Showing papers on "Cell culture published in 1986"

Purification, Characterization, and in vitro Differentiation of Cytotrophoblasts from Human Term Placentae*

Abstract: Highly purified functional cytotrophoblasts have been prepared from human term placentae by adding a Percoll gradient centrifugation step to a standard trypsin-DNase dispersion method. The isolated mononuclear trophoblasts averaged 10 microns in diameter, with occasional cells measuring up to 20-30 microns. Viability was greater than 90%. Transmission electron microscopy revealed that the cells had fine structural features typical of trophoblasts. In contrast to syncytial trophoblasts of intact term placentae, these cells did not stain for hCG, human placental lactogen, pregnancy-specific beta 1-glycoprotein or low mol wt cytokeratins by immunoperoxidase methods. Endothelial cells, fibroblasts, or macrophages did not contaminate the purified cytotrophoblasts, as evidenced by the lack of immunoperoxidase staining with antibodies against vimentin or alpha 1-antichymotrypsin. The cells produced progesterone (1 ng/10(6) cells . 4 h), and progesterone synthesis was stimulated up to 8-fold in the presence of 25-hydroxycholesterol (20 micrograms/ml). They also produced estrogens (1360 pg/10(6) cells . 4 h) when supplied with androstenedione (1 ng/ml) as a precursor. When placed in culture, the cytotrophoblasts consistently formed aggregates, which subsequently transformed into syncytia within 24-48 h after plating. Time lapse cinematography revealed that this process occurred by cell fusion. The presumptive syncytial groups were proven to be true syncytia by microinjection of fluorescently labeled alpha-actinin, which diffused completely throughout the syncytial cytoplasm within 30 min. Immunoperoxidase staining of cultured trophoblasts between 3.5 and 72 h after plating revealed a progressive increase in cytoplasmic pregnancy-specific beta 1-glycoprotein, hCG, and human placental lactogen concomitant with increasing numbers of aggregates and syncytia. At all time points examined, occasional single cells positive for these markers were identified. RIA of the spent culture media for hCG revealed a significant increase in secreted hCG, paralleling the increase in hCG-positive cells and syncytia identified by immunoperoxidase methods. We conclude that human cytotrophoblasts differentiate in culture and fuse to form functional syncytiotrophoblasts.

Recombinant human granulocyte colony-stimulating factor: effects on normal and leukemic myeloid cells

Abstract: Experiments were conducted to isolate and characterize the gene and gene product of a human hematopoietic colony-stimulating factor with pluripotent biological activities. This factor has the ability to induce differentiation of a murine myelomonocytic leukemia cell line WEHI-3B(D+) and cells from patients with newly diagnosed acute nonlymphocytic leukemia (ANLL). A complementary DNA copy of the gene encoding a pluripotent human granulocyte colony-stimulating factor (hG-CSF) was cloned and expressed in Escherichia coli. The recombinant form of hG-CSF is capable of supporting neutrophil proliferation in a CFU-GM assay. In addition, recombinant hG-CSF can support early erythroid colonies and mixed colony formation. Competitive binding studies done with 125I-labeled hG-CSF and cell samples from two patients with newly diagnosed human leukemias as well as WEHI-3B(D+) cells showed that one of the human leukemias (ANLL, classified as M4) and the WEHI-3B(D+) cells have receptors for hG-CSF. Furthermore, the murine WEHI-3B(D+) cells and human leukemic cells classified as M2, M3, and M4 were induced by recombinant hG-CSF to undergo terminal differentiation to macrophages and granulocytes. The secreted form of the protein produced by the bladder carcinoma cell line 5637 was found to be O-glycosylated and to have a molecular weight of 19,600.

