Interpretation of cloud-climate feedback as produced by 14 atmospheric general circulation models.

Understanding the cause of differences among general circulation model projections of carbon dioxide-induced climatic change is a necessary step toward improving the models. An intercomparison of 14 atmospheric general circulation models, for which sea surface temperature perturbations were used as a surrogate climate change, showed that there was a roughly threefold variation in global climate sensitivity. Most of this variation is attributable to differences in the models' depictions of cloud-climate feedback, a result that emphasizes the need for improvements in the treatment of clouds in these models if they are ultimately to be used as climatic predictors.

Interpretation of snow-climate feedback as produced by 17 general circulation models.

Snow feedback is expected to amplify global warming caused by increasing concentrations of atmospheric greenhouse gases. The conventional explanation is that a warmer Earth will have less snow cover, resulting in a darker planet that absorbs more solar radiation. An intercomparison of 17 general circulation models, for which perturbations of sea surface temperature were used as a surrogate climate change, suggests that this explanation is overly simplistic. The results instead indicate that additional amplification or moderation may be caused both by cloud interactions and longwave radiation. One measure of this net effect of snow feedback was found to differ markedly among the 17 climate models, ranging from weak negative feedback in some models to strong positive feedback in others.

Role of the membrane form of human colony-stimulating factor-1 (CSF-1) in proliferation of multipotent hematopoietic FDCP-mix cells expressing human CSF-1 receptor.

Because IL-3-dependent multipotential FDCP-Mix cells expressing human colony-stimulating factor-1 (CSF-1) receptor did not proliferate in response to soluble CSF-1, we investigated whether their proliferation would be induced in co-culture with adherent cells expressing the membrane form of CSF-1 (MemCSF-1). FDCP-Mix cells with high CSF-1R expression (NAF21 cells) were placed on stromal MS-5 cells or STO fibroblasts expressing MemCSF-1 (2M-1 cells and STO-M2 cells, respectively), in absence of IL-3. NAF21 cells bound significantly to 2M-1 cells as compared to control FDCP-Mix cells. Adhesion of NAF21 cells was inhibited by anti-huCSF-1 antibodies, as well as anti-huCSF-1R antibodies. Interestingly, NAF21 cells proliferated on both 2M-1 and STO-M2 cells but with very different kinetics. Moreover, NAF21 cell proliferation was also supported by glutaraldehyde-fixed 2M-1 cells or highly concentrated MS-5 cell culture supernatant, but not by CSF-1 coated on culture dishes. These results strongly suggest that MemCSF-1/CSF-1R interaction mediates a specific adhesion of NAF21 cells to stromal cells and allows stimulation of hematopoietic cells by stromal cell-derived factors expressed in a membrane-bound form or concentrated within the extracellular matrix. Thus, cytokine receptors deficient in mitogenic signalling may nevertheless have a regulatory role in hematopoietic progenitor cell proliferation by acting as adhesion molecules.

Expression of human CSF-1 receptor induces CSF-1-dependent proliferation in murine myeloid but not in T-lymphoid cells.

The receptor for human macrophage colony stimulating factor (CSF-1R) was introduced into hematopoietic cell lines of myeloid and T-lymphoid origin, both of which normally do not express the CSF-1R. Infection of an interleukin-3 (IL-3)-dependent mouse myeloid cell line (FDC-P1) with a high titer retroviral vector expressing the human c-fms c-DNA, enabled CSF-1-dependent proliferation in short-term liquid culture assays as well as in clonal culture systems. CSF-1-dependent cell lines could be established after sorting for CSF-1R positive cells. In contrast to FDC-P1 cells, expression of the CSF-1R in CTLL cells, an IL-2-dependent mouse cytotoxic T-cell line, and in T-cell growth factor III/P40-dependent helper T-cells, ST2/K9.4a2, did not lead to CSF-1-dependent proliferation. These observations lead to the conclusion that ectopically expressed CSF-1R may function on certain myeloid cells where it is normally not expressed, suggesting the presence of signal transduction pathways which can be utilized by that foreign receptor. In contrast, it appears that T-lymphoid cells lack such a signalling mechanism, indicating that quite different modes of transducing mitogenic signals from the cell membrane to the nucleus must have developed during myeloid and T-lymphoid differentiation.

Antiproliferative effect of D-aspartic acid beta-hydroxamate (DAH) on Friend virus-infected erythropoietic progenitor cells.

