High salt culture conditions inhibit serum- and NGF- but not PMA-induced Egr-1 gene transcription in rat C6 glioma cells.

Recent studies have suggested that glial cells may play a physiologically important role in the retention and restoration of neuronal cell integrity, proposing the possibility that the proliferation and/or differentiation of glial cells may be related to pathological changes in neural functions in neurodegenerative diseases, and hence, it seems interesting to investigate the expression of genes related to the proliferation and differentiation of glial cells. Following this basic concept, we have previously examined the influence of culture conditions on egr-1 gene expression in rat C6 glioma cells and have shown that brief exposure of these cells to high salt culture medium can induce the down-regulation of egr-1 gene expression. In contrast, the long-term culture of these cells in high salt medium has been shown to primarily reduce their proliferation and secondarily elevate egr-1 gene transcription as a consequence of arresting the cell-cycle progression. Therefore, the effect of high salt culture medium on egr-1 gene expression seems practically unconfirmed, and remains to be further investigated. Then, the effects of various egr-1 gene inducers, such as serum, NGF and phorbol ester PMA, on Egr-1 mRNA levels in the glioma cells were examined under the high salt culture conditions. The brief exposure to high salt culture medium inhibited the elevation of Egr-1 mRNA levels induced by serum replenishment and NGF, but not induced by PMA. These results suggest that the suppression of serum action on egr-1 gene transcription may be the primary and essential event leading to the down-regulation of egr-1 gene expression under the high salt culture conditions.