Duan Yingli, Liao Anne P, Kuppireddi Sumalatha, Ye Zhongde, Ciancio Mae J, Sun Jun
Department of Pathology, The University of Chicago, Chicago, IL 60637, USA.
Lab Invest. 2007 Jun;87(6):613-24. doi: 10.1038/labinvest.3700545. Epub 2007 Mar 26.
Wild-type (WT) Salmonella typhimurium causes acute intestinal inflammation by activating the nuclear factor kappa B (NF-kappaB) pathway. Interestingly, WT Salmonella infection also causes degradation of beta-catenin, a regulator of cellular proliferation. Regulation of beta-catenin and the inhibitor of NF-kappaB, IkappaBalpha, is strikingly similar, involving phosphorylation at identical sites, ubiquitination by the same E3 ligase, and subsequent proteasomal degradation. However, how beta-catenin directly regulates the NF-kappaB pathway during bacteria-induced inflammation in vivo is unknown. Using streptomycin-pretreated mice challenged with Salmonella, we demonstrated that WT Salmonella stimulated beta-catenin degradation and decreased the physical association between NF-kappaB and beta-catenin. Accordingly, WT Salmonella infection decreased the expression of c-myc, a beta-catenin-regulated target gene, and increased the levels of IL-6 and TNF-alpha, the NF-kappaB-regulated target genes. Bacterial infection directly stimulated phosphorylation of beta-catenin, both in vivo and in vitro. Closer examination revealed that glycogen synthase kinase 3beta (GSK-3beta) kinase activity was increased in response to WT Salmonella, whereas non-virulent Salmonella had no effect. siRNA of GSK-3beta was able to stabilize IkappaBalpha in response to WT Salmonella. Pretreatment for 24 h with LiCl, an inhibitor of GSK-3beta, reduced WT Salmonella induced IL-8 secretion. Additionally, cells expressing constitutively active beta-catenin showed IkappaBalpha stabilization and inhibition of NF-kappaB activity not only after WT Salmonella infection but also after commensal bacteria (Escherichia coli F18) and TNF-alpha treatment. This study suggests a new role for beta-catenin as a negative regulator of inflammation.
野生型（WT）鼠伤寒沙门氏菌通过激活核因子κB（NF-κB）途径引发急性肠道炎症。有趣的是，WT沙门氏菌感染还会导致细胞增殖调节因子β-连环蛋白的降解。β-连环蛋白和NF-κB抑制剂IκBα的调节方式惊人地相似，都涉及相同位点的磷酸化、由相同E3连接酶进行的泛素化以及随后的蛋白酶体降解。然而，在体内细菌诱导的炎症过程中，β-连环蛋白如何直接调节NF-κB途径尚不清楚。利用经链霉素预处理并用沙门氏菌攻击的小鼠，我们证明WT沙门氏菌刺激β-连环蛋白降解，并减少NF-κB与β-连环蛋白之间的物理结合。相应地，WT沙门氏菌感染降低了β-连环蛋白调节的靶基因c-myc的表达，并增加了NF-κB调节的靶基因IL-6和TNF-α的水平。细菌感染在体内和体外均直接刺激β-连环蛋白的磷酸化。进一步研究发现，响应WT沙门氏菌时糖原合酶激酶3β（GSK-3β）的激酶活性增加，而无毒力的沙门氏菌则无此作用。GSK-3β的小干扰RNA（siRNA）能够在响应WT沙门氏菌时稳定IκBα。用GSK-3β抑制剂氯化锂预处理24小时可减少WT沙门氏菌诱导的IL-8分泌。此外，组成型活性β-连环蛋白表达细胞不仅在WT沙门氏菌感染后，而且在共生细菌（大肠杆菌F18）和TNF-α处理后均显示IκBα稳定和NF-κB活性受到抑制。这项研究表明β-连环蛋白作为炎症的负调节因子具有新的作用。