D-aspartic beta-hydroxamate (DAH), an aspartic acid analog, exerts antitumoral activity on murine leukemia L5178Y, both in vitro and in vivo. In this study, we show that DAH is also active in vivo against Friend virus (FV-P)-induced erythroleukemia, and we report the effects of DAH in vivo an in vitro on FV-P target cells, i.e. the mature erythroid colony-forming cells (CFU-E). DAH treatment (2 g/kg/day) given for 95 days as a single daily i.p. injection to DBA/2 mice either 3 or 12 days following inoculation with a high dose (10(3) plaque-forming units) of FV-P resulted in a marked increase in the mean survival time of treated animals (212 and 191%, respectively). Since FV-P elicits spleen enlargement and polycythemia, we examined the effects of DAH on spleen size, spleen-nucleated cell number, and hematocrit, in normal and FV-P infected mice, at different times in the course of continuous DAH treatments. DAH treatment initiated 3 days after viral infection inhibits the virus-induced splenomegaly, with at day 26 p.i. 1.15 x 10(8) and 12.6 x 10(8) nucleated cells per spleen observed in DAH-treated mice and untreated mice respectively, whereas only 1.03 x 10(8) nucleated cells were observed in uninfected mice. Furthermore, DAH prevents virus-induced polycythemia: on day 26, an hematocrit of 39% was measured in DAH-treated mice as compared to 60% in untreated mice. DAH treatment initiated 12 days after viral infection reduces splenomegaly, the number of nucleated spleen cells and the hematocrit of infected mice. DAH treatment initiated 3 days after viral infection prevents the tremendous increase of CFU-E in the spleen of infected mice: on day 11, the spleen of infected mice contained 4.6 x 10(6) CFU-E, while the spleen of treated mice only contained 26 x 10(3) CFU-E, and on day 26 the spleen CFU-E numbers were 45.4 x 10(6) and 1.5 x 10(6) in untreated and treated infected mice, respectively. In control uninfected mice, DAH treatment induced a transient decrease in spleen CFU-E followed by a rebound phenomenon. In vitro, preincubation with DAH inhibits colony formation by FV-P infected CFU-E, at doses starting at 3 mM, as compared to uninfected CFU-E. These data show that DAH inhibits the expression of the retroviral infection, and appears to preferentially inhibit the proliferation of infected target cells (CFU-E) in vivo.

Mouse serum enables CFU-E to grow under physiologic concentration of erythropoietin in vitro.

Addition of normal mouse serum to cultures of mouse CFU-Es, not only increases the number of colonies as we recently reported (Blanchet et al. 1984), but also enhances the sensitivity of mouse CFU-Es to erythropoietin so that physiologic concentrations can be used with optimal colony development. These results were obtained as well with porcine or murine Epo. Thus, NMS exerts a stimulating and facilitating effect on CFU-E development. The stimulating activity was less resistant to heat treatment than was the facilitating one, an indication that both activities may be mediated by different molecules.

Isolation of a murine bone marrow cell line producing a novel erythroid-enhancing activity.

Erythroid differentiation requires hematopoietic factors to proceed from early erythroid progenitors, burst-forming units-erythroid (BFU-E), to mature red cells. A number of factors possessing burst-promoting activity (BPA) have been characterized, such as interleukin-3 (IL-3), stem cell factor (SCF), and granulocyte-macrophage colony-stimulating factor (GM-CSF). These factors have broad spectra of activity on different hematopoietic and nonhematopoietic cell lines. In this paper, we describe the effect of an apparently selective erythroid factor that acts on a class of mature BFU-E, giving rise to bursts containing a relatively small number of subcolonies. This activity is produced by a bone marrow cell line; it is a glycoprotein, since it is destroyed by proteases; it is retained on Concanavalin A/Sepharose; and it precipitates at low ammonium sulfate concentration, indicating high hydrophobicity. This activity, shown to be different from known hematopoietic cytokines having BPA, exhibits an apparent strict erythroid specificity. Since it increases the development of rather small bursts probably arising from mature BFU-E, we refer to it as murine burst maturation promoting activity (mBMPA).

IL-11 directly stimulates murine and human erythroid burst formation in semisolid cultures.

The effect of interleukin-11 (IL-11) on cultures of bone marrow cells was investigated. We found that IL-11 increased, in a dose-dependent manner, the number of bursts in the presence of Epo in murine or human cells cultures. This effect was also observed in cultures of murine cells established in serum-free conditions as well as in cultures of CD34+ enriched human cells in serum-containing (but not serum-free) cultures. A linear relationship between the number of bursts and the plated cell number was observed with murine bone marrow cells or non-adherent mononuclear cells (NA-MNC) human bone marrow cells. Moreover, the effect of IL-11 was not abrogated when either anti-stem cell factor-receptor (anti-SCF-R), anti-IL-3, or anti-granulocyte/macrophage colony-stimulating factor (GM-CSF), three cytokines known to greatly synergize with IL-11, was added to cultures. These results lead us to conclude that IL-11 directly stimulates the proliferation of murine and human burst-forming units-erythroid (BFU-E).

