Chromosomal translocations in tumors frequently produce fusion genes coding for chimeric proteins with a key role in oncogenesis. Recent reports described a BCR-JAK2 fusion gene in fatal chronic and ...acute myeloid leukemia, but the functional behavior of the chimeric protein remains uncharacterized. We used fluorescence in situ hybridization and reverse transcription polymerase chain reaction (RT-PCR) assays to describe a BCR-JAK2 fusion gene from a patient with acute lymphoblastic leukemia. The patient has been in complete remission for six years following treatment and autologous transplantation, and minimal residual disease was monitored by real-time RT-PCR. BCR-JAK2 codes for a protein containing the BCR oligomerization domain fused to the JAK2 tyrosine-kinase domain. In vitro analysis of transfected cells showed that BCR-JAK2 is located in the cytoplasm. Transduction of hematopoietic Ba/F3 cells with retroviral vectors carrying BCR-JAK2 induced IL-3-independent cell growth, constitutive activation of the chimeric protein as well as STAT5 phosphorylation and translocation to the nuclei, where Bcl-xL gene expression was elicited. Primary mouse progenitor cells transduced with BCR-JAK2 also showed increased proliferation and survival. Treatment with the JAK2 inhibitor TG101209 abrogated BCR-JAK2 and STAT5 phosphorylation, decreased Bcl-xL expression and triggered apoptosis of transformed Ba/F3 cells. Therefore, BCR-JAK2 is a novel tyrosine-kinase with transforming activity. It deregulates growth factor-dependent proliferation and cell survival, which can be abrogated by the TG101209 inhibitor. Moreover, transformed Ba/F3 cells developed tumors when injected subcutaneously into nude mice, thus proving the tumorigenic capacity of BCR-JAK2 in vivo. Together these findings suggest that adult and pediatric patients with BCR-ABL-negative leukemia and JAK2 overexpression may benefit from targeted therapies.
Abstract 4683
Chromosomal translocations in human tumors frequently produce fusion genes whose chimeric protein products play an essential role in oncogenesis. Recent reports have found a BCR-JAK2 ...fusion gene in cases of chronic or acute myeloid leukemia, but the protein had not been characterized. We describe a BCR-JAK2 fusion gene by fluorescence in situ hybridization and RT-PCR amplification from bone marrow at diagnosis of a patient with acute lymphoblastic leukemia. After induction therapy, real time PCR showed persistent molecular response correlating with hematological remission maintained up to present. BCR-JAK2 is a 110 KDa chimeric protein containing the BCR oligomerization domain fused to the JAK2 tyrosine-kinase domain. In vitro analysis showed that BCR-JAK2 was constitutively phosphorylated and was located to the cytoplasm. BCR-JAK2 transformed the IL-3-dependent murine hematopoietic cell line Ba/F3 into IL-3 independent growth and induced STAT5b phosphorylation and translocation into the cell nuclei. The treatment with a JAK2 inhibitor abrogated BCR-JAK2 and STAT5b phosphorylation, leading to apoptosis of transformed Ba/F3 cells. To test whether BCR-JAK2 has tumorogenic ability in vivo, we performed experiments with nude mice, in which we injected subcutaneously cells transduced with the control vector and cells expressing BCR-JAK2. Notably, we only obtained tumors in the flank injected with BCR-JAK2 expressing cells, thus confirming the tumorogenic activity of the BCR-JAK2 fusion protein. We conclude that BCR-JAK2 is a new tyrosine-kinase that induces proliferation and cell survival, which can be abrogated by JAK2 inhibitors. In vitro studies demonstrate that BCR-JAK2 displays transforming activity. Moreover, the nude mice model reveals its ability to cause tumors.
No relevant conflicts of interest to declare.
The role of molecular monitoring of minimal residual disease (MRD) in low-grade non-Hodgkin's lymphoma is controversial. We have performed a prospective study of the molecular behavior of 35 patients ...with follicular non-Hodgkin's lymphoma who received cyclophosphamide-vincristine-prednisone chemotherapy in conjunction with IFN-alpha 2b.
Bcl-2 and clonal immunoglobulin heavy chain (IgH) gene rearrangements were assayed at diagnosis by PCR in lymph node and bone marrow (BM) and sequentially after treatment.
Molecular markers were detected in BM of 29 (83%) patients at diagnosis: Bcl-2 rearrangement in 20 patients (90% major breakpoint and 10% minor cluster) and clonal IgH rearrangement in 9 of 15 patients negative for Bcl-2. Molecular and clinical response was noted in 25 (86%) patients after induction treatment. Progression-free survival at 5 years was 78.1 +/- 8%. A correlation between clinical and molecular response was found in 24 patients with molecular markers in BM at diagnosis and >2 years of follow-up: 94% of patients with undetectable MRD showed continuous clinical remission, whereas 50% of patients who reverted back to positive molecular markers relapsed (P < 0.05).
The rate of molecular response is high in patients treated with cyclophosphamide-vincristine-prednisone and IFN and MRD sequential analysis is useful for disease surveillance.
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