High salt culture conditions suppress proliferation of rat C6 glioma cell by arresting cell-cycle progression at S-phase.

As one of the in vitro model experiments for investigating a possible effect of extracellular environmental stresses on glial cell proliferation, the influence of high salt culture conditions on the growth of rat C6 glioma cells was examined. Exposure to the culture medium containing high concentrations of NaCl reduced the number of viable cells in a concentration-dependent manner without any significant change in their viability. In contrast, proliferation of these cells was not substantially altered by culturing them in hyperosmotic medium containing either sucrose or glycerol, both of which were osmotically almost equivalent to high salt culture medium. On the other hand, expression of the egr-1 gene, an immediate early gene related to the proliferation and differentiation of various cells, was enhanced by culturing glioma cells in high salt medium while the reduction of glial fibrillary acidic protein content, an index of glial cell differentiation, was observed under the same culture conditions. Further studies on the relationship between egr-1 gene expression and the cell cycle showed that cell-cycle progression was arrested at S-phase by culturing glioma cells in high salt medium. Moreover, both resveratrol and CPT-11, which are known to arrest cell-cycle progression, elevated egr-1 mRNA levels in glioma cells. Thus, these observations suggest that high salt culture conditions might suppress the proliferation of rat C6 glioma cells as a consequence of arresting cell-cycle progression at S-phase, resulting secondarily in the compensatory enhancement of egr-1 gene expression.