Effects of neurosteroids on glucocorticoid receptor-mediated gene transcription in LMCAT cells - A possible interaction with psychotropic drugs

Aberrant activity of hypothatamic-pituitary-adrenal (HPA) axis is often observed in psychiatric disorders and both antidepressant and antipsychotic drugs are known to ameliorate some deleterious effects of glucocorticoids on brain function. Some neurosteroids possess antidepressant and neuroteptic-tike properties and attenuate the stress -activated HPA axis activity. However, intraceLlular mechanism of neurosteroid interaction with gtucocorticoids has not been elucidated. We evaluated effects of some neurosteroids on functional activity of glucocorticoid receptor (GR) in vitro. A combined treatment with antipsychotic drugs and involvement of some protein kinases in allopregnanolone effect on GR function were also studied. The effects of allopregnanolone, its two isomers (5 beta-pregnan-3 alpha-ol-20-one and 50.-pregnan-3 beta-ol-20-one) and dehydroepiandrosterone sulfate (DHEAS) on the corticosterone-induced chloramphenicol acetyl transferase (CAT) activity were evaluated in mouse fibroblast cells stably transfected with mouse mammary tumor virus (MMTV)-CAT plasmid. We found that allopregnanolone (1-100 mu M) and, to a lesser extent, both its isomers inhibited the GR-mediated gene transcription in a concentration -dependent manner. In contrast, DHEAS at the concentration up to 100 mu M was inactive. Further experiments revealed that allopregnanolone and antipsychotic drugs (chlorpromazine and clozapine) showed a moderate, additive inhibitory effect on the GR function. With respect to intracellular mechanism of atlopregnanolone action, we showed that this neurosteroid inhibited protein kinase C (PKC) activity, decreased the level of PKC alpha isoenzyme in the membrane fraction and decreased the amount of active phosphorylated form of extracellular signal - regulated kinase-mitogen -activated protein kinase (ERK-MAPK) in LMCAT cells. Since PKC and ERK-MAPK inhibitors attenuate the corticosterone- mediated gene transcription, the above findings suggest that attopregnanotone effect on GR function involves interaction with these kinase pathways. On the other hand, allopregnanolone had no effect on protein kinase A (PKA) activity. These data indicate that pregnanolone derivatives, like antidepressants and antipsychotic drugs, may attenuate some gtucocorticoid effects via inhibition of GR-mediated gene transcription. Furthermore, the inhibitory effect of allopregnanotone on the corticosterone-induced gene transcription in LMCAT cells depended on the inhibition of PKC and ERK-MAPK pathways. (c) 2006 Elsevier B.V. and ECNP. All rights reserved.