The RUNX1:CBFB complex binds the promoter of the MIR27A gene, encoding microRNA miR-27a, and stimulates MIR27A transcription. Based on the analogy with the ITGA2B gene transcription, transcription of MIR27A is significantly upregulated by PRMT1-dependent arginine methylation of RUNX1, which interferes with the recruitment of the SIN3A (or, possibly, SIN3B) co-repressor (Zhao et al. 2008). The transcription activator complex at the MIR27A gene promoter includes the RUNX1:CBFB complex, PRMT1, the GATA1:ZFPM1 complex, histone acetyltransferases p300 (EP300) and PCAF (KAT2B), and the WDR5-containing histone methyltransferase MLL complex. The MLL complex produces the activating H3K4me3 mark on nucleosomes associated with the MIR27A gene promoter (Herglotz et al. 2013).
The transcription repressor complex at the MIR27A promoter is formed when SIN3A (or possibly SIN3B) co-repressor binds to the RUNX1:CBFB complex along with histone arginine methyltransferase PRMT6 and histone deacetylase HDAC1. Histone H3 arginine methylation by PRMT6 interferes with methylation of H3K4me2 to generate the activating H3K4me3 mark at the MIR27A gene promoter, thus contributing to transcriptional repression (Herglotz et al. 2013).
MicroRNA miR-27a binds the 3'UTR of RUNX1 mRNA and inhibits RUNX1 mRNA translation without affecting RUNX1 mRNA stability. RUNX1 and MIR27A thus constitute a negative feedback loop that regulates megakaryocytic differentiation and may be involved in erythroid/megakaryocytic lineage determination (Ben-Ami et al. 2009).