Abstract
The NUP98 gene is located at chromosome 11p15 and encodes the 98 kd component of the nuclear pore complex; this protein normally functions as a docking protein involved in nucleocytoplasmic transport. NUP98 is fused to at least 15 different partner genes by chromosomal translocation in a wide spectrum of hematological malignancies including acute myeloid leukemia (AML), myelodysplastic syndrome (MDS), chronic myelogenous leukemia (CML), and pre-T lymphoblastic leukemia (pre-T LBL). Over half of the known NUP98 gene fusions involve fusions to a HOX family member; these fusions invariably retain the amino terminal FG repeats of NUP98 and the homeodomain DNA-binding region of the HOX partner. The NUP98-HOXD13 fusion was initially identified in a patient with MDS that subsequently transformed to erythroleukemia, and has subsequently been identified in AML M1 and M2 patients as well. To model this disease in vivo, we generated transgenic mice which expressed the NUP98-HOXD13 (NHD13) fusion from vav regulatory elements.
The NHD13 transgene is ubiquitously expressed in hematopoietic tissues such as thymus, spleen, and bone marrow, and is not expressed in other tissues. Serial CBCs from clinically healthy mice aged 4–7 months demonstrated a progressive neutropenia, lymphopenia, anemia, and macrocytosis. Peripheral blood smears showed signs of dysplasia including giant platelets and hypersegmented neutrophils; bone marrow exam showed an increase number of dysplastic binucleate erythroblasts and increased apoptosis, consistent with a diagnosis of MDS. 10/10 (100%) of the NHD13 mice died of hematologic disease by 14 months of age; in contrast, none of the non-transgenic control littermates developed evidence of hematologic disease. We classified the hematologic diseases according to the Bethesda proposals. Three mice died with MDS, two mice had pre-T LBL, two had acute undifferentiated leukemia, one had megakaryocytic leukemia, one had myeloid leukemia with maturation, and one had both pre-T LBL and erythroid leukemia.
The malignant blasts from mice with pre-T LBL showed monoclonal T-cell receptor B gene rearrangements and were positive for CD3, 4, and 8. The mouse with megakaryocytic leukemia had serial CBCs documenting a platelet count of 3.2 million/uL, rising to >15million/uL at the time of death. This mouse had CD41+ megakaryocytes and megakaryoblasts invading the liver and spleen, and an osteosclerotic bone marrow reminiscent of chronic idiopathic myelofibrosis (CIMF). The mouse with concurrent pre-T LBL and erythroid leukemia had replacement of the thymus and infiltration of the lung with T-lymphoblasts which had a clonal TCRB gene rearrangement; interestingly, the spleen, liver, and bone marrow of this mouse were invaded with erythroblasts that were negative for CD3 and TCRB gene rearrangements.
We conclude that the NHD13 transgene consistently induces an MDS, of variable severity, in these mice. Some mice die of severe anemia due to MDS, and MDS transforms into an acute non-lymphoid leukemia in other mice. Still other mice die of pre-T LBL which we believe evolves in the thymus separately from the MDS. These data demonstrate that the NHD13 fusion gene is transforming in both lymphoid and myeloid cells.
Acute Myeloid Leukemia with Basophilic Differentiation Transformed from Myelodysplastic Syndrome
