<Originals> Trib1 and Trib2 inhibit granulocytic differentiation by suppressing Akt pathway

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[Abstract] Background :Overexpression of Tribbles homolog 1 (Tribl) and Tribbles homolog 2 (Trib2) in hematopoietic stem/progenitor cells evokes acute myeloid leukemia (AML) in murine transplantation models. Degradation of CCAAT-enhancer-binding-protein α (C/EBPα) plays a crucial role in Trib1 or Trib2-induced AML. However, because C/EBPα knockout mice do not develop AML, it is likely that Trib1 and Trib2 influence other signaling pathways besides C/EBPα. Elevated Akt phosphorylation is considered to contribute to the development of AML. In contrast, two groups recently reported that reduced Akt activity is involved in the pathogenesis of leukemia. We performed this study to reveal the role of Akt signaling in Trib family-induced AML.Methods : G-CSF-induced granulocytic differentiation of 32D cells was assessed morphologically and phenotypically. G-CSF-induced signaling wasassessed by Westernblotting. Results : Overexpression of Trib1 or Trib2 inhibited GCSF-induced granulocytic differentiation of 32D cells, which was accompanied by reduced Akt phosphorylation. Also, an Akt inhibitor API-2 blocked G-CSF-induced granulocytic differentiation independently of C/EBPα degradation.　Furthermore, retroviral C/EBPα restoration did not completely abolish the differentiation block caused by Trib1 and Trib2. Conclusion :Trib1 and Trib2 block granulocytic differentiation, at least partially, by suppressing Akt phosphorylation.

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