技术资料

Although practiced clinically for more than 40 years,the use of hematopoietic stem cell (HSC) transplants remains limited by the ability to expand these cells ex vivo. An unbiased screen with primary human HSCs identified a purine derivative,StemRegenin 1 (SR1),that promotes the ex vivo expansion of CD34+ cells. Culture of HSCs with SR1 led to a 50-fold increase in cells expressing CD34 and a 17-fold increase in cells that retain the ability to engraft immunodeficient mice. Mechanistic studies show that SR1 acts by antagonizing the aryl hydrocarbon receptor (AHR). The identification of SR1 and AHR modulation as a means to induce ex vivo HSC expansion should facilitate the clinical use of HSC therapy. View Publication

Cytosolic aldehyde dehydrogenase (ALDH),an enzyme responsible for oxidizing intracellular aldehydes,has an important role in ethanol,vitamin A,and cyclophosphamide metabolism. High expression of this enzyme in primitive stem cells from multiple tissues,including bone marrow and intestine,appears to be an important mechanism by which these cells are resistant to cyclophosphamide. However,although hematopoietic stem cells (HSC) express high levels of cytosolic ALDH,isolating viable HSC by their ALDH expression has not been possible because ALDH is an intracellular protein. We found that a fluorescent aldehyde,dansyl aminoacetaldehyde (DAAA),could be used in flow cytometry experiments to isolate viable mouse and human cells based on their ALDH content. The level of dansyl fluorescence exhibited by cells after incubation with DAAA paralleled cytosolic ALDH levels determined by Western blotting and the sensitivity of the cells to cyclophosphamide. Moreover,DAAA appeared to be a more sensitive means of assessing cytosolic ALDH levels than Western blotting. Bone marrow progenitors treated with DAAA proliferated normally. Furthermore,marrow cells expressing high levels of dansyl fluorescence after incubation with DAAA were enriched for hematopoietic progenitors. The ability to isolate viable cells that express high levels of cytosolic ALDH could be an important component of methodology for identifying and purifying HSC and for studying cyclophosphamide-resistant tumor cell populations. View Publication

Lifelong blood cell production is governed through the poorly understood integration of cell-intrinsic and -extrinsic control of hematopoietic stem cell (HSC) quiescence and activation. MicroRNAs (miRNAs) coordinately regulate multiple targets within signaling networks,making them attractive candidate HSC regulators. We report that miR-126,a miRNA expressed in HSC and early progenitors,plays a pivotal role in restraining cell-cycle progression of HSC in vitro and in vivo. miR-126 knockdown by using lentiviral sponges increased HSC proliferation without inducing exhaustion,resulting in expansion of mouse and human long-term repopulating HSC. Conversely,enforced miR-126 expression impaired cell-cycle entry,leading to progressively reduced hematopoietic contribution. In HSC/early progenitors,miR-126 regulates multiple targets within the PI3K/AKT/GSK3β pathway,attenuating signal transduction in response to extrinsic signals. These data establish that miR-126 sets a threshold for HSC activation and thus governs HSC pool size,demonstrating the importance of miRNA in the control of HSC function. View Publication

