技术资料

In order to investigate the biologic processes underlying and resulting from the megakaryocytic hyperplasia that characterizes idiopathic myelofibrosis (IMF),peripheral blood CD34+ cells isolated from patients with IMF,polycythemia vera (PV),and G-CSF-mobilized healthy volunteers were cultured in the presence of stem cell factor and thrombopoietin. IMF CD34+ cells generated 24-fold greater numbers of megakaryocytes (MKs) than normal CD34+ cells. IMF MKs were also shown to have a delayed pattern of apoptosis and to overexpress the antiapoptotic protein bcl-xL. MK hyperplasia in IMF is,therefore,likely a consequence of both the increased ability of IMF progenitor cells to generate MKs and a decreased rate of MK apoptosis. Media conditioned (CM) by CD61+ cells generated in vitro from CD34+ cells were then assayed for the levels of growth factors and proteases. Higher levels of transforming growth factor-beta (TGF-beta) and active matrix metalloproteinase-9 (MMP9) were observed in media conditioned with IMF CD61+ cells than normal or PV CD61+ cells. Both normal and IMF CD61+ cells produced similar levels of VEGF. MK-derived TGF-B and MMP-9,therefore,likely contribute to the development of many pathological epiphenomena associated with IMF. View Publication

Infection with a recombinant murine-feline gammaretrovirus,MoFe2,or with the parent virus,Moloney murine leukemia virus,caused significant reduction in B-lymphoid differentiation of bone marrow at 2 to 8 weeks postinfection. The suppression was selective,in that myeloid potential was significantly increased by infection. Analysis of cell surface markers and immunoglobulin H gene rearrangements in an in vitro model demonstrated normal B-lymphoid differentiation after infection but significantly reduced viability of differentiating cells. This reduction in viability may confer a selective advantage on undifferentiated lymphoid progenitors in the bone marrow of gammaretrovirus-infected animals and thereby contribute to the establishment of a premalignant state. View Publication

Chaetocin,a thiodioxopiperazine natural product previously unreported to have anticancer effects,was found to have potent antimyeloma activity in IL-6-dependent and -independent myeloma cell lines in freshly collected sorted and unsorted patient CD138(+) myeloma cells and in vivo. Chaetocin largely spares matched normal CD138(-) patient bone marrow leukocytes,normal B cells,and neoplastic B-CLL (chronic lymphocytic leukemia) cells,indicating a high degree of selectivity even in closely lineage-related B cells. Furthermore,chaetocin displays superior ex vivo antimyeloma activity and selectivity than doxorubicin and dexamethasone,and dexamethasone- or doxorubicin-resistant myeloma cell lines are largely non-cross-resistant to chaetocin. Mechanistically,chaetocin is dramatically accumulated in cancer cells via a process inhibited by glutathione and requiring intact/unreduced disulfides for uptake. Once inside the cell,its anticancer activity appears mediated primarily through the imposition of oxidative stress and consequent apoptosis induction. Moreover,the selective antimyeloma effects of chaetocin appear not to reflect differential intracellular accumulation of chaetocin but,instead,heightened sensitivity of myeloma cells to the cytotoxic effects of imposed oxidative stress. Considered collectively,chaetocin appears to represent a promising agent for further study as a potential antimyeloma therapeutic. View Publication

Genes that are strongly repressed after B-cell activation are candidates for being inactivated,mutated,or repressed in B-cell malignancies. Krüppel-like factor 4 (Klf4),a gene down-regulated in activated murine B cells,is expressed at low levels in several types of human B-cell lineage lymphomas and leukemias. The human KLF4 gene has been identified as a tumor suppressor gene in colon and gastric cancer; in concordance with this,overexpression of KLF4 can suppress proliferation in several epithelial cell types. Here we investigate the effects of KLF4 on pro/pre-B-cell transformation by v-Abl and BCR-ABL,oncogenes that cause leukemia in mice and humans. We show that overexpression of KLF4 induces arrest and apoptosis in the G1 phase of the cell cycle. KLF4-mediated death,but not cell-cycle arrest,can be rescued by Bcl-XL overexpression. Transformed pro/pre-B cells expressing KLF4 display increased expression of p21CIP and decreased expression of c-Myc and cyclin D2. Tetracycline-inducible expression of KLF4 in B-cell progenitors of transgenic mice blocks transformation by BCR-ABL and depletes leukemic pre-B cells in vivo. Collectively,our work identifies KLF4 as a putative tumor suppressor in B-cell malignancies. View Publication