Phenol red in tissue culture media is a weak estrogen: implications concerning the study of estrogen-responsive cells in culture

Abstract: Although much attention has been paid to the removal of hormones from sera and to the development of serum-free media for studies on hormone-responsive cells in culture, little consideration has been given to the possibility that the media components themselves may have hormonal activity. We have found that phenol red, which bears a structural resemblance to some nonsteroidal estrogens and which is used ubiquitously as a pH indicator in tissue culture media, has significant estrogenic activity at the concentrations (15-45 microM) at which it is found in tissue culture media. Phenol red binds to the estrogen receptor of MCF-7 human breast cancer cells with an affinity 0.001% that of estradiol (Kd = 2 X 10(-5) M). It stimulates the proliferation of estrogen receptor-positive MCF-7 breast cancer cells in a dose-dependent manner but has no effect on the growth of estrogen receptor-negative MDA-MB-231 breast cancer cells. At the concentrations present in tissue culture media, phenol red causes partial estrogenic stimulation, increasing cell number to 200% and progesterone receptor content to 300% of that found for cells grown in phenol red-free media, thereby reducing the degree to which exogenous estrogen is able to stimulate responses. The antiestrogens tamoxifen and hydroxytamoxifen inhibit cell proliferation below the control level only when cells are grown in the presence of phenol red; in the absence of phenol red, the antiestrogens do not suppress growth. The estrogenic activity of phenol red should be considered in any studies that utilize estrogen-responsive cells in culture.

Use of a recombinant retrovirus to study post-implantation cell lineage in mouse embryos.

Abstract: We show that a gene introduced into cells of mouse embryos by a retrovirus can serve as a heritable marker for the study of cell lineage in vivo. We constructed a defective recombinant retrovirus in which the Escherichia coli beta-galactosidase (lacZ) gene is inserted in the genome of a Muloney murine leukemia virus (M-MuLV). Expression of lacZ was detected with a histochemical stain that can be applied to cultured cells and embryonic tissue. Infection of cultured cells showed that lacZ has no detectable deleterious effects on cell viability or growth, that the enzyme is stably expressed in the progeny of infected cells for many generations in the absence of selective pressure, and that the virus can induce lacZ in a variety of cell types. Following injection of the virus into mid-gestation mouse embryos, clones of lacZ-positive cells were detected in skin, skull, meninges, brain, visceral yolk sac, and amnion. We identified the cell types comprising a series of lacZ-positive clones in the visceral yolk sac and skin to learn the lineage relationships of the labelled cells. In each tissue, we obtained evidence that several cell types have a pluripotential ancestor and that cell fate is progressively restricted as development proceeds.

Tumor Chemosensitivity Conferred by Inserted Herpes Thymidine Kinase Genes: Paradigm for a Prospective Cancer Control Strategy

Abstract: The lack of highly exploitable biochemical differences between normal tissues and some tumors can theoretically be circumvented by a strategy utilizing gene insertion prophylactically to create tissue mosaicism for drug sensitivity, thereby ensuring that any tumor arising clonally will differ from part of the normal cell population. Elements of the strategy were tested with neoplastic BALB/c murine cell lines bearing the herpes thymidine kinase gene. Exposure to the herpes thymidine kinase-specific substrate 9-([2-hydroxy-1-(hydroxymethyl)ethoxy]methyl)guanine ablated the clonogenic potential of the cells in vitro, and administration of this drug to BALB/c mice bearing tumors produced by the cell lines uniformly induced complete regression of the tumors. The observed responses to therapy imply that the strategy may prove valuable when the genetic technology needed for its human implementation becomes available.

Role of ion flux in the control of c-fos expression.

Abstract: There has been much interest in the biochemical and biophysical processes that couple extracellular signals to alterations in gene expression. While many early events associated with the treatment of cells with growth factors have been described (for example, ion flux and protein phosphorylation), it has proved difficult to establish biochemical links to gene expression. Recently, the study of such genomic control signals has been facilitated by the demonstration that the c-fos proto-oncogene is rapidly and transiently induced by treatment of several cell types with polypeptide growth factors and other growth modulating substances. In one particular system it has been shown that nerve growth factor (NGF) causes a transient induction of c-fos in the phaeochromocytoma cell line PC12, within 15 min. Furthermore, the magnitude of this induction can be modulated with pharmacological agents such as peripheral-type benzodiazepines (BZDs). Thus, the study of c-fos expression in PC12 cells could yield valuable clues to the coupling mechanisms linking cell surface activation to genomic events. Here we demonstrate that c-fos is induced in PC12 cells either by receptor-ligand interaction or by agents or conditions that effect voltage-dependent calcium channels.

