参考文献

During ontogenesis and the entire adult life hematopoietic stem and progenitor cells have the capability to migrate. In comparison to the process of peripheral leukocyte migration in inflammatory responses,the molecular and cellular mechanisms governing the migration of these cells remain poorly understood. A common feature of migrating cells is that they need to become polarized before they migrate. Here we have investigated the issue of cell polarity of hematopoietic stem/progenitor cells in detail. We found that human CD34(+) hematopoietic cells (1) acquire a polarized cell shape upon cultivation,with the formation of a leading edge at the front pole and a uropod at the rear pole; (2) exhibit an amoeboid movement,which is similar to the one described for migrating peripheral leukocytes; and (3) redistribute several lipid raft markers including cholesterol-binding protein prominin-1 (CD133) in specialized plasma membrane domains. Furthermore,polarization of CD34(+) cells is stimulated by early acting cytokines and requires the activity of phosphoinositol-3-kinase as previously reported for peripheral leukocyte polarization. Together,our data reveal a strong correlation between polarization and migration of peripheral leukocytes and hematopoietic stem/progenitor cells and suggest that they are governed by similar mechanisms. View Publication

Blebbistatin is a recently discovered small molecule inhibitor showing high affinity and selectivity toward myosin II. Here we report a detailed investigation of its mechanism of inhibition. Blebbistatin does not compete with nucleotide binding to the skeletal muscle myosin subfragment-1. The inhibitor preferentially binds to the ATPase intermediate with ADP and phosphate bound at the active site,and it slows down phosphate release. Blebbistatin interferes neither with binding of myosin to actin nor with ATP-induced actomyosin dissociation. Instead,it blocks the myosin heads in a products complex with low actin affinity. Blind docking molecular simulations indicate that the productive blebbistatin-binding site of the myosin head is within the aqueous cavity between the nucleotide pocket and the cleft of the actin-binding interface. The property that blebbistatin blocks myosin II in an actin-detached state makes the compound useful both in muscle physiology and in exploring the cellular function of cytoplasmic myosin II isoforms,whereas the stabilization of a specific myosin intermediate confers a great potential in structural studies. View Publication

The human peripheral B-cell compartment displays a large population of immunoglobulin M-positive,immunoglobulin D-positive CD27(+) (IgM(+)IgD(+)CD27(+)) memory" B cells carrying a mutated immunoglobulin receptor. By means of phenotypic analysis View Publication

It is unclear by which receptor cyclic adenosine monophosphate (cAMP) acts to promote neutrophil survival. We found that 8-(4-chlorophenylthio)-2'-O-methyl-cAMP,a specific activator of the recently discovered cAMP receptor,cAMP-regulated guanosine 5'-triphosphate exchange protein directly activated by cAMP,failed to protect human neutrophils from cell death. In contrast,specific activators of cAMP-dependent protein kinase type I (cA-PKI) could protect against death receptor [tumor necrosis factor receptor 1 (TNFR-1),Fas]-mediated apoptosis as well as cycloheximide-accelerated spontaneous" apoptosis. A novel "caged" cA-PK-activating analog View Publication

Human hematopoietic stem cells (HSCs) are commonly purified by the expression of cell surface markers such as CD34. Because cell phenotype can be altered by cell cycle progression or ex vivo culture,purification on the basis of conserved stem cell function may represent a more reliable way to isolate various stem cell populations. We have purified primitive HSCs from human umbilical cord blood (UCB) by lineage depletion (Lin(-)) followed by selection of cells with high aldehyde dehydrogenase (ALDH) activity. ALDH(hi)Lin(-) cells contained 22.6% +/- 3.0% of the Lin(-) population and highly coexpressed primitive HSC phenotypes (CD34(+) CD38(-) and CD34(+)CD133(+)). In vitro hematopoietic progenitor function was enriched in the ALDH(hi)Lin(-) population,compared with ALDH(lo)Lin(-) cells. Multilineage human hematopoietic repopulation was observed exclusively after transplantation of ALDH(hi)Lin(-) cells. Direct comparison of repopulation with use of the nonobese diabetic/severe combined immunodeficient (NOD/SCID) and NOD/SCID beta2 microglobulin (beta2M) null models demonstrated that 10-fold greater numbers of ALDH(hi)-Lin(-) cells were needed to engraft the NOD/SCID mouse as compared with the more permissive NOD/SCID beta2M null mouse,suggesting that the ALDH(hi)Lin(-) population contained committed progenitors as well as primitive repopulating cells. Cell fractionation according to lineage depletion and ALDH activity provides a viable and prospective purification of HSCs on the basis of cell function rather than cell surface phenotype. View Publication

Like their human counterparts,mouse plasmacytoid dendritic cells (pDCs) play a central role in innate immunity against viral infections,but their capacity to prime T cells in vivo remains unknown. We show here that virus-activated pDCs differentiate into antigen-presenting cells able to induce effector/memory CD8(+) T-cell responses in vivo against both epitopic peptides and endogenous antigen,whereas pDCs activated by synthetic oligodeoxynucleotides containing unmethylated cytosine-guanine motifs (CpG) acquire only the ability to recall antigen-experienced T-cell responses. We also show that immature pDCs are unable to induce effector or regulatory CD8(+) T-cell responses. Thus,murine pDCs take part in both innate and adaptive immune responses by directly priming naive CD8(+) T cells during viral infection. View Publication

