Sex-Dependent Mechanisms of Glucocorticoid Regulation of the Mouse Hypothalamic Corticotropin-Releasing Hormone Gene

To limit excessive glucocorticoid secretion following hypothalamic-pituitary-adrenal (HPA) axis stimulation, circulating glucocorticoids inhibit corticotropin-releasing hormone (CRH) expression in paraventricular nucleus (PVN) neurons. As HPA function differs between sexes and depends on circulating estradiol (E2) levels in females, we investigated sex/estrous stage-dependent glucocorticoid regulation of PVN Crh. Using NanoString nCounter technology, we first demonstrated that adrenalectomized (ADX'd) diestrous female (low E2), but not male or proestrous female (high E2), mice exhibited a robust decrease in PVN CRH mRNA following 2-day treatment with the glucocorticoid receptor (GR) agonist RU28362. Immunohistochemical analysis of PVN CRH neurons in Crh-IRES-Cre;Ai14 mice, where TdTomato fluorescence permanently tags CRH-expressing neurons, showed similarly abundant co-expression of GR-immunoreactivity in males, diestrous females, and proestrous females. However, we identified sex/estrous stage-related glucocorticoid regulation or expression of GR transcriptional coregulators. Out of 17 coregulator genes examined using nCounter multiplex analysis, mRNAs that were decreased by RU28362 in ADX'd mice in a sex/estrous stage-dependent fashion included: GR (males = diestrous females > proestrous females), signal transducer and activator of transcription 3 (STAT3) (males < diestrous = proestrous), and HDAC1 (males < diestrous > proestrous). Steroid receptor coactivator 3 (SRC-3), nuclear corepressor 1 (NCoR1), heterogeneous nuclear ribonucleoprotein U (hnrnpu), CREB binding protein (CBP) and CREB-regulated transcription coactivator 2 (CRTC2) mRNAs were lower in ADX'd diestrous and proestrous females versus males. Additionally, most PVN CRH neurons co-expressed methylated CpG binding protein 2 (MeCP2)-immunoreactivity in diestrous female and male Crh-IRES-Cre;Ai14 mice. Our findings collectively suggest that GR's sex-dependent regulation of PVN Crh may depend upon differences in the GR transcriptional machinery and an underlying influence of E2 levels in females.

Estradiol (E2)- and tamoxifen (Tmx)-bound ER-alpha (ERα) interact differentially with histone deacetylases 1 and 3 (HDACs 1 and 3)

Although ERα activation properties have been intensively studied, this is not the case for their repressive properties. In this report, the ERα ligand binding domain (LBD) is shown to interact both with a deacetylase function and with HDAC1 and HDAC3. Ligands do not affect binding to the deacetylase activity or to HDAC1. In distinction, E2 reduced LBD binding to HDAC3, whereas Tmx had no effect. Knock-down of either HDAC1 or 3 led to increased transcriptional activity by both HDACs, presumably by decreased repression. In distinction, only HDAC3 knock-down led to increased activity in the presence of Tmx. In summary, ERα differentially interacts with HDACs 1 and 3 to regulate transcriptional activity.

CpG methylation and the methyl CpG binding protein 2 (MeCP2) are required for restraining corticotropin releasing hormone (CRH) gene expression

The hypothalamic-pituitary-adrenal (HPA) axis plays a critical role in mounting a stress response and maintaining homeostasis. A dysregulated HPA axis and elevated levels of CRH are associated with a number of disorders. Although extensive research has been devoted to understanding molecular events associated with stimulated CRH gene, less is known about the mechanisms that restrain CRH expression. Using a cell culture system, we report here two molecular aspects of CRH gene regulation that are required for maintenance of basal level of CRH gene expression. These are a specific CpG methylation at a single CpG, and adequate levels of the methyl CpG binding protein 2 (MeCP2). The single site methylation allows the recruitment of MeCP2 to the CRH gene promoter region, and MeCP2 knockdown leads to increased expression of CRH gene. Taken together, the results indicate that site-specific methylation and MeCP2 are required for maintenance of basal levels of CRH gene expression.

