Alteration of the glucocorticoid receptor subcellular localization by non steroidal compounds

Sensory nerves directly promote osteoclastogenesis by secreting peptidyl-prolyl cis-trans isomerase D (Cyp40)

Given afferent functions, sensory nerves have recently been found to exert efferent effects and directly alter organ physiology. Additionally, several studies have highlighted the indirect but crucial role of sensory nerves in the regulation of the physiological function of osteoclasts. Nonetheless, evidence regarding the direct sensory nerve efferent influence on osteoclasts is lacking. In the current study, we found that high levels of efferent signals were transported directly from the sensory nerves into osteoclasts. Furthermore, sensory hypersensitivity significantly increased osteoclastic bone resorption, and sensory neurons (SNs) directly promoted osteoclastogenesis in an in vitro coculture system. Moreover, we screened a novel neuropeptide, Cyp40, using an isobaric tag for relative and absolute quantitation (iTRAQ). We observed that Cyp40 is the efferent signal from sensory nerves, and it plays a critical role in osteoclastogenesis via the aryl hydrocarbon receptor (AhR)-Ras/Raf-p-Erk-NFATc1 pathway. These findings revealed a novel mechanism regarding the influence of sensory nerves on bone regulation, i.e., a direct promoting effect on osteoclastogenesis by the secretion of Cyp40. Therefore, inhibiting Cyp40 could serve as a strategy to improve bone quality in osteoporosis and promote bone repair after bone injury.

Adrenal insufficiency is common amongst kidney transplant recipients receiving maintenance prednisolone and can be predicted using morning cortisol

BACKGROUND

Long-term glucocorticoid therapy is a key component of immunosuppression for kidney transplant recipients (KTRs), leading to significant cumulative glucocorticoid exposure. The aims of this study are to investigate the prevalence of adrenal insufficiency (AI) in KTRs taking prednisolone and to develop a screening algorithm to identify patients at the highest risk of AI.

METHODS

In this cross-sectional cohort study, 67 KTRs receiving prednisolone underwent a short synacthen test (SST) and measurement of cumulative glucocorticoid exposure.

RESULTS

A total of 72% (n = 48) of participants failed the SST. Participants with AI had a higher daily prednisolone dose (4.9 versus 4.2 mg/day; P = .002) and greater cumulative glucocorticoid exposure (289 versus 111 mg/kg; P = .03) than those with intact adrenal function. Participants with AI had lower baseline cortisol than participants with intact adrenal function (143 versus 303 nmol/L; P < .001). Morning cortisol of >288 nmol/L predicted a normal SST with 100% specificity [95% confidence interval (CI) 92-100] and 70% sensitivity (95% CI 56-78%), therefore excluding AI.

CONCLUSIONS

Our results suggest KTRs are at a higher risk for AI than previously reported. A morning serum cortisol measurement is a useful screening tool in this cohort, reducing the need for stimulatory testing by 44%. KTRs with AI need education regarding glucocorticoid sick rules, similar to patients with other forms of AI.

Characterization of β-Sitosterol for Potential Selective GR Modulation

BACKGROUND

Although glucocorticoids (GCs) are characterized as powerful agents to treat inflammatory afflictions, they are accompanied by metabolic side effects which limit their usage. β-Sitosterol, as a minor component found in extraction of vegetable oil, was reported to have anti-inflammatory effects in RAW 264.7 cells.

OBJECTIVE

To test whether β-sitosterol has an effect to dissociate transrepression from transactivation as a selective novel GR binder, this work evaluated the dissociated characteristics of β-sitosterol.

METHODS

The probable binding interaction between β-sitosterol and GR was explored by molecular docking. The GR transcriptional activity of β-sitosterol was assessed in the reporter gene assay. The ability of β-sitosterol to modulate the transactivation and transrepression of GR was evaluated by real-time quantitative PCR analysis.

RESULTS AND DISCUSSION

In the present study, β-sitosterol treatment cannot induce GR-mediated transactivation. β-Sitosterol exerted a potential to inhibited the expression of GR target transrepressed gene without activating the expression of GR transactivation dependent gene. Molecular docking demonstrated that β-Sitosterol was able to bind the ligand binding domain of GR but unable to induce GR activation.

CONCLUSION

This work offers evidence that β-sitosterol may serve as a selective GR modulator.

Regulation of FKBP51 and FKBP52 functions by post-translational modifications

FKBP51 and FKBP52 are two iconic members of the family of peptidyl-prolyl-(cis/trans)-isomerases (EC: 5.2.1.8), which comprises proteins that catalyze the cis/trans isomerization of peptidyl-prolyl peptide bonds in unfolded and partially folded polypeptide chains and native state proteins. Originally, both proteins have been studied as molecular chaperones belonging to the steroid receptor heterocomplex, where they were first discovered. In addition to their expected role in receptor folding and chaperoning, FKBP51 and FKBP52 are also involved in many biological processes, such as signal transduction, transcriptional regulation, protein transport, cancer development, and cell differentiation, just to mention a few examples. Recent studies have revealed that both proteins are subject of post-translational modifications such as phosphorylation, SUMOlyation, and acetylation. In this work, we summarize recent advances in the study of these immunophilins portraying them as scaffolding proteins capable to organize protein heterocomplexes, describing some of their antagonistic properties in the physiology of the cell, and the putative regulation of their properties by those post-translational modifications.

Potential Dissociative Glucocorticoid Receptor Activity for Protopanaxadiol and Protopanaxatriol

Glucocorticoids are steroid hormones that regulate inflammation, growth, metabolism, and apoptosis via their cognate receptor, the glucocorticoid receptor (GR). GR, acting mainly as a transcription factor, activates or represses the expression of a large number of target genes, among them, many genes of anti-inflammatory and pro-inflammatory molecules, respectively. Transrepression activity of glucocorticoids also accounts for their anti-inflammatory activity, rendering them the most widely prescribed drug in medicine. However, chronic and high-dose use of glucocorticoids is accompanied with many undesirable side effects, attributed predominantly to GR transactivation activity. Thus, there is a high need for selective GR agonist, capable of dissociating transrepression from transactivation activity. Protopanaxadiol and protopanaxatriol are triterpenoids that share structural and functional similarities with glucocorticoids. The molecular mechanism of their actions is unclear. In this study applying induced-fit docking analysis, luciferase assay, immunofluorescence, and Western blot analysis, we showed that protopanaxadiol and more effectively protopanaxatriol are capable of binding to GR to activate its nuclear translocation, and to suppress the nuclear factor-kappa beta activity in GR-positive HeLa and HEK293 cells, but not in GR-low level COS-7 cells. Interestingly, no transactivation activity was observed, whereas suppression of the dexamethasone-induced transactivation of GR and induction of apoptosis in HeLa and HepG2 cells were observed. Thus, our results indicate that protopanaxadiol and protopanaxatriol could be considered as potent and selective GR agonist.