A factor present in normal mouse serum stimulates late erythroid precursor proliferation.

A factor present in normal mouse serum stimulates proliferation of late erythroid precursors grown in cultures in vitro. This factor was shown not to have a corrective effect on culture conditions by the following criteria: (a) CFU-E frequency in the absence of NMS was at least as great as published data for various mouse strains, (b) an inhibitory effect of endotoxin was ruled out, (c) sensitivity of erythroid precursors to erythropoietin was similar in the presence or absence of NMS, and (d) the number of colonies was linearly related to the cell dose. The enhancing effect of NMS was independent of hemin, transferrin, or dexamethasone, products all known to be stimulators of erythropoiesis. It was shown to be specific for CFU-E. We propose that this material be termed erythropoietic stimulating cofactor (ESCF).

Mouse serum contains two erythroid progenitor-stimulating activities, one being highly increased in serum from anemic mice.

We previously observed that the addition of normal mouse serum to mouse bone marrow cell cultures increases the number of erythroid colonies arising from erythroid colony-forming units (CFU-E). In this paper, we show that the stimulating activity could be divided into two active fractions with 110 kd and 50 kd apparent molecular weight by gel filtration. The 50-kd fraction, in addition to its stimulating activity, increased the sensitivity of CFU-E to erythropoietin. The 110-kd activity was hardly detectable in normal mouse serum but was greatly increased in anemic mouse serum. This renders this activity of interest and suggests that it may play a regulatory role in mouse erythropoiesis.

Receptor for macrophage colony-stimulating factor transduces a signal decreasing erythroid potential in the multipotent hematopoietic EML cell line.

OBJECTIVE: To test the hypothesis that hematopoietic growth factors may influence lineage choice in pluripotent progenitor cells, we investigated the effects of macrophage colony-stimulating factor (M-CSF) on erythroid and myeloid potentials of multipotent EML cells ectopically expressing M-CSF receptor (M-CSFR). METHODS: EML cells are stem cell factor (SCF)-dependent murine cells that give rise spontaneously to pre-B cells, burst-forming unit erythroid (BFU-E), and colony-forming unit granulocyte macrophage (CFU-GM). We determined BFU-E and CFU-GM frequencies among EML cells transduced with murine M-CSFR, human M-CSFR, or chimeric receptors, and cultivated in the presence of SCF, M-CSF, or both growth factors. Effects of specific inhibitors of signaling molecules were investigated. RESULTS: EML cells transduced with murine M-CSFR proliferated in response to M-CSF but also exhibited a sharp and rapid decrease in BFU-E frequency associated with an increase in CFU-GM frequency. In contrast, EML cells expressing human M-CSFR proliferated in response to M-CSF without any changes in erythroid or myeloid potential. Using chimeric receptors between human and murine M-CSFR, we showed that the effects of M-CSF on EML cell differentiation potential are mediated by a large region in the intracellular domain of murine M-CSFR. Furthermore, phospholipase C (PLC) inhibitor U73122 interfered with the negative effects of ligand-activated murine M-CSFR on EML cell erythroid potential. CONCLUSION: We propose that signaling pathways activated by tyrosine kinase receptors may regulate erythroid potential and commitment decisions in multipotent progenitor cells and that PLC may play a key role in this process.

Murine interleukin 9 stimulates the proliferation of mouse erythroid progenitor cells and favors the erythroid differentiation of multipotent FDCP-mix cells.

Murine interleukin 9 (mIL-9) is a T-cell-derived growth factor that stimulates erythroid burst-forming units (BFU-E) from murine bone marrow. We further investigated this activity using enriched mouse bone marrow progenitors and the multipotent interleukin 3 (IL-3)-dependent FDCP-Mix cell line. We report here that mIL-9 stimulates erythroid burst formation of total bone marrow cells and accessory cell-depleted bone marrow cells, even in serum-free cultures. On the other hand, we observed that although mIL-9 could not support proliferation of FDCP-Mix cells, it favors erythroid differentiation of these cells in the presence of both IL-3 and erythropoietin. These results strongly suggest that mIL-9 acts directly on mouse erythroid progenitor cells.

A novel growth-factor-dependent myeloid cell line derived from mouse bone marrow cells contains progenitors endowed with high proliferative potential.

