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The signal transducer Stat5 plays a key role in the regulation of hematopoietic differentiation and hematopoietic stem cell function. To evaluate the effects of Stat5 signaling in the earliest hematopoietic progenitors, we have generated an embryonic stem cell line in which Stat5 signaling can be induced with doxycycline. Ectopic Stat5 activation at the point of origin of the hematopoietic lineage (from day 4 to day 6 of embryoid body differentiation) significantly enhances the number of hematopoietic progenitors with colony-forming potential. It does so without significantly altering total numbers or apoptosis of hematopoietic cells, suggesting a cell-intrinsic effect of Stat5 on either the developmental potential or clonogenicity of this population. From day-6 embryoid bodies, under the influence of Stat5 signaling, a population of semiadherent cells can be expanded on OP9 stromal cells that is comprised of primitive hematopoietic blast cells with ongoing, mainly myeloid, differentiation. When these cells are injected into lethally irradiated mice, they engraft transiently in a doxycycline-dependent manner. These results demonstrate that the hematopoietic commitment of embryonic stem cells may be augmented by a Stat5-mediated signal, and highlight the utility of manipulating individual components of signaling pathways for engineering tissue-specific differentiation of stem cells. View Publication

Pyrazole-based inhibitors of the transforming growth factor-beta type I receptor kinase domain (TbetaR-I) are described. Examination of the SAR in both enzyme- and cell-based in vitro assays resulted in the emergence of two subseries featuring differing selectivity versus p38 MAP kinase. A common binding mode at the active site has been established by successful cocrystallization and X-ray analysis of potent inhibitors with the TbetaR-I receptor kinase domain.

Differentiation of pluripotent embryonic stem (ES) cells is associated with expression of fate-specifying gene products. Coordinated development, however, must involve modifying factors that enable differentiation and growth to adjust in response to local microenvironmental determinants. We report here that the ephrin receptor, EphB4, known to be spatially restricted in expression and critical for organized vessel formation, modifies the rate and magnitude of ES cells acquiring genotypic and phenotypic characteristics of mesodermal tissues. Hemangioblast, blood cell, cardiomyocyte, and vascular differentiation was impaired in EphB4-/- ES cells in conjunction with decreased expression of mesoderm-associated, but not neuroectoderm-associated, genes. Therefore, EphB4 modulates the response to mesoderm induction signals. These data add differentiation kinetics to the known effects of ephrin receptors on mammalian cell migration and adhesion. We propose that modifying sensitivity to differentiation cues is a further means for ephrin receptors to contribute to tissue patterning and organization.

Chemokine receptors on T cells are frequently categorized as functioning either in immune system homeostasis within lymphoid organs, or in peripheral inflammation. CXCR3 is in the latter category and is reported to be expressed selectively on Th1 cells. We found that CXCR3 was expressed in vivo on newly activated tonsillar CD4(+) T cells. Using CD4(+) T cells from cord blood, we found that CXCR3 was induced by cellular activation in vitro independently of the cytokine milieu, although on resting cells, expression was maintained preferentially on those that had been activated in type 1 conditions. In inflamed tonsils, CXCR3(+)CD4(+) T cells were localized around and within germinal centers. The inference that CXCR3 has a role in germinal center reactions was supported by the finding that the CXCR3 ligand CXC chemokine ligand 9 was expressed in a pattern demarcating a subset of germinal centers both in tonsil and in lymph nodes from an HIV-infected individual. We next investigated the role of CXCR3 on peripheral effector/memory CD4(+) T cells by comparing its pattern of expression with that of CCR5, another Th1-cell associated chemokine receptor. Analysis of cells directly from peripheral blood and after activation in vitro suggested that CXCR3 expression preceded that of CCR5, supporting a model of sequential induction of chemokine receptors during CD4(+) T cell differentiation. Taken together, our data show that CXCR3 can be expressed at all stages of CD4(+) T cell activation and differentiation, bridging central function in lymphoid organs and effector function in peripheral tissues.

