ALBERT

Description: Background: Recent studies suggest that HERG K+ channel is an important regulator of non excitable cell proliferation and migration, and has been found in tumor cells including acute myeloid leukemia(AML), where HERG K+ channel is generally considered to be absent from their healthy counterparts. Bone marrow stromal cells constitutively secrete the stromal cell-derived factor-1 (SDF-1) which is a homeostatic chemokine that signals through CXCR4, SDF-1/CXCR4 axis and plays an important role in hematopoiesis development and leukemic cells migration. In this study, we investigated whether SDF-1-induced leukemic cell migration associated with HERG K+ channel. Methods: primary CD34+/CD38− leukemic stem cells (LSCs) were isolated by cell sorting using a FACS Vantage. Transwell was used to assess the effect of E-4031, a specific HERG K+ channel inhibitor, on leukemic cell migration, the lower chamber was filled with serum-free RPMI-1640 with 100ng/ml SDF-1. Flow cytometry was used to analyze the CXCR4 expression as well as phenotypical analysis of leukemia samples. HERG K+ channels were expressed in Xenopus oocyte by microinjection and the resulting currents were measured using the standard two microelectrode voltage clamp techniques. Results: numbers of HL-60 cells with and without E-4031 treatment migrated towards SDF-1 in the lower chamber were 1.58±0.98 ×104 and 3.47±0.81 ×104 respectively, indicating E-4031 significantly blocked the cell migration induced by SDF-1. The similar results were also observed in primary leukemic cells (n=7) and leukemic stem cells(n=3). From a holding potential of −80 mV varying potentials from −70 mV to +50 mV in 10 mV increments (2s) were applied to elicit activating currents. Each pulse was followed by a constant return pulse to −50 mV (2s) to evoke outward tail currents. 100 ng/ml SDF-1 increased HERG K+ current expressed in oocytes, for example, at +50 mV, HERG current increased about 30% (n=5). The HERG K+ current increase by SDF-1 might contribute to the mechanism of SDF-1 induced leukemic cell migration. There were no significant changes of CXCR4 expression on both HL-60 cells and primary leukemic cells regardless of untreated and treated with E-4031 for 24 hours (p〉0.05), suggesting that the leukemic cell migration induced by SDF-1 were specifically associated with HERG K+ channel, not by regulating CXCR4 expression. Conclusion: the data showed that HERG K+ channel was essential for leukemic cell migration induced by SDF-1. SDF-1 enhanced herg current suggested that SDF-1 promotes leukemic cell migration. Blocking HERG K+ channel with specific inhibitor could decrease leukemic cell and leukemic stem cell migration caused by SDF-1. Prospectively, HERG K+ channel may be a potential therapeutic target with specific inhibitors in leukemia treatment.

Description: Abstract 2995 Poster Board II-973 Introduction: The interaction of glycoprotein (GP) Ib-IX with subendothelial-bound von Willebrand factor (VWF) initiates circulated platelet transient adhesion on the injured vascular wall under flow conditions. VWF conformational changes in response to high shear stress are thought to be critical for initiating platelet adhesion, there is increasing evidences indicate that the interactions of intraplatelet proteins 14-3-3ζ and filamin A with the cytoplasmic domain of GPIbalpha also play key roles in the regulation of VWF binding function of GPIb-IX, whereas it is unclear whether their structural linkage has functional implication. This study was to explore the mechanism underlying the roles of 14-3-3ζ and filamin A in the regulation of the VWF binding function of GPIb-IX. Methods and Results: A truncation mutant of GPIbalpha (at residue 565) deleting the C-terminal 14-3-3ζ binding sites retains 14-3-3ζ binding function, in contrast, deletion of the C-terminal residues 551-610 of GPIbalpha totally abolished 14-3-3ζ binding, indicating that the residues 551-564 of GPIbalpha is important in the interaction between 14-3-3ζ and GPIb-IX. An antibody recognizing phosphorylated R557GpSLP561 sequence reacted with GPIbalpha suggesting phosphorylation of a population of GPIbalpha molecules at Ser559, and a membrane permeable phosphopeptide (MP-P), M-R557GpSLP561 corresponding to residues 557-561 of GPIbalpha eliminated the association of 14-3-3ζ with the truncation mutant of GPIbalpha . MP-P also promoted GPIb-IX association with the membrane skeleton, and inhibited ristocetin-induced platelet agglutination, VWF binding to platelets and platelet adhesion to immobilized VWF. Furthermore, a GPIb-IX mutant replacing Ser559 of GPIbalpha with alanine showed an enhanced association with the membrane skeleton, reduced ristocetin-induced VWF binding and diminished ability to mediate cell adhesion to VWF under flow conditions. Conclusions: These data suggest a phosphorylation-dependent binding of 14-3-3ζ to central filamin A binding site of GPIbalpha, and the dimeric 14-3-3ζ binding to both the C-terminal site and central RGpSLP site inhibits GPIb-IX association with the membrane skeleton and promotes the VWF binding function of GPIb-IX. Disclosures: No relevant conflicts of interest to declare.

