It has been well established that disruption of JAK2 signaling regulation is involved in various hematopoietic disorders; however, the detailed mechanism by which abnormal activation of JAK2 exhibits transforming activity remains to be elucidated. Here, to clarify the functional role of the erythropoietin receptor (EpoR) and its downstream transcription factor STAT5 in the abnormal activation of JAK2-induced hematopoietic diseases, we generated a stable transfectant of Ba/F3 cells expressing EpoR and analyzed the molecular mechanism of how JAK2 mutation induces cell growth disorder. JAK2 V617F mutant exhibited transforming activity when EpoR was coexpressed. According to a study utilizing several truncated mutants of EpoR, the ability of EpoR to facilitate the transforming activity of JAK2 V617F mutant required the intracellular domain to interact with STAT5. Strikingly, once the truncated EpoR (EpoR-H) was mutated on Tyr-343, the phosphorylation of which is known to be important for interaction with STAT5, JAK2 V617F mutant failed to exhibit transforming activity, suggesting that STAT5 is critical for JAK2 mutant-induced hematopoietic disorder. Furthermore, the expression of the constitutively active STAT5 mutant exhibited transforming activity in Ba/F3 cells, and short hairpin RNA-mediated knockdown of STAT5 significantly inhibited the transforming activity of JAK2 V617F mutant. Taking these observations together, STAT5 plays an essential role in EpoR-JAK2 V617F mutant-induced hematopoietic disorder. Although it remains unclear why the presence of EpoR is required to activate oncogenic signaling via the JAK2 mutant and STAT5, its interacting ability is a target for the treatment of these hematopoietic diseases.

A 66-year-old woman presented with dissecting aneurysms of the anterior cerebral artery (ACA) and accessory middle cerebral artery (MCA) manifesting as subarachnoid hemorrhage but without radiological evidence of the dissecting aneurysms. Intraoperative observation revealed that the vessel walls were dark purple in color, a typical finding of dissecting aneurysm. The abnormal A1 segment was trapped and the dissecting aneurysm of the accessory MCA was wrapped. In the case of SAH of unknown origin, dissecting aneurysm should always be kept in mind even if the angiogram does not show any abnormal finding. This is the first reported case of dissecting aneurysm of the accessory MCA.

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Patients with advanced hematological malignancies are less likely to be referred to specialist palliative care services compared with patients having solid tumors. It has been reported that one of the most important reasons for the lack of referral is difficulties in the prognostication of terminally ill patients with hematologic malignancies. The study objective was to evaluate the predictive accuracy of the Palliative Prognostic Index (PPI) and the prognostic model developed by Kripp et al in hospitalized patients under the care of a hematologist. Using clinical charts, we retrospectively calculated the above scores. We reviewed the records of 114 patients admitted to the hematology ward. The inclusion criterion was patient with disease considered incurable using standard treatments. The prognostic models were assessed according to the original reports. Using PPI cutoff points of 2 and 4, we divided the patients into 3 groups of significantly different survival times ( P < .01). Moreover, we confirmed the usefulness of predicting survival <3 and <6 weeks using PPI scores of 6 and 4 as cutoff points, respectively. When we classified patients according to the prognostic model of Kripp et al, the high-risk group survived significantly shorter times than the intermediate- and low-risk groups ( P < .001). However, there was no significant difference in survival between the intermediate- and low-risk groups. Use of these models might enable physicians to provide more appropriate end-of-life care and to refer patients to palliative care earlier.

JAK2 plays important roles in the regulation of a variety of cellular processes including cell migration, proliferation, and protection from apoptosis. Recently the L611S point mutation in JAK2 has been identified in a child with acute lymphoblastic leukemia. Here we analyzed the mechanism by which JAK2 exhibits its oncogenicity. In BaF3 murine hematopoietic cells, L611S mutant increased the expression of antiapoptotic proteins including X chromosome-linked inhibitor of apoptosis protein, inhibitor of apoptosis protein, and Bcl-XL. We also showed that JAK2 L611S mutant protects BaF3 cells from cytokine withdrawal-induced apoptotic cell death and leads to cytokine-independent cell growth. Furthermore BaF3 cells expressing JAK2 L611S mutant gained the ability to induce tumorigenesis in nude mice. The L611S mutant also exhibited malignancy, including prompt invasion and spreading into various organs, leading to rapid lethality of the mice. Finally we showed that a specific JAK2 inhibitor, AG490, potently inhibited cytokine-independent cell growth induced by JAK2 L611S mutant via the induction of apoptotic cell death. In addition, treatment with AG490 significantly inhibited the JAK2 L611S mutant-induced tumorigenesis in nude mice. Thus, our results both in vitro and in vivo strongly suggest that L611S mutant of JAK2 harbors potent oncogenic activity, and this probably requires the antiapoptotic signaling pathway.The tyrosine kinase Janus kinase 2 (JAK2) 2 is the essential component of various cytokine signal transductions. Recent studies showed that JAK2 activates the mitogen-activated protein kinase family (ERK, c-Jun NH 2 -terminal kinase (JNK), and p38), Akt, and the signal transducers and activators of transcription (Stat) family in various tissues and is involved in numerous biological functions such as cell growth, cell survival, and differentiation (1, 2). Therefore, it has been reported that the disruption of the regulation of JAK2 activity is associated with hematopoietic disorders and oncogenesis (3-5).JAK2 contains seven regions with significant sequence homology between the kinases, termed Jak homology (JH) domains (1, 2). The JH1 domain is located within the carboxyl terminus of the protein and contains the tyrosine kinase domain. The adjacent JH2 domain shows close homology to the JH1 domain; however, it lacks critical residues required for tyrosine kinase activity. Under normal conditions, this JH2 domain negatively regulates kinase activity. Theoretical models of JAK2 structure suggest that the JH1 and JH2 domains are facing each other and that the activation loop of JAK2 is buried at this interface (6). Upon activation of JAK2, phosphorylation of the activation loop at Tyr 1007/1008 occurs and is believed to prevent this JH1-JH2 interaction and therefore relieve inhibition (7-9).The JAK2 deletion mutant lacking JH2 domain exhibited receptor-independent constitutive activation (8, 9). Furthermore JH2 domain mutations have been demonstrated to be involved in various myeloproliferative diseases (10 -1...