A hematopoietic-specific transmembrane protein, Art-1, is possibly regulated by AML1

The functions of AML1 in hematopoietic differentiation are repressed by AML1-mutants including the AML1/ETO chimeric protein, which is seen in t(8;21) acute myeloid leukemia. Erythroid progenitors of the patients with t(8;21) AML expressed AML1/ETO. To investigate the effect of AML1/ETO in erythroid cells, we made a tetracycline-regulated AML1/ETO overexpression system in mouse erythroleukemic (MEL) cells. Enforced AML1/ETO repressed the terminal erythroid differentiation. Furthermore, we performed representational difference analysis using this MEL cell system to clone the downstream targets of AML1 in erythroid cell differentiation. We cloned a novel transmembrane protein, Art-1 (AML1-regulated transmembrane protein 1), which is a member of tetramembrane spanning superfamily. Art-1 expression was restricted in hematopoietic cells. It was upregulated by AML1 and downregulated by AML1/ETO in both erythroid and myeloid cells, and increased during erythroid cell differentiation. Art-1 may play an important role in the differentiation of erythroid cells, possibly as a direct downstream target of AML1.     

ETO, but not leukemogenic fusion protein AML1/ETO, augments RBP-Jkappa/SHARP-mediated repression of notch target genes

Notch is a transmembrane receptor that determines cell fates and pattern formation in all animal species. After specific ligand binding, the intracellular part of Notch is cleaved off and translocates to the nucleus, where it targets the DNA binding protein RBP-Jkappa. In the absence of Notch, RBP-Jkappa represses Notch target genes by recruiting a corepressor complex. We and others have previously identified SHARP as one component of this complex. Here, we show that the corepressor ETO as well as the leukemogenic fusion protein AML1/ETO directly interacts with SHARP, that ETO is part of the endogenous RBP-Jkappa-containing corepressor complex, and that ETO is found at Notch target gene promoters. In functional assays, corepressor ETO, but not AML1/ETO, augments SHARP-mediated repression in an histone deacetylase-dependent manner. Furthermore, either the knockdown of ETO or the overexpression of AML1/ETO activates Notch target genes. Therefore, we propose that AML1/ETO can disturb the normal, repressive function of ETO at Notch target genes. This activating (or derepressing) effect of AML1/ETO may contribute to its oncogenic potential in myeloid leukemia.     

Targeting miR‐193a‐AML1‐ETO‐β‐catenin axis by melatonin suppresses the self‐renewal of leukaemia stem cells in leukaemia with t (8;21) translocation

AML1‐ETO, the most common fusion oncoprotein by t (8;21) in acute myeloid leukaemia (AML), enhances hematopoietic self‐renewal and leukemogenesis. However, currently no specific therapies have been reported for t (8;21) AML patients as AML1‐ETO is still intractable as a pharmacological target. For this purpose, leukaemia cells and AML1‐ETO‐induced murine leukaemia model were used to investigate the degradation of AML1‐ETO by melatonin (MLT), synthesized and secreted by the pineal gland. MLT remarkedly decreased AML1‐ETO protein in leukemic cells. Meanwhile, MLT induced apoptosis, decreased proliferation and reduced colony formation. Furthermore, MLT reduced the expansion of human leukemic cells and extended the overall survival in U937T‐AML1‐ETO‐xenografted NSG mice. Most importantly, MLT reduced the infiltration of leukaemia blasts, decreased the frequency of leukaemia stem cells (LSCs) and prolonged the overall survival in AML1‐ETO‐induced murine leukaemia. Mechanistically, MLT increased the expression of miR‐193a, which inhibited AML1‐ETO expression via targeting its putative binding sites. Furthermore, MLT decreased the expression of β‐catenin, which is required for the self‐renewal of LSC and is the downstream of AML1‐ETO. Thus, MLT presents anti‐self‐renewal of LSC through miR‐193a‐AML1‐ETO‐β‐catenin axis. In conclusion, MLT might be a potential treatment for t (8;21) leukaemia by targeting AML1‐ETO oncoprotein.     

Inducible chromosomal translocation of AML1 and ETO genes through Cre/loxP-mediated recombination in the mouse

Transgenic mice have been used to explore the role of chromosomal translocations in the genesis of tumors. But none of these efforts has actually involved induction of a translocation in vivo. Here we report the use of Cre recombinase to replicate in vivo the t(8;21) translocation found in human acute myeloid leukemia (AML). As in the human tumors, the murine translocation fuses the genes AML1 and ETO. We used homologous recombination to place loxP sites at loci that were syntenic with the break points for the human translocation. Cre activity was provided in mice by a transgene under the control of the Nestin promoter, or in cultured B cells by infecting with a retroviral vector encoding Cre. In both instances, Cre activity mediated interchromosomal translocations that fused the AML1 and ETO genes. Thus, reciprocal chromosomal translocations that closely resemble rearrangements found in human cancers can be achieved in mice.