Modulation by vitamin B6 of glucocorticoid receptor-mediated gene expression requires transcription factors in addition to the glucocorticoid receptor

Neurotransmitters activate the human estrogen receptor in a neuroblastoma cell line

The human neuroblastoma cell line SK-N-SH has been used as a model system to study the interactions of the human estrogen receptor (hER) with neurotransmitters. We have successfully transfected these cells using an adenoviral delivery system and have reconstituted ligand-dependent responses to estradiol and ligand-independent responses to a series of dopamine D1 receptor agonists. The full agonist for the D1 receptor, SKF 82958, shows a robust activation of hER, comparable to that induced by estradiol. This activation is blocked by the protein kinase A inhibitor H-89, is mimicked by forskolin, and is therefore thought to be mediated in part through the cAMP/protein kinase A pathway. We have examined deletion mutants of hER for activation by SKF 82958 and find that both its transactivation domains, AF-1 and AF-2, must cooperate to impart the full response to the agonist. Significantly, an agonist of the muscarinic acetylcholine receptor, carbachol, though not active by itself, synergistically activates hER in conjunction with suboptimal doses of SKF 82958. This is the first reported instance of two neurotransmitters synergizing to activate a member of the nuclear receptor superfamily, and might predict a role for multiple neural inputs modulating the effects of these receptors in the central nervous system.

Analysis of chicken progesterone receptor function and phosphorylation using an adenovirus-mediated procedure for high-efficiency DNA transfer

The expression of heterologous DNA in mammalian cells is crucial to understanding physiological functions or determining biological properties of encoded proteins. However, expression for biological assay or at levels sufficient for recovery and subsequent physical analysis has been limited by the poor efficiency, variability, or cost of current DNA transfer methodologies. We have modified a DNA transfer procedure which exploits the capacity of replication-deficient adenovirus to infect a wide range of cell types, carrying with it transiently associated DNA. We have established conditions for achieving 80% transfection of CV1 cells and have used this procedure for DNA transfer into several mammalian cell lines and primary cell cultures. We have shown that biologically active avian progesterone receptor may be readily detected, both immunologically and functionally, using less than 1 ng of progesterone receptor-encoding plasmid DNA per 2 x 10(5) cells. We previously reported the identification of four phosphorylation sites in chicken progesterone receptor using oviduct tissue minces labeled with [32P]PO4 under nonequilibrium conditions. We now find, using adenovirus-mediated infection and equilibrium labeling conditions, that the same sites are phosphorylated in receptor expressed in CV1 cells and report that there are no additional major phosphorylation sites in chicken progesterone receptor. The ease, efficiency, sensitivity, and wide applicability of this DNA transfer method should simplify current efforts to study heterologous protein expression in mammalian cells.

Activation of the human androgen receptor through a protein kinase A signaling pathway

Aberrant activation of the androgen receptor through signaling pathways independent of androgen may be responsible for the progression of prostate tumors to the rapidly proliferating androgen-independent state. In this study, the effects of protein kinase A modulators on human androgen receptor activity were tested. Using an adenoviral DNA delivery system, we demonstrate that the androgen receptor can be activated by a protein kinase A activator, forskolin, in the absence of androgen when androgen receptor is co-transfected into monkey kidney CV1 cells or human prostate PC-3 cells with androgen-responsive reporters. Immunoblotting reveals that there is no significant change in androgen receptor protein level following forskolin treatment, suggesting that the enhanced activity is due to activation of the receptor. This activation can be blocked by a protein kinase A inhibitor peptide. Two potent anti-androgens, casodex and flutamide, can significantly reduce this activation, confirming that the ligand-independent pathway is an androgen receptor-mediated phenomenon. An intact DNA binding domain of the receptor is critical for this alternate signaling pathway since mutants with reduced DNA binding ability are inactive. The phosphorylation status of the androgen receptor or associated proteins may critically modulate receptor activity and should be considered when designing improved approaches to prostate cancer therapy.

Phosphorylation of Ser211 in the chicken progesterone receptor modulates its transcriptional activity

The chicken progesterone receptor has been shown to be phosphorylated in vivo at four major sites. Previous studies have shown that mutation of one of the hormone-dependent phosphorylation sites, Ser530, to alanine decreases the transcriptional activity of the receptor under conditions where ligand is limited. Here, we present evidence for the functional significance of another phosphorylation site, Ser211. Mutation of Ser211 to alanine results in a decrease in the transcriptional activity of the receptor and affects the phosphorylation-dependent decrease in mobility of the receptor in SDS-polyacrylamide gel electrophoresis. The degree of reduction in transcriptional activity is dependent on both the cell type and the reporters used in the studies but is independent of hormone concentration, suggesting that phosphorylation at Ser211 regulates the activity of the receptor through a mechanism distinct from Ser530 phosphorylation.