Activating mutations of c-KIT lead to ligand-independent growth. Internal tandem duplications (ITDs) of exon 11,which encodes the juxtamembrane domain (JMD),are constitutively activating mutations found in 7% of gastrointestinal stromal tumors (GISTs) but have not been described in childhood acute myeloid leukemia (AML). DNA and cDNA from 60 children with AML were screened by polymerase chain reaction (PCR) for mutations of the JMD. A complex ITD (kit cITD) involving exon 11 and exon 12 was identified with a relative frequency of 7% (4/60). The human kit cITDs were inserted into the murine c-Kit backbone and expressed in Ba/F3 cells. KIT cITD induced factorindependent growth and apoptosis resistance,and exhibited constitutive autophosphorylation. KIT cITD constitutively activated the PI3K/AKT pathway and phosphorylated STAT1,STAT3,STAT5,and SHP-2. Imatinib (IM) or rapamycin (Rap) led to complete inhibition of growth,with IC50 values at nanomolar levels. IM and Rap synergistically inhibited growth and surmounted KIT cITD-induced apoptosis resistance. IM but not LY294002 inhibited phosphorylation of STAT3 and STAT5,suggesting aberrant cross talk between PI3K- and STAT-activating pathways. The findings presented may have immediate therapeutic impact for a subgroup of childhood AML-expressing c-KIT mutations. View Publication

The 2 most frequent human MLL hematopoietic malignancies involve either AF4 or AF9 as fusion partners; each has distinct biology but the role of the fusion partner is not clear. We produced Mll-AF4 knock-in (KI) mice by homologous recombination in embryonic stem cells and compared them with Mll-AF9 KI mice. Young Mll-AF4 mice had lymphoid and myeloid deregulation manifest by increased lymphoid and myeloid cells in hematopoietic organs. In vitro,bone marrow cells from young mice formed unique mixed pro-B lymphoid (B220(+)CD19(+)CD43(+)sIgM(-),PAX5(+),TdT(+),IgH rearranged)/myeloid (CD11b/Mac1(+),c-fms(+),lysozyme(+)) colonies when grown in IL-7- and Flt3 ligand-containing media. Mixed lymphoid/myeloid hyperplasia and hematologic malignancies (most frequently B-cell lymphomas) developed in Mll-AF4 mice after prolonged latency; long latency to malignancy indicates that Mll-AF4-induced lymphoid/myeloid deregulation alone is insufficient to produce malignancy. In contrast,young Mll-AF9 mice had predominately myeloid deregulation in vivo and in vitro and developed myeloid malignancies. The early onset of distinct mixed lymphoid/myeloid lineage deregulation in Mll-AF4 mice shows evidence for both instructive" and "noninstructive" roles for AF4 and AF9 as partners in MLL fusion genes. The molecular basis for "instruction" and secondary cooperating mutations can now be studied in our Mll-AF4 model." View Publication

BACKGROUND AND OBJECTIVES: Campath-1H is used in conditioning regimens and more recently as an anti-leukemic therapy in acute lymphoblastic leukemias (ALL). We therefore investigated CD52 expression and campath-1H-mediated lysis of ALL cells in vitro. DESIGN AND METHODS: Complement-mediated cytotoxicity assays were performed on freshly isolated neoplastic cells and cell lines using human serum. Antibody-dependent cellular cytotoxicity (ADCC) was performed by calcein-AM release assays. RESULTS: CD52 was expressed in four out of eight ALL cell lines studied. Among 61 freshly isolated ALL samples CD52 was expressed at varying levels in 87% of cases. Whereas ADCC was equivalent in different CD52+ lines,complement-dependent cytotoxicity (CDC) was variable. The REH cell line bearing the t(12;21) translocation showed 47-60% lysis when treated with 10 microg/mL campath-1H compared to 0-6% for the other cell lines expressing equivalent amounts of CD52. Furthermore all nine ALL samples with t(12;21) showed very high CDC (mean 97%) compared to the other 24 CD52+cases (mean 24%)(ptextless0.0001). In t(12;21) samples,efficient CDC was obtained with as little as 1 microg/mL campath-1H. CDC correlated in part with CD52 levels,suggesting that CD52 expression and other yet undefined factors contribute to the particular sensitivity of t(12;21) cells. The resistance of non t(12;21) ALL cases could be overcome to a limited extent by increasing the concentration of campath-1H,blocking the CD55 and CD59 complement inhibitors,and more effectively by combining campath-1H with fludarabine. INTERPRETATION AND CONCLUSIONS: We conclude that most ALL samples express CD52 to a variable level and that campath-1H has cytotoxic activity against CD52+ALL,alone or in combination with cytotoxic drugs. View Publication

Deletions and/or mutations of p53 are relatively rare and late events in the natural history of B-cell chronic lymphocytic leukemia (B-CLL). However,it is unknown whether p53 signaling is functional in B-CLL and if targeted nongenotoxic activation of the p53 pathway by using nutlin-3,a small molecule inhibitor of the p53/MDM2 interaction,is sufficient to kill B-CLL cells. In vitro treatment with nutlin-3 induced a significant cytotoxicity on primary CD19(+) B-CLL cells,but not on normal CD19(+) B lymphocytes,peripheral-blood mononuclear cells,or bone marrow hematopoietic progenitors. Among 29 B-CLL samples examined,only one was resistant to nutlin-3-mediated cytotoxicity. The induction of p53 by nutlin-3 in B-CLL samples was accompanied by alterations of the mitochondrial potential and activation of the caspase-dependent apoptotic pathway. Among several genes related to the p53 pathway,nutlin-3 up-regulated the steady-state mRNA levels of PCNA,CDKN1A/p21,GDF15,TNFRSF10B/TRAIL-R2,TP53I3/PIG3,and GADD45. This profile of gene activation showed a partial overlapping with that induced by the genotoxic drug fludarabine. Moreover,nutlin-3 synergized with both fludarabine and chlorambucil in inducing B-CLL apoptosis. Our data strongly suggest that nutlin-3 should be further investigated for clinical applications in the treatment of B-CLL. View Publication

