Abstract
The ETV6/RUNX1 (E/R) gene fusion is generated by the t(12;21) and found in approximately 25% of childhood B-cell precursor acute lymphoblastic leukemia. In contrast to the overwhelming evidence that E/R is critical for the initiation of leukemia, its relevance for the maintenance of overt disease is less clear. To investigate this issue, we suppressed the endogenous E/R fusion protein with lentivirally transduced short hairpin RNA in the leukemia cell lines REH and AT-2, and found a distinct reduction of proliferation and cell survival. In line with the observed concurrent inactivation of the phosphoinositide 3-kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) pathway, pharmacological inhibition diminished the phosphorylation of AKT and ribosomal protein S6, and significantly increased the apoptosis rate in E/R-positive leukemias. Moreover, PI3K/mTOR inhibitors sensitized glucocorticoid-resistant REH cells to prednisolone, an observation of potential relevance for improving treatment of drug-resistant relapses. Of note, knockdown of the E/R fusion gene also severely impaired the repopulation capacity of REH cells in non-obese deficient/severe combined immunodeficient mice. Collectively, these data demonstrate that the E/R fusion protein activates the PI3K/AKT/mTOR pathway and is indispensible for disease maintenance. Importantly, these results provide a first rationale and justification for targeting the fusion gene and the PI3K/AKT/mTOR pathway therapeutically.
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Acknowledgements
We thank patients and their parents as well as physicians involved in this study. We like to acknowledge Veronika Sexl for support with xenograft mouse models, Andishe Attarbaschi for providing patient samples, Angela Schumich for assistance in flow cytometric analyses, Ruth Joas for support in quantitative real-time polymerase chain reaction, Ulrike Pötschger for help with statistics and Marion Zavadil for proofreading. This work was supported by the Austrian National Bank ÖNB (12213 and 13466), the St Anna Kinderkrebsforschung and GENAU-CHILD Projekt (GZ200.136/1–VI/1/2005) to RP-G.
AUTHOR CONTRIBUTIONS
GF designed and performed research, compiled data and drafted the manuscript. RG, AI, GK and UK carried out additional experimental work. HPK, EB and DS were responsible for mouse experiments, MK conducted bioinformatic analyses, MND assisted in phospho-flow stainings, OAH interpreted data and wrote the manuscript and RP-G conceived the study, analyzed and interpreted data and wrote the manuscript. All authors read and approved the manuscript.
Deposition of microarrays: Microarray data are available online at GEO (www.ncbi.nlm.nih.gov/geo/, accession number GSE29639).
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Fuka, G., Kantner, HP., Grausenburger, R. et al. Silencing of ETV6/RUNX1 abrogates PI3K/AKT/mTOR signaling and impairs reconstitution of leukemia in xenografts. Leukemia 26, 927–933 (2012). https://doi.org/10.1038/leu.2011.322
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DOI: https://doi.org/10.1038/leu.2011.322
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