The stem-cell pool is considered to be maintained by a balance between symmetric and asymmetric division of stem cells. The cell polarity model proposes that the facultative use of symmetric and asymmetric cell division is orchestrated by a polarity complex consisting of partitioning-defective proteins Par3 and Par6,and atypical protein kinase C (aPKCζ and aPKCλ),which regulates planar symmetry of dividing stem cells with respect to the signaling microenvironment. However,the role of the polarity complex is unexplored in mammalian adult stem-cell functions. Here we report that,in contrast to accepted paradigms,polarization and activity of adult hematopoietic stem cell (HSC) do not depend on either aPKCζ or aPKCλ or both in vivo. Mice,having constitutive and hematopoietic-specific (Vav1-Cre) deletion of aPKCζ and aPKCλ,respectively,have normal hematopoiesis,including normal HSC self-renewal,engraftment,differentiation,and interaction with the bone marrow microenvironment. Furthermore,inducible complete deletion of aPKCλ (Mx1-Cre) in aPKCζ(-/-) HSC does not affect HSC polarization,self-renewal,engraftment,or lineage repopulation. In addition,aPKCζ- and aPKCλ-deficient HSCs elicited a normal pattern of hematopoietic recovery secondary to myeloablative stress. Taken together,the expression of aPKCζ,aPKCλ,or both are dispensable for primitive and adult HSC fate determination in steady-state and stress hematopoiesis,contrary to the hypothesis of a unique,evolutionary conserved aPKCζ/λ-directed cell polarity signaling mechanism in mammalian HSC fate determination. View Publication

Aurora kinases play an important role in chromosome alignment,segregation,and cytokinesis during mitosis. We have recently shown that hematopoietic malignant cells including those from acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL) aberrantly expressed Aurora A and B kinases,and ZM447439,a potent inhibitor of Aurora kinases,effectively induced growth arrest and apoptosis of a variety of leukemia cells. The present study explored the effect of AZD1152,a highly selective inhibitor of Aurora B kinase,on various types of human leukemia cells. AZD1152 inhibited the proliferation of AML lines (HL-60,NB4,MOLM13),ALL line (PALL-2),biphenotypic leukemia (MV4-11),acute eosinophilic leukemia (EOL-1),and the blast crisis of chronic myeloid leukemia K562 cells with an IC50 ranging from 3 nM to 40 nM,as measured by thymidine uptake on day 2 of culture. These cells had 4N/8N DNA content followed by apoptosis,as measured by cell-cycle analysis and annexin V staining,respectively. Of note,AZD1152 synergistically enhanced the antiproliferative activity of vincristine,a tubulin depolymerizing agent,and daunorubicin,a topoisomerase II inhibitor,against the MOLM13 and PALL-2 cells in vitro. Furthermore,AZD1152 potentiated the action of vincristine and daunorubicin in a MOLM13 murine xenograft model. Taken together,AZD1152 is a promising new agent for treatment of individuals with leukemia. The combined administration of AZD1152 and conventional chemotherapeutic agent to patients with leukemia warrants further investigation. View Publication

The immunodeficiency disorder,X-linked agammaglobulinemia (XLA),results from mutations in the gene encoding Bruton tyrosine kinase (Btk). Btk is required for pre-B cell clonal expansion and B-cell antigen receptor signaling. XLA patients lack mature B cells and immunoglobulin and experience recurrent bacterial infections only partially mitigated by life-long antibody replacement therapy. In pursuit of definitive therapy for XLA,we tested ex vivo gene therapy using a lentiviral vector (LV) containing the immunoglobulin enhancer (Emu) and Igbeta (B29) minimal promoter to drive B lineage-specific human Btk expression in Btk/Tec(-/-) mice,a strain that reproduces the features of human XLA. After transplantation of EmuB29-Btk-LV-transduced stem cells,treated mice showed significant,albeit incomplete,rescue of mature B cells in the bone marrow,peripheral blood,spleen,and peritoneal cavity,and improved responses to T-independent and T-dependent antigens. LV-treated B cells exhibited enhanced B-cell antigen receptor signaling and an in vivo selective advantage in the peripheral versus central B-cell compartment. Secondary transplantation showed sustained Btk expression,viral integration,and partial functional responses,consistent with long-term stem cell marking; and serial transplantation revealed no evidence for cellular or systemic toxicity. These findings strongly support pursuit of B lineage-targeted LV gene therapy in human XLA. View Publication

