RESUMEN
How cell type-specific differences in chromatin conformation are achieved and their contribution to gene expression are incompletely understood. Here we identify a cryptic upstream orchestrator of interferon-gamma (IFNG) transcription, which is embedded within the human IL26 gene, compromised of a single CCCTC-binding factor (CTCF) binding site and retained in all mammals, even surviving near-complete evolutionary deletion of the equivalent gene encoding IL-26 in rodents. CTCF and cohesins occupy this element in vivo in a cell type-nonspecific manner. This element is juxtaposed to two other sites located within the first intron and downstream of Ifng, where CTCF, cohesins, and the transcription factor T-bet bind in a T helper 1 (Th1) cell-specific manner. These interactions, close proximity of other elements within the locus to each other and to the gene encoding interferon-gamma, and robust murine Ifng expression are dependent on CTCF and T-bet. The results demonstrate that cooperation between architectural (CTCF) and transcriptional enhancing (T-bet) factors and the elements to which they bind is required for proper Th1 cell-specific expression of Ifng.
Asunto(s)
Linfocitos T CD4-Positivos/inmunología , Interferón gamma/metabolismo , Proteínas Represoras/metabolismo , Proteínas de Dominio T Box/metabolismo , Células TH1/inmunología , Animales , Factor de Unión a CCCTC , Linfocitos T CD4-Positivos/metabolismo , Proteínas de Ciclo Celular/genética , Proteínas de Ciclo Celular/inmunología , Proteínas de Ciclo Celular/metabolismo , Células Cultivadas , Cromatina/inmunología , Cromatina/metabolismo , Proteínas Cromosómicas no Histona/genética , Proteínas Cromosómicas no Histona/inmunología , Proteínas Cromosómicas no Histona/metabolismo , Humanos , Interferón gamma/genética , Interferón gamma/inmunología , Interleucinas/genética , Interleucinas/inmunología , Interleucinas/metabolismo , Intrones/genética , Intrones/inmunología , Ratones , Ratones Endogámicos C57BL , Ratones Transgénicos , Ratas , Proteínas Represoras/genética , Proteínas Represoras/inmunología , Proteínas de Dominio T Box/genética , Proteínas de Dominio T Box/inmunología , Células TH1/metabolismo , CohesinasRESUMEN
During their development, T lymphocytes make sequential cell fate choices: T rather than B lymphocytes, then TCRalphabeta or TCRgammadelta, CD4 or CD8, and Th1 or Th2 lineage. These fate choices require the initiation of new programs of gene expression, and once initiated, these programs must be faithfully propagated in a heritable manner from parental cells to their progeny. With the exception of the T cell receptor, these changes in gene expression occur without a change in information encoded directly in the DNA sequence. Rather, these heritable programs of gene expression are imposed, at least in part, epigenetically through changes in chromatin structure and DNA methylation, allowing T cells to tune the threshold for expression of specific genes.
Asunto(s)
Diferenciación Celular/genética , Regulación de la Expresión Génica , Linfocitos T/fisiología , Diferenciación Celular/inmunología , Diferenciación Celular/fisiología , Citocinas/genética , Citocinas/metabolismo , Humanos , Linfocitos T/metabolismo , Transcripción GenéticaRESUMEN
How T cells regulate interleukin 4 (IL-4) expression is not completely understood. We show here that single-positive thymocytes express IL-4, but attenuate GATA-3 expression, recruit DNA methyltransferases (Dnmts) to the Il4-Il13 locus and downregulate IL-4 expression as they mature into T cells. Type 2 polarization blocks Dnmt1 recruitment, enhances histone H3 Lys4 methylation (indicative of accessible chromatin) and initiates DNA demethylation of the locus. Dnmt1-/- CD4 and CD8 T cells derepress IL-4 expression considerably, demethylate DNA and increase H3 Lys4 methylation without affecting GATA-3 expression, demonstrating that Dnmt1 and DNA methylation are essential for proper Il4 regulation. These results indicate that Dnmts, DNA and histone methylation, and transcription factors 'collaborate' to determine appropriate Il4 expression patterns.