Estradiol can protect the brain from a variety of insults by activating membrane-initiated signaling pathways, and thereby modulate gene expression and lead to functional changes in neurons. These direct neuronal effects of the
hormone have been well documented; however, it is less understood what effects
estradiol may have on nonneuronal cells of the central nervous system. There is evidence that
estradiol levels can induce the release of glial-derived
growth factors and other
cytokines, suggesting that
estradiol may both directly and indirectly protect neurons. To determine whether 17beta-estradiol (E2) can activate rapid signaling and modulate nonclassical transcription in astrocytes, we stably transfected the C6 rat
glioblastoma cell line with human
estrogen receptor (ER) alpha (C6ERalpha) or rat
ERbeta (C6ERbeta). Introduction of a cAMP response element-
luciferase reporter gene into C6, C6ERalpha, and C6ERbeta cells leads to the observation that E2 treatment reduced
isoproterenol-stimulated
luciferase activity by 35% in C6ERalpha but had no effect on reporter gene expression in C6ERbeta or untransfected C6 cells. A similar effect was seen with a membrane-impermeable
estrogen (E2-BSA), suggesting the modulation of nonclassical transcription by
estradiol treatment is mediated by the activation of a membrane-initiated signaling pathway. Furthermore, pretreatment with
wortmannin (phosphatidylinsositol 3-kinase) or
U73122 (
phospholipase C) attenuated the E2-induced reduction in nonclassical transcription. We conclude that E2 treatment reduces cAMP response element-mediated transcription in
glioma cells expressing
ERalpha and that this reduction is dependent on the activation of membrane-initiated signaling. These findings suggest a novel model of
estrogen rapid signaling in astrocytes that leads to modulation of nonclassical transcription.