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Cell fate during development is defined by transcription factors that act as molecular switches to activate or repress specific gene expression programmes. The POU transcription factor Oct-3/4 (encoded by Pou5f1) is a candidate regulator in pluripotent and germline cells and is essential for the initial formation of a pluripotent founder cell population in the mammalian embryo. Here we use conditional expression and repression in embryonic stem (ES) cells to determine requirements for Oct-3/4 in the maintenance of developmental potency. Although transcriptional determination has usually been considered as a binary on-off control system, we found that the precise level of Oct-3/4 governs three distinct fates of ES cells. A less than twofold increase in expression causes differentiation into primitive endoderm and mesoderm. In contrast, repression of Oct-3/4 induces loss of pluripotency and dedifferentiation to trophectoderm. Thus a critical amount of Oct-3/4 is required to sustain stem-cell self-renewal, and up- or downregulation induce divergent developmental programmes. Our findings establish a role for Oct-3/4 as a master regulator of pluripotency that controls lineage commitment and illustrate the sophistication of critical transcriptional regulators and the consequent importance of quantitative analyses. View Publication

Potent inhibition of Janus kinase 3 was found for a series of naphthyl(beta-aminoethyl)ketones (e.g. 7, pIC50 = 7.1+/-0.3). Further studies indicated that these compounds fragment in less than 1 h by retro-Michael reaction in the Jak3 in vitro ELISA assay procedure. The breakdown product of 7, 2-naphthylvinyl ketone (22, pIC50 = 6.8+/-0.3) showed very similar inhibitory activity to 7. Compounds 7 (in neutral buffer) and 22 will be useful pharmacological tools for the investigation of the Janus tyrosine kinase Jak3.

Adult human mesenchymal stem cells are primary, multipotent cells capable of differentiating to osteocytic, chondrocytic, and adipocytic lineages when stimulated under appropriate conditions. To characterize the molecular mechanisms that regulate osteogenic differentiation, we examined the contribution of mitogen-activated protein kinase family members, ERK, JNK, and p38. Treatment of these stem cells with osteogenic supplements resulted in a sustained phase of ERK activation from day 7 to day 11 that coincided with differentiation, before decreasing to basal levels. Activation of JNK occurred much later (day 13 to day 17) in the osteogenic differentiation process. This JNK activation was associated with extracellular matrix synthesis and increased calcium deposition, the two hallmarks of bone formation. Inhibition of ERK activation by PD98059, a specific inhibitor of the ERK signaling pathway, blocked the osteogenic differentiation in a dose-dependent manner, as did transfection with a dominant negative form of MAP kinase kinase (MEK-1). Significantly, the blockage of osteogenic differentiation resulted in the adipogenic differentiation of the stem cells and the expression of adipose-specific mRNAs peroxisome proliferator-activated receptor gamma2, aP2, and lipoprotein lipase. These observations provide a potential mechanism involving MAP kinase activation in osteogenic differentiation of adult stem cells and suggest that commitment of hMSCs into osteogenic or adipogenic lineages is governed by activation or inhibition of ERK, respectively.

Hematologic malignancies such as acute and chronic myeloid leukemia are characterized by the malignant transformation of immature CD34(+) progenitor cells. Transformation is associated with elevated expression of the Wilm's tumor gene encoded transcription factor (WT1). Here we demonstrate that WT1 can serve as a target for cytotoxic T lymphocytes (CTL) with exquisite specificity for leukemic progenitor cells. HLA-A0201- restricted CTL specific for WT1 kill leukemia cell lines and inhibit colony formation by transformed CD34(+) progenitor cells isolated from patients with chronic myeloid leukemia (CML), whereas colony formation by normal CD34(+) progenitor cells is unaffected. Thus, the tissue-specific transcription factor WT1 is an ideal target for CTL-mediated purging of leukemic progenitor cells in vitro and for antigen-specific therapy of leukemia and other WT1-expressing malignancies in vivo.

