CONTACT INHIBITION, MACROMOLECULAR SYNTHESIS, AND POLYRIBOSOMES IN CULTURED HUMAN DIPLOID FIBROBLASTS

Regulation of lipid synthesis from acetate in diploid fibroblast cultures -- variation with passage level and stage of cell growth

Regulation of lipid synthesis from acetate in human diploid fibroblast cultures has been studied at various passage levels and at different stages of cell growth. When cultures were transferred to lipid free medium, a stimulation of [14C]acetate incorporation into lipid occurred within three to six hours after removal of exogenous lipid. In early passage cultures, this stimulation was observed whether cells were transferred to protein-free medium or medium supplemented with delipidized serum protein. However, in late passage cultures the presence of delipidized serum protein was required for the stimulation of lipid synthesis. When logarithmically dividing and stationary phase cultures were compared, the cultures in log phase showed stimulation of acetate incorporation into lipid in the presence or absence of delipidized serum protein, whereas in the stationary cultures the delipidized serum protein was required. When cultures were partially synchronized by a thymidine block, stimulation of acetate incorporation into lipid in the blocked cells only occurred in the presence of delipidized serum protein; in released cells stimulation occurred in protein free medium. When inhibition of lipid synthesis from acetate was compared in young vs. old or dividing vs. stationary cultures, however, no differences were observed. The data indicate the response of diploid fibroblast cultres to change in exogenous lipid is dependent on passage level and state of growth.

Density-dependent regulation of proliferation rate in cultured, androgen-responsive, tumour cells

Short-term cultures of androgen-responsive Shionogi 115 (S115) cells exhibited density-dependent regulation of proliferation rate in the presence or absence of testosterone. The average surface area per cell exposed to the growth medium was inversely proportional to population density. By contrast, long-term cultures (serially passaged in testosterone-containing medium for several months) did not exhibit density-dependent regulation of proliferation rate when grown in testosterone-containing medium. In this medium, cells became elongated and no longer exhibited any obvious decrease in exposed surface area with increasing density. Nevertheless, when subcultured into testosterone-free medium, these cells reverted to an epithelial morphology and exhibited density-dependent regulation of proliferation rate. These relationships suggested that the proliferation rate of cells decreased with density in proportion to the decrease in exposed surface area...

Properties of growth-related acetylcholinesterase in a cell line of fibroblastic origin

We have previously reported the presence and regulation of an acetylcholine-hydrolyzing enzyme in high density suspension cultures of WRL-10A fibroblasts where its activity increases 100-fold when growth is arrested. Substrate specificity, substrate inhibition, and product identification studies indicate that this enzyme is acetylcholinesterase (AChE, EC 3.1.1.7). Treatment of whole cells with 5 mM diazotized sulfanilic acid revealed that most of the AChE is located on the external surface of the cell membrane. It was also found that the enzyme is released in the medium at a rate of 0.5 U/h/mg cell protein and that within a 24-h period the de novo synthesized and liberated AChE is equivalent to 90% of the activity associated with the cells. No similar synthesis of AChE was found in six order fibroblastic cell lines examined. These and related findings indicating that acetylcholine is also present in high density populations of WRL-10A cells suggest that this unique phenotype may be used profitably in exploring further the relationship between components of the cholinergic system and non-neuronal cell growth.

Biology in vitro of corneal epithelium and endothelium

Four main areas were explored: 1) the proper medium for culturing corneal tissue; 2) the effect of serum on tissue growth in vitro; 3) the interrelationships in vitro between corneal epithelium and endothelium, and 4) the biology of cultures of whole corneas (organ cultures). Modified Eagle's minimal essential medium (MEM) proved to be an excellent culture fluid. Corneal tissue could be grown in MEM without serum or clot, thus providing a defined culture medium. The biology in vitro of outgrowths of multilayered corneal epithelium and monolayered corneal endothelium are discussed. Contact inhibition between epithelium and endothelium is demonstrated in whole corneal (organ) cultures.

