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BCR/ABL and Other Kinases from Chronic Myeloproliferative Disorders Stimulate Single-Strand Annealing, an Unfaithful DNA Double-Strand Break Repair

Departments of ¹ Microbiology and Immunology and ² Biology, Temple University, Philadelphia, Pennsylvania; ³ Terry Fox Laboratory, British Columbia Cancer Agency, Vancouver, British Columbia, Canada; and ⁴ 2nd Department of Internal Medicine, Oncology and Hematology, Robert Bosch Hospital, Stuttgart, Germany

Requests for reprints: Tomasz Skorski, Department of Microbiology and Immunology, School of Medicine, Temple University, MRB, Room 548A, 3400 North Broad Street, Philadelphia, PA 19140. Phone: 215-707-9157; Fax: 215-707-9160; E-mail: tskorski{at}temple.edu.

Key Words: SSA • FTK • leukemia • genomic instability

Myeloproliferative disorders (MPD) are stem cell–derived clonal diseases arising as a consequence of acquired aberrations in c-ABL, Janus-activated kinase 2 (JAK2), and platelet-derived growth factor receptor (PDGFR) that generate oncogenic fusion tyrosine kinases (FTK), including BCR/ABL, TEL/ABL, TEL/JAK2, and TEL/PDGFβR. Here, we show that FTKs stimulate the formation of reactive oxygen species and DNA double-strand breaks (DSB) both in hematopoietic cell lines and in CD34⁺ leukemic stem/progenitor cells from patients with chronic myelogenous leukemia (CML). Single-strand annealing (SSA) represents a relatively rare but very unfaithful DSB repair mechanism causing chromosomal aberrations. Using a specific reporter cassette integrated into genomic DNA, we found that BCR/ABL and other FTKs stimulated SSA activity. Imatinib-mediated inhibition of BCR/ABL abrogated this effect, implicating a kinase-dependent mechanism. Y253F, E255K, T315I, and H396P mutants of BCR/ABL that confer imatinib resistance also stimulated SSA. Increased expression of either nonmutated or mutated BCR/ABL kinase, as is typical of blast phase cells and very primitive chronic phase CML cells, was associated with higher SSA activity. BCR/ABL-mediated stimulation of SSA was accompanied by enhanced nuclear colocalization of RAD52 and ERCC1, which play a key role in the repair. Taken together, these findings suggest a role of FTKs in causing disease progression in MPDs by inducing chromosomal instability through the production of DSBs and stimulation of SSA repair. [Cancer Res 2008;68(17):6884–8]