Estrogens as well as some antiestrogens have been shown to prevent bone loss in postmenopausal women. These compounds seem to inhibit bone resorption, but their anabolic effects have been less explored. In this study, bone marrow cultures were used to compare the effect of 17beta-estradiol (E2), and two triphenylethylene derivatives, tamoxifen (TAM), and FC1271a, and a benzothiophene derivative raloxifene (RAL) on differentiation of osteoblasts. All enhanced osteoblastic differentiation of 21-day cultures as indicated by increased mineralization and bone nodule formation. All, except RAL, stimulated cell proliferation during the first 6 days of the culture. However, in the presence of RAL the content of total protein was increased in 13-day cultures. SDS-PAGE and autoradiography of [14C]-proline labeled proteins revealed elevated level of the newly synthesized collagen type I. The pure antiestrogen ICI 182,780 abolished the increase of the specific activity of alkaline phosphatase by E2, TAM, and FC1271a but not the effect of RAL on protein synthesis. Our results show that E2 as well as TAM, FC1271a, and RAL stimulate bone formation in vitro but the mechanism of the anabolic action of RAL in bone clearly differs from that of E2, TAM, and FC1271a.

We report here the cloning, expression, and characterization of human PDE11A1, a member of a distinct cyclic nucleotide phosphodiesterase (PDE) family. PDE11A exhibits textless/=50% amino acid identity with the catalytic domains of all other PDEs, being most similar to PDE5, and has distinct biochemical properties. The human PDE11A1 cDNA isolated contains a complete open reading frame encoding a 490-amino acid enzyme with a predicted molecular mass of 55,786 Da. At the N terminus PDE11A1 has a single GAF domain homologous to that found in other signaling molecules, including PDE2, PDE5, PDE6, and PDE10, which constitutes a potential allosteric binding site for cGMP or another small ligand. Tissue distribution studies indicate that PDE11A mRNA occurs at highest levels in skeletal muscle, prostate, kidney, liver, pituitary, and salivary glands and testis. PDE11A is expressed as at least three major transcripts of approximately 10.5, approximately 8.5, and approximately 6.0 kb, thus suggesting the existence of multiple subtypes. This possibility is further supported by the detection of three distinct proteins of approximately 78, approximately 65, and approximately 56 kDa by Western blotting of human tissues for PDE11A isoforms. Recombinant human PDE11A1 hydrolyzes both cGMP and cAMP with K(m) values of 0.52 microM and 1.04 microM, respectively, and similar V(max) values. Therefore, PDE11A represents a dual-substrate PDE that may regulate both cGMP and cAMP under physiological conditions. PDE11A is sensitive to the nonselective PDE inhibitor 3-isobutyl-1-methylxanthine (IBMX) as well as zaprinast and dipyridamole, inhibitors that are generally considered relatively specific for the cGMP-selective PDEs, with IC(50) values of 49.8 microM, 12.0 microM, and 0.37 microM, respectively.

To investigate the difference in heart rate (HR) recovery after exercise between children and young adults, we administered a constant load of light exercise intensity and progressive treadmill exercise tests to nine children (aged 9 to 12 y, group A) and eight young adults (six male and two female, aged 17 to 21 y, group B) who had a history of Kawasaki disease without significant coronary arterial lesions. HR after both exercise protocols was analyzed. The low-frequency (LF) and high-frequency (HF) components of HR variability were measured, and LF/HF was calculated (log LF, log HF, log L/H). Arterial baroreflex sensitivity was assessed by the phenylephrine method. There were no differences between groups A and B in resting HR, peak HR, peak oxygen uptake, and decreases in systolic blood pressure during the recovery period. HR 1 and 2 min after peak exercise and 1 min after constant-load exercise was significantly lower in group A than in group B (p {\textless} 0.05), and the changes in HR from peak values after both exercise tests were also greater in group A than in group B (p {\textless} 0.05-0.01). Although no difference in arterial baroreflex sensitivity was observed, log HF was significantly higher in group A than in group B (p {\textless} 0.01), and log L/H was significantly lower in group A than in group B (p {\textless} 0.05). The value of log HF correlated inversely with the decrease in HR immediately after both exercise protocols (p {\textless} 0.05-0.01). Although log L/H correlated with the decrease in HR after peak exercise (p {\textless} 0.05-0.0005), the early decline in HR after constant-load exercise did not correlate with log L/H. Arterial baroreflex sensitivity did not correlate with the decrease in HR at any recovery time. These data suggest that the early phase of HR recovery after light to severe exercise is influenced by the cardiac parasympathetic nervous activity at rest and that the greater central cholinergic modulation of HR in children than in young adults may be responsible in part for children's faster HR recovery after exercise.

