Transcriptional regulation of the human MIP-1α promoter by RUNX1 and MOZ

The transcription factor RUNX1 (AML-1, PEBP2αB and CBFA2) is essential for definitive haematopoiesis, and chromosomal translocations involving the RUNX1 gene are frequently found in acute leukaemias. The gene encoding the histone acetyltransferase MOZ is also rearranged in some acute leukaemias, resulting in the expression of MOZ fusion proteins. MOZ has recently been shown to interact directly with RUNX1, indicating that MOZ fusion proteins act by deregulating RUNX1 function. Macrophage inflammatory protein-1α (MIP-1α) is a proinflammatory cytokine that also inhibits proliferation of haematopoietic stem cells. Amongst the conserved sequence elements in the human MIP-1α promoter are two consensus RUNX sites. We have investigated the role of these RUNX sites in the regulation of the MIP-1α promoter by PMA/PHA stimulation in Jurkat T-cells. RUNX1 can specifically bind to both RUNX sites in vitro and chromatin immunoprecipitation assays demonstrated that endogenous RUNX1 is constitutively bound to the endogenous MIP-1α promoter. Mutation of the RUNX sites demonstrated that the proximal RUNX site is essential for PMA/PHA-stimulated activation of the MIP-1α promoter. Activation of the promoter can also be inhibited by heterologous expression of the repressor protein AML-1/ETO. We further demonstrate that MOZ can activate the MIP-1α promoter and that this activation is largely dependent upon the proximal RUNX site. Moreover, we show that co-expression of MOZ and RUNX1 can synergistically activate the MIP-1α promoter. The regulation of MIP-1α expression by RUNX1/MOZ is discussed in the context of MIP-1α's role as an inhibitor of haematopoietic stem cell proliferation and its potential importance in leukaemias associated with RUNX1 or MOZ chromosomal rearrangements.