Abstract 2824: Charting the landscape of genomic instability in acute myeloid leukemia: Interaction between G-quadruplexes and heme oxygenase-1 in leukemia

Abstract Genomic instability contributes to the development and expansion of acute myeloid leukemia (AML). Therefore, identification of factors pivotal for the genome integrity is essential for basic science and translational medicine. We propose that interplay between G-quadruplexes (G4) and heme oxygenase-1 (HO-1) affects the response to DNA damage and switch from normal to malignant hematopoiesis. AML is associated with chromosomal translocations as well as single point mutations. The risk of mutagenesis is increased by guanine-rich DNA sequences, folding into G-quadruplexes (G4), which can abrogate the replication. In inorganic solutions G4 are stabilized by heme. Whether such stabilization occurs in the living cells and how it affects mutagenesis' rate have not been tested so far. Cellular heme is removed by heme oxygenase-1 (HO-1), which evokes differential effects depending on subcellular localization. Here we assessed the impact of HO-1 in conjunction with G4 on genomic instability of AML. To address the function of HO-1 in leukemia we established the MOLM13 cell line engineered to knock-down (KD) HO-1. Rescue studies were performed with wild type (WT) and nuclear export signal (NES)-containing HO-1 constructs. Ex vivo assays were done with murine and human bone marrow cells. Cellular localization of HO-1 and G4 was determined by immunofluorescence in hematopoietic stem and progenitor cells (HSPCs). Co-localization of HO-1 and G4 was further assessed by proximity ligation assay (PLA). DNA damage and viability were determined at the steady state and in response to doxorubicin. Finally, association of HO-1 expression with mutational status and progression of AML was evaluated in cohort of 80 control and AML patients. We demonstrated that in HSPCs HO-1 localizes mainly in the nucleus. In stem cells its expression is low and increases upon differentiation, with the highest amount in the myeloid progenitors. Immunostaining confirmed the presence of G4, relatively scarce in stem cells but more numerous in granulocyte-macrophage progenitors. Importantly, we found for the first time that HO-1 co-localizes with G4 and that it can regulate the abundance of DNA damage at the steady state, with HO-1 KD resulting in increased phosphorylation of histone H2AX, marker of double strand DNA breaks. Strikingly, doxorubicin treatment increased not only DNA damage but also expression of HO-1. Accordingly, in AML patients we found a correlation between lower HO-1 expression, higher incidence of FLT3 mutations and the dismal prognosis. HO-1 protein is present in the nucleus of hematopoietic and leukemic cells, where it can co-localize with G-quadruplexes and evoke important functional effects. HO-1 expression is associated with clinical outcome of AML and with FLT3 mutation rate. Citation Format: Anna Konturek-Ciesla, Anette Radziszewska, Maciej Cieśla, Alicja Czmoczek, Monika Zukowska, Jozef Dulak, Alicja Jozkowicz, Karolina Bukowska-Strakova. Charting the landscape of genomic instability in acute myeloid leukemia: Interaction between G-quadruplexes and heme oxygenase-1 in leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2824.