Roles for integrin very late activation antigen-4 in stroma-dependent erythropoiesis

Adhesion molecules are required for development of hematopoietic stem and progenitor cells in the respective hematopoietic microenvironments. We previously showed that development of the erythroid progenitor cells is dependent on their direct adhesion to the stroma cells established from the erythropoietic organs. In this stroma-dependent erythropoiesis, we examined the role of adhesion molecules in erythropoiesis by blocking antibodies. The development of the erythroid cells on stroma cells was inhibited by anti-very late activation antigen-4 (VLA-4 integrin) antibody, but not by anti-VLA-5 antibody, although the erythroid cells express both VLA-4 and VLA-5. Whereas high levels of expression of vascular cell adhesion molecule-1 (VCAM-1) and fibronectin, ligands for VLA-4, were detected in the stroma cells, the adhesion and development of the erythroid progenitor cells were partly inhibited by the blocking antibody against VCAM-1. VLA-5 and fibronectin could mediate adhesion of the erythroid progenitor cells to the stromal cells, but the adhesion itself may not be sufficient for the stroma-supported erythropoiesis. The stromal cells may support erythroid development by the adhesion through a new ligand molecule(s) for VLA-4 in addition to VCAM-1, and such collaborative interaction may provide adequate signaling for the erythroid progenitor cells in the erythropoietic microenvironment.

Apoptosis is induced at nonpermissive temperature by a transient increase in p53 in cell lines immortalized with temperature-sensitive SV40 large T-antigen gene

Hepatocyte (TLR2) and kidney tubule (TKC2) cell lines established from temperature-sensitive (ts) SV40 T-antigen gene transgenic mice not only were arrested in growth, but also exhibited cell death at nonpermissive temperature (39 degrees C). The cell death was determined to be caused by apoptosis from observations of nuclear fragmentation and DNA fragmentation. These cell lines contained relatively high levels of wild-type p53 which formed complexes with T-antigen at permissive temperature (33 degrees C), but after shift to a nonpermissive temperature, the inactivation of T-antigens led to the liberation of an abundance of p53 proteins from the complexes, apparently inducing apoptosis.

The helix-loop-helix protein Id inhibits differentiation of murine erythroleukemia cells

Id is considered to be a negative regulator of basic helix-loop-helix proteins, which play important roles in cell type-specific transcription and cell lineage commitment. The Id gene was first cloned in murine erythroleukemia (MEL) cells, which can be induced to differentiate toward erythrocytes with Me2SO, and its mRNA decreases after differentiation in various types of cells. In this report, we demonstrate that overexpression of Id interferes with MEL cell differentiation and that inhibition of differentiation is accompanied by reduction in expression of three erythroid-specific genes. While down-regulation of Id is an early event in the differentiation process of MEL cells, E-box binding activity of these cells increases only at a later stage of differentiation, and this late increase is reduced by the overexpression of Id in the early stage. Sequential changes in the activity of several basic helix-loop-helix proteins thus appeared to be involved in erythroid differentiation.

Establishment of gastric surface mucous cell lines from transgenic mice harboring temperature-sensitive simian virus 40 large T-antigen gene

We succeeded in establishing two gastric surface mucous cell lines (designated as GSM06 and GSM10), which produce periodic acid-Schiff (PAS)- and concanavalin A (Con A)-positive glycoproteins, from a primary culture of gastric fundic mucosal cells of adult transgenic mice harboring a temperature-sensitive simian virus 40 large T-antigen gene. At the permissive temperature (33 degrees C), GSM06 and GSM10 cells grew until confluent monolayers were formed and have now been in culture for more than 9 months with regular passaging. Con A-horseradish peroxidase- and PAS-positive staining indicated that these cells retain the characteristics of gastric surface mucous cells. GSM06 cells showed temperature-sensitive growth in culture and expressed SV40 large T-antigen at the permissive temperature but not at a nonpermissive temperature (39 degrees C). In contrast, GSM10 cells showed temperature-insensitive growth and expressed T-antigen at both permissive and nonpermissive temperatures. To our knowledge, this is the first report of the establishment of gastric surface mucous cell lines from animals. These immortalized cell lines with normal characteristics may serve as good experimental models for the basic and applied biology of gastric surface mucous cells.

Erythropoietin as a mitogen for fetal liver stromal cells which support erythropoiesis

Fetal liver stromal cells established from 13-day-old embryos support erythropoiesis in vitro in combination with erythropoietin (Epo). Epo stimulated growth of these stromal cells in a dose-dependent manner and mRNA for Epo receptor was detected. These results suggest the possible involvement of Epo in the generation of the fetal erythropoietic microenvironment during development.

c-Myc selectively regulates the latent period and erythroid-specific genes in murine erythroleukemia cell differentiation

During the latent period of murine erythroleukemia (MEL) cell differentiation, c-myc levels showed a significant change and the overexpression of the transferred c-myc gene inhibited the commitment and differentiation of MEL cells, suggesting that c-Myc may be a key molecule for the commitment. Since c-Myc may function as a DNA binding transcription factor, we examined whether c-Myc regulates the latent period genes (hsp and hsc70, MER5, Id and Spi-1 genes) and the erythroid-specific genes [beta-globin, glycophorin, delta-aminolevulinic acid synthase (ALAS-E), GATA-1 and erythropoietin receptor (EpoR)] in the MEL cell transformant having transferred c-myc gene. The overexpression of c-myc gene affected the latent period genes in different ways: hsc and hsp 70 genes and Id gene were positively regulated, while expression of MER5 gene was repressed. While c-myc is thought to be involved in DNA replication, its overexpression showed no effect on the expression of proliferating cell specific nuclear antigen or DNA polymerase a. The overexpression of c-myc repressed the expression of glycophorin, ALAS-E and beta-globin genes, of the five erythroid-specific genes, but had no effect on expression of GATA-1 or EpoR gene. These results suggest that c-Myc differentially regulates the expression of the latent period and erythroid-specific genes.