Mechanisms by Which 17β-Estradiol (E2) Suppress Neuronal cox-2 Gene Expression

E2 attenuates inflammatory responses by suppressing expression of pro-inflammatory genes. Given that inflammation is increasingly being associated with neurodegenerative and psychiatric processes, we sought to elucidate mechanisms by which E2 down-regulates a component of an inflammatory response, cyclooxygenase- 2 (COX-2) expression. Although inflammatory processes in the brain are usually associated with microglia and astrocytes, we found that the COX-2 gene (cox-2) was expressed in a neuronal context, specifically in an amygdalar cell line (AR-5). Given that COX-2 has been reported to be in neurons in the brain, and that the amygdala is a site involved in neurodegenerative and neuropsychiatric processes, we investigated mechanisms by which E2 could down-regulate cox-2 expression in the AR-5 line. These cells express estrogen receptors alpha (ERα) and beta (ERβ), and as shown here cox-2. At the level of RNA, E2 and the ERβ selective ligand diarylpropionitrile (DPN) both attenuated gene expression, whereas the ERα selective ligand propyl pyrazole triol (PPT) had no effect. Neither ligand increased ERβ at the cox-2 promoter. Rather, DPN decreased promoter occupancy of NF-κB p65 and histone 4 (H4) acetylation. Treatment with the non-specific HDAC inhibitor Trichostatin A (TSA) counteracted DPN's repressive effects on cox-2 expression. In keeping with the TSA effect, E2 and DPN increased histone deacetylase one (HDAC1) and switch-independent 3A (Sin3A) promoter occupancy. Lastly, even though E2 increased CpG methylation, DPN did not. Taken together, the pharmacological data indicate that ERβ contributes to neuronal cox-2 expression, as measured by RNA levels. Furthermore, ER ligands lead to increased recruitment of HDAC1, Sin3A and a concomitant reduction of p65 occupancy and Ac-H4 levels. None of the events, however, are associated with a significant recruitment of ERβ at the promoter. Thus, ERβ directs recruitment to the cox-2 promoter, but does so in the absence of being recruited itself.

Hypothalamic and amygdalar cell lines differ markedly in mitochondrial rather than nuclear encoded gene expression

Background

Corticotropin-releasing hormone (CRH) plays an important role in regulating the mammalian stress response. Two of the most extensively studied neuronal populations that express CRH are in the hypothalamus and amygdala. Both regions are involved in the stress response, but the amygdala is also involved in mediating response to fear and anxiety. Given that both hypothalamus and amygdala have overlapping functions, but their CRH-expressing neurons may respond differently to a given perturbation, we sought to identify differentially expressed genes between two neuronal cell types, amygdalar AR-5 and hypothalamic IVB cells. Thus, we performed a microarray analysis. Our hypothesis was that we would identify differentially expressed transcription factors, coregulators and chromatin-modifying enzymes.

Results

A total of 31,042 genes were analyzed, 10,572 of which were consistently expressed in both cell lines at a 95% confidence level. Of the 10,572 genes, 2,320 genes in AR-5 were expressed at ≥ 2-fold relative to IVBs, 1,104 genes were expressed at ≥2-fold in IVB relative to AR-5 and 7,148 genes were expressed at similar levels between the two cell lines. The greatest difference was in six mitochondrial DNA-encoded genes, which were highly abundant in AR-5 relative to IVB cells. The relative abundance of these genes ranged from 413 to 885-fold according to the microarray results. Differential expression of these genes was verified by RTqPCR. The differentially expressed mitochondrial genes were cytochrome b (MT-CYB), cytochrome c oxidase subunit 1 and 2 (MT-CO1 and MT-CO2) and NADH-ubiquinone oxidoreductase chain 1, 2, and 3 (MT-ND1, MT-ND2, MT-ND3).

Conclusion

As expected, the array revealed differential expression of transcription factors and coregulators; however the greatest difference between the two cell lines was in genes encoded by the mitochondrial genome. These genes were abundant in AR-5 relative to IVBs. At present, the reason for the marked difference is unclear. The cells may differ in mtDNA copy number, number of mitochondria, or regulation of the mitochondrial genome. The specific functions served by having such different levels of mitochondrial expression have not been determined. It is possible that the greater expression of the mitochondrial genes in the amygdalar cells reflects higher energy requirements than in the hypothalamic cell line.

The androgen metabolite, 5α-androstane-3β,17β-diol (3β-diol), activates the oxytocin promoter through an estrogen receptor-β pathway

