科研成果: “Tet2 is required to resolve inflammation by recruiting Hdac2 to specifically repress IL-6”

科研成果：曹雪涛课题组在《Nature》 杂志发表研究论文“Tet2 is required to resolve inflammation by recruiting Hdac2 to specifically repress IL-6 （2015）”。

机体免疫系统通过激发炎症免疫反应可以有效清除病原体，但过度和持续性炎症免疫反应会损伤机体自身。如何适度调控并及时终止炎症免疫反应、维持自身平衡稳态是免疫学重大科学问题。中国医学科学院基础医学研究所，“医学分子生物学国家重点实验室”的曹雪涛课题组首次提出表观遗传调控是炎症消退的决定性因素，而非以往普遍认为的信号转导的负调控。本研究首次报道了关键性表观酶Tet2不依赖于DNA修饰而发挥转录负调控功能，从促进炎症消退角度揭示了Tet2在肿瘤发生中的新机制。

【摘要】：Epigenetic modifiers have fundamental roles in defining unique cellular identity through the establishment and maintenance of lineage-specific chromatin and methylation status. Several DNA modifications such as 5-hydroxymethylcytosine (5hmC) are catalysed by the ten eleven translocation (Tet) methylcytosine dioxygenase family members, and the roles of Tet proteins in regulating chromatin architecture and gene transcription independently of DNA methylation have been gradually uncovered. However, the regulation of immunity and inflammation by Tet proteins independent of their role in modulating DNA methylation remains largely unknown. Here we show that Tet2 selectively mediates active repression of interleukin-6 (IL-6) transcription during inflammation resolution in innate myeloid cells, including dendritic cells and macrophages. Loss of Tet2 resulted in the upregulation of several inflammatory mediators, including IL-6, at late phase during the response to lipopolysaccharide challenge. Tet2-deficient mice were more susceptible to endotoxin shock and dextran-sulfate-sodium-induced colitis, displaying a more severe inflammatory phenotype and increased IL-6 production compared to wild-type mice. IκBζ, an IL-6-specific transcription factor, mediated specific targeting of Tet2 to the Il6 promoter, further indicating opposite regulatory roles of IκBζ at initial and resolution phases of inflammation. For the repression mechanism, independent of DNA methylation and hydroxymethylation, Tet2 recruited Hdac2 and repressed transcription of Il6 via histone deacetylation. We provide mechanistic evidence for the gene-specific transcription repression activity of Tet2 via histone deacetylation and for the prevention of constant transcription activation at the chromatin level for resolving inflammation.

相关结果已发表于《Nature》 杂志（2015，525(7569):389-93.），其作者为曹雪涛课题组博士研究生张迁，赵锴，重点室曹雪涛教授是本文的通讯作者。该研究工作得到了以下基金的支持：National Key Basic Research Program of China (2013CB530503) and the National Natural Science Foundation。

Tet2 binding partners for cytokine regulation

a, Co-immunoprecipitation assay using Tet2 antibody of nuclear fraction of murine BMDC stimulated with LPS for 8 h. Gene symbols of transcription factor deposited in KEGG database and their unique peptides identified by mass spectrometry analysis were tabled. b, IκBζ was silenced in BMDC using specific siRNA for 36 h and the BMDC were stimulated with LPS for 8 h. The protein levels of IκBζ were detected by immunoblot, with lamin A/C as the loading control. c, Hdac1/2 (blue circles) were subjected to interaction analysis with genes which had significant expression variations (red circles for upregulated, and green circles for downregulated) in BMDC 4 h after LPS stimulation. The linkers indicate interaction or regulation relationship between the two genes. d,e, Flag-tagged Hdac1 (d) or Hdac2 (e) were overexpressed in HEK293T cells together with Myc-tagged Tet2. Cell lysates were examined by IP and immunoblot with indicated antibodies. The whole-cell lysates (WCL) were used to examine the input of overexpressed proteins. f, BMDC were pretreated with 100 nM TSA for 1 h, and then stimulated by LPS for indicated time. mRNA levels of indicated genes were analysed by qPCR. g, h, BMDC (g) and peritoneal macrophages (h) were stimulated with LPS for the indicated time. Enrichments of H3Ac (g), H4Ac (h) at Tnfpromoters were analysed by ChIP-qPCR. i, Hdac2 was silenced in BMDC for 48 h and then the BMDC were stimulated with LPS for 8 h. The protein levels of Hdac2 were detected by immunoblot, with lamin A/C as the loading control. Full scans of blots are shown in Supplementary Fig. 1. Error bars represent s.d. of triplicate technical (g, h) or s.e.m. of triplicate biological (f) replicates and are representative of three independent experiments. **P < 0.01.

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