Coordinated expression of messenger RNAs for nerve growth factor, brain-derived neurotrophic factor and neurotrophin-3 in the rat hippocampus following transient forebrain ischemia

Changes in nerve growth factor, brain-derived neurotrophic factor and neurotrophin-3 messenger RNA expression in the rat hippocampus following 20 min of transient forebrain ischemia were evaluated using Northern blot analysis and in situ hybridization histochemistry. Twelve hours after the insult, the level of nerve growth factor messenger RNA increased markedly in the granular cell layer of the dentate gyrus and by day 2 returned to control levels. The level of brain-derived neurotrophic factor messenger RNA showed a persistent and moderate increase. The highest expression of brain-derived neurotrophic factor messenger RNA was seen in the dentate granule cells on day 2 after the insult, and then the expression returned to the control levels. At 2 days post-ischemia, contents of messenger RNAs for nerve growth factor and brain-derived neurotrophic factor were reduced in the CA1 region, which may represent delayed loss of vulnerable CA1 pyramidal neurons. In contrast to brain-derived neurotrophic factor and nerve growth factor messenger RNA expression, the level of neurotrophin-3 messenger RNA declined in the CA1, the CA2 and the dentate granular layer immediately after ischemic insult. In the CA1 region, the reduced expression persisted for at least seven days, but in the dentate gyrus, neurotrophin-3 messenger RNA expression returned to the control levels after two days of post-ischemic recovery. These results suggest that nerve growth factor, brain-derived neurotrophic factor and neurotrophin-3 genes are differentially regulated and that each of their gene products may play different roles in the central nervous system under pathophysiological conditions.

Functional domains of c-Myc involved in the commitment and differentiation of murine erythroleukemia cells

In the early event of the induction of mouse erythroleukemia (MEL) cell differentiation, c-myc mRNA levels show a drastic change. The elevated expression of a transfected c-myc gene inhibits the commitment and differentiation of MEL cell transformants. In the present work, we have introduced human c-myc mutants into MEL cells under the inducible promoter to define the functional domains of c-Myc involved in erythroid differentiation. The c-Myc domains necessary for commitment and differentiation are not co-localized; almost entire regions are required for inhibition of commitment, whereas domains II and IV that are essential for co-transforming activity with ras are required for inhibition of differentiation. Interestingly, mutants that delete domains for c-Myc dimerization motifs enhanced differentiation. These results suggest that c-Myc may regulate commitment and differentiation by interacting with proteins through different domains.

Role of c-Myc on erythroid differentiation

In the early event of the induction of mouse erythroleukemia (MEL) cell differentiation, c-myc mRNA levels show a biphasic change. The elevated expression of a transfected c-myc gene inhibits the commitment and differentiation of MEL cell transformants. In the present work, we have introduced human c-myc mutants into MEL cells under the inducible promoter to define the functional domains of c-Myc involved in erythroid differentiation. The c-Myc domains necessary for commitment and differentiation are not colocalized; almost entire regions are required for inhibition of commitment, whereas domains II and IV that are essential for co-transforming activity with ras are required for inhibition of differentiation. Interestingly, mutants that delete domains for c-Myc dimerization motifs enhanced differentiation. Thus, c-Myc interferes with MEL cell differentiation by interacting with c-Myc partners and the induced protein(s) through dimerization domains. These results suggest that c-Myc may regulate commitment and differentiation by interacting with proteins through different domains.

Identification of type I collagen-producing cells in human gastrointestinal carcinomas by non-radioactive in situ hybridization and immunoelectron microscopy

Invasive growth of cancer cells induces desmoplastic reaction as one of the host reactions. It has been a matter of controversy whether stromal collagen is produced by cancer cells or stromal fibroblasts. In the present study, we investigated the cellular origin of Type I collagen in human gastrointestinal carcinomas by in situ hybridization and immunoelectron microscopy. In situ hybridization technique with digoxigenin-labeled RNA probes revealed that spindle-shaped fibroblasts in the stromal area were abundantly positive for transcripts of pro alpha 1(I) collagen in intestinal-type adenocarcinoma. Gland-forming carcinoma cells were negative. In diffuse-type carcinoma of the stomach, spindle-shaped or stellate fibroblasts were positive, whereas dissociated, oval carcinoma cells were negative. A precise determination of cell type was done by immunoelectron microscopy. Intracellular immunoreactivity for Type I collagen was observed in rough endoplasmic reticulum of fibroblasts (including myofibroblasts) in the stromal area. No definite reactivity was obtained in cancer cells by either in situ hybridization or immunoelectron microscopy. Our results indicated that stromal Type I collagen is produced by stromal fibroblasts, which are activated by cancer invasion.