The human glucocorticoid receptor beta isoform. Expression, biochemical properties, and putative function

Alternative splicing of the human glucocorticoid receptor (hGR) primary transcript produces two receptor isoforms, hGRalpha and hGRbeta, which differ at their carboxyl termini. The hGRalpha isoform conveys endocrine information to target tissues by altering patterns of gene expression in a hormone-dependent fashion. In contrast to hGRalpha, very little is known about the hGRbeta splice variant. Using hGRalpha- and hGRbeta-specific riboprobes on human multiple tissue Northern blots, we show that the hGRbeta message has a widespread tissue distribution. We also prove by reverse transcriptase-polymerase chain reaction that the alternative splicing event underlying the formation of the hGRbeta message occurs in these tissues. Because the hGRbeta protein differs from hGRalpha at the extreme COOH terminus, we investigated several of the biochemical properties of hGRbeta expressed in transfected cells. hGRbeta does not bind the glucocorticoid agonist dexamethasone nor the glucocorticoid antagonist RU38486 in vivo. Moreover, in contrast to hGRalpha, hGRbeta is located primarily in the nucleus of transfected cells independent of hormone administration. Finally, in the absence of hGRalpha, hGRbeta is transcriptionally inactive on a glucocorticoid-responsive enhancer. However, when both isoforms are expressed in the same cell, hGRbeta inhibits the hormone-induced, hGRalpha-mediated stimulation of gene expression. Thus, hGRbeta potentially functions as a dominant negative inhibitor of hGRalpha activity.

The two faces of a steroid antagonist: when an antagonist isn't

Activation of protein kinase A potentiates the transcriptional response mediated by the glucocorticoid receptor in responsive fibroblasts and in mammary carcinoma cells. This potentiation is ligand-dependent and occurs in responsive fibroblasts and in mammary carcinoma cells. This potentiation is ligand-dependent and occurs without detectable change in the phosphorylation of receptor. The transcriptional response to glucocorticoid or progestin agonists can be blocked by potent antagonists like RU 486. However, upon activation of protein kinase A, the antagonist action of RU 486 on both receptors is blunted. Indeed, RU 486 can itself activate transcription of a hormone-responsive promoter. The conditional agonist activity is observed with type II antagonists, those which recapitulate many of the early steps of ligand-dependent receptor activation, but not type I antagonists, which do not. These studies have now been extended to antimineralocorticoids. In COS-1 cells transfected with a mineralocorticoid receptor expression vector, treatment with 8-BromocAMP potentiates the response to the agonist aldosterone and elicits additional agonist activity in mineralocorticoid antagonists. A model is proposed wherein type II antagonist-receptor complexes occupy receptor binding sites on the genome. The antagonist, however, fails to promote a receptor conformation that can interact productively with a coactivator mediating the communication between receptor and the basal transcription apparatus. Activation of protein kinase A results in the recruitment or activation of a coactivator that permits recovery of receptor-mediated activation function.(ABSTRACT TRUNCATED AT 250 WORDS)

Nitric oxide- and hydrogen peroxide-mediated gene expression by glucocorticoids and FK506 in histamine paw edema of mice

An immunosuppressant FK506 binds with a component (hsp 56) of glucocorticoid receptor (GR) complex. Dexamethasone (Dex) never suppressed histamine paw edema of mice before 1 hr after its dosing as new protein(s) synthesis is required. However, FK506 (0.01-10 mg/kg, oral) 1.5 hr before 0.1 mg/kg Dex (s.c.), suppressed edema at 30 min. This suppression and that at 3 hr, were abolished by nitric oxide (NO) synthesis inhibitors (1-300 mg/kg). Nitroprusside (NO donor), catalase and molybdate (GR complex stabilizing protease inhibitor) enhanced the suppression. FK506, not cyclosporin A, was demonstrated for the first time in vivo to enhance GR and a hypothesis is proposed that FK506 might enhance GR and AP-1 signalings in a system reciprocally controlled by NO and H2O2.