Absence of JAK-2 (Val617Phe) Point Mutations in Human Plasma Cell Myeloma.

Multiple myeloma (MM) is a terminal differentiated B cell chronic lymphoproliferative disorder characterized by the latent accumulation of plasma cells with a low proliferative index and an extended life span in bone marrow or extramedullary tissues. While studies on neoplastic cells isolated directly from MM patients or on MM-derived cell lines demonstrated that IL-6 is a major growth and survival factor for initiation of signaling in MM cells in an autocrine or paracrine manner, some MM cells independent on extracellular signaling such as IL-6 have been reported, suggesting other mechanisms may be involved in signal transduction pathways in MM cells. Accumulating evidence showed that IL-6 induces intracellular signaling through members of the signal transducers and activators of transcription (STAT) family of proteins by activating the janus kinase(JAK) family of protein tyrosine kinases, which subsequently phosphorylate and activate cytoplasmic Stat proteins. Activated Stat proteins dimerize and translocate to the nucleus, where they bind to specific DNA response elements and induce expression of Stat-regulated genes. Our previous studies demonstrated that one of the Stat family proteins, Stat3, was constitutively activated (phosphorylated) in the majority of MM patients, suggesting constitutive activation of JAK-2 kinase activities. However, other mechanisms might be also responsible JAK2 constitutive activation in MM cells, in particular in IL-6 independent MM cells. A specific point mutation of JAK-2 kinase gene has been identified recently showing its presence in higher frequency of certain types of chronic myeloproliferative disorders. The point mutation yields constitutive activation of JAK-2 kinase activity in the absence of extracellular signaling and plays an important role in the pathogenesis of those disorders. In this study, we try to determine whether JAK-2 (Val617Phe) point mutation was present in MM patients and if so, what kind of role it may play in the pathogenesis of MM. JAK-2 (Val617Phe) point mutation was analyzed by using an allele-specific polymerase chain reaction followed by separation and detection with capillary electrophoresis. The test has a detection sensitivity of up to 200 picogram mutated DNA. Bone marrow aspirates with various degrees of involvement by MM (ranged10–80%) were selected and all the cases have been verified by morphologic examination and demonstrated to have positive immunoglobulin heavy or kappa light gene rearrangements. Bone marrow specimens from total 59 MM patients were tested for JAK2 (Val617Phe) mutation and none of any MM cases with the specific point mutation were identified (0/59). The results indicated that JAK2 (Val617Phe) mutation was very infrequency or absence in MM patients, despite the fact that constitutional activation of JAK2 kinase as well as Stat3 activation was commonly seen in MM patients. The study suggests that other yet unknown mechanisms may also involve JAK2 activation, particularly in IL-6 independent MM cells.