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W Engström

Publications and source records attributed to W Engström.

At least 55 records · Page 3Linked to original sources
PubMed1986

Immediate effects of serum depletion on dissociation between growth in size and cell division in proliferating 3T3 cells.

Proliferating nonconfluent 3T3 cells become committed to proceed through the cell cycle or to enter G0 during the first post-mitotic part of G1 (G1pm). The decision to proceed through G1pm is dependent on the presence of serum growth factors in the culture medium. Cells that have passed this particular growth-factor-dependent cell cycle stage are independent of serum growth factors and undergo mitosis on schedule. We report here that G1ps, S, and G2 cells cease to increase in size when serum is withdrawn. As a result the mitotic cell size after 8 hours serum starvation is reduced to approximately 60% of the normal mitotic cell. This reduced growth in cell size is due to a rapid decrease in protein synthesis and some increase in protein degradation. This dissociation between growth in size and cell-cycle progression within a single cell cycle provides a new approach to study the two processes separately.

Animals↗
PubMed1986

Differential effects of epidermal growth factor (EGF) on cell locomotion and cell proliferation in a cloned human embryonal carcinoma-derived cell line in vitro.

The effects of epidermal growth factor (EGF) on clones from a human embryonal carcinoma-derived cell line (Tera-2) have been studied. Cells were plated at clonal densities, whereafter the effects of serum and EGF on cell locomotion and cell proliferation were examined. The addition of 50 ngEGF ml-1 resulted in increased migration, as judged by increased colony diameter in the presence of EGF. However, the effect of EGF on cell locomotion was rarely accompanied by any effect on cell proliferation. It was concluded that EGF exerts a preferential effect on cell migration in human embryonal carcinoma cells in vitro.

Cell Division↗
PubMed1986

Stimulatory effects of insulin-like growth factors on DNA synthesis in the human embryonic cornea.

10- to 12-week-old human embryonic eye globes were microdissected so that a passage was opened between the outer environment and the anterior chamber which rendered free access of tissue culture medium to the endothelial cell monolayer. The dissected eye globes were maintained in organ culture for 24 h in the continuous presence of tritiated thymidine. Cross sections were cut through the whole eye globes and subjected to autoradiographic analysis in order to estimate the mitogenic response of human embryonic corneal endothelial cells to externally supplied growth factors and hormones. It was found that the corneal endothelial cells could be stimulated to initiate DNA synthesis by exposure to insulin-like growth factor I (IGF-I). The thymidine-labelling index doubled after IGF-I supplementation. Northern blot analysis revealed the abundant presence of IGF-II transcripts in the posterior eye. In contrast, the anterior portion of the eye, including the cornea, contains barely detectable levels of IGF-II transcripts. IGF-I transcripts were detected in both parts of the eye at much lower concentrations than those for IGF-II. No insulin transcripts were found. These results demonstrate that mRNA for both IGF-I and IGF-II is present in the late first trimester eye. The observed stimulatory effects of IGF-I in organ culture suggest that local production of IGF-I and IGF-II may stimulate cell proliferation in vivo.

Autoradiography↗
PubMed1985

Phylogenetical aspects on islet hormone families: a minireview with particular reference to insulin as a growth factor and to the phylogeny of PYY and NPY immunoreactive cells and nerves in the endocrine and exocrine pancreas.