Description: Background: The precise mechanism of rituximab (R) plus CHOP (R-CHOP) therapy in diffuse large B-cell lymphoma (DLBCL) is not fully elucidated. Besides overcoming bcl-2 mediated chemoresistance, antibody-dependent cellular cytotoxicity (ADCC), which is activated by effector cells via IgG fragment C receptors (FcR), was also proposed as a mechanism of Rituximab. The current study evaluated the impact of FcR polymorphism on the response to R-CHOP therapy for DLBCL with the basis that FcR polymorphism can affect R’s affinity for ADCC effector cells. Patients and Methods: The FcγRIIIa and FcγRIIa gene polymorphisms were determined in DLBCL patients receiving R-CHOP (n=113) comparing to CHOP therapy (n=85). Results: The FcγRIIIa valine (V) allele was significantly correlated with higher complete response rate to R-CHOP compared to phenylalalnine (F) allele (88% in V/V versus 79% in V/F versus 50% in F/F, p=0.002), while no difference was found between FcγRIIa polymorphism. In addition, V/V allele was associated with faster achievement of response than other alleles. The impact of FcγRIIIa gene polymorphism on response rate was not noted in CHOP group. In terms of overall or event-free survival, no difference was found according to FcγRIIIa or FcγRIIa alleles. Conclusion: The FcγRIIIa SNP is predictive of response to R-CHOP, but does not correlate with survival in DLBCL patients.

Description: Outside-in signaling of β3 integrins induces and requires phosphorylation at tyrosine-747 (Y747) and tyrosine-759 (Y759) of the β3 subunit, but the mechanism for this requirement is unclear. On the other hand, a key consequence of integrin signaling, cell spreading, is inhibited by calpain cleavage of β3 cytoplasmic domain. Here we show that tyrosine phosphorylation in the synthetic β3 cytoplasmic domain peptide inhibits calpain cleavage. In platelets, tyrosine phosphates inhibitor, sodium vanadate, enhances thrombin-induced phosphorylation at Y747 and Y759, which is associated with the reduced integrin cleavage by calpain. The effects of sodium vanadate is unlikely to be caused by its effects on calpain activity but is likely to be caused by the susceptibility of integrin cytoplasmic domain, because sodium vanadate did not affect the calpain cleavage of another substrate, fodrin, in platelets. To further support the protective effect of tyrosine phosphorylation against calpain cleavage, we show that mouse β3 (DiYF) with both Y759 and Y747 mutated to phenylalanine is more susceptible to calpain cleavage than wild type during thrombin-induced platelet aggregation. Furthermore, phosphorylation at Y747 and Y759 of β3 in the focal adhesion sites and the leading edge of spreading platelets was differentially regulated. Selective dephosphorylation of Y759 is associated with calpain cleavage at Y759. Thus, one mechanism by which tyrosine phosphorylation promotes integrin signaling and cell spreading is its inhibition of calpain cleavage of the β3 cytoplasmic domain.