The small heat-shock protein HSP25 is expressed in the heart early during development, and although multiple roles for HSP25 have been proposed, its specific role during development and differentiation is not known. P19 is an embryonal carcinoma cell line which can be induced to differentiate in vitro into either cardiomyocytes or neurons. We have used P19 to examine the role of HSP25 in differentiation. We found that HSP25 expression is strongly increased in P19 cardiomyocytes. Antisense HSP25 expression reduced the extent of cardiomyocyte differentiation and resulted in reduced expression of cardiac actin and the intermediate filament desmin and reduced level of cardiac mRNAs. Thus, HSP25 is necessary for differentiation of P19 into cardiomyocytes. In contrast, P19 neurons did not express HSP25 and antisense HSP25 expression had no effect on neuronal differentiation. The phosphorylation of HSP25 by the p38/SAPK2 pathway is known to be important for certain of its functions. Inhibition of this pathway by the specific inhibitor SB203580 prevented cardiomyocyte differentiation of P19 cells. In contrast, PD90589, which inhibits the ERK1/2 pathway, had no effect. Surprisingly, cardiogenesis was only sensitive to SB203580 during the first 2 days of differentiation, before HSP25 expression increases. In contrast to the effect of antisense HSP25, SB203580 reduced the level of expression of the mesodermal marker Brachyury-T during differentiation. Therefore, we propose that the p38 pathway acts on an essential target during early cardiogenesis. Once this initial step is complete, HSP25 is necessary for the functional differentiation of P19 cardiomyocytes, but its phosphorylation by p38/SAPK2 is not required.

Retinoic acid derivatives (retinoids) exert their pleiotropic effects on cell development through specific nuclear receptors, the retinoic acid receptors and retinoid X receptors. Despite recent progress in understanding the cellular and molecular mechanisms of retinoid activity, it is unknown which of the retinoid receptor pathways are involved in the specific processes of sebocyte growth and development. In this study, we investigated the roles of specific retinoid receptors in sebocyte growth and differentiation, by testing the effects of selective retinoic acid receptor and retinoid X receptor ligands at concentrations between 10-10 M and 10-6 M in a primary rat preputial cell monolayer culture system. Cell growth was determined by number of cells and colonies, and cell differentiation by analysis of lipid-forming colonies. All-trans retinoic acid and selective retinoic acid receptor agonists (CD271 = adapalene, an RAR-beta,gamma agonist; CD2043 = retinoic acid receptor pan-agonist; and CD336 = Am580, an RAR-alpha agonist) caused significant decreases in numbers of cells, colonies, and lipid-forming colonies, but with an exception at high doses of all-trans retinoic acid (10-6 M), with which only a small number of colonies grew but they became twice as differentiated as controls (42.2 +/- 4.0% vs 22.6 +/- 2.7%, mean +/- SEM, lipid-forming colonies, p textless 0.01). Furthermore, the RAR-beta,gamma antagonist CD2665 antagonized the suppressive effects of all-trans retinoic acid, adapalene, and CD2043 on both cell growth and differentiation. In contrast, the retinoid X receptor agonist CD2809 increased cell growth slightly and lipid-forming colonies dramatically in a clear dose-related manner to a maximum of 73.7% +/- 6.7% at 10-6 M (p textless 0. 001). Our data suggest that retinoic acid receptors and retinoid X receptors differ in their roles in sebocyte growth and differentiation: (i) retinoic acid receptors, especially the beta and/or gamma subtypes, mediate both the antiproliferative and antidifferentiative effects of retinoids; (ii) retinoid X receptors mediate prominent differentiative and weak proliferative effects; (iii) the antiproliferative and antidifferentiative effects of all-trans retinoic acid are probably mediated by retinoic acid receptors, whereas its differentiative effect at high dose may be mediated by retinoid X receptors via all-trans retinoic acid metabolism to 9-cis retinoic acid, the natural ligand of retinoid X receptors.

