Regulation of the adaptor molecule LAT2, an in vivo target gene of AML1/ETO (RUNX1/RUNX1T1), during myeloid differentiation

Abstract

Summary The leukaemia‐specific fusion oncoprotein RUNX1/RUNX1T1 (AML1/ETO), resulting from the chromosomal translocation (8;21) in acute myeloid leukaemia (AML), imposes a striking genotype–phenotype relationship upon this distinct subtype of AML, which is mediated by multiple, co‐ordinate downstream effects induced by this chimeric transcription factor. We previously identified the LAT2 gene, encoding the adaptor molecule LAT2 (NTAL, LAB), which is phosphorylated by KIT and has a role in mast cell and B‐cell activation, as a target of the repressor activity of RUNX1/RUNX1T1. These results were confirmed and extended by demonstrating downregulation of the LAT2 protein in response to conditional RUNX1/RUNX1T1 expression, and its absence in primary AML with the t(8;21). In contrast, in a cohort of 43 AML patients, higher levels of LAT2 were associated with myelomonocytic features. Differentiation of HL‐60 and NB4 cells towards granulocytes by all trans‐retinoic acid (ATRA) resulted in downregulation of LAT2; conversely, it was upregulated during phorbol ester‐induced monocytic differentiation of HL‐60 cells. Forced expression of LAT2 in Kasumi‐1 cells resulted in a striking block of ATRA‐ and phorbol ester‐induced differentiation, implicating disturbances of the graded expression of this adaptor molecule in the maturation block of myeloid leukaemia cells.

The AML1/ETO target gene LAT2 interferes with differentiation of normal hematopoietic precursor cells

“…A delay of maturation was observed in the LAT2-overexpressing cells in comparison to the control cells (Fig. 2E), confirming our previous results on the induced myeloid differentiation of leukemia cell lines [14]. …”

“…LAT2 levels vary depending on the FAB subtypes, suggesting a dichotomy in the function of LAT2 in the granulocytic and monocytic lineage. Furthermore, the forced expression of LAT2 blocks all-trans retinoid acid (ATRA)- and phorbol ester (PMA)-induced myeloid differentiation [14]. …”

The HDAC class I-specific inhibitor entinostat (MS-275) effectively relieves epigenetic silencing of the LAT2 gene mediated by AML1/ETO

“…Employing a conditional AML1/ETO expression model based on an ecdysone-inducible system in myeloid U937 cells (9/14/ 18-U937 cells), we had identified LAT2 mRNA by complementary DNA-representational difference analysis as a strongly repressed transcript after 48 h of conditional expression of AML1/ETO (Fliegauf et al, 2004). This was confirmed by western blot (data not shown) and in a large series of primary AML blasts (Duque-Afonso et al, 2011).…”

“…After its phosphorylation and activation, LAT2 regulates several signalling pathways interacting with cytoplasmic partner proteins, including GRB2 (Brdicka et al, 2002;Stork et al, 2004) and CBL (Brdicka et al, 2002). Recently, we could show that, LAT2 inhibits the in vitro myeloid differentiation of AML1/ETO-positive cells (Duque-Afonso et al, 2011).…”

Genome-wide repression of eRNA and target gene loci by the ETV6-RUNX1 fusion in acute leukemia

“…We also investigated E/R targets between different RUNX1 fusions and observed LAT2 (linker for activation of T-cells family member 2), a signaling transmembrane protein, as a shared target for E/R and the RUNX1-RUNX1T1 fusion (Brdicka et al 2002;Janssen et al 2003;Duque-Afonso et al 2011a). In acute myeloid leukemia, binding of the RUNX1-RUNX1T1 fusion results in widespread alterations throughout the epigenome (Ptasinska et al 2012(Ptasinska et al , 2014.…”