Testosterone has been shown to suppress the acute stress-induced activation of the hypothalamic-pituitary-adrenal axis; however, the mechanisms underlying this response remain unclear. The hypothalamic-pituitary-adrenal axis is regulated by a neuroendocrine subpopulation of medial parvocellular neurons in the paraventricular nucleus of the hypothalamus (PVN). These neurons are devoid of androgen receptors (ARs). Therefore, a possibility is that the PVN target neurons respond to a metabolite in the testosterone catabolic pathway via an AR-independent mechanism. The dihydrotestosterone metabolite, 5α-androstane-3β,17β-diol (3β-diol), binds and activates estrogen receptor-β (ER-β), the predominant ER in the PVN. In the PVN, ER-β is coexpressed with oxytocin (OT). Therefore, we tested the hypothesis that 3β-diol regulates OT expression through ER-β activation. Treatment of ovariectomized rats with estradiol benzoate or 3β-diol for 4 days increased OT mRNA selectively in the midcaudal, but not rostral PVN compared with vehicle-treated controls. 3β-Diol treatment also increased OT mRNA in the hypothalamic N38 cell line in vitro. The functional interactions between 3β-diol and ER-β with the human OT promoter were examined using an OT promoter-luciferase reporter construct (OT-luc). In a dose-dependent manner, 3β-diol treatment increased OT-luc activity when cells were cotransfected with ER-β, but not ER-α. The 3β-diol-induced OT-luc activity was reduced by deletion of the promoter region containing the composite hormone response element (cHRE). Point mutations of the cHRE also prevented OT-luc activation by 3β-diol. These results indicate that 3β-diol induces OT promoter activity via ER-β-cHRE interactions.

The ERβ ligand 5α-androstane, 3β,17β-diol (3β-diol) regulates hypothalamic oxytocin (Oxt) gene expression

The endocrine component of the stress response is regulated by glucocorticoids and sex steroids. Testosterone down-regulates hypothalamic-pituitary-adrenal (HPA) axis activity; however, the mechanisms by which it does so are poorly understood. A candidate testosterone target is the oxytocin gene (Oxt), given that it too inhibits HPA activity. Within the paraventricular nucleus of the hypothalamus, oxytocinergic neurons involved in regulating the stress response do not express androgen receptors but do express estrogen receptor-β (ERβ), which binds the dihydrotestosterone metabolite 3β,17β-diol (3β-diol). Testosterone regulation of the HPA axis thus appears to involve the conversion to the ERβ-selective ligand 5α-androstane, 3β-diol. To study mechanisms by which 3β-diol could regulate Oxt expression, we used a hypothalamic neuronal cell line derived from embryonic mice that expresses Oxt constitutively and compared 3β-diol with estradiol (E2) effects. E2 and 3β-diol elicited a phasic response in Oxt mRNA levels. In the presence of either ligand, Oxt mRNA levels were increased for at least 60 min and returned to baseline by 2 h. ERβ occupancy preceded an increase in Oxt mRNA levels in the presence of 3β-diol but not E2. In tandem with ERβ occupancy, 3β-diol increased occupancy of the Oxt promoter by cAMP response element-binding protein and steroid receptor coactivator-1 at 30 min. At the same time, 3β-diol led to the increased acetylation of histone H4 but not H3. Taken together, the data suggest that in the presence of 3β-diol, ERβ associates with cAMP response element-binding protein and steroid receptor coactivator-1 to form a functional complex that drives Oxt gene expression.

Estrogen receptors and the regulation of neural stress responses

It is now well established that estrogens can influence a panoply of physiological and behavioral functions. In many instances, the effects of estrogens are mediated by the 'classical' actions of two different estrogen receptors (ERs), ERα or ERβ. ERα and ERβ appear to have opposing actions in the control of stress responses and modulate different neurotransmitter or neuropeptide systems. Studies elucidating the molecular mechanisms for such regulatory processes are currently in progress. Furthermore, the use of ERα and ERβ knockout mouse lines has allowed the exploration of the importance of these receptors in behavioral responses such as anxiety-like and depressive-like behaviors. This review examines some of the recent advances in our knowledge of hormonal control of neuroendocrine and behavioral responses to stress and underscore the importance of these receptors as future therapeutic targets for control of stress-related signaling pathways.

Histone deacetylase 1 (HDAC1) participates in the down-regulation of corticotropin releasing hormone gene (crh) expression

The paraventricular nucleus of the hypothalamus (PVH) plays a central role in regulating the hypothalamic-pituitary-adrenal (HPA) axis. Medial parvocellular neurons of the PVH (mpPVH) integrate sensory and humoral inputs to maintain homeostasis. Humoral inputs include glucocorticoids secreted by the adrenals, which down-regulate HPA activation. A primary glucocorticoid target is the population of mpPVH neurons that synthesize and secrete corticotropin-releasing factors, the most potent of which is corticotropin-releasing hormone (CRH). Although CRH gene (crh) expression is known to be down-regulated by glucocorticoids, the mechanisms by which this process occurs are still poorly understood. To begin this study we postulated that glucocorticoid repression of crh involves HDAC recruitment to the region of the crh proximal promoter. To evaluate this hypothesis, we treated hypothalamic cells that express CRH with the HDAC inhibitor trichostatin A (TSA). As predicted, treatment with TSA led to increased CRH mRNA levels and crh promoter activity. Although co-treatment with Dex (10(-7)M) reduced the TSA effect on mRNA levels, it failed to reduce promoter activity; however co-transfection of HDAC1 but not 3 restored Dex inhibition. A distinction between HDAC1 and 3 was also apparent with respect to crh promoter occupancy. Dex led to increased HDAC1 but not HDAC3 occupancy. In vivo studies revealed that CRH-immunoreactive (-ir) neurons contained HDAC1- and HDAC3-ir. Collectively, these data point to a role for HDAC1 in the physiologic regulation of crh.