Description: Chemerin is a potent chemoattractant for cells that express the serpentine receptor CMKLR1 (chemokine-like receptor 1), such as plasmacytoid dendritic cells and tissue macrophages. Chemerin circulates in the blood in a relatively inactive form (prochemerin). Its chemotactic activity is unleashed following proteolytic cleavage of carboxyl-terminal amino acids by serine proteases including plasmin, factor XIIa and VIIa. Recruitment of plasmacytoid dendritic cells and macrophages by chemerin may play a role in local tissue immune and inflammatory responses. The shortest bioactive chemerin peptide NH2-YFPGQFAFS-COOH (9mer) is present in the carboxyl-terminal domain. In this work, we show that plasma carboxypeptidase N (CPN) and B (CPB or activated thrombin-activatable fibrinolysis inhibitor (TAFIa)) (30 nM) remove the C-terminal lysine (K) from YFPGQFAFSK (10mer) (200nM) and enhance the migration of CMKLR1-transfected cells by ∼16-fold. To investigate if sequential proteolysis by plasmin and carboxypeptidases can modulate the activity of chemerin peptides, we generated the carboxyl-terminal 15mer of prochemerin, NH2-YFPGQFAFSKALPRS-COOH. Plasmin cleavage (1 μM) generated a 10mer, which was further processed to 9mer by CPN or CPB (30 nM) cleavage. These sequential cleavages were paralleled by corresponding increases in chemotactic activity. At concentrations as high as 1 μM the 15 mer did not induce chemotaxis; after plasmin cleavage and conversion to 10mer, however, significant chemotactic activity was demonstrated. Treatment with CPN or CPB further enhanced this chemotactic activity. We observed a similar enhancement in bioactivity following sequential plasmin/CPN-or-CPB cleavage of full-length prochemerin. Endogenous plasma CPN supports the activation (∼2.5 fold increase in bioactivity) of plasmin-cleaved prochemerin (0.2 nM). This activation was blocked by incubating plasma with MGTA (DL-2-mercaptomethyl-3-guanidinoethylthiopropanoic acid), a specific CPN inhibitor. In addition, we show that platelets are a rich source of chemerin (20–30 ng of chemerin/5x108 platelets). Chemerin released from activated platelets triggers CMKLR1-transfectant chemotaxis, which was blocked by anti-chemerin antibodies. Thus, the circulating humoral factors reported here (platelets, serine proteases, and carboxypeptidases) may contribute to the regulation of chemerin bioactivity in vivo and therefore play a critical role in CMKLR1-mediated immune responses.

Description: Retroviruses can induce hematopoietic disease via insertional mutagenesis of cancer genes and provide valuable molecular tags for cancer gene discovery. Here we show that insertional mutagenesis can also identify genes that promote the immortalization of hematopoietic cells, which normally have only limited self-renewal. Transduction of mouse bone marrow cells with replication-incompetent murine stem cell virus (MSCV) expressing only neo, followed by serial passage in liquid culture containing stem cell factor (SCF) and interleukin-3 (IL-3), produced immortalized immature myeloid cell lines with neutrophil and macrophage differentiation potential in about 50% of the infected cultures. More than half of the lines have MSCV insertions at Evi1 or Prdm16. These loci encode transcription factor homologs and are validated human myeloid leukemia genes. Integrations are located in intron 1 or 2, where they promote expression of truncated proteins lacking the PRDI-BF1-RIZ1 homologous (PR) domain, similar to what is observed in human leukemias with EVI1 or PRDM16 mutations. Evi1 overexpression alone appears sufficient to immortalize immature myeloid cells and does not seem to require any other cooperating mutations. Genes identified by insertional mutagenesis by their nature could also be involved in immortalization of leukemic stem cells, and thus represent attractive drug targets for treating cancer.