Decreased expression of neurotrophin-3 mRNA in the rat hippocampus following transient forebrain ischemia

The expression profile of neurotrophin-3 (NT-3) mRNA in the rat hippocampus after forebrain ischemia was investigated by Northern blot and S1 nuclease protection analyses. The NT-3 transcripts in the hippocampus immediately decreased after ischemic insult, became undetectable within 3 h and remained at undetectable levels for at least 7 days. In contrast, the expression of c-fos and c-jun mRNA transiently increased both in the cerebral cortex and in the hippocampus. These results suggest that brain ischemia triggers dynamic changes in gene expression including a neurotrophic factor, which may cause functional and/or morphological changes of the neuronal network.

Combined action of c-kit and erythropoietin on erythroid progenitor cells

Mutations at the murine dominant-white spotting locus (W) (c-kit) affect various aspects of hematopoiesis. We have made antibodies against c-Kit with the synthetic peptides deduced from the murine c-kit gene and examined the role of c-Kit in erythropoiesis. The antibody inhibited the stromal cell-dependent large colony formation of the erythroid progenitors. In the culture of erythropoietin-responsive erythroid progenitors of the anemia-inducing Friend virus-infected mouse spleen, the antibody inhibited only proliferation, but not differentiation of the progenitor cells. The inhibition was effective only at the early phase (within 6 hours after erythropoietin addition) before the cells start to proliferate induced by erythropoietin. During the early phase, erythropoietin down-regulated c-kit gene expression. These results suggest a mechanism of combined action of c-Kit with erythropoietin on the lineage-restricted erythroid progenitor cells.

c-Myc interferes with the commitment to differentiation of murine erythroleukemia cells at a reversible point

When murine erythroleukemia (MEL) cells, containing the transferred rat c-myc gene under the control of human metallothionein II gene promoter, are induced to differentiate with dimethyl sulfoxide, the level of differentiation is dependent on the c-Myc level, which is modulated by the addition of Zn ions. In this work, we examined the point of inhibition of differentiation by elevated levels of c-Myc in one (clone 38-2) of the typical transformants. Commitment assay indicated that elevated levels of c-Myc interfere with entry of the transformant into the commitment event, but when c-myc expression was reduced by removing Zn ions from the medium, the cells could reenter the commitment program. However, once the cells were committed, such cells could not return to the uncommitted state. In addition, time-dependent expression of two erythroid specific genes was inhibited by elevated levels of c-Myc in time-dependent manner. These results suggest that c-Myc modulates MEL cell differentiation at a reversible point of commitment.

A tubule cell line established from transgenic mice harboring temperature-sensitive simian virus 40 large T-antigen gene

Immortalization of cell lines with specific functions is important for examination of organ-specific functions in vitro. We established a kidney tubule cell line (TKC2) exhibiting a specific physiological response to hormone from the primary culture of kidneys of adult transgenic mice harboring temperature-sensitive SV40 large T-antigen gene. TKC2 cells showed temperature-sensitive growth in culture and exhibited characters of distal tubule cells such as dome formation at confluent culture and stimulation of cAMP synthesis by arginine vasopressin. These phenotypes are maintained after long passages in culture and may provide a new experimental system for studying renal physiology.

Functional characterization of SV40-transformed adherent synovial cells from rheumatoid arthritis

A total of 14 transformed cell clones were obtained by micro-injecting origin-defective SV40 DNA into three types of cloned adherent synovial cells (ASC) (dendritic cells (DCs), macrophage-like cells (MCs), and fibroblast-like cells (FCs)) from two rheumatoid arthritis patients (five DC clones (SV40-DCs), five MC clones (SV40-MCs) and four FC clones (SV40-FCs)). All the transformed cell nuclei expressed SV40-specific T antigen. The cells which formed a colony had a few times shorter doubling time than the original cells. IL-1 alpha, IL-1 beta and prostaglandin E2 were detected in the culture supernatant from the unstimulated transformed cells like untransformed cells. The SV40-DCs showed the most potent accessory cell function in oxidative mitogenesis assay among the three types of SV40-ASCs. Granulocyte macrophage colony stimulatory factor (GM-CSF) was detected only in the culture supernatant from the SV40-MCs without stimulation. Extensive phenotypic analysis revealed relatively cell-specific markers. SV40-DCs were HLA-DP+ and glial fibrillary acidic protein positive. SV40-MCs stained positive for 5'-nucleotidase and nonspecific esterase. These transformed ASCs retained much of the original cellular physiology of rheumatoid arthritis (RA) ASCs and may be a useful tool for characterizing the role of ASCs in the pathogenesis of RA.

Hepatocyte cell lines established from transgenic mice harboring temperature-sensitive simian virus 40 large T-antigen gene

To establish cell lines exhibiting differentiation phenotypes, the immortalized cell lines were rapidly established from the primary culture of different tissues of transgenic mice harboring SV40 temperature-sensitive large T-antigen gene. The established cell lines grew at permissive temperature (33 degrees C), but not at nonpermissive temperature (39 degrees C). Several different cell types could be rapidly immortalized and cloned from the adult transgenic mice tissues. Among those cell lines, the established hepatocyte cell lines (TLR cell lines) exhibited liver-specific morphological and biochemical properties, but their properties were not coupled with the growth condition modified by temperature. The hepatocyte cell lines showed an inducibility of P450IA1 by 3-methylcholanthrene as observed in rat livers and this liver-specific function was stable even after 6 months of culture by continuous passages.

