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Poor survival of human embryonic stem (hES) cells after cell dissociation is an obstacle to research, hindering manipulations such as subcloning. Here we show that application of a selective Rho-associated kinase (ROCK) inhibitor, Y-27632, to hES cells markedly diminishes dissociation-induced apoptosis, increases cloning efficiency (from approximately 1% to approximately 27%) and facilitates subcloning after gene transfer. Furthermore, dissociated hES cells treated with Y-27632 are protected from apoptosis even in serum-free suspension (SFEB) culture and form floating aggregates. We demonstrate that the protective ability of Y-27632 enables SFEB-cultured hES cells to survive and differentiate into Bf1(+) cortical and basal telencephalic progenitors, as do SFEB-cultured mouse ES cells.

OBJECTIVES: Recent data show that Imatinib mesylate (IM) also affects haematopoietic stem cells (HSC), T lymphocytes and dendritic cells that do not harbour constitutively active tyrosine kinases. MATERIALS AND METHODS: We evaluated possible effects of IM on human bone marrow-derived mesenchymal stem cells (MSC) in vitro. RESULTS: Screening the activity of 42 receptor tyrosine kinases revealed an exclusive inhibition of platelet-derived growth factor receptorbeta (PDGFRbeta). Analysis of downstream targets of PDGFRbeta demonstrated IM-mediated reduction of Akt and Erk1/2 phosphorylation. Culture of MSC with IM led to the reversible development of perinuclear multi-vesicular bodies. The proliferation and clonogenicity of MSC were significantly reduced compared to control cultures. IM favoured adipogenic differentiation of MSC whereas osteogenesis was suppressed. The functional deficits described led to a 50% reduction in the support of clonogenic haematopoietic stem cells, cultured for 1 month on a monolayer of MSC with IM. CONCLUSION: In summary, inhibition of PDGFRbeta and downstream Akt and Erk signalling by IM has a significant impact on proliferation and differentiation of human MSC in vitro.

A first step in hematopoiesis is the specification of the lymphoid and myeloid lineages from multipotent progenitor cells in the bone marrow. Using a conditional ablation strategy in adult mice, we show that this differentiation step requires Patched (Ptch), the cell surface-bound receptor for Hedgehog (Hh). In the absence of Ptch, the development of T- and B-lymphoid lineages is blocked at the level of the common lymphoid progenitor in the bone marrow. Consequently, the generation of peripheral T and B cells is abrogated. Cells of the myeloid lineage develop normally in Ptch mutant mice. Finally, adoptive transfer experiments identified the stromal cell compartment as a critical Ptch-dependent inducer of lymphoid versus myeloid lineage commitment. Our data show that Ptch acts as a master switch for proper diversification of hematopoietic stem cells in the adult organism.

Novel derivatives of 1,2,4-triazoles are described as potent ATP-competitive inhibitors of vascular endothelial growth factor receptors I and II (VEGFR-1/2). A number of compounds display VEGFR-2 inhibitory activity comparable to that of Vatalanib and Vandetanib in both homogenous time-resolved fluorescence enzymatic and cellular assays. Several active molecules feature high intrinsic permeability (textgreater30 x 10(-5) cm/min) across Caco-2 cell monolayer.

JAK2V617F and MPLW515L/K represent recently identified mutations in myeloproliferative disorders (MPD) that cause dysregulated JAK-STAT signaling, which is implicated in MPD pathogenesis. We developed TG101209, an orally bioavailable small molecule that potently inhibits JAK2 (IC(50)=6 nM), FLT3 (IC(50)=25 nM) and RET (IC(50)=17 nM) kinases, with significantly less activity against other tyrosine kinases including JAK3 (IC(50)=169 nM). TG101209 inhibited growth of Ba/F3 cells expressing JAK2V617F or MPLW515L mutations with an IC(50) of approximately 200 nM. In a human JAK2V617F-expressing acute myeloid leukemia cell line, TG101209-induced cell cycle arrest and apoptosis, and inhibited phosphorylation of JAK2V617F, STAT5 and STAT3. Therapeutic efficacy of TG101209 was demonstrated in a nude mouse model. Furthermore, TG101209 suppressed growth of hematopoietic colonies from primary progenitor cells harboring JAK2V617F or MPL515 mutations.

