Abstract 4005: The leukemia-associated fusion protein DEK-NUP214 induces proliferation through an mTOR-dependent mechanism

Abstract

Abstract Acute myeloid leukemia (AML) is characterized by the dysregulated proliferation and impaired differentiation of myeloid precursor cells. The majority of these leukemias harbor genetic translocations, which determine both the molecular mechanistics and the prognosis of the disease. The t(6;9)(p22;q34) chromosomal translocation is found in 1% of AML, where it is associated with young age and poor prognosis. The translocation occurs between specific introns in the gene DEK on chromosome 6 and the gene NUP214 on chromosome 9, creating the fusion gene DEK-NUP214. The role of DEK-NUP214 in leukemogenesis is still largely uncharacterized. To obtain an experimental model of the disease, we expressed the fusion gene in the myeloid cell line U937 and studied the phenotype of the stable clones. We show that cells expressing DEK-NUP214 proliferate faster and also sustain their proliferative capacity longer in culture than their normal counterparts. Cellular proliferation is regulated by a wide range of signaling pathways, but many converge on the activating phosphorylation of the mechanistic target of rapamycin (mTOR) at Ser2448. Western blot analysis of the clones revealed that cells expressing DEK-NUP214 have higher levels of both phosphorylated and total mTOR protein. To determine the effect on downstream cellular functions, we proceeded to study mTOR-dependent translation and metabolism. We performed a global translation assay where the incorporation of radioactively labeled amino acids into newly synthesized proteins reflects the rate of translation. The results show that cells expressing DEK-NUP214 have a markedly increased translation rate. Cellular metabolism was studied by measuring the consumption of glucose and the production of lactate in cell supernatant. We demonstrate that cells expressing DEK-NUP214 produce less lactate, despite equal glucose consumption and increased proliferation. In concordance with increased mTOR activity, our results suggest that cells expressing DEK-NUP214 shift their metabolism from glycolysis to oxidative phosphorylation. The increased activity of mTOR thus leads to translational and metabolic changes that could play a role in the leukemogenic effect of DEK-NUP214. Interestingly, proliferation induced by DEK-NUP214 is highly dependent on mTOR. Treatment with the mTOR inhibitor everolimus (RAD001) reduces the proliferation of the DEK-NUP214 cells to the level of the control cells, without affecting the control cells. This pivotal role of mTOR suggests that leukemias harboring the t(6;9)(p22;q34) translocation may be susceptible to treatment with either rapamycin or the novel mTOR inhibitors that are approaching the clinic. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4005. doi:10.1158/1538-7445.AM2011-4005