Support of early B-cell differentiation in mouse fetal liver by stromal cells and interleukin-7

We compared the development of B-cell progenitors with that of myeloid progenitors in fetal liver cells at various gestational ages. Day 12 to 14 fetal liver cells did not form pre-B-cell colonies. Pre-B-cell colonies were developed from day 15 fetal liver cells. The incidence of colonies increased with increases in gestational age and reached a maximum on days 18 to 19. In contrast, the incidence of myeloid colonies formed in the presence of interleukin-3 (IL-3) and erythropoietin did not change significantly during days 13 to 21 of gestation. After coculturing day 13 fetal liver cells with IL-7-producing stromal cell line ST-2, they could respond to IL-7 and proliferate. Analysis of the phenotypes showed that day 13 fetal liver cells were B220-, IgM-, while culturing day 13 fetal liver cells with ST-2 and untreated day 18 fetal liver cells contained the population of B220+ cells. Even in the presence of IL-7-defective stromal cell line FLS-3, IL-7-responsive cells could be induced from day 13 fetal liver cells. IL-7 acted on B220+ cells and induced pre-B-cell colonies that contained IgM+ cells in the methylcellulose culture. IL-7 mRNA was expressed in days 13 and 18 fetal liver cells but not in pre-B cells or adult liver cells. From these findings, it is suggested that stromal cells or stromal-derived factors but not IL-7 were required for the differentiation from B220- cells to B220+ cells. In the second stage, B220+, IgM- cells proliferated and some of them differentiated to IgM+ cells in the presence of IL-7 alone. The two-step model can apply to in vivo early B lymphopoiesis.

Overexpression of c-Myc inhibits the appearance of a specific DNase I hypersensitive site in the beta-globin chromatin in murine erythroleukemia cells

To investigate the molecular mechanism of regulation of differentiation by c-Myc, we examined the acquisition of DNase I hypersensitivity by beta-globin chromatin in an MEL cell transformant (38-2) in which the c-myc gene was placed under the control of a metallothionein gene promoter. Of the three DNase I hypersensitive sites around the beta-globin gene which were detected in MEL cells after DMSO treatment, the appearance of a specific DNase I hypersensitive site near the promoter was greatly reduced by the overexpression of c-Myc. This result suggests that c-Myc regulates beta-globin expression by interfering with the establishment of an active chromatin conformation around the beta-globin gene.

Continued blood cell formation in spherical bodies in a long-term mouse spleen culture

During the primary culture of spleen fragments of newborn mice, a spherical body (d = circa 200 to 300 microns) as a three-dimensional cellular organization was formed. Continued production of blood cells from the spherical body was observed without changing its size for about 2 months of culture. Without growth factor, the spherical bodies produced mainly lymphocytes and macrophages. Addition of interleukin-3 enhanced their granulocyte formation, and this enhancement was observed even after a prolonged maintenance without growth factors. The spherical bodies were composed of a uniform mixture of endothelial cells and fibroblasts within the body, and cell-cell contacts between lymphocytes and fibroblasts were notable in the periphery. With prolonged culture, the spherical bodies showed a definite change in their structure by sorting two cell types and the blood cell production gradually decreased. These results suggested that a three-dimensional structure was required for the maintenance, growth, and differentiation of blood cell progenitors in the long-term spleen culture.

Endothelial cells create a hematopoietic inductive microenvironment preferential to erythropoiesis in the mouse spleen

The spleen is an erythropoietic organ in mouse. To reconstruct a microenvironment essential for erythropoiesis in vitro, the stroma (MSS31) cell line had been established from a newborn mouse spleens. MSS31 cells exhibited properties of endothelial cells: (a) the cells showed the activity to uptake acetylated low-density lipoprotein (Ac-LDL) and (b) the cells can form a capillarylike structure by a phenotypic modulation in collagen matrices. MSS31 cells selectively supported the proliferation and differentiation of the erythroid progenitor cells by direct cell-to-cell contact in a semisolid medium in the presence of erythropoietin. These layers also supported erythrocyte maturation and enucleation of erythroblasts. This suggests that spleen endothelial cells are a new type of stromal cell with erythropoietic stimulation activity and may have a critical function in the hemopoietic inductive microenvironment of the mouse spleen.

Microenvironment created by stromal cells is essential for a rapid expansion of erythroid cells in mouse fetal liver

Mouse stromal cell lines (FLS lines), established from the livers of 13-day gestation mouse fetus, supported the proliferation and differentiation of the erythroid progenitor cells from mouse fetal livers and bone marrow in a semisolid medium in the presence of erythropoietin. A large erythroid colony of over 1000 benzidine-positive erythroid cells was developed from a single erythroid progenitor cell on the FLS cell layer after 4 days of culture. When in close contact with the layer, the erythroid progenitor cells divided rapidly with an average generation time of 9.6 h and mature erythroid cells, including enucleated erythrocytes, were produced. The present studies demonstrate that the microenvironment created by the stromal cells can support the rapid expansion of erythropoietic cell population in the fetal liver of mice.

Antisense RNA of the latent period gene (MER5) inhibits the differentiation of murine erythroleukemia cells

The MER5 cDNA was cloned from RNA preferentially synthesized in murine erythroleukemia (MEL) cells during the early period of MEL cell differentiation. To understand the role of the MER5 gene in the differentiation, we have transferred the MER5 cDNA into MEL cells in both sense and antisense orientations under control of the promoter of the human metallothionein gene. Only in the transformants with the antisense MER5 cDNA, did their elevated expression inhibit differentiation. The result suggests that the MER5 gene product may promote early events in the differentiation of MEL cells.

