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Biomedical subjects

R W Holley

Publications and source records attributed to R W Holley.

10 recordsLinked to original sources
PubMed1979

Epidermal growth factor and the control of proliferation of Balb 3T3 and benzo[a]pyrene-transformed Balb 3T3 cells.

Benzo[a]pyrene-transformed Balb 3T3 cells (BP3T3) exhibit "normal" growth controls at low concentrations of serum. Epidermal growth factor (EGF) stimulates DNA synthesis and cell division in both Balb 3T3 and BP3T3 cells at physiological concentrations. The growth response of BP3T3 cells to EGF is qualitatively the same as that of 3T3 cells, however, the transformed cells have a lower quantitative requirement. Both 3T3 and BP3T3 cells show a density-dependent response to EGF, but the shift in the dose response curve for BP3T3 cells at high cell density is smaller than that seen for 3T3 cells. One cause of the restricted growth of 3T3 cells at high cell density compared with BP3T3 cells is the increased concentration of growth factor needed for stimulation of 3T3 cells at higher cell densities. A lower rate of depletion of other growth factory by BP3T3 cells may also explain the smaller effect of cell density on the EGF response of these cells.

Animals↗
PubMed1979

Binding, internalization, and degradation of epidermal growth factor by balb 3T3 and BP3T3 cells: relationship to cell density and the stimulation of cell proliferation.

Epidermal growth factor (EGF) stimulates the growth of both benzo[a]pyrene-transformed Balb 3T3 cells (BP3T3) and untransformed Balb 3T3 cells. We describe here the binding, internalization, and degradation of [125I]-EGF by BP3T3 cells and 3T3 cells. Binding of [125I]-EGF reaches a maximum after 45 to 90 minutes incubation at 37 degrees C. In both BP3T3 and 3T3 cells the extent of EGF binding required to stimulate DNA synthesis is density dependent; sparse cultures require a 15-30% occupancy to elicit a maximal response whereas dense cultures require a 70-85% occupancy. At physiological concentrations the total binding of [125I]-EGF to 3T3 cells is higher than to BP3T3 cells, and this difference increases at higher cell densities. The rate of degradation of [125I]-EGF is directly proportional to the total [125I]-EGF binding in each cell type. This supports the hypothesis that one cause of the diminished serum requirement of BP3T3 cells is a reduced rate of utilization of serum growth factors.

Animals↗
PubMed1978

Density-dependent regulation of growth of BSC-1 cells in cell culture: control of growth by low molecular weight nutrients.

BSC-1 cells, epithelial cells of African green monkey kidney origin, show pronounced density-dependent regulation of growth in cell culture. Growth of the cells is rapid to a density of approximately 1.5 x 10(5) cells/per cm(2) in Dulbecco-modified Eagle's medium supplemented with 10% calf serum. Above this "saturation density," growth is much slower. It has been found that the glucose concentration in the culture medium is important in determining the "saturation density." If the glucose concentration is increased 4-fold, the "saturation density" increases approximately 50%. Reduction of the "saturation density" of BSC-1 cells is also possible by decreasing the concentrations of low molecular weight nutrients in the culture medium. In medium supplemented with 0.1% calf serum, decreasing the concentrations of all of the organic constituents of the medium, from the high levels present in Dulbecco-modified Eagle's medium to concentrations near physiological levels, decreases the "saturation density" by approximately half. The decreased "saturation density" is not the result of lowering the concentration of any single nutrient but rather results from reduction of the concentrations of several nutrients. When the growth of BSC-1 cells is limited by low concentrations of all of the nutrients, some stimulation of growth results from increasing, separately, the concentrations of individual groups of nutrients, but the best growth stimulation is obtained by increasing the concentrations of all of the nutrients. The "wound healing" phenomenon, one manifestation of density-dependent regulation of growth in cell culture, is abolished by lowering the concentration of glutamine in the medium. Density-dependent regulation of growth of BSC-1 cells in cell culture thus appears to be a complex phenomenon that involves an interaction of nutrient concentrations with other regulatory factors.

Biological Transport↗
PubMed1978

Density-dependent regulation of growth of BSC-1 cells in cell culture: growth inhibitors formed by the cells.

