CYCLIC AMP-MEDIATED INDUCTION OF THE GLIAL FIBRILLARY ACIDIC PROTEIN IS INDEPENDENT OF PROTEIN-KINASE-A ACTIVATION IN RAT C6 GLIOMA

N-6-0'(2)-dibutyryl cAMP (dbcAMP), N-6-monobutyryl cAMP (N-6-mbcAMP), 8-Chloro cAMP (ClcAMP), and O'(2)-monobutyryl cAMP (O'(2)-mbcAMP) were used to study glial fibrillary acidic protein (GFAP) induction in rat C6 glioma. With the exception of O'(2)-mbcAMP these cAMP analogs indu ced GFAP after stimulation of cells with a concentration of 0.5-1 mM. Only dbcAMP and N-6-mbcAMP increased the intracellular concentration o f cAMP. Protein kinase A (PKA) activation is often proposed to be invo lved in GFAP expression in astrocytes. Ion-exchange chromatography ind icated that protein kinase activity is associated with PKA type II in C6. dbcAMP, N-6-mbcAMP, and CLcAMP upregulated the amount of cAMP-bind ing proteins approximately twofold. RI was upregulated in the cytosol and particulate fraction, whereas RII was not affected after stimulati on with dbcAMP. Concomitant, the PKA activity decreased approximately 60% and 40% in the cytosol and particulate fraction, respectively. CRE B is constitutively expressed in C6 and is downregulated after stimula tion with dbcAMP. The membrane-permeable PKA inhibitor N-[2-p-bromocin namylamino) ethyl]-5-isoquinoline sulfonamide (H89) did not suppress t he induction of GFAP-mRNA and its translation into GFAP. On the contra ry, depending on the time difference between H89 and dbcAMP addition t o C6, GFAP synthesis could even be potentiated more than twofold. Expe riments in the presence of cycloheximide showed that protein synthesis is necessary for GFAP transcription. Although all components of the P KA signal transduction pathway are present in C6, GFAP synthesis is no t dependent on PKA activation but required the synthesis of an unident ified factor. (C) 1997 Wiley-Liss, Inc.