Astrocytes regulate GFAP mRNA levels by cyclic AMP and protein kinase C‐dependent mechanisms

Glial fibrillary acidic protein (GFAP) mRNA and protein levels in rat astrocyte cultures and in the human astrocytoma line U‐373MG were examined in order to determine the effects of agents that regulate cAMP‐dependent kinase and protein kinase C. Treatment of cells with dibutyryl cAMP or forskolin and 3‐isobutyl‐1‐methylxan‐thine increased steady‐state GFAP mRNA levels. Short‐term treatment of cells with phorbol‐12‐myristate‐13‐acetate (PMA) increased GFAP mRNA levels, but prolonged treatment of cells with PMA or 1‐oleoyl‐2‐acetyl‐rac‐glycerol produced a dramatic decrease in GFAP mRNA; 4‐beta‐phorbol had no effect. Thus, both cAMP‐dependent kinase and protein kinase C may exert regulatory roles in determining GFAP mRNA levels. Nuclear run‐off studies showed no change in GFAP mRNA synthesis after cAMP or PMA treatment, suggesting post‐transcriptional mechanisms. Western blot analysis revealed that the effect of PMA on U‐373MG cells shows specificity in that GFA protein levels decline, while those of other major cytoskeletal proteins were unaltered.