Gaku Oshikawa

c-Cbl and Cbl-b Ligases Mediate 17-Allylaminodemethoxygeldanamycin-induced Degradation of Autophosphorylated Flt3 Kinase with Internal Tandem Duplication through the Ubiquitin Proteasome Pathway

The class III receptor-tyrosine kinase Flt3 regulates normal hematopoiesis. An internal tandem duplication (ITD) in the juxtamembrane domain of Flt3 (Flt3-ITD) contributes to transformation and is associated with poor prognosis in acute myeloid leukemia. Here, we demonstrate that, as compared with wild-type Flt3 (Flt3-WT), Flt3-ITD more rapidly undergoes degradation through the proteasomal and lysosomal pathways in model hematopoietic 32D cells and in human leukemic MV4-11 cells. The Hsp90 inhibitor 17-allylaminodemethoxygeldanamycin (17-AAG) preferentially induced the polyubiquitination and proteasomal degradation of Flt3-ITD autophosphorylated on Tyr-591 in these cells. The E3 ubiquitin ligases c-Cbl and to a lesser extent Cbl-b facilitated at least partly Lys-48-linked polyubiquitination of autophosphorylated Flt3-ITD when coexpressed in 293T cells. Moreover, c-Cbl and Cbl-b facilitated degradation of Flt3-ITD in 293T cells and significantly enhanced the 17-AAG-induced decline in autophosphorylated Flt3-ITD. The enhancement of Flt3-ITD degradation was also observed in 32D cells inducibly overexpressing c-Cbl or Cbl-b. Furthermore, overexpression of loss-of-function mutants of both c-Cbl (c-Cbl-R420Q) and Cbl-b (Cbl-b-C373A) together in 32D cells retarded the degradation of autophosphorylated Flt3-ITD and significantly inhibited the 17-AAG-induced degradation of Flt3-ITD to confer the resistance to cytotoxicity of 17-AAG on these cells. These results suggest that c-Cbl as well as Cbl-b may play important roles in Hsp90 inhibitor-induced degradation of Flt3-ITD through the ubiquitin proteasome system and in regulation of the basal expression level of Flt3-ITD in leukemic cells.

Inhibition of the PI3K/Akt/GSK3 Pathway Downstream of BCR/ABL, Jak2-V617F, or FLT3-ITD Downregulates DNA Damage-Induced Chk1 Activation as Well as G2/M Arrest and Prominently Enhances Induction of Apoptosis

Constitutively-activated tyrosine kinase mutants, such as BCR/ABL, FLT3-ITD, and Jak2-V617F, play important roles in pathogenesis of hematopoietic malignancies and in acquisition of therapy resistance. We previously found that hematopoietic cytokines enhance activation of the checkpoint kinase Chk1 in DNA-damaged hematopoietic cells by inactivating GSK3 through the PI3K/Akt signaling pathway to inhibit apoptosis. Here we examine the possibility that the kinase mutants may also protect DNA-damaged cells by enhancing Chk1 activation. In cells expressing BCR/ABL, FLT3-ITD, or Jak2-V617F, etoposide induced a sustained activation of Chk1, thus leading to the G2/M arrest of cells. Inhibition of these kinases by their inhibitors, imatinib, sorafenib, or JakI-1, significantly abbreviated Chk1 activation, and drastically enhanced apoptosis induced by etoposide. The PI3K inhibitor GD-0941 or the Akt inhibitor MK-2206 showed similar effects with imatinib on etoposide-treated BCR/ABL-expressing cells, including those expressing the imatinib-resistant T315I mutant, while expression of the constitutively activated Akt1-myr mutant conferred resistance to the combined treatment of etoposide and imatinib. GSK3 inhibitors, including LiCl and SB216763, restored the sustained Chk1 activation and mitigated apoptosis in cells treated with etoposide and the inhibitors for aberrant kinases, PI3K, or Akt. These observations raise a possilibity that the aberrant kinases BCR/ABL, FLT3-ITD, and Jak2-V617F may prevent apoptosis induced by DNA-damaging chemotherapeutics, at least partly through enhancement of the Chk1-mediated G2/M checkpoint activation, by inactivating GSK3 through the PI3K/Akt signaling pathway. These results shed light on the molecular mechanisms for chemoresistance of hematological malignancies and provide a rationale for the combined treatment with chemotherapy and the tyrosine kinase or PI3K/Akt pathway inhibitors against these diseases.

