PS993 DE NOVO ADULT ACUTE MYELOID LEUKEMIA PATIENTS DISPLAY AT DIAGNOSIS FUNCTIONAL DEREGULATION OF REDOX BALANCE CORRELATED WITH MOLECULAR SUBTYPES AND OVERALL SURVIVAL
Authors: J. Mondet, C. Lo Presti, C. Garrel, K. Skaare, C. Mariette, S. Carras, M. Carré, S. Park, C.-E. Bulabois, L. Molina, R. Gressin, A. Thiebaut, S. Courby, N. Socoro-Yuste, P. Faure, A. Mc Leer-Florin, J.-Y. Cahn, P. Mossuz
Journal: HemaSphere (2019)

Background: The Musashi 2 (MSI2) gene belongs to an RNA-binding protein family, which bind to target mRNAs and posttranscriptionally regulate them. MSI2 is recently emerging as a potent oncogene in human leukemia including chronic myeloid leukemia (CML) with translocation t (7;17) and acute myeloid leukemia (AML) with translocation t(10;17). To understand the function of this protein, it is important to identify the bound and regulated targets of MSI2. Previously, we identified several targets of MSI2 using PAR-CLIP. One of the most highly regulated targets includes BACH1/BRIP1 protein. The protein encoded by this gene is a DNA-dependent ATPase and 5’ to 3’ DNA helicase required for the maintenance of chromosomal stability. This gene is predicted to be a target of germline cancer-inducing mutations. Moreover, BACH1/BRIP1 plays a role in protecting cells from oxidative stress response. However, the functional consequences of the interplay between BACH1/BRIP1 and MSI2 remain unclear. Aims: The objective of this study was to establish the relationship between MSI2 and BACH1/BRIP1 and the significance of this interplay in the context of leukemia. Methods: We applied PAR-CLIP on MSI2 in our previous study and identified 116 targets bound and regulated by this gene. Among these targets, BACH1/BRIP1 was one of the most highly regulated genes, which was further analyzed via luciferase assays, knockdown experiments coupled to NGS und further functional studies. Results: To functionally validate the interaction predicted from the high throughput sequencing (PAR-CLIP), we performed knockdown studies and noticed that BACH1/BRIP1 was significantly upregulated upon MSI2 KD and vice-versa upregulation of MSI2 downregulated BACH1/BRIP1 expression. The half-life of BACH1/BRIP1 significantly increased upon decreased MSI2 expression indicating that MSI2 regulates the stability of the BACH1/BRIP1 mRNA transcript. Next, we confirmed the direct binding of these two proteins by means of luciferase assays and mobility shift assays. It is already known that cells are protected from oxidative stress when BACH1/BRIP1 is overexpressed. Therefore, we investigated, if downregulation of MSI2 had a similar effect on the cells (H2-DCFDA assay). We induced oxidative stress to MSI2 downregulated cells by treating the cells with hydrogen peroxide and noticed that these cells were indeed more resistant to oxidative stress compared to control cells. This shows that the regulation of BACH1/BRIP1 by MSI2 also affects the oxidative stress responses of the cells. Since BACH1/BRIP1 is important for genomic stability, its downregulation in several leukemias could also render genetic instability to the cells. Further functional studies on the BACH1/BRIP1 – MSI2 interaction are ongoing. Taken together our study identified MSI2 as an important transcriptional regulator of BACH1/BRIP1 and the full elucidation of the interaction between these two genes will shed further light on the oncogenic activity of MSI2. Summary/Conclusion: Our study identified a BACH1/BRIP1 as a novel target of oncogenic Musashi protein (MSI2). MSI2 binds and regulates the expression of this gene and their interaction affects the oxidative stress responses of the cells.