Depletion of c-Rel from Cytokine Gene Promoters Is Required for Chromatin Reassembly and Termination of Gene Responses to T Cell Activation

Abstract

The role of the Nuclear Factor κB (NF-κB) transcription factor family in T cell function has been well described. The c-Rel family member is of particular importance in initiating T cell responses to antigen and regulating activation of inflammatory cytokine genes, including the Interleukin-2 (IL-2) and Granulocyte macrophage colony stimulating factor (GM-CSF) genes. c-Rel is required for chromatin remodeling of these gene promoters, which involves depletion of histones from the promoters in response to T cell activating signals. These chromatin remodeling events precede transcriptional activation of the genes. The subsequent down-regulation of cytokine gene expression is important in the termination of an immune response and here we examine this process at the murine GM-CSF and IL-2 genes. We show that the cytokine mRNA levels rapidly return to basal levels following stimulus removal and this is associated with reassembly of histones onto the promoter. Histone reassembly at the GM-CSF and IL-2 promoters occurs concomitantly with depletion of RelA, c-Rel and RNA polymerase II from the promoters. Furthermore we show that transcriptional down-regulation and chromatin reassembly is dependent on depletion of c-Rel from the nucleus, and that this is regulated by the nuclear translocation of the NF-κB inhibitor, IκBα. The nuclear activation of c-Rel therefore not only regulates the initiation of GM-CSF and IL-2 gene activation in response to T cell activation, but also the termination of these gene responses following the removal of the activating signal.

Chromatin priming elements establish immunological memory in T cells without activating transcription

“…This mechanism will suppress low‐level chronic activation of a pro‐inflammatory response at the point in time when the response needs to be resolved and shut down again. This represents an alternate means of shutting down regulatory elements which otherwise can remain active and nucleosome‐free until the activating factors are depleted . This process of nucleosome repositioning is reminiscent of the recently described process of “assisted loading” whereby transient binding of TFs can direct nucleosome repositioning in a hit‐and‐run mechanism to assist the binding of a second TF .…”

CD4+T cells require Ikaros to inhibit their differentiation toward a pathogenic cell fate

“…Transcription of the Csf2 gene is controlled by the Csf2 promoter and two enhancers, one located ~1.5 kb upstream and a conserved non-coding sequence (CNSa) ~34 kb downstream of the transcriptional start site (18)(19)(20). The promoter contains binding sequences for the transcription factors NFAT, NFkB, AP-1 and Brg1, and is sensitive to changes in chromatin accessibility (21)(22)(23)(24)(25)(26)(27)(28). Csf2 promoter activity is potentiated upon NFAT and AP-1 binding to the upstream enhancer, and NFkB and Brg1 binding to the CNSa region (19,20).…”

Activation of Silenced Cytokine Gene Promoters by the Synergistic Effect of TBP-TALE and VP64-TALE Activators

“…We wanted to know if these artificially constructed TALE activators were able to activate the IL-2 gene expression by directly binding to the chromatin as reported by others [21] or if chromatin remodeling was necessary. Within naïve T-cells, the IL-2 chromatin architecture is maintained in an inaccessible state, formed by nucleosome accumulation within the proximal promoter region, which masks TCR-specific response elements [30] , [31] , [37] – [41] . Consequently, nucleosome masking of these elements prevents TFs from binding to their cognate target sites and inhibits IL-2 gene transcription.…”