Inhibition of G1 cyclin expression and G1 cyclin-dependent protein kinases by cAMP in an astrocytic cell line.

The effects of cAMP on cell cycle progression were examined using an astrocytic cell line. We show that forskolin and 8-bromo-cAMP block the basic Fibroblast Growth Factor-induced DNA synthesis, do not inhibit mitogen activated protein kinase activation whereas they reduce G1 cyclin (E and D1) expression without modification of cyclin A level. Furthermore, they inhibit the activation of cyclin A- and cyclin E-dependent histone H1 kinases. These results suggest that cAMP may exert its antiproliferative effects through the regulation of cyclin synthesis and cyclin-dependent kinase activation.