The SCL transcriptional network and BMP signaling pathway interact to regulate RUNX1 activity

Abstract

Hematopoietic stem cell (HSC) development is regulated by several signaling pathways and a number of key transcription factors, which include Scl/Tal1, Runx1, and members of the Smad family. However, it remains unclear how these various determinants interact. Using a genome-wide computational screen based on the well characterized Scl ؉19 HSC enhancer, we have identified a related Smad6 enhancer that also targets expression to blood and endothelial cells in transgenic mice. Smad6, Bmp4, and Runx1 transcripts are concentrated along the ventral aspect of the E10.5 dorsal aorta in the aorta-gonad-mesonephros region from which HSCs originate. Moreover, Smad6, an inhibitor of Bmp4 signaling, binds and inhibits Runx1 activity, whereas Smad1, a positive mediator of Bmp4 signaling, transactivates the Runx1 promoter. Taken together, our results integrate three key determinants of HSC development; the Scl transcriptional network, Runx1 activity, and the Bmp4/Smad signaling pathway.hematopoiesis ͉ SMAD6 ͉ hematopoietic stem cell ͉ aorta-gonad-mesonephros ͉ bioinformatics T he coordinated expression of genes lies at the heart of metazoan development, with complex gene-regulatory networks governing the spatial variation and temporal sequence with which genes are expressed (reviewed in ref. 1). Transcription factors and the cis-regulatory sequences to which they bind form the building blocks of gene-regulatory networks (2). Recognizing the components and hierarchy of gene-regulatory networks and their interactions with cell-signaling pathways not only provides insights into biology but also is fundamental to understanding how deregulation of networks contributes to pathology.In the postgenomics era, classical methods to screen for potential gene-regulatory regions, such as DNase I hypersensitivity mapping by Southern blotting of selected loci, are being superseded by new genome-wide techniques such as ChIP coupled to genomic tiling arrays (ChIP/chip) (3)or high-throughput sequencing of sequence tags indicating DNase I hypersensitivity (4). Although these largescale screening techniques may rapidly identify the positions of large numbers of candidate regulatory elements, they do not accurately predict their function, i.e., whether a given element is an enhancer or silencer, nor the pattern of activity in cell types other than those analyzed. Moreover, the large amounts of biological material required prevent use of these techniques in the study of early developmental programs and adult stem cell systems. Consequently, in silico approaches are increasingly used to perform genome-wide identification of candidate regulatory elements. Transcription factors often act as components of multiprotein complexes binding to clusters of binding sites. Well characterized regulatory modules with known combinations of transcription factor-binding sites can greatly facilitate the in silico prediction of other cis-regulatory modules that may be important in regulating the same biological process. This method is proving to be a powerful tool in ...

Differential effects of inhibition of bone morphogenic protein (BMP) signalling on T‐cell activation and differentiation

“…7D). Given that RUNX1 activates IL2 transcription [8] and that pRUNX1 is increased by the activation of RUNX1 [16], these results suggested that BMP signalling regulated IL-2 transcription via activating RUNX1 in T cells.…”

“…First, IL-2 production is the crucial mechanism of T-cell activation. Second, IL2 transcription is known to be regulated by several key transcription factors, one of which is AML1/ RUNX1, a well-established downstream target of BMP signalling in hematopoietic lineage cells [8,14,15].…”

“…As AML/RUNX proteins are reported to be involved in BMP signalling in other tissues such as hematopoitic stem cells [8] and RUNX1 is reported as an important transcription factor for T-cell function including IL-2 production [15], we investigated the molecular mechanism of BMP signalling by analysing RUNX1. The phosphorylated form of RUNX1 with phosphorylation sites including Ser249 is believed to be the activated form of the transcription factor [16].…”

“…It is known that the SMAD complex interacts with the transcription factor RUNX2, which is a major target of BMP signalling for the differentiation of osteoblasts [7]. In hematopoietic stem cells, BMP4/SMAD signalling is reported to regulate RUNX1 activity [8]. Preceding studies indicate that BMP activates not only the SMAD pathway but also other pathways such as mitogen-activated protein kinase (MAPK) family of molecules including ERK1/2 and p38 [9].…”

A Runx1-Smad6 Rheostat Controls Runx1 Activity during Embryonic Hematopoiesis

“…At a posttranscriptional stage, Runx1 levels can be controlled by miR-27a in a feed-back loop, which involves the positive regulation of miR-27a by Runx1 (4). At a posttranslational stage, we have reported previously that Runx1 levels are controlled by Smad6/Smurf1-mediated proteasome degradation (28), but how this control mechanism is integrated within the hematopoietic transcriptional network is not clear. Smad6 is an inhibitor of Bmp4 signaling (14), a key driver of HSC development (18).…”