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Cancer Res. 2019 Aug 1;79(15):3862-3876. doi: 10.1158/0008-5472.CAN-18-3215. Epub 2019 Jun 7.

An ERG Enhancer-Based Reporter Identifies Leukemia Cells with Elevated Leukemogenic Potential Driven by ERG-USP9X Feed-Forward Regulation.

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Department of Pathology, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel.
Department of Pediatric Hemato-Oncology, Schneider Children Medical Center Petah-Tikva, Israel.
The Gene Development and Environment Pediatric Research Institute, Pediatric Hemato-Oncology, Edmond and Lily Safra Children's Hospital, Sheba Medical Center, Tel Hashomer, Ramat Gan, Israel.
Department of Molecular Human Genetics and Biochemistry, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel.
Princess Margaret Cancer Centre, University Health Network and Department of Molecular Genetics, University of Toronto, Toronto, Ontario, Canada.
Department of Pathology, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel.
Contributed equally


Acute leukemia is a rapidly progressing blood cancer with low survival rates. Unfavorable prognosis is attributed to insufficiently characterized subpopulations of leukemia stem cells (LSC) that drive chemoresistance and leukemia relapse. Here we utilized a genetic reporter that assesses stemness to enrich and functionally characterize LSCs. We observed heterogeneous activity of the ERG+85 enhancer-based fluorescent reporter in human leukemias. Cells with high reporter activity (tagBFPHigh) exhibited elevated expression of stemness and chemoresistance genes and demonstrated increased clonogenicity and resistance to chemo- and radiotherapy as compared with their tagBFPNeg counterparts. The tagBFPHigh fraction was capable of regenerating the original cellular heterogeneity and demonstrated increased invasive ability. Moreover, the tagBFPHigh fraction was enriched for leukemia-initiating cells in a xenograft assay. We identified the ubiquitin hydrolase USP9X as a novel ERG transcriptional target that sustains ERG+85-positive cells by controlling ERG ubiquitination. Therapeutic targeting of USP9X led to preferential inhibition of the ERG-dependent leukemias. Collectively, these results characterize human leukemia cell functional heterogeneity and suggest that targeting ERG via USP9X inhibition may be a potential treatment strategy in patients with leukemia. SIGNIFICANCE: This study couples a novel experimental tool with state-of-the-art approaches to delineate molecular mechanisms underlying stem cell-related characteristics in leukemia cells.

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