A Quantitative Study of Internal and External Interactions of Homodimeric Glucocorticoid Receptor Using Fluorescence Cross-Correlation Spectroscopy in a Live Cell

Glucocorticoid receptor (GRα) is a well-known ligand-dependent transcription-regulatory protein. The classic view is that unliganded GRα resides in the cytoplasm, relocates to the nucleus after ligand binding, and then associates with a specific DNA sequence, namely a glucocorticoid response element (GRE), to activate a specific gene as a homodimer. It is still a puzzle, however, whether GRα forms the homodimer in the cytoplasm or in the nucleus before DNA binding or after that. To quantify the homodimerization of GRα, we constructed the spectrally different fluorescent protein tagged hGRα and applied fluorescence cross-correlation spectroscopy. First, the dissociation constant (K_d) of mCherry₂-fused hGRα or EGFP-fused hGRα was determined in vitro. Then, K_d of wild-type hGRα was found to be 3.00 μM in the nucleus, which was higher than that in vitro. K_d of a DNA-binding-deficient mutant was 3.51 μM in the nucleus. This similarity indicated that GRα homodimerization was not necessary for DNA binding but could take place on GRE by means of GRE as a scaffold. Moreover, cytoplasmic homodimerization was also observed using GRα mutated in the nuclear localization signal. These findings support the existence of a dynamic monomer pathway and regulation of GRα function both in the cytoplasm and nucleus.

Solubility-promoting function of Hsp90 contributes to client maturation and robust cell growth

The Hsp90 chaperone is required for the maturation of signal transduction clients, including many kinases and nuclear steroid hormone receptors. The binding and hydrolysis of ATP by Hsp90 drive conformational rearrangements in three structure domains. Two intrinsically disordered regions of Hsp90 located between these domains and at the C terminus have traditionally been considered to impart flexibility. We discovered that the charged nature of these acid-rich disordered regions imparts a solubility-promoting function to Hsp90 that is important for its cellular activity in yeast. Both the solubility-promoting function and ATPase activity must occur in the same Hsp90 molecule in order to support robust growth, suggesting that the solubility-promoting function is required during the ATP-driven client maturation process. Expression of model clients together with Hsp90 variants indicated interdependent solubilities mediated by the aggregation propensities of both the client and Hsp90. We propose a model whereby the charge-rich disordered regions of Hsp90 serve a solubility-promoting function important for complexes with aggregation-prone clients. These findings demonstrate a novel biological function of the intrinsically disordered regions in Hsp90 and provide a compelling rationale for why their charged properties are conserved throughout eukaryotic evolution.

Fluorescent protein-labeled glucocorticoid receptor alpha isoform trafficking in cultured human trabecular meshwork cells

PURPOSE

To characterize the roles of the cytoskeleton and heat shock protein 90 (HSP90) in steroid-induced glucocorticoid receptor alpha (GRα) translocation in cultured human trabecular meshwork cells.

METHODS

Stably transfected red fluorescent protein (RFP)-GRα NTM5 cell lines were developed. Nuclear localization of RFP-GRα in NTM5 cells treated with vehicle (ethanol), dexamethasone (DEX), or RU486 was measured in cytosolic and nuclear fractions by western blotting and laser confocal microscopy. Cytochalasin D, colchicine, and 17-demethoxygeldanamycin (17AAG, an HSP90 inhibitor), were tested for their abilities to affect GRα trafficking. Nuclear export of RFP-GRα was studied using confocal microscopy following DEX or RU486 removal.

RESULTS

NTM5 cells transfected with RFP-GRα showed a clear cytosolic localization of receptor that underwent nuclear localization after DEX treatment. RFP-GRα translocation was temperature sensitive, occurring at 37°C but not at room temperature. Neither cytochalasin D nor colchicine blocked DEX-induced or RU486-induced RFP-GRα nuclear translocation; however, 17AAG prevented DEX-induced RFP-GRα nuclear translocation. Both nuclear import and export of DEX-induced RFP-GRα were faster than RU-486-induced nuclear shuttling.

CONCLUSIONS

RFP-GRα receptor behaves similarly to the wild-type GRα with its cytosolic localization and shuttling to nucleus after DEX or RU486 treatment. HSP90 is required for nuclear translocation, but the disruption of cytoskeleton had no effect on nuclear translocation of RFP-GRα.

Prospective controlled protocol for three months steroid withdrawal with tacrolimus, basiliximab, and mycophenolate mofetil in renal transplant recipients

During the past few years, new immunosuppressants, such as tacrolimus, mycophenolate mofetil (MMF) and basiliximab, have been shown to successfully decrease the incidence of acute rejection, possibly acting as potent substrates for safe steroid withdrawal. Therefore, clinical outcome of 3 months steroid withdrawal, while using the above immunosuppressants, was analyzed. Clinical trial registry No. was NCT 01550445. Thirty de novo renal transplant recipients were enrolled, and prednisolone was slowly withdrawn 3 months post-transplantation by 2.5 mg at every two weeks, until 8 weeks. During steroid withdrawal, 10 patients (30.0%) discontinued the protocol and they were maintained on steroid treatment. Among 20 steroid free patients, 8 patients (40.0%) re-started the steroid within 12 months post-transplantation. By the study endpoint, 12 (40%) recipients did not take steroid and survival of patients and grafts was 100%. In conclusion, in kidney transplant patients, 3 months steroid withdrawal while taking tacrolimus, basiliximab and mycophenolate mofetil was not associated with increased mortality or graft loss. Despite various causes of failure of steroid withdrawal during the follow-up period, it is a strategy well advised for kidney transplant recipients with regard to long-term steroid-related complications.

Macromolecular synthesis inhibitors perturb glucocorticoid receptor trafficking

The ability of inhibitors of transcription and translation to prevent glucocorticoid-induced apoptosis has been interpreted to indicate that the cell death machinery requires de novo protein synthesis. The transcriptional inhibitors actinomycin D (Act D) and DRB as well as the translational inhibitors CHX and puromycin inhibited early loss of mitochondrial membrane integrity in a dose-dependent manner. This effect was not observed with the transcriptional inhibitor α-amanitin suggesting they may have additional effects. Their role in the glucocorticoid receptor (GR) intracellular trafficking was therefore investigated. Here, we show that Act D and CHX reduced glucocorticoid binding, GR turnover and impaired GR nuclear translocation. We performed the same experiments in different thymocyte subpopulations of Balb/c mice. At the highest dose tested, actinomycin D and cycloheximide abolished glucocorticoid-induced cell death of CD4+CD8+ and CD4+CD8-. In all subsets, Act D, DRB, as well as CHX and puromycin prevented receptor nuclear translocation, indicating a general alteration of GR trafficking. Overall, our data support a direct effect of macromolecular inhibitors on GR activation and trafficking. Finally, direct alterations of the functional properties of the glucocorticoid receptor might be responsible for cell death prevention by actinomycin D, DRB, cycloheximide and puromycin.

