triggers signalling cascades that converge on pathways important for cell survival and inflammation, specifically nuclear factor κB (NF-κB), c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase pathways. Here, we investigated the function of baculoviral inhibitors of apoptosis repeat containing (BIRC) proteins in regulating TNF signalling cascades.
TNF regulation of Birc genes was studied by mRNA expression and promoter analysis. Birc gene control of cell signalling was studied in beta cell lines, and in islets from Birc2(-/-) and Birc3(-/-) mice, and from Birc3(-/-) Birc2Δ beta cell mice that selectively lack Birc2 and Birc3 (double knockout [DKO]). Islet function was tested by intraperitoneal glucose tolerance test and transplantation.
TNF-α selectively induced Birc3 in beta cells, which in turn was sufficient to drive and potentiate NF-κB reporter activity. Conversely, Birc3(-/-) islets exhibited delayed TNF-α-induced IκBα degradation with reduced expression of Ccl2 and Cxcl10. DKO islets showed a further delay in IκBα degradation kinetics. Surprisingly, DKO islets exhibited stimulus-independent and TNF-dependent hyperexpression of TNF target genes A20 (also known as Tnfaip3), Icam1, Ccl2 and Cxcl10. DKO islets showed hyperphosphorylation of the JNK-substrate, c-Jun, while a JNK-antagonist prevented increases of Icam1, Ccl2 and Cxcl10 expression. Proteosome blockade of MIN6 cells phenocopied DKO islets. DKO islets showed more rapid loss of glucose homeostasis when challenged with the inflammatory insult of transplantation.
CONCLUSIONS/INTERPRETATION: BIRC3 provides a feed-forward loop, which, with BIRC2, is required to moderate the normal speed of NF-κB activation. Paradoxically, BIRC2 and BIRC3 act as a molecular brake to rein in activation of the JNK signalling pathway. Thus BIRC2 and BIRC3 fine-tune NF-κB and JNK signalling to ensure transcriptional responses are appropriately matched to extracellular inputs. This control is critical for the beta cell's stress response.
目的/假设：对于β细胞，与 TNF-α的接触会引发信号级联反应，这些反应集中在细胞存活和炎症的重要途径上，特别是核因子κB（NF-κB）、c-Jun N 末端激酶（JNK）和 p38 丝裂原活化蛋白激酶途径。在这里，我们研究了杆状病毒凋亡抑制剂重复包含（BIRC）蛋白在调节 TNF 信号级联反应中的作用。
通过 mRNA 表达和启动子分析研究 TNF 对 Birc 基因的调节。通过β细胞系以及 Birc2(-/-)和 Birc3(-/-)小鼠胰岛，以及选择性缺乏 Birc2 和 Birc3（双重敲除 [DKO]）的 Birc3(-/-) Birc2Δβ细胞小鼠研究 Birc 基因对细胞信号的控制。通过腹腔内葡萄糖耐量试验和移植测试胰岛功能。
TNF-α 选择性诱导β细胞中的 Birc3，而 Birc3 足以驱动和增强 NF-κB 报告基因活性。相反，Birc3(-/-)胰岛表现出 TNF-α 诱导的 IκBα 降解延迟，Ccl2 和 Cxcl10 的表达减少。DKO 胰岛的 IκBα 降解动力学进一步延迟。令人惊讶的是，DKO 胰岛表现出刺激非依赖性和 TNF 依赖性 TNF 靶基因 A20（也称为 Tnfaip3）、Icam1、Ccl2 和 Cxcl10 的过度表达。DKO 胰岛 JNK 底物 c-Jun 的过度磷酸化，而 JNK 拮抗剂可阻止 Icam1、Ccl2 和 Cxcl10 表达的增加。MIN6 细胞的蛋白酶体阻断模拟了 DKO 胰岛。DKO 胰岛在受到移植炎症损伤的挑战时，更快地失去葡萄糖稳态。
结论/解释：BIRC3 提供了一个正反馈回路，与 BIRC2 一起，是调节 NF-κB 激活速度的必要条件。矛盾的是，BIRC2 和 BIRC3 充当分子刹车，以抑制 JNK 信号通路的激活。因此，BIRC2 和 BIRC3 微调 NF-κB 和 JNK 信号以确保转录反应与细胞外输入相匹配。这种控制对于β细胞的应激反应至关重要。
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