Recent observations indicate that, in several types of human cancer, only a phenotypic subset of cancer cells within each tumor is capable of initiating tumor growth. This functional subset of cancer cells is operationally defined as the cancer stem cell" (CSC) subset. Here we developed a CSC model for the study of human colorectal cancer (CRC). Solid CRC tissues�

Definitive erythropoiesis occurs in islands composed of a central macrophage in contact with differentiating erythroblasts. Erythroid maturation including enucleation can also occur in the absence of macrophages both in vivo and in vitro. We reported previously that loss of Rb induces cell-autonomous defects in red cell maturation under stress conditions, while other reports have suggested that the failure of Rb-null erythroblasts to enucleate is due to defects in associated macrophages. Here we show that erythropoietic islands are disrupted by hypoxic stress, such as occurs in the Rb-null fetal liver, that Rb(-/-) macrophages are competent for erythropoietic island formation in the absence of exogenous stress and that enucleation defects persist in Rb-null erythroblasts irrespective of macrophage function.

Hyper-IgM (HIGM) syndromes are primary immunodeficiencies characterized by defects of class switch recombination and somatic hypermutation. HIGM patients who carry mutations in the CD40-ligand (CD40L) gene expressed by CD4(+) T cells suffer from recurrent infections and often develop autoimmune disorders. To investigate the impact of CD40L-CD40 interactions on human B cell tolerance, we tested by ELISA the reactivity of recombinant antibodies isolated from single B cells from three CD40L-deficient patients. Antibody characteristics and reactivity from CD40L-deficient new emigrant B cells were similar to those from healthy donors, suggesting that CD40L-CD40 interactions do not regulate central B cell tolerance. In contrast, mature naive B cells from CD40L-deficient patients expressed a high proportion of autoreactive antibodies, including antinuclear antibodies. Thus, CD40L-CD40 interactions are essential for peripheral B cell tolerance. In addition, a patient with the bare lymphocyte syndrome who could not express MHC class II molecules failed to counterselect autoreactive mature naive B cells, suggesting that peripheral B cell tolerance also depends on major histocompatibility complex (MHC) class II-T cell receptor (TCR) interactions. The decreased frequency of MHC class II-restricted CD4(+) regulatory T cells in CD40L-deficient patients suggests that these T cells may mediate peripheral B cell tolerance through CD40L-CD40 and MHC class II-TCR interactions.

OBJECTIVE: Abnormal expression of the hepatic gluconeogenic genes (glucose-6-phosphatase [G6Pase] and PEPCK) contributes to hyperglycemia. These genes are repressed by insulin, but this process is defective in diabetic subjects. Protein kinase B (PKB) is implicated in this action of insulin. An inhibitor of PKB, Akt inhibitor (Akti)-1/2, was recently reported; however, the specificity and efficacy against insulin-induced PKB was not reported. Our aim was to characterize the specificity and efficacy of Akti-1/2 in cells exposed to insulin and then establish whether inhibition of PKB is sufficient to prevent regulation of hepatic gene expression by insulin. RESEARCH DESIGN AND METHODS: Akti-1/2 was assayed against 70 kinases in vitro and its ability to block PKB activation in cells exposed to insulin fully characterized. RESULTS: Akti-1/2 exhibits high selectivity toward PKBalpha and PKBbeta. Complete inhibition of PKB activity is achieved in liver cells incubated with 1-10 mumol/l Akti-1/2, and this blocks insulin regulation of PEPCK and G6Pase expression. Our data demonstrate that only 5-10% of maximal insulin-induced PKB is required to fully repress PEPCK and G6Pase expression. Finally, we demonstrate reduced insulin sensitivity of these gene promoters in cells exposed to submaximal concentrations of Akti-1/2; however, full repression of the genes can still be achieved by high concentrations of insulin. CONCLUSIONS: This work establishes the requirement for PKB activity in the insulin regulation of PEPCK, G6Pase, and a third insulin-regulated gene, IGF-binding protein-1 (IGFBP1); suggests a high degree of functional reserve; and identifies Akti-1/2 as a useful tool to delineate PKB function in the liver.

