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4116 A Patient-Derived EZH2 Mutant Induces MDS-like Diseases with Derepressed ABCG2 Expression in Mice

Myelodysplastic Syndromes – Basic and Translational Studies
Program: Oral and Poster Abstracts
Session: 636. Myelodysplastic Syndromes – Basic and Translational Studies: Poster III
Monday, December 7, 2015, 6:00 PM-8:00 PM
Hall A, Level 2 (Orange County Convention Center)

Kimihito Cojin Kawabata, MD, PhD1*, Daichi Inoue, MD, PhD1*, Jiro Kitaura, MD, PhD1,2*, Yuka Harada, MD, PhD3, Susumu Goyama, MD, PhD1, Hironori Harada, MD, PhD4, Hiroyuki Aburatani, MD, PhD5* and Toshio Kitamura, MD, PhD1

1Institute of Medical Science, Division of Cellular Therapy, The University of Tokyo, Tokyo, Japan
2School of Medicine, Juntendo University, Tokyo, Japan
3Department of Clinical Laboratory Medicine, Bunkyo Gakuin University, Tokyo, Japan
4Department of Hematology, Juntendo University School of Medicine, Tokyo, Japan
5Genome Science Division, Research Center for Advanced Science and Technology, The University of Tokyo, Tokyo, Japan

A histone H3 Lysine 27 (H3K27)-methyltransferase, enhancer of zeste homolog 2(EZH2) is known as a tumor-associated gene. Physiological role of EZH2 is an enzymatic component of polycomb repressive complex 2 (PRC2) to inhibit expression of target genes. While EZH2 plays oncogenic roles by repressing the expression of tumor suppressors in solid tumors and some lymphomas, it plays rather tumor-suppressive roles in myeloid malignancies. We have generated a short-form EZH2 that lacks the catalytic SET domain (EZH2-dSET). Using this EZH2 mutant we could produce serially transplantable MDS-like diseases. Microarray analysis using the MDS-like bone marrow cells enabled us to identify novel targets of EZH2 in MDS tumorigenesis, including ATP-binding cassette (ABC) transporters. Derepression of Abcg2 via decreased H3K27-trimethylation was confirmed. Retroviral transduction of EZH2-dSET to MDS-like cell lines increased surface ABCG2-high populations and those cells functioned to exclude anticancer drugs as expected. Intriguingly, with Abcg2 expression alone, primary bone marrow cells could produce an MDS-like cytopenic disease in our BMT model. In our clinical specimens, ABCG2 high expressions were observed in MDS samples but not in de novo AML and CML samples. In two MDS patients, ABCG2 expression decreased along with leukemic transformation. Interestingly, two out of 33 MDS patients with extremely high expression of ABCG2 harbored the same U2AF1 mutation (Q157P). In addition, somatic mutations of EZH2 and those of either U2AF1 or SRSF2 were mutually exclusive in all investigated cases. Interestingly, U2AF1 mutants (S34F and Q157P) reduced EZH2 expression, leading the derepression of ABCG2 via decreased H3K27-trimethylation. These results indicate a link between U2AF1 mutations and ABCG2 expression via disrupted EZH2. In conclusion, different mechanisms are supposed to converge at dysregulated EZH2 in MDS. And a short form of EZH2 upregulates ABCG2 expression resulting in MDS advancing to secondary leukemia. Thus, either mutations affecting the EZH2 function or mutations of EZH2 itself could play an important role in MDS, and one of the downstream targets of EZH2 suppression in MDS pathogenesis is aberrant expression of ABCG2.

Disclosures: No relevant conflicts of interest to declare.

*signifies non-member of ASH