The G-CSF Induced MiR-143 Targets MAPK-Family Proteins and Is a Prognostic Factor for RIC-Transplanted AML Patients

Acute myeloid leukemia (AML) is a heterogeneous clonal disorder of defective hematopoiesis of white blood cells and often characterized by limited treatment options and a poor prognosis. MicroRNAs, a class of small non-coding RNAs, have been reported over the last years to play an important role in the regulation of “normal” and pathological processes. By binding to the 3`UTR of their target mRNAs, microRNAs lead to the translational repression of their target gene. Deregulation of a certain microRNA thereby may lead to disrupted signal pathways, such as MAPK-signaling, and to tumorigenesis. However, the role of microRNAs in hematopoietic differentiation and blood cancer development remains largely unknown. In AML only few miRNAs are functionally characterized, and the clinical relevance of these miRNAs still remains to be determined. In this study we identified microRNA-143 (miR-143) to be highly upregulated in G-CSF stimulated CD34+ cells. We could also show the granulopoietic association of miR-143 in several hematopoietic cell line models. In addition, we show that miR-143 is upregulated in APL patients after ATRA treatment. QPCR analysis of pri-miR-143 expression in RIC (reduced intensity conditioning) transplanted AML patients reveal that high expression of miR-143 is associated with high event-free and overall survival. In functional studies, stable overexpression of miR-143 in K562-C/EBPα-p42 cells enhances the C/EBPalpha induced granulocytic differentiation significantly. In contrast, stable knock down of miR-143 reduced the ability of K562-C/EBPα-p42 cells to undergo granulocytic differentiation upon β-estradiol treatment. Moreover, chromatinimmunoprecipitation (ChIP) analysis show the direct binding of C/EBPα to the promoter region of miR-143. By in silico prediction, we found MAPK protein family members (MAPK1, MAPK3 and MAPK7) as predicted targets of miR-143. Western blot analysis of AML patient samples and G-CSF stimulated CD34+ cells clearly show an inverse correlation of miR-143 and MAPK7 (ERK5) protein expression. By transient overexpression of miR-143 we could show a strong downregulation of MAPK protein family member expression in NB4 cells. These studies suggest miR-143 as an essential factor in granulocytic differentiation driven by G-CSF. Deregulation of miR-143 may play an important role in the development of AML. Furthermore, we propose miR-143 as prognostic marker for AML patients undergoing RIC transplantation therapy.