c-fos proto-oncogene expression in astrocytes associated with differentiation or proliferation but not depolarization

Expression of the c- fos proto-oncogene in rat neocortical astrocytes in culture was examined using Northern blotting and immunocytochemistry. Marked induction of c- fos mRNA in astrocytes was observed after treatment with epidermal growth factor (EGF), basic fibroblast growth factor (bFGF), dibutyryl cyclic AMP (db-cAMP), and phorbol diester (TPA; 12- O-tetra-decanoylphorbol 13-acetate), which are known to induce the proliferation or differentiation of astrocytes. Increase of c- fos protein immunoreactivity (IR) was obtained after treatment with fetal calf serum, EGF, bFGF, db-cAMP and TPA. High concentrations of calcium ionophore A23187, which were lethal to cultured astrocytes, also increased c- fos protein-IR. Treatment with lower concentrations of calcium ionophore (which slightly increase Ca 2+ uptake), higk K + and nerve growth factor had no detectable effect on c- fos expression. These results show that depolarization does not induce c- fos in astrocytes and suggest that c- fos may play a role in differentiation and proliferation of astrocytes.