Hypoxia-inducible factor-1α-induced differentiation of myeloid leukemic cells is its transcriptional activity independent

Hypoxia or hypoxia mimetic has been shown to induce differentiation together with the accumulation of hypoxia-inducible factor-1 alpha (HIF-1 alpha) protein of myeloid leukemic cells and normal hematopoietic progenitors. To provide direct evidence for the role of HIF-1 alpha in acute myeloid leukemia (AML) cell differentiation and its mechanisms, we generated myeloid leukemic U937T transformants, in which HIF-1 alpha was tightly induced by tetracycline withdrawal. The results showed that the conditional HIF-1 alpha induction triggered granulocytic differentiation of these transformants, while the suppression of HIF-1 alpha expression by specific short hairpin RNAs (shRNAs) effectively inhibited hypoxia-induced differentiation of U937 cells, as evidenced by morphology, maturation-related antigens as well as expressions of myeloid differentiation signatures and hematopoietic cells- specific cytokine receptors. The specific shRNAs-inhibited expression of HIF-1 beta, an essential partner for transcription activity of HIF-1 alpha failed, while the inhibition of hematopoietic differentiation-critical CCAAT/enhancer-binding protein-a (C/EBPa) significantly eliminated HIF-1 alpha-mediated myeloid leukemic cell differentiation. Collectively, this work provided several lines of direct evidence for the role of HIF-1 alpha protein through its nontranscriptional activity in myeloid cell differentiation, in which C/EBP alpha elicitsa role as an effector downstream to HIF-1 alpha. These discoveries would shed new insights for understanding mechanisms underlying leukemogenesis and designing the new therapeutic strategy for differentiation induction of AML.