MiR-132 and MiR-212 as Regulators of WT1 and GATA2 in Acute Myeloid Leukemia.

Abstract 1283

Poster Board I-305

Wilms' tumor 1 (WT1) and GATA binding protein 2 (GATA2) transcription factors are highly expressed in hematopoietic stem cells and progenitors. Differentiation of precursor blood cells towards mature blood cells is accompanied by rapid downregulation of both transcription factors. Overexpression of WT1 has been observed in the majority of acute myeloid leukemia (AML) cases. Furthermore, in 10-15% of the AML cases mutations in the WT1 gene occur, which have been correlated with poor prognosis. Aberrant expression of GATA2 in AML has been described as well, but no mutations in this gene have been reported in AML so far. How the (aberrant) expression of WT1 and GATA2 is controlled is not completely clear. A regulatory role for microRNAs (miRNAs) has been described for several transcription factors which regulate hematopoiesis. MiRNAs negatively regulate gene expression by translational repression or degradation of target messenger RNAs (mRNAs). In the present study we investigated the interplay between miRNAs and transcription factors that are involved in myeloid development and malignant transformation towards AML. We studied the expression of 158 miRNAs in the APL cell line NB4 during induction of granulocytic differentiation with all-trans retinoic acid (ATRA). Quantitative PCR specific for mature miRNAs was performed (Applied Biosystems). Twenty out of 158 miRNAs were more than 10-fold upregulated upon differentiation induction with ATRA. MiR-132 and miR212, which are derived from the same pri-miRNA transcript, were most strongly upregulated during ATRA-induced granulocytic differentiation (1200- and 350-fold respectively at 96 hours after ATRA-stimulation). In vitro ATRA-induction of primary APL cells also resulted in upregulation of miR-132 and miR-212. Computational target prediction algorithms were used to identify transcription factors which may be targeted by miR-132 and miR-212. Subsequently, the expression pattern of the predicted targets was determined experimentally in NB4 cells before and after differentiation induction with ATRA using microarray-based mRNA profiling (Affymetrix). In addition, further verification of target gene expression during ATRA-induced differentiation was performed using quantitative PCR. The transcription factors WT1 and GATA2 were predicted as targets of miR-132 and miR-212 by two out of four different prediction programs that were used. Both transcription factors contained putative binding sites for miR-132 and miR-212 in their 3'UTR. When tested on microarray and by quantitative PCR, the expression of WT1 and GATA2 was indeed strongly downregulated during ATRA-induced granulocytic differentiation of NB4 cells (65- and 165-fold respectively at 96 hours after ATRA stimulation) as well as in primary leukemia cells derived from APL patients (30- and 10-fold respectively at 48 hours after ATRA-stimulation). During ATRA-induced differentiation the expression levels of WT1 were positively correlated with the expression levels of GATA2. In addition, WT1 expression was also strongly correlated with GATA2 expression in a cohort of 27 pre-treatment AML cases as well as in 7 healthy controls, suggesting that these genes might be co-regulated to a large extent. To directly prove that WT1 and GATA2 are indeed targeted by miR-132 and miR-212, we are currently performing lentiviral-based overexpression studies of both miRNAs to determine the effect on endogenous WT1 and GATA2 mRNA expression. MicroRNAs which target WT1 and GATA2 may be valuable tools in controlling the aberrant expression of WT1 and GATA2 observed in AML.