Constitutive expression of human colony-stimulating factor-1 receptor (CSF-1R) confers long-lasting CSF-1-dependent proliferation to mouse myeloid cell lines. We developed mice transgenic for human CSF-1R because mouse CSF-1 cannot activate human CSF-1R. Then bone marrow cells from transgenic mice were plated onto MS-5 stromal cells expressing the membrane form of human CSF-1 (2M-1 cells) in order to combine the hematopoietic supporting properties of stromal cells and the proliferative effects of CSF-1. Thus, we were able to derive a hematopoietic cell line, called 47.10, that grew indefinitely under these conditions, whereas no cell line could be developed from nontransgenic mice. Proliferation of 47.10 cells is severely affected by neutralizing anti-CSF-1R monoclonal antibodies. Morphologic and cytofluorometry analysis established that most 47.10 cells are immature myelomonocytic cells. Consistent with this phenotype, the myeloid transcription factor PU.1, but not the erythroid transcription factor GATA-1, is expressed in 47.10 cells. A few 47.10 cells (3-5%) do not express lineage specific markers; they differentiate spontaneously to lineage-positive cells after replating on 2M-1 cells. In agar cultures, 47.10 cells form 7- and 14-day colonies in response to a cocktail of granulocyte/macrophage colony-stimulating factor (2.5 ng/mL), interleukin-3 (1 ng/mL), and mouse CSF-1 (10 ng/mL). Under these conditions, about 0.5% of 47.10 cells formed large 14-day colonies (>1 mm) composed of mature monocytes and granulocytes, reflecting the presence of progenitors endowed with high proliferative potential (HPP-47.10 cells). In conclusion, we have characterized a novel continuous myeloid cell line presenting a hierarchical structure similar to that of the bone marrow progenitor cell compartment.

Colony-stimulating factor-1 impairs both proliferation and differentiation signals of erythropoietin during the commitment of bipotential NFS-60 cell line to the monocytic lineage.

The interleukin-3 (IL-3) dependent cell line NFS-60 contains bipotential progenitors that exhibit both erythroid and myelomonocytic potentials. In order to study their commitment to the monocytic lineage, NFS-60 cells were retrovirally transduced with mouse c-fms cDNA, which encodes the colony-stimulating factor-1 receptor (CSF-1R), resulting in the N-Fms cell line. N-Fms cells proliferated in response to CSF-1 with a growth rate similar to that obtained in response to IL-3 and progressively differentiated from myeloid blasts to monocytic cells within 3 days of culture. When maintained in IL-3, about 3% of N-Fms cells formed large hemoglobinized colonies in semisolid cultures supplemented with erythropoietin (EPO). However, this property was lost after a 24-hour cultivation in the presence of CSF-1 or, interestingly, both CSF-1 and IL-3. This loss of response to EPO was reverted following a brief passage (24 hours) in IL-3, but the rescued colonies did not undergo terminal erythrocytic differentiation. Furthermore, CSF-1 also affected proliferative response to EPO of N-Fms cells constitutively expressing EPO receptors. Our data strongly suggest that CSF-1 can suppress erythroid potential in bipotential N-Fms cells by altering proliferative and differentiation signal of EPO.

Characterization of a novel erythropoiesis-inhibiting human protein.

We have isolated an erythropoiesis-inhibiting protein, DIP (differentiation-inhibiting protein), from the blood of a 60-year-old woman suffering from pure red cell aplasia. This protein inhibits the growth and differentiation of normal human and murine BFU-E, but not CFU-E, cells as well as dimethyl sulfoxide-induced hemoglobin synthesis by Friend murine erythroleukemia cells. It appears that DIP primarily affects differentiation rather than proliferation, because it does not inhibit the proliferation of untreated Friend erythroleukemia cells. DIP seems to function like a recently described 45-kDa autocrine differentiation-inhibiting protein factor (ADIF) which is secreted by tsAEV-transformed chicken erythroleukemia cells. Both proteins selectively block the differentiation of normal human and murine BFU-E cells as well as the differentiation (but not the proliferation) of Friend murine erythroleukemia cells. However, the human DIP is not an autocrine product of the patient's bone marrow cells, nor does it affect chicken erythroid cells.

Erythroid precursors cultured from adult mice are sensitive to H2O2 toxicity.

The growth of late erythroid precursors (CFU-Es) from adult bone marrow is inhibited when Iscove 's modified Dulbecco's medium supplied in liquid form is used. Catalase and other H2O2 destroying compounds restore the capacity of culture medium to support colony development. However early precursors from adult bone marrow and fetal liver CFU-Es were resistant to H2O2.