PIWIL4 Acts as a piRNA Binding, Epigenetically Active and Growth Regulatory Protein in Human Acute Myeloid Leukemia

Piwi proteins are critically important for maintaining the self-renewing stem cell population in lower organisms through epigenetic silencing of transposable elements via DNA methylation and H3K9me3 marks, in close interaction with a novel class of non-coding RNA called piwi interacting RNA (piRNA)

VENTX induces expansion of primitive erythroid cells and contributes to the development of acute myeloid leukemia in mice

Homeobox genes are key regulators in normal and malignant hematopoiesis. The human Vent-like homeobox gene VENTX, a putative homolog of the Xenopus laevis Xvent-2 gene, was shown to be highly expressed in normal myeloid cells and in patients with acute myeloid leukemia. We now demonstrate that constitutive expression of VENTX suppresses expression of genes responsible for terminal erythroid differentiation in normal CD34(+) stem and progenitor cells. Transplantation of bone marrow progenitor cells retrovirally engineered to express VENTX caused massive expansion of primitive erythroid cells and partly acute erythroleukemia in transplanted mice. The leukemogenic potential of VENTX was confirmed in the AML1-ETO transplantation model, as in contrast to AML1-ETO alone co-expression of AML1-ETO and VENTX induced acute myeloid leukemia, partly expressing erythroid markers, in all transplanted mice. VENTX was highly expressed in patients with primary human erythroleukemias and knockdown of VENTX in the erythroleukemic HEL cell line significantly blocked cell growth. In summary, these data indicate that VENTX is able to perturb erythroid differentiation and to contribute to myeloid leukemogenesis when co-expressed with appropriate AML oncogenes and point to its potential significance as a novel therapeutic target in AML

MEIS2 Is an Oncogenic Partner in AML1-ETO-Positive AML

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The leukemogenicity of Hoxa9 depends on alternative splicing.

Although the transforming potential of Hox genes is known for a long time, it is not precisely understood to which extent splicing is important for the leukemogenicity of this gene family. To test this for Hoxa9, we compared the leukemogenic potential of the wild-type Hoxa9, which undergoes natural splicing, with a full-length Hoxa9 construct, which was engineered to prevent natural splicing (Hoxa9FLim). Inability to undergo splicing significantly reduced in vivo leukemogenicity compared to Hoxa9-wild-typed. Importantly, Hoxa9FLim could compensate for the reduced oncogenicity by collaborating with the natural splice variant Hoxa9T, as co-expression of Hoxa9T and Hoxa9FLim induced AML after a comparable latency time as wild-type Hoxa9. Hoxa9T on its own induced AML after a similar latency as Hoxa9FLim, despite its inability to bind DNA. These data assign splicing a central task in Hox gene mediated leukemogenesis and suggest an important role of homeodomain-less splice variants in hematological neoplasms

Aml1-eto collaborates with the homeobox genes meis1 and meis2 in inducing aml

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