Post‐transplant maintenance therapy with azacitidine and gemtuzumab ozogamicin for high‐risk acute myeloid leukaemia

166, 702–710. Moreau, P., Pylypenko, H., Grosicki, S., Karamanesht, I., Leleu, X., Grishunina, M., Rekhtman, G., Masliak, Z., Robak, T., Shubina, A., Arnulf, B., Kropff, M., Cavet, J., Esseltine, D.L., Feng, H., Girgis, S., van de Velde, H., Deraedt, W. & Harousseau, J.L. (2011) Subcutaneous versus intravenous administration of bortezomib in patients with relapsed multiple myeloma: a randomised, phase 3, noninferiority study. The Lancet Oncology, 12, 431–440. Reeder, C.B., Reece, D.E., Kukreti, V., Chen, C., Trudel, S., Hentz, J., Noble, B., Pirooz, N.A., Spong, J.E., Piza, J.G., Zepeda, V.H., Mikhael, J.R., Leis, J.F., Bergsagel, P.L., Fonseca, R. & Stewart, A.K. (2009) Cyclophosphamide, bortezomib and dexamethasone induction for newly diagnosed multiple myeloma: high response rates in a phase II clinical trial. Leukemia, 23, 1337–1341. Reeder, C.B., Reece, D.E., Kukreti, V., Mikhael, J.R., Chen, C., Trudel, S., Laumann, K., Vohra, H., Fonseca, R., Bergsagel, P.L., Leis, J.F., Tiedemann, R. & Stewart, A.K. (2014) Long-term survival with cyclophosphamide, bortezomib and dexamethasone induction therapy in patients with newly diagnosed multiple myeloma. British Journal of Haematology, 167, 6563–6564. Richardson, P.G., Weller, E., Lonial, S., Jakubowiak, A.J., Jagannath, S., Raje, N.S., Avigan, D.E., Xie, W., Ghobrial, I.M., Schlossman, R.L., Mazumder, A., Munshi, N.C., Vesole, D.H., Joyce, R., Kaufman, J.L., Doss, D., Warren, D.L., Lunde, L.E., Kaster, S., Delaney, C., Hideshima, T., Mitsiades, C.S., Knight, R., Esseltine, D.L. & Anderson, K.C. (2010) Lenalidomide, bortezomib, and dexamethasone combination therapy in patients with newly diagnosed multiple myeloma. Blood, 116, 679–686.

Clonal evolution with double Ph followed by tetraploidy in imatinib-treated chronic myeloid leukemia with e19a2 transcript in transformation

Chronic myeloid leukemia (CML) with the e19a2 transcript coding for p230 is typically associated with a benign clinical course unless accompanied at presentation with additional chromosomal abnormalities. We report here a case of CML with e19a2 who did not show additional chromosomal abnormalities at diagnosis, but progressed to the fatal advanced stage in approximately 2 years. The patient was initially treated with imatinib, which, however, could be administered only intermittently at reduced doses because of recurrent thrombocytopenia and fluid retention. Nine months after starting imatinib, fluorescence in situ hybridization (FISH) with the BCR/ABL-ES fusion probe revealed 96% and 3% of bone marrow cells with one and two BCR/ABL1 fusion signals, respectively. Two years after starting therapy, leukocytosis recurred and the bone marrow contained 8.2% large and bizarre myeloblasts. Cytogenetic analysis revealed double Ph clones as well as tetraploid cells with four to five Ph chromosomes. FISH analysis confirmed the presence of cells with two to five BCR/ABL1 fusion signals. The patient died of disease progression in 2 months. No point mutation was detected in the region coding for the BCR/ABL tyrosine kinase domain by sequence analysis. It is speculated that the amplification of the BCR/ABL1 fusion gene by duplication of Ph and tetraploidy led to the progression of CML with the e19a2 transcript.