7-oxysterols modulate glucocorticoid activity in adipocytes through competition for 11beta-hydroxysteroid dehydrogenase type

Obesity is associated with an increased risk of diabetes type 2, dyslipidemia, and atherosclerosis. These cardiovascular and metabolic abnormalities are exacerbated by excessive dietary fat, particularly cholesterol and its metabolites. High adipose tissue glucocorticoid levels, generated by the intracellular enzyme 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1), are also implicated in the pathogenesis of obesity, metabolic syndrome, and atherosclerosis. 11beta-HSD1 also interconverts the atherogenic oxysterols 7-ketocholesterol (7KC) and 7beta-hydroxycholesterol (7beta-HC). Here, we report that 11beta-HSD1 catalyzes the reduction of 7KC to 7beta-HC in mature 3T3-L1 and 3T3-F442A adipocytes, leading to cellular accumulation of 7beta-HC. Approximately 73% of added 7KC was reduced to 7beta-HC within 24 h; this conversion was prevented by selective inhibition of 11beta-HSD1. Oxysterol and glucocorticoid conversion by 11beta-HSD1 was competitive and occurred with a physiologically relevant IC(50) range of 450 nm for 7KC inhibition of glucocorticoid metabolism. Working as an inhibitor of 11beta-reductase activity, 7KC decreased the regeneration of active glucocorticoid and limited the process of differentiation of 3T3-L1 preadipocytes. 7KC and 7beta-HC did not activate liver X receptor in a transactivation assay, nor did they display intrinsic activation of the glucocorticoid receptor. However, when coincubated with glucocorticoid (10 nm), 7KC repressed, and 7beta-HC enhanced, glucocorticoid receptor transcriptional activity. The effect of 7-oxysterols resulted from the modulation of 11beta-HSD1 reaction direction, and could be ameliorated by overexpression of hexose 6-phosphate dehydrogenase, which supplies reduced nicotinamide adenine dinucleotide phosphate to 11beta-HSD1. Thus, the activity and reaction direction of adipose 11beta-HSD1 is altered under conditions of oxysterol excess, and could impact upon the pathophysiology of obesity and its complications.

In vitro modulation of the glucocorticoid receptor by antidepressants

Clinical studies have demonstrated an impairment of glucocorticoid receptor (GR)-mediated negative feedback on the hypothalamus-pituitary-adrenal (HPA) axis in patients with major depression (GR resistance), and its resolution by antidepressant treatment. Accordingly, reduced GR function has also been demonstrated in vitro, in peripheral tissues of depressed patients, as shown by reduced sensitivity to the effects of glucocorticoids on immune and metabolic functions. We and others have shown that antidepressants in vitro are able to modulate GR mRNA expression, GR protein level and GR function. This paper reviews the in vitro studies that have examined the effect of antidepressants on GR expression, number and function in human and animal cell lines, and the possible molecular mechanisms underlying these effects. Antidepressants are shown to both increase and decrease GR function in vitro, based on different experimental conditions. Specifically, increased GR function is likely to be mediated by an increased intracellular concentration of glucocorticoids, while decreased GR function seems to be the consequence of GR downregulation. We suggest that the study of the effects of antidepressants on glucocorticoid function might help clarify the therapeutic action of these drugs.

Heat shock protein 90 acts as a molecular chaperone in late-phase activation of extracellular signal-regulated kinase 1/2 stimulated by oxidative stress in vascular smooth muscle cells

AIM

To investigate whether cytosolic heat shock protein 90 (HSP90) acts as a molecular chaperone on the activated extracellular signal-regulated kinase 1/2 (ERK1/2) and cell proliferation stimulated by reactive oxygen species (ROS) in rat vascular smooth muscle cells (VSMC).

METHODS

VSMC were exposed to 1 micromol/L LY83583 (6-anilinoquinoline-5,8-quinolinedione, producer of ROS) for 120 min in the presence or absence of 5 micromol/L geldanamycin, a specific inhibitor of HSP90. Then the total, soluble, and insoluble proteins of the cells were collected. HSP90, ERK1/2, and phosphor-ERK1/2 in the cell lysate were measured by Western blotting. The interaction of HSP90 and phosphor-ERK1/2 was analyzed by immunoprecipitation assay, and the nuclear phosphor-ERK1/2 was measured by Western blotting and immunofluorescence. Cell proliferation was tested by cell counting and 3-(4,5-dimethylthiazol-2-y1)-3,5-di-phenyltetrazolium bromide (MTT).

RESULTS

The cytosolic HSP90 of VSMC was upregulated by LY83583 in a time-dependent manner with the peak at 120 min, which is consistent with the late peak of phosphor-ERK1/2. Immunoprecipitation and Western blotting analyses showed that LY83583 increased the interaction of HSP90 with phosphor-ERK1/2, the phosphor-ERK1/2 level, and the soluble phosphor-ERK1/2 level by 1.8-, 2.5-, and 2.9-fold, respectively. In contrast, the insoluble phosphor-ERK1/2 of VSMC was decreased. Interestingly, LY83583 treatment promoted the nuclear phosphor-ERK1/2 by 7.6-fold as confirmed by Western blotting and immunofluorescence assays. Furthermore, cell counting and the MTT assay showed that LY83583 stimulated VSMC proliferation with the increased expression of HSP90 and levels of soluble and nuclear phosphor-ERK1/2. Pretreatment of geldanamycin antagonized the effect of LY83583.

CONCLUSION

HSP90 could mediate the oxidative stress-stimulated, late-phase activation of ERK1/2 and VSMC proliferation by promoting the ERK1/2 phosphorylation, the association of itself with phosphor-ERK1/2, and the solubility and nuclear translocation of phosphor-ERK1/2.

Function of nuclear steroid receptors in apoptosis: role of ursodeoxycholic acid

Nuclear steroid receptors such as the glucocorticoid and the mineralocorticoid receptors modulate apoptosis in different cell types through transactivation-dependent and -independent mechanisms. They are involved in both the induction and prevention of apoptosis depending on cell type. However, it is unclear how nuclear steroid receptors can affect expression of the same gene in opposing ways for different cells. In addition to their function as modulators of gene expression, nuclear steroid receptors often act as nuclear transporters of other regulatory molecules, thus indirectly regulating several apoptosis-related genes. Curiously, nuclear steroid receptors are thought to cooperate with the antiapoptotic endogenous bile acid, ursodeoxycholic acid, to prevent programmed cell death. The next decade will almost certainly unveil the remarkable role of nuclear steroid receptors in modulating the life and death struggle of cells and organ systems in human development and function.

The core component of the mammalian SWI/SNF complex SMARCD3/BAF60c is a coactivator for the nuclear retinoic acid receptor

Retinoic acid receptors (RARs) activate transcription by recruiting coactivator complexes such as histone acetyltransferases (HAT) and the mediator complex, to increase chromatin accessibility by general transcription factors and to promote transcription initiation. Indirect evidences have suggested a role for the ATP-dependent chromatin remodeling complex SWI/SNF in RAR-mediated transcription. Here we demonstrate that two highly related subunits of the core SWI/SNF complex, BAF60c1 and BAF60c2, interact physically with retinoid receptors and are coactivators for RARs. This coactivating property is dependent on SRC1 expression, showing that HATs and SWI/SNF cooperate in this retinoid-controlled transcriptional process.