A common feature in the phylogeny of the four islet hormones (insulin, somatostatin, glucagon, PP) is that they do not seem to occur in the most primitive metazoan animals investigated so far, namely the coelenterates. However, already in the earliest protostomian invertebrates, such as flatworms and annelids, somatostatin and PP immunoreactive nerve fibres were found. In highly developed forms of protostomian invertebrates, such as insects, all the four islet hormones are represented as immunoreactive nerve cells and nerve fibres in the brain. In deuterostomian invertebrates a brain-gut-axis has evolved as regards somatostatin and PP, whereas insulin and glucagon now seem to occur exclusively as cells of open type in the gut mucosa. This brain-gut-axis for somatostatin and PP persists in all the vertebrates. The insulin cells, however, leave the gut mucosa already in the earliest forms of vertebrates and then appear only as cells in the islet parenchyma and in the mucosa of the bile duct (Agnatha) or in the pancreatic ducts (Gnathostomi). To some extent, glucagon islet cells evolve in a similar manner; here, however, cells immunoreactive with the precursor hormone, glicentin (enteroglucagon), persist in the gastrointestinal tract mucosa. A few PYY immunoreactive cells have been found in the pancreatic islet parenchyma of reptiles and mammals, often as disseminated cells in the acinar tissue. In the pancreas of these phyla NPY only occurs in neurons and nerve fibres. In pilot studies the effects of hagfish insulin as a growth factor have been compared with those of pig insulin on Swiss 3T3 mouse embryonic fibroblasts.

Animals↗
PubMed1985

Proliferation of a human embryonal carcinoma-derived cell line in serum-free medium: inter-relationship between growth factor requirements and membrane receptor expression.

Substantial multiplication in vitro of cloned cells from a human embryonal carcinoma cell line, Tera 2, has been obtained in a basal medium (DMEM/Ham's F12,50:50, v/v) supplemented with 10 micrograms low density lipoprotein/ml, 100 micrograms high density lipoprotein/ml, 100 ng multiplication stimulating activity/ml, 100 ng insulin/ml and 1 microgram transferrin/ml. The growth rate appears to be similar to that obtained in 10% serum. Furthermore, studies on the expression of cell surface receptors revealed that cloned Tera 2 cells express high-affinity receptors for IGF-II but not for insulin. The cells also express receptors for Epidermal Growth Factor (EGF) even though the addition of EGF does not stimulate their proliferation in serum-free medium. These results suggest that the expression of specific growth factor receptors is not an absolute determinant of hormone responsiveness.

Cell Division↗
PubMed1985

Cell-cycle-specific induction of quiescence achieved by limited inhibition of protein synthesis: counteractive effect of addition of purified growth factors.

We have previously shown that Swiss 3T3 cells located in the first part of G1 (post-mitotic G1 cells younger than 4.0 h or G1pm cells) were arrested after 9-10 h in the cell cycle by a short (1-8 h) exposure to serum-free medium or by a short (2-4 h) exposure to low doses of the protein synthesis inhibitor cycloheximide (CH). Kinetic data indicate that such G1pm cells rapidly return to G0 during this brief treatment and thereafter require a preparatory period of 8 h before continuing to G1. Cells older than 4 h, i.e. cells in mid or late G1 are already committed to DNA synthesis (presynthesis or G1ps cells). These cells as well as S and G2 cells were consequently unaffected by the brief serum starvation or the brief treatment with cycloheximide. In the present paper we show that the 10-h intermitotic delay that follows a 1-2 h exposure to serum-free medium can be completely counteracted by the presence of any one of the purified growth factors, epidermal growth factor (EGF), insulin or platelet-derived growth factor (PDGF). In contrast, the intermitotic delay following a longer exposure (8 h) to serum-free medium could no longer be counteracted by EGF or insulin. However, PDGF was still active in this respect. Most interestingly, the 12 h gross intermitotic delay induced by a 4h exposure to CH could be efficiently counteracted by EGF, PDGF or insulin. However, this effect on CH-treated cells could be counteracted by the growth factor only in the presence of 10% serum. This indicates the existence of a cooperative effect between PDGF, EGF or insulin and an unidentified serum factor. The effects on the cell cycle time of brief serum starvation and exposure to CH were compared with the effects on rate of protein synthesis and degradation. Although the effects of serum starvation on protein synthesis and degradation were found to be partially normalized by growth factors, we suggest that growth factors prevent cells from leaving the cell cycle by another mechanism and not merely by affecting the level of overall protein accumulation.

