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Epigenetic Regulation of TLR4 Gene Expression in Intestinal Epithelial Cells for the Maintenance of Intestinal Homeostasis¹

Food and Physiological Functions Laboratory, College of Bioresource Sciences, Nihon University, Fujisawa-shi, Kanagawa, Japan

Intestinal epithelial cells (IECs) are continuously exposed to large numbers of commensal bacteria but are relatively insensitive to them, thereby averting an excessive inflammatory reaction. In this study, we show that the low responsiveness of human IEC lines to LPS was mainly brought about by a down-regulation of TLR4 gene transcription. Additionally, the presence of an IEC-specific repressor element in the 5' region of the TLR4 gene and binding of a NF to the element was shown. The transcription factor ZNF160, which was expressed more abundantly in a LPS-low responder IEC line than in a LPS-high responder IEC line, repressed TLR4 gene transcription. ZNF160 is known to interact with the scaffold protein KAP1 via its N terminus to recruit histone deacetylase. Histone deacetylation, as well as DNA methylation, at the 5' region of the TLR4 gene was significantly higher in LPS-low responder IEC lines than in a monocyte line or a LPS-high responder IEC line. It was demonstrated that TLR4 gene transcription was repressed by these epigenetic regulations, which were, at least in part, dependent on ZNF160. Down-regulaton of TLR4 gene expression by these mechanisms in IECs possibly contributes to the maintainance of homeostasis in the intestinal commensal system.

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ This work was supported in part by a Grant-in Aid for Young Scientists from the Ministry of Education, Culture, Sports, Science, and Technology of Japan (to K.T.) and a Grant-in Aid for Scientific Research from Japan Society for the Promotion of Science (to S.K.).

² Address correspondence and reprint requests to Dr. Kyoko Takahashi, Food and Physiological Functions Laboratory, College of Bioresource Sciences, Nihon University, 1866 Kameino, Fujisawa-shi, Kanagawa 252-8510, Japan. E-mail address: ktaka{at}brs.nihon-u.ac.jp

³ Abbreviations used in this paper: IEC, intestinal epithelial cell; DN, dominant negative; qPCR, quantitative PCR; ChIP, chromatin immunoprecipitation; 5-aza-dC, 5-aza-2'-deoxycytidine; TSA, trichostatin A; siRNA, small interfering RNA; KRAB, Kruppel-associated box; KAP, KRAB-associated protein; ICSBP, interferon consensus sequence-binding protein.