Phosphorylation of a conserved serine in the deoxyribonucleic acid binding domain of nuclear receptors alters intracellular localization

Nuclear receptors (NRs) are a superfamily of transcription factors whose genomic functions are known to be activated by lipophilic ligands, but little is known about how to deactivate them or how to turn on their nongenomic functions. One obvious mechanism is to alter the nuclear localization of the receptors. Here, we show that protein kinase C (PKC) phosphorylates a highly conserved serine (Ser) between the two zinc fingers of the DNA binding domain of orphan receptor hepatocyte nuclear factor 4alpha (HNF4alpha). This Ser (S78) is adjacent to several positively charged residues (Arg or Lys), which we show here are involved in nuclear localization of HNF4alpha and are conserved in nearly all other NRs, along with the Ser/threonine (Thr). A phosphomimetic mutant of HNF4alpha (S78D) reduced DNA binding, transactivation ability, and protein stability. It also impaired nuclear localization, an effect that was greatly enhanced in the MODY1 mutant Q268X. Treatment of the hepatocellular carcinoma cell line HepG2 with PKC activator phorbol 12-myristate 13-acetate also resulted in increased cytoplasmic localization of HNF4alpha as well as decreased endogenous HNF4alpha protein levels in a proteasome-dependent fashion. We also show that PKC phosphorylates the DNA binding domain of other NRs (retinoic acid receptor alpha, retinoid X receptor alpha, and thyroid hormone receptor beta) and that phosphomimetic mutants of the same Ser/Thr result in cytoplasmic localization of retinoid X receptor alpha and peroxisome proliferator-activated receptor alpha. Thus, phosphorylation of this conserved Ser between the two zinc fingers may be a common mechanism for regulating the function of NRs.

Targeting of the glucocorticoid hormone receptor with plasmid DNA comprising glucocorticoid response elements improves nonviral gene transfer efficiency in the lungs of mice

BACKGROUND

It has been previously demonstrated that plasmid DNA transport into the nucleus could be increased by transcription factor binding. We chose the glucocorticoid responsive element (GRE) which binds to the glucocorticoid receptor (GR), a transcription factor which is shuttled into the nucleus upon ligand binding such as dexamethasone.

METHODS

We cloned two, four, and eight repetitive sequences of the GRE into the reporter plasmid pEGFPLuc. Binding of the pEGFPLuc-GRE to the GR was examined by electrophoretic mobility shift assay (EMSA) experiments. GR expression in bronchiolar and alveolar epithelial cells was confirmed by Western blotting. Intracellular trafficking of GR was examined using a fusion protein of cyano-fluorescent protein (CFP) and GR. Transfection efficiencies of pEGFPLuc compared to pEGFPLucGRE(2-8) were examined in vitro and in vivo upon tail vein injection of cationic liposome gene vectors containing dexamethasone (safeplexes) and aerosol application of polyethylenimine (PEI)-pDNA particles.

RESULTS

Binding of GRE containing plasmids to the GR was shown in EMSA experiments and intranuclear shuttling of CFP-GR after ligand stimulation was confirmed. Enhanced gene transfer efficiency of pEGFPLucGRE(2) in vitro was only observed on confluent cells. A 2.5-fold increase in gene expression in the lungs of mice after tail vein injection of pEGFPLucGRE(2) complexed with safeplexes compared with pEGFPLuc was observed. PEI-mediated aerosol gene delivery of pEGFPLucGRE(2) was 4.7-fold higher than pEGFPLuc only after intraperitoneal dexamethasone.

CONCLUSION

The results suggest that inclusion of GRE sequences into plasmid DNA vectors combined with dexamethasone application could improve transgene expression in the lungs in vivo.

Unliganded and hormone-bound glucocorticoid receptors interact with distinct hydrophobic sites in the Hsp90 C-terminal domain

Unlike most chaperones, heat-shock protein 90 (Hsp90) interacts with a select group of "client proteins" that regulate essential biological processes. Little is known about how Hsp90 recognizes and binds these proteins. The glucocorticoid receptor (GR) is a well characterized Hsp90 client protein, whose hormone binding, nuclear-cytoplasmic trafficking, and transcriptional activity are regulated by Hsp90. Here, we provide evidence that unliganded and hormone-bound GR interact with two distinct, solvent-exposed hydrophobic sites in the Hsp90 C-terminal domain that contain the sequences "MxxIM" (HM10) and "L/MxxIL" (HM9). Our results indicate that binding of Hsp90 HM10 to unliganded GR stabilizes the unliganded ligand-binding pocket of GR indirectly by promoting an intramolecular interaction between the C-terminal alpha-helix (H12) and a solvent-exposed hydrophobic groove in the GR ligand binding domain. In the presence of hormone, Hsp90 appears to bind the hydrophobic groove of GR directly by mimicking the interactions of GR with transcriptional coactivators. The identified interactions provide insights into the mechanisms that enable Hsp90 to regulate the activity of both unliganded and hormone-bound GR and to sharpen the cellular response to hormone.

Functional Modulation of Nuclear Steroid Receptors by Tauroursodeoxycholic Acid Reduces Amyloid β-Peptide-Induced Apoptosis

Tauroursodeoxycholic acid (TUDCA) prevents amyloid beta-peptide (Abeta)-induced neuronal apoptosis, by modulating both classical mitochondrial pathways and specific upstream targets. In addition, activation of nuclear steroid receptors (NSRs), such as the mineralocorticoid receptor (MR) and the glucocorticoid receptor (GR) differentially regulates apoptosis in the brain. In this study we investigated whether TUDCA, a cholesterol-derived endogenous molecule, requires NSRs for inhibiting Abeta-induced apoptosis in primary neurons. Our results confirmed that TUDCA significantly reduced Abeta-induced apoptosis; in addition, the fluorescently labeled bile acid molecule was detected diffusely in both cytoplasm and nucleus of rat cortical neurons. Interestingly, experiments using small interfering RNAs (siRNAs) revealed that, in contrast to GR siRNA, MR siRNA abolished the antiapoptotic effect of TUDCA. Abeta incubation reduced MR nuclear translocation while increasing nuclear GR levels. Notably, pretreatment with TUDCA markedly altered Abeta-induced changes in NSRs, including MR dissociation from its cytosolic chaperone, heat shock protein 90, and subsequent translocation to the nucleus. Furthermore, when a carboxy terminus-deleted form of MR was used, nuclear trafficking of both MR and the bile acid was abrogated, suggesting that they translocate to the nucleus as a steroid-receptor complex. Transfection experiments with wild-type or mutant MR confirmed that this interaction was required for TUDCA protection against Abeta-induced apoptosis. Finally, in cotransfection experiments with NSR response element reporter and overexpression constructs, pretreatment with TUDCA significantly modulated Abeta-induced changes in MR and GR transactivation. In conclusion, these results provide novel insights into the specific cellular mechanism of TUDCA antiapoptotic function against Abeta-induced apoptosis and suggest targets for potential therapeutic intervention.

