参考文献

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

Creation of fusion genes by balanced chromosomal translocations is one of the hallmarks of acute myeloid leukemia (AML) and is considered one of the key leukemogenic events in this disease. In t(12;13)(p13;q12) AML,ectopic expression of the homeobox gene CDX2 was detected in addition to expression of the ETV6-CDX2 fusion gene,generated by the chromosomal translocation. Here we show in a murine model of t(12;13)(p13;q12) AML that myeloid leukemogenesis is induced by the ectopic expression of CDX2 and not by the ETV6-CDX2 chimeric gene. Mice transplanted with bone marrow cells retrovirally engineered to express Cdx2 rapidly succumbed to fatal and transplantable AML. The transforming capacity of Cdx2 depended on an intact homeodomain and the N-terminal transactivation domain. Transplantation of bone marrow cells expressing ETV6-CDX2 failed to induce leukemia. Furthermore,coexpression of ETV6-CDX2 and Cdx2 in bone marrow cells did not accelerate the course of disease in transplanted mice compared to Cdx2 alone. These data demonstrate that activation of a protooncogene by a balanced chromosomal translocation can be the pivotal leukemogenic event in AML,characterized by the expression of a leukemia-specific fusion gene. Furthermore,these findings link protooncogene activation to myeloid leukemogenesis,an oncogenic mechanism so far associated mainly with lymphoid leukemias and lymphomas. View Publication

Meis1 and Hoxa9 expression is upregulated by retroviral integration in murine myeloid leukemias and in human leukemias carrying MLL translocations. Both genes also cooperate to induce leukemia in a mouse leukemia acceleration assay,which can be explained,in part,by their physical interaction with each other as well as the PBX family of homeodomain proteins. Here we show that Meis1-deficient embryos have partially duplicated retinas and smaller lenses than normal. They also fail to produce megakaryocytes,display extensive hemorrhaging,and die by embryonic day 14.5. In addition,Meis1-deficient embryos lack well-formed capillaries,although larger blood vessels are normal. Definitive myeloerythroid lineages are present in the mutant embryos,but the total numbers of colony-forming cells are dramatically reduced. Mutant fetal liver cells also fail to radioprotect lethally irradiated animals and they compete poorly in repopulation assays even though they can repopulate all hematopoietic lineages. These and other studies showing that Meis1 is expressed at high levels in hematopoietic stem cells (HSCs) suggest that Meis1 may also be required for the proliferation/self-renewal of the HSC. View Publication

Interleukin-6 (IL-6) is a critical factor in the regulation of stromal function and hematopoiesis. In vivo bromodeoxyuridine incorporation analysis indicates that the percentage of Lin(-)Sca-1(+) hematopoietic progenitors undergoing DNA synthesis is diminished in IL-6-deficient (IL-6(-/-)) bone marrow (BM) compared with wild-type BM. Reduced proliferation of IL-6(-/-) BM progenitors is also observed in IL-6(-/-) long-term BM cultures,which show defective hematopoietic support as measured by production of total cells,granulocyte macrophage-colony-forming units (CFU-GMs),and erythroid burst-forming units (BFU-Es). Seeding experiments of wild-type and IL-6(-/-) BM cells on irradiated wild-type or IL-6-deficient stroma indicate that the hematopoietic defect can be attributed to the stromal and not to the hematopoietic component. In IL-6(-/-) BM,stromal mesenchymal precursors,fibroblast CFUs (CFU-Fs),and stroma-initiating cells (SICs) are reduced to almost 50% of the wild-type BM value. Moreover,IL-6(-/-) stromata show increased CD34 and CD49e expression and reduced expression of the membrane antigens vascular cell adhesion molecule-1 (VCAM-1),Sca-1,CD49f,and Thy1. These data strongly suggest that IL-6 is an in vivo growth factor for mesenchymal precursors,which are in part implicated in the reduced longevity of the long-term repopulating stem cell compartment of IL-6(-/-) mice. View Publication

Abnormal differentiation of myeloid cells is one of the hallmarks of cancer. However,the molecular mechanisms of this process remain elusive. In this study,we investigated the effect of tumor-derived factors on Janus kinase (Jak)/STAT signaling in myeloid cells during their differentiation into dendritic cells. Tumor cell conditioned medium induced activation of Jak2 and STAT3,which was associated with an accumulation of immature myeloid cells. Jak2/STAT3 activity was localized primarily in these myeloid cells,which prevented the differentiation of immature myeloid cells into mature dendritic cells. This differentiation was restored after removal of tumor-derived factors. Inhibition of STAT3 abrogated the negative effects of these factors on myeloid cell differentiation,and overexpression of STAT3 reproduced the effects of tumor-derived factors. Thus,this is a first demonstration that tumor-derived factors may affect myeloid cell differentiation in cancer via constitutive activation of Jak2/STAT3. View Publication

We have characterized several potential stem cell markers and defined the membrane properties of rat fetal (E10.5) neural stem cells (NSC) by immunocytochemistry,electrophysiology and microarray analysis. Immunocytochemical analysis demonstrates specificity of expression of Sox1,ABCG2/Bcrp1,and shows that nucleostemin labels both progenitor and stem cell populations. NSCs,like hematopoietic stem cells,express high levels of aldehyde dehydrogenase (ALDH) as assessed by Aldefluor labeling. Microarray analysis of 96 transporters and channels showed that Glucose transporter 1 (Glut1/Slc2a1) expression is unique to fetal NSCs or other differentiated cells. Electrophysiological examination showed that fetal NSCs respond to acetylcholine and its agonists,such as nicotine and muscarine. NSCs express low levels of tetrodotoxin (TTX) sensitive and insensitive sodium channels and calcium channels while expressing at least three kinds of potassium channels. We find that gap junction communication is mediated by connexin (Cx)43 and Cx45,and is essential for NSC survival and proliferation. Overall,our results show that fetal NSCs exhibit a unique signature that can be used to determine their location and assess their ability to respond to their environment. View Publication