Animals↗
PubMed1985

Consequences of parental exposure to serum-free medium for progeny cell division.

Proliferating serum-dependent 3T3 cells prolong their intermitotic time by 9-10 h after exposure to serum-free medium for only 1 h. This delay was only observed in cells younger than 4 h, i.e. cells in the postmitotic G1 phase (G1pm), as defined by time elapsed since previous mitosis. These data confirm earlier findings that cells are very sensitive to growth factor or serum depletion during the first part of G1 and that only a short exposure to serum-free medium is sufficient for the cells to leave the cell cycle. However, such cells that have delayed their first cell cycle in response to a short exposure to serum-free medium in early G1 exhibit a reduced capacity to delay the subsequent cycle in response to a repeated exposure to serum-free medium. In contrast cells older than 4 h that are exposed for short periods to serum-free medium undergo cell division on schedule, but delay the subsequent cell cycle by several hours. This delay of the progeny cycle is mainly ascribable to the postmitotic part of G1 (G1pm). These data suggest that short exposures to serum-free medium exert an indirect effect on the progeny cell cycle and demonstrate that cycle times are not necessarily determined de novo in the lifetime of every cell, but may be influenced by events in the preceding cycle.

Animals↗
PubMed1984

The relative effects of different types of growth factors on DNA replication, mitosis, and cellular enlargement.

It was recently demonstrated that growth in cell size can be dissociated from DNA synthesis and mitosis. 3T3 cells starved to quiescence in low serum concentration can be stimulated to undergo DNA synthesis and one cell division without growing in size (unbalanced growth) (42-44). We report here that in cells stimulated to undergo unbalanced growth, the cell nucleus undergoes balanced growth, i.e., nearly doubles in size prior to mitosis. The reduced ability to grow in cell size under unbalanced growth conditions is thus mainly ascribable to the cytoplasm. Furthermore, the extent to which cells grow in size prior to mitosis is dependent on the serum concentration in the tissue culture medium (44). This data suggests that some macromolecular factor or factors in serum are required for growth in cell size prior to mitosis. We report in this study that epidermal growth factor (EGF) alone exerts a small but significant stimulatory influence on DNA synthesis and mitosis but does not affect cellular enlargement. In contrast, insulin added at supraphysiological concentrations does not stimulate quiescent cells to enter S phase but instead stimulates growth in cell size in the small fraction of dividing cells. Furthermore, cells stimulated to proliferate by EGF could be induced to undergo balanced growth when insulin was added concomitantly. Finally, platelet-derived growth factor (PDGF) stimulates quiescent sparse 3T3 cells to undergo DNA synthesis and mitosis. PDGF also exerts a limited but significant effect on cellular enlargement. However, PDGF alone could not induce a complete balanced growth, i.e., a doubling in cell size prior to mitosis.

Animals↗
PubMed1984

The relationship between purines, pyrimidines, nucleosides, and glutamine for fibroblast cell proliferation.

Previous studies indicate that glutamine is a critical requirement for cell proliferation in vitro. We recently showed that depletion of glutamine from the culture medium supporting growing cells significantly reduced the proportion of cells undergoing DNA synthesis. Similarly glutamine depletion significantly reduced the stimulatory response of quiescent cells to 10% serum. This study shows that the inhibitory effects of depletion of glutamine--in either of these two situations--can be overcome by the addition of adenine or adenosine. Adenine was the only nitrogen base and adenosine was the only nucleoside for which this effect was observed. Such effects could, however, also be achieved by addition of the purine metabolites hypoxantine and inosine. Furthermore, it was found that glutamine (or adenine/adenosine) is only required during a limited interval coinciding with the late part of the G1-phase and the beginning of S-phase. These data suggest the possibility that glutamine exerts its main regulatory effects on cell proliferation by acting as a precursor for adenine and adenosine.

Adenine↗
PubMed1984

Permissive effect of substratum contact on DNA synthesis in concanavalin A-treated lymphocytes.

