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Pretreatment of Mouse Striatal Neurons in Primary Culture with 17β‐Estradiol Enhances the Pertussis Toxin‐Catalyzed ADP‐Ribosylation of Gαo,i Protein Subunits

Abstract: Pretreatment of striatal neurons from mouse embryos in primary culture with 17β‐estradiol (10−9M, 24 h) enhanced the ADP‐ribosylation of Gαo,i proteins catalyzed by pertussis toxin (PTX). As estimated by quantitative ADP‐ribosylation of Gαs with cholera toxin and immunoblot experiments using anti‐Gαo and anti‐Gβ sera, 17β‐estradiol pretreatment did not modify the levels of the major GTP‐binding protein (G protein) constituent subunits Gαs, Gαo, and Gβ. Thus, 17β‐estradiol should induce a qualitative modification of these G proteins, perhaps by stabilizing the association of the heterotrimers Gαo,iβγ, which are the targets of PTX. Such a hypothesis is in agreement with observations indicating that 17β‐estradiol both suppressed the D2 dopamine‐ and opiate receptor‐induced inhibitions of adenylate cyclase activity and enhanced the positive coupling between biogenic amine receptors (D1 dopamine, β‐adrenergic, and A2 adenosine) and adenylate cyclase. In addition, PTX pretreatment, which is known to uncouple receptors associated with Go,i proteins and thus to impair the dissociation of the heterotrimers Gαo,iβγ, mimicks the effects of the steroid on the responses of adenylate cyclase to inhibitory and stimulatory agonists. Finally, the chemical specificity of the steroids was the same in the ADP‐ribosylation as in the adenylate cyclase experiments: Testosterone (10−9M) mimicked the effects of 17β‐estradiol, whereas 17α‐estradiol, progesterone, and dexamethasone did not. Because 17β‐estradiol enhanced uniformly the PTX‐catalyzed ADP‐ribosylation of Gαo and Gαi proteins, it can be expected that transducing systems other than adenylate cyclase involving these G proteins, such as ionic channels or phospholipases, are also affected by the steroid pretreatment of striatal neurons.