RUNX proteins regulate gene expression in long-term hematopoietic stem cells by mediating interaction of distal and proximal regulatory elements

The transcription factor RUNX1 is essential to establish the
haematopoietic gene expression programme; however, the
mechanism of how it activates transcription of haematopoietic
stem cell (HSC) genes is still elusive. Here, we
obtained novel insights into RUNX1 function by studying
regulation of the human CD34 gene, which is expressed in
HSCs. Using transgenic mice carrying human CD34 PAC
constructs, we identified a novel downstream regulatory
element (DRE), which is bound by RUNX1 and is necessary
for human CD34 expression in long-term (LT)-HSCs.
Conditional deletion of Runx1 in mice harbouring human
CD34 promoter-DRE constructs abrogates human CD34
expression.We demonstrate by chromosome conformation
capture assays in LT-HSCs that the DRE physically interacts
with the human CD34 promoter. Targeted mutagenesis
of RUNX binding sites leads to perturbation of this
interaction and decreased human CD34 expression in LT-HSCs. Overall, our in vivo data provide novel evidence
about the role of RUNX1 in mediating interactions between
distal and proximal elements of the HSC gene CD34.