title: Transforming and tumorigenic activity of JAK2 by fusion to BCR: molecular mechanisms of action of a novel BCR-JAK2 tyrosine-kinase.
abstract: 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.
authors.affiliation: Molecular Biology Unit, Hospital Universitario de la Princesa, Instituto de Investigación Sanitaria Princesa and Red Española de Investigación en Patología Infecciosa, Madrid, Spain.
authors.forename: Álvaro
authors.initials: Á
authors.lastname: Cuesta-Domínguez
authors.forename: Mara
authors.initials: M
authors.lastname: Ortega
authors.forename: Cristina
authors.initials: C
authors.lastname: Ormazábal
authors.forename: Matilde
authors.initials: M
authors.lastname: Santos-Roncero
authors.forename: Marta
authors.initials: M
authors.lastname: Galán-Díez
authors.forename: Juan Luis
authors.initials: JL
authors.lastname: Steegmann
authors.forename: Ángela
authors.initials: Á
authors.lastname: Figuera
authors.forename: Eva
authors.initials: E
authors.lastname: Arranz
authors.forename: José Luis
authors.initials: JL
authors.lastname: Vizmanos
authors.forename: Juan A
authors.initials: JA
authors.lastname: Bueren
authors.forename: Paula
authors.initials: P
authors.lastname: Río
authors.forename: Elena
authors.initials: E
authors.lastname: Fernández-Ruiz
mesh_terms: D000818:Animals; D017209:Apoptosis; D002460:Cell Line; D005260:Female; D057809:HEK293 Cells; D006801:Humans; D053614:Janus Kinase 2 / Q000378:metabolism*; D008297:Male; D051379:Mice; D008819:Mice, Nude; D008875:Middle Aged; D015514:Oncogene Proteins, Fusion / Q000378:metabolism*; D010766:Phosphorylation; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D051562:Proto-Oncogene Proteins c-bcr / Q000378:metabolism*; D060888:Real-Time Polymerase Chain Reaction / Q000379:methods; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D051020:bcl-X Protein / Q000378:metabolism
chemical_list: C494811:BCL2L1 protein, human; C494812:Bcl2l1 protein, mouse; D015514:Oncogene Proteins, Fusion; D051020:bcl-X Protein; D053614:Janus Kinase 2; C496613:BCR protein, human; C496614:Bcr protein, mouse; D051562:Proto-Oncogene Proteins c-bcr