MicroRNA hsa-mir-155 Blocks Myeloid and Erythroid Differentiation of Human CD34+ Cells.

In a large microRNA-array and bioinformatics study, we determined all of the microRNAs (miRs) expressed by human CD34+ hematopoietic stem-progenitor cells (HSPCs) from bone marrow and G-CSF mobilized blood. When we combined miR expression data, mRNA expression data from a previous study (Georgantas et al, Cancer Research 64:4434), and data from various published miR-target prediction algorithms, we were able to bioinformaticly predict the actions of miRs within the hematopoietic system. MircoRNA hsa-mir-155 was highly expressed in CD34+ HSPCs, and was predicted by our bioinformatics database to target several HSPC-expressed mRNAs (CREBBP, CXCR4, Jun, Meis-1, PU.1, AGTRI, AGTRII, Fos, and GATA3) that encode proteins known to be involved in myeloid and/or erythroid differentiation. We used luciferase-3′UTR reporter constructs to confirm that protein expression from these mRNAs were in fact down regulated by microRNA. As an initial test of mir-155′s effect on hematopoietic differentiation, K562 cells were transduced with hsa-mir-155 lentivirus and then exposed to TPA to induce megakaryocyte differentiation, or to hemin to induce erythroid differentiation. Compared to controls, miR-155 reduced K562 megakaryocyte differentiation by ~70%, and erythroid differentiation by >90%. Thus, mir-155 appears to be sufficient to inhibit both megakayrocyte and erythroid differentiation. K562 proliferation was not affected by mir-155, showing that the differentiation block was not due to cell cycle arrest. MicroRNA hsa-mir-155-transduced human mobilized blood CD34+ cells generated >70% fewer myeloid and erythroid colonies than controls in colony forming (CFC) assays, further indicating that mir-155 blocks both myeloid and erythroid differentiation. We are currently further testing the effects of mir-155 on differentiation of CD34+ cells in vitro, and also in vivo on their ability to engraft immunodeficient mice.