The regulation of protein synthesis in animal cells by serum factors

We have investigated the regulation of protein synthesis in animal cells by serum factors. Withdrawal of serum from the medium of actively dividing Vero cells resulted in an immediate decline in the rate of peptide chain elongation (Hassell and Engelhardt, 1973). Assay of elongation factor I (EFI) activity in the post-ribosomal supernatant as well as that associated with the ribosomes revealed that serum deprivation resulted also in reduction in the activity of this factor. The decline in the activity of EFI after serum deprivation occurred to the same extent and at the same time as the decline in the in vivo rate of protein synthesis and the in vitro peptide synthetic capacity of cell-free extracts. A temporal correlation therefore exists among the in vivo rate of protein synthesis, the peptide synthetic activity of cell-free extracts, and the activity of EFI. The activity of peptidyl transferase was not altered by serum deprivation. The loss of extract peptide synthetic activity resulting from serum deprivation was reversible since serum addition to previously serum-starved cultures resulted in full restoration of activity for polyphenylalanine (polyPhe) synthesis within 3 h. Moreover, RNA synthesis was not required for this turn-on of polyPhe synthesis. Vased on these data we conclude that a translational control mechanism is operative in Vero cells deprived of serum.

Control of the uptake of amino acids by serum chick embryo cells, untransformed or transformed rous sarcoma virus

Forty to fifty minutes after removal of serum, the net total uptake of amino acids in growing secondary cultures of normal or virus-transformed chick embryo cells, stopped or proceeded only at a highly reduced rate. In both normal and transformed cells, the initial (0-40 min) rate of the above uptake was the same in the absence of serum as in its presence. The initial rate of the total uptake of amino acids in growing transformed cells was about the same as in growing normal cells. Neither in the normal nor in the transformed cells was the rate of the total uptake of amino acids reduced by cell confluence alone. In highly dense, hyperconfluent cultures of normal cells in which cell growth was arrested, the rate of uptake in the absence or in the presence of serum was four- to fivefold lower than the rate obtained in growing normal cells under similar conditions; in the absence of serum, the net uptake stopped after 40 min in the hyperconfluent cultures as well. It appears that cells growing in tissue culture require a serum factor for maintenance of the required high rates of uptake of amino acids and that the inhibition of growth at high cell densities is a result of depletion of this factor from serum, or the inability of the cells in a dense culture to respond to the factor. A serum factor is apparently also required for maintenance of the reduced rates of uptake of amino acids observed in hyperconfluent cultures.

Anchorage dependent changes in transport of glucose, adenosine, uridine and leucine in 3T3 cells

There is a low uptake of leucine in suspension cultures of 3T3 cells relative to the uptake in sparse monolayer cultures. The pattern of uptake of deoxyglucose is similar in suspension and monolayer cultures and changing the medium or adding serum stimulates uptake under both culture conditions. The uptake of uridine and adenosine is greater in suspension culture than in monolayer culture. Cells do not multiply in suspension culture but do multiply in monolayer culture and thus there is a correlation between uptake of leucine and conditions which stimulate cell multiplication, but not correlation of the uptake of deoxyglucose, uridine and adenosine with these conditions.

Effects of withdrawal of a serum stimulus on the protein-synthesizing machinery of cultured fibroblasts

3T6 cells resting in medium containing 0.5% serum were stimulated to prepare for multiplication by the addition of medium containing 10% serum. After a number of hours, when the rate of preribosomal RNA synthesis, total RNA content (mainly ribosomal), and the cytoplasmic content of poly A (a measure of poly A(+) mRNA) were considerably elevated, the serum-rich medium was withdrawn, and the original medium replaced. The rate of preribosomal RNA synthesis began to drop within 30 minutes, but required a much longer time to fall to a new resting level. When the serum-rich medium was withdrawn after 12 hours of stimulation, the total RNA content required 12-18 hours to fall to the resting level, whereas cytoplasmic poly A content and the rate of protein synthesis declined more rapidly, reaching a new resting level within eight hours. During the 12 hours following withdrawal of the serum-rich medium an appreciable fraction of the cells initiated DNA synthesis. Presumably, the cellular preparations for DNA synthesis cannot be immediately reversed because of the inertial factors related to the protein-synthesizing machinery.