The hemopoietic stem cell (HSC) compartment encompasses cell subsets with heterogeneous proliferative and developmental potential. Numerous CD34(-) cell subsets that might reside at an earlier stage of differentiation than CD34(+) HSCs have been described and characterized within human umbilical cord blood (UCB). We identified a novel subpopulation of CD34(-)CD133(-)CD7(-)CD45(dim)lineage (lin)(-) HSCs contained within human UCB that were endowed with low but measurable extended long-term culture-initiating cell activity. Exposure of CD34(-)CD133(-)CD7(-)CD45(dim)lin(-) HSCs to stem cell factor preserved cell viability and was associated with the following: 1) concordant expression of the stem cell-associated Ags CD34 and CD133, 2) generation of CFU-granulocyte-macrophage, burst-forming unit erythroid, and megakaryocytic aggregates, 3) significant extended long-term culture-initiating cell activity, and 4) up-regulation of mRNA signals for myeloperoxidase. At variance with CD34(+)lin(-) cells, CD34(-)CD133(-)CD7(-)CD45(dim)lin(-) HSCs maintained with IL-15, but not with IL-2 or IL-7, proliferated vigorously and differentiated into a homogeneous population of CD7(+)CD45(bright)CD25(+)CD44(+) lymphoid progenitors with high expression of the T cell-associated transcription factor GATA-3. Although they harbored nonclonally rearranged TCRgamma genes, IL-15-primed CD34(-)CD133(-)CD7(-)CD45(dim)lin(-) HSCs failed to achieve full maturation, as manifested in their CD3(-)TCRalphabeta(-)gammadelta(-) phenotype. Conversely, culture on stromal cells supplemented with IL-15 was associated with the acquisition of phenotypic and functional features of NK cells. Collectively, CD34(-)CD133(-)CD7(-)CD45(dim)lin(-) HSCs from human UCB displayed an exquisite sensitivity to IL-15 and differentiated into lymphoid/NK cells. Whether the transplantation of CD34(-)lin(-) HSCs possessing T/NK cell differentiation potential may impact on immunological reconstitution and control of minimal residual disease after HSC transplantation for autoimmune or malignant diseases remains to be determined.

The effects of the agonist enantiomer S(-)Bay K 8644 on gating charge of L-type Ca channels were studied in single ventricular myocytes. From a holding potential (Vh) of -40 mV, saturating (250 nm) S(-)Bay K shifted the half-distribution voltage of the activation charge (Q1) vs. V curve -7.5 +/- 0.8 mV, almost identical to the shift produced in the Ba conductance vs. V curve (-7.7 +/- 2 mV). The maximum Q1 was reduced by 1.7 +/- 0.2 nC/microF, whereas Q2 (charge moved in inactivated channels) was increased in a similar amount (1.4 +/- 0.4 nC/microF). The steady-state availability curves for Q1, Q2, and Ba current showed almost identical negative shifts of -14.8 +/- 1.7 mV, -18.6 +/- 5.8 mV, and -15.2 +/- 2.7 mV, respectively. The effects of the antagonist enantiomer R(+)BayK 8644 were also studied, the Q1 vs. V curve was not significantly shifted, but Q1max (Vh = -40 mV) was reduced and the Q1 availability curve shifted by -24.6 +/- 1.2 mV. We concluded that: a) the left shift in the Q1 vs. V activation curve produced by S(-)BayK is a purely agonistic effect; b) S(-)BayK induced a significantly larger negative shift in the availability curve than in the Q1 vs. V relation, consistent with a direct promotion of inactivation; c) as expected for a more potent antagonist, R(+)Bay K induced a significantly larger negative shift in the availability curve than did S(-)Bay K.