Proliferation and survival signaling from both Jak2-V617F and Lyn involving GSK3 and mTOR/p70S6K/4EBP1 in PVTL-1 cell line newly established from acute myeloid leukemia transformed from polycythemia vera.

The gain of function mutation JAK2-V617F is very frequently found in myeloproliferative neoplasms (MPNs) and is strongly implicated in pathogenesis of these and other hematological malignancies. Here we report establishment of a new leukemia cell line, PVTL-1, homozygous for JAK2-V617F from a 73-year-old female patient with acute myeloid leukemia (AML) transformed from MPN. PVTL-1 is positive for CD7, CD13, CD33, CD34, CD117, HLA-DR, and MPO, and has complex karyotypic abnormalities, 44,XX,-5q,-7,-8,add(11)(p11.2),add(11)(q23),−16,+21,−22,+mar1. Sequence analysis of JAK2 revealed only the mutated allele coding for Jak2-V617F. Proliferation of PVTL-1 was inhibited and apoptosis was induced by the pan-Jak inhibitor Jak inhibitor-1 (JakI-1) or dasatinib, which inhibits the Src family kinases as well as BCR/ABL. Consistently, the Src family kinase Lyn was constitutively activated with phosphorylation of Y396 in the activation loop, which was inhibited by dasatinib but not by JakI-1. Further analyses with JakI-1 and dasatinib indicated that Jak2-V617F phosphorylated STAT5 and SHP2 while Lyn phosphorylated SHP1, SHP2, Gab-2, c-Cbl, and CrkL to induce the SHP2/Gab2 and c-Cbl/CrkL complex formation. In addition, JakI-1 and dasatinib inactivated the mTOR/p70S6K/4EBP1 pathway and reduced the inhibitory phosphorylation of GSK3 in PVTL-1 cells, which correlated with their effects on proliferation and survival of these cells. Furthermore, inhibition of GSK3 by its inhibitor SB216763 mitigated apoptosis induced by dasatinib but not by JakI-1. Together, these data suggest that apoptosis may be suppressed in PVTL-1 cells through inactivation of GSK3 by Lyn as well as Jak2-V617F and additionally through activation of STAT5 by Jak2-V617F. It is also speculated that activation of the mTOR/p70S6K/4EBP1 pathway may mediate proliferation signaling from Jak2-V617F and Lyn. PVTL-1 cells may provide a valuable model system to elucidate the molecular mechanisms involved in evolution of Jak2-V617F-expressing MPN to AML and to develop novel therapies against this intractable condition.

DNA Damage Stress and Inhibition of Jak2-V617F Cause Its Degradation and Synergistically Induce Apoptosis through Activation of GSK3β

