Regulation of the synthesis of S-100 protein in rat glial cells

Ethanol inhibits C6 cell growth: fetal alcohol syndrome model

Maternal consumption of ethanol produces a pattern of malformations, including nervous system abnormalities, in the developing fetus, a state called Fetal Alcohol Syndrome. We report the dose-dependent inhibition by ethanol of the growth of a glioma derived cell line, C6 cells; the effects occur at ethanol concentrations commonly encountered in the blood during human intoxication. The effects occur with different morphological subtypes of the cell line and do not occur when the cells are exposed to iso-osmolar concentrations of other chemicals. The results demonstrate that C6 cells are a model for the study of the effects of ethanol on nervous system cell growth.

Cytodifferentiation and expression of alpha-smooth muscle actin mRNA and protein during primary culture of aortic smooth muscle cells. Correlation with cell density and proliferative state

To investigate a possible correlation between cytodifferentiation, proliferation, and actin expression, smooth muscle cells from the 9-week-old rabbit aortic media were enzyme-dispersed into single cells and were plated in primary culture at different initial seeding densities. The volume fraction of myofilaments (Vv myo) in cells seeded moderately densely fell from 39.5% +/- 1.2% in the intact aortic media to 11.5% +/- 1.6% on Day 5, one day before the onset of logarithmic growth. The Vv myo remained low over the next 3 days, then began to rise as the density of cells increased, returning almost to the original levels after confluency and 1.84 cumulative population doublings (CPD). The expression of alpha-smooth muscle actin mRNA followed a similar time course of change, falling from 84.7% +/- 1.2% of total actin mRNA in freshly isolated cells to 54.0% +/- 6.5% on Day 5, returning to 87.5% +/- 0.5% after confluency. In these cultures, the alpha-smooth muscle actin protein content was 93.7% +/- 2.9% of total actin in freshly isolated cells, 68.7% +/- 3.1% on Day 5, and 73.3% +/- 2.5% 3 days after confluency. In densely seeded cultures, the Vv myo and expression of alpha-smooth muscle actin mRNA fell only slightly on Day 5 and rose to original levels upon confluency after 0.33 CPD. However, at the protein level, alpha-smooth muscle actin decreased on Day 5 and remained low on Day 12. The Vv myo, alpha-smooth muscle actin mRNA, and actin protein of sparsely seeded cells fell on Day 5 and then remained low throughout the culture period, including 5 days after confluency (Day 24), when the cells had undergone 5.37 CPD. Cells that were maintained subconfluent but quiescent on Day 7 in culture had the same low Vv myo, low alpha-actin mRNA expression, and low alpha-actin protein content as actively proliferating cells. The results show that Vv myo and alpha-smooth muscle actin mRNA undergo parallel changes during primary culture according to seeding density, but not to replication, and that alpha-smooth muscle actin protein decreases in culture then remains low irrespective of culture conditions.

Regulation of the S100 protein and GFAP genes is mediated by two common mechanisms in RT4 neuro-glial cell lines

RT4-AC cells express both neuronal and glial properties and undergo cell-type conversion in culture to three distinct derivatives, described as either neuronal-like or glial-like. A coordinate induction of glial fibrillary acidic protein (GFAP) and S100 protein and GFAP gene expression is coordinately induced by cAMP. In addition, for the first time we provide direct evidence that the ability to express both the S100 and GFAP genes is conserved with cell-type conversion to the glial derivative cell types, but is coordinately lost with conversion to the neuronal derivative cell types. These results make it highly likely that the GFAP and S100 genes are regulated by two common mechanisms in RT4-AC cells: (1) cAMP-mediated control of gene expression; and (2) a mechanism that allows these two genes to be coordinately expressed or not expressed as a consequence of cell-type conversion.