Estradiol regulates corticotropin-releasing hormone gene (crh) expression in a rapid and phasic manner that parallels estrogen receptor-alpha and -beta recruitment to a 3',5'-cyclic adenosine 5'-monophosphate regulatory region of the proximal crh promoter

In the central nervous system, CRH regulates several affective states. Dysregulation of neuronal crh expression in the paraventricular nucleus of the hypothalamus correlates with some forms of depression, and amygdalar crh expression may modulate levels of anxiety. Because estrogens modulate these states, we sought to determine 17beta-estradiol (E2) effects on crh expression. CRH mRNA levels were measured in the AR-5 amygdaloid cell line by RT-PCR analysis. They increased by 1 min of E2 treatment, suggesting that crh behaves as an immediate-early gene. After peaking at 3 min, CRH mRNA returned to basal levels and then increased by 60 min. To dissect some of the molecular mechanisms underlying these events, we measured occupancy of the crh promoter by estrogen receptors (ERs) and coactivators, using chromatin immunoprecipitation. Because this promoter does not contain palindromic estrogen response elements, we targeted the region of a cAMP regulatory element (CRE), implicated in crh regulation. The temporal pattern of the mRNA response was mimicked by recruitment of ERalpha and -beta, phospho-CRE-binding protein, coactivators steroid receptor coactivator-1 and CRE-binding protein-binding protein (CBP), and an increase in histone 3 and 4 acetylation. Lastly, ERalpha and -beta loading were temporally dissociated, peaking at 1 and 3 min, respectively. The ER peaks were associated with coactivators and acetylation patterns. ERalpha associated with phospho-CRE-binding protein, CBP, steroid receptor coactivator-1, and increased acetylated histone 3. ERbeta associated with CBP and increased acetylated histone 4. The tight temporal correlation between E2-induced CRH mRNA levels and promoter occupancy by ERs strongly suggest that E2 regulates crh expression through an ERalpha- and/or ERbeta-CRE alternate pathway.

The protein kinase C-eta isoform induces proliferation in glioblastoma cell lines through an ERK/Elk-1 pathway

Glioblastoma multiforme (GBM) is the highest grade of astrocytoma. GBM pathogenesis has been linked to receptor tyrosine kinases and kinases further down signal-transduction pathways - in particular, members of the protein kinase C (PKC) family. The expression and activity of various PKC isoforms are increased in malignant astrocytomas, but not in non-neoplastic astrocytes. This suggests that PKC activity contributes to tumor progression. The level of PKC-eta expressed correlates with the degree of phorbol-12-myristate-13-acetate (PMA)-induced proliferation of two glioblastoma cell lines, U-1242 MG and U-251 MG. Normally, U-1242 cells do not express PKC-eta, and PMA inhibits their proliferation. Conversely, PMA increases proliferation of U-1242 cells that are stably transfected with PKC-eta (U-1242-PKC-eta). PMA treatment also stimulates proliferation of U-251 cells, which express PKC-eta. Here, we determined that extracellular signal-regulated kinase (ERK) and Elk-1 are downstream targets of PKC-eta. Elk-1-mediated transcriptional activity correlates with the PKC-eta-mediated mitogenic response. Pretreatment of U-1242-PKC-eta cells with inhibitors of PKC or MAPK/ERK kinase (MEK) (bisindolyl maleimide (BIM) or U0126, respectively) blocked both PMA-induced Elk-1 transcriptional activity and PMA-stimulated proliferation. An overexpressed dominant-negative PKC-eta reduced the mitogenic response in U-251 cells, as did reduction of Elk-1 by small interfering RNA. Taken together, these results strongly suggest that PKC-eta-mediated glioblastoma proliferation involves MEK/mitogen-activated protein (MAP) kinase phosphorylation, activation of ERK and subsequently of Elk-1. Elk-1 target genes involved in GBM proliferative responses have yet to be identified.