Nanoscale intracellular organization and functional architecture mediating cellular behavior

Cells function based on a complex set of interactions that control pathways resulting in ultimate cell fates including proliferation, differentiation, and apoptosis. The inter-workings of this immensely dense network of intracellular molecules are influenced by more than random protein and nucleic acid distribution where their interactions culminate in distinct cellular function. By probing the design of these biological systems from an engineering perspective, researchers can gain great insight that will aid in building and utilizing systems that are on this size scale where traditional large-scale rules may fail to apply. The organized interaction and gradient distribution in intracellular space imply a structural architecture that modulates cellular processes by influencing biochemical interactions including transport and binding-reactions. One significant structure that plays a role in this modulation is the cell cytoskeleton. Here, we discuss the cytoskeleton as a central and integrating functional structure in influencing cell processes and we describe technology useful for probing this structure. We explain the nanometer scale science of cytoskeletal structure with respect to intracellular organization, mechanotransduction, cytoskeletal-associated proteins, and motor molecules, as well as nano- and microtechnologies that are applicable for experimental studies of the cytoskeleton. This biological architecture of the cytoskeleton influences molecular, cellular, and physiological processes through structured multimodular and hierarchical principles centered on these functional filaments. Through investigating these organic systems that have evolved over billions of years, understanding in biology, engineering, and nanometer-scaled science will be advanced.

Mechanisms of glucocorticoid-induced apoptosis in hematologic malignancies: updates

PURPOSE OF REVIEW

Glucocorticoids remain a central component of the therapeutic armamentarium for a broad spectrum of hematologic malignancies. There is an extensive body of evidence suggesting that the efficacy of glucocorticoids stems from their ability to mediate apoptosis in leukemia, lymphoma, and myeloma cells.

RECENT FINDINGS

Traditionally, glucocorticoid-induced apoptosis is divided into three stages: an initiation stage, which involves glucocorticoid receptor activation and glucocorticoid receptor-mediated gene regulation; a decision stage, which engages the prosurvival and proapoptotic factors at the mitochondrial level; and an execution stage, which implicates caspases and endonuclease activation. Recent discoveries have clarified many aspects of the apoptotic pathway, including activation of the caspases cascade and multicatalytic proteasome, suppression of prosurvival transcription factors such as AP-1, c-myc, nuclear factor-kappaB, as well as cross-talk between the T-cell receptor and cytokine signaling pathways.

SUMMARY

This review focuses primarily on insights gained during recent years into the mechanism of the signaling pathways responsible for mediating glucocorticoid-induced apoptosis in hematologic malignancies. This information provides a scientific basis to explore synergistic approaches that may enhance glucocorticoid-induced apoptosis and may bypass mechanism of resistance.

Modulation of nuclear steroid receptors by ursodeoxycholic acid inhibits TGF-beta1-induced E2F-1/p53-mediated apoptosis of rat hepatocytes

We have recently shown that both ursodeoxycholic acid (UDCA) and tauroursodeoxycholic acid (TUDCA) prevent transforming growth factor beta1 (TGF-beta1)-induced hepatocyte apoptosis by modulating the E2F-1/p53/Bax pathway. In addition, activation of glucocorticoid (GR) and mineralocorticoid receptors (MR) inhibits apoptosis in various systems. UDCA induces a ligand-independent activation of the GR, thus potentially regulating a number of targets. In this study, we investigated the role of GR and MR during TGF-beta1-induced hepatocyte apoptosis, and identified additional antiapoptotic targets for UDCA. Our results showed that in primary hepatocytes, TGF-beta1 induced 40-50% decreases in gr and mr mRNA expression (p < 0.01), together with up to 10-fold reductions in their protein levels (p < 0.01). Notably, pretreatment with UDCA resulted in a significant upregulation of nuclear steroid receptors (p < 0.05), which coincided with 2- and 3-fold increases in the level of GR and MR nuclear translocation, respectively, when compared with that of TGF-beta1 alone (p < 0.05). Similarly, TUDCA induced GR and MR nuclear translocations (p < 0.05) and markedly prevented MR protein changes associated with TGF-beta1 (p < 0.05) without affecting GR protein levels. Moreover, when interference RNA was used to inhibit GR and MR, UDCA no longer protected hepatocytes against TGF-beta1-induced apoptosis. In fact, the protective effect of UDCA in TGF-beta1-associated caspase activation decreased from 65 to <10% when GR or MR function was blocked. Finally, the TGF-beta1-induced E2F-1/Mdm-2/p53 apoptotic pathway, normally inhibited by UDCA, was not regulated by the bile acid after GR or MR silencing. These results demonstrate that UDCA protects against apoptosis through an additional pathway that involves nuclear receptors GR and MR as key factors. Further, the E2F-1/Mdm-2/p53 apoptotic pathway appears to be a prime target for UDCA-induced steroid receptor activation.

Do antidepressants regulate how cortisol affects the brain?

Although the effects of antidepressants on glucocorticoid hormones and their receptors are relevant for the therapeutic action of these drugs, the molecular mechanisms underlying these effects are unclear. Studies in depressed patients, animals and cellular models have demonstrated that antidepressants increase glucocorticoid receptor (GR) and mineralocorticoid receptor (MR) expression and function; this, in turn, is associated with enhanced negative feedback by endogenous glucocorticoids, and thus with reduced resting and stimulated hypothalamic-pituitary-adrenal (HPA) axis activity. In a series of studies conducted over the last few years, we have shown that antidepressants modulate GR function in vitro by inhibiting membrane steroid transporters that regulate the intracellular concentration of glucocorticoids. In this paper, we will review the effects of membrane steroid transporters and antidepressants on corticosteroid receptors. We will then present our unpublished data on GR live microscopy in vitro, showing that ligand-induced translocation of the GR starts within 30 seconds and is completed within minutes. Furthermore, we will present our new data using an in situ brain perfusion model in anaesthetised guinea-pigs, showing that entry of cortisol to the brain of these animals is limited at the blood-brain barrier (BBB). Finally, we will present a comprehensive discussion of our published findings on the effects of chemically unrelated antidepressants on membrane steroid transporters, in mouse fibroblasts and rat cortical neurones. We propose that antidepressants in humans could inhibit steroid transporters localised on the BBB and in neurones, like the multidrug resistance p-glycoprotein, and thus increase the access of cortisol to the brain and the glucocorticoid-mediated negative feedback on the HPA axis. Enhanced cortisol action in the brain might prove to be a successful approach to maximise therapeutic antidepressant effects.

