Ikaros represses the transcriptional response to Notch signaling in T-cell development.
Notch activity is essential for early T-cell differentiation, but aberrant activity induces T-cell transformation. Thus, Notch target genes must be efficiently silenced in cells where Notch activity is no longer required. How these genes are repressed remains poorly understood. We report here that the Ikaros transcription factor plays a crucial role in repressing the transcriptional response to Notch signaling in T-cell development. Using the Notch target gene Hes-1 as a model, we show that Ikaros and RBP-Jkappa, the transcriptional mediator of Notch signaling, compete for binding to two elements in the Hes-1 promoter in immature thymocytes. This antagonistic interaction likely occurs at the CD4(-) CD8(-) CD3(-) double-negative 4 (DN4) stage, where Ikaros levels and binding to the Hes-1 promoter increase sharply and wild-type thymocytes lose their capacity to transcribe Hes-1 upon Notch stimulation. Nonresponsiveness to Notch signaling requires Ikaros, as Ikaros-deficient DN4 and CD4(+) CD8(+) double-positive (DP) cells remain competent to express Hes-1 after Notch activation. Further, Hes-1 promoter sequences from Ikaros-deficient DP cells show reduced trimethylated H3K27, a modification associated with silent chromatin. These results indicate that Ikaros functions as a transcriptional checkpoint to repress Notch target gene expression in T cells.
Institut de Génétique et de Biologie Molééculaire et Cellulaire, Department of Cancer Biology, Illkirch F-67400, France.
Eva
E
Kleinmann
Anne-Solen
AS
Geimer Le Lay
MacLean
M
Sellars
Philippe
P
Kastner
Susan
S
Chan
D000818:Animals; D001483:Base Sequence; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics / Q000378:metabolism; D019556:COS Cells; D002454:Cell Differentiation; D002478:Cells, Cultured; D002522:Chlorocebus aethiops; D018507:Gene Expression Regulation, Developmental; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D051740:Ikaros Transcription Factor / Q000235:genetics / Q000378:metabolism*; D051819:Immunoglobulin J Recombination Signal Sequence-Binding Protein / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D051880:Receptors, Notch / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment; D015398:Signal Transduction / Q000502:physiology*; D013601:T-Lymphocytes / Q000166:cytology / Q000502:physiology*; D013950:Thymus Gland / Q000166:cytology; D014158:Transcription, Genetic
D051792:Basic Helix-Loop-Helix Proteins; D018398:Homeodomain Proteins; D051740:Ikaros Transcription Factor; D051819:Immunoglobulin J Recombination Signal Sequence-Binding Protein; D051880:Receptors, Notch