OBJECTIVE: Ionizing radiation (IR) and busulfan (BU) are commonly used as preconditioning regimens for bone marrow transplantation (BMT). We examined whether induction of apoptosis in murine bone marrow (BM) hematopoietic cells contributes to IR- and BU-induced suppression of their hematopoietic function. METHODS: The hematopoietic functions of hematopoietic stem cells (HSCs) and progenitors were analyzed by the cobblestone area-forming cell (CAFC) assay. Apoptosis was determined by measuring 3,3'-dihexyloxacarbocyanine iodide (DiCO6) uptake,annexin V staining,and/or sub-G(0/1) cells. Four cell types were studied: murine BM mononuclear cells (BM-MNCs),linage-negative hematopoietic cells (Lin-) cells),Lin- Scal+ c-kit+ cells,and Lin- Scal- c-kit+ cells by flow cytometry. RESULTS: Exposure of BM-MNCs to IR (4 Gy) or incubation of the cells with BU (30 microM) resulted in a significant reduction in CAFC frequency (ptextless0.001). The survival fractions of various day-types of CAFC for the irradiated cells were less than 10%,while that for BU-treated cells was 71.3% on day 7 and progressively declined to 5.3% on day 35. Interestingly,IR significantly induced apoptosis in BM-MNCs,Lin- cells,HSCs,and progenitors,whereas BU failed to increase apoptosis in these cells. In addition,preincubation of BM-MNCs with z-Val-Ala-Asp (OCH3)-fluoromethylketone,methyl ester (z-VAD) attenuated IR-induced reduction in CAFC but not that induced by BU. CONCLUSION: IR and BU differentially suppress the hematopoietic function of HSCs and progenitors by fundamentally different mechanisms. IR inhibits the function primarily by the induction of HSC and progenitor apoptosis. In contrast,BU suppresses HSC and progenitor function via an apoptosis-independent mechanism. View Publication

We have observed karyotypic changes involving the gain of chromosome 17q in three independent human embryonic stem (hES) cell lines on five independent occasions. A gain of chromosome 12 was seen occasionally. This implies that increased dosage of chromosome 17q and 12 gene(s) provides a selective advantage for the propagation of undifferentiated hES cells. These observations are instructive for the future application of hES cells in transplantation therapies in which the use of aneuploid cells could be detrimental. View Publication

CD4+ T cells are required for immunity against many viral infections,including HIV-1 where a positive correlation has been observed between strong recall responses and low HIV-1 viral loads. Some HIV-1-specific CD4+ T cells are preferentially infected with HIV-1,whereas others escape infection by unknown mechanisms. One possibility is that some CD4+ T cells are protected from infection by the secretion of soluble HIV-suppressive factors,although it is not known whether these factors are produced during primary antigen-specific responses. Here,we show that soluble suppressive factors are produced against CXCR4 and CCR5 isolates of HIV-1 during the primary immune response of human CD4+ T cells. This activity requires antigenic stimulation of naïve CD4+ T cells. One anti-CXCR4 factor is macrophage-derived chemokine (chemokine ligand 22,CCL22),and anti-CCR5 factors include macrophage inflammatory protein-1 alpha (CCL3),macrophage inflammatory protein-1 beta (CCL4),and RANTES (regulated upon activation of normal T cells expressed and secreted) (CCL5). Intracellular staining confirms that CD3+CD4+ T cells are the source of the prototype HIV-1-inhibiting chemokines CCL22 and CCL4. These results show that CD4+ T cells secrete an evolving HIV-1-suppressive activity during the primary immune response and that this activity is comprised primarily of CC chemokines. The data also suggest that production of such factors should be considered in the design of vaccines against HIV-1 and as a mechanism whereby the host can control infections with this virus. View Publication

The CCAAT/enhancer binding protein alpha (C/EBPalpha) is an essential transcription factor for granulocytic differentiation. C/EBPalpha mutations are found in approximately 8% of acute myeloid leukemia (AML) patients. Most of these mutations occur in the N-terminal coding region,resulting in a frame shift and the enhanced translation of a dominant-negative 30-kDa protein,which may be responsible for the differentiation block observed in AML. To test this hypothesis,we introduced a cDNA encoding an N-terminal mutated C/EBPalpha (mut10) into primary hematopoietic progenitors using a retroviral vector. Expression of mut10 in human CD34+ cord blood cells dramatically inhibited differentiation of both myeloid and erythroid lineages. Immunohistochemical analysis demonstrated coexpression of both myeloid and erythroid markers in the immature transformed cells. Surprisingly,mut10 did not block myelocytic differentiation in murine progenitors but did alter their differentiation kinetics and clonogenicity. Experiments were performed to confirm that the differential effect of mut10 on murine and human progenitors was not due to species-specific differences in C/EBPalpha protein sequences,expression levels,or inefficient targeting of relevant cells. Taken together,our results underline the intrinsic differences between hematopoietic controls in mouse and human and support the hypothesis that mutations in CEBPA are critical events in the disruption of myeloid differentiation in AMLs. View Publication