Glucocorticoid receptor alpha, beta and gamma expression vs in vitro glucocorticod resistance in childhood leukemia

Alternative splicing of the primary glucocorticoid receptor (GR) transcript, resulting in glucocorticoid receptor alpha GRalpha, glucocorticoid receptor beta GRbeta and glucocorticoid receptor gamma GRgamma, may influence glucocorticoid (GC) resistance in childhood leukemia. To test this hypothesis, we determined GRalpha/beta protein and GRalpha/beta/gamma mRNA expression levels in 43 initial acute lymphoblastic leukemia (iALL), 10 initial myeloid leukemia (iAML), 11 relapsed ALL (rALL) samples and one rAML sample. The results were correlated with in vitro GC resistance. GRalpha mRNA correlated with protein expression (rho=0.39-0.56, P<0.05), but the protein to mRNA ratio was median 2.2-fold lower in rALL than in iALL (P<0.05). GRbeta mRNA was median 137-fold lower than GRalpha mRNA and correlated with GRalpha mRNA expression (rho=0.71, P<0.0001). GRbeta could not be detected at the protein level. GRgamma accounted for a median of 2.8% (range 0.95-7.4%) of all GR transcripts. GRalpha (protein and mRNA) and GRbeta (mRNA) expressions or GRalpha/GRbeta ratios did not correlate with in vitro GC resistance in iALL, but GRgamma (mRNA) did (rho=0.52, P=0.007). These results suggest that GRbeta is not involved in GC resistance in childhood leukemia. The association between GRgamma expression and in vitro GC resistance in iALL and the decreased protein/mRNA ratio in rALL, a subgroup resistant to GCs, warrants further exploration.

Chlamydia pneumoniae activates epithelial cell proliferation via NF-kappaB and the glucocorticoid receptor

Chlamydia pneumoniae is an obligate intracellular eubacterium and a common cause of acute and chronic respiratory tract infections. This study was designed to show the effect of C. pneumoniae on transcription factor activation in epithelial cells. The activation of transcription factors by C. pneumoniae was determined in human epithelial cell lines (HL and Calu3) by electrophoretic DNA mobility shift assay, Western blotting, and luciferase reporter gene assay. The activation of transcription factors was further confirmed by immunostaining of C. pneumoniae-infected HL cells and mock-infected controls. The effect of transcription factors on C. pneumoniae-induced host cell proliferation was assessed by [(3)H]thymidine incorporation and direct cell counting in the presence and absence of antisense oligonucleotides targeting transcription factors or the glucocorticoid receptor (GR) antagonist RU486. The activation of the GR, CCAAT-enhancer binding protein (C/EBP), and NF-kappaB was induced within 1 to 6 h by C. pneumoniae. While the interleukin-6 promoter was not activated by C. pneumoniae, the GR-driven p21((Waf1/Cip1)) promoter was increased 2.5- to 3-fold over controls 24 h after infection. C. pneumoniae dose-dependently increased the DNA synthesis of the host cells 2.5- to 2.9-fold, which was partly inhibited either by RU486 or by NF-kappaB antisense oligonucleotides. Furthermore, we provide evidence that heat-inactivated C. pneumoniae does not cause a significant increase in cell proliferation. Our results demonstrate that C. pneumoniae activates C/EBP-beta, NF-kappaB, and the GR in infected cells. However, only NF-kappaB and the GR were involved in C. pneumoniae-induced proliferation of epithelial cells.

The antidepressant clomipramine regulates cortisol intracellular concentrations and glucocorticoid receptor expression in fibroblasts and rat primary neurones

Incubation of LMCAT fibroblasts cells with antidepressants potentiates glucocorticoid receptor (GR)-mediated gene transcription in the presence of cortisol, but not of corticosterone. We have suggested that antidepressants do so by inhibiting the LMCAT cells membrane steroid transporter and thus by increasing cortisol intracellular concentrations. We now confirm and extend this model to primary neuronal cultures. Clomipramine, a tricyclic antidepressant, increased the intracellular accumulation of 3H-cortisol, but not 3H-corticosterone, in LMCAT cells (+80%) and primary rat neurones (+20%). The latter finding is the first demonstration that a membrane steroid transporter is present in neurones. Moreover, verapamil, a membrane steroid transporter inhibitor, reduced the effects of clomipramine on the intracellular accumulation of 3H-cortisol in LMCAT cells. Finally, clomipramine also decreased GR expression (whole-cell Western blot) in LMCAT cells (50% reduction) and primary rat neurones (80% reduction). This GR downregulation can explain the reduced GR-mediated gene transcription previously described under experimental conditions that do not elicit the effects on the LMCAT cells steroid transporter. This work further supports the hypothesis that membrane steroid transporters regulating the access of glucocorticoids to the brain in vivo are a fundamental target for antidepressant action.

Expression of heat-shock protein 90 in glucocorticoid-sensitive and -resistant childhood acute lymphoblastic leukaemia

Early reduction of leukaemic cells by chemotherapy is a strong predictor for treatment outcome in childhood acute lymphoblastic leukaemia (ALL). In ALL-(Berlin-Frankfurt-Münster) trials, early treatment response is assessed by the in vivo response to glucocorticoids (prednisone response, PR), the molecular background of which is unknown. The intracellular effects of glucocorticoids (GCs) are mediated by the glucocorticoid receptor (GR). In the absence of GC, the inactive GR resides within a multiprotein complex, consisting predominantly of the chaperone protein hsp90 (heat-shock protein 90). Until now, studies targeting GC resistance mainly focused on GR disorders and alterations of genes known to be associated with drug resistance. In addition, the GR multiprotein complex was associated with GC resistance in in vitro studies. We performed a case-control study for PR to investigate the association of in vivo GC resistance and hsp90 expression in childhood ALL. Hsp90 expression was assessed using a real-time PCR approach (Taqman technology) and Western blot technology. In this setting, we found no association of in vivo GC resistance and hsp90 expression. Therefore, we conclude that the expression of hsp90, the major component of the GR activating complex, is of minor importance for the in vivo GC resistance in childhood ALL.

The interplay between the glucocorticoid receptor and nuclear factor-kappaB or activator protein-1: molecular mechanisms for gene repression

The inflammatory response is a highly regulated physiological process that is critically important for homeostasis. A precise physiological control of inflammation allows a timely reaction to invading pathogens or to other insults without causing overreaction liable to damage the host. The cellular signaling pathways identified as important regulators of inflammation are the signal transduction cascades mediated by the nuclear factor-kappaB and the activator protein-1, which can both be modulated by glucocorticoids. Their use in the clinic includes treatment of rheumatoid arthritis, asthma, allograft rejection, and allergic skin diseases. Although glucocorticoids have been widely used since the late 1940s, the molecular mechanisms responsible for their antiinflammatory activity are still under investigation. The various molecular pathways proposed so far are discussed in more detail.

