NKX6-3 in B-Cell Progenitor Differentiation and Leukemia.

Early B-cell development is primarily regulated at the transcriptional level and comprises the consecutive differentiation stages B-cell progenitor, pro-B-cell and pre-B-cell. These entities provide the cells of origin in B-cell precursor acute lymphoid leukemia (BCP-ALL) that show aberrations of developmental transcription factors (TFs), representing major oncogenic drivers. Analysis of physiological TFs in these developmental entities helps us to understand their normal and disturbed activities and regulatory connections. Here, we focused on NKL-subclass homeodomain TF NKX6-3, which is active in both normal B-cell progenitors and TCF3::PBX1 fusion gene-positive BCP-ALL cases. By performing siRNA-mediated knockdown and forced expression experiments in BCP-ALL model cell lines, we established a gene regulatory network for NKX6-3 together with TALE-class homeodomain TFs IRX1 and MEIS1, as well as ETS-TF SPIB. Importantly, NKX6-3 was activated by TCF3::PBX1, underlying their co-expression in BCP-ALL. Furthermore, comparative expression profiling analysis of public BCP-ALL patient data revealed TGFb-pathway in-hibitor CD109 as a downregulated target gene of NKX6-3. TGFb-signalling, in turn, enhanced NKX6-3 expression, indicating mutual activation. Finally, RNA-seq analysis of BCP-ALL cell line RCH-ACV after NKX6-3 knockdown revealed MPP7 as an upregulated target gene of both NKX6-3 and TCF3::PBX1, revealing a role for the HIPPO-pathway in B-cell progenitors and TCF3::PBX1-positive BCP-ALL. Collectively, our data introduce novel players and regulatory connections to normal and aberrant TF-networks in B-cell progenitors to serve as potential diagnostic markers or therapeutic targets.