Antipsychotic drugs inhibit the human corticotropin-releasing-hormone gene promoter activity in Neuro-2A Cells - an involvement of protein kinases

Antipsychotic drugs can regulate transcription of some genes, including those involved in regulation of hypothalamic - pituitary - adrenal (HPA) axis, whose activity is frequently disturbed in schizophrenic patients. However, molecular mechanism of antipsychotic drug action on the corticotropin-releasing hormone (CRH) gene activity has not been investigated so far. This study was undertaken to examine the influence of conventional and atypical antipsychotic drugs on the CRH gene promoter activity in differentiated Neuro-2A cell cultures stably transfected with a human CRH promoter fragment linked to the chloramphenicol acetyltransferase ( CAT) reporter gene. It has been found that chlorpromazine (0.1 - 5.0 mu M), haloperidol (0.5 - 5.0 mu M), clozapine ( 1.0 - 5.0 mu M), thioridazine ( 1.0 - 5.0 mu M), promazine (5.0 and 10 mu M), risperidone (5.0 and 10.0 mu M), and raclopride (only at the highest used concentrations, ie 30 and 100 mu M) present in culture medium for 5 days inhibited the CRH-CAT activity. Sulpiride and remoxipride had no effect. Since CRH gene activity is most potently enhanced by cAMP/protein kinase A pathway, the effect of antipsychotics on the forskolin-induced CRH-CAT activity was determined. Chlorpromazine ( 1.0 - 5.0 mu M), haloperidol ( 1.0 - 5.0 mu M), clozapine ( 1.0 - 5.0 mu M), thioridazine (3.0 and 5.0 mu M), and raclopride ( 30 and 100 mu M), but not promazine, sulpiride, risperidone, and remoxipride, inhibited the forskolin-stimulated CRH gene promoter activity. A possible involvement of protein kinases in chlorpromazine and clozapine inhibitory action on CRH activity was also investigated. It was found that wortmannin ( 0.01 and 0.02 mu M), an inhibitor of phosphatidylinositol 3-kinase (PI3-K), significantly attenuated the inhibitory effect of chlorpromazine and clozapine on CRH gene promoter activity. In line with these results, a Western blot study showed that these drugs increased phospho-Ser-473 Akt level, had no effect on total Akt, and decreased glycogen synthase kinase-3 beta level. Additionally, we found that clozapine decreased protein kinase C (PKC) level and that its action on CRH activity was attenuated by PKC activator (TPA, 0.1 mu M). The obtained results indicate that inhibition of CRH gene promoter activity by some antipsychotic drugs may be a molecular mechanism responsible for their inhibitory action on HPA axis activity. Clozapine and chlorpromazine action on CRH activity operates mainly through activation of the PI3-K/Akt pathway. Moreover, PKC-mediated pathway seems to be involved in clozapine action on CRH gene activity.