Studies on the regulation of the three enzymes of the Leloir pathway in cultured mammalian cells. I. Effect of substitution of galactose for glucose as the sole hexose in the medium in human diploid cell strains and in a rat hepatoma line

In human diploid cell strains, the substitution of galactose for glucose as the sole hexose in the medium had no measurable effect on the specific activity of the cell protein for any of the three enzymes of the Leloir pathway. These enzymes are galactokinase, alpha-D-galactose-1-phosphate: UDP glucose uridyl transferase and UDP galactose 4-epimerase. A cell strain from a patient with galactosemia had no detectable activity for the transferase. The substitution of galactose for glucose in the medium of these cells (which has been shown to cause the cells to accumulate galactose-1-phosphate) also failed to affect cellular activity for the three enzymes. Similarly, the three activities failed to respond to the substitution of galactose for glucose in cultures of a rat hepatoma line. Cells of this line have been shown by others to perform a number of the tissue-specific functions of liver. The failure of galactose to stimulate increasd cellular activity for the three enzymes represents a striking difference between the behavior of these enzymes in human diploid cell strains and their behavior in E. coli.

Variations in the cell-free translating apparatus of cultured animal cells as a function of time during cell growth

Vero M3 cells, a line derived from the kidney of an African Green Monkey, display certain alterations in their protein synthetic apparatus as a function of time during a growth cycle. (Growth cycle here refers to exponential growth of unsynchronized cells in culture and their subsequent passage into the stationary phase.) The capacity of cytoplasmic extracts of these cells to promote endogeneous mRNA-mediated polypeptide synthesis or poly U-mediated polyphenylalanine synthesis declines from the second day after the initiation of the growth cycle. The ribosome sedimentation profile indicates that after the second day of growth a decrease also occurs in the total amount of ribosomes per cell, and that a shift occurs from predominantly polyribosome structures to predominantly subunits and monoribosomes structures. The activity of the translation factor, elongation factor 1, also progressively decreases after the second day of growth. Furthermore, when crude factor preparations from cells in the second day of growth (Exponential phase) and from cells in the fifth day of growth (Stationary phase) are compared for leucyl-tRNA synthetase and prolyl-tRNA synthetase activities, it is found that the extracts from fifth-day cells have significantly less activity. The activity of another enzyme, acid phosphatase, remains relatively unaffected as a function of time during the cell growth cycle. When HeLa S3 plating cells are grown under the same conditions, they do not display the same responses.

The control of cell growth regulation by tumour-inducing viruses: a challenging problem

Among the signals controlling the growth of cultured cells are medium factors and, for epithelial cells, the available attachment surface. The growth factors in serum cause, in addition to the mitogenic effect, a complex response including changes in the rates of transport of small molecules into the cells, modification of surface features, and of the intra-cellular concentration of cyclic nucleotides. Are these changes essential components of the mitogenic effect or distracting side effects? This question will be approached, by using two mitogenic stimuli different from serum growth factors: an increase in Ca 2+ concentration in the medium, and the oncogenic polyoma virus. The virus stimulates growth of both epithelial and fibroblastic cells, which differ markedly in their response to serum factors. These approaches will allow a clarification of some characteristics of the growth control mechanism, although its central nature still remains obscure. Further understanding may derive from the study of oncogenic viruses because it seems that the stimulation of cell growth they produce is related to their inability to transform cells and induce cancer. All these effects probably result from the expression of a viral transforming gene, whose nature and properties begin to be understood.

Effect of pH on plating efficiency, serum reguirement, and incorporation of radioactive precursors into human cells

The plating efficiencies of two cell lines (HeLa-AT and WI26 Va) and one cell strain (KL2) appeared to be optimal at pH 7.6 At the optimal pH, ,sing organic buffers, the serum concentration could be reduced by one-half without affecting the initial growth rate or the final population density of the human skin fibroblast strain, KL2. It is suggested that an optimal pH lowers the serum requirement of the cells. The incorporation of [3-H]thymidine, [3-H]uridine, [-3H]fucose and [-14C]amino acids into KL2 was maximal at the pH which normally permits optimal growth of this cell strain. Protein turnover, as measured by loss to the medium of amino acids from prelabeled cells, was pH-independent. Thymidine incorporation did not correlate with culture growth in the cell strain, MS2A.

