Increased Reactive Oxygen Species Induced by NUP98-HOXD13 Fusion Gene in MDS Mouse Model

Abstract

The myelodysplastic syndromes (MDSs) comprise a group of pre-malignant hematologic disorders characterized by ineffective hematopoiesis, dysplasia, and transformation to acute myeloid leukemia (AML). The causative agents for de novo or therapy-related MDS (t-MDS) include exposure to known genotoxins, such as benzene and other solvents, anti-cancer chemotherapy, and ionizing radiation. It is known that MDS is closely related to chromosomal aberrations including deletions, amplifications, inversions, and translocations, however, the molecular mechanism of disease progression from MDS to AML not been completely elucidated. Recently, several studies have reported that oxidative stress contributes to the disease progression mechanism in MDS. Reactive oxygen species (ROS) play a role in regulating several biologic phenomena involving activation of signaling pathways in response to cytokines, and the gene expression induced by this signaling. ROS is also known to induce oxidative DNA damage which generates DNA base modifications and DNA helix alterations. Therefore, increased intracellular levels of ROS can induce mutations which lead to transformation of MDS to AML. A mouse model for MDS, generated by expressing a NUP98-HOXD13 (NHD13) fusion gene was exploited to investigate ROS levels in this study. Lineage negative (Linneg) bone marrow mononuclear cell (BMNC) from NHD13 mice with MDS had a 7.8±5.6 fold increased level of ROS compared with wild-type (WT) Linneg BMNC, while ROS levels of unfractionated BMNC were similar in NHD13 and WT mice. The increase ROS level in NHD13 Linneg BMNC was associated with an increase in G2/M phase (2 fold). Interleukin 3 (IL-3) dependent NHD13 ‘knock-in’ cell lines also showed an increased level of ROS (3 to 5 fold), in comparison with other IL-3 dependent cell lines, BaF3 and 32D. To determine if the increase in ROS could be generated by an NHD13 fusion, BaF3 and 32D cell were transfected with an NHD13 expression vector. The BaF3 and 32D transfectant showed 2 fold (2.1±0.3 and 1.9±0.6 fold) increase ROS level compared to controls transfected with an empty vector. These findings suggest that expression of an NHD13 fusion gene can induce ROS in hematopoietic progenitor cells, which may contribute to the development of MDS and subsequent disease progression to AML through DNA damages.