Alterations of CREB and DARPP-32 phosphorylation following cocaine and monoaminergic uptake inhibitors

The cAMP response element-binding protein (CREB) is a transcription factor that can contribute to drug-induced changes in gene expression. It is well known that the dopamine and cAMP-regulated phosphoprotein (DARPP-32), via activation, is converted into a potent inhibitor of protein phosphatase-1 (PP-1), which regulates the activity of CREB. We previously reported that the continuous infusion of cocaine for 7 days produced a significant increase in prodynorphin mRNA in the rat caudate putamen and we also studied the role of the different monoamines in these cocaine effects. Since multiple cAMP response element (CRE) sequences are present on the prodynorphin gene promoter, the aim of our study was to investigate the effects of cocaine and monoaminergic uptake inhibitors on CREB and DARPP-32 phosphorylation and moreover the possible correlation with the changes already observed on prodynorphin gene expression. Here we investigated the alterations on phospho-Ser133 CREB, phospho-Thr34 DARPP-32 and phospho-Thr75 DARPP-32 induced by continuous infusions of cocaine, GBR12909, fluoxetine and nisoxetine. A significant decrease in both phospho-CREB at Ser133 and phospho-DARPP-32 at Thr34 in the rat caudate putamen was produced by cocaine, GBR 12909, fluoxetine or nisoxetine. No alterations were observed on phospho-Thr75 DARPP-32 levels. We hypothesize that the decrease in phospho-Thr34 DARPP-32 could evoke an increase in PP-1 activity which is responsible for the reduction of CREB activation. These effects could in turn elicit the reduction in the transcriptional cascade of the prodynorphin gene in the caudate putamen, observed following chronic fluoxetine and nisoxetine. On the other hand, these mechanisms do not seem to be involved in cocaine- or GBR 12909-induced effects.[...]