Growth control in primary fetal rat liver cells in culture

Primary fetal rat liver cells cultured in medium deficient in, but not free of, arginine in the presence of dialyzed fetal calf serum grow until the final cell density is attained and cells become quiescent in the Go phase of the cell cycle. When growing cells are transferred into arginine free medium, cells become reversibly arrested in Go. Fetal rat liver cells can be induced to synthesize DNA by addition of high levels of arginine to serum free medium. Low arginine levels in the culture medium do not induce cell growth unless serum is present. Serum stimulates arginine uptake in fetal rat liver cells suggesting that serum growth factor(s) act by increasing intracellular arginine levels high enough to initiate the growth cycle. Fractionation of fetal calf serum by gel filtration on G-200 Sephadex yields a partially purified arginine uptake stimulating activity which is eluted from the column in the same fractions that contain fetal rat liver cell growth promoting activity. Insulin induces DNA synthesis in quiescent fetal rat liver cells. Glucagon reverses the stimulatory effects of insulin. N-6,O-2-Dibutyryl adenosine 3:5-cyclic monophosphoric acid (But2c-AMP) (10-minus4 M) and theophilline (10-minus3 M) inhibit arginine uptake and the initiation of DNA synthesis by serum. The role of arginine in the control of DNA synthesis in fetal rat liver cells and the mechanism of action of serum growth factors are discussed.

In vitro biology of corneal epithelium and endothelium

Four main areas are explored: (1) the proper culture medium for corneal tissue; (2) the effect of serum on in vitro tissue growth; (3) the in vitro interrelationships between corneal epithelium and endothelium; and (4) the biology of cultures of whole corneas (organ cultures). Modified Eagle's minimal essential medium (MEM) proved to be an excellent culture fluid. Corneal tissue could be grown in MEM without serum or clot, thus providing a defined culture medium. The in vitro biology of outgrowths of multilayered corneal epithelium and monolayered corneal endothelium are discussed. Contact inhibition between epithelium and endothelium is demonstrated in whole corneal (organ) cultures.

Cyclic nucleotides and growth control in cultured mouse cells: correlation of changes in intracellular 3':5' cGMP concentration with a specific phase of the cell cycle

The commencement of cell growth following serum addition to quiescent cultures of mouse fibroblasts is preceded by transient changes in intracellular concentrations of cAMP and cGMP. By artificial depletion of the culture medium for different nutrients, cell growth can be reversibly arrested in various phases of the cell cycle. Here it is shown that the major cGMP increases are only observed when cultures which are arrested in the G(0) phase are stimulated to grow or when synchronized growing cells pass through the G(1) phase. In addition to its concomitant decrease, cAMP exhibits rhythmic changes during the cell cycle. This suggests that the increase in cGMP could act as a specific signal for movement of cells out of the G(0) or G(1) phase of the cell cycle by activating the pleiotypic and mitogenic program of the cell.

Some biochemical properties of Chinese hamster cells sensitive and resistant to actinomycin D

A graded series of drug-resistant Chinese hamster sublines has been examined for biochemical changes accompanying resistance to actinomycin D. The most highly resistant subline, DC-3F/AD X, is maintained at 10 microg/ml of the antibiotic. It was shown that over 250 times more actinomycin D is required to inhibit RNA synthesis in this subline than in the parental DC-3F line. The DC-3F/AD X subline was also shown to have a somewhat reduced capacity to transport uridine as compared to parental cells. Sensitive cells took up over 50 times more tritiated antibiotic than the most resistant cells, as determined in a 1-h assay. Uptake of actinomycin D was shown to be temperature-dependent in both resistant and sensitive cells and was not influenced by various metabolic inhibitors. Resistance could not be explained by a rapid uptake and release of the antibiotic, as demonstrated in efflux experiments, or by its metabolism. In addition, highly resistant cells which are cross-resistant to puromycin were shown to have a reduced capacity to take up labeled puromycin. These studies provide further evidence indicating that the mechanism of resistance to actinomycin D is reduced permeability to drug and suggesting that cell membrane alteration accounts for resistance to both actinomycin D and puromycin.

Growth control in cultured mouse fibroblasts: induction of the pleiotypic and mitogenic responses by a purified growth factor

Addition of serum to quiescent mouse fibroblasts induces a series of macromolecular changes (a pleiotypic response) followed by DNA synthesis and cell division. A new pituitary hormone, fibroblast growth factor, and hydrocortisone acting at physiological concentrations can completely replace exogenously added serum for the induction of these events in lines of BALB/c 3T3 cells. The induction of cell growth is specific for cultured fibroblasts; no stimulation is observed for mouse epithelial cells or virally transformed fibroblasts.