Estrogen receptor (ER)beta isoforms rather than ERalpha regulate corticotropin-releasing hormone promoter activity through an alternate pathway

The hypothalamic-pituitary-adrenal axis regulates mammalian stress responses by secreting glucocorticoids. The magnitude of the response is in part determined by gender, for in response to a given stressor, circulating glucocorticoids reach higher levels in female rats than in males. This gender difference could result from estrogen regulation of the corticotropin-releasing hormone (CRH) promoter via either of its receptors: estrogen receptor (ER)alpha or ERbeta. Immunocytochemistry revealed that a subset (12%) of medial parvocellular CRH neurons in the rat hypothalamus contain ERbeta but not ERalpha. To determine whether ERs could regulate CRH promoter activity, we cotransfected cells with a CRH promoter construct and either ERalpha or individual ERbeta isoforms. ERalpha weakly stimulated CRH promoter transcriptional activity in a ligand-independent manner. Conversely, all ERbeta isoforms tested stimulated CRH promoter activity with different ligand profiles. ERbeta1 and ERbeta2delta3 displayed constitutive activity (ERbeta1 more than ERbeta2delta3). Ligand-dependent activity of beta isoforms 1 and 2 was altered by an Exon3 splice variant (delta3) or by the additional 18 amino acids in the ligand-binding domain of ERbeta2 isoforms. Lastly, we suggest that ER regulation of CRH takes place through an alternate pathway, one that requires protein-protein interactions with other transcription factors or their associated complexes. However, a pure ER-activator protein-1 alternate pathway does not appear to be involved.

Regulation of KLF5 involves the Sp1 transcription factor in human epithelial cells

Human Kruppel-like factor 5 (hKLF5) is a transcription factor with a potential tumor suppressor function in prostate and breast cancers. In the majority of cancer samples examined, a significant loss of expression for KLF5 has been detected. Whereas hemizygous deletion appears to be responsible for KLF5's reduced expression in about half of the cases, the mechanism for reduction is unknown in the remaining half; gene promoter methylation does not appear to be involved. In this report, we studied the regulation of KLF5 and cloned and functionally characterized a 1944-bp fragment of the 5'-flanking region of the hKLF5 gene. Several mitogens as well as global demethylation induced the expression of KLF5, implicating multiple factors in the regulation of KLF5. KLF5's promoter lacks a TATA box and has a GC-rich region. Deletion mapping in combination with promoter activity assay showed that multiple cis-elements are involved in the transcriptional regulation of KLF5, some of which may play a repressor role whereas some others play an enhancer role. The Sp1 site between position -239 and -219 is essential for a basal promoter activity. Deletion or mutations of this Sp1 site significantly reduced promoter activity in several epithelial cell lines. Electrophoretic mobility shift assays (EMSAs) revealed that the Sp1 site binds Sp1 protein in nucleic extracts of different cell lines. In addition, overexpression of Sp1 protein transactivates KLF5 promoter activity. These findings suggest that Sp1 is a key transcription factor in KLF5's dynamic transcriptional regulation.

A conserved lysine in the estrogen receptor DNA binding domain regulates ligand activation profiles at AP-1 sites, possibly by controlling interactions with a modulating repressor

Background

Estrogen receptors alpha and beta (ERα and ERβ) differentially activate genes with AP-1 elements. ERα activates AP-1 targets via activation functions with estrogens (the AF-dependent pathway), whereas ERβ, and a short version of ERα (ERα DBD-LBD) activate only with anti-estrogens (AF-independent pathway). The DNA binding domain (DBD) plays an important role in both pathways, even though neither pathway requires ERE recognition.

Results

Mutations of a highly conserved DBD lysine (ERα.K206A/G), lead to super-activation of AP-1 through activation function dependent pathways, up to 200 fold. This super-activity can be elicited either through ER AFs 1 or 2, or that of a heterologous activation function (VP16). The homologous substitution in ERβ, K170A, or in ERα DBD-LBD leads to estrogen-dependent AP-1 activation and loss of the usually potent anti-estrogen effects. Each of numerous K206 substitutions in ERα, except K206R, eliminates anti-estrogen activation and this loss correlates perfectly with a loss of ability to titrate a repressive function from the RU486 bound progesterone receptor.

Conclusion

We conclude that ER DBDs contain a complex regulatory function that influences ligand activation profiles at AP-1. This function, which requires the integrity of the conserved lysine, both allows for activation at AP-1 with anti-estrogens (with ERβ and ERα DBD-LBD), and prevents ERα from becoming superactive at AP-1 with estrogens. We discuss the possibility that a repressor interaction with the DBD both mediates the AF-independent pathway and dampens the AF dependent pathway. Mutations in the conserved lysine might, by this model, disrupt the binding or function of the repressor.