Hereditary hemochromatosis (HH),an iron overload disease associated with mutations in the HFE gene,is characterized by increased intestinal iron absorption and consequent deposition of excess iron,primarily in the liver. Patients with HH and Hfe-deficient (Hfe-/-) mice manifest inappropriate expression of the iron absorption regulator hepcidin,a peptide hormone produced by the liver in response to iron loading. In this study,we investigated the contribution of Hfe expression in macrophages to the regulation of liver hepcidin levels and iron loading. We used bone marrow transplantation to generate wild-type (wt) and Hfe-/- mice chimeric for macrophage Hfe gene expression. Reconstitution of Hfe-deficient mice with wt bone marrow resulted in augmented capacity of the spleen to store iron and in significantly decreased liver iron loading,accompanied by a significant increase of hepatic hepcidin mRNA levels. Conversely,wt mice reconstituted with Hfe-deficient bone marrow had a diminished capacity to store iron in the spleen but no significant alterations of liver iron stores or hepcidin mRNA levels. Our results suggest that macrophage Hfe participates in the regulation of splenic and liver iron concentrations and liver hepcidin expression. View Publication

BCR-ABL and v-ABL are oncogenic forms of the Abl tyrosine kinase that can cause leukemias in mice and humans. ABL oncogenes trigger multiple signaling pathways whose contribution to transformation varies among cell types. Activation of phosphoinositide 3-kinase (PI3K) is essential for ABL-dependent proliferation and survival in some cell types,and global PI3K inhibitors can enhance the antileukemia effects of the Abl kinase inhibitor imatinib. Although a significant fraction of BCR-ABL-induced human leukemias are of B-cell origin,little is known about PI3K signaling mechanisms in B-lineage cells transformed by ABL oncogenes. Here we show that activation of class I(A) PI3K and downstream inactivation of FOXO transcription factors are essential for survival of murine pro/pre-B cells transformed by v-ABL or BCR-ABL. In addition,analysis of mice lacking individual PI3K genes indicates that products of the Pik3r1 gene contribute to transformation efficiency by BCR-ABL. These findings establish a role for PI3K signaling in B-lineage transformation by ABL oncogenes. View Publication

The t(12;21)(p13;q22) translocation is the most common chromosomal abnormality yet identified in any pediatric leukemia and gives rise to the TEL-AML1 fusion product. To investigate the effects of TEL-AML1 on hematopoiesis,fetal liver hematopoietic progenitor cells (HPCs) were transduced with retroviral vectors expressing this fusion protein. We show that TEL-AML1 dramatically alters differentiation of HPCs in vitro,preferentially promoting B-lymphocyte development,enhancing self-renewal of B-cell precursors,and leading to the establishment of long-term growth factor-dependent pre-B-cell lines. However,it had no effect on myeloid development in vitro. Further experiments were performed to determine whether TEL-AML1 also demonstrates lineage-specific activity in vivo. TEL-AML1-expressing HPCs displayed a competitive advantage in reconstituting both B-cell and myeloid lineages in vivo but had no effect on reconstitution of the T-cell lineage. Despite promoting these alterations in hematopoiesis,TEL-AML1 did not induce leukemia in transplanted mice. Our study provides a unique insight into the role of TEL-AML1 in leukemia predisposition and a potential model to study the mechanism of leukemogenesis associated with this fusion. View Publication

We studied the actions of geldanamycin (GA) and herbimycin A (HMA),inhibitors of the chaperone proteins Hsp90 and GRP94,on B chronic lymphocytic leukemia (CLL) cells in vitro. Both drugs induced apoptosis of the majority of CLL isolates studied. Whereas exposure to 4-hour pulses of 30 to 100 nM GA killed normal B lymphocytes and CLL cells with similar dose responses,T lymphocytes from healthy donors as well as those present in the CLL isolates were relatively resistant. GA,but not HMA,showed a modest cytoprotective effect toward CD34+ hematopoietic progenitors from normal bone marrow. The ability of bone marrow progenitors to form hematopoietic colonies was unaffected by pulse exposures to GA. Both GA and HMA synergized with chlorambucil and fludarabine in killing a subset of CLL isolates. GA- and HMA-induced apoptosis was preceded by the up-regulation of the stress-responsive chaperones Hsp70 and BiP. Both ansamycins also resulted in down-regulation of Akt protein kinase,a modulator of cell survival. The relative resistance of T lymphocytes and of CD34+ bone marrow progenitors to GA coupled with its ability to induce apoptosis following brief exposures and to synergize with cytotoxic drugs warrant further investigation of ansamycins as potential therapeutic agents in CLL. View Publication