Inhibitors formed by a monkey epithelial cell line, BSC-1, play an important role in limiting growth at high cell densities. At least three inhibitors are formed: lactic acid, ammonia, and an unidentified inhibitor that may be an unstable protein. The unidentified inhibitor is destroyed by shaking the conditioned medium, by bubbling gas through the medium, or by heating or storing the medium in the absence of cells. The concentrations of lactic acid and ammonia that accumulate in conditioned medium inhibit growth when added to fresh medium. These results, together with earlier studies, indicate that density-dependent regulation of growth of BSC-1 cells results from the combined effects of (a) inhibitors formed by the cells, (b) decreased availability of receptor sites for serum growth factors as the cells become crowded, and (c) limiting concentrations of low molecular weight nutrients in the medium. In contrast, density-dependent regulation of growth in 3T3 mouse embryo fibroblasts results almost entirely from inactivation of serum factors.

Ammonia↗
PubMed1978

Regulation of growth of fibroblasts.

Present knowledge on regulation of fibroblast growth is based on in vitro culture of fibroblasts from different sources. The research has focused on 2 problems: identification of the signal that reaches the fibroblast from outside and tells it to grow and identification of metabolic reactions inside the cell that commit it to initiate DNA synthesis after the signal arrives. Although the signal and the metabolic reactions have not yet been clearly identified, and the relationship between in vivo conditions and the result of these in vitro studies still has to be determined, the large body of data collected so far and the steadily growing information concerning these problems suggest a complex interrelation between cellular environment and metabolic processes involved in growth regulation.

Animals↗
PubMed1977

Density-dependent regulation of growth of BSC-1 cells in cell culture: control of growth by serum factors.

BSC-1 cells grow slowly, to high cell density, in medium with 0.1% calf serum. An increase in the serum concentration increases both the growth rate of the cells and the final cell density. The serum can be replaced to some extent by epidermal growth factor (EGF). Initiation of DNA synthesis in BSC-1 cells that have spread into a "wound" in a crowded cell layer requires the addition of a trace of serum or EGF, if the cells have previously been deprived of serum. The binding of 125I-labeled EGF to low-density and high-density BSC-1 cells has been studied. Binding is faster to low-density cells. Cells at low cell density also bind much more EGF per cell than cells at high cell density. The fraction of bound 125I-labeled EGF that is present on the cell surface as intact EGF is larger at low than at high cell density. The results indicate that the number of available EGF receptors per cell decreases drastically as the cell density increases. It is suggested that a decrease in the number of available EGF receptor sites per cell, and the accompanying decrease in sensitivity of the cells to EGF, contributes to density-dependent regulation of growth of these cells.

Binding Sites↗
PubMed1976

Control of growth of benzo(a)pyrene-transformed 3T3 cells.

The growth controls observed in benzo[a]pyrene-transformed 3T3 cells (BP3T3) are compared with those of virus-transformed and normal 3T3 cells. Superficially, the chemically transformed BP3T3 cells have the same behavior as virus-transformed SV3T3 cells. Both grow to high cell density in culture medium with 10% serum, both form colonies in Methocel, and both are tumorigenic. Closer examination, however, has disclosed that BP3T3 cells exhibit "normal" growth controls at low serum concentrations. In contrast to the behavior of SV3T3 cells, the initiation of DNA synthesis in BP3T3 cells is still dependent on a serum factor. If BP3T3 cells are grown in medium with 0.2% serum, the cells become quiescent, with growth arrested in the Gu or G0 phase of the cell cycle. The addition of serum or the fibroblast growth factor (FGF) to such quiescent cells leads to the initiation of DNA synthesis and the resumption of growth. As with normal 3T3 cells, if the growth rate of BP3T3 cells is limited by a suboptimal concentration of serum, the growth rate of the cells is increased by the addition of FGF. Also, BP3T3 cells show density-dependent regulation of growth, if the medium contains a low concentration of serum. BP3T3 cells, therefore, have the behavior of "transformed" cells when cultured in medium with 10% serum, but behave as "normal" cells in medium with low serum. In comparison with normal 3T3 cells, the difference in growth behavior of BP3T3 cells appears to be due to a substantial decrease in the cells' requirement for a serum growth factor of the FGF type. Exploration of possible causes of this substantial decrease indicates that the primary cause is a lower rate of depletion of the serum growth factor from the culture medium by BP3T3 cells. The decrease in rate of depletion is sufficient to account for the uncontrolled growth of BP3T3 cells in medium with 10% serum. It is suggested that a decreased rate of depletion of a growth factor may contribute to tumorigenicity of cells in vivo.

Benzopyrenes↗