title: A silencer-proximal intronic region is required for sustained CD4 expression in postselection thymocytes.
abstract: It has been proposed that differential kinetics of CD4/CD8 coreceptors regulate fate choice of selected thymocytes. Sustained signals by interaction between MHC class II and TCR/CD4 is required for commitment to the CD4 helper lineage. Although prematurely terminated MHC-TCR/CD4 interaction in transgenic mouse models results in lineage redirection, it is unclear whether CD4 expression is actively maintained by endogenous cis-elements to facilitate prolonged signaling under physiological conditions. In this article, we show that sustained CD4 expression in postselection thymocytes requires an intronic sequence containing an uncharacterized DNase I hypersensitivity (DHS) site located 3' to the silencer. Despite normal CD4 expression before selection, thymocytes lacking a 1.5-kb sequence in intron 1 including the 0.4-kb silencer and the DHS, but not the 0.4-kb silencer alone, failed to maintain CD4 expression upon positive selection and are redirected to the CD8 lineage after MHC class II-restricted selection. Furthermore, CpG dinucleotides adjacent to the DHS are hypermethylated in CD8(+) T cells. These results indicate that the 1.5-kb cis-element is required in postselection thymocytes for helper lineage commitment, presumably mediating the maintenance of CD4 expression, and suggest that inactivation of the cis-element by DNA methylation may contribute to epigenetic Cd4 silencing.
authors.affiliation: Department of Pathology and Immunology, Washington University School of Medicine, St. Louis, MO 63110.
authors.forename: David M
authors.initials: DM
authors.lastname: Henson
authors.forename: Chun
authors.initials: C
authors.lastname: Chou
authors.forename: Nagisa
authors.initials: N
authors.lastname: Sakurai
authors.forename: Takeshi
authors.initials: T
authors.lastname: Egawa
mesh_terms: D000818:Animals; D015704:CD4 Antigens / Q000235:genetics / Q000276:immunology*; D015496:CD4-Positive T-Lymphocytes / Q000166:cytology / Q000276:immunology; D018414:CD8-Positive T-Lymphocytes / Q000166:cytology / Q000276:immunology; D019175:DNA Methylation / Q000276:immunology; D005786:Gene Expression Regulation / Q000235:genetics / Q000276:immunology*; D020868:Gene Silencing / Q000276:immunology*; D007438:Introns / Q000276:immunology*; D051379:Mice; D018345:Mice, Knockout; D037941:Silencer Elements, Transcriptional / Q000276:immunology*; D060168:Thymocytes / Q000166:cytology / Q000276:immunology*
chemical_list: D015704:CD4 Antigens
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