Inter-alpha inhibitor protein (IalphaIp) is an endogenous serine protease inhibitor in human plasma. Circulating IalphaIp levels were lower in 51 patients with severe sepsis than in healthy volunteers. Mean levels were 688+/-295 mg/L in patients with severe sepsis who survived (n=32), 486+/-193 mg/L in patients with sepsis who died (n=19), and 872+/-234 mg/L in control subjects (n=25). IalphaIp levels were lower in patients with shock versus those without (540+/-246 [n=33] vs. 746+/-290 [n=18] mg/L; P=.0102). IalphaIp levels were inversely correlated with 28-day mortality rates and Acute Physiology and Chronic Health Evaluation II scores and directly correlated with antithrombin III, protein C, and protein S levels. The administration of IalphaIp (30 mg/kg body weight intravenously) increased the 50% lethal dose in mice by 100-fold after an intravenous challenge of Escherichia coli. Thus, human IalphaIp may be a useful predictive marker and potential therapeutic agent in sepsis.

To investigate whether altered megakaryocyte morphology contributes to reduced platelet production in idiopathic thrombocytopenic purpura (ITP), ultrastructural analysis of megakaryocytes was performed in 11 ITP patients. Ultrastructural abnormalities compatible with (para-)apoptosis were present in 78% +/- 14% of ITP megakaryocytes, which could be reversed by in vivo treatment with prednisone and intravenous immunoglobulin. Immunohistochemistry of bone marrow biopsies of ITP patients with extensive apoptosis showed an increased number of megakaryocytes with activated caspase-3 compared with normal (28% +/- 4% versus 0%). No difference, however, was observed in the number of bone marrow megakaryocyte colony-forming units (ITP, 118 +/- 93/105 bone marrow cells; versus controls, 128 +/- 101/105 bone marrow cells; P =.7). To demonstrate that circulating antibodies might affect megakaryocytes, suspension cultures of CD34+ cells were performed with ITP or normal plasma. Morphology compatible with (para-)apoptosis could be induced in cultured megakaryocytes with ITP plasma (2 of 10 samples positive for antiplatelet autoantibodies). Finally, the plasma glycocalicin index, a parameter of platelet and megakaryocyte destruction, was increased in ITP (57 +/- 70 versus 0.7 +/- 0.2; P =.009) and correlated with the proportion of megakaryocytes showing (para-) apoptotic ultrastructure (P =.02; r = 0.7). In conclusion, most ITP megakaryocytes show ultrastructural features of (para-) apoptosis, probably due to action of factors present in ITP plasma. View Publication

Imatinib is a novel tyrosine kinase inhibitor used for the treatment of Philadelphia chromosome-positive leukemias and other malignancies. Side effects are mostly moderate; however, a dose-dependent hematologic toxicity affecting all hematopoietic lineages is observed clinically. The aim of this study was to investigate the effect of imatinib on normal hematopoietic stem and progenitor cells in vitro. A dose-dependent decrease in proliferation potential was found when CD34+ cells were expanded in serum-free medium supplemented with 6 growth factors and imatinib. Functionally, a decrease in colony-forming capacity was observed under increasing doses of imatinib. However, no such effect on more primitive cobblestone area-forming cells was detectable. Both withdrawal of stem cell factor from our expansion cultures or functional inhibition of c-kit led to a similar degree of inhibition of expansion, whereas the effect of imatinib was substantially greater at all dose levels tested. These data suggest a significant inhibitory effect of imatinib on normal CD34+ progenitor (but not stem) cells that is largely independent of c-kit signaling.

Mice deficient in early B cell factor (EBF) are blocked at the progenitor B cell stage prior to immunoglobulin gene rearrangement. The EBF-dependent block in B cell development occurs near the onset of B-lineage commitment, which raises the possibility that EBF may act instructively to specify the B cell fate from uncommitted, multipotential progenitor cells. To test this hypothesis, we transduced enriched hematopoietic progenitor cells with a retroviral vector that coexpressed EBF and the green fluorescent protein (GFP). Mice reconstituted with EBF-expressing cells showed a near complete absence of T lymphocytes. Spleen and peripheral blood samples were textgreater95 and 90% GFP+EBF+ mature B cells, respectively. Both NK and lymphoid-derived dendritic cells were also significantly reduced compared with control-transplanted mice. These data suggest that EBF can restrict lymphopoiesis to the B cell lineage by blocking development of other lymphoid-derived cell pathways. View Publication