Formation of 8-hydroxyguanine moiety in cellular DNA by agents producing oxygen radicals and evidence for its repair

Abstract: 8-Hydroxydeoxyguanosine (8-OH-dG) was detected in DNA isolated from HeLa cells after the cells in tissue culture had been irradiated with X-rays and from the liver of mice after the whole animals had been irradiated with gamma-rays. The amounts of 8-OH-dG in DNA after in vivo irradiation were three orders of magnitude lower than those after in vitro irradiation (0.008-0.032 8-OH-dG residue/10(5) dG/krad). The 8-OH-dG produced in liver DNA by irradiation of mice decreased with time, suggesting the presence of a repair enzyme(s) acting on 8-OH-dG in mouse liver. Treatment of Salmonella typhimurium cells with hydrogen peroxide also caused increase in the 8-OH-dG content. These results indicate that 8-OH-dG is formed in vivo in cellular DNA on treatment with various oxygen radical-producing agents and that it is repairable.

Heparin protects basic and acidic FGF from inactivation

Abstract: The ability of heparin or that of hexuronyl hexosaminoglycan sulfate (HHS-4) to protect basic or acidic fibroblast growth factor (FGF) from acid or heat inactivation has been analyzed. Both freshly prepared basic and acidic FGF stimulate the growth of baby hamster kidney (BHK-21) cells exposed to medium supplemented with transferrin and insulin. Freshly prepared basic FGF was 10 fold more potent than acidic FGF. The addition of heparin to the medium decreased the potency of basic FGF while it potentiated that of acidic FGF. Upon storage of FGF at -80 degrees C, a decline in potency of both basic and acidic FGF was observed. Heparin, when added to the medium, potentiated their activities, which became similar to that of freshly prepared basic FGF. In order to test whether heparin could protect basic or acidic FGF from inactivation, both mitogens were exposed to acid conditions (1% trifluoroacetic acid, pH 1.08, 2 h) or heat (65 degrees C, 5 min) which inactivate basic or acidic FGF. When exposed to such treatment in the presence of heparin or HHS-4, basic and acidic FGF retained their potency. The effect of heparin and HHS-4 on the bioactivity of basic and acidic FGF is truly of a protective nature, since they had no effect when added after inactivation of the mitogens. Potentiation of the bioactivity of the protected mitogens or of the inactivated one could only be observed when cells were exposed to high heparin or HHS-4 concentrations. This indicates that heparin and HHS-4, in addition to protecting FGF from inactivation, also acts at another locus, as yet unidentified.

Transforming growth factor-alpha: a more potent angiogenic mediator than epidermal growth factor

Abstract: Transforming growth factor-alpha (TGF-alpha) and epidermal growth factor (EGF) are structurally related peptides. Purified human TGF-alpha produced in Escherichia coli and pure natural mouse EGF were compared for their ability to bind to target cells in vitro and to promote angiogenesis in the hamster cheek pouch bioassay. Both polypeptides were found to bind in vitro to several target cells, including endothelial cells, and to stimulate their DNA synthesis in an equipotent fashion. In vivo, however, TGF-alpha was more potent than EGF in promoting angiogenesis and, because TGF-alpha is known to be secreted by a variety of human tumors, it is suggested that this growth factor may contribute to tumor-induced angiogenesis.

cDNA sequence and chromosomal localization of human platelet-derived growth factor A-chain and its expression in tumour cell lines

Abstract: The amino-acid sequence of the precursor of the human tumour cell line-derived platelet-derived growth factor (PDGF) A-chain has been deduced from complementary DNA clones and the gene localized to chromosome 7. The protein shows extensive homology to the PDGF B-chain precursor. Expression of the PDGF A-chain gene is independent of that of the PDGF B-chain in a number of human tumour cell lines, and secretion of a PDGF-like growth factor of relative molecular mass 31,000 correlates with expression of A- but not B-chain messenger RNA.

Role of the HTLV-III/LAV envelope in syncytium formation and cytopathicity.

