The anti-inflammatory activity of estrogen in glial cells is regulated by the PKC-anchoring protein RACK-1

It has recently been suggested that estrogen inhibits glial activation and the release of neurotoxic mediators. The mechanisms involved in this anti-inflammatory effect are unclear. We found that an nM concentration of 17-β estradiol inhibits protein kinaseC-βII translocation induced by lipopolysaccharide in primary astrocytes. Estradiol treatment did not change the total content of kinaseC-βII or of lipopolysaccharide receptor, but dose-dependently reduced the levels of receptors for activated C kinases-1 (RACK-1), the anchoring protein involved in protein kinase C (PKC) shuttling. This decrease could thus account for the defective protein kinaseC-βII activation. Pre-treatment with 1 nM β-estradiol, which reduced by ∼35% the expression of RACK-1, prevented the lipopolysaccharide-induced expression of tumour necrosis factor-α mRNA and of the inducible form of nitric oxide (NO) synthase. As a consequence, the production of tumour necrosis factor-α and NO were decreased. An antisense oligonucleotide for RACK-1 also reduced tumour necrosis factor-α and nitric oxide production on lipopolysaccharide stimulation. These results demonstrate that estrogen reduction of the RACK-1 expression, leading to a defective protein kinase-C activation counteracts the inflammatory response in astrocytes.