Earlier reports have suggested that the BCR/ABL oncogene,associated with chronic myeloid leukemia,induces a mutator phenotype; however,it is unclear whether this leads to long-term changes in chromosomes and whether the phenotype is found in primary chronic myelogeneous leukemia (CML) cells. We have addressed both these issues. BCR/ABL-expressing cell lines show an increase in DNA breaks after treatment with etoposide as compared to control cells. However,although BCR/ABL-expressing cell lines have an equivalent cell survival,they have an increase in chromosomal translocations after DNA repair as compared to control cells. This demonstrates that BCR/ABL expression decreases the fidelity of DNA repair. To see whether this is true in primary CML samples,normal CD34+ progenitor cells and CML progenitor cells were treated with etoposide. CML progenitor cells have equivalent survival but have an increase in DNA double-strand breaks (DSBs). Spectral karyotyping demonstrates new chromosomal translocations in CML cells,but not normal progenitor cells,consistent with error-prone DNA repair. Taken together,these data demonstrate that BCR/ABL enhances the accumulation of DSBs and alters the apoptotic threshold in CML leading to error-prone DNA repair. View Publication

BCR/ABL kinase-positive chronic myelogenous leukemia (CML) cells display genomic instability leading to point mutations in various genes including bcr/abl and p53,eventually causing resistance to imatinib and malignant progression of the disease. Mismatch repair (MMR) is responsible for detecting misincorporated nucleotides,resulting in excision repair before point mutations occur and/or induction of apoptosis to avoid propagation of cells carrying excessive DNA lesions. To assess MMR activity in CML,we used an in vivo assay using the plasmid substrate containing enhanced green fluorescent protein (EGFP) gene corrupted by T:G mismatch in the start codon; therefore,MMR restores EGFP expression. The efficacy of MMR was reduced approximately 2-fold in BCR/ABL-positive cell lines and CD34(+) CML cells compared with normal counterparts. MMR was also challenged by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG),which generates O(6)-methylguanine and O(4)-methylthymine recognized by MMR system. Impaired MMR activity in leukemia cells was associated with better survival,accumulation of p53 but not of p73,and lack of activation of caspase 3 after MNNG treatment. In contrast,parental cells displayed accumulation of p53,p73,and activation of caspase 3,resulting in cell death. Ouabain-resistance test detecting mutations in the Na(+)/K(+) ATPase was used to investigate the effect of BCR/ABL kinase-mediated inhibition of MMR on mutagenesis. BCR/ABL-positive cells surviving the treatment with MNNG displayed approximately 15-fold higher mutation frequency than parental counterparts and predominantly G:C--textgreaterA:T and A:T--textgreaterG:C mutator phenotype typical for MNNG-induced unrepaired lesions. In conclusion,these results suggest that BCR/ABL kinase abrogates MMR activity to inhibit apoptosis and induce mutator phenotype. View Publication

Drug resistance resulting from emergence of imatinib-resistant BCR-ABL point mutations is a significant problem in advanced-stage chronic myelogenous leukemia (CML). The BCR-ABL inhibitor,nilotinib (AMN107),is significantly more potent against BCR-ABL than imatinib,and is active against many imatinib-resistant BCR-ABL mutants. Phase 1/2 clinical trials show that nilotinib can induce remissions in patients who have previously failed imatinib,indicating that sequential therapy with these 2 agents has clinical value. However,simultaneous,rather than sequential,administration of 2 BCR-ABL kinase inhibitors is attractive for many reasons,including the theoretical possibility that this could reduce emergence of drug-resistant clones. Here,we show that exposure of a variety of BCR-ABL+ cell lines to imatinib and nilotinib results in additive or synergistic cytotoxicity,including testing of a large panel of cells expressing BCR-ABL point mutations causing resistance to imatinib in patients. Further,using a highly quantifiable bioluminescent in vivo model,drug combinations were at least additive in antileukemic activity,compared with each drug alone. These results suggest that despite binding to the same site in the same target kinase,the combination of imatinib and nilotinib is highly efficacious in these models,indicating that clinical testing of combinations of BCR-ABL kinase inhibitors is warranted. View Publication