Control of translation in cultured cells: continued synthesis and accumulation of messenger RNA in nondividing cultures

Nontransformed animal fibroblasts in tissue culture regulate total protein and ribosomal RNA synthesis coordinately with changes in the cellular growth state. Here it is shown that the amounts and rates of synthesis of cytoplasmic poly(A)-containing RNA, presumed to be mRNA, do not appreciably change with alterations in growth state. In nongrowing (resting) cultures of BALB/c 3T3 cells presumptive mRNA molecules predominantly accumulate as cytoplasmic ribonucleoprotein particles; the RNA from which can be chased into the polyribosomal structure upon activation of the resting cultures with animal sera. It is suggested that the decreased protein synthetic rate in resting as compared with growing cells is in part due to a failure of preexisting mRNAs to attach to ribosomes and that addition of serum to the tissue culture medium can partially overcome this translational lesion.

Effect of adenosine 3'-5'-cyclic monophosphate on cell proliferation

Secondary cultures of human diploid fibroblasts, which demonstrate density-dependent inhibition of cell growth, were used to study the effect of adenosine 3'-5'-cyclic monophosphate (cAMP) on cell proliferation. DNA synthesis in nonconfluent cultures and in contact-inhibited cultures stimulated to grow by refeeding with fresh medium was found to be inhibited by exogenous cAMP. The properties of this inhibition of DNA synthesis, together with the alterations in cAMP metabolism observed in confluent cultures of cells stimulated with fresh medium to resume growth, strongly suggest that cAMP is involved in contact-inhibition of cell proliferation.

A review of the central response to peripheral nerve injury and its significance in nerve regeneration

✓ Chromatolysis is a morphological term used to describe a sequence of light microscopic changes occurring in the cell bodies (perikarya) of peripheral neurons after injury to their peripherally directed axons. The authors have attempted to interpret the significance of chromatolysis to peripheral nerve regeneration and to describe how central regenerative activity may be affected by peripheral regeneration. Electron microscopic perikaryal changes following peripheral nerve injuries initially appear to be manifestations of a nonspecific cellular insult with possible loss of trophic influence, and secondarily a reflection of neuronal readjustment to a decrease in peripheral axon demands. Sectioning of peripheral axons results initially in decreased perikaryal axonal cytoplasm synthesis. Return of normal and sometimes greater than normal perikaryal cytoplasm production and a return of normal perikaryal morphology are characteristics of the maturation phase of peripheral nerve regeneration and occur only if peripheral axon regrowth is successful.

Buffer combinations for mammalian cell culture

The growth and metabolism of cultured mammalian cells are markedly affected by the pH variation in ordinary hicarbonate-buffered media (pH 8.0 to 6.9). Those pH swings can be reduced and the pH of the culture can be stabilized as desired in the range pH 6.4 to 8.3 by appropriate combinations of two or three organic buffers, each at 10 to 15 millimolar, in conjunction with phosphate and bicarbonate. The initial alkalinization in sparse cultures is then minimized, and the metabolic acidificatiotn in 24 hours is usually less than 0.4 pH unit except in heavy cultutres.

Gene activation in WI-38 fibroblasts stimulated to proliferate: requirement for protein synthesis

Confluent monolayers of WI-38 human diploid fibroblasts can be stimulated to divide by fresh medium containing 30% fetal-calf serum. Up to 80% of the cells are stimulated to divide, with a peak of DNA synthesis between 15 and 21 hr. 1 hr after the change of medium there is a 70% rise in chromatin template activity. Cycloheximide inhibited the increase in chromatin template activity. A requirement for RNA synthesis was investigated by incubating stimulated and unstimulated cells with 10 mug/ml of actinomycin D. In spite of a 95% inhibition of RNA synthesis in whole cells, purified chromatin from stimulated cells showed the usual increase in template activity. These experiments implicate a requirement for protein synthesis in template activation, and imply that the synthesis of this (or these) protein(s) is independent of RNA synthesis and regulated by a purely translational mechanism.