Cyclic AMP-mediated induction of the glial fibrillary acidic protein is independent of protein kinase A activation in rat C6 glioma
Abstract
N6-O'2-dibutyryl cAMP (dbcAMP), N6-monobutyryl cAMP (N6-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 induced GFAP after stimulation of cells with a concentration of 0.5-1 mM. Only dbcAMP and N6-mbcAMP increased the intracellular concentration of cAMP. Protein kinase A (PKA) activation is often proposed to be involved in GFAP expression in astrocytes. Ion-exchange chromatography indicated that protein kinase activity is associated with PKA type II in C6. dbcAMP, N6-mbcAMP, and ClcAMP upregulated the amount of cAMP-binding proteins approximately twofold. RI was upregulated in the cytosol and particulate fraction, whereas RII was not affected after stimulation with dbcAMP. Concomitant, the PKA activity decreased approximately 60% and 40% in the cytosol and particulate fraction, respectively. CREB is constitutively expressed in C6 and is downregulated after stimulation with dbcAMP. The membrane-permeable PKA inhibitor N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinoline sulfonamide (H89) did not suppress the induction of GFAP-mRNA and its translation into GFAP. On the contr...Continue Reading
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