Induction of CYP3As in HepG2 cells by several drugs. Association between induction of CYP3A4 and expression of glucocorticoid receptor

The cytochrome P-450 3A (CYP3A) enzyme family is responsible for most of the drug metabolism in the human liver. In this study, we demonstrated the inductive effects of phenobarbital, rifampicin, carbamazepine, phenytoin, prednisolone, ciclosporin and clotrimazole on CYP3A4, CYP3A5 and CYP3A7 mRNA expression, and established the relationship between the expression of human glucocorticoid receptor alpha (hGR) mRNA and the induction of CYP3A4 mRNA in cultured HepG2 cells by reverse transcription polymerase chain reaction (RT-PCR). Treatment with prednisolone, rifampicin and carbamazepine rapidly induced the level of CYP3A4 mRNA expression by 3- to 6-fold. However, phenytoin and phenobarbital gradually induced CYP3A4 mRNA level by 3 to 4-fold. The induction of CYP3A4 mRNA expression by clotrimazole and ciclosporin was negligible. Treatment with phenytoin, rifampicin, carbamazepine and ciclosporin induced approximately 2-fold increases in the expression of CYP3A5 mRNA, although prednisolone, phenytoin and clotrimazole had no effect. Treatment with rifampicin, phenytoin, clotrimazole and ciclosporin resulted in approximately a 2-fold induction of the CYP3A7 mRNA level. Treatment with rifampicin and ciclosporin induced the expression of hGRalpha mRNA significantly in comparison with controls, although the induction of hGRalpha mRNA following treatment with other drugs was negligible. In cluster analysis, the induced level of CYP3A4, CYP3A5, CYP3A7 and hGRalpha mRNA by these drugs could be classified into four major clusters. This suggested that each cluster might be associated with different mechanism(s) of induction by these drugs. Furthermore, we studied the associations between the expression of hGRalpha mRNA and the induced level of CYP3A4 mRNA by prednisolone and ciclosporin. Treatment with both prednisolone and ciclosporin showed synergistic effects on induction of CYP3A4 mRNA and, following treatment with both drugs, the expression level of CYP3A4 mRNA was 2-fold greater compared with prednisolone alone after the fifth day. Positive correlations were observed between the levels of hGRalpha mRNA expression and those of CYP3A4 mRNA. This observation shows that the regulation of CYP3A4 gene expression was hGRalpha-dependent and that ciclosporin may function as a regulator of expression via hGRalpha.

Mechanism of antiandrogen action: key role of hsp90 in conformational change and transcriptional activity of the androgen receptor

Activation of the androgen receptor (AR) is induced by ligand binding through conformational changes leading to control of gene expression. Antiandrogens compete with androgens for AR occupancy and subsequently block at least one step in AR action. Analysis of nuclear transfer kinetics using the GFP-AR fusion protein and partial proteolysis analysis provided evidence that the ligand-bound receptor was in equilibrium between at least two distinct conformations, leading to the production of 35 and 29 kDa trypsin-resistant fragments. It also indicated that this equilibrium may regulate the rate of nuclear transfer. The slowing of nuclear transfer by antiandrogens was correlated with the amount of receptor in conformation leading to the 35 kDa trypsin-resistant fragment. To establish the role of heat shock protein (hsp) 90 activity in antiandrogenic action, the effect of geldanamycin (GA) was evaluated in both in vitro assays and live cells. We demonstrated that in vitro hsp90s are required to stabilize the receptor in the inactive conformation and that hsp90 activity is involved in the integrity and nuclear transfer of agonist- and antagonist-bound AR. Furthermore, nuclear transfer is not the only step affected by GA since this compound was also active on a constitutively nuclear AR (GFP-NLS-AR). Hsp90 inactivation impedes interaction of androgen-bound GFP-NLS-AR with nuclear components and inhibits transcriptional activity. We conclude that hsp90s are required for the acquisition of active conformation in agonist-bound AR to regulate nuclear transfer, nuclear matrix binding, and transcriptional activity. Pure antiandrogens block the transconformational change of AR in an intermediary complex unable to acquire the active conformation and to dissociate the hsp90.

Unique behavior of a dictyostelium homologue of TRAP-1, coupling with differentiation of D. discoideum cells

Dd-TRAP1 is a Dictyostelium homologue of TRAP-1, a human protein that binds to the type 1 tumor necrosis factor (TNF) receptor. TRAP-1 has a putative mitochondrial localization sequence and shows significant homology to members of the HSP90 family. Although TRAP-1 is mainly localized to mitochondria in several mammalian cells, in certain tissues it is also localized at specific extramitochondrial sites. In Dictyostelium cells, Dd-TRAP1 is predominantly located in the cell membrane/cortex during growth and just after starvation. Double staining of vegetatively growing cells with the anti-Dd-TRAP1 antibody and TRITC-phalloidin has demonstrated colocalization of Dd-TRAP1 and F-actin at the leading edge of cortical protrusions such as pseudopodes. Coupled with differentiation, however, Dd-TRAP1 located at the cortical region is translocated to mitochondria in spite of the absence of the mitochondrial localization sequence at its N-terminus. The translocation of this protein raises interesting and fundamental questions regarding possible mechanisms by which Dd-TRAP1 is involved in cellular differentiation.

RU486 antagonizes the inhibitory effect of peroxisome proliferator-activated receptor alpha on interleukin-6 production in vascular endothelial cells

Peroxisome proliferator-acitivated receptor alpha (PPARalpha) is a member of nuclear receptor superfamily. Recent studies have shown that the activators for PPARalpha inhibit the expression of some inflammatory molecules in vascular endothelial cells (ECs) and vascular smooth muscle cells, indicating the anti-inflammatory roles of PPARalpha on vascular walls. In this investigation, we showed that RU486, already proved to be an active anti-glucocorticoid and anti-progesterone agent, blocked the inhibition of tumor necrosis factor (TNF)-alpha-stimulated interleukin-6 (IL-6) production by the PPARalpha activator fenofibrate in human umbilical vein ECs. Transient transfection of bovine aortic ECs with an IL-6 promoter construct demonstrated that RU486 blocked the inhibitory effect of fenofibrate on TNF-alpha-induced IL-6 promoter activity. By fluorescence microscopy, RU486 was found to prevent fenofibrate-induced nuclear translocation of PPARalpha. Thus, RU486 has an antagonizing effect on PPARalpha-mediated down-regulation of IL-6 in vascular ECs. This effect may be exerted by its interference with the nuclear translocation of PPARalpha.

Molecular mechanisms of immunomodulatory activity of glucocorticoids

The development and function of cells in the immune system are regulated by many intrinsic and extrinsic factors. One class of molecule that affects immune cells belongs to the neuroendocrine system and the best-studied mediators in this category are glucocorticoids. These are small lypophilic molecules that participate in a wide number of normal and pathologic processes. This paper concentrates on their physiologic and pharmacologic effects on the immune response.