The cytoplasmic tyrosine kinase Jak2 plays a crucial role in cytokine receptor signaling in hematopoietic cells. The activated Jak2-V617F mutant is present in most cases of BCR/ABL-negative myeloproliferative neoplasms and constitutively activates downstream signals from homodimeric cytokine receptors, such as the erythropoietin receptor (EpoR). Here we examine the effects of DNA damage stress on Jak2 or Jak2-V617F and on induction of apoptosis in hematopoietic cells. Etoposide or doxorubicin dose-dependently decreased the expression level of Jak2 in UT7 or 32D cells expressing EpoR in the absence of Epo and that of exogenously expressed Jak2-V617F in UT7 cells when cotreated with the Jak2 inhibitor JakI-1 or AG490. Studies with pharmacological inhibitors and genetic manipulations further showed that downregulation of the PI3K/Akt pathway leading to the activation of GSK3β may be involved in downregulation of Jak2 or Jak2-V617F as well as in synergistic induction of Bax activation and apoptosis. The downregulation of Jak2 was inhibited by the proteasome inhibitor MG132 or by expression of both of loss-of-function mutants of c-Cbl and Cbl-b, E3 ubiquitin ligases which facilitated ubiquitination of Jak2-V617F when co-expressed in 293T cells. The pan-caspase inhibitor Boc-d-fmk also inhibited the Jak2 downregulation as well as appearance of a 100-kDa fragment that contained the N-terminal portion of Jak2 in response to DNA damage. Together, these data suggest that DNA damage stress with simultaneous inhibition of the kinase activity causes degradation of Jak2 or Jak2-V617F by caspase cleavage and proteasomal degradation through GSK3β activation, which is closely involved in synergistic induction of apoptosis in hematopoietic cells.

Extranodal NK/T cell lymphoma, nasal type, of the small intestine diagnosed by double-balloon endoscopy

Extranodal NK/T-cell lymphoma (ENKL), nasal type, is rare and the small intestine is quite extraordinary as a primary lesion site. We report a 47-year-old man with ENKL of the small intestine. He was referred to our hospital because of bloody stool and the diagnosis was made by double-balloon endoscopy (DBE) of the small intestine without surgical procedure. His clinical stage was IVB and he was categorized in group 4 by prognostic index of ENKL. He went into complete remission (CR) after intensive chemotherapy (DeVIC) and subsequently underwent allogeneic bone marrow transplantation (BMT). Although he remained in CR for about 8 months after BMT, he died of disease recurrence 14 months after the diagnosis was made. ENKL of the small intestine follows a highly aggressive course. We describe the usefulness of DBE for diagnosis and management for ENKL of the small intestine. Additional cases, however, should be accumulated to establish optimal treatment strategy.

A novel MYD88 mutation, L265RPP, in Waldenström macroglobulinemia activates the NF-κB pathway to upregulate Bcl-xL expression and enhances cell survival.

A novel MYD88 mutation, L265RPP, in Waldenstrom macroglobulinemia activates the NF-κB pathway to upregulate Bcl-xL expression and enhances cell survival

PECAM-1 is involved in BCR/ABL signaling and may downregulate imatinib-induced apoptosis of Philadelphia chromosome-positive leukemia cells

PECAM-1 (CD31) is an immunoreceptor tyrosine-based inhibitory motif (ITIM)-containing surface glycoprotein expressed on various hematopoietic cells as well as on endothelial cells. PECAM-1 has been shown to play roles in regulation of adhesion, migration and apoptosis. The BCR/ABL fusion tyrosine kinase is expressed in chronic myeloid leukemia and Philadelphia-positive (Ph+) acute lymphoblastic leukemia cells, and its inhibition by the clinically used tyrosine kinase inhibitors imatinib or dasatinib induces apoptosis of these cells. In the present study, we demonstrate that PECAM-1 is tyrosine phospho rylated in its ITIM motifs in various BCR/ABL-expressing cells including primary leukemia cells. Studies using imatinib and dasatinib as well as transient expression experiments in 293T cells revealed that PECAM-1 was phosphorylated directly by BCR/ABL, which was enhanced by the imatinib-resistant E255K and T315I mutations, or partly by the Src family tyrosine kinases, including Lyn, which were activated dependently or independently on BCR/ABL. We also demonstrate by using a substrate trapping mutant of SHP2 that tyrosine phosphorylated PECAM-1 binds SHP2 and is a major substrate for this tyrosine phosphatase in BCR/ABL-expressing cells. Overexpression of PECAM-1 in BCR/ABL-expressing cells, including K562 human leukemia cells, enhanced cell adhesion and partially inhibited imatinib-induced apoptosis involving mitochondria depolarization and caspase-3 cleavage, at least partly, in an ITIM-independent manner. These data suggest that PECAM-1 may play a role in regulation of apoptosis as well as adhesion of BCR/ABL-expressing cells to modulate their imatinib sensitivity and would be a possible candidate for therapeutic target in Ph+ leukemias.