Abstract: Acquired immune deficiency syndrome (AIDS) is characterized by marked depletion of the T4+ helper subset of T cells. The aetiological agent of the disease, the human T-lymphotropic virus type III (HTLV-III)/lymphadenopathy-associated virus (LAV), specifically kills T4+ cells in vitro. Part of this specificity for the T4+ population residues in the relative efficiency with which HTLV-III infects these cells, as a result of a specific interaction between the T4 molecule and the virus envelope glycoprotein. In addition, the cytotoxic consequences of HTLV-III replication are dependent on cell type, as certain lymphoid and myeloid cells can be productively infected without notable cytopathic effect. Here we investigate the basis for the specific cytotoxicity of the virus, and report that high-level expression of the HTLV-III envelope gene induces syncytia and concomitant cell death in T4+ cell lines but not in a B-lymphocyte line. Syncytium formation depends on the interaction of envelope-expressing cells with neighbouring cells bearing surface T4 molecules. These results explain, at least in part, the specific cytopathic effect of HTLV-III infections.

B cell stimulatory factor-1 enhances the IgE response of lipopolysaccharide-activated B cells.

Abstract: Supernatants from some mouse helper T cell (TH) lines contain an activity that can enhance IgE production by lipopolysaccharide (LPS)-stimulated B cells by at least two orders of magnitude. During purification, this activity could not be resolved from B cell stimulatory factor-1 (BSF-1). Highly purified BSF-1 from a different source, the T lymphoma cell line EL-4, enhanced IgE production to the same extent as TH supernatants, which suggests that BSF-1 is responsible for this increase in IgE production. Monoclonal antibody to BSF-1 totally inhibits the IgE-enhancing activity of a TH supernatant, lending further support to this conclusion. The effects of BSF-1 on LPS-stimulated B cells are specific for IgE and, as previously reported, IgG1 and IgG3, because the levels of IgM, IgG2a, IgG2b, and IgA in the cultures change relatively little when BSF-1 is added.

Transforming growth factor beta is an important immunomodulatory protein for human B lymphocytes.

Abstract: The growth and differentiation of B cells to immunoglobulin (Ig)-secreting cells is regulated by a variety of soluble factors. This study presents data that support a role for transforming growth factor (TGF)-beta in this regulatory process. B lymphocytes were shown to have high-affinity receptors for TGF-beta that were increased fivefold to sixfold after in vitro activation. The addition of picogram quantities of TGF-beta to B cell cultures suppressed factor-dependent, interleukin 2 (IL 2) B cell proliferation and markedly suppressed factor-dependent (IL 2 or B cell differentiation factor) B cell Ig secretion. In contrast, the constitutive IgG production by an Epstein Barr virus-transformed B cell line was not modified by the presence of TGF-beta in culture. This cell line was found to lack high-affinity TGF-beta receptors. The degree of inhibition of B cell proliferation observed in in vitro cultures was found to be dependent not only on the concentration of TGF-beta added but also on the concentration of the growth stimulatory substance (IL 2) present. By increasing the IL 2 concentrations in culture, the inhibition of proliferation induced by TGF-beta could be partially overcome. In contrast, the inhibition of Ig secretion induced by TGF-beta could not be overcome by a higher concentration of stimulatory factor, demonstrating that the suppression of B cell differentiation by TGF-beta is not due solely to its effects on proliferation. Furthermore, it was demonstrated that B lymphocytes secrete TGF-beta. Unactivated tonsillar B cells had detectable amounts of TGF-beta mRNA on Northern blot analysis, and B cell activation with Staphylococcus aureus Cowan (SAC) resulted in a twofold to threefold increase in TGF-beta mRNA. Supernatants conditioned by unactivated B cells had small amounts of TGF-beta, SAC activation of the B cells resulted in a sixfold to sevenfold increase in the amount of TGF-beta present in the supernatants. Thus, B lymphocytes synthesize and secrete TGF-beta and express receptors for TGF-beta. The addition of exogenous TGF-beta to cultures of stimulated B cells inhibits subsequent proliferation and Ig secretion. TGF-beta may function as an autocrine growth inhibitor that limits B lymphocyte proliferation and ultimate differentiation.