The effects of contact with a solid surface (in the form of adhesive microcarrier beads (Cytodex)) on the induction of proliferation of human blood lymphocytes after exposure to concanavalin A (Con A) were investigated. The duration of the lag phase preceding DNA synthesis was identical in the presence and absence of beads. The kinetic course of initiation of DNA synthesis was exponential but with different rate constants both in the presence and in the absence of beads during the first 4 days of the culture period. Cytodex exerted its effect by increasing the proportion of cells initiating DNA synthesis in response to Con A. To elucidate whether lymphocytes responded to Con A exposure in a dose-dependent manner, cells were seeded at different concentrations and exposed to Con A for different times. At 36 and 48 h after start of stimulation the proportion of cells synthesizing DNA increased with increasing cell number in the cultures. In contrast, the portion of cells synthesizing DNA was markedly decreased at high cell densities 60, 72 and 96 h after start of stimulation. In the presence of microcarrier beads, however, the proportion of cells synthesizing DNA was proportional to the cell number in the cultures also after 60, 72 and 96 h.

Adult↗
PubMed1983

Phosphate and the regulation of DNA replication in normal and virus-transformed 3T3 cells.

3T3 cells were cultured in media with different phosphate concentrations and the effects on DNA synthesis were examined. Even a modest phosphate depletion markedly inhibited DNA synthesis and cell multiplication in proliferating cultures. Furthermore, the decrease in the proportion of DNA-synthesizing cells observed after phosphate starvation followed the same time-course as the decrease seen after serum starvation. Cells starved to quiescence in a medium with a 100-fold decrease in phosphate concentration remained viable but non-proliferating for up to 3 weeks, i.e. they had entered a state of quiescence comparable with that seen after serum starvation. Addition of phosphate to phosphate-depleted cultures restored DNA synthesis within 24h. Furthermore, the kinetics of [3H]thymidine labelling after phosphate addition were nearly identical with the labelling kinetics following addition of serum to serum-depleted cultures. In contrast, phosphate deprivation had no inhibitory effects on DNA synthesis in simian-virus-40-transformed 3T3 cells. Furthermore, the inhibitory effects on DNA synthesis in such cells caused by a complete removal of serum could not be further enhanced by decreasing the phosphate concentration in the culture medium.

Animals↗
PubMed1983

Induction of DNA synthesis and mitosis in the absence of cellular enlargement.

Swiss 3T3 cells, starved to quiescence in low serum concentration, initiate DNA synthesis and undergo mitosis in low serum concentration (less than 0.1%) after a short exposure (2-10 min) to alkaline medium (pH 8.5-10). This study shows that initiation of DNA synthesis and mitosis can be dissociated from growth in cell size. Alkaline-stimulated cells do not increase in size before mitosis (unbalanced growth) in contrast to quiescent cells stimulated by 10% serum, which approximately double their protein content before mitosis (balanced growth). The exposure to the alkaline medium per se does not render the cells incapable of growing in size, since alkaline-treated cells, which are subsequently cultured in 10% serum, undergo balanced growth to the same extent as cells only stimulated by 10% serum without alkaline pretreatment. This study also shows that the small proportion of cells undergoing background proliferation in low serum concentration (less than 0.1%) do not increase in size before mitosis. The extent to which alkaline-stimulated cells, as well as cells undergoing background proliferation, grow in size before mitosis, is correlated to the serum concentration in the culture medium (DMEM). In 0.1% serum or less the cells do not grow in size. In 0.5% serum the cells increase in size by 30% before mitosis and complete balanced growth is achieved in medium containing 2% serum or more. These findings indicate that some macromolecular factor or factors in serum are required for growth in cell size before mitosis.

Animals↗
PubMed1982

Growth activation of resting cells: induction of balanced and imbalanced growth.

