The transcription factor c-Myc enhances KIR gene transcription through direct binding to an upstream distal promoter element

Abstract

4,5 Therefore, an elucidation of the factors that influence KIR gene transcription and a more thorough understanding of how KIR signaling affects NK-cell development are needed to understand how to manipulate the innate immune system for therapeutic purposes.Progress in the elucidation of how KIR genes are regulated has been limited because of the complexity of the KIR gene locus and the fact that KIR genes are not present in model rodent species, which are amenable to genomic manipulation. The conventional 250-bp core promoter located in the 5Ј region just proximal to the translational start site has been characterized in detail for many KIR genes. 6-8 However, an entire 2-kb intergenic region exists upstream of the translational start site for each KIR gene, with the exception of KIR2DL4, which has a 14-kb upstream intergenic region. 9 A recent report has identified the presence of active distal KIR promoter elements and spliced transcripts originating from these elements. 10 Because the distal promoter contains a Myc-binding site, 10 we hypothesized that c-Myc can bind to the distal promoter element and directly affect KIR expression. c-Myc is a basic helix-loophelix leucine zipper transcription factor that binds E-box DNA motifs as a heterodimer with Max, resulting in transcriptional activation or silencing of target genes. 11-13 Many major cellular processes, including cell cycle entry, 14 proliferation, 15 cell size regulation, 16 and apoptosis, 17 are influenced by c-Myc. 18,19 c-Myc is particularly interesting in the context of KIR transcriptional regulation because c-Myc functions as a downstream component of the interleukin-15 (IL-15) signaling pathway during CD8 ϩ T-cell homeostasis, 20 and the IL-15 pathway is critical for NK-cell maturation, 21 activation on infection in the periphery, 22 and homeostasis. 23 In the present study, we demonstrate a direct, functional interaction between c-Myc induced by IL-15 and the distal KIR promoter element and show that full-length KIR transcripts are transcribed from the distal promoter element early during development of the NK-cell KIR repertoire. MethodsElectric mobility shift assay of c-Myc binding to the distal KIR promoter element Nuclear extracts were prepared from YT-Indy cells using the CellLytic NuCLEAR extraction kit (Sigma-Aldrich, St Louis, MO). Protein concentration was measured with a Bio-Rad protein assay (Hercules, CA), and

Education of hyporesponsive NK cells by cytokines

“…Therefore, we cannot exclude that some NK cells have received in vivo an additional signal leading to the initiation of KIR expression and that cytokines would only promote the preferential expansion of this committed subset in vitro. However, a recent report from Cichocki et al demonstrated that IL-15 or IL-2 induce c-Myc binding to an upstream distal KIR promoter element that promotes KIR transcription [14], supporting the idea that cytokines are directly required for induction of KIR expression and do not only allow the proliferation/differentiation of a subset of committed NK cells. Even if we cannot rule out that further unknown signals might be required, our data clearly show that cytokines are essential to induce stable KIR de novo expression and demethylation of the corresponding promoter in a subset of hyporesponsive NK cells.…”

Natural killer–cell differentiation by myeloid progenitors

“…We recently found that myc binds to KIR promoters, driving expression. 33 Interestingly, myc expression is linked to M-CSFR signaling and myeloid development. 34 Recently, a thymic pathway of NK-cell development was shown in rodents.…”

Transcription Regulation and Epigenetic Control of Expression of Natural Killer Cell Receptors and Their Ligands

“…However, a further study suggested that AML has a general inhibitory influence on KIR expression in mature NK cells and that AML exerts its repressor function by binding directly to the promoter of the different KIR genes (Trompeter et al, 2005). Recently, it was reported that the transcription factor c-Myc upregulated KIR gene transcription through direct binding to an upstream distal promoter element in peripheral blood NK cells, and that IL-15 promoted this effect (Cichocki et al, 2009). It was suggested that the role of the traditional transcription factors in KIR gene expression is different from that in other genes.…”