The bleomycin group antitumor antibiotics have long been of interest as a consequence of their efficacy in the treatment of certain tumors, not to mention their unique structures and properties in mediating dioxygen activation and sequence selective degradation of DNA. At a chemical level, the structure originally assigned to bleomycin was subsequently reassigned and the new structure has been confirmed by total synthesis. Through the elaboration of structurally modified bleomycin congeners and fragments, synthetic efforts have also facilitated an understanding of the contribution of individual structural domains in bleomycin to sequence selective DNA binding and cleavage, and have also provided insights into the nature of the chemical processes by which DNA degradation takes place. Within the last several years, it has also become apparent that bleomycin can mediate the oxidative degradation of all major classes of cellular RNAs; it seems entirely plausible that RNA may also represent an important locus of action for this class of antitumor agent. In parallel with ongoing synthetic and mechanistic efforts using classical methods, the study of bleomycins attached to solid supports has been shown to provide important mechanistic insights, and the actual elaboration of modified bleomycins by solid phase synthesis constitutes a logical extension of such efforts.

We studied the suitability of collagen-based semisolid medium for assay of endogenous erythroid colony formation performed in myeloproliferative disorders. Bone marrow (BM) mononuclear cells (MNC) from 103 patients suspected of having polycythemia vera (PV, 76 patients) or essential thrombocythemia (ET, 27 patients) were grown in collagen-based, serum-free, cytokine-free semisolid medium. Colony analysis at day 8 or 10 showed that this collagen assay is specific, as endogenous growth of erythroid colonies was never observed in cultures of 16 healthy donors and 6 chronic myelogenous leukemia (CML) patients. Endogenous erythroid colony formation was observed in 53.3% of patients suspected of PV, with only 15.4% of positive cultures for patients with 1 minor PV criterion and 72% (p = 0.009) of positive cultures for patients with textgreater or =2 minor or 1 major PV criterion. Similarly, endogenous growth of erythroid colonies was found in 44.4% of patients suspected of ET, with 31.6% of positive cultures for patients with 1 ET criterion versus 75% for patients with textgreater or =2 ET criteria. In addition, we found that in collagen gels, tests of erythropoietin (EPO) hypersensitivity in the presence of 0.01 or 0.05 U/ml of EPO and tests of endogenous colony-forming units-megakaryocyte (CFU-MK) formation cannot be used to detect PV or ET, as these tests were positive for, respectively, 21.4% and 50% of healthy donors and 83% and 50% of CML patients. A retrospective analysis suggests that collagen assays are more sensitive than methylcellulose assays to assess endogenous growth of erythroid colonies. In summary, serum-free collagen-based colony assays are simple and reliable assays of endogenous growth of erythroid colonies in myeloproliferative diseases. They also appear to be more sensitive than methylcellulose-based assays.

The Dishevelled (Dvl) gene family encodes cytoplasmic proteins that are necessary for Wnt signal transduction. Utilizing the yeast two-hybrid system, we identified protein phosphatase 2Calpha (PP2C) as a Dvl-PDZ domain-interacting protein. PP2C exists in a complex with Dvl, beta-catenin, and Axin, a negative regulator of Wnt signaling. In a Wnt-responsive LEF-1 reporter gene assay, expression of PP2C activates transcription and also elicits a synergistic response with beta-catenin and Wnt-1. In addition, PP2C expression relieves Axin-mediated repression of LEF-1-dependent transcription. PP2C utilizes Axin as a substrate both in vitro and in vivo and decreases its half-life. These results indicate that PP2C is a positive regulator of Wnt signal transduction and mediates its effects through the dephosphorylation of Axin.