The ZMYM2-FGFR1 (formerly known as ZNF198-FGFR1) fusion kinase induces stem cell leukemia-lymphoma syndrome (SCLL), a hematologic malignancy characterized by rapid transformation to acute myeloid leukemia and T-lymphoblastic lymphoma. In the present study, we demonstrate frequent, constitutive activation of Notch1 and its downstream target genes in T-cell lymphomas that arose in a murine model of ZMYM2-FGFR1 SCLL. Notch up-regulation was also demonstrated in human SCLL-and FGFR1OP2-
IntroductionStem cell leukemia-lymphoma syndrome (SCLL) 1 is an atypical myeloproliferative disease-associated lymphoma. 2 Hepatosplenomegaly is common in SCLL patients, and, except for some cases with B-cell acute lymphoblastic lymphoma, 3 most patients exhibit T-lymphoblastic lymphoma. The clinical course for SCLL is aggressive, with rapid transformation to acute myeloid leukemia (AML) and lymphoblastic lymphoma of common T-cell origin. [3][4][5] Conventional chemotherapy is often not effective, 3 making early allogeneic transplantation the only treatment. 6 The characteristic 8;13 reciprocal chromosome translocation 7 results in a chimeric protein consistently involving the fibroblast growth factor receptor-1 (FGFR1). 5 To date, ϳ 10 different gene partners have been shown to fuse to FGFR1, including ZMYM2, 4,7 CEP110, 8 and FGFR1OP, 9 among other more rare combinations. 10 In all cases, the fusion partner provides a dimerization domain for constitutive activation of FGFR1. ZMYM2-FGFR1 is the most common translocation, in which the zinc-finger-containing N-terminal part of ZMYM2 enables dimerization of FGFR1. 4 The FGFR1 rearrangement can be found in both myeloid and lymphoid cells in SCLL patients, suggesting a multipotent hematopoietic progenitor cell origin. Constitutive activation and mislocalization of the FGFR1 kinase leads to abnormal phosphorylation of downstream proteins such as PLC␥, PI3K, and various members of the STAT family of transcription factors. [11][12][13] We described previously a mouse model of ZMYM2-FGFR1 SCLL that closely resembles the clinical characteristics of patients with the ZMYM2-FGFR1 translocation, having a distinct myeloproliferative disorder and severe T-lymphoblastic leukemia. The constitutive and ligand-independent activation of the FGFR1 signal transduction pathway is believed to be essential for disease pathogenesis. [13][14] Evidence of tumor oligoclonality and normal differentiation of thymocytes in these animals, however, indicates that additional genetic alterations are required for disease development and progression. Array comparative genomic hybridization demonstrated Tcra and Tcrd gene deletion in leukemic cells in these animals. Lymphomas were CD4 ϩ /CD8 ϩ double-positive (DP), representing an arrest in the late stages of T-cell development, because rearrangement of Tcra is critical for these final maturation stages. However, because Tcra-null mice do not develop T-cell lymphoma, [15][16] it is clear that deletion of Tcra in itself is also not sufficient to induce T-lymphoblastic ly...