Characterization of a new endothelial cell growth factor (f-ECGF) partially purified from the supernatant of human fibroblast cells

A new endothelial cell growth factor (f-ECGF) was partially purified from the cultured medium of human fibroblast cells of embryonic lungs. The partially purified f-ECGF induced neovascularization in rabbit cornea. It showed a selective growth stimulatory activity on the endothelial cells in vitro, whereas acidic- and basic-fibroblast growth factors (a- and b-FGFs) showed a broad spectrum of growth stimulation among tissues or cells. f-ECGF did not compete with the binding of a-FGF to the cell surface receptor in HEP-G2 hepatoblastoma cell lines. These results indicated that f-ECGF is a new endothelial cell growth factor distinct from a- and b-FGFs which are known to be potent endothelial cell growth factors.

Spleen stromal cell lines selectively support erythroid colony formation

Mouse stromal cell lines (MSS lines) have been established from the spleens of newborn mice in culture at a low serum concentration. These MSS lines support the proliferation and differentiation of the erythroid progenitor cells from mouse fetal livers and bone marrow in a semisolid medium in the presence of erythropoietin. Larger colonies of over 1,000 benzidine-positive erythroid cells were developed from the fetal liver cells on the MSS cell layers after 6 days of incubation. These layers also support the maturation of the erythroid cells since the enucleation process of the latter was observed in large erythroid colonies. Metabolically active MSS cells are apparently required to support the proliferation and differentiation of the erythroid progenitor cells, because neither the MSS cells inactivated with fixation nor the conditioned media of MSS cells promoted the erythroid colony formation. These studies demonstrate that MSS lines specifically support the proliferation and differentiation of the erythroid progenitor cells in vitro and that stroma cells may have a critical function in blood formation in the mouse spleen.

A balance between self-renewal and commitment in the murine erythroleukemia cells with the transferred c-myc gene; an in vitro stochastic model

When murine erythroleukemia (MEL) cells, having the transferred rat c-myc gene under the control of human metallothionein II gene promoter, are induced to differentiate with dimethyl sulfoxide (DMSO), the level of differentiation is dependent on the c-myc levels which are modulated by the Zn++ ion. The clonal transformant cell line (38-2) can continuously grow in the presence of both DMSO and Zn++ ion. The proportion of differentiated cells in a population of the continuous culture is strongly affected by the concentration of Zn++ ions. These results suggested that a balance between self-renewal and commitment to differentiation of MEL cells is determined by the c-myc level, and that this cell line may be suitable for studying the stochastic process of growth and differentiation of hemopoietic stem cells.

Cloning of a housekeeping-type gene (MER5) preferentially expressed in murine erythroleukemia cells

DNA complementary to mRNA preferentially produced in murine erythroleukemia (MEL) cells was cloned from a cDNA library of anemic mouse spleen mRNAs. An open reading frame was noted in the cloned DNA, and was tentatively designated MER5. The MER5 mRNA is abundant in three MEL cell lines, but less in other tissues or cell lines. The levels of the MER5 mRNA changed periodically during MEL cell differentiation and decreased as globin mRNA accumulated. The MER5 promoter region contained no typical TATA-like sequence, but possible target sequences for AP1, AP2, SP1 and octamer-binding protein. More interestingly, this promoter contained the duplicated CACCC boxes, which are common in the adult beta-globin promoter from many species, but uncommon for promoters of other eukaryotic genes.

Selective suppression of endogenous beta-globin gene expression by transferred beta-globin/TK chimeric gene in murine erythroleukemia cells

To examine the effect of gene transfer on expression of the endogenous beta-globin gene in murine erythroleukemia (MEL) cells, a beta-globin/TK chimeric gene was introduced into MEL cells. In some of the transformants, expression of the endogenous beta-globin gene was only weakly induced with the addition of DMSO, while expression of the introduced beta-globin/TK chimeric gene was well induced. Suppression of the endogenous beta-globin gene is selective for beta-globin gene, since expression of alpha-globin gene was only weakly affected in its induction in the transformants. Analysis of nine individual transformants indicated that suppression of the endogenous gene correlates more closely with the transcriptional activity than the copy number of the exogenous gene. Thus, the selective suppression can be explained by competition of positive trans-acting factor(s), present in limiting amounts, with high copy number of the exogenous gene the conformation of which is active.

Isolation of the cDNA clone for mouse glycophorin, erythroid-specific membrane protein

The cDNA clone for a major mouse glycophorin, transmembrane glycoprotein of erythrocytes has been isolated from a mouse spleen erythroblast cDNA library. The primary structure of a major glycophorin indicates that the protein is a single polypeptide chain of 168 amino acids (aa) clearly organized in three domains distinct in the glycophorin of other species. A strong homology of the mouse major glycophorin with human glycophorin A or B, but not with human glycophorin C is observed only in the hydrophobic stretch of 23 nonpolar aa, indicating that the major mouse glycophorin species cloned is similar to human glycophorin A. The glycophorin mRNA is absent in all non-erythroid organs or cell lines examined. The glycophorin mRNA is induced during the differentiation of murine erythroleukemia cells with dimethyl sulfoxide.

