Chromosomal translocations in tumors frequently produce fusion genes coding for chimeric proteins with an integral role in oncogenesis. to the JAK2 tyrosine-kinase domain. analysis of transfected cells showed that BCR-JAK2 is located in the cytoplasm. Transduction of hematopoietic Ba/F3 cells with retroviral vectors carrying induced IL-3-independent cell growth constitutive activation of the chimeric protein as well as STAT5 phosphorylation and translocation to the nuclei where gene expression was elicited. Primary mouse progenitor cells transduced with also showed increased proliferation and survival. Treatment with the JAK2 inhibitor TG101209 abrogated BCR-JAK2 and STAT5 phosphorylation decreased expression and triggered apoptosis of transformed Ba/F3 cells. Therefore BCR-JAK2 is a Geranylgeranylacetone 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 overexpression may benefit from targeted therapies. Introduction Acute lymphoblastic leukemia (ALL) is a malignant disease characterized by the clonal expansion of lymphoid progenitors. Outcome is poorer in adults than in children probably due to the higher frequency of Philadelphia (Ph’) chromosome-positive ALL . The Ph’ chromosome results from a translocation t(9;22)(q34;q11) which leads to the fusion gene. One-third of adult ALL patients with the Ph’ chromosome show major (M)-BCR rearrangements (resulting in a 210-kDa protein) whereas two-thirds have minor (m)-BCR rearrangements (resulting in a 190-kDa protein). These chimeric proteins are Rabbit Polyclonal to EGFR (phospho-Ser1026). hyperactive tyrosine kinases (TK) that are located in the cytoplasm where they recruit downstream effectors of cell proliferation and survival. Chromosomal rearrangements other than t(9;22)(q34;q11) are found in ALL although they are less frequent (http://AtlasGeneticsOncology.org). JAK2 is a non-receptor TK protein that is essential for signaling through a variety of cytokine receptors and is required for normal hematopoiesis  . Activation of the JAK2-cytokine receptor complex leads to the recruitment and JAK2-mediated phosphorylation of STAT5 proteins whose subsequent Geranylgeranylacetone dimerization and nuclear translocation induces target gene transcription . The role of constitutively activated JAK2 or STAT5 in cellular transformation has been established . Geranylgeranylacetone Several fusion proteins involving the catalytic active JH1 domain of JAK2 have been reported to be associated with leukemia as follows: 1) TEL-JAK2 was found in both pre-B-lineage and pre-T-lineage ALL and atypical chronic myelogenous leukemia (CML)   2) gene fusion resulting from t(8;9)(p22;p24) in Geranylgeranylacetone eosinophilia-associated atypical CML ALL acute myeloid leukemia (AML) and T cell lymphoma  and 3) gene fusion as the result of t(9;22)(p24;q11) was found in atypical CML   and AML . Other putative JAK2 translocations include in pre-B ALL  in childhood ALL  and in classical non Hodgkin lymphoma . Moreover gain-of-function JAK2 mutations are common in myeloproliferative neoplasms  and in up to 15% of adult and high-risk pediatric B-ALL lacking and rearrangements   . These observations have supported the search for selective inhibitors of JAK2   and several compounds are currently undergoing clinical trials for myelofibrosis  . Here we provide for the first time evidence of the transforming and tumorigenic activity of JAK2 through fusion with BCR. Materials and Methods Ethics Statement Patient written informed consent was obtained before bone marrow biopsies were taken. This protocol was carried out according to current Spanish legislation on clinical research in humans and was approved by the Hospital Universitario de la Princesa Clinical Investigation Ethics Committee (Approval ID: PI-424). All experimentation with mice was carried out in accordance Geranylgeranylacetone with institutional guidelines from the animal care and use committee from Centro de Investigaciones Tecnológicas y Medioambientales (CIEMAT) and approved by them with approval ID: HEM 4-09. Case description A 58-year-old male presented with asthenia abdominal pain and slight hepatosplenomegaly. The Geranylgeranylacetone blood.