Opposing action of estrogen receptors alpha and beta on cyclin D1 gene expression

Induction of cyclin D1 gene transcription by estrogen receptor alpha (ERalpha) plays an important role in estrogen-mediated proliferation. There is no classical estrogen response element in the cyclin D1 promoter, and induction by ERalpha has been mapped to an alternative response element, a cyclic AMP-response element at -57, with possible participation of an activating protein-1 site at -954. The action of ERbeta at the cyclin D1 promoter is unknown, although evidence suggests that ERbeta may inhibit the proliferative action of ERalpha. We examined the response of cyclin D1 promoter constructs by luciferase assay and the response of the endogenous protein by Western blot in HeLa cells transiently expressing ERalpha, ERalphaK206A (a derivative that is superactive at alternative response elements), or ERbeta. In each case, ER activation at the cyclin D1 promoter is mediated by both the cyclic AMP-response element and the activating protein-1 site, which play partly redundant roles. The activation by ERbeta occurs only with antiestrogens. Estrogens, which activate cyclin D1 gene expression with ERalpha, inhibit expression with ERbeta. Strikingly, the presence of ERbeta completely inhibits cyclin D1 gene activation by estrogen and ERalpha or even by estrogen and the superactive ERalphaK206A. The observation of the opposing action and dominance of ERbeta over ERalpha in activation of cyclin D1 gene expression has implications for the postulated role of ERbeta as a modulator of the proliferative effects of estrogen.

Estrogen receptor pathways to AP-1

Estrogen receptor (ER) binds to estrogen response elements in target genes and recruits a coactivator complex of CBP-pl60 that mediates stimulation of transcription. ER also activates transcription at AP-1 sites that bind the Jun/Fos transcription factors, but not ER. We review the evidence regarding mechanisms whereby ER increases the activity of Jun/Fos and propose two pathways of ER action depending on the ER (alpha or beta) and on the ligand. We propose that estrogen-ERalpha complexes use their activation functions (AF-1 and AF-2) to bind to the p 160 component of the coactivator complex recruited by Jun/Fos and trigger the coactivator to a higher state of activity. We propose that selective estrogen receptor modulator (SERM) complexes with ERbeta and with truncated ERalpha derivatives use their DNA binding domain to titrate histone deacetylase (HDAC)-repressor complexes away from the Jun/Fos coactivator complex, thereby allowing unfettered activity of the coactivators. Finally, we consider the possible physiological significance of ER action at AP-1 sites.

Radiologic-pathologic findings in raccoon roundworm (Baylisascaris procyonis) encephalitis

A 13-month-old boy developed eosinophilic meningoencephalitis, retinitis, and a protracted encephalopathy with severe residual deficits. The initial MR examination revealed diffuse periventricular white matter disease, and follow-up images showed atrophy. Brain biopsy, serology, and epidemiologic studies lead to the diagnosis of Baylisascaris procyonis infection, a parasitic disease contracted through exposure to soil contaminated by the eggs of a common raccoon intestinal roundworm. The pathologic, epidemiologic, and imaging features of this disease are herein reviewed.

Nuclear receptor-binding sites of coactivators glucocorticoid receptor interacting protein 1 (GRIP1) and steroid receptor coactivator 1 (SRC-1): multiple motifs with different binding specificities

The activity of the AF-2 transcriptional activation function of nuclear receptors (NR) is mediated by the partially homologous transcriptional coactivators, glucocorticoid receptor interacting protein 1 (GRIP1)/transcriptional intermediary factor 2 (TIF2) and steroid receptor coactivator 1 (SRC-1). GRIP1 and SRC-1 bound nine different NRs and exhibited similar, but not identical, NR binding preferences. The most striking difference was seen with the androgen receptor, which bound well to GRIP1 but poorly to SRC-1. GRIP1 and SRC-1 contain three copies of the NR binding motif LXXLL (called an NR Box) in their central regions. Mutation of both NR Box II and NR Box III in GRIP1 almost completely eliminated functional and binding interactions with NRs, indicating that these two sites are crucial for most of GRIP1's NR binding activity. Interactions of GRIP1 with the estrogen receptor were more strongly affected by mutations in NR Box II, whereas interactions with the androgen receptor and glucocorticoid receptor were more strongly affected by NR Box III mutations. One isoform of SRC-1 has an additional NR Box (NR Box IV) at its extreme C terminus with an NR-binding preference somewhat different from that of the central NR-binding domain of SRC-1. GRIP1 has no NR Box in its C-terminal region and therefore no C-terminal NR-binding function. In summary, GRIP1 and SRC-1 have overlapping NR-binding preferences, but specific NRs display both coactivator and NR Box preferences that may contribute to the specificity of hormonal responses.

