Stat5-dependent transcriptional activity was inhibited by transfection of NPM/ALK-transformed cells with a dominant-negative Jak2 expression construct or treatment with AG490.     ///    We investigated the role of Jak2 in the context of NPM/ALK-mediated oncogenesis.     ///    NPM/ALK-transformed cells were treated with the Jak2 inhibitor AG490 or transfected with wild-type or dominant-negative Jak2 expression constructs to measure 3[H]-thymidine incorporation.     ///    "Also, NPM/ALK was present in immunoprecipitates of Jak2. "    ///    Jak2 was found to be constitutively tyrosine phosphorylated in ALCL cells and in NPM/ALK-transformed hematopoietic cells.     ///    Constitutive activation of Jak2 contributes to proliferation and resistance to apoptosis in NPM/ALK-transformed cells..     ///    "Constitutive activation of Jak2 constitutes a pro-proliferative, anti-apoptotic signaling pathway in NPM/ALK-transformed hematopoietic cells.. "    ///    Inhibition of Jak2 led to a reduction of NPM/ALK-mediated proliferation and induced apoptosis.     ///    NPM/ALK exerts its transforming potential via activation of multiple signaling pathways promoting growth factor independence and protection from apoptosis. 