The role of reactive oxygen species in differentiation of acute myeloid leukemia

Abstract

Development of acute myeloid leukemia (AML) involves dysregulation of myeloid key transcription factors that regulate hematopoietic differentiation. Although AML cells fail to undergo terminal differentiation naturally, they can be induced to differentiate by various chemical agents, such as phorbol 12-myristate 13-acetate (PMA). PMA initiates terminal differentiation by inducing cell cycle arrest and macrophage gene expression. Previous study demonstrated that ROS mediates the cell cycle arrest through activation of the MEK/ERK signaling pathway. However, the role of ROS in controlling macrophage gene expression remains unclear.

My study aims to study the role of ROS during PMA-induced AML terminal differentiation and to investigate the association of ROS with the key transcription regulators and signaling pathways that are involved in the macrophage differentiation process.

My results demonstrated that short period (2 hours) of PMA treatment is sufficient to differentiate leukemic U937 cells to macrophage, resulting in morphological change and increased expression of CD11b (macrophage surface marker). Addition of ROS scavenger N-acetyl-L-cysteine (NAC) after PMA treatment resulted in cell cycle arrest; nevertheless, the treated cells failed to differentiate, suggesting that ROS is also required in later stage of macrophage genes expression. It supports the idea that cell cycle arrest and macrophage gene expression are two cellular events that are regulated by different ROS-dependent signaling pathways.

In view of monocyte/macrophage differentiation can be triggered by transcription factor MAFB, PU.1 and its co-factor c-Jun. I investigated the role of ROS in controlling these transcription regulators. During PMA-induced differentiation of U937 cells, PU.1, JUN and MAFB were up-regulated. The up-regulation of these transcription regulators was reduced by NAC, suggesting that ROS abolish the PMA-induced differentiation by suppressing the expression of multiple transcription regulators.

JNK signaling is a ROS-dependent pathway that contributes to the stability of c-Jun. It also participates in the ROS-dependent differentiation process of hematopoietic progenitor in Drosophila. Therefore, I used JNK inhibitor to investigate the involvement of JNK signaling in PMA-induced differentiation. My results showed that the differentiation of U937 cells was impaired by JNK inhibitor, suggesting that JNK signaling is involved in the PMA-induced differentiation pathway. However, the correlation between JNK signaling and ROS in AML differentiation remains to be elucidated.

In conclusion, my study discovered a novel role of ROS in controlling key transcription regulators during AML differentiation. On the other hand, my study proposes the involvement of JNK signaling in the terminal differentiation process and provides a framework for further study of the detail mechanisms of ROS in terminal differentiation of AML.