Previously, a small molecule, reversine, was identified that reverses lineage-committed murine myoblasts to a more primitive multipotent state. Here, we show that reversine can increase the plasticity of C2C12 myoblasts at the single-cell level and that reversine-treated cells gain the ability to differentiate into osteoblasts and adipocytes under lineage-specific inducing conditions. Moreover, reversine is active in multiple cell types, including 3T3E1 osteoblasts and human primary skeletal myoblasts. Biochemical and cellular experiments suggest that reversine functions as a dual inhibitor of nonmuscle myosin II heavy chain and MEK1, and that both activities are required for reversine's effect. Inhibition of MEK1 and nonmuscle myosin II heavy chain results in altered cell cycle and changes in histone acetylation status, but other factors also may contribute to the activity of reversine, including activation of the PI3K signaling pathway.

Recently, passive immunization of human immunodeficiency virus (HIV)-infected individuals with monoclonal antibodies (MAbs) 2G12, 2F5, and 4E10 provided evidence of the in vivo activity of 2G12 but raised concerns about the function of the two membrane-proximal external region (MPER)-specific MAbs (A. Trkola, H. Kuster, P. Rusert, B. Joos, M. Fischer, C. Leemann, A. Manrique, M. Huber, M. Rehr, A. Oxenius, R. Weber, G. Stiegler, B. Vcelar, H. Katinger, L. Aceto, and H. F. Gunthard, Nat. Med. 11:615-622, 2005). In the light of MPER-targeting vaccines under development, we performed an in-depth analysis of the emergence of mutations conferring resistance to these three MAbs to further elucidate their activity. Clonal analysis of the MPER of plasma virus samples derived during antibody treatment confirmed that no changes in this region had occurred in vivo. Sequence analysis of the 2G12 epitope relevant N-glycosylation sites of viruses derived from 13 patients during the trial supported the phenotypic evaluation, demonstrating that mutations in these sites are associated with resistance. In vitro selection experiments with isolates of four of these individuals corroborated the in vivo finding that virus strains rapidly escape 2G12 pressure. Notably, in vitro resistance mutations differed, in most cases, from those found in vivo. Importantly, in vitro selection with 2F5 and 4E10 demonstrated that resistance to these MAbs can be difficult to achieve and can lead to selection of variants with impaired infectivity. This remarkable vulnerability of the virus to interference within the MPER calls for a further evaluation of the safety and efficacy of MPER-targeting therapeutic and vaccination strategies.

We asked whether the hypoxia-regulated factor, insulin-like growth factor binding protein-3 (IGFBP3), could modulate stem cell factor receptor (c-kit+), stem cell antigen-1 (sca-1+), hematopoietic stem cell (HSC), or CD34+ endothelial precursor cell (EPC) function. Exposure of CD34+ EPCs to IGFBP3 resulted in rapid differentiation into endothelial cells and dose-dependent increases in cell migration and capillary tube formation. IGFBP3-expressing plasmid was injected into the vitreous of neonatal mice undergoing the oxygen-induced retinopathy (OIR) model. In separate studies, GFP-expressing HSCs were transfected with IGFBP3 plasmid and injected into the vitreous of OIR mice. Administering either IGFBP3 plasmid alone or HSCs transfected with the plasmid resulted in a similar reduction in areas of vasoobliteration, protection of the developing vasculature from hyperoxia-induced regression, and reduction in preretinal neovascularization compared to control plasmid or HSCs transfected with control plasmid. In conclusion, IGFBP3 mediates EPC migration, differentiation, and capillary formation in vitro. Targeted expression of IGFBP3 protects the vasculature from damage and promotes proper vascular repair after hyperoxic insult in the OIR model. IGFBP3 expression may represent a physiological adaptation to ischemia and potentially a therapeutic target for treatment of ischemic conditions.