A T cell activity that enhances polyclonal IgE production and its inhibition by interferon-gamma.

Abstract: The addition of concanavalin A-stimulated supernatants of the helper T cell clone, D9.1, to cultures of lipopolysaccharide (LPS)-stimulated T-depleted mouse spleen cells caused more than a 100-fold increase in immunoglobulin (Ig) E production. These supernatants cause a 10-fold to 15-fold increase in IgG1, a fivefold to 10-fold increase in IgA, and a fivefold to 10-fold decrease in IgG3. These effects are optimal when the supernatants are added 1 to 2 days after stimulation with LPS. Cells from mouse strains that normally give little or no IgE response in vivo give normal IgE levels in response to LPS plus the supernatant of Concanavalin A-stimulated D9.1 cells in vitro. The enhancement of both IgE and IgG1 can be completely inhibited by relatively low concentrations of interferon-gamma (IFN-gamma). Both the IgE-enhancing activity and IFN-gamma act directly upon purified B cells.

Human growth hormone as a reporter gene in regulation studies employing transient gene expression.

Abstract: The human growth hormone (hGH) transient assay system described here is based on the expression of hGH directed by cells transfected with hGH fusion genes. Levels of secreted hGH in the medium, measured by a simple radioimmunoassay, are proportional to both levels of cytoplasmic hGH mRNA and the amount of transfected DNA. The system is extremely sensitive, easy to perform, and is qualitatively different from other transient expression systems in that the medium is assayed and the cells themselves are not destroyed. The hGH transient assay system is appropriate for analyses of regulation of gene expression and was utilized here to investigate the effect of the simian virus 40 enhancer on the herpes simplex virus thymidine kinase promoter and the effect of zinc on the mouse metallothionein-I promoter. The expression of hGH can also be used as an internal control to monitor transfection efficiency along with any other transient expression system. All cell types tested thus far (including AtT-20, CV-1, GC, GH4, JEG, L, and primary pituitary cells) were able to secrete hGH into the medium.

A Highly Conserved Vascular Permeability Factor Secreted by a Variety of Human and Rodent Tumor Cell Lines

Abstract: We have previously reported that rodent tumor cell lines secrete a potent vascular permeability factor with a molecular weight of 34,000-42,000 (Senger et al. Tumor cells secrete a vascular permeability factor that promotes accumulation of ascites fluid. Science (Wash. DC), 219: 983-985, 1983). This tumor-secreted vascular permeability factor (VPF) causes a rapid and completely reversible increase in microvascular permeability in the species (guinea pig or rat) from which the tumors were derived without causing mast cell degranulation or endothelial cell damage or exciting an inflammatory cell infiltrate. This VPF may be responsible, at least in part, for the increased permeability which is commonly displayed by solid and ascites tumor vessels. We have now examined 7 human tumor cell lines and have determined that 5 of them also secrete this same VPF. Antibody raised to guinea pig line 10 VPF neutralized more than 90% of the vascular permeability-increasing activity secreted by these 5 human tumor lines. Furthermore, VPFs from both guinea pig and human tumor sources bound to and were eluted similarly from immobilized heparin and comigrated identically on sodium dodecyl sulfate-polyacrylamide gels. Finally, 2 tumorigenic (in nude mice) human cell lines were found to secrete at least 14-fold more VPF than their directly matched, nontumorigenic counterparts, suggesting that elevated expression of this permeability factor may correlate with neoplastic transformation. These data suggest that a broad spectrum of tumor cells from several species, including humans, secretes a highly conserved molecule that enhances local vascular permeability and that this function may be important for tumor growth.

Reversible inhibition of normal human prokeratinocyte proliferation by type beta transforming growth factor-growth inhibitor in serum-free medium.

Abstract: Type beta transforming growth factor-growth inhibitor (TGF beta/GI) causes normal human prokeratinocytes to arrest growth predominantly in the G1 phase of the cell cycle within 48 h after log phase cultures are exposed to the factor in serum-free medium. The growth arrest induced by TGF beta/GI is reversible because the cells from treated cultures can be replated into fresh medium and grown into large colonies. Normal prokeratinocytes are demonstrated to secrete TGF beta/GI-like molecules into the culture medium and to have specific cell surface receptors for this molecule. In contrast, a human squamous cell carcinoma, SCC-25, does not arrest growth when exposed to TGF beta/GI. These cells, unlike the normal prokeratinocytes, do not exhibit detectable cell surface receptors for the factor.

