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 mM), haloperidol (0.5-5.0 mM), clozapine (1.0-5.0 mM), thioridazine (1.0-5.0 mM), promazine (5.0 and 10 mM), risperidone (5.0 and 10.0 mM), and raclopride (only at the highest used concentrations, ie 30 and 100 mM) 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 mM), haloperidol (1.0-5.0 mM), clozapine (1.0-5.0 mM), thioridazine (3.0 and 5.0 mM), and raclopride (30 and 100 mM), 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 mM), 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-3b 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 mM). 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.
Major depression is frequently associated with hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis. Clinically effective therapy with antidepressant drugs normalizes the disturbed activity of HPA axis, in part, by decreasing corticotropin-releasing hormone (CRH) synthesis, but the mechanism of this action is poorly recognized. In order to find out whether antidepressants directly affect CRH gene promoter activity, we studied their effect on undifferentiated and differentiated Neuro-2A cells, and for comparison the effect of the selected antidepressants on AtT-20 cells was also determined. The cells were stably transfected with a human CRH promoter fragment (À663 to þ 124 bp) linked to the chloramphenicol acetyltransferase (CAT) reporter gene. The regulation of CRH gene promoter activity is similar in Neuro-2A cells, both intact and differentiated, and in AtT-20 cell line, and cAMP/PKA-dependent pathway plays an important role in the stimulation of CRH gene. It was found that imipramine, amitryptyline, desipramine, fluoxetine, and mianserin, present in the culture medium for 5 days, in a concentration-dependent manner inhibited basal hCRH gene promoter activity in undifferentiated Neuro-2A cells, while other drugs under study (citalopram, tianeptine, moclobemide, venlafaxine, reboxetine, mirtazapine, and milnacipram) were inactive. In the differentiated cells, all examined antidepressants, except moclobemide (no effect) and tianeptine (increase), inhibited hCRH gene transcription. Moreover, in differentiated cells, the drugs acted stronger and were effective at lower concentrations. Forskolin-induced CAT activity was attenuated by imipramine and fluoxetine and to a lesser degree by amitriptyline and desipramine in differentiated cells, whereas other drugs were inactive. Moreover, imipramine and fluoxetine, but not tianeptine, showed moderate inhibitory effect on CRH gene promoter activity also in AtT-20 cell line, commonly used in CRH gene regulation studies. These results indicate that neuron-like differentiated Neuro-2A cells are a better model than pituitary and intact neuroblastoma to investigate the mechanism of psychotropic drug action. Inhibition of CRH gene promoter activity by antidepressant drugs may be a molecular mechanism by which these drugs inhibit the activity of HPA axis.
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