Different signalling pathways are used in the commitment of murine erythroleukemia cells (TSA8) to differentiate, and in the erythropoietin action on progenitor cells

The murine erythroleukemia (MEL) cell line, TSA8, becomes responsive to erythropoietin after induction with dimethyl sulfoxide (DMSO). We examined the signalling pathways involved in the commitment of TSA8 cells to become the erythroid progenitor cells responsive to erythropoietin, comparing them with the pathway used in an erythropoietin-induced change of the progenitor cells. Amiloride, an inhibitor of the Na+/H+ antiporter, completely blocked the commitment of TSA8 cells to become responsive to erythropoietin at a concentration that did not affect cell proliferation, while it showed no effect on the differentiation or proliferation of the erythroid progenitor cells derived from TSA8 cells by erythropoietin. Ethyleneglycol-bis (beta-aminoethyl ether) N,N,N',N'-tetra acetic acid (EGTA) inhibited the commitment of TSA8 cells to CFU-E-like cells without affecting colony formation. In contrast, EGTA did not inhibit erythropoietin-induced differentiation of the progenitor cells, but did inhibit their proliferation. These results indicate that erythropoietin uses different signalling pathways from those used in the induction of the commitment of TSA8 cells.

Analysis of the expression of two phosphoglycerate kinase genes in a mouse cultured cell line during activation and inactivation of the c-myc gene

The effect of a change in the concentration of c-myc protein on the expression of genes for two phosphoglycerate kinase isozymes was investigated. The steady state levels of messenger ribonucleic acids (mRNAs) for sperm-type and non-sperm-type proteins were determined by blot hybridization using the RNA of the mouse cell line 38-2 containing the inducible rat c-myc gene cultured under various conditions. Without induction the c-myc gene. mRNA for non-sperm-type protein was detected at a level that remained essentially constant during both activation and inactivation of the c-myc gene. mRNA for sperm-type protein was not detected in 38-2 cells cultured under any conditions used. Change in the amount of c-myc protein alone does not appear to bring about a switch of the expression of the two phosphoglycerate kinase genes during spermatogenesis in mouse testis.

Mechanism of erythropoietin action on the erythroid progenitor cells induced from murine erythroleukemia cells (TSA8)

Erythropoietin is a well-known erythroid differentiation and growth factor, but the mechanism of its action is not well understood. In this work, we have examined its mechanism of action on the erythropoietin-responsive murine erythroleukemia cells (TSA8). TSA8 cells become responsive to erythropoietin after induction with DMSO. Stimulatory effects on erythropoietin response are observed with the addition of compounds affecting the cAMP level such as forskolin, phosphodiesterase inhibitor and cholera toxin only in the presence of erythropoietin. cAMP analogues themselves show no stimulatory effect on TSA8 cells, nor does erythropoietin increase cAMP level in the cells. Thus, it is suggested that cAMP does not act as a direct second messenger for signal transduction through erythropoietin receptors, but as a stimulator of the erythropoietin receptor pathway and/or as a second messenger in combination with the receptor pathway. The mechanism for acquisition of responsiveness to growth and differentiation factors of progenitor cells is discussed.

Effect of c-myc gene expression on early inducible reactions required for erythroid differentiation in vitro

By employing cell fusion between two genetically marked mouse erythroleukemia (MEL) cells in which an artificially introduced c-myc gene had been placed under the control of human metallothionein promoter, we investigated the mechanism of the suppressive action of c-myc gene expression in erythroid differentiation. The results indicated that the expression of the c-myc gene blocked the induction of dimethyl sulfoxide-inducible activity, one of the two early activities required for triggering the differentiation.

Probability that the commitment of murine erythroleukemia cell differentiation is determined by the c-myc level

During the commitment of mouse erythroleukemia cell differentiation, c-myc mRNA levels change dramatically. To examine the involvement of c-myc in the commitment of these cells, we have introduced the rat c-myc gene driven by inducible, heterologous (human metallothionein IIA) gene promoter into murine erythroleukemia cells and we have examined the ability of the transformed cells to undergo commitment to terminal differentiation. The induction of the exogenous c-myc gene expression inhibited the commitment of these cells. Time-dependent inhibition of the commitment was observed with the addition of zinc at an appropriate time after the induction with dimethyl sulfoxide. The result clearly indicated that late decline, not early decline, is required for the commitment. By examining the transformants expressing the exogenous c-myc mRNA at different levels, and the induction of the exogenous c-myc mRNA by varying the concentration of zinc, we demonstrated that the commitment may be determined by a stoichiometric amount of c-myc in the defined period. The data also suggest that the probability value for the commitment process occurring in a stochastic manner is well-correlated with the amount of c-myc mRNA.

Differentiation of erythroid progenitor (CFU-E) cells from mouse fetal liver cells and murine erythroleukemia (TSA8) cells without proliferation

Erythropoietin (epo) appears to play a significant role in influencing the proliferation and differentiation of erythroid progenitor (CFU-E) cells. To determine the mechanism of action of epo, the effect of drugs on the in vitro colony formation of CFU-E cells induced from a novel murine erythroleukemia cell line, TSA8, was examined. While cytosine arabinoside inhibited colony formation and terminal differentiation of the CFU-E cells responding to epo, herbimycin, which is a drug that inhibits src-related phosphorylation, inhibited colony formation only. The same effect of herbimycin was observed with normal CFU-E cells from mouse fetal liver cells. These results suggest that epo induces two signals, one for proliferation and the other for differentiation, and that the two signals are not linked in erythroid progenitor cells.