Description: Imatinib has impressive response rates and good tolerability quickly led to its adoption as frontline therapy for all patients with chronic-phase CML (chronic myeloid leukemia), but the therapeutic effect of imatinib is poor in the blast crisis, and imatinib resistance has become a major problem in CML. The possible mechanisms of imatinib resistance include the amplification of BCR-ABL fusion gene and its expression increase, the point mutant of BCR-ABL kinase domain and the effects of other tyrosine kinases such as Src, Hck and Lyn and so on. However, the second-generation tyrosine kinase inhibitors (such as nilotinib and dasatinib), which were developed to overcome imatinib resistance resulting from the point mutant or the activation of other tyrosine kinases, even can not prevent all patients with CML progression to drug resistance. So there would be the other potential factor in imatinib resistance. Our previous studies generated a new imatinib-resistant BCR/ABL-positive cell line, K562-R. The 50% inhibitory concentration of imatinib was 15-fold higher in K562-R than in the wild-type K562. The expression of RhoA gene is up-regulated in K562-R by microarray analyses. RhoA, a small GTPase (24KD), has been found overexpression in breast, colon, head and neck squamous cell carcinoma, bladderand testicular cancer, lung and gastric cancer. It plays an important role in the initiation as well as the progression of human cancer, but the potential role of RhoA related to imatinib resistance has yet been unknown. In this study, we firstly detect the biologic characteristic of K562-R cells with RhoA down-expression by RNA interference. When K562-R cells were transfected with 150nM siRNA-RhoA for 48 hours, the percentage of apoptotic K562-R cells is respectively 12.82% by AnnexinV-PI assay and 9.0% by Hoechst 33258 staining and both have significant increase, cell cycle analysis found significant G0/G1 arrest, the expression of CD29 increase and that of CD71 and GPA have no difference. Secondly, The K562-R cells were treated with three selective inhibitors, including PD98059 (Ras/MAPK inhibitor), LY294002 (PI3K/AKT inhibitor) and AG490(JAK/STAT inhibitor) for 2,4 and 8 hours and the expression of RhoA were analyzed by Western-Blotting. The expression of RhoA is arrested in the K562-R cells treated with PD98059 and AG490 and no different with LY294002. These results indicate that RhoA would be an important target in the down-stream of multi-signal pathways related to imatinib resistance and the potential function of RhoA in imatinib resistance involve in increasing of cell proliferation, resistance to cell apoptosis and changes of cell adhesion.

Description: Dyskeratosis congenita (DC) is a rare inherited bone marrow failure syndrome. Classically, DC presents with progressive bone marrow failure, abnormal skin pigmentation, nail dystrophy, and mucosal leukoplakia. The pattern of inheritance in families with DC suggests an X-linked recessive, an autosomal dominant, and an autosomal recessive form of DC. However, in the majority of patients the occurrence of the disease is sporadic or the family history is unknown. Mutations in four different genes have been associated with DC so far. Mutations in DKC1 have been shown to account for the X-linked form of DC and DKC1 de novo mutations account for about one third of male patients with sporadic disease. Mutations in the telomerase RNA TERC and in the catalytic subunit of telomerase, TERT, have been shown to be responsible for the autosomal dominant form of DC. Interestingly, patients with heterozygous mutations in TERC and TERT often show a milder form of disease and a later age of onset and often lack the classic mucocutaeous features, thus are classified as atypical DC. Very recently homozygosity for a mutation in NOP10 has been identified in one family with autosomal recessive disease. The products of the genes mutated in DC are all components of the telomerase complex, suggesting that disease in patients with DC is caused by a defect in telomere maintenance. Here we investigated two patients, one UPN # 199.001 presenting with the classic manifestations of DC and the other UPN# 284.001 presenting with progressive bone marrow failure but no other clinical features suggestive of DC. In both patients the telomeres measured in peripheral blood mononuclear cells were very short, being defined as being below the 1st percentile. Mutation analysis in the genes associated with DC revealed that patient 199.001 was homozygous for a novel TERT (C2110T) gene mutation, causing an amino acid change (P704S) within the RT domain of TERT. Both parents were heterozygous for the C to T transition. Interestingly however, the father was in addition heterozygote for a second mutation in TERT (C1234T; H412Y) a mutation which has previously been described and has been shown to reduce telomerase activity by 50%. Investigations of the family revealed that the parent’s were distantly related, explaining the same TERT sequence alteration in both parents. Both arms of the family contained members with pulmonary fibrosis. In the second patient 284.001 we identified two different novel TERT gene mutations. One A2537G causes the amino acid change Y846C in the RT domain of TERT whereas the other C2628G causes H876Q also in the RT domain. One of the mutations was inherited from each parent and the parent with the A2537G mutation also had very short telomeres. These two families illustrate that the pattern of inheritance in patients with DC may be complex and show for the first time that homozygous or compound heterozygous TERT gene mutation may be associated with DC. Co-dominance of the three different TERT gene mutations and the inheritance of short telomeres have possibly contributed to development of disease in these patients who were thought to have sporadic DC and idiopathic aplastic anemia.