Animal cell culture.

Abstract: A process for the batch culture of animal cells comprises culturing the cells in nutrient medium characterised in that during the culture the medium is supplemented with a combined feed of one or more energy sources and one or more amino acids, and culturing is continued into the decline phase of the culture to provide the product(s) of the cells. The process is particularly applicable to genetically modified cells, especially hybridoma cell cultures to produce monoclonal antibodies. Preferably, the supplemental feed is fed to the culture at a slow rate over a prolonged period. Very significant enhancement of overall product yield may be obtained.

Type beta transforming growth factor is the primary differentiation-inducing serum factor for normal human bronchial epithelial cells.

Abstract: Type beta transforming growth factor (TGF-beta) was shown to be the serum factor responsible for inducing normal human bronchial epithelial (NHBE) cells to undergo squamous differentiation. NHBE cells were shown to have high-affinity receptors for TGF-beta. TGF-beta induced the following markers of terminal squamous differentiation in NHBE cells: (i) increase in Ca ionophore-induced formation of crosslinked envelopes; (ii) increase in extracellular activity of plasminogen activator; (iii) irreversible inhibition of DNA synthesis; (iv) decrease in clonal growth rate; and (v) increase in cell surface area. The IgG fraction of anti-TGF-beta antiserum prevented both the inhibition of DNA synthesis and the induction of differentiation by either TGF-beta or whole blood-derived serum. Therefore, TGF-beta is the primary differentiation-inducing factor in serum for NHBE cells. In contrast, TGF-beta did not inhibit DNA synthesis of human lung carcinoma cells even though the cells possess comparable numbers of TGF-beta receptors with similar affinities for the factor. Epinephrine antagonized the TGF-beta-induced inhibition of DNA synthesis and squamous differentiation of NHBE cells. Although epinephrine increased the cyclic AMP levels in NHBE cells, TGF-beta did not alter the intracellular level in NHBE cells in either the presence or absence of epinephrine. Therefore, epinephrine and TGF-beta appear to affect different intracellular pathways that control growth and differentiation processes of NHBE cells.

Functional role for the 170- to 180-kDa glycoprotein specific to drug-resistant tumor cells as revealed by monoclonal antibodies.

Abstract: An overexpression of the plasma membrane glycoprotein of relative molecular size 170-180 kDa is consistently found in different multidrug-resistant human and animal cell lines, although the functional role of the protein in multidrug resistance is not known. Two monoclonal antibodies that interfere with biochemical functions were generated against the human myelogenous leukemia K-562 cells resistant to adriamycin (K-562/ADM). These antibodies, designated MRK16 and MRK17, are specifically reactive to K-562/ADM and a human ovarian cancer cell line resistant to adriamycin (2780AD). MRK16 modulated vincristine and actinomycin D transport in the resistant cells, while MRK17 specifically inhibited the growth of the resistant cells. Both antibodies recognized the 170- to 180-kDa glycoprotein. These data indicate that the 170- to 180-kDa glycoprotein is involved, directly or indirectly, in the drug transport mechanisms and the proliferation of multidrug-resistant tumor cell lines.

Tumor cell autocrine motility factor

Abstract: A cell motility-stimulating factor has been isolated, purified, and partially characterized from the serum-free conditioned medium of human A2058 melanoma cells. We term this activity "autocrine motility factor" (AMF). AMF has the properties of a protein with an estimated size of 55 kDa. At concentrations of 10 nM or less, AMF stimulated the random or directed motility of the producer cells. However, AMF is not an attractant for neutrophils. Amino acid analysis of the purified AMF protein revealed a high content of serine, glycine, glutamic acid, and aspartic acid residues. The activity of AMF was not replaced or blocked by known growth factors such as epidermal growth factor or type beta transforming growth factor. Mechanistic studies showed that AMF stimulated the incorporation of [3H]methyl into cell membrane phospholipids after incubation with [methyl-3H]methionine with a sustained increase in the methylation of phosphatidyldimethylethanolamine to phosphatidylcholine. In contrast, AMF did not affect the incorporation of [1,2-14C]choline into phosphatidylcholine. AMF was produced in large amounts by three different clones of ras oncogene-transfected metastatic NIH 3T3 cells but not by the nontransformed parental cells. AMF may play a major role in the local invasive behavior of tumor cells and may also facilitate the concerted invasion by groups of tumor cells.