Levels and distribution of the calcium-modulated proteins S100 and calmodulin in rat C6 glioma cells

To understand better the mechanisms involved in the transduction of a calcium signal into an intracellular response via multiple calcium-modulated proteins, we have examined the calcium-modulated proteins, S100 and calmodulin, and their intracellular targets in rat C6 glioma cells. Subconfluent, confluent, and postconfluent C6 cells contain predominantly, if not exclusively, the S100 beta polypeptide. The level of S100 beta in C6 cells increases approximately 20-fold from subconfluency to postconfluency whereas the level of calmodulin increases only about two-fold. The subcellular distribution of S100 beta and calmodulin in mitotic cells is similar. However, the subcellular distribution of these proteins in interphase cells is different and appears to change with cell density. Gel overlay analysis demonstrated that the S100- and calmodulin-binding protein profiles are significantly different and that some of the binding proteins appear to change in intensity with cell density. These data demonstrate that S100 beta is the predominant S100 polypeptide in C6 cells and suggest that changes in S100 beta and S100 beta-binding proteins may be involved in regulating S100-mediated intracellular processes in C6 cells. Our studies also suggest that the levels of S100 and calmodulin may be differentially regulated in C6 cells.

Differentiation of purified astrocytes in a chemically defined medium

Homogeneous cultures of astrocytes and oligodendrocytes provide an excellent model system for studying the regulation of glial structure and function. Recently, a chemically defined (CD) medium was developed for purified cultures of astrocytes, thus eliminating the requirement for serum and providing a controlled system for the study of astroglial properties. Due to the widespread use of astrocyte cultures and the potential benefits to be gained from using a defined medium, astrocyte cultures raised in CD medium were analyzed for purity as well as morphological and biochemical properties. Purity was assessed using immunocytochemical staining for glial fibrillary acidic protein (GFAP) and fibronectin. Astrocytes raised in CD medium are 95% pure using the expression of GFAP as a criterion. Fewer than 1% of the cells in CD medium stained positive for fibronectin eliminating the possibility that CD medium is selective for meningeal or endothelial cells. Astrocytes raised in CD medium exhibit a striking degree of morphological differentiation as seen in scanning electron micrographs. They also exhibit a high degree of biochemical differentiation illustrated by increases in the specific activity of S-100 protein and the induction of glutamine synthetase by glucocorticoids. A defined medium that supports the proliferation of rat astrocytes and enhances numerous morphological and biochemical properties should greatly facilitate the study of factors controlling glial proliferation and differentiation.

Ion binding to calmodulin. A comparison with other intracellular calcium-binding proteins

Over the past few years calcium has emerged as an important bioregulator. Upon external stimulation, the cell generates a transient Ca2+ increase, which is transformed into a cellular event through a molecular cascade. The first step in this cascade is the binding of calcium to proteins present in the cytosol. These proteins capable of binding Ca2+ under physiological conditions all belong to the same evolutionary family that evolved from a common ancestor. However, they strongly differ in the properties of their calcium binding sites. Calmodulin, the ubiquitous calcium binding protein present in all eukaryotic cells, is very close to the ancestor protein, presents four calcium binding sites which bind calcium, magnesium and monovalent ions competitively and is involved in the triggering of cellular processes. Parvalbumin, another member of the family, is more specialized and found mostly in fast-twitch skeletal muscle. It binds calcium and magnesium with high affinity and seems to be involved in muscle relaxation. On the other hand, troponin C which confers Ca2+ sensitivity to acto-myosin interaction exhibits both triggering and relaxing sites. The study of intracellular Ca2+ binding proteins has shown that calcium binding proteins have evolved from a simple common structure to fulfill different functions.

S-100 protein synthesis in cultured glioma cell is G1-phase of cell cycle dependent

The kinetics of S-100 protein synthesis was studied in synchronized cultured glioma (C6) cells. The peak of the synthesis was detected at G1-phase of the cell cycle and apparently was not population density-dependent, since sparsely cultured G1-phase cells synthesized the same proportion of the protein per cell as that of confluent cultures, whereas the total cellular protein synthesis was found steadily increasing throughout the intermitotic phases.

Density-dependent regulation of cell growth: an example of a cell-cell recognition phenomenon

Cell-to-cell contact can result in a variety of changes in the cell's physiology. For different cell types, this may include both the initiation as well as the cessation of cell growth and changes in the state of differentiation. This review examines in detail one such phenomenon, density-dependent inhibition of growth, which is observed with many fibroblasts in culture. Data are summarized which demonstrate that the cessation of growth at high cell density is in part a consequence of cell-to-cell contact. An approach to the study of the molecular basis of this phenomenon is presented based on the demonstration that plasma membranes, when bound to sparse growing cells, mimic contact inhibition of growth. The present status of attempts to purify plasma membrane proteins responsible for this effect are summarized, and the properties of these membrane proteins are compared to those of previously described "soluble" proteins that inhibit cellular growth.