Clinical impact of CD25 expression on outcomes of allogeneic hematopoietic stem cell transplant for cytogenetically intermediate-risk acute myeloid leukemia

Approximately 50% of adult patients with acute myeloid leukemia (AML) do not show clonal chromosome aberrations at diagnosis, and although this group shows an intermediate prognosis, a minority of patients eventually become long-term survivors. [1]. Th is emphasizes the need for new molecular markers that can be used to predict disease aggressiveness and to determine the leukemic response to treatment, including allogeneic hematopoietic stem cell transplant (allo-HSCT) [2]. Recent data have shown that molecular analysis of the presence of mutated FMS-like tyrosine kinase-3 (FLT3), nucleophosmin 1 (NPM1), CCAAT/ enhancer-binding protein alpha (CEBPA), mixed lineage leukemia (MLL) or neuroblastoma RAS viral oncogene homolog (N-Ras) may be useful for this purpose [3]. However, molecular analyses may be costly and not always available, as not all the mutations are detected by sequencing. As an alternative approach, we may be able to focus on distinct clinical features that depend on specifi c genetic aberrations. For example, patients with a FLT3-internal tandem duplication (ITD) mutation tend to have higher white blood cell count and blast count [4], and moreover a high percentage of these patients may have high CD25 (the α -chain of the interleukin-2 [IL-2] receptor) antigen expression as observed with fl ow cytometry [5 – 7]. Recent studies have shown that CD25 is highly expressed in chemotherapy-resistant, cell cycle-quiescent leukemic stem cells, and high CD25 expression may be associated with an unfavorable outcome after conventional chemotherapy, including autologous and allogeneic transplant [5 – 7]. Th us, evaluation of CD25 expression may be an alternative, cost-eff ective non-molecular tool for cytogenetically intermediate (CI)-AML. Here we report the clinical impact of surface expression of the CD25 antigen on transplant outcomes in a total of 40 patients with CI-AML who underwent allo-HSCT in a single institution. In this study, intermediate-risk AML included patients with a normal or indeterminate karyotype. Bone marrow and peripheral blood samples from 40 patients with CI-AML were available for analysis of CD25 expression at the initial diagnosis. Th ese patients eventually underwent allo-HSCT in our institution between January 2001 and January 2013. We list the chemotherapies, conditioning regimens and outcomes (Supplementary Table I to be found online at http://informahealthcare.com/doi/ abs/10.3109/10428194.2014.974044). Patients with French – American – British (FAB) classifi cation M3 were excluded. Flow cytometry analyses were performed in-house using standard immunofl uorescence methods with monoclonal antibodies directed against CD2, CD3, CD4, CD5, CD7, CD8, CD10, CD11b, CD13, CD14, CD19, CD20, CD25, CD33, CD34, CD38, CD41, CD56 and human leukocyte antigen (HLA)-DR antigens, and were considered to be positive if at least 20% of leukemic blasts expressed the antigen [5]. Th e cut-off level of CD25 depends on the report, for example 10% [6,7] and 20% [5]. Generally the cut-off level of 20% has been known as the standard, and we consider this as the best cut-off level to exclude false-positive results. Transplant procedures have been described in detail elsewhere [8]. Myeloablative conditioning mainly included busulfan (3.2 mg/kg for 4 days) and cyclophosphamide (60 mg/kg for 2 days). Th e main preparative regimen for the reduced-intensity procedure consisted of fl udarabine (30 mg/m 2 for 6 days), melphalan (40 mg/m 2