Cellular and biochemical events in mammalian cells during and after recovery from physiological stress.

Abstract: We have examined and compared a number of cellular and biochemical events associated with the recovery process of rat fibroblasts placed under stress by different agents. Metabolic pulse-labeling studies of cells recovering from either heat-shock treatment, exposure to sodium arsenite, or exposure to an amino acid analogue of proline, L-azetidine 2-carboxylic acid, revealed interesting differences with respect to the individual stress proteins produced, their kinetics of induction, as well as the decay in their synthesis during the recovery period. In the initial periods of recovery, the major stress-induced 72-kD protein accumulates within the altered nucleoli in close association with the pre-ribosomal-containing granular region. During the later times of recovery from stress, the nucleoli begin to regain a normal morphology, show a corresponding loss of the 72-kD protein, and the majority of the protein now begins to accumulate within the cytoplasm in three distinct locales: the perinuclear region, along the perimeter of the cells, and finally in association with large phase-dense structures. These latter structures appear to consist of large aggregates of phase-dense material with no obvious encapsulating membrane. More interestingly we show, using double-label indirect immunofluorescence analysis, that much of the perinuclear and cell perimeter-distributed 72-kD protein coincides with the distribution of the cytoplasmic ribosomes. We discuss the possible implications of the presence of the 72-kD stress proteins within the pre-ribosomal-containing granular region of the nucleolus as well as its subsequent colocalization with cytoplasmic ribosomes in terms of the translational changes which occur in cells both during and after recovery from physiological stress.

Long-term cultures of HTLV-III--infected T cells: a model of cytopathology of T-cell depletion in AIDS.

Abstract: Long-term cultures were established of HTLV-III-infected T4 cells from patients with the acquired immune deficiency syndrome (AIDS) and of T4 cells from normal donors after infection of the cells in vitro. By initially reducing the number of cells per milliliter of culture medium it was possible to grow the infected cells for 50 to 60 days. As with uninfected T cells, immunologic activation of the HTLV-III-infected cells with phytohemagglutinin led to patterns of gene expression typical of T-cell differentiation, such as production of interleukin-2 and expression of interleukin-2 receptors, but in the infected cells immunologic activation also led to expression of HTLV-III, which was followed by cell death. The results revealed a cytopathogenic mechanism that may account for T4 cell depletion in AIDS patients and suggest how repeated antigenic stimulation by infectious agents, such as malaria in Africa, or by allogeneic blood or semen, may be important determinants of the latency period in AIDS.

Constitutive c- myc oncogene expression blocks mouse erythroleukaemia cell differentiation but not commitment

Abstract: Mouse erythroleukaemia cells (also called Friend cells) can be isolated from the spleen of certain strains of mice that have been infected with the Friend virus complex1. The cells resemble pro-erythroblasts and, when exposed to dimethyl sulphoxide (DMSO) or a variety of other chemicals, can be induced to undergo a programme of differentiation which closely resembles the final stages of normal erythropoiesis2. This includes the cessation of proliferation and large increases in the production of messenger RNA for both α- and β-globin. In addition, DMSO induces a rapid (<2h) decrease in c-myc mRNA levels3,4. The c-myc oncogene is expressed in the majority of proliferating normal cells5 and altered expression of the gene has been implicated in the genesis of a wide variety of tumours6–9. To study the influence of oncogene activation on differentiation, we have transfected viral-promoter-driven c-myc genes into mouse erythroleukaemia cells. Constitutive c-myc expression was found to block DMSO-induced differentiation.