Differentiating embryonic stem (ES) cells are an increasingly important source of hematopoietic progenitors,useful for both basic research and clinical applications. Besides their characterization in colony assays,protocols exist for the cultivation of lymphoid,myeloid,and erythroid cells. With the possible exception of mast cells,however,long-term expansion of pure hematopoietic progenitors from ES cells has not been possible without immortalization caused by overexpression of exogenous genes. Here,we describe for the first time an efficient yet easy strategy to generate mass cultures of pure,immature erythroid progenitors from mouse ES cells (ES-EPs),using serum-free medium plus recombinant cytokines and hormones. ES-EPs represent long-lived,adult,definitive erythroid progenitors that resemble immature erythroid cells expanding in vivo during stress erythropoiesis. When exposed to terminal differentiation conditions,ES-EPs differentiated into mature,enucleated erythrocytes. Importantly,ES-EPs injected into mice did not exhibit tumorigenic potential but differentiated into normal erythrocytes. Both the virtually unlimited supply of cells and the defined culture conditions render our system a valuable tool for the analysis of factors influencing proliferation and maturation of erythroid progenitors. In addition,the system allows detailed characterization of processes during erythroid proliferation and differentiation using wild-type (wt) and genetically modified ES cells. View Publication

Although extracellular nucleotides support a wide range of biologic responses of mature blood cells,little is known about their effect on blood cell progenitor cells. In this study,we assessed whether receptors for extracellular nucleotides (P2 receptors [P2Rs]) are expressed on human hematopoietic stem cells (HSCs),and whether activation by their natural ligands,adenosine triphosphate (ATP) and uridine triphosphate (UTP),induces HSC proliferation in vitro and in vivo. Our results demonstrated that CD34(+) HSCs express functional P2XRs and P2YRs of several subtypes. Furthermore,stimulation of CD34(+) cells with extracellular nucleotides caused a fast release of Ca(2+) from intracellular stores and an increase in ion fluxes across the plasma membrane. Functionally,ATP and,to a higher extent,UTP acted as potent early acting growth factors for HSCs,in vitro,because they strongly enhanced the stimulatory activity of several cytokines on clonogenic CD34(+) and lineage-negative CD34(-) progenitors and expanded more primitive CD34(+)-derived long-term culture-initiating cells. Furthermore,xenogenic transplantation studies showed that short-term preincubation with UTP significantly expanded the number of marrow-repopulating HSCs in nonobese diabetic/severe combined immunodeficiency mice. Our data suggest that extracellular nucleotides may provide a novel and powerful tool to modulate HSC functions. View Publication

Histone acetylation is a diagnostic feature of transcriptionally active genes. The proper recruitment and function of histone acetyltransferases (HATs) and deacetylases (HDACs) are key regulatory steps for gene expression and cell cycle. Functional defects of either of these enzymes may lead to several diseases,including cancer. HATs and HDACs thus are potential therapeutic targets. Here we report that garcinol,a polyisoprenylated benzophenone derivative from Garcinia indica fruit rind,is a potent inhibitor of histone acetyltransferases p300 (IC50 approximately 7 microm) and PCAF (IC50 approximately 5 microm) both in vitro and in vivo. The kinetic analysis shows that it is a mixed type of inhibitor with an increased affinity for PCAF compared with p300. HAT activity-dependent chromatin transcription was strongly inhibited by garcinol,whereas transcription from DNA template was not affected. Furthermore,it was found to be a potent inducer of apoptosis,and it alters (predominantly down-regulates) the global gene expression in HeLa cells. View Publication

Human bone marrow-derived mesenchymal stem cells (MSCs) have the potential to differentiate into mesenchymal tissues like osteocytes,chondrocytes,and adipocytes in vivo and in vitro. The aim of this study was to investigate the in vitro differentiation of MSCs into cells of the endothelial lineage. MSCs were generated out of mononuclear bone marrow cells from healthy donors separated by density gradient centrifugation. Cells were characterized by flow cytometry using a panel of monoclonal antibodies and were tested for their potential to differentiate along different mesenchymal lineages. Isolated MSCs were positive for the markers CD105,CD73,CD166,CD90,and CD44 and negative for typical hematopoietic and endothelial markers. They were able to differentiate into adipocytes and osteocytes after cultivation in respective media. Differentiation into endothelial-like cells was induced by cultivation of confluent cells in the presence of 2% fetal calf serum and 50 ng/ml vascular endothelial growth factor. Laser scanning cytometry analysis of the confluent cells in situ showed a strong increase of expression of endothelial-specific markers like KDR and FLT-1,and immunofluorescence analysis showed typical expression of the von Willebrand factor. The functional behavior of the differentiated cells was tested with an in vitro angiogenesis test kit where cells formed characteristic capillary-like structures. We could show the differentiation of expanded adult human MSCs into cells with phenotypic and functional features of endothelial cells. These predifferentiated cells provide new options for engineering of artificial tissues based on autologous MSCs and vascularized engineered tissues. View Publication