Stage-specific gene expression in erythroid progenitor cells (CFU-E)

In erythropoietic differentiation, mature red blood cells are generated from specific progenitor cells through the action of specific growth regulatory molecules. To know the mechanism of differentiation, it is important to examine the control of gene expression in these progenitor cells in combination with growth regulatory molecules. We have cloned two genes expressing at a maximal level in the CFU-E (colony forming unit-erythroid), one of the erythroid progenitor cells from novel murine erythroleukemia (MEL) cell line (TSA8) which can be induced to CFU-E in vitro. The expression of these genes is well correlated with the appearance of CFU-E during induction of TSA8 cells, and is higher in the CFU-E-cells enriched from mouse fetal livers than in the more differentiated erythroid cells. Combining these with our previous results, it is suggested that in the erythropoiesis the progenitor cells have distinct patterns of gene expression. This expression is replaced through each progenitor cell rather than by the continuous increase in the expression of a set of genes specific to the mature erythroid cell following the commitment process.

Factors controlling induction of commitment of murine erythroleukemia (TSA8) cells to CFU-E (colony forming unit-erythroid)

On addition of DMSO, the MEL cell line TSA8 becomes committed into erythroid progenitor cells (CFU-E) which can form differentiated colonies in the presence of erythropoietin. To understand the mechanism of cellular commitment, the number and the affinity of the receptors for erythropoietin were estimated. The affinity of the receptors did not change before or after induction. The number of receptors changed depending on the growth phase, but was not dependent on the addition of the inducer. Thus, the presence of the receptors for erythropoietin may be required, but are not essential for responsiveness to erythropoietin. Further examination of the optimum conditions for commitment suggests that the concomitant actions of induced factor(s) with the receptors may control commitment of TSA8 cells to CFU-E.

Characterization of trans-acting factor(s) regulating beta-globin gene expression by in vivo competition

A beta-globin/TK fusion gene was microinjected into non-erythroid cells (Ltk- cells) and erythroid cells (murine erythroleukemia (MEL) cells), and the interactions of the regulatory cellular factors with the beta-globin sequences were investigated by the in vivo competition experiment. The fusion gene was expressed efficiently in Ltk- cells. This expression was inhibited by a co-injection with a three-fold molar excess of the 5'-flanking sequence of the beta-globin gene or with a nine-fold molar excess of the mammary tumor virus LTR, but not with the alpha-globin gene. The fusion gene was expressed very poorly in the uninduced MEL cells and highly in the induced MEL cells. The co-injection of the beta-globin gene did not affect expression in the MEL cells in either uninduced or induced conditions.

[Factors controlling the differentiation and cancerization of murine erythroleukemia cells]

Cultured murine erythroleukemia (MEL) cells can be induced to differentiate into erythrocytes. During this induced differentiation, a certain type of sequentially programmed gene expression and repression appears to occur in addition to the induction of globin mRNA. This system provides a commitment model for erythrodifferentiation and decancerization. By transfection of a beta-globin/TK chimeric gene into a B8/3 cell line, we examined the regulatory factors controlling beta-globin gene expression. Our results suggested that the timing of the appearance of inducible, positive trans-acting factor (s) and activation of chromatin conformation occur during induction. We demonstrated that a novel MEL cell line, TSA 8, could be induced to be committed to CFU-E, an erythropoietin-mediated progenitor cell, with the addition of DMSO. In the commitment process, we observed an asymmetric cell division, which could explain the self-renewal and the commitment of multipotential hemopoietic stem cells. For this commitment, the receptor for erythropoietin is required, but is insufficient and the other factor (s) are induced in the earlier phase of induction. Finally, we found that erythropoietin induced two signals for proliferation and differentiation of the progenitor cells and that these two signals are not coupled.

Molecular cloning and nucleotide sequence of cDNA encoding hydroxyindole O-methyltransferase of bovine pineal glands

Messenger RNA for hydroxyindole O-methyltransferase (EC 2.1.1.4) was partially purified from poly(A)+ RNA isolated from bovine pineal glands by sucrose density gradient centrifugation. The enriched mRNA was used to prepare a cDNA library by use of expression vector lambda gt11. The library was screened with monoclonal antibodies to the enzyme, and three cDNA clones were isolated. These cloned cDNAs cross-hybridized with one another, and their fusion proteins reacted to the monoclonal antibodies with different binding properties. Hydroxyindole O-methyltransferase enzymatic activity was demonstrated in the bacteria lysate infected with lambda HIOMT-A16, the clone that contained the longest insert. An almost full-length cDNA clone was isolated from lambda gt10 cDNA library by use of the lambda HIOMT-A16 cDNA as a probe. The primary structure of hydroxyindole O-methyltransferase was determined by analyzing the nucleotide sequence of the cDNAs. It consisted of 1939 nucleotides including a 1050-nucleotide region coding for 350 amino acids. RNA transfer blot analysis indicated that mRNA encoding hydroxyindole O-methyltransferase was present only in the pineal gland and not in the brain, retina, and liver of cow.