Association of the chaperone glucose-regulated protein 58 (GRP58/ER-60/ERp57) with Stat3 in cytosol and plasma membrane complexes

Glucose-regulated protein 58 (GRP58/ER-60/ERp57), best known as a chaperone in the endoplasmic reticulum lumen, was previously identified by us as one of several accessory proteins in the S100 cytosol fraction of human hepatoma Hep3B cells that was differentially coshifted by anti-Stat3 antibody in an antibody-subtracted differential protein display assay. In the present study, the association between GRP58 and Stat3 in different cytoplasmic compartments was evaluated using cross-immunoprecipitation and cell-fractionation techniques. In the S100 cytosol fraction, three different anti-GRP58 polyclonal antibodies (pAb) cross-immunoprecipitated Stat3 (but not Stat1), and, conversely, anti-Stat3 pAb cross-immunoprecipitated GRP58. Both cytosolic Stat3 and GRP58 eluted during Superose-6 gel-filtration chromatography in complexes of size 200-400 kDa (statosome I), and anti-Stat3 pAb cross-immunoprecipitated GRp58 from these FPLC elution fractions. Using differential sedimentation and density equilibrium flotation methods, Stat3 and GRP58 were observed to be coassociated with cytoplasmic membranes enriched for the plasma membrane marker 5' nucleotidase but not with those containing the endoplasmic reticulum marker BiP/GRP78. The Stat3 and GRP58-containing plasma membrane fraction also contained Stat1, Stat5b, and gp130. Stat activation by orthovanadate caused the accumulation of PY-Stat3 in the GRP58-containing plasma membrane fraction. However, this PY-Stat3 was DNA-binding deficient. Likewise, excess exogenous recombinant human GRP58 prepared using a baculovirus expression system preferentially inhibited Stat3 DNA-binding activity in the S100 cytosol, suggesting that GRP58 may sequester activated Stat3. The new data confirm the association between GRP58 and Stat3 in cytosolic 200-400-kDa statosome I complexes and show that both GRP58 and Stat family members coassociate in the plasma membrane compartment. We suggest that the chaperone GRP58 may regulate signaling by sequestering inactive and activated Stat3.

Estradiol-induced phosphorylation of ERK1/2 in explants of the mouse cerebral cortex: the roles of heat shock protein 90 (Hsp90) and MEK2

Confocal laser scanning microscopy was used to identify the cells within organotypic slice cultures of the developing mouse cerebral cortex that respond to estradiol treatment by phosphorylation of ERK1 and ERK2. Estrogen-responsive cells resembled neurons morphologically and expressed the neuronal marker microtubule-associated protein 2B. The intracellular distribution of the phospho-ERK signal was both cytoplasmic and nuclear, but inhibition of protein synthesis abolished the appearance of the nuclear signal. ERK1and ERK2 also coimmunoprecipitated with heat shock protein 90 (Hsp90) in the cerebral cortical explants. Geldanamycin effectively disrupted this association and prevented ERK phosphorylation. Surprisingly, MEK2 but not MEK1 was the principal mediator of estradiol-induced activation of ERK. Our data demonstrate the requirement for Hsp90 in estrogen-induced activation of ERK1 and ERK2 by MEK2 in the developing mouse cerebral cortex and also provide insight into alternative mechanisms by which estradiol may influence cytoplasmic and nuclear events in responsive neurons via the MAP kinase cascade.

Functional modulation of the glucocorticoid receptor and suppression of NF-kappaB-dependent transcription by ursodeoxycholic acid

Ursodeoxycholic acid (UDCA) is the current mainstay of treatment for various liver diseases including primary biliary cirrhosis. UDCA acts as a bile secretagogue, cytoprotective agent, immunomodulator, and inhibitor of cellular apoptosis. Despite this cumulative evidence of the cytoprotective and immunosuppressive effects of UDCA, both the target molecule and pathway of UDCA action remain unknown. We previously described that, in the absence of glucocorticoid ligand, UDCA activates the glucocorticoid receptor (GR) into DNA binding species but does not elicit its transactivational function in a transient transfection assay. Here we further studied the molecular mechanism of UDCA action and revealed that the ligand binding domain of the GR is responsible for UDCA-dependent nuclear translocation of the GR. Indeed, we demonstrated that UDCA acts on the distinct region of the ligand binding domain when compared with the classical GR agonist dexamethasone, resulting in loss of coactivator recruitment and differential regulation of gene expression by the GR. Our data clearly indicated that UDCA, at least in part via activation of the GR, suppresses NF-kappaB-dependent transcription through the intervention of GR-p65 interaction. Together with the established clinical safety of UDCA, we may propose that UDCA could be a prototypical compound for development of a novel and selective GR modifier.

Mutational analysis of the CYP2B2 phenobarbital response unit and inhibitory effect of the constitutive androstane receptor on phenobarbital responsiveness

A 163-base pair enhancer in the CYP2B2 5' flank confers phenobarbital (PB) inducibility and constitutes a PB response unit (PBRU). By transfection of primary hepatocytes, we analyzed the function of elements comprising the PBRU and evaluated the role of the constitutive androstane receptor (CAR) in PB responsiveness. A 51-base pair PB-responsive enhancer module (PBREM) within the PBRU confers near-maximal PB response when fused to a tk promoter. However, replacing the PBRU with the PBREM in the CYP2B2 5' flank in the natural sequence context reduced PB responsiveness by approximately 4-fold. Mutational analysis also demonstrated that PBRU sequence elements outside the PBREM are essential for maximal PB responsiveness. The PBRU contains two putative nuclear receptor binding sites, NR1 and NR2. CAR binds to retinoic acid beta2 response elements (betaRARE) and to the NR1 and NR2 sites of the PBRU and activates transcription of reporter genes in cell lines. However, conversion of NR1 into betaRARE was the equivalent of an inactivating mutation, indicating that CAR does not activate PB-dependent transcription via NR1 in the natural sequence context. A betaRAREx2-tk reporter construct was inducible by all-trans-retinoic acid (at-RA) as expected and also responded to PB. The latter can be attributed to nuclear accumulation of CAR after PB exposure. Exogenous CAR increased both the basal and PB-induced response of betaRAREx2-tk but reduced PBRU-dependent PB response. Furthermore, exogenous CAR also reduced the at-RA response of the betaRAREx2-tk construct. Thus, CAR acts negatively on PB responsiveness mediated by the CYP2B2 PBRU just as it prevents maximal at-RA responsiveness mediated by betaRARE.

Functional properties of the R154X HNF-4alpha protein generated by a mutation associated with maturity-onset diabetes of the young, type 1

Mutations in the hepatocyte nuclear factor 4alpha (HNF-4alpha) gene are associated with one form of maturity-onset diabetes of the young (MODY1). The R154X mutation generates a protein lacking the E-domain which is required for normal HNF-4alpha functions. Since pancreatic beta-cell dysfunction is a feature of MODY1 patients, we compared the functional properties of the R154X mutant in insulin-secreting pancreatic beta-cells and non-beta-cells. The R154X mutation did not affect nuclear localisation in beta-cells and non-beta-cells. However, it did lead to a greater impairment of HNF-4a function in beta-cells compared to non-beta-cells, including a complete loss of transactivation activity and a dominant-negative behaviour. .