Steroid-independent translocation of the glucocorticoid receptor by the antidepressant desipramine.

The glucocorticoid receptor (GR) is a ligand-regulated transcription factor that in its unactivated form resides primarily in the cytoplasm. After being bound by steroid, the GR undergoes a conformational change and translocates to the nucleus, where it influences gene transcription. Because the GR mediates negative feedback exerted by circulating glucocorticoid hormones on the hypothalamic-pituitary-adrenal (HPA) axis, it has been hypothesized that abnormalities in GR expression and/or function may underlie the HPA axis hyperactivity described in patients with major depression. In further support of this hypothesis, animal studies have shown that long term in vivo treatment with antidepressants enhances glucocorticoid feedback inhibition, possibly through a direct effect on the GR. To examine this latter possibility, we evaluated translocation of the GR from the cytoplasm to the nucleus after 24-hr in vitro treatment of L929 cells (mouse fibroblasts) with the tricyclic antidepressant desipramine (0.1-10 microM) in the presence or absence of the synthetic steroid dexamethasone. In addition, GR-mediated gene transcription was measured with the use of L929 cells stably transfected with the mouse mammary tumor virus-chloramphenicol acetyltransferase reporter gene. Desipramine was found to (i) induce GR translocation from the cytoplasm to the nucleus in the absence of steroids (with no effect alone on GR-mediated gene transcription) and (ii) potentiate dexamethasone-induced GR translocation and dexamethasone-induced GR-mediated gene transcription. Treatment with desipramine for 24-96 hr had no effect on the expression of GR protein as measured by cytosolic radioligand receptor binding. We suggest that one important aspect of the effects of antidepressants in vivo may be to facilitate GR-mediated feedback inhibition on the HPA axis, by facilitating GR translocation and function, and thereby reverse glucocorticoid hypersecretion in depression.