Functional And Mechanism Analysis Of MicroRNA-23a/27a/24-2in Human Erythropoiesis

MicroRNAs (miRNAs) play important roles in erythropoeisis. Although several microRNAs were shown to regulate erythroid differentiation, it still remained unclear how the key erythropoeisis regulator GATA-1directly orchestrates the differentiation through microRNAs pathway.In the first part of work, we identified in erythropoiesis miR-23a as a key regulator upregulated both during erythroid differentiation and in GATA-1gain-of-function experiments by microRNA expression profiling analysis. In human primary CD34+hematopoietic progenitor cells (HPCs), we validated miR-23a increases in a GATA-1dependent manner during erythroid differentiation. Gain or loss-of-function analysis of miR-23a in mice or zebrafish demonstrated it is essential for the normal morphology of the terminally differentiated erythroid. Further studies defined a protein tyrosine phosphatase SHP2was the down-stream target of miR-23a, and mediated miR-23a regulation of erythropoiesis. Taken together, this work provided a strategy of identification of a key GATA-1-microRNAs axis in erythroid differentiation. In the second part of work, we reported that GATA-1and GATA-2co-regulated the expression of two miRNA genes through competitively binding to the site-557bp up to TSS of their promoter, microRNA-27a and microRNA-24, with critical roles in regulating erythroid differentiation. In general, GATA-2occupied the miR-27a～24promoter and repressed their transcription in immature erythroid progenitor cells. As erythropoiesis proceeded, GATA-1directly activated miR-27a/24transcription, and this involved a GATA-1-mediated displacement of GATA-2from chromatin, a process termed "GATA switch". Furthermore, the mature miR-27a and miR-24cooperatively inhibited GATA-2translation and favoured the occupancy switch from GATA-2to GATA-1, thus completing a positive feedback loop to promote erythroid maturation. In line with the essential role of GATA factors, ectopic expression of miR-27a or miR-24accelerated erythropoiesis in human primary CD34+haematopoietic progenitor cells (HPCs) and mice, while attenuated miR-27or miR-24level led to impaired erythroid phenotypes in HPCs and zebrafish. Taken together, these data integrated miRNA expression and function into GATA factor coordinated networks, and provided mechanistic insight into a regulatory circuit that comprised GATA1/2switch and miR-27a/24in erythropoiesis.