Tissue and differentiation stage specific expression of CALM/AF10 is required for leukemogenesis

The translocation t(10,11)(p13;q14) resulting in the formation of the CALM/AF10 fusion gene is involved in various hematological malignancies including acute myeloid leukemia, T-cell acute lymphoblastic leukemia, and malignant lymphoma and is usually associated with poor prognosis. We established a knock-in mouse model allowing tissue-specific CALM/AF10 expression from the Rosa26 locus using a loxP-STOP-loxP cassette to study leukemic transformation by the CALM/AF10 fusion protein during hematopoiesis. vav-Cre induced pan-hematopoietic expression of the CALM/AF10 fusion gene led to acute leukemia with a median latency of 12 months. Leukemias were either myeloid or had myeloid feature and showed expression of the B cell marker B220. Gene expression profiling of leukemic bone marrow cells revealed the overexpression of Hoxa cluster genes and the Hox co-factor Meis1. The long latency to leukemia development suggested that additional, collaborative genetic lesions are required. We identified an average of 2 to 3 additional mutations per leukemia using whole-exome sequencing. When CALM/AF10 was expressed in the B lymphoid compartment using mb1-Cre or CD19-Cre inducer lines no leukemia development was observed. Our results indicate that CALM/AF10 needs to be expressed from the stem or early progenitor cell stage onward to permit the acquisition of additional mutations required for leukemic transformation.

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Dutta S, Krause A, Vosberg S, Herold T, Ksienzyk B, Quintanilla-Martinez L, Tizazu B, Chopra M, Graf A, Krebs S, Blum H, Greif PA, Vetter A, Metzeler K, Rothenberg-Thurley M, Schneider MR, Dahlhoff M, Spiekermann K, Zimber-Strobl U, Wolf E, Bohlander SK