CD4CD8 Lineage Commitment Is Regulated by a Silencer Element at the ThPOK Transcription-Factor Locus
ABSTRACT The transcription factor ThPOK is necessary and sufficient to trigger adoption of the CD4 lymphocyte fate. Here we investigate the regulation of ThPOK expression and its subsequent control of CD4+ T cell commitment. Treatment of immature thymocytes with anti-TCR (T cell receptor) showed that TCR signals were important in ThPOK induction and that the CD4+8lo stage was the likely target of the inductive TCR signal. We identified at the ThPOK locus a key distal regulatory element (DRE) that mediated its differential expression in class I- versus II-restricted CD4+8lo thymocytes. The DRE was both necessary for suppression of ThPOK expression in class I-restricted thymocytes and sufficient for its induction in class II-restricted thymocytes. Mutagenesis analysis defined an essential 80bp core DRE sequence and its potential regulatory motifs. We propose a silencer-dependent model of lineage choice, whereby inactivation of the DRE silencer by a strong TCR signal leads to CD4 commitment, whereas continued silencer activity leads to CD8 commitment.
Nature Immunology 06/2014; 15(7):593-594. DOI:10.1038/ni.2927 · 24.97 Impact Factor
[Show abstract] [Hide abstract]
ABSTRACT: Lineage fate in the thymus is determined by mutually exclusive expression of the transcription factors ThPOK and Runx3, with ThPOK imposing the CD4(+) lineage fate and Runx3 promoting the CD8(+) lineage fate. While it is known that cytokine signals induce thymocytes to express Runx3, it is not known how ThPOK prevents thymocytes from expressing Runx3 and adopting the CD8(+) lineage fate, nor is it understood why ThPOK itself imposes the CD4(+) lineage fate on thymocytes. We now report that genes encoding members of the SOCS (suppressor of cytokine signaling) family are critical targets of ThPOK and that their induction by ThPOK represses Runx3 expression and promotes the CD4(+) lineage fate. Thus, induction of SOCS-encoding genes is the main mechanism by which ThPOK imposes the CD4(+) lineage fate in the thymus.Nature Immunology 06/2014; DOI:10.1038/ni.2917 · 24.97 Impact Factor
[Show abstract] [Hide abstract]
ABSTRACT: Differentiation of CD4(+) helper and CD8(+) cytotoxic αβ T cells from CD4(+)CD8(+) thymocytes involves upregulation of lineage-specifying transcription factors and transcriptional silencing of CD8 or CD4 coreceptors, respectively, in MHC class II or I (MHCII or I)-restricted thymocytes. In this study, we demonstrate that inactivation of the Dicer RNA endonuclease in murine thymocytes impairs initiation of Cd4 and Cd8 silencing, leading to development of positively selected MHCI- and MHCII-restricted mature CD4(+)CD8(+) thymocytes. Expression of the antiapoptotic BCL2 protein or inactivation of the p53 proapoptotic protein rescues these thymocytes from apoptosis, increasing their frequency and permitting accumulation of CD4(+)CD8(+) αβ T cells in the periphery. Dicer-deficient MHCI-restricted αβ T cells fail to normally silence Cd4 and display impaired induction of the CD8 lineage-specifying transcription factor Runx3, whereas Dicer-deficient MHCII-restricted αβ T cells show impaired Cd8 silencing and impaired induction of the CD4 lineage-specifying transcription factor Thpok. Finally, we show that the Drosha RNA endonuclease, which functions upstream of Dicer in microRNA biogenesis, also regulates Cd4 and Cd8 silencing. Our data demonstrate a previously dismissed function for the microRNA biogenesis machinery in regulating expression of lineage-specifying transcription factors and silencing of Cd4 and Cd8 during αβ T cell differentiation.The Journal of Immunology 09/2014; 193(8). DOI:10.4049/jimmunol.1401359 · 5.36 Impact Factor