The differential molecular mechanisms underlying proenkephalin mRNA expression induced by forskolin and phorbol-12-myristic-13-acetate in primary cultured astrocytes

In rat astrocytes, forskolin (FSK; 5 muM) and phorbol- 12-myristic-1 3-acet ate (PMA; 2.5 muM) increase the proenkephalin (proENK) mRNA level via diffe rent pathways. FSK-induced proENK mRNA expression is independent of protein de novo synthesis, and well correlated with CREB phosphorylation. This is in contrast to PMA-induced proENK mRNA expression that is dependent on prot ein de novo synthesis and is well correlated with the increase of AP-I DNA binding activity rather than CREB phosphorylation. Differential regulation of BP-l proteins by PMA and FSK was also observed. While c-Fos, Fra-2 and J unB were increased in response to either stimuli, only Fra-l, c-Jun and Jun D were increased by PMA. The combined treatment with FSK and PMA additively increased the proENK mRNA level, which was correlated with AP-1 or ENKCRE- 2 DNA binding activity, and CREB phosphorylation. Dexamethasone (DEX; 1 muM ) further enhanced FSK- or PMA-induced proENK mRNA expression, which was no t correlated with the activation of AP-1 expression and CREB phosphorylatio n, suggesting that synergistic interaction of glucocorticoid with PKA or PK C pathway for the regulation of proENK mRNA expression appears to be mediat ed by other pathways rather than CREB and AP-1 families. (C) 2000 Elsevier Science B.V. All rights reserved.