Transcriptional activities of estrogen and glucocorticoid receptors are functionally integrated at the AP-1 response element

Estrogens and glucocorticoids often act in opposition to regulate physiological responses. We investigated whether this might reflect the opposing actions of hormone-bound receptors on target genes regulated by the AP-1 response element. We performed a series of transfection experiments in which transcriptional activation, mediated by the AP-1 response element, was reflected in reporter gene activity. As previously described, we found that estrogens stimulate, whereas the glucocorticoid dexamethasone (Dex) inhibits, transcription through a model promoter from the collagenase gene (-73 to +63). This promoter bears a consensus AP-1 response element. When HeLa cells were treated with both estradiol and Dex, the steroids counteracted each other's transcriptional effects. The amount of transfected estrogen and glucocorticoid receptors (ER and GR) determined the extent to which Dex blunted estrogen stimulation or estrogen prevented Dex inhibition. The ER/GR interaction was observed both in the presence of estradiol and tamoxifen, which has previously been shown to have estrogen-like action at an AP-1 response element. The AP-1 family member c-Jun enhanced Dex inhibition and estradiol stimulation of transcriptional activation. c-Fos potentiated the effect of cotransfected c-Jun on estradiol stimulation but not Dex inhibition. The pattern of steroid responses was retained in the presence of the c-Jun activator phorbol 12-myristate 13-acetate. However, estradiol stimulation was lost in the presence of the c-Jun activator tumor necrosis factor-alpha. The ER/GR/AP-1 response element interaction was present, not only in a cell line originally derived from a uterine cervical adenocarcinoma (HeLa), but also in a cell line derived from the hypothalamus (GT1-1). Lastly, both progesterone receptor types A and B also interacted with the ER at the AP-1 site. These data indicate that opposing steroid influences can be mediated at the level of transcription through the AP-1 site and suggest that the integration of hormone action at this response element may underlie some of the opposing actions of estrogens and glucocorticoids or progestins on physiological responses.

Tamoxifen activation of the estrogen receptor/AP-1 pathway: potential origin for the cell-specific estrogen-like effects of antiestrogens

We find that tamoxifen is a potent activator of estrogen receptor (ER)- mediated induction of promoters regulated by AP-1 sites including the human collagenase gene promoter and constructs in which an AP-1 site is fused to the herpes thymidine kinase promoter. This contrasts with the inability of tamoxifen to activate otherwise identical promoters bearing classical estrogen response elements. Tamoxifen agonism at AP-1 sites is cell type specific, occurring in cell lines of uterine, but not of breast, origin. It thus parallels tamoxifen agonism in vivo. AP-1 proteins such as Jun or Jun/Fos are needed for tamoxifen stimulation, and tamoxifen increases the transcriptional efficiency of these proteins even when they are provided at optimal amounts. The DNA binding domain (DBD) of ER is required for tamoxifen activation at AP-1 sites. In contrast, estrogen activation is partially independent of this domain. This suggests the existence of two pathways of ER action at AP-1: an alpha (DBD-dependent) pathway activated by tamoxifen, and a beta (DBD-independent) pathway activated by estrogen. Fusing VP16 transcriptional activation functions to ER potentiates the beta, but not the alpha, pathway. We discuss models for the two pathways and the possibility that the AP-1 pathway is a major route by which ER affects target tissue growth and differentiation in vivo.

Glucocorticoids are Required for Food Deprivation-Induced Increases in Hypothalamic Neuropeptide Y Expression