Description: Proapoptotic Bcl-2 family member Bax is a crucial protein in the induction of apoptosis, and its activation is required for this process. Here we report that Bax is a short-lived protein in malignant B cells and Bax protein levels decreased rapidly when protein synthesis was blocked. Malignant B cells were relatively resistant to tumor necrosis factor–related apoptosis inducing ligand (TRAIL)–induced apoptosis, and this correlated with low basal Bax protein levels. Furthermore, during treatment with TRAIL, the resistant cell lines showed prominent Bax degradation activity. This degradation activity was localized to mitochondrial Bax and could be prevented by truncated Bid, a BH3-only protein; in contrast, cytosolic Bax was relatively stable. The proteasome inhibitor bortezomib is a potent drug in inducing apoptosis in vitro in malignant B-cell lines and primary chronic lymphocytic leukemic (CLL) cells. In CLL cells, bortezomib induced Bax accumulation, translocation to mitochondria, conformational change, and oligomerization. Accumulation and stabilization of Bax protein by bortezomib-sensitized malignant B cells to TRAIL-induced apoptosis. This study reveals that Bax instability confers resistance to TRAIL, which can be reversed by Bax stabilization with a proteasome inhibitor.

Description: Objectives : To explore the role of fluorescence in situ hybridization (FISH) monitoring sex chromosome chimeric status in the identification of leukemic extramedullary relapse and post-transplant lymphoproliferative disease (PTLD) in acute lymphocytic leukemia (ALL) after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Methods: Six ALL patients who received sex-mismatched allo-HSCT manifested extravisceral lymphadenectasis or local lump were investigated. The sex chromosome chimeric status in tumor tissues and bone marrow (BM) were monitored by FISH, and EBV-RNA in the tumor tissues were detected by in situ hybridization (ISH). Results: The sex chromosomes in BM of all 6 patients were 100% donor-derived. Among the sex chromosome chimeric status of tumor tissues, those of three patients were mainly recipient-derived, and the percentage of sex chromosomes derived from recipients were 100%, 100% and 98.0%, respectively, and then they were diagnosed leukemic extramedullary relapse. And those of the other 3 patients were donor-derived, the percentage was 98.5%, 96.0% and 91.5%, respectively, and diagnosed PTLD. EBV-RNA and latent membrane protein (LMP-1) were positive in 2 patients with PTLD and negative in the other 4 patients. One patient with extramedullary relapse obtained partial remission, one with PTLD gained complete remission, and the others died eventually after therapy. Conclusion: Monitoring the sex chromosome chimeric status by FISH is an effective method to distinguish leukemic extramedullary relapse from PTLD in ALL received sex-mismatched donor HSCT.