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-methylxanthine 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.