Binding of [3H]triamcinolone acetonide to glucocorticoid receptors in brain cytosol fractions of rats with intact adrenals

Transcription factors and drugs in the brain

In mammalian cells, protein de novo synthesis is mainly regulated at the stage of gene transcription by RNA polymerase II in the nucleus. Transcription factors are proteins that bind to the specific nucleotide sequences at promoter or enhancer regions on target genes to control the transcription of mRNA from genomic DNA. In this article, we have outlined the signal responsiveness of different transcription factors to particular drugs in the brain. Nuclear transcription factors rapidly respond to a variety of extracellular signals carried by neurotransmitters, hormones and autacoids as a third messenger in frequent situations. Translated proteins are responsible for a number of physiological and pathological events for a long period in the brain. We have also discussed possible involvement of transcription factors in molecular mechanisms underlying development of tolerance and dependence to drugs following acute and chronic administration.

Consolidation of transient ionotropic glutamate signals through nuclear transcription factors in the brain

Long-lasting alterations of neuronal functions could involve mechanisms associated with consolidation of transient extracellular signals through modulation of de novo synthesis of particular functional proteins in the brain. In eukaryotes, protein de novo synthesis is mainly under the control at the level of gene transcription by transcription factors in the cell nucleus. Transcription factors are nuclear proteins with an ability to recognize particular core nucleotides at the upstream and/or downstream of target genes, and thereby to modulate the activity of RNA polymerase II that is responsible for the formation of mRNA from double stranded DNA. Gel retardation electrophoresis is widely employed for conventional detection of DNA binding activities of a variety of transcription factors with different protein motifs. Extracellular ionotropic glutamate (Glu) signals lead to rapid and selective potentiation of DNA binding of the nuclear transcription factor activator protein-1 (AP1) that is a homo- and heterodimeric complex between Jun and Fos family members, in addition to inducing expression of the corresponding proteins, in a manner unique to each Glu signal in murine hippocampus. Therefore, extracellular Glu signals may be differentially transduced into the nucleus to express AP1 with different assemblies between Jun and Fos family members, and thereby to modulate de novo synthesis of the individual target proteins at the level of gene transcription in the hippocampus. Such mechanisms may be operative on synaptic plasticity as well as delayed neuronal death through consolidation of alterations of a variety of cellular functions induced by transient extracellular signals in the brain.

Androgenic up-regulation of androgen receptor cDNA expression in androgen-independent prostate cancer cells

The expression of the androgen receptor (AR) gene is regulated by androgens. Although androgens down-regulate AR mRNA in most cell lines and tissues, including the prostate, up-regulation occurs in some tissues. Androgen-mediated reduction in AR mRNA is reproduced in COS1 cells and in the androgen-sensitive human prostate cancer cell line LNCaP when each expresses the AR cDNA. We have previously established that the AR cDNA contains the requisite sequences for this down-regulation. Here we shown that androgen promoted up-regulation of AR mRNA in two androgen-independent human prostate cancer cell lines, PC3 and DU145, when each was transfected with a human AR cDNA. This effect was due to the AR cDNA and not to the heterologous promoter driving AR expression. In addition to up-regulation of AR mRNA, androgen induced comparable increases in AR protein levels in PC3 cells stably expressing an AR cDNA (PC3/AR). Up-regulation of AR in PC3/AR cells was accompanied by failure of these cells to undergo desensitization or inactivation of AR following prolonged (96 h) androgen administration, whereas the same conditions resulted in desensitization of AR transactivation in LNCaP cells and in CVl cells that stably express the AR cDNA. Androgen treatment of PC3/AR cells resulted in induction of an androgen-regulated reporter gene (MMTV-CAT) as well as the native prostate-specific antigen gene, which is silent in untransfected PC3 but is androgen up-regulated in LNCaP and in the prostate. These results suggest that ectopic expression of AR in androgen-independent prostate cancer cell lines establishes both typical and atypical androgenic responses in a target gene-specific manner. Androgenic up-regulation of AR cDNA expression may be due to distinct signaling mechanisms that influence androgen action in androgen-independent prostate cancer cells.

Distinction between binding of [3H]triamcinolone acetonide to a ligand binding domain on the glucocorticoid receptor complex in cytosol fractions of brain and liver from the rat with intact adrenals

Binding of [3H]triamcinolone acetonide (TA) was examined to evaluate possible differences in biochemical and pharmacological profiles of a ligand binding domain on the naive glucocorticoid (GC) receptor complex between cytosol fractions of brain and liver obtained from the rat with intact adrenals. Unlabeled TA was 3-times less potent in displacing [3H]TA binding at equilibrium in the presence of Na2MoO4 at 2 degrees C in brain than in liver, while dexamethasone was more than 15-times more potent in displacing brain binding than liver binding. Both progesterone and aldosterone caused more than 20-times more potent displacement of [3H]TA binding in brain than in liver. However, zinc ions were effective in similarly inhibiting binding at equilibrium via lowering the affinity without affecting the density. In contrast to these experiments done at 2 degrees C, the addition of Na2MoO4 potentiated binding in brain and liver in a transient manner at 30 degrees C. Prolongation of incubation period from 30 min to 5 h induced a rightward shift of concentration-response curves of Na2MoO4 for [3H]TA binding at 30 degrees C in brain and liver in an irreversible fashion. The potentiation by Na2MoO4 was prevented by the addition of leupeptin but not 5 other protease inhibitors in brain cytosol fractions. Ion exchange chromatography revealed that elution profiles were entirely different from each other for [3H]TA binding between brain and liver cytosol fractions. These results suggest that GC receptors may respond to a variety of signals mediated by different steroid hormones through broader pharmacological spectrum of the ligand binding domain in brain than in liver.