Raloxifene reduces bone loss and prevents vertebral fractures in postmenopausal women. Its skeletal effects are mediated by estrogen receptors (ER) and their modulation of paracrine osteoblastic factors. Receptor activator of nuclear factor-kappa B ligand is essential for osteoclasts and enhances bone resorption, whereas osteoprotegerin (OPG) neutralizes receptor activator of nuclear factor-kappa B ligand. Here, we assessed the effects of raloxifene on OPG production in human osteoblasts (hOB). Raloxifene enhanced gene expression of ER-alpha and progesterone receptor. Moreover, raloxifene increased OPG mRNA levels and protein secretion by hOB in a dose- and time-dependent fashion by 2- to 4-fold with a maximum effect at 10(-7) M and after 72 h (P textless 0.001). Treatment with the ER antagonist ICI 182,780 abrogated the effects of raloxifene on OPG production. Moreover, raloxifene enhanced osteoblastic differentiation markers, type 1 collagen secretion, and alkaline phosphatase activity by 3- and 2-fold, respectively (P textless 0.001). In addition, raloxifene inhibited expression of the bone-resorbing cytokine IL-6 by 25-45% (P textless 0.001). In conclusion, our data suggest that raloxifene stimulates OPG production and inhibits IL-6 production by hOB. Because OPG production increases with osteoblastic maturation, enhancement of OPG production by raloxifene could be related to its stimulatory effects on osteoblastic differentiation.

1. The mechanism of Ca2+ release from intracellular stores was studied in defolliculated Xenopus laevis oocytes by measuring whole-cell currents using the two-electrode voltage-clamp method. 2. The extracellular application of ionomycin, a selective Ca2+ ionophore, evoked an inward current consisting of a spike-like fast component followed by a long-lasting slow component with few superimposed current oscillations (fluctuations). The ionomycin response occurred in a dose-dependent manner and was dependent on Cl-. 3. No apparent refractory period was observed for repetitively evoked small ionomycin responses when the concentration of ionomycin was low (0.1 microM). In contrast, a larger ionomycin response (1 microM), consisting of fast and slow components, was followed by refractory period. Washing for 50-90 min was necessary for full recovery of the ionomycin response. 4. The response to ionomycin was suppressed by the extracellular application of acetoxymethyl ester of bis-(O-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid (BAPTA AM, 1-10 microM), a membrane-permeable intracellular Ca2+ chelator. 5. The ionomycin response was not affected by pertussis toxin (PTX, 0.3-2.0 microgram/ml), a blocker of guanine nucleotide-binding regulatory proteins (G proteins). In contrast, the response to acetylcholine (ACh), which is known to occur via a G protein, was suppressed by PTX. 6. The fast component was not affected by removing Ca2+ from the bathing medium or by replacing extracellular Ca2+ with Ba2+ or Mn2+ (all of these solutions were supplemented with 2 mM EGTA), whereas the slow component was suppressed. 7. Injection of inositol 1,4,5-trisphosphate (IP3) following a response to extra-cellularly applied ionomycin did not evoke an appreciable membrane current. In contrast, ionomycin evoked a small inward current when it was applied after an inward-current response evoked by IP3 injection, whereas a second injection of IP3 did not evoke any appreciable current. 8. The results indicate that (a) ionomycin releases Ca2+ from its intracellular stores without the involvement of G proteins, resulting in activation of Ca(2+)-activated Cl- channels, (b) ionomycin mainly acts on the same intracellular Ca2+ stores as IP3, and (c) entry of Ca2+ from outside the cell considerably contributes to the slow component of the ionomycin response, whereas its fast component is predominantly dependent on the release of Ca2+ from the intracellular stores.