Complete replacement of serum in primary cultures of chick embryo brain cells by growth-promoting alpha-globulin

Growth related changes in sugar determinants on the surface of C6 glioma cells in culture: a cytochemical lectin-binding study

The cell surface sugar determinants (CSSD) were examined in C6 glioma cells in cultures at different conditions of growth by peroxidase conjugates of the lectins: peanut agglutinin (PNA), Ricinus communis agglutinin (RCA), Helix pomatia agglutinin (HPA), wheat germ agglutinin (WGA), lentil agglutinin (LCA), laburnum bork agglutinin (LABA), and lotus agglutinin (TPA). It was found that the cells bound more intensively WGA, LCA, and RCA compared to PNA, HPA; the weakest staining was provided by LABA and TPA. Binding intensity for PNA significantly increased after pretreatment of the cells with neuraminidase. This indicates that a part of the beta-D-galactose residues on the surface membrane of C6 glioma cells is covered by sialic acid. The process of sialization was increased during the culturing of C6 glioma cells. Addition of cis-DDP or dBcAMP to cultures growing in medium with 10% of CS increased the number of Gal residues which are not covered by sialic acid. The expression of beta-D-galactose (Gal), N-acetyl-D-galactosamine (NAcDGal), and fucose (Fuc) residues appeared to be most responsive to changes in growth conditions and degree of cell differentiation. The expressions of N-acetyl-D-glucosamine (NAcDGlc) and mannose (Man) residues were high and seems did not depend on changing of the conditions of culturing. In C6 glioma cells cultures in which the rate of cell division, formation of the cell processes, and adhesiveness of the cells to the substratum were reduced by growing cells in MEM+, expression of beta-Gal, NAcDGal, and Fuc was considerably reduced. The decrease of expression of beta-Gal, NAcDGal, and Fuc on the surface of cell membrane was more pronounced in MEM+ with 1% of CS than in MEM+ with 10% of CS. In DbcAMP and cis-DDP treated cultures, grown in medium with 1% serum, in which cell division was inhibited without obvious changes in cell adhesiveness to the substratum, binding of PNA and HPA was increased due to higher expression of beta-Gal and NAcDGal. From these observations it was concluded that the pattern of expression of sugar residues on the cell surface varies according to the biological state of the cells and are easily affected by tissue culture conditions.

Fetuin: its enigmatic property of growth promotion

A variety of cell types in culture respond to fetuin, a glycoprotein from fetal bovine serum, which is often an important supplement to many serum-free media. Bovine fetuin preparation has been shown to inhibit trypsin activity and promote cellular attachment, growth, and differentiation in many different culture systems. In addition, fetuin associates with various growth factors or growth-promoting substances. However, whether the growth-promoting activity of fetuin preparation is due to fetuin per se or to its minor contaminant(s) has been a long-standing puzzle. The present review surveys the literature concerning this enigmatic property of fetuin and summarizes three possibilities: 1) fetuin itself is active, although the majority of studies do not support this; 2) various contaminants of fetuin preparations, including potentially unidentified ones, are responsible for the activity, a possibility supported by numerous reports; and 3) one of the fetuin subspecies, one of its contaminants, or a combination of both of these is responsible for growth of a specific cell type. In addition, the basic physicochemical properties and other biological functions of fetuin have also been presented.