Neuropeptide Y (NPY), a 36 amino-acid peptide found within the hypothalamus, is thought to be an important regulator of food intake. Hypothalamic NPY gene expression, synthesis and secretion are all known to be increased in models of increased metabolic demand in which serum glucocorticoids are also elevated. The present studies were designed to test the hypothesis that glucocorticoids are required for increased hypothalamic preproNPY mRNA levels induced by food deprivation (FD). First, animals underwent bilateral sham-adrenalectomy (sham) or not (control), and were subjected to 72 h FD, or not. Total RNA was isolated from hypothalamic tissue blocks and the content of preproNPY mRNA was measured by solution hybridization/RNase protection analysis. This study revealed that there was no significant difference in hypothalamic preproNPY mRNA content between shamfed and control-fed groups, or between sham-FD and control-FD groups. In the second experiment, animals underwent bilateral adrenalectomy (ADX), were allowed to feed ad libitum and were sacrificed 1 day, 4 days and 7 days after ADX. Nuclease protection analysis revealed no significant effect of ADX on hypothalamic preproNPY mRNA levels over this time-course. Finally, we examined the role of glucocorticoids in regulating NPY gene expression following FD. Animals underwent bilateral ADX, or not. At the time of surgery, ADX animals received placebo, or corticosterone (B) replacement in the form of constant release pellets, at one of two doses. Food was removed from half of the animals in each group 24 h after surgery; all animals were sacrificed 72 h thereafter. There was no difference in preproNPY mRNA content between the ADX-FD and ADX-fed groups, relative to the fed controls. Replacement with corticosterone [ADX(B)] did not alter preproNPY mRNA content in fed animals, however preproNPY mRNA content in FD animals was increased 2.5-fold. These studies demonstrate that glucocorticoids are necessary and serve a stimulatory role in the increase in hypothalamic preproNPY mRNA levels observed under conditions of FD, and suggest that hypothalamic NPY gene expression may be directly responsive to peripheral metabolic and hormonal signals.

Demonstration of glucocorticoid receptor-like immunoreactivity in glucocorticoid-sensitive vasopressin and corticotropin-releasing factor neurons in the hypothalamic paraventricular nucleus

Many parvocellular neurons in the paraventricular nucleus of the hypothalamus express high levels of corticotropin releasing factor (CRF) or vasopressin following adrenalectomy. To determine whether glucocorticoids feed back directly on these neurons, a mouse monoclonal antibody directed against the rat liver glucocorticoid receptor was used in combination with polyclonal antisera directed against either vasopressin or CRF to permit simultaneous visualization of either peptide with glucocorticoid receptor-like immunoreactivity (IR). Rats were adrenalectomized (ADX) for 2 weeks to optimize numbers of vasopressin - and CRF-IR neurons. Six hours prior to sacrifice, a separate group of adrenalectomized rats was treated with corticosterone (40 mg/kg). This short-term replacement resulted in nuclear localization of glucocorticoid receptor-like-IR but did not attenuate the increased numbers of CRF- and vasopressin-IR neurons observed after adrenalectomy. It was therefore possible to visualize vasopressin- or CFR-IR and nuclear glucocorticoid receptor-like-IR simultaneously. Cell counts of double-labeled neurons in the paraventricular nucleus of the hypothalamus (PVH) demonstrated that glucocorticoid receptor-like-IR is colocalized in virtually all the CRF and vasopressin immunoreactive parvocellular neurons studied, which respond to adrenalectomy by increased peptide expression. These data suggest that a major feedback effect of glucocorticoids on the hypothalamic-pituitary-adrenal axis is exerted directly within nuclei of CRF and vasopressin neurons.

Ultrastructural localization of glucocorticoid receptor (GR) in hypothalamic paraventricular neurons synthesizing corticotropin releasing factor (CRF)

Corticotropin releasing factor (CRF) synthesizing neurons, located in the hypothalamic paraventricular nucleus (PVN), are the main central regulators of the pituitary-adrenal cortex endocrine axis. The hormone production and release of CRF-synthesizing neurons is regulated by neuronal messages and feedback action(s) of glucocorticoids secreted by the adrenal gland. In order to characterize the latter mechanism, glucocorticoid receptor (GR)-immunoreactive (IR) sites were studied in hypothalamic paraventricular neurons of intact, long-term adrenalectomized, and adrenalectomized plus glucocorticoid treated animals, by means of ultrastructural immunocytochemical labelling. In intact animals, glucocorticoid receptor immunoreactivity was found predominantly in the nuclei of parvocellular neurons. Following adrenalectomy GR-immunoreactivity was localized in the cytoplasm of the cells, and there was a concomitant disappearance of the label from the nuclei. After corticosterone administration to adrenalectomized animals, GR-IR sites were again concentrated within the cell nuclei. Immunocytochemical double labelling studies performed on adrenalectomized plus corticosterone-replaced animals demonstrated glucocorticoid receptor-IR sites in the cell nuclei of parvocellular paraventricular neurons that expressed CRF-immunoreactivity in their cytoplasm. These ultrastructural data indicate that the intracellular location of glucocorticoid receptor is dependent on the availability of glucocorticoids by the neurons. The simultaneous expression of GR- and CRF-immunoreactivity in parvocellular paraventricular neurons supports the concept of a direct feedback action of glucocorticoids upon CRF-synthesizing neurons.