Little is known about how mitogenic factors generate growth regulatory signals and how these are mediated within the cell. We have developed three different types of mitogenic stimuli in order to identify the possible existence of common denominators in a complex and perhaps pleiotypic signal-response system. 3T3 cells, starved to quiescence by reducing the serum content of the culture medium 100-fold, can be irreversibly committed to undergo DNA replication and mitosis in a serum-free medium after an initial exposure of short duration to (a) serum factors and cholesterol, (b) a relative excess of glutamine, or (c) alkaline pH. Cells stimulated by any of these procedures, and subsequently incubated in serum-free Dulbecco's modified Eagle's medium (DMEM) undergo DNA replication and mitosis in the absence of concomitant cellular enlargement (imbalanced growth). However, cellular enlargement is induced after the initial mitogenic stimuli (a, b, and c, as described previously) if the cells are subsequently incubated in DMEM containing greater than or equal to 0.5% serum, supraphysiological concentrations of insulin, or normal concentrations of somatomedin C.

Animals↗
PubMed1981

Glutamine and the regulation of DNA replication and cell multiplication in fibroblasts.

Several studies indicate that glutamine is a critical requirement for cell growth in vitro. Growing and quiescent (serum-starved) 3T3-fibroblasts were exposed to media (Dulbecco's modified Eagle's minimal essential medium) in which the concentration of the 13 essential amino acids had been lowered to 1/100 or 1/1,000 of that in DMEM - either all together or one by one. The effects on DNa synthesis were measured by autoradiographic determinations of the percentage of labeled cells after 24 hours exposure to 3H-thymidine. a reduction of all 13 essential amino acids to 1/100 or 1/1,000 of the normal concentration in the medium resulted only in a minor growth inhibitory effect during the first cell cycle. A similar growth inhibitory effect was caused by the depletion of one of the 13 essential amino acids (except glutamine) from the medium. However, a depletion of glutamine from the medium resulted in a marked inhibition of growth. Conversely, a relative excess of glutamine, when the other 12 amino acids were lowered to 1/1,000 of the normal concentration, counteracted the growth inhibitory effect of serum starvation. It was even possible to stimulate quiescent cells to undergo DNa synthesis by exposing them to a serum-depleted (0.5% serum) medium with a relative excess of glutamine.

Amino Acids↗
PubMed1981

Effects of mitogenic stimulation on the exchangeable pool of calcium in 3T3-cells.

The exchange of calcium between cells and external medium was studied in quiescent and mitogenic stimulated sparse 3T3-cells. It was found that mitogenic stimulation caused a rapid reduction of the size of a calcium containing compartment that is exchangeable with the culture medium. Furthermore the mitogenic stimuli caused a translocation of calcium from this exchangeable compartment to a much less exchangeable compartment that is possibly located intracellularly.

Animals↗
PubMed1981

Calcium requirements for mitogenic stimulation of 3T3-cells in low and high serum concentration.

The calcium requirements during mitogenic stimulation of quiescent 3T3-cells in low or in high serum concentration was investigated. It was found that calcium played an equally important role for growth stimulation in low as in high serum concentration. Calcium was not required during the first 6 hours after mitogenic stimulation. However, calcium had to be present thereafter for the cells to initiate DNA-synthesis. The absence of calcium during the first six hours after onset of stimulation did not delay the initiation of DNA-synthesis.

Animals↗
PubMed1981

Membrane protein detachment and mitogenic stimulation induced by alkaline pH.

The stimulatory effects on DNA-synthesis by a short alkaline treatment in low serum concentration on quiescent 3T3-cells in sparse cultures was investigated. It was found that a short alkaline treatment performed at 4 degrees C stimulated quiescent cell to initiate DNA-synthesis to the same extent as a short alkaline treatment at 37 degree C. Furthermore, an alkaline treatment caused a detachment of membrane bound proteins. The quantity of these proteins that were detached during the alkaline treatment, was closely correlated to the stimulatory effects on DNA-synthesis.

Animals↗