Transcriptional Modulation by the Zinc Finger Factor 423ß in Leukemogenesis at Childhood

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The acute lymphoblastic leukemia is the most common cancer of childhood. The underlying mechanisms of disease are incompletely understood including the maturation arrest as a general hallmark of acute leukemia. A variety of structural aberrations have been described in transcription factors directing B-lymphopoiesis that cause a differentiation arrest in progenitor cells such as in PAX5, IKZF1, and EBF-1. We have recently identified a perturbed epigenetic and transcriptional regulation of the zinc finger factor 423ß (ZNF423ß) as a novel mechanism hampering B-cell differentiation in ALL. In a combinatorial manner hypomethylation of ZNF423 enhancer sequences and BMP2 signaling lead to transactivation of ZNF423 whose ß-isoform encodes a nucleosome remodeling and histone deacetylase complex-interacting domain. ZNF423 and its murine homologue Zfp423 are physiologically expressed in embryonic stem cells and in the central nervous system during olfactory neurogenesis and cerebellar development, respectively, but they are absent in normal hematopoiesis. Aberrant expression of ZFN423 during lymphopoiesis results in disruption of the EBF-1 dependent transcriptional program at least in part through physical interaction between ZNF423 and EBF-1. To add another layer of regulatory complexity ZNF423 has been shown to direct bone morphogenetic protein 2-mediated signaling activity in a ternary SMAD1-SMAD4 transcription factor complex, which in turn is inhibited by EBF-1. Hence ZNF423 appears to operate in a mutually exclusive manner in independent BMP- and EBF-1 mediated reaction pathways. ETV6-RUNX1 rearranged ALL revealed a remarkably high ZNF423 and SMAD activity, which raises the question whether ZNF423 exerts its inhibitory effect on differentiation by sequestration of EBF-1, by transcriptional modulation of SMAD complexes or by yet unknown mechanisms. Furthermore, it will be of great interest to evaluate if aberrant ZNF423 constitutes a decisive momentum to induce frank leukemia in the context of ETV6-RUNX1, which is not leukemogenic in its own right.The research proposed herein aims at deciphering the mode of action of ZNF423 in B-precursor ALL integrating its protein-protein interaction with EBF-1 and SMAD1-SMAD4 complexes by genome-wide DNA binding studies of ZNF423 and EBF-1 complemented with transcriptome sequencing. Moreover, the impact of aberrant ZNF423ß on leukemogenesis will be studied in ETV6-RUNX1/Etv6-RUNX1 positive hematopoietic stem cells in vivo utilizing conditional knock-in/transplantation mouse models. In a reciprocal experiment we will assess the effect of ZNF423 depletion/deletion on the differentiation of ALL cells in vitro and in vivo.