Modulation of the transferred mouse 26K casein gene in mouse L cells by glucocorticoid hormone

The cloned 26K casein gene was transferred to mouse L-cells and its expression was measured by Northern blot hybridization. When the lambda clone with 5'- and 3'-flanking sequences was transferred, transcripts were detected without glucocorticoid, but in the presence of glucocorticoid, the level of the transcripts of heterogeneous sizes increased and their pattern was similar to that observed in the mammary glands of non-lactating mice. When the 6.7 kb EcoRI fragment containing most of the coding region was transferred, putative precursor and mature mRNAs were detected without glucocorticoid. Surprisingly, with the addition of glucocorticoid, the level of the transcripts greatly decreased. The presence of multiple sequences responsible for glucocorticoid receptor binding was detected in the 5'-flanking region of the gene in a competition assay using the subfragments of casein gene and on sequence analysis. These results suggest that the 26K casein gene has multiple regulatory domains which interact with glucocorticoid receptors, and these domains may play different roles in the regulation of the casein gene.

Replication timing: histone genes replicate during early S phase in cleavage-stage embryos of sea urchin

Newly synthesized DNA was separated from the bulk of the DNA by pulse-labeling with BUdR and centrifugation in an alkaline CsCl buoyant density gradient. The content of histone gene in the newly synthesized DNA was determined by DNA dot hybridization. The gene contents in DNA replicated during the early half of S phase and during the whole S phase were compared. Results showed that histone genes were replicated during the first half of the S phase in embryos in the early cleavage stage.

Cloning and expression of human lymphotoxin mRNA derived from a human T cell hybridoma

We cloned human lymphotoxin (LT) cDNA from a cDNA library prepared from phorbol myristate acetate (PMA) and Con A-stimulated human T cell hybridoma (AC5-8) cells, The nucleotide sequence of the cDNA insert in the plasmid, pLT13, was determined and compared with those of peripheral blood mononuclear cell derived LT cDNA and the LT gene. Four stretches, containing 14 nucleotides in total, were different among the three sequences. The differences included one base change from C to A in the coding region. Because this change was expected to result in a change in the amino acid at position 26 from Thr to Asn, we constructed an E. coli expression plasmid (pLT13tac6-8.2) and a mammalian cell expression plasmid (pSV2-LT) in order to confirm that pLT13 contains the coding sequence of human LT. Both plasmids were found to synthesize active LT molecules after transfection into JM105 and COS-1 cells, respectively, and their lytic activities were found to be completely neutralized by anti human LT serum. Using an insertion mutant and a deletion mutant, we examined the role of the C terminal domain in the LT activity. The results obtained strongly suggested that the intactness of the C terminal less than 10 residues is required for the LT activity.

Post-transcriptional control of 26 k casein genes during lactogenesis in mouse mammary glands

Stage-specific gene expression of 26 k casein, a major milk protein, was examined in mouse mammary glands. Mature mRNA (1.1 kb) with putative precursor RNA (k kb) was detected in the lactating gland. In contrast, the putative precursor RNA (5 kb) was also detected in the mammary glands of virgin or weaned mice when milk was not produced, although mature mRNA was not detected. The RNA transcripts showing heterogeneous size distribution were abundant in the nonlactating stages. These RNAs are shown to be transcribed in the opposite direction to the mature mRNA. These results suggest the regulation at the post-transcriptional level in the synthesis of caseins in the mammary glands.

Essential structure in the cloned transforming DNA that induces gene amplification of the Bacillus subtilis amyE-tmrB region

Bacillus subtilis B7, a mutant which acquired gene amplification of the amyE-tmrB region, showed, as a result, hyperproductivity (about a 5- to 10-fold increase) of alpha-amylase and tunicamycin resistance. The mutational character was transferred to recipient cells by competence transformation. A 14-kilobase (kb) EcoRI chromosomal DNA fragment of strain B7 was found to have the transforming activity. We cloned a 6.4-kb EcoRI fragment on a phage vector lambda Charon 4A through a spontaneous deletion of 7.6 kb from the 14-kb fragment and subcloned a 1.6-kb HindIII fragment on pGR71. The cloned 6.4-kb EcoRI and 1.6-kb HindIII fragments retained the transforming activity of inducing gene amplification of the amyE-tmrB region. At the junction point (J) of the repeating units (16 kb), the tmrB gene was linked to a DNA region (M) located 4 kb upstream of amyE. The essential structure of the cloned, transforming (gene amplification-inducing) DNA was deduced to be that around J. The subcloned 1.6-kb HindIII fragment that retained the transforming activity was shown to be almost solely composed of the tmrB-J-M region. In addition, the DNA sequence around J was determined.

Induction of commitment of murine erythroleukemia cells (TSA8) to CFU-E with DMSO

The commitment of novel mouse erythroleukemic (MEL) cells (TSA8) to colony-forming units of erythroid (CFU-E) by dimethylsulfoxide (DMSO) was investigated. After exposure to the inducer in liquid culture, the cells were transferred to a semi-solid culture to examine their ability to form erythroid colonies which were dependent on erythropoietin. Exposure to DMSO for 2 days is optimum for CFU-E type colony formation and colonies induced in this manner are equivalent to CFU-E. The induction occurred in a synchronous manner. Partly stained colonies appeared prior to CFU-E formation and are thought to be a result of asymmetric cell division. Appearance of these partly stained colonies suggested that the number of erythropoietin receptors is important in the complete responsiveness to erythropoietin. TSA8 cells constitute a suitable model system in which to analyse the mechanism of commitment in early erythropoiesis.